Audio September 1954
SEPTEMBER, 1954 .
ENGINEERING
MUSIC
SOUND
REPRODUCTIOr\
...
68.
VOLTAGE
FEEDB ACK
lSI STAGE
OUTPUT
TRANS.
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CURREN T
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2200
FEEDBACK
C .l-~m 'd
Only recently have the advantages of an adjustable
damping factor been explored. A simple and practical circuit provides complete control. See page 31.
Long familiar to attdio engineers, the principle of maintaining
the level of reproduced sound equivalent to the original is
clarified amusingly. S ee From Hi gh Fidelity to Music, page 28_
. VERSATILE ' CONTROL UNIT FOR THE WILLIAMSON
IMPROVING LOUDSPEAKER PERFORMANCE
FROM HIGH FIDELITY TO MUSIC
A TRANSISTOR REMOTE AMJ>LIFIER
Gladiolapft
on
· .. and for magnetic
DATA RECORDING
it pays to specify
Type
E P*
Glldiotape
*Extra Precision magnetic recording tape for telemetering,
electronic computers and other
specialized applicatiQns.
• Specially produced from the
most carefully selected materials
and ingredients, to meet the most
exacting requirements for uniformity and freedom from microscopic voids or imperfections.
Available in any desired
width, on standard plastic base and on I, 1%
and 2 mil "Mylar". Ask
for Bulletin No. 207.
Mylar:t: or plastic base
BALANCED PERFORMANCE preserves the
:x
full brilliance of the original live sound
AUDIOTAPE'S oxide coating has been developed and perfected to
.t1. provide maximum uniformity of response throughout the entire audible frequency range. This assures utmost realism in the
reproduction of every sound - brings out the best in any tape
recorder.
Now this same truly fine performance can be obtained in a tape
of exceptional strength, stability and permanence - Audiotape on
"Mylar" polyester film! Almost unbreakable and virtually immune
to extremes of temperature and humidity, this new polyester tape
has already found many profitable applications in the professional
recording field. It is available on 1, 1 % and 2 mil "Mylar", in 300
to 2500 foot reels. Ask your dealer for Audiotqpe bulletin No. 201;
or write to:
tDuPont trade mark for their polyester film
AUDIO DEVICES, Inc.
444 MADISON AVE., NEW YORK 22, N. Y.
Offices in Hollywood - Chicago
Export Dept., 13 East 40th St., New York 16. N. Y., Cables "ARLAB"
SEPTEMBER, 1954
Vol. 38, No.9
Successor to RADIO, Est. 1917.
ENGINEERING
MUSIC
VARIABLE D*
SOUND REPROD UCTION
C. G. McProud. Editor and Publisher
CARDIOID
DYNAMIC
Henry A. Schober, Business ~anager
Harrie K. Richardson, Associate Editor
Florence Rowland, Production Mana; er
Edgar E. Newman, Circulation Director
S. L. Cahn, Advertising Director
H. N. Reizes, Advertising Manager
. ,
for TVandBC
I
Representatives
H. Thorpe Covington, Special Representative
7530 North Sheridan Road, Chicago 26, Ill.
Sanford R. Cowan, Mid· West Representative
67 W. 44th St., New York 36, N. Y.
West Coast
James C. Galloway
J. W. Harbison
816 W. 5th St., Los Angeles 17, Calif.
CONTENTS
Audio Patents-Richard H. Dort . . ......... .... . .. . " . . .. .. . . .. .. . . .. .
Letters . ' .' ......... . . . '. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
New Literature. . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..
About Music-Harold Lawrence. . . . . ... .. . .. . . ... . . . .. .... .. ... . . .. ...
Editor's Report ... . . ............. .. ... .... .. ... . . . .. . .. . . . .... . . . . :..
Versatile Control Unit For The Williamson-Charles R. Mille-r .... . . .. ...
Improving Loudspeaker Performance-David B. Weems..................
Accurate Design of Phono Equalizers-In Two Part'S, Part 2Charles F. Hempstead and Hamilton Barhydt .... . ........ ... .... ...
A Transistor Remote Amplifier-Paul Penfield, Jr. .. .. . ..... .. . .. .......
From High Fidelity to Music-Zygmunt Hot. .. . . .. .... ............ . . . .
Variable Damping Factor Control-Charles A. Wilkin1s .. . ... ....... . . . ..
Damping of Loudspeaker Cabinet Panels-M. Rettinge'Y ........... . ......
Better Audio Specs Needed-Nathan Grossman... . . . . . . . . . . . . . . . . . . . . . .
Selecting and Improving FM Receivers-Charles Erw/:n Cohn. . . . . .. . . ...
Audio Tin1e-1954 ......... ........ . .. ............ .' ... : ......... ... ..
Equipment Report-National Company's H or·izon 20 A·mplifier,
Horizon 5 Pream plifier, and Criterion AM-FM Tu,n er .. .. .. .. . .. ... .
Record Revue-Edward Tatnall Canby. .. ... . .. . . .. .. .. . . . .. . . .. . . .. . . .
Audio ETC-Edward! Tatn'all Canby ..... .. .. : . . ... .. .. .. . . . . .. . . . . ....
New Products . ..... , .. . . . ... .. . . . . . ... .. .. .............. ........ .. : ..
Employment Register . ... . ... . ... . .... .... .... ........... .. ..... . .. ..
Coming Events . . . .. ........... ... ...... . . ........ .. .. ......... .. . ,.
Industry People ........... .. . .. . . . ... .... .. .......... .. .. ..... . ... ..
Advertising Index . . .. ..... . .. . . ................ . ..... .... ...........
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8
12
14
16
19
22
24
26
28
31
34
36
42
44
46
52
58
62
76
77
79
80
OUTPERFORlJ"'S ALL OTHERS
Combines ruggedness of single
dynamic element with new acoustic
principle. Eliminates pick-up of
ambient noise; unwanted
reverberation and equipment rumble.
Uniformly smooth response 30-15,000
cps, laboratory controlled. Highest
front-to-back discrimination.
Virtually no proximity effect. Output
-57 db. E-V Acoustalloy diaphragm.
Blast filter. Detachable clamp.on
swivel 's tand coupler. Weighs only
11 oz. 73-l! " X 13-l!". TV
gray. 20' cable. 50 ohms. ~
Readily changed to
150 or 250 ohms.
•
Model 666 Microphone. List $245
Model 366 Boom Mount.
list $40
Model 300 Stand Coupler.
'List $10
Madel 420 Desk Stand.
list $20
Normal Trade Discount Applies
eE_V Pat. Pend.
AUDIO (title registered U. S. Pat. Off.) is pllbll,hed monthly hy Radio Magazines. Inc.• Henry A. Schober, President;
C. O. }fePrand. Secretary. Executive a nd EdUorial Offires. ~O.J Front St., l\fineols. N. Y. Subscription rates-U. S. ,
Possessions, C~tll l1 (I ;1 li nd I\lexico. $4.00 for onE' YNtr, $7.00 ror two years , all other countries, $5 .00 per ycar. Single
copies 50c. Prin ted in U. S. A. at Business Press, Inc., 10 l\ldlovern Ave., Lancaster. Pa. AU righlq rC:-lcrvcd. Entire
contents copyright 1954 by Radio Magazines. Inc. Entered as Se(,()llrt Cia" Matter February 9, 1950 at tho Post Omce,
Lancaster. Pa. under tbe Act of March S. 1 879.
RADIO MAGAZINES, INC., P . O. Box 629, MINEOLA, N.
AUDIO
•
SEPTEMBER , 1954
'I.
Write for Data Sheet No. 39
BUCHANAN, MICHIGAN
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with
experien ce i n
: the fields of
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Communication
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Engineers
Circuit
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: Development
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: ElectroI mechanical
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: Equipment
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Advancements in the
fields of wave propagation, translation of inforInation, C0111I11Unication
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theory, circllit techniques
and equipment miniaturization have created a
number of new openings
for qualified engineers in
the Hughes Advanced
Electronics Laboratory.
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AREAS I
OF
WORK
The comm uni cation
group is concerned with
the design and development of unique radio
conullunication systelllS
and with exploiting new
radio communication
techniques. Specialists in
propagation phenomena, .
Assurance is
required that
relocation of
applicallt will
antenna systenls ) n e t-
Hot calise
disruption '!f
all urgent:
lIlilftary project. :
RICHARD H. DORP
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: Information
I Theory
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THE
OPENINGS
AUDIO PATENTS
work theory, magnetic
recordin g, wid e~ban d
amplification, and intrica te electromechanical
devices are active in this
program.
T
HE FILES OF THE PATENT OFFICE are
chock full of tone-control circuits,
since it seems that any of the large
companies whose engineers design a new
tone control immediately have the patent
department put the circuit into an application just as a matter of course. Most of
them are of some use outside the particular
equipment they were designed for, but few
have any very special aspects to recommenci
themselves to those who appreciate and
can use something with a little original
thought behind it.
For certain applications, a new tone control invented by Harry J. R eed, J r., of
Pleasantville, N. J.. has two r ather interesting merits. First, it is very simple. Secondand more important, it has only half the
attenuation (insertion loss) in db of the
usual bass-treble control system. The patent
is numbered 2,680,231, and it is ass igned
to General Precision Laboratory, Inc.
I t is routine to design dual tone controls
in such a manner that each control introduces an insertion loss equal or more than
equal to the maximum emphasis to be
afforded. If, for example, a maximum bass
boost of 6 db is wanted, the bass circuit
causes an initial loss of 6 db or more at
aU frequencies, then allows the operator
to reduce that attenuation at the bass fre quencies. A treble control operates similarly. When both bass and treble controls
are desired, the net insertion loss (which
is permanent for the midband) is at least
somewhat greater than the sum in decibels
of the maximum boosts required for both
ends of the spectrum. A bass-treble control
capable of 6 db of boost at each end has
a midband loss of 12 db, etc.
With Mr. Reed's circuit, the midband
attenuation amounts only to a little more
th an th e boost required of either bass or
treble-not the sum of the two. Figul·e 1
shows his circuit, with typical values set
up for maximum emphasis of about 6! db
in both bass and treble; yet the midband
attenuation is only 8! db instead of the
* A14dio COlls1{ifan t, 255 W . 84th S t.,
New Y ork 24, N. Y.
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perhaps IS or more required for conventional app roaches. Figure 2 shows the maximum results for both boost and attenuation
obtainable at both ends of the range, with
the midsetting (flat response) on the solid
line. Bass and treble controls are separate
and independent.
Circuit Requirements
The input tube V 1 is a medium-mu triode
whose output is little affected by its load;
V 2 is a tube of any sort, present merely to
offer a nonloading grid impedance to the
tone control output. The tone control consists of R 1 through R 4 and C 1 through C s·
Consider first that the attenuation at midband must not vary appreciably with the
setting of either control. Disregarding the
bass network (R, -Rz-R s ) for a moment,
this will be true if the treble c<;mtrol RJ.
is much smaller than the reactance of either
C 2 or C s at the midband frequency, which
in this example is 800 cps. That follows ,
because the midband attenuation depends
on the action of Cz and Cs as the series
and shunt legs respectively of a -voltage
divider. The values for C 2 and C $ shown
in parentheses are their approximate reactances at 800 cps. Comparing these relatively large reactan:es with the resistance
of R 1. , it is apparent that at 800 cps the
setting of the slider will not make much
difference in th e voltage applied to the
grid. As frequency decreases, the capacitive
reactances become larger still, with the
obvious total result that from midband down
to lowest bass frequency the setting of R.
will not affect output.
At frequenc ies above the midband, however, the C 2 and C s reactances become
smaller and R1. becomes more and more
of a maj or factor in the voltage-divider
action controlling output. Thus, at higher
frequencies raising the slider of R J, away
from ground increases output, while moving it toward ground reduces output. This
effect becomes more and more pronounced
as frequency rises, so that the extreme settings of R4 give the treble emphasis and
attenuation shown by the two dashed curves
at the right in Fig. 2.
The bass network is simply resistive, CI
being mer ely a d.c. blocking capacitor. of
any ' value which will allow bass current
to flow through R,-Rz-R s without appre(C ontimled on page 6)
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Hughes
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atldEllgilleering
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RESEARCH AND I
CULVER CITY,
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DEVELOPMENT : LOS ANGELES
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LABORATORIES :
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COUNTY,
CALIFORNIA
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FREQUENCY IN CYCLES PER SECOND
20
800
20000
0 , - - __
/ ....
"'0
-10
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-20
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--//",,-
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TREBLE
..,8
C3
0::1)
'"
t'°056
~5,o00)
T
0.
I::;)
o
-30
/
--- ,
......... .. . .:
"
/
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Fig. 2
Fig. I
AUDIO
•
SEPTEMBER, 1954
Ampex magnetic tape recorders
• • • lasting
quality for every professional use
Ampex machines are built with sustained quality and durability
- the prime requirements of the major broadcast networks and
recording studios. These perfectionists have chosen Ampex, some
as long as six years ago, and their machines are still in use today.
For example, one Ampex, after 18,000 hours of heavy duty still
maintains p erformance equal to published specifications for new
machines! This is the kind of lasting value that is the Ampex
standard of excellence in sound recording.
MODEL 600
• Frequency Response - 40 to 15,000 cps,
• Tape Speed -7~ in/sec.
• Signal-to-Noise - over 55 db,
o Flutter and Wow - under 0.25 %_
SERIES 350 THE MOST VERSATILE AMPEX
0
The 350 Series is universally preferred for original and delayed broadcasts, exchanging taped programs,
music and drama rehearsals and
other perfonnances requiring extensive cueing and editing. Tape edit. ing is remarkably fast with "feather
touch" controls mounted within easy
reach on a 30°-slanted top-plate.
The 350 Series is unusually accessible for installation and servicing,
and is available in a variety of tape
speeds and mounting styles.
The 300 Series comprises the most
perfect sound recording machines yet
offered by any manufacturer. They
are unexcelled for performances
deserving the finest recording and
reproduction it is possible to make.
Superb design and flawless mechanical stability achieve the utmost in
program fidelity, operating reliability
and timing accuracy.
Frequency Respo11$e - 30 to 15,000 cps.
Tape Speed-7~ and 15 in/sec.
Signal-to-Noise - over 60 db.
Flutter and Wow - under 0.1 % .
•
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MODEL 4500 FOR BACKGROUND MUSIC
Frequti'ncy Response - 30 to 15,000 cps.
Tape Speeds - 7~ and 15 ips, or 3% and
Signal-to-Noise - over 60 db.
Flutter and Wow - under 0.2 % .
7~
ips.
SERIES 5-32000 FOR TAPE DUPLICATION"
This Series of machines achieves true
mass duplication of previously recorded tapes while preserving the
superb fidelity of the master recording. Up to 10 exact replicas can be
made simultaneously, and up to
2500 hours of program material can
be produced in an 8-hour day (or
one hour in 10 seconds I ) . The
S-3200 Series duplicates both single
and double track masters and 2 track
stereophonic tapes, of any standard
speed, in one pass either "forward"
or "backward."
The Model 450 is a reproducer which
, provides sustained high fidelity background music anywhere. It is ideal
for the finer hotels, restaurants, department stores, funeral parlors, factories and other users of pre-recorded
programs. It plays continuously for
8 hours. Starting, stopping, reversing
and repeating can be controlled automatically.
•
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THE NEWEST AMPEX
The Ampex 600 is a portable model that weighs less
than 28 pounds. It is an Ampex in design and perfonnance and gives the same -class of fidelity, accuracy
of timing and reliability as other Ampex recorders.
It is the ideal instrument for radio stations, music
conservatories, educators, high fidelity eath-usiasts-a-Fld
other professional and semi-professional users.
SERIES 300 0 THE FINEST AMPEX
•
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Frequency Response - 50 to 7,500 cps.
Tape Speed - 3% in/sec.
Signal-to-Noise - over 50 db.
Flutter and Wow - under 0.4% .
•
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Frequency Response - 30 to 15,000 cps.
Tape Speed - 30 and 60 in/sec.
Signal-to-Noise - over 45 db.
Flutter and Wow - under 0.2 % .
WRITE FOR FURTHER INFORMATION AND COMP LETE SPECIF ICATIONS TO DEPT. B-1723.
934 Charter Street
0
Redwood City, California
Branch offices: New York, Chicago, Atlanta, San Francisco al1d
College Park, Maryland (W(lshington D.C. area)
Distributors in principal cities (Listed in Telephone Directory under "Recording Equipment")
Canadian General Electric Company in Canada
AUDIO
•
SEPTEMBER, 1954
4
AUDIO
•
SEPTEMBER, 1954
tape gives
New
50% more recording time!
A revolutionary development for radio stations,
recording studios-in fact all users of magnetic
tape! New "Scotch" Brand Extra-play Magnetic
Tape 190A makes it possible to record entire
symphonies, lengthy news and sports events
without stopping for reel change. With 50%
more tape on each reel, new Extra-play tape
offers the same recording time found on 172 reels
of standard tape. •
.
Exclusive feature of new "Scotch" Brand 190A
tape is a thinner magnetic coating. Made of
high-potency oxide, the new coating has been
reduced from standard 0.6 mils to 0.3 mils and
the high frequency range ~xtended appreciably.
A 30% thinner tape backing offers more uniform
hi fi response with crisper, cleaner tones, yet
maintains "Scotch" Brand's reputation for
sturdy, long-life tape construction.
8
-...
3db
I-
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I-
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o
r
_
- 190
••• '" 'II
-
24 IN. HEIGHT·
l
~
~
t ••
•
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SINGLE STRANO
OF NEW "190
FREQUENCY
EXTRA THIN TAPE-50% thinner, more
potent oxide coating, 30% thinner backing
permit more 190A tape to be wound on
standard-size reel. Result: one roll of new
tape_does job of lYl! reels of standard tape.
INCREASED FREQUENCY range of new
E xtra-play tape enables tape machines to
produce recordings with grepter hi fi response than formerly possible with most
conventional magnetic tapes.
REG. U. s. PAT. OFF.
'J~H
oz. STEEL BALL
DROPPED FROM
-----11\\""-~
\ ""-
TAPE
STRENGTH TO SPARE-New 190A tape
stands up under even grueling steel ball
drop test. Naturally it's tough enough to
withstand severe stresses of sudden machine
stops, starts and reverses.
EiJML&.Magnetic Tape 190A
The term "SCOTCH" and th: plaid design are registered trademarks for Magnet ic Tape made in U .S.A. by M INNESOTA MINING AND MFG. CO.,
St. Paul 6, Minn. General Export: 122 E. 42nd St., N ew York 17, N. Y. In Canada: London, Ontario, Canada.
AUDIO'
0
SEPTEMBER. 1954
{#ii
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PATENTS
(f1-om page 2)
ciable attenuation. This means that if the
grid of V 2 were connected only to the bass
control and not to the treble control, R!
would simply act as a volume control without frequency discrimination.
As it is, however, the grid is connected
to both. At midband the bass control has
little effect on the output voltage because
its impedances from any slider setting on
R2 both to ground and to the V, plate are
large relative to those of the treble network
-which itself, as we have shown earlier,
allows little change in midband level.
At high frequ encies a portion of R . and
the low reactance of C s are shunted between
the slider of R 2 and ground, making a very
low impedance for the shunt leg of a
voltage divider. The portion of R . above
the slider, if any, and the resistanc~ of R 1
are the high-impedance series leg of the
divider. As a total result, the bass network
cannot appreciably affect output at and
above the midband frequencies.
At lower frequencies, however, the reactance of C. becomes rapidly larger,
quickly exceeding the resistance between
the slider of R o and ground. This raises
the impedance of the shunt leg of the bass
voltage divider. Since R 2 is very large with
respect to Rl and R s' the setting of R 2 has
the maj or effect on output of the bass
voltage divider, so that it gives the maximum and minimum relative bass shown by
the dashed lines at left in Fig. 2.
The only midband attenuation is necessitated by the treble circuit and is due to the
ratio between C2 and Ca. The bass control
is . added like a kind of tail on the dog,
as added signal for . boost and as an effective shorting of C3 for attenuatilom, so it
does not cause an insertion loss as ordinary
circuits do.
The values shown in Fig. 1 are only a
sample for one particular kind of use. To
aid anyone who may wish to do something
different, the following design data is summarized.
Midband attenuation is approximately
Presenting the only
BROADCAST MICROPHONE
with "aU three"-!
• Small size, slim design !
• Smooth, extended
frequency response !
• World-famous, pate nted,
Uniphase system !
UNIDIRECTIONAL
MI CROPHONE
Ou t of the Shure Laborato r ies has
come a slim, small Broadcast m icrophone so remarkab le in its over-all performance that we have given it a special
name-the "C oncert-Line. "
'Jbe "333" is tbe only small, slim Broadenst micropbone in tbe world witb tbe rooddfamous , pa ten ted, 'Unipbase system!
The small; slim "333" provides the fin e
qua lity formerly fo u nd on ly in the
conventional- type, I arge size Broadcast
microphones. T he C oncert-L}ne "333"
is truly a n important advancement in
microphone deve lopment and design .
Bout
Bin
2
For this to be true
Mode l "333"
Conc ert-Li ne
Microphone
List Price
$250.00
ZB»ZT'
where Z B is the sum of R l ' R2 and R.t
and,Z T is the sum of the midband reactanct:~
of C2 and Ca and the resistance of R 4
(actually ' the complex impedance). T o
render midband output independen t of. th e
setting of R .,
R 4 «XC2 +Xcs·
To keep midband output from being affected
by settings of R 2 , values ot R l and R .
should be small relative to R 2 , and R2
should be large with respect to the midband
reactances of C2 and Cs. This is approximated when
T he U nidirectional "333" is AVAILABLE NOW - in limited quantities for the most discrim inating users.
.
R _
R s_
. -RJ :;: 2 to 5, and R:;: 2 to 5.
"
5 West Huron Street
Chicogo 10, lfIinois
Cable Address, SHUREM ICRO
6
C2
=C C • •
You may obtain a copy of this or any
other U. S. patent for 2S ¢ from The Commissioner of Patents, Washington 25,
D.C.
AUDIO
•
SEPTEMBER, 1954
£.~ TYPE AL Speak.
ENJOY EXTRA PROFITS
by offering LOWELL Low Level Sound
Distribution Systems
e r Baffles are designed espe.
<'iall y for low ceiling areas.
They are modernistic, 'at.
trartive and provide perfec tly controlled 360·
sound coverage. Ideal for markets, shops, hos.
pitals, dubs, etc.
£0WiJ.L TYPE RS' Speak.
The profit potential for those selling LOWELL
low level sound is tremendous!
On'e need only consider the nation's record
smashing construction, program - running into
many billions of dollars - which, according to national authority F. W . . Dodge Corporation, js the
largest in all history.
Airports, schools', churches , hospitals and
many many othel t~Tpes of construction need modern sound systems -. and LOWELL low level sound
is as modern as tomorrow.
Many states are considering legislation requiring that sound systems be fireproof in all public
buildings for reasons of safety.
Originators of low level sound, LOWELL offers a single, complete source of supply for all types
of construction - either new or existing.
Why don't you investjgate the tremendous
profit potential of this rich market?
er Baffles are especially
adapted fo,r use where
speakers must he recessed
in walls or ceilings. Widely
u sed in wired music installations wh ere directional characteristics are needed.
£~ TYPE M8 Speaker Baffles are d es igned to
match and r eplace standard
acoustical tile block. They
provide a completely hidden speaker sys tem that
is ex trem ely easy to install and service.
The LOWELL line also includes a complete
ran ge of protective sp eaker enclosures such as
the CP Series (for n ew construction) and the
XCP Series (for existing conGiruction). Protects
sp eaker from dust or fire and falling mortar and
prevents rodents from damaging speaker cone.
Both types are also made in double-face and
adjustable fac e Inodels.
LOWELL, originators <If low level sound di stribution, manufa ctures a complete line of direc·
tional and non·directional speaker baffles and
labor sav ing mounting accessories. See the
LOWELL Section 3la/Lo in Sweets Architectural
Design files.
Write - wire - or
phone today for the
new LOWELL cata·
log. You'll be glad
you did!
00
AUDIO
•
SEPTEMBER, 1954
7
•
LETTERS
CE Pickup Response
SIR:
high U's
to heartbeats
With the lowest distortion,
widest useful dynamic and frequency ranges,
flattest response and finest balance
available today for critical listeners,
Bozak Loudspeake11S and Speaker Systems
recreate every audible sound
with its most subtle qualities that
contribute t~e last whisper of realism.
•.
.:-- - -
-----
Chosen as the standard
by leading acoustical laboratories .••
selected above all others for
the clinical study of heartbeat sounds .••
purchased time and again by
musicians and music critics
who know true sound quality ..•
the Bozaks remain unchallenged for
The Very Best in Sound
Room 713
Chicago High-Fidelity Show
Septem ber 30th - October 2nd
-:;: ~-- _-~-=
~±~
New York Audio Fair
October 14th - 17th
.fp
t
ROZAK
Co.
~ :e_~~:::;,..:.K
u# 1. :#'
h-:1
"~-'.=-:' _.
~~~~
~ ~1J;1 '.
_~_ ::
Street
•
Stamford • Connecticut
,,'-
We were pleased to notice that the June
issue of AUDIO contained an article on the
subject of the effect of lead capacitance on
the frequency r esponse of the General Elec'tric variable-reluctance cartridges. The effect of excesive capacitance across an un loaded cartridge is not well understood and
can be important under specialized circumstances. You will probably be interested
in the following comments on the technical
information in the article.
The authors substituted a 340-ohm fixed
resistor for the internal resistance of the
cartridge. Under conditions of d.c. and
low-frequency a.c. measurement this substitution is valid, but the cartridge coils
have been constructed in such a manner
that the a.c. resistance rises to high values
even at moderate audio frequencies. For
this reason the cartridge inherently damps
the resonances to which the authors refer
and the. values of peaking are much lower
than those shown in Fig. 2. .
For example, you will notice that whereas
Fig. 2 in the article shows a rise of IS db
at 16 kc with 140 \LlLf shunt capacitance,
the actual value using a cartridge is only
about 2 db. Furthermore, the peak is very
broad, extending from + 1 db at 8000 cps
to + 2 db across the range of 9000 to 14,000
cps, dropping to the zero axis at 15 kc. This
amount and type of peaking is inaudible
and is actually beneficial when playing vinyl
recordings due to the inherent elasticity of
the vinyl material and the tendency of the
elasticity to cause a drop in high-frequency
response. The curves from which these
data are taken were run using a standard
shellac frequency record used in laboratory
and factory control.
For smooth, wide-range reproduction we
recommend not exceeding a value of lead
capacitance of about 250' ILlLf, a requirement
which can be met with easily available
cable (25 ILlLf per foot) even with lengths
up to 10 feet. Advantage can be taken of
the action of large values of shunt capacitance to provide very effective and inexpensive high-frequency cutoffs for noisy
or distorted records, as shown in the
following:
.0015 ILf shunted by 22 000 ohms :
7000-cps cutoff .
•004 ILf shunted by 13000 ohms :
4000-cps cutoff.
No other load resistor is used with these
networks.
The condition under which the cartridge
will operate without any load . resistance
will be very rare since it is recommended
that equalization of the record high-frequency characteristic be accomplished by
applying load resistance to the cartridge,
common values being 3900 through 15,000
ohms. As indicated in your article, such low
values of load resistor remove the effect
of resonance due to reasonable values of
shunt capacitance, and when the r ecording
pre-emphasis is added to the resultant output curve it will be found that the response
is flat for all practical purposes.
The addition of a cathode follower between the cartridge and preamplifier will
decrease the signal-to-noise ratio, and only
a cathode follower having very excellent
characteristics would match the high signalto-noise ratio obtainable from a properly
designed preamplifier. Hum and noise from
the preamplifier stage will add to that from
the cathode follower. It is always desirable
to amplify the cartridge output as much
(Contimw d on page 73 )
8
I
AUDIO
•
SEPTEMBER, 1954
it a Uni-Level amp or a "station attendant" ... either name tells the total potential
value to both large and small audio operations.
This unit is ideal for controlling level changes
encountered between different program sources
such as remotes, network, transcriptions, and
film projection.
ALL
C
Yes, in any studio, you can count on the
BA-9-A to provide higher average output
~og'ess Is Ovr'Most Imporlt!Jnf Prot/vel
GENERAL. ELECTRIC
levels. Count on it to save time and effort while
performance is greatly improved.
,
I
.
Get all the facts today on this important new
audio development. Complete specifications
will be on the way to you as soon as we receive
the coupon below. Be sure to fill it in now!
p----------------------
I
I
I
I
I
I
I
I
I
•
General Electric Company, Section ·X4494
Electronics Parj(, Syracuse, New York
Please send me inform~tion and detailed specs on
the new G-E Uni-Level Amplifier.
NAM E.................................._.......__..___........_.... _...._................._ _
ADDRESS ........................ _ __._____.... __... _ ....___.__ ._.__ ._ _
CITY..........................................__.._.._.._..._......._... STATE ... _.._. __...._
The magic mood of music is easily shattered by the slightest noise, hiss or hum.
..
Your mood is safe. when the music is played through National's magnificent new
audio achievement - the new HORIZON series of intermatched tuner and amplifiers.
Even hiss and noise between FM stations have been conquered by National's exclusive
MUT AMATle tuning. Stations leap in out of velvety silence - stay locked in.
All tube noise, hum and distortion in tuner and amplifier have been reduced to an inaudible minimum.
It's more than high-fidelity . . . It's a wholly new listening experience!
[email protected]~~·N·
~
atlona~
FOR COMPLETE SPECIFICATIONS WRITE DEPT. A AT'
Never before a tuner so versatile!
You can enjoy full-band AM!
You can listen to matchless, drift-free FM!
You can hear both at the same time, using dual
sound systems!
You can receive revolutionary new binaural broadcasts as
they are made available in your area! Two gain controls
and separate tuning condensers are provided - one for AM ,
one for FM!
Exclusive Mutamatic FM Tuning eliminates all hiss and
noise between stations, so annoying when tuning conventional
tuners! Stations leap out of velvety silence - stay locked in
automatically! Unit features new "linear impedance" detection. Superior design eliminates drift.
An exceptional capture ratio rejects all unwanted signals
up to 80% of the strength of the desired signal. The FM
sensitivity proves the name - "the Criterion" - by which
all other tuners are judged.
AM-FM TUNER $169.95 (SIZE: 16 112" x 7")
To surpass the present ·high level of amplifier design.
National proudly introduces new power amplifiers with a revolutionary new output circuit employing unity coupling.
With unity coupling, the output transformer is no longer
required to supply the coupling between output tubes for
distortion cancellation as in normal push-pull circuits. Instead,
the transformer supplies only the impedance matching between the tubes and the speaker system, thus eliminating
impulse distortion created by transformers. Music is reproduced with an unclouded transparency - at all listening
levels - never before achieved!
The HORIZON 20 is a 20-watt amplifier with a total
harmonic distortion of less than .3% and total intermodulation distortion of less than 1'10 at full rated output.
Frequency response is ± .1 db 20 cps to 20 kcs ; ± I db
10 cps to 100 kcs. Power response at rated output is ± .15 db,
20 cps to 20 kcs. Hum and noise is 80 db below rated output.
' UUU~X::/UU 20
20-WATT AMPLIFIER $84.95 (SIZE: 14if2" x 4")
Incorporating the revolutionary new unity-coupled circuit
in a 10-watt amplifier design, the fiORIZON 10 offers performance never before achieved at such a moderate price!
The built-in preamp-control unit offers a choice of 3 inputs,
3 record equalization curves, a loudness control and separate
bass and treble controls.
Harmonic distortion is less than .5%; intermodulation distortion, less than 2% at rated output. Frequency response is
± I db, 20 cps to 20 kcs; power response, ± 2· db, 20 cps
to 20 kcs. Hum and noise are better than 70 db below rated
output on high-level input, better than 50 db on low
level input.
U U\JUUUU>x::.'UIJ
•
10
10-WATT AMPLIFIER/ PREAMP $79.95 (SIZE: 14if2" x 4'~ J
The HORIZON 5 achieves a new high in frequency response
(± I db, 20 cps to 100 kcs) and ·voltage output (up to 10
volts) - a new low in . distortion (less than .2'10 harmonic,
.3'10 intermodulation)!
Four inputs, 7 record equalization curves, a loudness-volume
control and bass and treble controls are provided.
Entire unit slips quickly, easily into either the . tuner or
20-watt amplifier.
NATIONAL
CO.,
INC. ,
61
PREAMPLIFIER-CONTROL UNIT $49.95.. (SIZE: 2W! lC (OW~J
SHERMAN
ST. ,
MALDEN
48.
MA S S.
NEW LITERATURE
• Newoomb Audio Products Company, Inc.,
6824 Lexington Ave., Hollywood 38, Calif.,
has performed an industry service with
the publication of a new institutional
booklet titled "Hi-Fi is for E v erybody."
A simple, easy-to-read book, it c onvinces
its readers 'that high fide lity is neither
difficult nor expensive. For the b e ginner,
this handsomely-produced 32-pa ge book is
exceptionally worthwhile rea ding. Requests for copy must be accompa nied by
twenty-five cents to cover costs of handling a nd mailing.
• David Bogen Company, Inc., 29 Ninth
Ave .• New York 14, N. Y ., tells just about
all there is to know about public-address
amplifiers, ·sound systems, and appropriate
accessories in newly release d Catalog
PA,554. Of pa rticular v a lue t o novice
buyers is a section titled "Hints for Selecting the Proper · Sound Syste m, " which
discusses the more important factors involved in determining which equipment t o
use for various types and sizes of installations. In addition to individual items, the '
catalog lists complete Bogen-engineered
sound systems for permanent installations, both indoors and outdoors, as well
as portable systems. The catalog is available from Bogen dist ributors or by writing the company direct.
With the new Melodist loudspeaker-amplifier combination
Altec Lansing brings true high fidelity, in a small package, within
the reach of everyone. The Melodist is the latest development of
the outstanding engineering force that has made Altec the leader
in professional sound equipment. It's a combination amplifier and two-way
speaker system that provides the maximum performa.nce possible in a
limited volume enclosure. And its specifications are guaranteed accurate!
• Electric-Voice, Ino., Buchanan, MiCh ..
gives basic facts about the company's
many products for the audio and video
fields in a new condensed catalog designated No. 119. Illustrate d and d e scribed
are microphones for TV, broadcasting,
public address, recording, and communications. Other listings ~nclude high-fidelity
speakers, enclosures, phono cartridges,
CDP public address speaker sys tems, FM
and TV boosters, and v a rious other miscellaneous accessories. Co py m a y be obtained free from any E-V distributor or
direct from the company.
• Jensen Manufacturing Company, 6601 S.
Laramie Ave., Chicago 38, Ill., is issuing a
new catalog, No. 1040, and two n ew data
sheets, Nos. 164 and 165. Cata log 1040
covers the Jensen line of g enera l purpose
and commercial sound sp eak ers, a s well as
accessory cabinets, volume controls and
transformers. Data shee t 164 introduces
the Weather Master drive-in theater
speaker line and No. 16 5 lists the latest
Jensen high-fidelity equipm ent. Copies
may be obtained from J e n sen dis tributors
or direct from the company.
A-339A Melodist Amplifier
700A Melodist Speaker
Dimensions: 13 x 4Ye x 9%
Range: 20-22,000 cps'
Power : 10 watts, less than 2% t.h.d .
Impedance: 4, 8, 16 ohms
Inputs: 1 for mag. phono or mic .
2 for ceramic. crystal, tape or tuner
Volume: 3 individual volume adjustments
Loudness: compensated loudness control
Tone: Treble,15 db boost or droop,10,000 cps
Bass, 13 db boost or droop, 50 cps
Crossovers: European, LP, old RCA,
new AES (NARTB, RIAA, RCA
orthophonic)
Price: Only $129.00
Dimensions: 22% x l1X x lO y'
Range: 90-22,000 cps
Power Capacity: 20 watts
Impedance: 8 ohms
Components : 10" bass speaker , high
frequency speaker, multicellular horn,
3000 cps dividing network
Price: Only $99.00
In blond or mahogany
ALTEC FIDELITY l!i HIGHEST FIDELITY!
AITE&
••
12
! ,itbii il€.awzp"·"!(l,uw
.................. . . f ..... . ..... .
9356 Santa Monica Blvd., Beverly Hills, California
161 Sixth Avenue, New York 13, N. Y.
• Eester Solder Company, 4201 Wrightwood Ave., Chicago 39, Ill., h as made a
greatly-nee ded contribution t o technical
literature in an auth orita tive 80-page
trea tise on the subject of Solder . Titled
"SOLDER . . . its funda m entals a nd usa ge," the book required more tha n three
years to c ompile and was written by Clifford L. Barber, K e ster r e search director.
Purpose of the book, acc ording to Dr.
B a rber, is to rectify bas ic liter a ture ina dequa cies on solder a nd t o provi de the
s older user with a thoro ughly s cientific
study. The book is being offer e d without
c harge to intereste d m a nufa cturers, laboratories, universities, vocationa l institutions, a nd qualified indiv iduals. Requests
for copy should be a ddressed to Dept_ TP.
• Minnesota Mining and Manufacturing
Co., 900 Fauquier St., St. P a ul 6, Minn., in
"Sound T a lk" Bulletin N o. 28, fea tures a
paper title d "Recent Progr ess in the Production of Error-Free Ma gnetic Computer
Tape." The four-page illu s tra t e d bulletin
discusses t he physical cause s of signal
dropouts in modern digita l computers des igned to use magnetic t a pe a s a longp eriod storage medium. In addition, it
covers the reasons why errors arise from
s uch defects, steps t a ken t o elimina te err ors, and a summary of progress made
during 1953. Available upon w r itten req uest.
(C ontinu.ed on page 61 )
AUDIO
•
SEPTEMBER, 1954
After more than five years of study and
development, we present our most prized
accomplishment, the RONDINE. We are
satisfied that it is the finest 12-inch turntable unit we have ever built . . . and that
its performance is years ahead of high
fidelity standards as we know them today.
The Rondine achieves almost complete
acoustical isolation between motor and
·turntable. Rumble-has been reduced to a
minimum. Wow and flutter are virtually
non-existent.
REK-O-KUY.
proudly announces
the
NEW
Features include: • Single selector-knob
for setting speed: 33Y3, 45 or 78
• Three-speed strobe disc,
affixed, for instantaneous
records - no adapter required •
cork-neoprene mat material to \oU1Ul .. ' ' '.'''''-._ _" ,
record slippage • Neon pilot light
• Rectangular chassis fits most changer
boards-pre-drilled and tapped for standard pickup arms.
12-INCH 3-SPEED
precision turntable-s
The Rondine embodies other well KnIOW~_..,.,_...,-._ _ _ _ _ _ _ _ _ _ _ _ _ _- - - - - . . . . , . . . - _ - - - - - ; : - - . . . ,
time-tested, Rek-O-Kut features :
turntable is cast aluminum, and exerts
'pull' on magnetic cartridges. An
heavy rim is precisely lathe-turned and
dynamically balanced for smooth
action. Internally rim-driven with a
prene-compound idler, perfect drive
tion is assured. All inter"moving parts
case-hardened, ~nd ground to a
finish .
RONDINE, Model B-12-with .
designed l:.r.ole induction motor - noise
level better than 40db below avera e
recording level. . ...................................$69.9.5
RONDINE Deluxe, Model B-12H-wi
new type custom-built !ty'steresis synchronous, self-lubricating motor - noise
level better than 50db below average
recording level. .......................................$119.95
See the Rondine at the
HIGH FIDELITY SHOW
September 30th through October 2nd
Room 733, Palmer House, Chicago
AUDIO
•
SEPtEMBER, 1954
For Complete Specifications, write to Dept. QJ-I
REK-O-KUT
COMPANY
Makers of Fine Recording and Playback Equipment
Engineered for the Studio • Designed for the Home
38.01 QUEENS BOULEVARD, LONG ISLAND CITY 1, N. Y.
HAROLD LAWRENCE
Is "Live" Music on the Way Out?
"f
the whole technically more proficient than
OR YEARS the performer has been
eliminating the composer. Now it's
in 1869, frequently fall into the same cateour turn I" This ominous statement gory. , At a recent recording session of a
by a contemporary American composer may new symphony, the conductor planted no
not chill the spine of the American Federaless than forty microphones around and
tion of Musicians-yet. But it is symp- within the orchestra. Where antiphonal
tomatic of a silent electronic revolution
effects were indicated in the score ( that is,
that, according to some, may ,,~ell trans- , where woodwinds were pitted against brass,
form the very nature of our musIcal world.
or strings against percussion) the results
A few years ago a film vers ion of Cannell were incoherent and damaging to the comwas produced in France. The names of the
poser's intentions . .In a number of passages,
stars, set designer, producer, director,
the conductor-against the composer's admake-up artist and wardrobe mistress were vice-altered tempo and rhythm instrucparaded before our eyes in glittering lettions. Even the orchestral musician had his
ters. Then, in almost microscopic print, ap- say. The xylophone was to be played with
peared the following credit: "Music by G.
soft sticks so as to blend with the other
Bizet." In similar fashion the movie star
instruments. Protesting that he could not be
system applies to the concert world in which
heard, the xylophone player moved his inthe performer has been raised to an exalted strument to a strategic place bel}eath one
postion and the composer is a sort of mus"i- of the microphones and-:-to add insult to
cal Cyrano de Bergerac. We refer to
injury-performed his part with hard
Gieseking's Debussy., Rubinstein's Chopin,
sticks. To the composer's dismay, each time
Serkin's Beethoven and Landowska's Bach. the xylophone was ·struck, its tone stood
Critics, musicians and laymen alike indulge out boldly and defiantly above the sound
in the rarified pastime of analyzing a of the entire orchestra, even during I1ltt·j
Mozart symphony in the light of perform- passages.
ances by Busch, Boult, Blech, Barbirolli,
In moments like these, the composer must
Beecham and van Beinum; or Krips,
have thought how wonderful it would be if
Krauss, Kleiber, Keilberth, Klemperer,
his music could be conveyed to the audience
Knappertsbusch, Koussevitzky and von
straight from his mind's ear and untouched
Karajan. The critic preparing a review of by human hands. For thirty-odd years now,
a Brahms concerto for next morning's
such a dream has gone beyond the stage
breakfast table or subway strap must of of a' Jules Verne fantasy, due primarily to
necessity confine his comments to the
the electro-musical research of another
interpretation.
imaginative Frenchman, the composer. EdMusic's middle man, the performer, has
gar Varese. One of the most extraordmary
often been a thorn in the side of the comminds of our age, Varese came to the
poser. An inept or unsympathetic rendering United States during World War I and has
has handicapped many a new musical work.
been studying every new development in
Take the case of Handel. A young English
electrical instruments and other scientific
singer named Gordon was rehearsing his
discoveries in the r ealm of sound. "We
only a ria in Flavia with the composer at
have at last," he said recently, "the right
the harpsichord. When Gordon complained
to hope for the sound-producing (not rethat the accompaniment was being playe·d. producing) machine which will free musiwrong, a violent quarrel ensued. Like the
cal expression." Although Varese jealously
spoiled young nobleman in Shaw's Misguards his experiments behind an electronic
alliance, Gordon threatened to jump up and curtain, we know that his aim is to redown on the harpsichord until is was
construct and control the whole spectrum
smashed to bits if Handel persisted in acof sound. Seated at his "composing macompanying him. With sudden calm, Handel
chine," the composer of the future will not
replied: "Oh, let me know when you wiIJ
only be able to find his lost chord, but
do that, and I will advertise it; for I am
orchestrate and record it simultaneously
sure more people will come to see you jump
without once putting pen to paper. With
than to hear you sing."
the proper formulas at hand, any sound
Shy, gentle Cesar Franck lacked Handel's from anvils, Chinese blocks, string-drums,
robust sense of humor. After a concert at
rattles, sirens and violins can be producedwhich one of his works had been premiered,
as well as an infinite number and combinahe was found by his son sitting in an armtion of new sounds. If the composer should
chair in a state of collapse. "The music is feel the urge to shift ' gradually from horn
beautiful, believe me, my son;" Franck
to oboe, one timbre could be made to "melt"
protested, "those performing people do not
into the other. At current estimates, the
understand it."
Today's performing people, although on
(C oHtintled an page 72)
.
CINEMA ENGINEERING CO.
DIVISION AEROVOX CORPORATION
1100 CHESTNUT
STRE~T
• BURBANK, CALIF.
FACTORY REPRESENTATIVES
THROUGHOUT THE NATION
EXPORT AGENTS : Frazar & Hansen, ltd.
301 Clay St.' San Francisco, Calif . . U.S.A.
14
AUDIO
. ' SEPTEMBER, 1954
A REED IS A REED IS A REED ••• if it's recorded, on
Soundcraft 'magnetic recording tape
A reed is never
a flute ... or a flue
pipe. So, to be sure of
capturing all the haunting
brilliance of reed instrumentsand the full range of sounds of the entire
orchestra - always use Soundcra ft T a pes!
Why?
l3ecause Soundcraft Tapes, and ollly
Soundcraft Tapes, combine:
• Constant depth oxide for uniform middleand low-frequency response.
• M:icro-Polished<!l coating , a patented
Soundcraft process that eliminates unnecessary head wear and gives uniform highfrequency response right from the start.
THE
WORLD'S
• Pre-Coated adhesive applied directly ,to
base-firmly anchors the oxide in place.
• Surfa ce-lubrication on both sides! No friction, no chatter, no squeal.
• Chemical balance throughout to prevent
cupping, curling, peeling, chipping.
• Uniform output of ± 7.i' db. within a reel,
±% db. reel-to-reel.
SOUNDCRAFT TAPES FOR
EVERY PURPOSE
Soundcraft Tape for all high-fidelity recording .
Soundcraft Professional Tape for radio, TV
and recording studios. Splice-free up to 2400
feet. Standard or professional hubs.
FINEST
TAPES ... VET
Soundcraft LIFETiME<!l Tape for priceless recordings. For rigorous use. F{)[ ,p erfect program timing . It's on a base of DuPont
"Mylar" Polyester Plastic. A third as strong
as steel. Store it anywhere. Guaranteed for a
lifetime.
'
Get the Soundcraft Recording Tape you
need t09ay: Your dealer has it.
REEVES
SOUNDCRAFT
CORP.
Dept .. 89
10 East 52nd St., N. Y. 22, N. Y.
FOR EVERY SOUND REASON
THEY
COST
NO
MORE
ED,ITOR'S
REPORT
•
AUDIO VACATIONS ARE OVER
N
EARL Y EVERYONE seems to take a hiatus from indoor
sports during the summer months, and construction .
of new equipment and the improvement of the old
is usually relegated to the background while we do
things that are more in keeping with the hot weather
and with the normal human desire for physical relaxation. And while many of us would possibly rather spend
our vacations at home with sufficient time to do a complete refurbishing job on our " systems," we are likely
to be coerced into spending our time in the open airgetting sunburned and mosquito-bitten, and finding out
about muscles we never dreamed of having.
But with the coming of September, new blood appears
and our activities are stepped up-possibly because of
the relaxation-and we begin anew with our continual
striving for better sound. Equipment that has been on
the drawing boards for the previous six months or so
is introduced, simplifications and circuit innovations that
intrigue and excite our interest a:re publicized, andmost important-the time is available to do the things
we have been planning for months.
Among the interesting activities of the Fall months
are the audio exhibits-the largest being the Audio Fair
in October, but others of greater importance in their
particular localities being ,the International Sight and
Sound ExpositiQn at the Palmer House in Chicago on
September 30, October 1 and 2, and the New England
High Fidelity Music Show at Hotel Touraine in Boston
on October 22-23-24. Since the Chicago event comes
first and since there is another issue between now and
the other twO'shows, our most immediate' concern is the
one nearest at hand.
The first International Sight and Sound E xposition
was held last year early in September during one of the
hottest weeks that Chicago had experienced. In spite of
the -weather, however, many thousands of audiQ-fans
attended and were suitably impressed by the year's new
equipment. Surveys made at the time indicated that the
typical visitor to the show was a "white-collar" married
man with a good income, well within the age when he
was making the major acquisitions to his hOine, and that
he expected to spend somewhere between $250 and
$1000 for his music system. The survey showed further
that the average hi-fi enthusiast is relatviely new to this
electronics hobby, has a better than average appreciation
of music, and that he and his wife are well agreed as
to the desirability of having high quality sound reproduction in their home.
With this survey as a guide, the second year's show
is likely to be more specifically directed to the "typical"
visitor, and is likely to present some innovations in en tertainment, although plans are not complete at press
time.
But regardless of ent5rtainment and other sideline
attractions, the real value of an audio show lies in the
opportunity given to the public to study at first hand.
the latest models of speakers and enclosures, amplifiers,
and equipment furniture, as well as to see-perhaps for
the first time, in many instances-the time tested equip-
16
ment which, while not " new" to most of our readers, ha ~
still not been'seen and heard by those who are cautiously
testing the temperat4re of the hi-fi hobby before jumping
in wholeheartedly. So we look forward with considerable
interest to the first show of the season, and we have '
already booked reservations to, at, and from the second
International Sight and Sound Exposition. This year's
show is open to the public-no admission charge- for
three days, Thursday to Saturday, September 30 to
October 2.
See you in Chicago ?
ONLY THE CHOIICE OF THE RECORDS
Joe Dickey, one of our readers and an occasional contributor, resurrected a copy of Catalog No. 9 of the
William B. Duck Co., a Toledo mail-order house back
in 1915 when this catalog was published. This select bil
of advertising copy appeared on page 267 of the catalog :
"Of the capacity of the Victor for the lighter forms
of entertainment, it might be said that catholicity of
taste is one of the Victor's virtues. Just as the Genius
of the Lamp, whose acquaintance we make in the story
of 'Aladdin and the Wonderful Lamp,' worked with
equal heart for the virtuous lad and for his wicked uncle.
the Moorish magician, so the Victor will record, with
equal imp¥tiality, the highest achievement of a Caruso
and the liveliest rag of the music hall comedian. It gives.
in short, a variety of entertainment in the widest sense
of the term, and looking through the [email protected] of Victor
records, one will find that no decent taste remains uncared for; therefore it goes without saying that the
greater includes the less and the instrument that will
satisfactorily render Grand Opera .or a symphony .can
be depended upon to do equally well with vaudeville or
'ragtime.' It is only a matter of the choice of records."
Knifing through the confusion that invariably attends
the introduction of new items, we find this bit of logic:
"And while it (the
a'[l other instruments
plement them all; for
- for which there is
phonograph) will never supersede
of music, it should certainly supit fills a place made by itself alone
no substitute."
It would be enlightening to know what the author of
that copy would think of his description were he to
reread it now, almost forty years later. It still applies,
and to a considerably greater degree, and we like it.
We had those catalogs way back then, too, but not the
foresight to save them, so we are greatefuI to Mr. Dickey
for culling out these few lines.
SOUND REPRODUCTION COURSE ·
Edgar Villchur's course on "The High Fidelity Re. production of Sound" will be given this Fall at the
Division of General Education, New York Uinversity.
Washington Square, N ew York City, on Wednesdays
from 7 :00 to 9 :45 p.m. R egistration begins on September 13.
( Con.tinued on page 77 )
AUBIO
•
SEPTEMBER, 1954
You're in the best of company if you use a Pickering ~~#tt Cartridge. You have this in common witH:
1. Leading record companies who use Pichering Cartridges lor quality control.
2. Leading FM/ AM good music stations and networh studios.
3. Leading manufacturers 0/ pro/es~ional equipment lor radio stations. recording studios. wired music systems and automatic phonographs. wllO install
Pickering Cartridges lor the maximum per/6rmance 0/ their equipment.
*'4v Picke-rlng ~~#tt Pickups are the
Choice of Recording and Broadcast Engineers!
"All modern disc recordings are made with ~~J7~
cutters. Within the geometrical and mechanical limitations of recording and. reproducing equipment, a
Pickering Pickup will re-gener~te an exact replica of
~4i=J7~ cutter response to the original program' of
music, speech or sound. This is a fundamentally inherent characteristic of the Pickering Pickup, supported by basic electromagnetic theory and countless
precise laboratory measurements. This is why Pickering ~~J7~ Pickups provide the most nearly perfect
coupling possible, between reproducing equipment
and original program. This is why tfiey ~ound cleaner
... less distorted.
"Through the medium of the disc material~ the reproducing system is effectively driven by the cutter
electrical response itself."
-'''''''''''--~=., ~»"~~i§~" "~?-"W~~~-~'
eOl"II'9r,at4ed • Oce""8,[email protected]~ L.I.~ N,@rf)'Fork
..
_.~"~C_~"~_-"'-''''''_~~_:_·'''''~'~»<'''_'~';''''''''''''_''';· f.<i«<i«;w.;' ;'''i;.<->;;%''''''''''_''''
PICKERING PROFESSIONAL AUDIO COMPONENTS
5",' ;
Ollmon,',o,.eI "anel .o/el by leoeling Roelio Po,', Di."i6ulors everywhere. For/he
AUDIO
•
SEPTEMBER, 1954
QIIe.
neor ••' you uncI
1.00
eleloileel lileroture; writ. Dept. A-S
17
Fastening wires with new tool.
Since telephony began, there has been just
one way to install telephone wires on poles:
have a trained man climb up and fasten
them there. Now Bell Lab oratOlies engineers have developed a special pole line for
rural areas. The entire line can be erected
without dim bing a pole.
The whole job is done from the ground.
Light-weight poles are quickly and easily
erected. Newly created ' tools enable men
to fasten wires to cross arms 10 to 25 feet
over their heads.
This inexpensive line promises more service in sp ar sely p opulat ed pla ces. From
original design to testing, it exemplifies a
Bell Telephone L aboratories team operation
in widening telephone service and keeping;
costs down.
Bell Telephone Laboratories
IMPROVING TELEPHONE SERVICE FOR AMERICA PROVIDES CAREERS FOR
CREATlV~
MEN IN SCIENTIFIC AND TECHNICAL FIELDS
K ey to t il e n ew " clim.bl ess"
p ol e is t hi s ·i nsu lato>". G"ottncl
C1'ews use l onu-handl ecl to ol s'
to p lace the wi.r e in p osition
and then lock it fast.
C;~a::'" 0...8
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Fig. 2. Complete sche matic di agram exce pt for d.c. hea te r supply.
Versatile-Contro·1 Unit
For The Williamson
/
CHARLES R. MILLER*
A combination preamplifier, tone controls, and bandpass filter
giving minimum noise and distortion and maximum convenience.
reproduc.tion, the Williamson amplifier and its
I11Gldifications have come to enjoy preeminence due to outstanding performance, but there has been no similar standardi zation in tone-control and preampli. fi er units intended to complement the
W illiamson. The unit described in this
article is an attempt to meet that need,
F unctionally, the unit is divided into
five sections as shown in F ig . 1. First, it
was deci ded that to preserve a high signal-to-noise ratio, all .tubes were to be
operated with direct current on the heaters, and secondly that all the sections
must be capable of l'ow-distortion performa nce matching the W illiamson. The
first specification can be met most easily
I
N THE F I ELD OF HOME MUS I C
by using all the heaters in series as the
cathode-bias resistor of the power tubes.
using a method to be descr ibed later. It
was felt, further, that the second could
be met only by using negative feedback
on each stage. While it may be argued
th at the signal in low-level stages is so
small that negative feedback is not
needed, it has been shown that this is
not the case:
1 W . B. Bernard, ~' D isto rti on in voltage
amplifiers," AUDIO E N GI N EERING, Feb. 1953.
The complete circuit appears in F ig. 2.
The design of the preamplifier V J-V. is
fairly conventional, with the equalizer
values Rt, R ., CJ, and C. being obtained
by appropriate transformation of the
networks given by Boegli2 • • for record
2 C. P . Boegli, "A preamplifier for magnetic and crystal pickups," R adio and T elevision News, July 1950.
3 C. P. Boegli, "An improved equalizerpreamp," Ra,dio and T elevision News, April
1951.
Fig. 1. Block diagram
of the con t rol un it.
CATHODE
TONE
OUTPUT
FILTER
PRE AM P
FOLLOWER
CONTROL
* T he Graduate H ouse, M ass. Inst. of
T echnology, Cambridge 39, M ass.
AUDIO
•
SEPTEMBER, 1954
19
compensation. The gain-frequency characteristics of the preamplifier for various
equalizer values is as shown in Fig. 3. If
simplicity is desired, the network shown
as the compromise network can be used
and any additional correction 11eeded '
obtained through the tone controls. It
should be noted that in no event are halfwatt resistors used, these generating a
much higher noise level than would be
predicted on the basis of thermal noise.
Furthermore, cathode bias is used in the
second stage to reduce distortion'
There may be some question as to the
use of the 12AX7 as the preamplifier
tube for low-noise service instead of the
12AY7. Fairly extensive tests were made
011 the noise and hum level to be expecfed
from various tubes. In particular, about
two dozen 12AX7's and 12A Y7's were
checked for noise equivalent input at the
grid. The equivalent hum and noise input
were compared, both for a.c. and d.c.
heater operation, with the only point of
superiority of the 12A Y7 being in the
matter of hum with a.c. heater operation.
With d.c. heater operation and the usual
gain vs. frequency characteristics for
phonograph equalization, the most important source of noise is flicker noise,
presumably caused by cathode poisoning. 4
Flicker noise varies inversely as the
square of the frequency and hence the
output due to flicker noise varies inversely as the cub/,! of the frequency. For
the tests mentioned, there was more variation within a given tube type than
from one type to another. In any event,
the average 12AX7 was better than the
average 12A Y7 for flicker noise. Repre·sentative 12AX7's in the preamplifier
gave an unweighted signal-to-noise ratio
of 68 db for a nominal 1 volt output (10
mv input at 1 kc). As predicted, the output noise spectrum had the sharply rising low-frequency characteristic typical
of flicker noise. Hum level was so far
below this noise as to be unmeasurable.
In the complete schematic (Fig. 2) CJO,
R", and RII are for the purpose of elim• VaHey and Wallman, "Vamutn Tube
Amplifiers," Radiation Lab Series, Vol. 18,
McGraw-HiH, New York; 1948.
Filter and Equalizer
The tone control stage V. perhaps
needs explanation. This is simply an
anode follower" with feedback voltage
determined by the impedances between
input, control grid, and plate. If the internal gain of the stage is infi'n ite and
the input impedance at the grid infinite,
the over-all gain can be shown to be in
the ratio Z ,j Z,) where Z. is the impedance from plate to grid and Z, the. impedance from input to grid. More simply,
the actual input signal is determined by
the setting of the two controls, Ru and
R... Bass signals go through the upper
• J. E. Lilienfeld and C. R. Miller, "Distribution of conductivity within dielectric
films on aluminum," Jour.. Electrachem.
Soc., May 1953.
o P. ]. Baxandall, "Negative 'feedback
tone control," W ireless World, October
1952.
BASS
III
I
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RCAAES
l,LCOMPROMISE
§: t;;::
r- ~ ~~ r/ COL. LP 1
COL . 78. ffrr
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section and treble through the lower.
With either control arm nearer the input, the corresponding output signal is
boosted, and with the arm nearer the
output, the eutput is attenuated. The resulting frequency response is as shown
in Fig. 4. One advantage of this system
is that at boost positions, there is still
enough negative feedback to insure very
low distortion. One disadvantage if the
circuit were to be used with a.c. heater
operation is that the actual grid signal is
'very low and consequently hum trouble
might be expected. Note one important
precaution-the potentiometers used are
linear-taper units and are not the usual
logarithmic controls used in conventional
tone circuits.
The bandpass filter is of conventional
design with a '12-db-per-octave slope at
the high-frequency end. To preserve balanced response e,. was selected to give
low-frequency cutoff matching that at
the high-frequency end, as it was felt
that an additional 12-db-per-octave highpass filter at the low end was not justified. The- Chicago Transformer NSI-l
unit was specified since tests showed this
cheke to have the highest self-resonant
frequency of any of the commercially
available units. Note that if the sel£capacitance of the choke is too high, the
filter is converted from constant-k to mderived operation, with consequently less
satisfactory transient response. The
values of resistance and capacitance
were chosen for critical damping and not
for maximally flat response. The resulting behavior is shown in Fig. 5.
The power supply for the control unit
is somewhat unconventional. The heater
current is taken from the main amplifier
by using the cathode currents of the output tubes, about 15 rna drain from B+ as
shown in Fig. 6. Previous tests on the
Williamson have shown an almost constant current taken by the output tubes
for any power level up to the overload
point. To prevent a burnout of one of the
heaters from pulling the cathode voltage
up to B+, a neon lamp is inserted as
shown. In normal operatio1'l the lamp- is
below 50 volts and thus will not fire or '
affect operation. Burnout of a heater is
signified by the neon lamp glowing, at
inating switching transients due to
changes in d.c. level.
The input cathode follower V, and the
output cathode follower V. are perfectly
conventional, serving the purpose of isolation and impedance transformation. A
dual-potentiometer gain control gives
best compromise between minimization
of distortion and noise. If only an input
gain control were used, noise generated
in the following stages would reduce signal-to-noise ratio and if only an output
gain control were used, di::.tortion might
be caused in the preceding stages due to
overloading. It may be asked why electrolytic capacitors were not used in the
cathode followers. First, it is the writer's
experience that such capacitors are a
source of noise and distrJrtion and should
be avoided whenever possible: Secondly,
a , definite low-frequency cutoff was
wanted to insure stability. Wow in a
turntable can easily overload a poorly
designed system in which the amplifier
is very nearly at the motorboating point.
It is idle to talk about flat response down
to subaudible frequency unless the listener is prepared to "listen" wit!l airtight seals between his ear 'drums ,(l,ci the
loudspeaker cone.
-
-rrrnlTI
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. .
"
,
",
-
.,
' 0000
' 0000
FREQUENCY IN CY C LES PER SECONO
Fig. 3. (left). These curves show the equalization afforded by t he various combinations of C, -C2 -R, -R 2• Fig. 4 (right). The range of ton e control
availab1e from the circuit.
20
AUDIO
•
SEPTEMBER, 1954
•
-I-~
t-t-- -
- --+-- 11-
--- ---
1000'V TWIN- T NULL CCT
AUDIO
~~
OSCILL ATOR
SET AT ike
v~v
~ -10 I-Vt-..lA"i---t-+++I-l-I-- - I -
1-
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1
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,
).
IN
CYCLES
PER
Y T VM .
f--
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ike
'n
PREAMP
TONE
CONTROL
: 0 _1MEG.0
I
~
I
0-
•t
0 .1MEG. :
4000~~f l
I
l __ __________ ...
---:r
VERT
INPUT
HORIZONTAL
INPUT
ike EXTERNAL
011
~
I+-
OSCILLOSCOPE
Fig. 5. (left). The five positions of the bandpass filter switch give
these results.
10000
1000
FREOUEN CY
~N\\
- I-l---I-HI-I-I--H-I----\~\
-
---I-H-I--t-I- - - / - -I.
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PREAMP INPUT
SE COND
Fig. 7. (above). Test setup for distortion measurements.
which time the system should of course
be turned off and the trouble fixed . This
scheme has the further advantage of preventing B+ from rising to
value destructive to the electrolytics if one of the
heaters should burn out. The second feature of the power supply is that B+ for
the control unit is taken from voltageregulator tubes. This simple precaution
will save a good deal of grief in trying
to design for decoupling adequate to prevent motorboating. It is also usually
more economical than the electrolytic capacitors needed to give the-same low-frequency stability.
a
Final Results
To test the total distortion generated
by the unit, an .intermodulation analyzer
would be best. Without access to such a
unit, the follow ing test procedure was
adopted. Equipment layout was as shown
in Fig. 7. With the tone controls set at
flat posItion and the gain control at maximum, the signal from the GR Microvolter was raised until the output was at
the desired level. At the design outflut
level of 1 volt, the distortion was unmea.~~rable for any setting of the tone con-
troIs or the filter. For 10 volts output
and maximum bandpass, the distortion
was about 0.1 per cent. With 10 volts
output and minimum bandpass, the distortion increased to 0.3 per cent. However, since 10 volts represents a value 20
dt- above overload for the main ampli fier.
it is felt that for normal operation, both
harmonic and intermbdulation distortion
will be negligible. Since most of the distortion is caused by the fi lter loading the
tone control output, thi s could be made
negligible by insertion of a third cathode
follower to drive the filter. For the 1volt operating level, thi s was not deemed
necessary.
The mechanical layout is quite normal.
The entire control unit is built within an
8 x 12 x 3-inch chassis ( see Fig. 8), with
the tubes being arranged on a terminal
board, which itself is shock mounted by
means of grommets. To keep electrostatic coupling from getting hum into
the signal circuits, the power switch and
pilot light are external to the main chassis as shown in the photograph. There is
thus no 60-cps source within the chassis.
Magnetic coupling is prevented by the
usual wiring practice of a ground bus
connected to the chassis only at the input. The shorting switches used for the
signal circuits ·are the new Centralab
PA2000 series, which both are smaller
and give better performance than the
usual wafer type: The additional tube
socket is for a proposed microphone preamplifier. When and if this is used, the
12AU6 tone-control tube will be replaced
by a 6BH6, with a second 6BH6 for the
microphone preamplifier. In any event,
the total heater voltage will be 36 volts
for the series string. The electrolytic capacitor used for filtering B+ within the
control unit is mounted on a Mallory
PS-6 socket for easy replacement. Ventilation holes are drilled in the bottom
plate.
(Continued on page 78 )
+440Y
FINAL POWER
AM PLIFIER STAGE
+
o-jll---::-..--+-
~
If5ma
§
1f)-
'"
12AU6
o4ll-+-+----I-
12AT7
Fig. 8. Photo of the
underside shows
terminal-board co. nstruction .
12AX7
Fig. 6. D.c. for the heaters is taken in this
manner from the cathode circuit of the final
stage of the Williamson.
AUDIO
• • SEPTEMBER, 1954
21
Improving Loudspeaker Performance
DAVI'D B.
WEEMS ~:
How to improve low-frequency response from inexpensive loudspea~ers
with the e'xpenditure of less than a dollar and an hour or so of your time.
'R- Briggs
by BarritP and speaker will minimize the effects of resohave described methods of nance. We are concerned, however, with
-increasing the compliance of the the qualities of the speaker itself and how
cone suspension of inexpensive speakers. we can improve them.
The fundamental resonant frequency
The method proposed by Barritt consisted of "slotting" the rim of the cone of a loudspeaker may be determined
and subsequently treating it with a plas- mathematically from the formula:
ticizer. Briggs suggested experimentaf,- = _--=1==
tion wi th a cloth 5urround and cutting be V McCms
away part of the spider assembly. Initial
where
f,.
=
resonant
'f requency of the
trials seemed to prove the latter method
speaker in cps,
to be more effective but rather hazardM c = mass of cone, vQice coil, ann
ous; also glue t ravel in the cloth someair load in grams, _
times prevents optimum compliance.
Cms = compliance of the suspenAfter considerable experimentation was
sion system in centimeters
inspired by these ideas, the writer has
per dyne.
evol.ved a system of alterations that not
Assuming a constant air load, examionly seems to be superior in increasing
the compliance of a speaker, but also may nation of this formula shows that as
allow use of the unit not only as a woofer either the mass or the compliance of a
cone is increased, the resonant frequency
but also as a general-purpose speaker.
is lowered. While increasing the mass of
Benefits of High Compliance
the cone lowers resonance, it also limits
Among the most important charac- high-frequency response and results in a
teristics of the ideal speaker are w ide- deterioration of transient ability. Inrange frequency response and low dis- creasing compliance thus seems to be the
tortion. The fundamental cone resonance best approach toward lower fundamental
of a· speaker is closely associated with cone resonance. High compliance also
both its bass range and its distortion aids in obtaining wider range and lower
content at low frequencies., because the distortion.
output falls off rapidly with an increase
It may be argued that higher compliin intermodulation effects and frequency ance in cheap units may produce greater
doubling below resonance. It is a well intermodulation distortion due to the
known fact that the proper baffling of a movement of the voice coil beyond the
loudspeaker in such mountings as bass- area of maximum flux density. There are
reflex and horn-loaded enclosures lowers several answers. The first is that at northe resonant frequency, and an amplifier mal volume levels such movement will
that presents a low impedance to the probably not occur. Secondly, if it does
the use of multiple woofers will
'* 11327 Misso!tri Ave., Los Angeles 25, occur
it and at the same time provide
eliminate
Calif.
one of the most practical means available
1 R.
Cameron Barritt, "Speaker treat- to the home constructor of accomplishment for improved bass," AUDIO ENGIN-EERing truly superior low-frequency reprolNG, December 1952, p. 23.
duction. Finally, regardless of the theo2 G. A. Briggs, "TEe loudspeaker," High
Fidelity, Sept.-Oct. 1952, p. 39.
ECENT
ARTICLES
2
Fig. 1. Materials needed for treating speakerschamois, solvent, cement, tweezers, scissors,
razor blade, scalpel, and in some cases c1othessprinkler head.
i2
Fig. 2. Removing the dust cover with tweezers.
retical possibility of excessive voice-coil
movement, the net result of higher compliance for cheap speakers has been better sound. In speaker design we cannot
always predict, like Old Man Mose, what
will provide subjective enjoyment. With
this premise firmly in mind and with
courage in our hearts, we shall now proceed to the task of speaker improvement.
Procedure
The materials to be assembled are an
'inexpensive 8-to-12-inch speaker, plus
(Fig. 1) a small piece of the softest,
thinnest, a nd most pliable chamois available, radio solvent (optional ), household
g lue, tweezers, small scalpel (optional ),
barber's scissors or other pointed scissors, a new razor blade, and an aluminum
clothes sprinkler head. The chamois may
require some shopping around because
of the enormous variation of thickness
and pliability, but usually the small, ;11oSt
inexpensive pieces found at the five and
dime will include a few that have the
desi red characteristics. The aluminum
sprinkler w ill only be required for certain very inexpensive units as will be
described.
The operation should be performed on
a clean bench or table. First, tear away
the dust cover with the tweezers (Fig.
2), taki ng care not to disturb the voicecoil leads. Next, place shims of film negative or paper around the center pole to
maintain the voice-coil form in position,
as in Fig. 3. Usually four narrow shims
located at equal intervals around the
pole a re sufficient. The solvent may then
be used to satura te the juncture of the
outer rim of the cone, the frame, and the
Fig. 3. Inserting shims to hold the voice coil in
position.
AUDIO
•
SEPTEMBER, 1954
CON E
REMAINING
SPIDER - FOUR
EQUAL SECTION S
CUT AWAY
PORT ION
Fig. 5. The spide r is cut away except for four
sectors which hold it in position wh ile allowing
greater compl ia nce.
Fig. 4. Slitting the outer edge of t he con e to
remove it from mechani cal engag eme nt with
the f rame.
gasket. While the solvent is acting on
the glue, the rim of the cone may be cut
away at the middle of the inside corrugation (Fig. 4) leaving a "lip" past
the smooth part qf the cone. The entire
outer corrugations and gasket may now
be lifted out. If solvent was not available, this part can be loosened with a
knife after it is cut loose from the cone.
The spider should be cut away with
either the scalpel or pointed scissors,
leaving four strips about 0 to y,( inch in
width at equal intervals (see Fig . S).
Now attach four strips of Scotch tape to
the outer rim of the cone, evenly spaced,
and then fasten them to the frame without applying tension to the cone. If desi red, the shims may be removed and the
speaker tested for trueness of centering.
If it will respond to loud musical- passages that include low frequencies without rattling, the assumption may be
made that the centering was adequately
done, and the shims may be replaced as
before.
The Scotch tape should be replaced,
one piece at a time, by pieces of chamois
about 2 inches wide (see Fig . 6). The
chamois pieces should first be g lued to
the lip left when cUfting away the rim of
the cone, then to the frame . The chamois
should be tightened j ust enough to remove. wrinkles. but not stretched. After
this operation the speaker may be' tested
again .
Now the four large gaps around the
cone rim may be filled by cutting large
pieces of chamois to fit them. These
large sections should be installed very
loosely, leaving a deep wrinkle between
the cone I·im and the frame as shown in
the end-product photo of Fig. 7. Their
purpose is to eliminate the e~change of
air between the rear and front of the
cone, not to support and impede it; so
they are left loose, allowing only the four
narrow strips to suspend the cone. The
gasket should be trim r.led of or ig inal
cone remnants and reghl! d into posi tion.
The dust cover mayor may .not be reused, depending on the ultimate purpose
AUDIO
•
SEPTEMBER, 1954
of the speaker as described later. In
every instance the glue should be used
spar ingly, especially on the cone. When
the chamois is glued to the frame, the
g lue should be spread near the outer rim
of the frame only; this will allow a
longer chamois suspension and preserve
its pliability.
When the job is completed, we have a
cone that is suspended at four points by
the spider, and at four points on soft
chamois at the outer rim. It would be
difficult to conceive of a more compliant
suspension. An ordinary replacement
speaker, purchased for about five dollars
in a radio supply store was thus treated
and then compared to a I S-inch speaker
costing more than 10 times as much. T he
cheaper 12-inch unit appeared to be distinctly cleaner, although the overall response was admittedly somewhat rough
and shrill due to inherent characteristics
and the removal of cone resonance as a
contributor of bass.
This phenomenon of shrillness may be
removed by two general methods, the
use of the speaker as a woofer only, or
frequency correction of the speaker itself. T he latter may be achieved by a
mechanical means that the writer has
found surpri singly effective and that
seems to smooth the high range. It is to
be recommended only for inexpensive
speakers of the replacement class (and
then only on 10 and 12-in. units), but
these are the units that most need further alteration.
The method consists of gluing a small
perforated aluminum dome over the center of the cone in place of the dust cover.
This .dome may be obtained from an
aluminum . clothes-sprinkler head .. TJ~e
sprinklers are obtainable from most
var iety stores for about a nickel. The rim
that clamps the dome in place should be
removed by inserting a sharp knife blade
under it and lifting it away from the
dome. A small amount of household glue
should then be placed around the rim of
the dome, and after positioning, a small
weight on the dome will hold it in place
until the glue has set. The speaker should
now be ready to mount and tryout.
Fig. 6. Four strips of the soft chamois are glued
in place to hold the cone centered.
Fig. 7. Spaces between the four original chamois
strips are filled with loosely hung chamois to
help seal front off from rear a ir without restricting cone movement.
Alternate Method
Some owners of speakers that do not
have the usual felt dust covers so typical
of the replacement speaker class may
wish to adopt the chamois treatment.
This is made possible by a slightly different technique. An example is the GE
1203A shown in F ig. 8.
(Continlled on page 71)
Fig . 8. ·A complet e job done on a GE 1203A
speaker.
23
Accurate Design of Phono Equalizers
CHARLES F. HEMPSTEAD AND HAMILTON BARHYDT::
In Two Parts-Part 2
..,~
Design of the treble section of the equalizer and
a complete preamplifier designed by the authors.
T
H ERE ARE THREE commonly used
methods of obtaining treble ro11off
eq ualization: an inverse-feedback
circuit, an interstage R-C attenuator, or
a low-resistance loading of the magnetic
phonograph pickup. Only the last of
these fulfills our requirements of high
quality performance, economy, and simplicity of design. The disadvantages of
the first two of these methods will be discussed briefly to bring out the advantages
of the third method.
By simply shifting the turnover frequency to a higher value we can use the
feedback equalizer already described to
obtain treble rolloff. The response will
be the same as that shown in Fig. 34
where i. replaces i" il replaces i" and
Am/At replaces Ab/Am. At is the minimum value of the amplification Act) at
high freq uencies, as shown in Fig. 1.
The equation for the curve in the treble
region is more conveniently written as
I::
A(f) =
Am '\j
(At/A", t/i.);.
1 + (t/t.)'
Since the feedback factor cannot exceed
unity, the minimum value of the amplification A (f) for any frequency is slightly
greater than . unity. The output is fed
back to the cathode of the firs.t tube so
that the load impedance which the feedback loop presents to the output of the
ampli fier becomes at high frequencies
very. nearly A Ef) x R k, where Rk is the
cathode resistor of the first tube. Since
Rk is on the order of a few thousand
ohms, the load impedance presented by
S N. Pickering, "Effect of load impedance
on magnetic pickup response," AUDIO E NGINEERING, March 1953, page 19.
* Com !?/I
4
U1Iiv ersity, I thaca, N. Y.
See Part 1, August 1954.
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the feedback loop becomes too low for
the amplifier to drive without excessivedi stortion when A (f) falls below about
5, thus limiting At to a value greater
than 5. In order to provide treble equalization for Columbia LP recordings out to
12,000. cps with .0 db a ccuracy Am/At
must be 20. It would be convenient to
combine the treble equalizer with the
bass equalizer, using two reactances 111
one feedback loop, so as to reduce the
number of vacuum tubes required. We
have shown that to obtain proPer bass
equalization down to 30 cps requires
Ab/ A·II/. equal to 40 and that Ao/ Ab of at
least 2 is desirable. Thus, to build this
feedback equalizer one would need an
amplifier with a gain of at least
Ao At Am
Ao = - - - --At = 2 x40 X 20 X 5 =8000.
Ab Am Ab
This would require two pentode amplifiers driving a cathode-follower output
stage.
A further disadvantage of this method
is that it requires that the phonogmph
pickup be loaded so that its output is
constant out to the highest frequency to
be rep roduced. In a recent articleS Pickering discusses this problem. To obtain
s11ch a flat response it is necessary to use
a large value of loading resistance, which
makes the treble response very sensitive
to capacitive loading. For flat response
out to 12,000 cps with the GE cartridge,'
for example, the rotal shunting capacitance must be less than 50 ~~f. Such a
low capacitance is virtually imposs ible
to obtain in practice since shielded wir-
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SOLID LINE • DESIRED RESPONSE
<> CIRCLED POINTS · MEASURED RESPONSE
-?oroo
1000
10,000
FREQl£NCY IN CYCLES PER SECOND
24
Fig. 4. Various treble
rolloffs obtainable
from the GE pickup
with different values
of load resistance .
Two sharp cutoffs
obtained with loads
including paralleled R
and C are also shown.
ing must be used and since triode tubes,
which are usually used in audio amplifiers, present input capacitances frequently higher than 100 ~~f due to the
Miller effect. (Large amounts of inverse
feedback introduced into the cathode circuit, however, reduce this effect.)
We turn our attention now to the interstage R-C attenuator equalizer. This
type of equalizer is popular for treble
rolloff since it has no loss below the
treble frequencies and gives a full 6 do
per octave attenuation above the turnover frequency; so it is not subject to
the first set of limitations of the feedback
equalizer just discussed. It does require,
however, that the pickUp be loaded to
provide flat frequency response with the
attendant disadvantages. Such an equalizer would have to be outside the feedback loop for bass equalization, but it
could be fitted in elsewhere. If equalization is not applied before amplification
though, the high-frequency components
of the signal l1)ay be amplified to large
amplitudes and produce distortion in a
particularly annoying ·frequency range.
In order to avoid these disadvantages
the authors feel that the best method of
obtaining treble rolloff is by loading the
pickup cartridge with a low resistance,
providing proper treble equalization before any amplification and making the
treble response relatively insensitive to
shunt capacitance across the pickup. The
turnover frequency is given app roximately by
Rr. +Ra
2rcL
where R L is the load resistance, Ro is the
series resistance of the pickup, and L is
the series inductance of the pickup, as
explained in Pickering's article.
If the effective inductance of the
pickup were constant over the audio frequency range, then the treble rolloff provided by the low res istance loading woul d
be 6 db per octave. There is considerable
;'lterwinding capacitance in the coils of
the pickup, however, which causes a decrease in the effective inductance with
increasing frequency, especially above
1,000 cps. In the case of the GE pickup
the effectiye inductance at 10,000 cps is
only 0.6 that at 1,000 cps. The result of
th is is that the slope of the roll-off obtamed is somewhat less than 6 db per
octave. Nevertheless good equalization
can be obtained, fitting the desired curves
to within 1 db, as shown in Fig. 4. It also
conventiently turps out that as one goes
to higher turnover frequencies the roll-
AUDIO
•
SEPTEMBER, 1954
,
off rate decreases enough so that one can
obtain good equalization for the Decca
ffrr records, which require a 3 db per
octave rolloff starting at 3,000 cps. These
loading resistors can be shunted with up
to 250 !J.!J.f with neglig ible effect on the
response curves, affording ample allowance for shunt capacitance introduced by
the shielded input cable and by the input
capacitance of the preamplifier including
the Millel' effect. This type of equalizer
can also be used to provide 12-db-peroctave scratch filters by placing a sufficiently large capacitance in shunt ac ross
the load r esistor, as explained in Pickering's article. Two examples of this are
shown in Fig. 4.
All the curves in Fig. 4 were obtained
experimentally by the method outlined
by Pickering and shown in his F'ig. 16.
The values of load resistance found experimentally by this method ar e the same
as those recommended by GE6 for the '
two cases, LP and AES, for which they .
give specific information. In private correspondence with the General E lectric
Company their engineers stated that this
method should give results very close to
those obtained from a true constant-velocity source. They pointed out that this
methc;>d gives results more accurate than
commercially available vinyl frequency
records. These records have deviations
as high as 4 db at the high-frequency
end due to groove compliance which may
vary considerably depending upon the
exact g roove dimensions, the number of
plays on the stylus and the record the
ambient temperature, etc. The cl~sest
practical approach to an ideal constantvelocity source is a carefully recorded
shellac record, not avai lable to consumers.
If vi nyl frequency records vary as
much as 4 cib in their high-frequency response, one would expect that all other
vi nyl ini crogroove recordings would also
vary thi s much or even more. The highfreq uency response of anyone record
wi ll also vary considerably from the outside grooves to the in side grooves ev en
though partial compensation for this effec t may be made by special equali zation
during r ecording7. Hence attempting
exact treble equalization is fruitless, and
the listener should expect to have to use
his treble tone control to compensate for
variations of l'ecords from the ideal recording. characteristics.
The circuit diagram of the preamplifier design finally arrived at by t he authors is given in Fig. S. Care . must be
taken in the construction of such a ci1'cuit in order to r educe the hum and noise
to a satisfactorily low level, but many
excellent articles considering these problems have been publisheds so they will
not be discussed here. Ao will depend on
the transconductance of the particular
+300V
•
SEPTEMBER, 1954
12AU 7
8200
~
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~~~~~~=~~-;-
d:.
(THE CAPACITIES INCLUDE
ALL STRAY EFFEC TS)
TREBLE
POSITION
1
2
3
4
5
6
7
3:'
3:'
ill:l;
0
0
0
0
§
+ 100
'"
'"
_ ____-+_""-:-I~::4-:;-:::;:-I---i~--o
5.9MEG.
73000
RECORD
COL. LP 6 NARTB
RCA
AES
LONDON Ifrr L P
DECCA If rr 6 LONDON flrr 78
4 kc SHARP CU T OFF
8 kc SHARP CU T OFF
GND.
.00427
BASS
POSITION
RECORD
1
COL. L P
2
RCA
3
AES (400-)
4
NART B
5
6
(Ab/Am)
5
10
7
500 300 -
BOTH SWITCHES ARE . SHORTING TYPE
Fig. 5. A complete preamplifier-equalizer, with variable characteristics, designed by the authors
in accordance with t heir method.
12AX7 used, but the large amount of
feedbaci): used makes the circuit insensitive to reasonable variations in gill.. A
typical value of Ao is 2,000, while Alit is
25, The application of a large amount of
feedback around three stages requires
some care to maintain stability.· 'Direct
coupling to the cathode follower reduces
the number of phase-shifting networks
inside the feedback loop. Large decoupling time constants ru'enecessary and the
coupling time constant between V, and
V. is chosen to reduce the gain at frequencies below 20 · cps. With <conventional hum balancing methods when the
heaters are operated on a .c. the hum and
noise output is easily held below 2 millivolts rm5, which is 42 db below the average output of the preamplifier when
using a GE cartridge. The use of d.c. on
the heaters reduces the hum by another
20 db or more.
The method of changing bass equalization is somewhat unconventional. Since
a d.c. feedback path is used, there will
inevitably be changes in the d.c. v;pltages across the feedback capacitors if
these and their shunting resistors are
switched. Conventional click suppression
techniques are not sufficient to reduce
the annoying clicks which appear at the
output -of the preamplifier in this case.
To avoid this diffiiculty a fixed bass
equalization having f. = 500 cps and f' =
12.5 cps. (i.e., Ab/ Am:::40) is introduced
into the feedback net'V.9rk. Other bass
egualiz_atiori ch aracteris~ics: are obtained
by placing outside the ieedbac_k loop R-C
equalizers to provide the small changes
necessary. T o shift the turnover frequency to other values, equalizers with
characteristics shown in Fig. 6 are inserted, making f' (of this correction
<equalizer) = 500 cps and f. the ne':V turnover frequency. To obtain low-frequency
bass de-emphasis, such as in the Columbia' LP characteristic, a simple R-C
coupling circuit having the turnover frequency required for de-emphasis is used.
The net result is equalization which is
accurate to within 1 db down to 30 cps,
while below 20 cps the gain drops off
rapidly, g iving good stability_ and low
noise at low frequencies. The drop below
20 cps is caused by the lower turnover
of the feedback equalizer and the choice
of coupling time constants.
The treble equalization is obtained by
low-resistance loading of the phonograph pickup as previously described.
We would Eke to point out that the provision for RCA recordings is a 6 db per
octave roll-off starting at 2, 120 cps
ratheL. than the frequently used 2.5 db
per octave at 1,000 cps, in accordance
with the information in reference 1. All
the treble equalizations are shown in
Fig. 4. Two sharp cutoff positions are
provided for old or scratchy records. It
( Continued on page 65)
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AUDIO
,'0
6800
Z
6 "Variable Reluctance Application Data,"
General Electric guide for the audio hob,
byist.
7 See reference 1 last month .
S R. H. Brown "High Fidelity Phonograph Preamplifier Design," AUDIO ENGINEERING, April 1953, page 19,
.
3900
5100
A.
I
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I
I
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I
" - - - - - - - - -1-I - -(-I
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FREQUENCY (LOG SCALEl.-
FREQUENCY (LOG SCALE) -
Fig. 6. Additional equalizers with respo nses as shown are inserted to shift t urnove r frequency.
25
A ·Transistor Remote Amplifier
P~UL
PENFIELD
JR. ~:
Construction details of a completely portable, light-weight remote amplifier, which utilizes transistors for ruggedness, size, and economy.
R
is a student-run
extracurricular activity of Amherst
College, and as such much of the
programming is devoted to the interests
of the college, both students and faculty.
Although heard throughout the town of
Amherst, its main responsibility lies toward the college. W AMF broadcasts' all
college football and most basketball and
baseball games, both at home and away,
play by play. In addition, lectures, musical programs, and other events of college
interest are broadcast on the spot. To
facilitate our rather extensive remote
pro"gramming, we decided recently to
build a second remote amplifier, with
certain features not found in most commercial units of this type.
The most important "extra" wanted
was operation from self-contained batteries. Although most of our remotes are
done indoors or from press boxes, often
it is difficult to find a power outlet, and
on those occasional outdoor broadcasts,
it usually turns out to be next to impossible. One nearby college has no 117-volt
service at its baseball diamond, and we
once found it necessary to run nearly
1,000 feet of drop line to reach our vantage point. Two microphone inputs of
medium impedance seemed desirable for
greater versatility; our previous remote
amplifier had only one. The completed
unit was to be as small and lightweight
as practical for ease of handling arid setting up .
ADIO STATION WAMF
* Chief Engi1i'eer, Ra.dio Sta.tion W AMF,
Amherst C oileg£;, Amhe·rst, M assacJmsetts.
Figure 1 shows the outside view, wi.th
the cover open, of the completed remote
amplifier, which we believe to be the first
of its kind. Three Raytheon junction
transistors and a 3V4 give ample power
output. Transistor types CK-721 and
CK-722 were both investigated, and it
was found that the cheaper CK-722 was
too noisy for this application. Transformer coupling between stages was not
found to be necessary, in spite of the
radically different input and output impedances of the grounded-emitter tt-ansistor. A vacuum tube was used in the
output stage because high-power transistors were not on the market at time
of construction. No doubt the presently
available power transistors could have
been used with much better efficiency
and less weight.
The unit is housed in a 15 X 6 x 3-inch
steel box left over from war-surplus purchases. No attempt was made to keep
physical size down to a minimum; nevertheless it is smaller than most comparable commercial amplifiers. The batteries
are housed in the right-hand third, as
can be seen in Fig. 2. A hinged cover
protects them. A spare "A" battery is
generally carried with the amplifier in
case of failure during a broadcast. Replacement takes only a few seconds, and
the program can go on with a minimum
of interrupti on. The 3V4 tube also faces
into this compartment, for easy replacement.
All sheet-metal parts, with the exception of the case itself, are of aluminum,
and were fot-med by hand . As can be
;
)
.
:
'
26
Fig. 1. Over-all view
of the remote amplifier with the cover
raised. A rugged canvas handle on the
cover makes the unit
t~uly portable. Note
the battery compartment at the right.
seen 111 Fig. 2, the heavy components,
notably the output transformer, are
mounted near the center for good weight
distribution. The hinged cover of the
case protects the controls and the VU
meter from accidental damage. A mechanical interlock prevents an absentminded engineer from closing the cover
with the power turned on. The mike connectors are of the Cannon P3 series, and
the output binding posts ar e made by the
Heath Company. These latter were
mounted horizontally, providing a maximum of finger room, while still clearing
the cover as it closes. All controls, soldering strips, wiring, and other parts are
mounted on a sub chassis, with only the
shafts of the controls sticking through
the outside panel. The ' structural parts
are held in with sheet-metal screws, and
the whole unit is removable, as seen in
Fig. 2.
The Circuit
Electronically, the use of transistors
made construction possible using a minimum of parts. The circuit diagram is
shown in Fig. 3.
A medium-impedance microphone can
feed directly into a grounded-emitter
transistor stage without too serious a
mismatch. The unusually large size of
the coupling capacitors C" C" C" Co, C"
and C. is necessary for good low-frequency response, due to the relatively
low input impedance of ·the transistor
stage. Values up to 50 p.f, as used here,
are not uncommon for this application.
The lowest voltage rating is ample, of
course, since the maximum voltage present in that part of the circuit is generated
by the 4.5-volt transistor battery.
The base resistors R" R4, and R7, are
chosen to give the correct base current.
The -load resistors R ., R" and R ., are a
compromise between the relatively high
output impedance of the transistor stage
and a value low enough to allow sufficient collector current to pass.
The attenuators R . and R. were designed to present a constant impedaNce
to the following stage, to prevent the setting of one control from affecting the attenuation of the other. The load resistor
of the previous stage tends to upset this
relationship to a certain extent; for best
results a T-pad should be used. However
space and financial" considerations prevented their use in this particular model.
The final-stage tube required 4.5 volts
peak to drive the grid, so a step-up transformer was used. A small UTC ouncer
output transformer connected in reverse
AUDIO
•
SEPTEMBER, T954
did the trick. No d.c. runs through this
transformer. A high-quality output
transformer, a Chicago BO-2, was used
following the final stage.
Two earphone monitor outputs a re
provided and are isolated from the line
by two 2,000-ohm resistol'S to prevent
loading. Adequate earphone volume is
obtained. A lthough no send-receive
switch is incorporated in the amplifier,
the monitor can receive talk-back from
the studios, and the second monitor jack
is for the announcer. The VU meter
level is determined by resistors RIO, RI1,
and RII, which comprise both the series
r esistor and the attenuator required for
meter operation at +8 VU. This is of
course the maximum level allowed by the
telephone company on their radio loops.
Fig. 2. Interior view
of the amplifier. The
chassis comes out in
one piece.
Amplifier Performance
The amplifier was not specifically designed around high-fidelity standards;
however a general review of its operating characteristics will prove of interest.
Rough frequency response tests indicate
that the unit is flat within ±2db hom 50
to 15,000 cps. The harmonic distortion
was measured on a null type of distortion
meter and turned out to be less than two
per cent at operating level, most of it
second-order distortion. There is, of
course, no hum problem with this battery-operated amplifier. However the
noi se becomes bothersome at t imes.
The operating signal-to-noise ratio is
in the neighborhood of 50 db in one
channel, and 43 db in the other. The difference is due to variations in the transistors themselves. The three CK-72 1
transistors were each tested for noise,
and the noisiest one put in the second
stage, where noise is less of a problem.
In practice, the noise is just audible between spoken sentences. Whereas this is
no problem at sports events, with the
general high backg round noise, for lectures and concerts it has proved to be
somewhat annoying.
Let the writer emphasize that this amplifier is not a "gadget." Transistors
were used not because their use would
be novel or educational, but because they
presented the easiest solution to the problem at hand. The freedom from 117-volt
power lines has made this remote amplifier more useful than first expected. During the traditional freshman-sophmore
rivalry at Amherst Coll ege in 1953, one
of the station announcers had the unit
strapped to his back, and he wandered
about during the riot tra iling just one
pair of wires behind him. The wire went
to a tape recorder set up in a nearby
building. Such a set-up could be useful
during emergenci es or for on-the-spot
disaster reporting.
the 5-prong subminiature hearing-aidtube sockets.
Much has been made of the claim that
transistors have such a high life expectancy that they can be soldered or welded
directly into place, without the use of
sockets. However, the heat of a soldering iron applied to the leads is enough
to burn out present transistors, as the
writer found out by bitter experience.
Holding the lead nex t to the body of the
transistor with long -nosed pliers to conduct away the heat is helpful, but still
does not solve the problem. Also, the
leads have the unfor tunate habit of
breaking off, invariably (it seems) right
at the body of the transistor. The simplest way around these two difficulties is
to use a socket. Contacts 2 and 4 of the
socket are removed simply by pulling
them out, and contacts 1, 3, and 5 are left
in for use. One end is painted red, to
correspond with the r ed dot next to the
collector lead of the transistor. The lead
wires of the transistor are cut to a
quarter of an inch to fit snug ly into the
socket.
Transistors burn out electrically very
easily, and too Iowa value oi base resistance will allow too much base current
and thus too much collector current.
Also, on p-n-p junction transistors. like
the CK-721 and CK-722, the B-supply is
reversed from vacuum tube practice and
so all polarized components like electrolytic capacitors and d.c. meters, must be
connected in reverse. Being absentminded and connecting the collector lead
to the positive battery terminal instead
of the negative terminal effectively
biases the collector-base junction forward and instantly burns out the transi stor.
At present the only obstacles to more
widespread use of transistors in audio
circuitry seem to be cost, availability,
and noise. With each new trans istor release, noise is becoming less and less of
a problem. In a few years, the cost will
undoubtedly dip to below the cost of
comparable vacuum tubes, and transistors will become more plentiful, so it
behooves every audio engineer to get in
some experience with transistors before
their use b.ecomes widespread.
T2
CHICAGO BO'2
OUT
Z·500fi
Handling Transistors
Not much has appeared in the literaabout the "care and feeding" of t ransistors. A few comments here on this
important subject may prevent reader s
from making some of the same mistakes
the writer has . Since transistors are still
relatively costly, these comments are
well worth reading. The transistors were
adapted to plug into sockets. These are
AUDIO
•
SEPTEMBER, 1954
S2
+
S3 B3 4 .5V
'---~~-------+~-IIIIIIi.
Fig. 3. Schematic diagram of t he amplifier. Use of transistors makes construction possible
using a minimum of parts. Two mike channels with independent attenuators are provided.
27
,.
The orchestra & the lone listener.
From High Fidelity to Music
ZYGMUNT HOP
Loudness· controls may be the solution to music reproduction for those who must, for one reason or
another, play their ' records at lower-than-normal volume , but for optimum. listening the old adage that
"music can have its original tone quality only wheri reprod uced at its origina l volume" is the best rule.
I knew that J im had off the lights and the first bars from the
a secret method of record reproduc- speaker filled the room, everyone's face
tion. Now I am able to tell you that showed an expression like a gourmet's
secret for I tracked him down and made taking the first mouthful of a famous
him talk.
dish; these connoisseurs tasted, with
There wer e a great many music lovers wide open ears, both for tone quality and
in our town, all of them playing records the substance of the recorded piece. Of
at home with whatever equipment they course, at the end of the party, the visicould buy or construct. As they got to- tors would not make any open remarks
gether, meeting in the record and radio to the host but their appreciation of his
shops, those fellows who could afford a concert could be evaluated from the atbetter reproducing system or a superior tendance at the next occasion.
selection of records took their pride inI knew a dozen or so of these private
viting their less lucky neighbors to pri- concert promoters personally, as they
vate recorded concerts. That was a k ind used to consult me on matters of equipof social event: Every two or three ment, and I guess there must have been
-weeks these musical hosts collected what- at least a score of them in town. SGme
ever chairs they could find and put them had quite a reputation as record hobbyin rows before their loudspeaker. When ists. But there was one outstanding
the guests arr ived, mostly on a Sunday among them, one I heard spoken of with
afternoon, and settled down in those admiration, one of whose recorded concasually arranged chai rs, they received certs were a series of acclaimed suca n icely printed pr:ogram. lt was re- cesses, and that was J im. Some had
markable how well the rules of the con- . ·sought_my advice before. I had given it
cert were observed: No talk, no refresh- as honestly and as well as I could. I had
ments, absolute quite and concentration helped them to construct and improve
011 listening. It was pleasant but serious
their audio system; I had told them how
entertainment. When the host switched to manipulate it and its gadgets, which
can often be quite confusing to beginners. They used to listen to my pro* 1 West 89th S t., New Y ark 24, N. Y. fess
ional explanations, with patience, but
they came back with doubts and quesIllustrations by J. Gordon Holt
F
OR A LONG T I ME
.....
-
28
tions again and again.
Naturally I was startled when these
same people began, one after the other,
to talk as if they had found perfection
in recorded music, at last. What on earth
had brought about that change? Perhaps
they had found the perfect amplifier, I
asked them. No, they had still their old
equipment ; some was cheap stuff, and
some self-constructed, but they played it
the way J im did. And this was about all
these ungrateful persons would tell me.
lt was not easy to get in touch with
J im, of private concert fame. I had met
one of his best fr iends, Rich Bill. He was
the owner of several oil-wells and bought
a complete new set of hi-fi equipment
every two months. Every time he did so.
at a price that never ran under fou r
figures, he sent his previous outfit as a
gift to a hospital or institution. Invariably, he had to spend hours afterward ~ · :
with those people, explaining to the perplexed staff and doctors now to hvist a
dozen knobs.
Through Bill,) was introduced to.Jim.
We met in a comfortable corner of the
"Audio and Steak" Shop, and I immediately began to question him.
Jim's equipment turned out to be one
of those ordinary, commercially-built,
medium-priced jobs. H e had bought it
. AUDIO
•
SEPTEMBER, 1954
•
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SOLID LINES • FU~OAMEN TAL TONES ACTUALLY
PLAYED AND REACHING THE EAR .
DOT TE D LINES· COMBINATION TONES~
PROOUCED AND ADO 0 BY
THE EAR.
Music ca n ha ve its original tone qua lity only
when playe d at its original level.
in a radio store. I asked if he had
changed anything. Maybe he had used
one of the "distortionless circuits" that
appeared in the literature; or did he use,
perhaps, in his concerts such modern
ideas as "stereophonic" listening?
If that means, said Jim, that one
should hear the music as coming from
different directions, then the fundamental problem was, whether the music
came from a point source or from a
widely dispersed body of players. Suppose it was a solo performance, then
the music originated from a point, anel
it should appear to come from one point
also, when reproduced from a record.
In the different case of a huge orchestra of a hundred or more players this
body usually dwindled in a full-sized
auditorium with several thousand seats,
to the dimension of a spot and the ear
had the impression that the music was
coming from point rather than from a
whole area. Of course, if one listened
to the recording of a monster orchestra
in one's own home, then the situation
was reversed: The audience was a lone
person, the orchestra a giant body. But
the lone listener would not accept this
superiority of the orchestra; he would
prefer to -imagine himself in a concert
hall amidst thousands, when the orchestra looked like a small group far below.
In either case, Jim did not see any nt;ed
for stereophonic reproduction. Incidentally, its only effect upon Ji'm, and he .
had heard the most elaborate stereophonic demonstrations, had been that
the music seemed to corne from a distance.
I always go for the real music, said
Jim. In this great battle of audio design
and high fidelity we have forgotten what
it is all for. What do we want fr om record; and record reprofiiuction? We want
AUDIO
•
SEPTEMBER, 1954
life-like music. But, first of all, do you
know what music is?
Jim had caught me unprepared. Certainly I had an idea what music was. But
I had my doubts if one could regard
some super-modern 'compositions as what
I understood music should be. I hesitated.
Music is sound with spirit and delight
in it, he told me.
Said Jim: Good music is anything you
should like to hear again. Very good
music are those pieces you would hear all
your life again and again. But if you say,
"once, and never again", it's bad music.
These rules are my guide when I choose
the programs for my cO/1certs. For I
want to hear good music. Again, only if
I know what I want to hear, can I play
records in the correct manner. I want to
hear music as it really sounds, natural
music, with nothing artificial added .
But how do we know how the original
music sounds? I asked.
'
Nothing easier than that, answered
Jim. Do you see the couple over there?
They are pupils of Uptown Music
Schoo!. Violin and piano, mainly. Did
you ever try to invite music students to
give a performance at your home? Tell
them you are going to play a record,
Sonata so-and-so, played by famous
So-and-so, and then they should play
another item, but for the same instruments. Surely, they have time. They
come and rehearse. While they play, I
listen intensively, and with the sound of
true music still in my ears, I adjust the
controls of my audio system so that the
record reproduction sounds exactly as
the original music. My concerts are:one
half "live," one half "recorded" concerts.
You should see how pleased these
local students from the conservatoriums
are when they are able to show their
talents, and th~ audience likes an improvised, fresh performance and gives them
'
a warm appreciation.
You should see the revelation that
comes upon those listeners when they
g'et clear, real music into their speakertortured ears. Once they have heard
how. musical instrument.s actually sOllnd
in a room, 'they drop the usual misconceptions of tone quality because they
have something to hold on and compare.
When I start playing the recorded part
of a concert, I have "music" in mind and
nothing else. So I hide the speaker. No
round openings or machinery, or baffles
are visible. I shut off the main lights.
Only a spotlight is left to single out an
object which symbolizes "music". A
violin on a table, a flower-decorated bust
of a famous compose'r, or an open score
on a music stand, illuminated by a green
beam, will occupy the sight of the listeners during the concert, will make them
unconsciously forget that what they hear
is a record, and keep their thoughts on
"music."
Jim, don't try to fool me, I said. You
haven't told me your top secret of record
reproduction yet.
Well, said Jim, come in at rehearsing
time, one hour before my next concert
begins.
* * *
Hardly had I entered Jim'~ living
room which was c1"Owded with empty
chairs of all styles, when Jim asked me
at once to play a record. I turned the
changer on and let it go. Immediately,
the room was filled with beautiful cham- .~:
ber n1usic. But the v01ulne, as it was set, '~
seemed unnecessa.rily loud' to me, and :'"
when the music went into a crescendo, ~
I followed a sudden urge and cut it down .
to what I regarded as a "tolerable" vol- ~
ume.
After the first movement Jim faded the
record out and introduced a trio of
musicians to me who had modestlv
stayed away in a corner. These gentlemen will now play the same item, he said,
and, in a moment, the same beautiful
melody as before filled the room.
Could it be, I thought, ,t hat three
musicians make such a lot of noise? Can
three instruments, without an amplifier,
be as loud as that? I had never imagined
a trio had such a volume. In fact, it was
as loud as, .. . trtjly, as loud as the
music from the record had been before
I cut the volume down .
Does real music sound too loud to
you? Jim asked. Turn those instruments
low, if you can! That is music at its
natural volume. Nothing to be corrected.
Here is the crescendo. Can you bear it?
Ope rati ng t he Hi-Fi Sound System
29
•
This is music, come free, out of the cage.
It flies as high as it likes. And that's why
it is beautiful.
.
The musicians had finished. Jim
started the record once again. Turn the
volume control up and down, he told me.
I did.
Now listen carefully to the record. As
you turn down the volume you come to
a certain position of the control knob
where it sounds like music. Beyond tnat
point it is unnaturally loud, below it
sounds rather flat. Now you are at the
correct position. Stay there!
I noticed that the musicians had
started to play simultaneously the same
item. Jim flipped a switch. The record
cut out and I could hear the musicians
playing alone. I compared. There seemed
no difference between record and live
music. The same tone quality, the same
loudness.
The room went quiet.-If you want
to hear music from records, you have to
obey a fundamental rule of record reproduction: "Music Can Have Its Original
Tone Quality Only If Played At Its
Original Volume", said Jim.
But isn't it possible to compensate for
tone at a different volume? I asked.
No! said Jim. I shall prove it.
Suddenly I found myself in Jim's laboratory.
There were three audio oscillators,
each one set to produce a different tone.
The frequencies of the tones were one
in the bass, one in the middle and one in
the treble region of the spectrum. All
three were fed together into an oscilloscope. I could see on the screen of the
scope that the tones had the perfect,
undistorted shape of sine waves.
Mark the amplitudes down!, said Jim.
I did so, measuring the size of each torie
on the screen.
Jim connected the three oscillators to
a speaker. What do you hear? he asked.
It sounds beautiful , I said. But I would
not believe that it is only three tones
that I hear. It is rather a combination
of many tones.
Jim cut the volume of all three tones
down. I could see the waves on the scope
shrink, each an equal amount. How does
it sound now? he asked.
It seems more like three tones alone,
but it sounds flat, I said.
Jim turned the volume up. The waves
!)/1
I
I
I
I
I
I
Grampa and . the 200-watt Amplifier
30
on the scope grew each double as high
as they had been in the first case. They
still had a perfect shape. But the sound
that I heard seemed composed of many
tones and was shrill, t}npleasant.
I wonder why I hear more tones than
I can see on the scope, I said. I wonder
why I hear distortion right now, while
the scope does not show it.
Said Jim: These are the facts of hearing: Exactly 200 years ago Tartini discO'v ered that the ear adds to t1:le tones
which actually reach it, combinations of
these same tones. About 100 years ago,
Helmholtz showed by experiments, by
mathematics, and by an analysis of the
ear's mechanism that the combination '
tones produced in the ear were a fact;
that they may give to music either a
pleasant or unpleasant character; and
that these combination tones, which we
hear additionally, increase steeply with
the intensity of the fundamental tones
reaching the ear.
·If music is to sound pleasant, therefore, it must be played with a certain
intensity, at which enough combination
tones are produced in the ear to give it
a well flavored, easily accepted, smoothly
consumed sensation. If the music is too
low, less combination tones are produced
in the ear, giving less stimuli to the
nerves, p,nd it sounds flat. But if the
music is too loud, it sounds sharp and
distorted. For as the fundamental tones,
which reach the ear, become louder, the
combination tones, which are produced
from them in the ear, grow more and
more in intensity and attack the ear in
transient shocks. This is surely not
pleasant to the ear.
Now I understand, I said, why one
can hear distortion from an absolutely
distortionless amplifier. When all other
sources of distortion are eliminated, the
ear alone can be the offender. To prove
this, modern theory would say that the
ear has a nonlinear transfer characteristic, owing to unsymmentry in its mechanism, and then the theory proceeds to
run equations off a curved line.
Helmholtz did it with energy equations, said Jim. He set the three audio
oscillators to the output, which I had
measured first, when the combined sound
was beautiful and pleasant, and connected them to a tape recorder. He made
a steady recording of long duration and
played it back on the .oscilloscope and
over the speaker. The reproduced tones
were set to the same amplitude as the
original ones and had the same perfect
sine wave shape. The reproduction
was beautiful, too, just as the original.
In other words, for all the tones to
blend together in the .ear, you must play
the reproduction at the same level as the
original
Returning to Jim's living room, I
asked: Is this your top secret?
Yes, said Jim. The first and all-important thing to do when you adjust
'your amplifier controls, is to set the volume control to the original loudness of
the reproduced item. A violin on a record sounds like a violin, if it is played
just as loud as a real violin. A piano on
a record sounds like a piano, if it is
played just as loud as a real piano.
Still, I said, the instruments seem to
loud that way.
This is your fault, said Jim, because
you seldom go to live concerts. Cramped
close to the loudspeaker, with the amplifier whispering, like noise-frightened
grandpa, you are used to listen to a
weak, ghost-like performance of mllsic,
satisfied to grasp only the idea of its
contents. But in the concert hall, music
is full of power, brilliance, vitality.
Original music has its natural volume.
Keep it at that, get used to it!
Well, I said. I could agree to playa
small group of instruments or voices
from records at their natural volume at
home. But how about a big orchestra?
That's different, said Jim, because
even a concert auditorium may be too
small for a full orchestra. It depends
rather on the acoustical design of the
hall than on its dimensions whether a
mass concert sounds well in it. What the
listener desires in an orchestra performance is "distinction."
* * *
I shall never forget my first experience with modern acoustical architecture
at the.. Royal Festival Hall in London. I
had a seat far up in the rear but I could
hear the voice of each instrument separately. I could distinguish each one of
the instruments with its characteristic
color, with every shade of its personality
and partnership in the performance. And
still, the orchestra was one body. I enjoyed this concert, because of the
heavenly sound of the music, as I never
did one before. And I have attended uncounted concerts during my life.
How do I adjust the volume when I
play an' orchestra record at home? Since,
above all, I want to hear the different
instruments distinctively, I choose a passage when only one instrument predominates and the volume control at once
so that this one instrument sounds like '
the original. That should make the other
instruments also sound like the original,
if the recording is properly done.
As I saw Rich Bill entering at this
moment, I said; It would be fine if it
were necessary to adjust only one single
control. By the way, Bill, how many controls have you got in your latest amplifier?
Let me see, answered Bill ... Two for
the equalizer, two tone controls, and a
number of pushbuttons, and some
switches, and ...
Do you use all of them? I asked.
No, said Bill. I myself set the tone
controls, etcetera, but the volume control is always adjusted by my wife.
AUDIO
•
SEPTEMBER, 1954
Variable Damping Factor
Control
CHARLES A. WI LKI NSt~
The virt ~es of a high damping fa ctor in an am plifier have been th~ subjec~ of unending discussion. The circuit prese nted here ena bles the user to determ me for himself t he damping factor which will resu lt in optimum reproduction through his own speaker system .
E
of motional impedance 2.11 and that given
a DF sufficiently high the damping of
ZM may be made equivalent to pel'feet
horn loadiag. The question that remain,;
is how much damping can we use profitably? The ultimate limit is imposed by
the occurrence of oscillation in the LC R
circuit comprising ZM. If R D is made infinite, ZM will become critically oscillatory. This condition can be produced
by ma king Ra equal to - Rc and corresponds to an amplifier DF of -l. This is
the same a,s saying that R c is exactly
cancelled out by a negative Ra.
Another limit we can observe, if all
that interests us is damping of cone or
enclosure transients at resonance, is
the reduction of the Q of ZM at resonance. When the Q of a resonant circuit
is made equal to 1, the frequency response is flat throughout the range of
res·o nance but there is some transient
overshoot. If the Q is made equal to
0.5, the circuit is said to be critically
dalnped and there is no transient overshoot but the frequency response begins
to droop below the range of resonance.
This effect is shown in Fig. 2. The droop
below resonance is explained by considering (b) of Fig . 1. The R" of the
speaker diaphragm (or apparent diaphragm at the horn rr:outh if the speaker
is horn loaded) beg1l1s to decrease as
the square of the wavelength below the
critical wavelength (the wavelength that
is equal to the circumference of the diaphragm) . This effect alone will produce
a 12 db/octave droop in sound output
below the critical wavelength. The reactance of C E, the compliance of the air
in the enclosure, and CS the compliance
of the cone suspension, become increasingly large below the fundamen tal res~­
nant heque11cy and a<,:count ~or an additional 6 . db /octave droop below
resonance. (M c is the ma5S of the cone
and MA is the mass of the air.) The Q
of the resonant circuit can be decr.eased
by increasing the value of either R,\
or Z1O. An increase in R ,\ can be produced
by horn loading and will result in a
higher critical wavelength. On the other
hand an increase in ZE will not alter the
criti~al wavelength but will have the
same effect on damping as horn loading.
So we see t hat in a speaker system that
has its critical wavelength at a higher
frequency than its fundament al resonant
frequency, the effect of resonance may
be used to reinforce the response between these two critical frequencies.
Fig. 1. Electrical and m e c~anical eq u iv~l ~ nt
By mabng the Q equal to 1, we will
ci rcuits of loudspeaker drIVen by a mplifier.
reproproductIOn seem to hold either of
two widely divergen t opinions on
the desirability of high damping for
loudspeaker loads. Those in favor claim
that a high damping factor (low amplifier output impedance) increases the
magnetic damping of the motion of the
voice coil thereby reducing spurious excursions caused by . mechanical and
acoustical I'esonances and improving the
transient response, while those against
claim that a high damping factor deThe Bogen D030A, wh ich incorporates t he
grades either the high- or low-frequency
dampin g factor control described in t his article.
response (or both) of the speaker thereby degrading the transient response.
The damping factor of an amplifier
Let us examine these claims by reis defined as
ferring to the equivalent circuit of an
(6)
enclosed-cabinet single-cone loudspeaker
shown in Fig. 1. Constant-voltage generators are shown in the electrical equi- where-ZL is the impedance of the ampli valent circuits at (a) and (c), and a fier load, and Ra is the amplifier source
constant-force generator in the mechaniresistance. If the load is a speaker syscal equivalent circuit at (b). Equatiun . tem ZL = Za + ZM at high frequencies and
( 4) represents the total resist.ance RD ZL =R c + ZM at low frequencies. It is
acting in series with the reactive com- . seen that DF increases as R a decreases,
p011,ents of motional impedance ~M to and when Ra equals zero DF equals inproduce damping. Any l11crease 111 ~he finity. If R a should be made a negative
value of RD will increase the dampl!1g value, DF would also become negative.
on motion of the speaker cone. Inspection of both Eq. (4) and (b) of Fig. 1 Opti m um Da mpin g
shows that an increase in radiation reIt has been shown that a high DF
sistance RAJ mechanical l'esistance RSJ is equivalent to higher magnetic damping
or gap flux density B will incre~se the
damping. Conversely, a decrease l!1 ~m­
(b) MECHANICAL CIRCUIT
to} ELECTRICAL CIRCUIT
pli fier source resistance Ra or d.c. vOlcecoil res istance Ro will increase the damping. Horn loading will increase !?-A. R s
is designed into the speaker and 1I1.Sp~C­
tion of Eq. (5) shows that as R s IS 111creased the efficiency !k of the speaker
decreases . This makes it desirable to
have R s as small as possible in relation
F. BIE/IOlR,,+ Rtl
(I I
to RA if damping can be obtained from
l('(BI}2 /1 0'i(RG+RC)
121
com" (Bl)2 I l w
III
another source. B can be increased by
Ro. RA+ Rs +(Blr/ IO'(RG' Rt) (4)
using a larger more expensive magnet
than is obtainable in speakers of modleI TOTAL ELECTRICAL EOUIVALENT CIRCUIT
erate cost. The winding length l can be
increased by using more turns of wire
on the voice coil, but since there is only
a limited amount of space in the voicecoil gap and resorting to smaller diameter wire will increase RC there is an
optimum wire size and winding length
beyond which little improvement can be
gained. Ra can be decreased by decl1easing the amplifie r source resistance, and
as far as damping is concerneEi, a de( BI)2 R,
I~l
jJ. ' IBl}t (RA+R,)+(Rc+RC1 U RA+RS)t +IX"C+ ')( "A-)(C'-XC[I~
crease in Ra is exactly equivalent to
increasing the gap flux density B.
NTHUSIA::>TS OF HIGH - QUALITY
J
* Assistant Chief Eng·ineer, David Bogen
Co., Inc. 29 Ninth Ave., N. Y., N . Y.
AUDIO
•
SEPTEMBER, 1954
J
31
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Variable Damping Factor circuit.
RESON ANT FREQUENCY
2 .0
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achieve optimum flatness in the frequency response. The Q of the mechanical equivalent circuit of (b) in Fig. 1
may be expressed as
X"
- ZI1+R,,+Rs
(7a)
where XM represents the total inductive
reactance of (M .. + M 0). In the total
electrical equivalent circuit of (c) in
F~g. 1, the equivalent expression for the
Q is
(Bl)Z
XM .
(7b)
Q ==
RA
Rs
RG+Ra+ (Bl)z+ (Bl) 2
If we have an ideal exponential horn of
infini te length, infinite mouth a rea, and
zero rate of flare, we can expect RA to
be infi nite throughout the frequen'\:y
range, making the critical wavelength
infinite (zero cps). The effect of (; E
and Cs will be eliminated, the Q at resonance will be reduced to zero, and the
damping w ill be perfect. But since such
an ideal condition is impossible, let us
examine what will happen on the other
hand if we take a less than perfect system (with or without horn loading) ,
and make Z" infinite by employing a DF
of -1. The effeGt of CE and Cs will be
eliminated, the Q at l-esonance w ill 'be
reduced to zero, the damping will be
perfect, but the critical wavelength will
remain unchanged. At frequenci'es below
the critical wavelength, the response w ill
dr??p at a rate of 12 db/octave. The
cntlcal wavelength can be made to occur at a sufficiently low frequency either
by employing a speaker with an adequate
dlaphragm a rea, or by employing a horn
with an adeq uate mouth area: For such
-r
RA Eo
L - - - _ - " HMIv-4--'-'
Fig, 4, Variation of amplifier source resistance
permitted by OF control when using a resistive
load.
5.0
f
. --;;-
Fig. 2. Relative response of loudspeaker for
different values of G.
Q_
11111111:::,
1111 111
rHD8ACi<
!--
1/
ACTUA l
~
F.ig. 5. Equivalent circuit of amplifier with positive current feedback driving loudspeaker load
(for purpose of distortion analysis).
32
".
FEEDBACK
ItO
a large area as would be needed, say,
for a 30- to 50-cps cutoff, the horn
offers the better solution- and the effect
of infinite ZE would be a great advantage
in damping the violent resonances that
occur in a less-than-perfect horn. The1"e
is, however, another mod~ of ,a ttacking
the problem. The 12-db/octave droop
could be equalized electrically if the
critical wavelength occurs at too hi gh
a frequency. If we can reduce the distortion attendant with the degree of
equalization that would be required to
restote the low frequenc ies, this method
would be a legitimate mode of attack.
It will be shown later that a DF of -1
will result in a drastic reduction of all
types of distortion in the speaker system.
High-Frequency Damping
The forego ing analysis, while based
on the low-frequency range, is valid for
the complete. speaker range, providing
allowances are made for the voice coil
inducta>\tce La and for the coefficient of
.c9upling between the voice coil and the
resonances due to cone break-up. Generally speaking, the· coupling between
break-up resonances and voice coil is
small, thereby minimizing the benefits
deriving from a high DF. Horn loading
of the cone for high frequencies appears
to be the only means at our disposal for
damping these resonances effectively.
However, the voice-coil inductance Lo
may have an effect in fi ltering out the
extreme high frequencies as (Ro + Ro)
is reduced. Of course, the magnitude of
this effect depends upon the value of Lo.
In some speakers tested Lo was sufficiently high in value to produce a rolloff ~i th in t;he passband of the speaker
but 111 most speakers Lo was so smaIl
that its effect was limited to the range
above the passband.
From this discussion, we have seen
that there are as many optimum amplifier damping factors as there are different speakers, different enclosures, and
different combinations of the two. This
is a fact, regardless whether optimum
DF is defined as that required to reduce
the Q of the system to 1, or to 0.5, or
that requj,red to cancel out R o. It follows
that it would be of great benefit to incorporate a contr.ol into an amplifier
WhlCh could be adj usted to optimize the
D F 101' each. individual speaker" system.
Such a Vanable Damping Factor control has been incorporated into Bogen
Models DB20-DF and D030A. The
bare bones of the circuit are shown
Fig. 3.
In
Circuit Description
. Th,e ~i r c uit employs ?- simple bridge
Ci rcUlt ll1serted into the common side
of the o~tput transformer seconda~y . A
voltage IS developed"a cross the 0.41-ohm
and ,the 0.27 -ohm resistors that is proportIOnal to the current flowing through
t~le speaker lo~d. This current-proportIonal "'v oltage IS sampled by the slide!on the 25-ohm potentiometer and fed
back through low-pass filter RC as cur rent feedback to the cathode of the first
stage where it is added with the over-all
negative voltage feedback. A t 'a certain
position of the potentiometer slider there
will be no voltage developed b~tween
slider and ground and, therefore, no
current feedback. On either side of thi s
position the slider wi ll sample either a
positive or a negative current-proportional voltage depending whether the
slider is moved toward the 0.47 -ohm
or th~ 0.27-ohm resistor, respectively.
By thlS means the effective source resistance of the amplifier may be varied
be,tween w ide limits in the positive (negatIve current feedback) as well as the
n~gat~ve (~ositive current feedback)
dlr~ct~on. F~gure 4 shows the range · of
vanatlOn plotted for both source resistance and DP, Inasmuch as these curves
were taken for the purpose of calibrating
the DF control, a 16-ohm resistive load
wa,s used across the 16-ohm secondary,
~ lth ~ sJ?"eaker load, the range of va riatIon WIll De a function of the Ro and Z,r
of the speaker. For a speaker with a
rated impedance of 16 ohms, the R c will
be much less than 16 ohms and the ZJr
-
~-+-+-+-+++l-
o
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.... -: or
C~TROI. S~T ~OIl'~AI..
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..
000
FREQUENCY IN CYCL ES PER SECOND
Fig. 6. Cu rves showing the effect of amplifiei"
OF on distortion generated by loudspeaker
system. 5% harmonic distortion contours are
shown. (NORM. DF is equal to + 30.)
AUDIO
•
SEPTEMBER, 1954
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,
" 6 Tell
10,000
l
Z
20,000
Fig, 8. (left). Sound pressure response of IS- in, coaxial speaker mounted in 8 cu, ft, bass-reflex enclosure with amplifier OF set at + 3. Dotted li ne
represents impedance of speaker. Fig, 9 (right). Sound pressure response of speaker of Fig. 8 with amplifier OF set at - 1.2.
r,
- iii
will be a function of fr equency. So we
The voltage developed across RA and
can state that with a speaker load the
Z is
rAt
II::!
action of the DF circuit is two-fold.
,.jlli:fJl
Eo=-A(es+IRt)
1J.i
With the DF control set to introduce
+ IRa + IRe + IRt
(9)
negative current feedback, the source
which can be arranged as
4
resistance is grllater than the basic Ro
b
of the amplifier (Ra with no current
r,
Eo= - Acs+I(Ra+Ra)
r'
feedback) and the voice-coil drive volt-IRt(A-1) (10)
n
rwm
age is directly proportional to the
'I'J
To make Eo a faithful replica of es we
speaker system impedance. With the
must make
DF control set to introduce positive curEo =-Aes
(11)
rent feedback, the source resistance is
c
d
less than the basic Ra of the amplifier
This can be done by making
and the voice-coil drive-voltage is ·in- Fig. 7, Sound pressure waveforms showing the
Rt(A - 1)=Ra+Ra
(12)
versely proportional to the speaker sys- effect of amplifier OF on acoustical transient
tem impedance. The matter of degree response of loudspeaker system. Solid line so that these two terms will cancel. The
shows motion of speaker cone after applicavalue of R t required is
depends on the DF control setting.
The RC filter limits the effect of the t io n of square pulse (dashed line), (a) OF =
_Ra+Rc
(13)
control to frequencies below 300 cps- + 0.1 , (b) OF= + 3, (c) OF= 00, and (d) OF
.R t- A-1
= - 1.2.
(1), to avoid the possibility of the
speaker oscillating at its frequency of
and is the value that will produce a DF
minimum impedance (usually between Distortion Reduction
equal to - 1 by making RG sufficiently
200 and 400 cps); (2), to restrict the
negative to canceL the effect of. Ro and
One of the most important benefits Rt, This also checks the conclusion made
damping to the 10w-freque:1cy range
where it is most needed and most effec- gainea from the use of positive current earlier that if ZE were made infinite,
tive; and (3), to avoid the possibility feedback is the drastiC reduction of alI the effects of C E and C s on the frequency
of the tweetel' oscillating at its resonant types of distortion in the speaker system. response would be eliminated.
Figure 5 shows the equivalent circuit
frequency (if a tweeter is used).
The curves of Fig, 6 show actual
The type of curves shown in Fig. 4 of an amplifier driving a speaker load, sound pressure measurements made on
were found desirable to compensate for Eo is the useful voltage developed across a typical 12-inch coaxial speaker housed
both the rise in low-frequency sound the radiation resistance R" of the speaker in a 5 cu. ft. bass-reflex enclosure. The
output produced with low damping and system. Any non-linear element that speaker was driven by a Bogen D030A
the roll-off produced with high damping produces distortion and frequency di s- amplifier which was adjusted to give
by changing the appare'n t efficiency ~ crimination can be represented as an different damping factors. These curves
of the speaker system. This can be seen impedance Z in parallel with RA. The represent 5 per cent harmonic distortion
clearly by inspecting Eq. (5) in Fig, 1. current through RA and Z develops a contours for different values of DF and
If the term (Ra + Rc) increases in value
voitage across Rt, This voltage is added show the effect of DF on maximum
the efficiency is reduced. Conversely, if with the input signal voltage es as posi- sound power obtainable at 5 per cent
(Ro + R c) decreases, efficiency is intive current-proportional feedback.
distortion in the low-frequency range.
creased. However, this change in effiThe total current through Rt is the From Fig. 6 we see that with a DF of
ciency is. ~nly apparent since it requires sum of the useful current through RA - 1.2 this speaker can be driven about .
that addItional power be dissipated in and the distortion current through Z 30 db harder at 20 cps than is possible
(Ra + R a) for its accomplishment.
I=idi.
(8)
(Continued on page 66)
.."
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2
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FREQUENCY IN CYCLES PER SECOND
.
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455789'
20
100
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~4567egl
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1,000
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10,000
2
20,000
FREQUENCY IN CYCLES PER SECOND
:Ilo'1~ om(left).
SO~~d tes~ur;. resl~on(s~ hof speaker system of Fig. 8 driven by commercial laboratory sta ndard a mpl ifie r wh ich has fixed OF of
pa re
Ig.. Ig.
rig t), Sound pressu.re respo nses of speaker system of Fig. 8 showing effect of 300-cps filter. Dashed curve
WI
IS
AUDIO
•
SEPTEMBER, 1954
same as solid curve of Fig, 9,
33
\.
~----------~--~--------------
AUDIO
•
SEPTEMBER, 1954 ,
59
A
•
Damping 'of Loudspeaker Cabinet Panels
M. REDINGER';'
A discussion of the need for damping of enclosure panels and suggestions for
realizing the required result. Considerable improvement in speaker performance can be obtained with relatively little expenditure of money or energy.
T
often
produces undesirable vibratory motion of the cabinet panels. It is well
known that any surface excited into flexural vibration has families of resonant
frequencies, so that the radiated spectrum is not the same as that produced by
the primary signal forces. How to avoid
the effect which reinforces certain frequencies and thus provides selective radiation is an old problem, and the usual
recommendation for cure is to brace the
enclosure walls. However, increasing the
stiffness merely raises the resonant frequencies. True, the amplitudes of the
higher resonant frequencies can be more
easily damped ; yet the total radiation
may be more pronounced on account of
the larger number of vibrating surfaces.
Thus stiffening tends more to change the
character of the radiation than to eliminate it.
Another undesirable effect of panel vibration is poor transient response of the
radiated sound. This is produced by the
long buildup and decay periods of the excited panels, compared to the short periods associated with a well constructed
loudspeaker. The qualitative effect is one
of poor vocal and instrumental definition,
of blurriness of tone and lack of crispness and clarity. Such panels are spoken
of as having a high mechanical Q or
ratio of mechanical reactance to mechanical resistance.
Increasing the damping of a mechanical vibratile surface reduces its radiated
sound output. A common example of
damping is seen in the application of an
undercoat, such as mastic or glassfiberboard, to automobile hoods, fenders , and
door panels. Such materials act in two
ways: (1) to convert vibratory energy
into heat by mechanical resistance: and
(2) to lower the vibration amplitude by
providing a higher mechanical impedance.
It should be noted that damping is
most effective at the resonant frequencies, since the larger bending amplitudes
alternately stretch and compress the
damping material, which thus dissipates
the vibrational energy in its mechanical
resistance. Adding mass to the panel
causes it to vibrate with a smaller amplitude for the same applied exciting for.ce.
If the panel were mass-controlled, its
velocity would be F / M where F . is the
vibromotive force and M is the mass of
the panel.
HE LOUDSPEAKER IN A CABINET
* RCA
Victor Division, 1560 North Vin e
Street, Hollywood, California.
act in shear, while applied to the exterior
There are a number of ways by which of a panel its action is less restrained.
If the damping material not used as a
damping can be added to a loudspeaker
is sound absorbent, certain other
filler
cabinet panel. One means consists in
building the panel up in layers of wood, desirable results occur, of course. These
fastened together at numerous points by have frequently been discussed in conscrews. Bending of the panels causes the nection with the interior acoustic treatsandwiched layers to rub against each ment of loudspeaker cabinets. Briefly,
other, thus creating frictional damping. such materials reduce the standing-wave
Another means is to use laminated panels effects in the enclosure and make for all
composed of alternate layers of plywood acoustically larger volume. Some compromise may have to be effected in this
and felt, cork, rubber, or lead.
A convenient if perhaps not very rig- respect in practice, because the economic
orous way to determine the frictional co- aspect of a cabinet is also important. But
efficient or damping constant of such a from a purely idealistic point of view,
compound structure is to take a sample the most effective way to damp a panel
is to use the damper as a filler of the
of the material between thumb and fore(compound) panel. If additio12.al (soundfinger of the left hand and rap it with
the knuckles of the right hand or strike absorptive) material is required on the
inside of the cabinet, this constitutes an
it with a stick and observe the duration
of the resultant sound. A vibratile plate additional requirement.
An exact evaluation of the damping
so excited behaves in much the same way
that it would if excited by sound waves, quality of a material is not simple, howand the duration of the noise produced ever. What is usually done in the laborais a fair measure of its damping proper- tOI'Y is to suspend the panel from the
ties. If it radiates a dull thud the damp- , ceiling at one or two points by fine wires
ing is high, while a long ring would in- or cables. A ball of wood, rubber, or cork
dicate low damping. Some experience, -a regulation baseball has been found
of course, is necessary to correlate the very sati sfactory for this purpose-also
sound given off with the frictional re- hung from the ceiling, is permitted to fall
sistance, particularly if measurements from a predetermined height to strike the
are to be made on a wide variety of test panel. to which a vibration pickup has
been fastened. It is important that this
panels.
In the writer's experience, two types pickup be very light; otherwise it will
of cabinet panels have proven especially itself act as a damper. The output of the
pickup is displayed on an oscillograph,
effective as a laminated structure to give so that the successive reduced amplitudes
damping of a high order. One consists of of the transient wave-train can be meatwo 0-in.-thick plywood panels with a sured. The quantity of interest is the
y,; -in.-thick neoprene layer sandwiched ratio of successive amplitudes spaced a
between them. The other consists of two full cycle apart. Some books prefer to
such plywood panels with a sandwiched consider the amplitudes when spaced a
filler of corrugated, waffled, or honey- half-cycle apart ; but a study of succescombed plastic of the type frequently sive amplitudes on the same side of the
used for aircraft panels. Using the time axis appears more common.
. What is known as the logarithmic
damping material as a filler is far more
effective than applying it to one side of decrement-the vital quality in all these
the panel only, because as a filler it can tests-is given by
At
d -= loge A.'
Damping Panels
g ~Ai
..~
~'f~NA2
TlME--
Fig. 1. Oomped wave train resulting from stimulus to panel, showing two wave maxima a
given number of cycles apart at which measurements are made and on which compu~ations
of logarithmic decrement are based.
where A, is the first and A . the second
measured amplitude. In practice, the
evaluation of d! does not usually comprise
taking the logarithm of the ratio of two
successive amplitudes (since they may
be but slightly different to allow their
exact determination), but consists of
determining the ratio of two amplitudes
which are a number N cycles apart. IJl
that case (see Fig. 1)
1
Al
d="loge~A
Iv
N
( C ontimr.ed on page 64)
AUDIO
•
SEPTEMBER, 1954
DIFFERENCE
MAKE
r,~
P.A.
~
A HI-FI INSTALLATION
I!..¢
.
MODEL
BLe
FULL RANGE
......n..
P_.r
C. p.cIty
'!IIP....ne.
Dlap.rll.n
70.11,000
120d.,r•••
....ntI"'
1100 ...u....... "u" Itlet.
DI_nll. n.
22 Vol ' dle...t.r, 9 " d.pth
TEM permits uncompromising design of the
"woofer" and "tweeter" sections for greatest efficiency. Hear
it penetrate · noise with remarkable fidelity and intelligibility.
Less Dislortio • SEPARATE lOW AND
HIGH FREQUENCY DRIVER SYSTEMS w ith
electri cal crossover reduces intermodulation
and acoustic phase distortions common to
other systems which attempt to use two different horns on a single diaphragm.
CAL DESIGN meet the challenge of diversified a pplication and environmental
hazards . Rugged, and conservatively
rated-y ou can rely on the BlC.
LOUDS PEAKERS
80 SOUTH KENSICO AVENUE
AUDIO
•
SEPTEMBER, 1954
35
Better Audio Specs Needed
NATHAN GROSSMAN *
A plea fo r grea ter cla rification in the publi shed specifications of ampl ifiers, loudspea kers, tran sf orm ers . . Fuller information could be given for all types of eq ui pment.
who desires to
purchase audio equipment w ill fin d
that the catalogues contain specifi cati ons which read somewhat as follows:
a. Ampli fie rs: % watts output ; y%
harmonic distortion ; frequency response
a to b cycles ± 10 db. ; (some also include: n db . of inverse feedback ) ;
b. Output transformers: z watts; frequency response a to b cycles ± 10 db.;
impedance ( pri mary) q ohms, (secondary) 4, 8, 16, etc., ohms; core size: r"
x s',' weight: t lbs.; outer di mensions:
1t" x v" x w' .
c. Loudsp~akers : diaphragm : g" diameter ; h watts; vo ice coil impedance:
i ohms; frequency response j to k cycles
± 5 db.; magnet: l ozs. alnico V;
d. Baffles: outer dimensions: e" x dt ' x
en ; type: r eflex, H elmholtz, etc.; cutout
fo r loudspeaker : f' in diameter.
A
H I- FI ENTHUSIAST
Yet these specifications do not tell the
prospective purchaser enough to enable
him to know what will be the performance of the pa rts or components. They
a re not based on the same standard of
excellence. They tell him nothing about
the very important matter of the efficiency of the equip ment.
W hile harmonic distortion produced
in an amplifier is important, the usual
specifications make no mention of the
;Lmount of distorti on which is produced
by the very mechani sm which changes
electrical energy into sound-the loudspeaker- and by the mechanism which
couples the louds peakel' to the amplifier
-the output t ransformer. Nevertheless,
these t wo are capable of producing much
mo re distortion tha n the ampli fie r itself.
When the term wattage is used in describing an amplifi er , it means r elati vely
undistorted power ; whereas, when used
in describing an output transformer or
a loudspea ker, it means power ha ndling
capacity r egardless of t he harmonics
which mig ht be produced at the stated
power.
W hen the specifications state that an
a mplifier produces 1· per cent ha rmonic
distortion, it generally refers to measurements made at 400 or 1000 cps which is
the frequency at which there is most frequently low harmonic distorti on and best
t ransfer of energy. Serious distortion of
all kinds often develops below 400 and
above 7000 cps a nd increases as the frequency being reproduced extends away
fr om these. A n ampli fi er which delivers
10 watts with 1 per cent harmonic distortion at 1000 cps may deliver only 4
* 2017 E . 24th St., Brooklyn
36
29, N . Y.
watts (and possibly less) w it h a li ke
amount of di stortion at 50 cps. T hi s is
very serious as the greatest amoun t ot
program energy falls between 50 and 500
cps and compensation for F letcherMunson effects requires a considerable
increase in power output w ith the decrease in f requency below 500 cps. In
other words, the greatest dema nd fo r undistorted energy is just where the amplifie r may perform the worst. It fo llows
then that, except for the reproduct ion of
speech, the maximum performa nce of an
ampli fi er is determined by what it can
do in the bass frequencies, so that a 10watt amplifier is really only a 4-watt
ampli fie r, if that is all the undistorted
ene rg~ it can deliver in the bass f requencies.
For like reasons an ampli fier whose
frequency response shows a loss of 3 db
in the bass should be rated at 50 per cent
lower power output. T he prospective
purchaser who realizes this ' might save
money by buying a n ampli fier which has
no loss in the bass ( to the cut-off frequency) than one which has a 100 per
cent higher power output rating but w ith
that amo unt of loss of response in the
bass .
Where a manufacturer states that so
many db' of inverse feedback has been incor porated into the ampli fie r circuit, it
refer s agai n to a meas urement made at
1000 cps. The very factors which produce increased distortion below 400 and
above 7000 cps also decrease the amount
of inverse feedback at these portions of
the sound spectrum so that the ameli orati ve effects of such circuitry ar e often reduced by 50 per cent or more at the points
at whi ch they are most needed. It would
be of considerable help to the unini tiated
audio enthusiast to have the minimum
amount of inverse feedback in the audio
spectrum expressed.
Frequency Response
T he fre quency response curves pubI ished by manufacturers fo r output transfo rmers are misleading unless there is
mentioned in connection therewith the
power t ubes and the operating conditions
under whi ch the measurements were
made. For example, a t ransformer with
a 2500-ohm impedance when measured
with a 6L6 and 6B4 at 250 volts on the
plates w ill give less bass response for the
for mer and less treble response fo r the
la tter. T hi s di fference in resul ts is caused
by the great diffe rence in the plate impedance of these two types of tubes.
I t is the current practice to make output transformers with prima ries having
an inductance of 7- 8 henries ( no d.c.
load ) when they a re to be used in "standa rd" ainplifiers and an in ductance of 1520 henries ( no d.c. load) when they are
to be used in "high fidelity" ampli fie rs,
regardless of the type of a mplifier or
tubes with which they a re to be used,
whether fOI' sing le ended or push-pull
operation, or whether fo r tubes requiring as little as a 2500 oh m or as high as
a 14,000 ohm nominal load impedance.
T hese diffe rences a re accommodated by
the turn r atios whi ch make fo r differ ent
impedances reflected from the loudspeakers to which the secondaries a re to be
attached. The other differences amongst
these t ransforme rs are in the core a nd
wire s izes which make fo r diffe rent
power handling ca pacities .
Tests made by this wr iter show that
the low prima ry inductance of 7-8 henries is often productive of hig h harmoni c
distortion a round 3000-4000 cps and of
a kind which is not altogether responsive
to the amelio rative effects of inverse
fee dback. T hese low pr ima ry inductances
also cause hig h ha rmoni c distortion and
poor energy t ransfer in the bass frequencies. T o obv iate such effects the W illiamson ampli fier calls fo r a primary which
has the hig h' inductance of 100 henries
or more.
W here an output tra nsformer is used
in a class AB2 operation the leakage reactance of the transformer may be a serious source of intermodulation distortion.
Losses as high as 50 per cent may result from the inserti on of the output
t ransformer into the ampli fier circuit.
I magine the f rustration of the constructor seeking to build a 20-watt amplifier, a nd on usi ng a poor quality
transforme r fi nds that it yields only 10
watts. T hese losses may be due to the
design of the core and the d.c. J'esistance
of the windings. The permeability of
the core mater ial as well as its size infl uence the power handling capacity and
the ability to transfer energy. Mo reover,
a few hund red ext ra ohms of d.c. res istance in the prima ry may cause a 10
per cent lowering of the plate voltage,
which in turn means a 20 per cent loss
of power output. T he d.c. resistance of
both the pr imary and secondary windings changes the electrical energy of the
amplifier from potential sound into the
waste form of heat.
l oudspeake rs
The rela tive inefficiency of the loudspeaker is what makes power a mp1ifiers
so necessa ry. Interestingly enough, accor ding to some r ec ~nt literature and the
AUDI O
•
SEPTEMBER, 1954
"
Only ·the New
MIRACORD XA-IOO
has the nMAGIC
and push button controll
Stabilizing plates and pusher arms are no longer
needed because of the
unique construction
of the "MAGIC
WAND"
To the music lover the MIRACORD XA-100 has become a symbol
of everything that could be asked for in a 3-speed automatic changer.
Wow and rumble are eliminated and the "Pausamatic" feature allows the
user to select "pause" time between records of from 5 seconds to 5 minutes .
. The MIRACORD XA-100 comes complete with the "Magic Wand" and single
play spindles. An automatic record spindle for 45 RPM is available as an accessory. Every unit is shipped completely assembled with leads and plugs attached
ready for operation. The MIRACORD XA-100 is superbly finished in rich burgundy
with surf-white trim.
The manually operated MIRAPHON XM-ll 0 is also ovailable, and this unit incorporates the same superb quality found in the MIRACORD XA-100. Send for descriptive
literature, or see these rema rkable units at leading distributors throughout the United States.
AUDIOGERSH
CORPORATI~ ~ept. A
-:;tl
254 Grand Avenue, New Haven 13, Conn.
AU DlOG ERS H1iI ( 0 RP 0 RAT ION
Exclusive Distributors in the U. S. for HAC Record Players
Please send me descripti ve literature .
Nome
...... ...................... .... .. .. ....... ..... ............................ ... .... ..... ..
Address .... .... ... .. ... ........... ................... .. ........ .......... ................ .... ..
~
City .. ... ...... ................... .. ...•...... Zone ........ State .. .....• .. ......... .
I
I
-------AUDIO
•
SEPTEMBER, 1954
37
assertions of several manufacturers,
h~gher loudspeaker efficiency seems to
lower the amount of harmonic distortion
generated by the sound transducer and to
permit the amplifier to be operated at
lower power levels, and so at lower
levels of harmonic distortion.
If information were available as to
the actual efficiency of the loudspeaker
which is to be used in a sound system,
the amount of power needed for satisfactory operation could be determined in
advance. While none of the manufacturers publish the actual efficiency of the
loudspeakers they produce, some do state
that their products are "more efficient."
One manufacturer has, however, published frequency response curves of a
number of its models on a decibel scale
from which a comparison of their relative efficiency can be made. Figure 1
shows the response curves of these
loudspeakers and the relative amount of
power which is needed for each to produce the same amount of acoustical
power. Model # 1 is a tweeter-woofer
loudspeaker system, and models #2 and
# 3 are single loudspeakers especially
designed for broad frequency response.
Model #2 with a 7-watt amplifier will
produce about the same acoustical power
as model #3 with a 20-watt amplifier.
The current difference in price between
models #2 and #3 is about $25. The
current difference in price between a
good 7-watt amplifier and a good 20- ·
watt amplifier is npt less than $50. So,
by purchasing the first mentioned combination there will result a saving of $25
without any loss of quality or volume.
An accurate judgment of a loudspeaker cannot be made from its frequency response curve without knowing
its actual efficiency. Fig~tre 2 shows the
frequency response curves as published
by the manufacturers of two loudspeakers of the same price, tone range, power
handling capacity, and size of diaphragm.
They are shown superimposed to facilitate comparison. It would appear that
loudspeaker A has a better response than
loudspeaker B in the tone range below
500 cps. Neither manufacturer stated
the frequency which was taken as the
reference point for decibel calculation.
Should 350 cps be taken as the common
reference point for such calculation, then
the resulting <;urves when superimposed
would be as in Fig. 3. This shows loudspeaker B to have a better bass response
than loudspeaker A in the frequency
range between 90 and 500 cps and below
50 cps. A direct listening comparison
seems to indicate that the response of
these two 10Jldspeakers falls somewhere
between Figs. 2 and 3. This is confirmed
bv the fact that loudspeaker B has a
hirger magnet by 40 per cent, and probably a magnetic flux density greater by
that percentage, than loudspeaker A.
The size of the magnet employed is not
the sole determinant of the magnetic flux
density. The other factor is the amount
of space across which the magnetic flux
must flow. It is possible then to have
loudspeakers with 9000-10,000 gauss
units (the measure of magnetic flux
density) with magnets ranging in size
from 3 to 14 ozs. The larger magnets,
38
~~
b~
ulffi
a: en
~g~~
ex
1X
vf;x
2'\hX
~~g.J
tilii
Fig. 1. Typical response
curves of
three different loudplotted
speakers
against actual sound
output for a fixed
given input to show
comparative efficiency.
.55
.0
'0
",lUlU
::1:>
50
3
ex
1X
70
100
200
300
500
FREQUENCY IN CYCLES PER SECOND
however, permit more space to be available in the voice coil gap which increases
the power handling capacity of the loudspeaker. Therefore, to be able to estimate the relative conversion efficiency of
a loudspeaker it is more important to
know the number of gauss units in its
voice coil gap than to know the size of
the magnet being used with it.
From the standpoint of efficiency we
should also know the d.c. resistance of
the voice coil because a few extra ohm,;
may mean a considerable loss of sound
energy. The a.c. impedance of the voice
coil is not an indicator of its d.c. resistance.
The "present linearity standard for
loudspeakers of ± 5-db variation in frequency response will not enable the prospective purchaser to know therefrom
whether the 10uQspeaker under consideration will sound bassy, shrill, or just
right. It is very important to konow
whether there is a ± 5 db (or sometimes
even morc) at 50 cps and at 12,000 cps.
It is even more important to know the
decibel differences in performance between these two frequencies and those
at 1000 and 3000 cps. The performance
at 1000 cps will determine the usual
listening level. Should the efficiency of
response at 50 cps drop 5 db from that
at 1000, it will-because of FletcherMunson effects-be heard as a drop of
7 db, and will sound as if there were
very little bass. For the same reason, a
peak of 5 db in the bass will be heard
as a 7-db rise, and will sound very bassy.
Also, should the response at 3000 cps
be higher than at 1000, there will be a
tendency to cut down on the treble because the ear is most sensitive at about
3000 cps. Should the response of the
loudspeaker in addition suffer from a
5-db drop at 12,000 cps, such cutting
down of treble would increase this drop,
which is further aggr€vated by FletcherMunson effects, so that such a loudspeaker would sound as if the "edge"
~DSPEAKER A
lL
0
.0
'0
-10
LOUDSPEAKER B
-,
.........~
f
....--.. -...
.---.... LOUDSPEAKER B
I
30
I
frequencies had practically disappeared.
Only recently has any manufacturer
of loudspeaker baffles given any specificati<ms as to the effect of its product
on the tone range, harmonic distortion,
and efficiency of loudspeakers which it
is to house. Different types of baffles of
the same size produce different amounts
of harmonic distortion, and can either
extend or cut off the tone range, and can
either increase or decrease efficiency in
specific bass frequencies. Baffles sometimes produce unintended effects. Thus,
it has been observed that horn type
tweeters of a certain manufacture lose in
response to the "edge" frequencies when
recessed in a compartment with their
mouths completely behind the front line
of the loudspeaker cabinet, and that they
sound best when mounted with their
mouths completely outside of the loudspeaker cabinets.
In view of the foregoing, specifications for audio equipment in addition to
those generally mentioned should include:
a. -For amplifiers: undistorted power
output and ratio or factor of inverse
feedback at 50, 1000, and 12,000 cps;
b. For output transformers: frequency
response under specific operating conditions; per cent of harmonic distortion at
50, 1000, 4000, and 12,000 cps; amount
of inductance and leakage reactance in
the primary; per cent loss on insertion
into amplifier circuit; d.c. resistance of
,
,vindings; permeability of core;
c. For loudspeakers: per cent of harmonic distortion at 50, 1000, 3000, and
12,000 cps; actual efficiency; amount Of
magnetic flux density across voice coil
gap; differences in response at 50, 1000,
3000, and 12,000 cps; d.c. resistance of
voice coil;
d. For baffles: effect on frequency response, efficiency, and harmonic distortion of loudspeakers with which to be
used.
I
40
100
200
300
500
FREQUENCY IN CYCLES PER SECOND
Fig. 2. Comparison between two loudspeakers
plotted for equal output at 125 cps. Compare
with Fig. 3.
.0
'0
30
40
100
2
300
500
FREQUENCY IN CYCLES PER SECOND
Fig. 3. Same loudspeakers as in Fig. 2 but
plotted for equal output at 350 cps. Note
difference such a plotting would couse.
AUDIO
•
SEPTEMBER, 1954
CORPORATION
Toronto
New E-V integrated 3-way Triaxial
reproducer, at lowest cost ever!
ENJOY WIDER-RANGE
WITH SENSATIONAL NEW
3-in-1 12 inch 12TRXB
$59
for only
70
A=HILE
NET
A thrilling new experience in high fidelity listening awaits you in the
12TRXB. You discover quickly how the distortion-free wider-range reproduction found in E-V separate 3-way systems is now made economically
available to all music lovers, in one compact Triaxial speaker. Exclusive
new 3-in-! concentric design combines the advantages of the famous E-V
RADAX and SUPER-SON Ax-gets the most from each reproducing element
for each portion of the audie spectrum-assures even, smooth, full coverage
with all tones at all listening positions in the room.
Phenomenal bass response, full-bodied mid-range and silky-smooth upper
octaves to the highest audible frequencies provide accurate musical balance
without masking effects or imposed distortions. This recreates your favorite
music with effective realism and presence. Adjustable high-frequency level
control for remote mounting permits matching to room acoustics, compensating for high frequency absorptive effects of rugs and draperies. The new
E-V 12TRXB 12" Triaxial can be installed in direct radiator type cabinets
or in recommended E-V Aristocrat folded horn enclosure. A demonstration
leads the way to greater enjoyment, at lowest cost ever!
Frequency Respon se: ± 6 db, 30 to 15,000 cps
in Recommend ed Aristocrat Enc losure
Edgewise Wound Voice Coil D esign Affords
18% More Efficiency
Full 12 db Per Octave Crossover Network
Minimizes Disto rtion Products
Mechanical Crossover: 2000 cps
Free-Space Con e Resonance: 50 cps
Magnet Weight: 1X Ibs.
Integrated Di e-Cast Frame Assembly
Size: 12X" D iam. x 6IA," D eep Overall
Requires Baffle Opening of 11 inches
Net Wt: 12 Ibs. Shpg. WI. 13X Ibs.
Electrical Crossover: 3500 cps
RETMA Sensiti vity Rating: 46 db
Nominal Rated Imp edance at 400 cps: 16 ohms
Power Handling: 20 W atts Pro gram Material,
30 Watts on Peaks
Critical Damping Factor : 4.0 i n Recomm ended
Aristocrat Enclosure , 2.5 on Infi(lite Baffle
OTHER E·V 3-WAY TRIAXIAL REPRODUCERS
Model 15TRX 15". list Price, $225 .00
Audiophile Net, $135.00
Model 12TRX 12". list Price $190.00
Audiophile Net, $114.00
Includes X-36-1 crossover network
and AT37 brilliance control
Model 12TRXB. Combines features
of SP12B Radax and T35B Super Sonax.
In c lud es High-Frequency Level
Control and Built-in Electrical and
Mechanical Crossovers.
List Price $99 .50 Audiophile Net $59.70
Write for complete information
ELECTRO-VOICE,INC_
BUCHANAN, MICHIGAN
Export: 13 E. 40th St., N.Y. 16, U.S.A.
HIGH FIDELITY SPEAKER SYSTEMS. AMPLIFIERS. MICROPHONES. PHONO-CARTRIDGES. AND OTHER ELECTRO-ACOUSTIC PRODUCTS
Selecting and Improving FM
Receivers
CHARLES ERWIN COHN>!'
The important characteristics to watch for in selecting the best tuner or receiver for your area and
performance requirement, plus two modifications for decreasing noise and bettering the audio quality.
an PM receiver or tuner is required equipment for the lover of serious music, since "quality" FM stations exist in
most of the major cities. This equipment
may range from the inexpensive tablemodel AM-FM combinations to large,
deluxe, hi-fi tuners. Since not everybody can afford the best, the writer attempts in this article to show how to
pick a good set in the desired price
class, one suited to the buyer's needs.
Simple improvements which cost little
but can add much to any 5et will be
described as well. Discussion will be
restricted to the r.f. and detector CIrcuits.
Before considering the selection and
improvement of FM sets, we must decide just what is wanted. The requirements for any set can be summarized
by the following four items, listed in
approximate order of importance:
A
T THE PRESENT TIME,
1. Good linearity and adequate i.f.
bandwidth.
2. Adequate sensitivity for reception
conditions.
3. Good AM rejection.
4. Freedom from drift.
The first of these qualities-good linearity and adequate i.f. bandwidth-is
what makes for low distortion, and thus
is a necessity for music listening. Fortunately, this quality is fairly easy to obtain in the usual superhet circuit, and
thus is adequatf' in even the low-priced
sets, provided they are properly aligned
and are receiving ample signal. However, if a set dq.es not have it, the receiver cannot be"'improved by any meas-
* 7720
Marquette Ave., Chicago 49, Ill.
LAST I.F.
STAGE
OR
LIMITER
B+
Fig. 1. Where the area is very noisy or the
i.f. amplification is insufficient to saturate the
limiters with the available signal, two c~ystal
diodes make a very effective additional limiter.
ure short of complete re-engineering.
Therefore, when purchasing an FM set
it is most important to check its linearity
by a listening test. This should be done
with a signal with high modulation (fortissimo passages) but the volume control
should be turned down so that distortion
produced in the audio stages Cif it is not
a hi-fi set) will not mask the distortion
produced in FM detection.
The next quality-adequate sensitivity
for requirements-means just that. You
do not need a set with umpteen stages if
you live two blocks from the station. In
areas with plenty of signal strength, a
large expensive set will provide no better
performance than a small set, other
things being equal. Also, sensitivity depends as much on the antenna as on the
set itself, and a small sum spent on a
good outdoor antenna can often make a
much greater improvement than a
greater amount spent on a more elaborate receiver. If you already have an outdoor or attic TV antenna you can try
connecting it to the FM set; if it makes
an improvement, a two-set coupler or
changeover switch ca:n be permanently
installed. If it does not help, an outdoor
FM antenna mounted on the same mast
or tower will usually be of great benefit.
Nol~~ Limiting
Since freedom from noise and interference is one of the major advantages
claimed for FM, it is necessary that a
receiver have good AM rejection in order to make full use of the medium. Conventionally, this is done either with limiting d. amplifiers or with the ratio
detector. However, both of these systems
have disadvantages. The limiter-discriminator circuit requires a multiplicity 0f
i.f. circuits, while the ratio detector, although simple, is critical with respect to
alignment and varies in efficiency with
signal level. In general, the higherpriced sets use the limiter-discriminator
circuit which is usually satisfactory
when the signal str~.ngth is high enough.
However, the simple circuit shown in
Fig. I can be applied to any set in which
the AM rejection is not what it should
be. It consists merely of two crystal diodes connected back to back across the
primary of the ratio detector or discriminator transformer. Its operation depends on the nonlinear characteristics of
the crystal diodes, and can be understood
42
VOLTAG E
Fig. 2. This curve shows that a disproportionately large current flows through the diodes when the voltage across them increases
beyond a small value. Above that value the
diodes effectively short-circuit the discrimina for transformer of Fig. 1 and provide limiting.
by reference to the current-voltge characteristic curve shown in Fig. 2.
Since a pentode acts as a "constantcurrent" generator, it can be thought of
as sending a current signal through the
load circuit. For small signals, the resistance of the diodes is fairly high, and the
effect is thus small. However, as the
signal increases, the diode resistance decreases rapidly, so that after a certain
point an increase in signal input does
not cause a corresponding increase in
output, which of course is the action of
a limiter. The resistance of the IN56
diode is about 100 ohms when the applied potential is 1 volt, so the action is
evident. The IN56 is the best diode to
use in this circuit, because its high forward conductance gives a lower limiting
threshhold.
Due to the complete absence of time
constants, this circuit should give a better performance on ignition noise than
the grid-bias limiter, and thus might be
used to supplement it. The only disadvantage is low output, since it clamps
all signals down to less than 0.1 volt at
the detector input. This means that additional audio amplification will be required, the output from a ratio detector
with this circuit becoming comparable to
that from a magnetic pickup. Furthermore, the output from the discriminator
will not be sufficient to operate tuning
indicators or a.f.c. systems. However,
audio amplification is cheap, and the sets
which most need this circuit are the
cheaper ones which dO,not have the frills .
Another possible application of the circuit is to intercarrier TV sets, where an
excellent reduction of buzz should be obCContinued on page 67)
AUDIO
~
I
•
SEPTEMBER, 1954
PILOTONE
AMPLIFIERS
$39.95
William'san type Amplifier with special inler-leoNed
woun/{ Outpul, Transformer and push-pull output.
Contoln~' 5 tubes lncludin'g reclifier, Frequency Re"
sponse. :;;t; (dl>, J5 to 40,000 cycles at '10 won
, ., ' putput. D i sloflion· les~ Iha'n 1% 01 IOwolls 'and less '
'';'': Ihoii d % dt 1"(011 frQm 30 10 i 5,00Q cycles: Proy'ided with spe .. ~er oulpul impedances of 4, 8 and
ohm,S.
Underwrlters
Laboratories Approved
' ,I.
.,....
+
",.
.6
the ultimate in electronic
SKill engineered bll
P~~OtRADIO CORP.
$69.50
. Williamson
with buill-in
Preamplifier. .Seven ·tubes including Rectifier and
..·push-pull oulput tubes . .On-Off Volume, separale
, ',' Boss. "and Treble Conlrols and Equalizer selector
' switch . for' .LP, NAB, AES and Foreign recordings,
. Frequency Response ± I db. 15 10 40,000 cycles.
Dhlorlion less than 1 % 01 10 walls. Hum Level
70 'db below 1 volt: Three inputs for Radio and
" " Auxiliary equipment and one variable impedance
_ input; ,
•
AA·410 PILOTONE A~PLlF..IER ,$49.50
) Unexcelled Williamson-type High" fide,lity Ampli~er
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Four tubes and Rectifier.
Frequency Response: ± 0.1' db. 15 cps. to_20,000 ,
cps. at raled oulput. Talal Harmonic Distortion: less
Ihan 'I %. Inlermodulalion Dislorlion: Less Ihan 2%.
Hum and Noise Level: 90 db. below rated output.
Polled oulput Iransfarmer construcied with intetleaved winding for, reduced leakage inductance.
$99.50
U~surpassed
Williamson Iype high fidelily audio
amplifier with push -pull 5881 '5 for full 15 wall oulput combined with professional ' preamplifier for
maximum efficiency and flexibilily ,in most convenienl 'space saving format. Six lubes plus Rectifier. ~
frequency Response : ± 1.0 db. 15 cps. 10 20,000
cps. at raled outpul. Total Harmonic Dislortion:
Less than 1 %. 'Intermodulalion Dislortion : Less than
2% at roled C/utput. Hum and Noise Level: 80 db.
be!.ow roled !?ulput. .
Dual .e qualization switches . provide five positions
of Ireble roll-off and five po's itions of boss turnover.
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¢""",,""""
Slightly higher west of Rockies
I;
PltqT RADIO CORPORATION
L-~__________~
LONG ISLAND (.TYI,
Write for Free Booklet A-9
AUDIO
•
SEPTEMBER, 1954
-
. AA.904 P.ILOTONE AMPLIFIER
NEW YORK
$89.50
Audio Time-1954
September is Audio Time, when the Fall season commences in earnest and renewed interest manifests itself throughout the country. But October is Audio
Fair time, and time for the Annual Convention of the Audio Engineering Society.
I
AUDIO FAIR TIME again! The
dates, October 14 throug h 17-the
place -M a nhattan's famo us Hotel New
Yorker. A nd as always, admission to
everybody- music lovers, hobbyists, and
profess ionals alike-is absolutely fr ee.
The 1954 Fair will play host to the
la rgest assembly of audio fans ever to
gather fo r a single event, a ccording to
Ha r ry N. Reizes, Fair manager. An
estimated 30,000 visitors will come to
view the latest developments in equipment as displayed by vir't ually every
leading manufacturer in the Audio field.
rn a departu re from the a r rangement
which has prevailed at_ previous Audio
Fairs, the 1954 event will include a
Sunday in its schedule. " In this manner
we hope to bring the Fair to many persons who a re prevented by occupation
from attending on week days," Mr.
Reizes a nno unced.
A lthough the Fair was conducted
orig ina Hy as an event of primary inter est to music lovers, hi- fi hobbyists
and professional audio engineers, it
has become the pr incipal buying mart
for audio equipment on a commercial
level as well. Registration r ecords of
the 1953 Fair included executives and
purchasing agents r epresenting ma jor
dealers and distributors from all parts
of the U. S . as well as a number of
fore ign countr ies, and advance hotel
registrations give assurance that attendance of wholesale buyers this year
will be considerably g reater.
Since its inception the Fair has been
sponsored by the A udio E ngineer ing
T'S
Society, and_is held in conj uncti on with
the Society's annual convention. Together the two events have achieved
wo rld-wide recognition, and today a re
rega rded internationall y as the mos t
prom inent of t he annual displays and
fo rums devoted solely to the science of
r eproduced sound.
Althoug h normally, and understandably, most exhibitors attach a -topsecret classi fication to any info rmation
which might divulge the natu re of their
displays to competitors, the grapevine
gossip indicates that visitors to t he 1954
Fair will be in on the int roductory
showing of many new items which w ill
establish mil estones in audio hi stor y.
H i-F i-in-M iniatu re will be the theme of
one exhi bit, another will feature the
fi rst public showing of a super-h ighfi delity electrostatic speaker, while many
other s will emphasize economicallypriced tape recorde rs which approach
professional standa rds in performance.
Matching a new high in attendance
will be a record-breaki ng nu mber of
exhi bitors. I ndicative of indust ry g rowth
is the fact that the 1954 Fair w ill occupy
four floo rs of the hotel as compared to
the t wo fl oors wh ich sufficed only t wo
years ago.
J oining in announcement of the annua l
audio conclave, Jerry B. Minter, President of the Audio Engineeri ng Society,
announced that this yea r's Society convention will IJear a greater variety of
technical papers than has ever before
been presented at a single gathering.
T he annual Society banquet will be
held on the night of October 13, at which
va rious awards for disting uish ed accompli shment w ill be presented to outstanding audio eng ineers.
Because A udio has become an accepted entity in the panorama of A merican life, the coined word "Audiorama"
will express the theme around which the
1954 Fair will be conducted.
Convention Papers
T he prelimina ry list of papers to be
presented at the convention shows a
strong leaning toward subjects which
are of greatest interest to the audiofan
for the Satu rday sessions- the more
professional papers being scheduled for
the fi r st two days of the convention. T he
T hu rs day morn ing sess ion is devoted to
Microphones, with the fo llowing t itles
g iven as the tentative program:
"Cathode fo llower circuits app lied to a m icro·
phone," by John K. H illiard and James JNoble, both of Altec Lansing Corporation;
"lVl icroph ones for informal u se," by L. lVI.
W igington and R. M . Carr ell, of Electronics
Products D ivision, RCA;
"Uniaxial microphones," by Dr. Harry F. O lson,
J ohn Preston, and J. C. B leazey, of RCA
Laborator i e~ ;
"Design of a condenser micl"ophone/' by an
en gineer fro m Kellogg Switch board Compan y;
and
" A m ethod for the quantitative measuremen t of
wind noise sensitivity in microph ones," by R .
M. Carrell, E lectronics Products Division, RCA.
T he Thursday ' aftern oon session is
devoted to lVIiscetlaneous Cl/n.d Tape
M qchines, and the fo llowing titl es are
tentati vely scheduled:
"A moving coil feedback disc r ecorder" by C.
C. Davis, \\Iestrex Corporation;
"A n external auto matic sweep generator for use
with cath ode ray oscilloscopes," by Alan B loch .
A udio Ins t rumen t Com pany;
"An experimen tal study of distort ion," by C. J
LeBel, Aud io Ins trument Company;
"Transistori zed magnetic tape recorder," by A.
1. A r onson, Electronics Products Division,
RCA;
"A new min iaturized tape recorder," by A. C.
Travi s, Jr., Broadcast Equipment Specialties
Corp _;
"Design, developmen t , an d operating feat ures of
a new tape record ing machi ne,'J by Robert
W inston, Audio & Video Recor ding Company ;
and
"Definite stereophonic sound," by Col. R. H.
Ranger, Rangertone, Inc.
Tape lVI ed1'a is the subject of the
F riday mo rni ng sess ion, and the tentative list of papers includes:
HF r equency modu lation no ise in magnetic tape,"
by Robert A. von Beh r en an d Rober t JYoungquist, :M innesota M in ing & Nlanufactur·
ing Co.;
"1\1agnetic recording meas uremen ts," by "va lter
H. Erikson, Electronics Products D ivision.
RCA;
" Defects
in
magnetic recordi n g t ape-their
causes a nd cures ," by Frank Radocy Audio
Devices, Inc. ;
"Locating defects in magnetic recording tape,"
by Andreas Kramer, A udio Devices, Inc. ; and
" 'New uses and new magn etic products in tape,
fi lm, and instr umental appli cations during- the
past t wo years," by E. W. F r anck and E.
Schmidt, R eeves Sound craft Corp_
I
Officials of the Audio Engineering Society meet with Harry N. Reizes, manager of the Audio
Fair, to complete arrangements for the 1954 event which will be conducted in conjunction
with Society's annual convention. Shown left to right are C. R. Sawyer, AES president Je rry
B. Minter, Mr. Reizes, and Walter O. Stanton. Sawyer and Stanton are AES governo-rs.
44
( Cant-in'n ed an page 65)
AUDIO
•
SEPTEMBER, 1954
The Tannoy Dual-Concentric makes the
word" loudspeaker" completely out-of-date.
Here is a precision acoustic transducer
which sets a new standard in high fidelity
reproduction . .. an instrument rather than
a mere mechanism, designed with the most
exacting American standards firmly in mind,
and built by skilled British engineers in the
best traditions of British craftsmanship.
The Tannoy Dual-Concentric relies no more
on revolutionary ideas and startling
secrets than does the unsurpassed product
of Mr. Rolls and Mr. Royce. Its superlative
performance is due simply to an
uncompromising choice of materials and
an uncompromising choice of craftsmen
to work with them.
manufactured by
TECHNICAL
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
SPECIFICATION
Frequency response of both Ir and 15 models,
sui t ably housed, ± 3dB, 35 to 20,000 c.p.s. with
a useful response outside these limits.
H
Impedance for Crossover
Flux density, LF gap
Flux density, HF gap
Power handling capacity
Polar distribution for
}
60 degrees included angle
Intermodulation products
12" MODEL
IS" MODEL
18 ohms
10,000 gauss
15,000 gauss
15 watts
- 3 dB at
10,000 c.p.s.
<2%
15 ohms
12,000 gauss
18,000 gauss
25 watts
- 4 dB at
10,000 c.p.s.
<2%
PRODUCTS LIMITED
WEST NORWOOD . LONDON . ENGLAND
North American Distribution
TANNOY(CANADA) LTD
36 Wellington Street East, Toronto I, Onta rio, Canada •
AUDIO
•
SEPTEMBER, 1954
We shall be exhibiting
TANNOY DUAL CONCENTRICS
at the
AUDIO FAIR ' HOTEL NEW YORKER' 14 to 17 OCTOBER
A number of new Tannoy products in the
same tradition will be on view for the first time.
_ __ _ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _. .
45
AES,78-HOISY
"Fe,'
It.TJJ.
. ),
1-=
Equipment Report
11111 11
PHONOGRAPH EQUALIZATION
~"'-! ~
+ <0 rttwml
0
I
11111
+20 .~
The National Company's Horizon 20 Am pl ifie r, Horizon 5 Pream pl ifier, and Criterion AM-FM Tuner
,
FOR
"'"
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,rt,
IAA
. ..
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. ..
,.Jtt:OUOolCT IN
II
. . . ,-
~C:LQ
~
. ' COHO
11 11111
1:::1
!TONE CONTROL
~
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v/..;,;
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1fi''';';0I'<.c<
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~
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.,....
-r'U:OYDfeT IN
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NATIONAL
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to
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A T IONAL C OM P ANY,
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LP
.
0
I NC., long known
for a high-quality line of amateur
radio equipment, has entered the audio
fie ld with four individual units which refl ect the company's experience in the " ham"
field. Some of the constructional characteristics are more closely related to professional equipment than to home-type amplifi ers and tuners, and on the whole th e
equipment is solidly built and exhibits good
performance.
T he H orizon 20- listed as a 20-watt amplifier- reaches an output of 37.5 watts
before the intermodulation distor tion becomes 5 per cent- the 2-per-cent point being
at 24 watts. Thus it is seen that the 20-watt
rating is conservative. On sine-wave signals,
the slightest fl attening of the waveform is
noted at 29 watts at frequencies from 20
to 10,000 cps, with equivalent flattening
being noted at 28 watts fo r 20,000 cps, 24
watts at 30,000 cps, and 15 watts at 50.000
cps. Square-wave response is excellent
throughout the audio range, with a slight
ringing noted at a fr equency of 78 kc when
power output is increased above about 20
watts .
N
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-to
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PO'WO\! OUT PUT - WATTS
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.
The amplifier circuit is unusual in that
the output stage does not operate as a
conventi onal push-pull arrangement, but
one output tube is plate loaded and the
other is cathode loaded. The coupling between the output tubes is independent of
the characteristi cs of the output t ransfo rmer. whi ch reduces cer tain forms of
distorti on. The amplifier can be used as a
"package" of gain, with controls elsewhere
if desired, or the H orizon 5 prea mplifier
may be plugged in to provide a completely
controllable amplifier system suitable for
pho)1o, radio, or tape r eproduction. W hen
the preamplifier is not used, a satin-finished
aluminum plate covers the opening, and
either the plate or the preamplifier must
be in place to actuate an interlock switch.
The amplifier housing must be in place
to furni sh power to the transform er , much
as with T V r eceivers. When the preamplifi er is not being used, a shorting strip (F ,
in the schematic, Fig. 2) must be in place to
energize the a.c. circuits. The unit is
solidly built, well venti lated, and of attractive appearance. I -watt output is obtained
with an input signal of 0.3 volts, with an
Fig . 1 (left) . Performance curves for t he Nat ional Horizon 20 amplifier and the Horizon 5
preqmplifie r. Fig. 2 (be low) . Ove r-all sch ema t ic of the Horizon 20 amplifier .
.,,
3900
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RESISTOR VALUES - OHI/S
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AU DIO
•
SEPTEMBER, 1954
You haven;t seen anyfJiing like it ••.
THE HARRISON
HIGH FIDELITY '
RECORD
CATALOG
*The HARRISON HIGH FIDELITY
RECORD CATALOG
P-"..".""'-....
EVERY really hi·fi record made by EVERY
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•• • at your finger tips.
ALL the information you need about hi-fi
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!f you're a hi·fi set owner or planner, this
IS for you .•• for more and better hi·fi en·
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Ask your neighborhood record shop for The
Harrison High Fidelity Recor.d Catalog or
send us the name and address of your record
dealer and we will see that he gets a copy
for you.
Write to Harrison Catalogs, 274 Madison
Ave., New York 16, N. Y.
* By the Publishers of Record Retailing • The
Opera Catalog • The Children's Catalog • The
EP 45 RPM Catalog • The Convention Dally of
the National Association Df Music Merchants.
AUDIO
•
SEPTEMBER, 1954
47
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Fig. 3. Complete sc hematic of the Horizon 5 pream plifier.
inp ut potentiometer being available to set
the over-all gain of the amplifier to suit
individual conditions. Intermodulation distortion for the complete power amplifier
is shown in the bottom section of Fig. l.
The Preamplifie r
The Horizon 5 preamplifier, designed to
plug into either the 20-watt power amplifier or into a similar opel1ing on the tuner,
is 'extremely compact yet provides adequate
amplification, tone control, and circuit
selection to meet today's requirements. Four
inputs are provided-tuner, tape, TV, and
phono. For a 0.3-volt output-which corresponds to a 1-watt output from the power
amplifier-the tuner input is 0.22 valts,
that from tape and TV is .003 volts with
separately adjustable level controls. Phono
input for the same output is .0019 volts,
sufficiently sensitive for all modern pickups.
A study of the circuit, Fig. 3, will show
that the arrangement is somewhat unusual
-the rolloffs being accomplished ahead of
the first amplifier stage and the turnover
control being located between the last two
stages of the unit. The tone-control circuits
are also unusual, but provide for different
inflection points in the bass and treble
controls as well as for greatly increased
bass response without undue increase in
distortion. Also unusual is the use of a
dual volume control-one section being used
for the AM portion of the tuner for binaural
reception, and with no tone-control action
being available. For other positions of the
selector switch on the tuner, the tone-control action is available, as well as for
phono, tape, and TV inputs.
The curves available for phono reproduction are shown in the top section of Fig. 1,
while tone control action and loudness com-
48
pensation are shown in the center section.
A push-button switch on the front panel
cuts loudness compensation in or out as
desired. Much of the compactness of the
control unit is the result of the use of
printed circuits. For those applications
where the preamplifier is to be used with
other amplifiers or tuners, a plug and cable
set is available to permit making the necessary connections.
The AM-FM Tuner
Numerous modern features not heretofore
encountered in tuners are employed in the
Criterion. A single intermediate amplifier
is used for both AM and FM recejJtionwhich is not unusual-but this is the first
model reviewed that can use the i.f. amplifier for both types of signals simultaneously.
The FM section has a cascode r.f. amplifier,
a mixer an~ oscillator, three i.f. amplifier
stages, two limiter stages, and a countertype detector (which can be shown to have
some advantages over discriminators or
ratio detectors). A built-in squelch circuit
which is adj ustable as to threshold cuts off
the limi ters entirely in the absence of a
signal, thus eliminating interstation noise
(it is not eliminated intrinsically in the
counter-detector circuit). This gives an
"in-out" character to the FM signals, and
as the tuning knob is turned, stations are
either heard properly tuned in, or else
they are not heard at all. The counter
detector is not as critical to tuning as is
the discriminator, so no a.f.c. is necessary.
One output from the FM section is
labeled MULTIPLEX, and is provided for use
with thi s method of broadcasting when it
comes into use. This output is ahead of the
de-emphas'is network, since the multiplex
circuits provide their second channel some-
where around 35 kc. Another FM output
is available on the FM BINAURAL jack at
the tuner, while still another is at the
T UNER OUTPUT jack when the selector switch
is in any position except AM. A tape recorder input can be taken from the FM
BINAURAL output jack, if desired, or separate
outputs to two power amplifiers can be
taken from the t wo BINAURAL outputs for
this type of reception.
The AM section employs a pentode d.
amplifier, a mixer-oscillator, two i.f. stages,
and a diode detector. All outputs from the
tuner (except FM MULTIPLEX) are through
cathode followers ensuring low impedance
and a minimum of effect from lead length.
The construction of the tuner is unusual
in that almost all of the components are
above the chassis. Underside is seen only
the printed-circuit wiring, which makes a
neat unit. It appears to be sturdily built,
and it is undeniably attractive-although
it may appear too professional for the hypercritical homemaker. There are many advantages, however, to a unit which provides
both AM and FM outputs at the same
time, each with a separate volume control
as well as station selector. And with its
high sensitivity and quiet operation, this
tuner offers features which are undeniably
desirable for many users. Both mechanically and electrically it is an interesting unit,
and the reputation of its manufacturer ensures quality construction.
The Horizon 10 Amplifier
This unit, the fourth of the line, has
not been measured, but is a 10-watt amplifier with a built-in preamplifier which is
somewhat less flexible than the Horizon 5
preamplifier.
AUDIO
•
SEPTEMB,ER, 1954
Jensen-world's quality standard for more than a quarter century.
Division of the Muter Co.
6601 S. Laramie, Chicago 38, Illinois
A
II true "Corner" Speaker Systems which utilize the walls as part of the amplifying and dispersion set-up, owe
their origin to Maximilian Weil, who invented this system in 1925 • • • All high fidelity television and radio sound
systems ~tilizing a small diaphragm (tweeter) for high frequencies and. a large diaphragm (woofer) for low frequencies,
owe their origin to the Well 2 -way Electronic Reproducer System (1927-8) • • • The first Electronic Reproducer introduced commercially (1.227.) was by Weil, who developed the world-famous Chromatic Reproducer only a
few years ago, and who recently perfected a higher output Chromatic Reproducer, the Hi-Q7 • • • Maximilian Weil
has scores of other inventions to his credit, and his latesf-described on the facing page- is as important to music reproduction as it is simple.
Introducing.
• •
-
(STYLUS BALANCE)
Stylus pressure is the No.1 factor in record wear
and in stylus durability. It is established that over
60 % of cartridges now in use operate with too .
light or too heavy point pressure. The result of
either-stylus and record destruction! A 50 %
sub-normal pressure causes almost three times more
wear and a 50% above-normal pressure .virtually
doubles the wear-hence the high importance of
Maximilian Weil's newest audio milestone . .
Until now it has been impossible to check point
pressure closer than 2 or 3 grams one way or the
other. When the point pressure was an ounce or
two (28 to 56 grams) such small tolerances were
of little consequence--but with today's "feather
touch" pressure, a difference of 2 .01' 3 grams
means 30910 to 50910 off-correct!
Weil's MICRO-POISE obtains-for ANYONE
-the correct stylus pressure as specified by the
Bring ing Hi -Q7 into pl'oper ba la n ce with lIIICRO-PO I SE
No Springs ••• No Scale to Reatl •• • Nothing to Bold
cartridge manufacturer himself. NOT a scale,
Basically, MICRO-POISE works like a pharmacis~'s balance. Precision all-metal construction performs, in one simple step, the
stylus-saving, record-sparing function so long
awaited by record enthusiasts.
but a simple indicator of the one thing it is so important to be sure of-that the stylus pressure is
neither too light nor too heavy-but CORRECT!
As a stroboscope indicates correctness or
incorrectness of turntable speed-so MICROPOISE indicates correctness or incorrectness
of stylus pressure.
FINISHED IN GOLD
Room 629 ·at the New York AUDIO FAIR
FREE "Electronic Phono Facts"
at your dealer . . .
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Net . .. $4.80
AUDllK COMPANY
500 Fifth Avenue
Dept. A
New York 36, N. Y.
Creators of Fine Audio-Electronic Apparatus for over 25 years
EDWARD TATNALL CANBY ':'
Classics on Westminster
A S1IALL COlliPANY to do when
it begins to expand into a larger
company? Westminster's expansion
is an interesting example. This company
was an early trail blazer in small-company
LP with a superb series of recordings made
mostly in Vienna that set unapproachably
high standards of excellence, both in the performance and in the recording and processing techniques. That Westminster series still
continues-classic sonatas, chamber music,
divertimenti, small symplionies, the cream
of central European older music, much
of it not overly well known in this hemisphere until Westminster's recording made it
"come alive." These Westminsters, now
augmented by recordings from other musical
centers on a similar plane of excellence,
make up the finest collection of its kind in
the whole field of recorded music, both as to
recorded excellence and as to the authoritative musical standards.
But expansion has carried this company
into other areas in various directions, and
not always with the unfailing uniformity of
excellence of the Vienna operation. Big
conductors and standard symphoni repertory are the dangerous temptations for any
small company about to get bigger-dangerous, because it is always a risky business
to break into the big-time competition, any
way you look at it.
Big conduct0r? Westminster's Scherchen
did memorable Haydn, not to be surpassed,
and he took Westminster slam into hi-fi
with the famous Haydn "Military" Symphony, complete with huge drums and
clashing cymbals. But the ambitious Scherchen Beethoven symphonies showed the
conductor to be temperamental even among
conductors, who are always temperamental.
The Beethovens are without exception
beautifully recorded, but the series, to this
ear at least, is not musically ou a par with
its extensive big-company competition.
Scherchen's monumental choral. work series
also stunningly recorded and designed to fill
an impressive part of the Westminster coverage again to this ear suffers from the same
eccentricities of a very strong-willed conductor. His Bach Mass, Handel Messiah,
the long series of Bach Cantatas, do not set
the authoritative musical standard that the
Vienna chamber recordings have set.
Hi-fi? Westminster's British "Nixa" recordings are unsurpassed for arresting and
exciting hi-fi sound. Vaughan-Williams'
"The Wasp" and "King Cole," "Belshazzar's Feast" of Walton, Holst's "The
Planets," belong in anybody's hi-fi collection
W
HAT IS
* 780
52
Greenwich St., N. Y. 14, N. Y.
of sensational audio. Add to these numerous
Westminster semi-pops items, nothing much
musically but recorded with top quality, and
you'll find Westminster a leader in the hi-fi
category-and for that matter, the Viennese
records rate hi-fi tops, too, for fans who
happen to love Schubert and Mozart and
Beethoven and Brahms.
The ultimate temptation for a small company moving towards bigger things is a
recording spot in the U.S. But symphonic
recording over here costs a fortune as everybody knows. Westminster's first symphonic
records from the Nat ional Symphony in
Vv'ashington haven't offered much challenge
to the super-powered competition hereabouts
and the choice of repertory-so far- has
been decidedly risky: the Brahms Violin
Concerto, for instance, a type of piece that
is strictly for th e big operators; or the two
Creston Symphonies, too modern for many
hi-fi listeners and not of profound interest
to the modern-minded. (AUDIO, July 1954)
Better things may be in the offing, we can
hope.
And so this department still votes Westminster's European small-ensembles series
as its top offering, still unbeatable anywhere. Here are some recent examples :
Mozart: Serenade for 13 Winci Instruments,
K. 361. Vienna Phi Iharmonic Wind Group.
Westminster WL 5229
I'm ready to toss this one into the ring as the
finest wind recording I've ever heard, bar none.
The music is impressive, with no less than
thirteen solo wind players instead of the usual
four or five in the average work for wind solos,
and though nominally it falls into Mozart's
Ulight entertainment" category, this is actually
a major Mozai:t, opus with some extremely cogent
musical- thought beneath the pleasing exterior.
The recording by Westminster is remarkable.
The combination of a big, warm liveness and
exactly the right close·to mike pick up makes the
group sound impressively large, as it should
(l;nger, indeed, than many a full symphon y
sounds on records), and yet each instrument
sounds forth with the m ost startlingly natural
realism and presence, beautifully balanced against
(or with) the ensemble. Maybe it was luck in
the miking-but I doubt it; and I know that it
takes hairbreadth precision mike placement to
hit such an exact "resonance" of balance. Many
a new hi-fi record, superficially impressive, sadly
lacks this sort of balance between the total live·
ness and the individual elements. In this one
you' ll hear the "edge" to the wind tone, the
pecu liar reedy sound of clarinets and bassoons,
the tubby sound of horns, as you've never heard
them, with precisely the right amount of keyrattling and thumping to add presence without
reaching 'to exaggeration. A beautifully exact
musical ensemble and the expected highly musi·
cal, somewhat serious playing of the Viennese
school make this record a superb value.
Beethoven: Wind Trio, op. 87; Variations
on Mozart' s "Reich mir die Hand" (La ci
darem); Rondino in E Flat. Vienna Philharmonic Wind Group.
Westminster WL 5261
Here is a similar technique applied to smaller
groups with equally fine results. The Beethoven
Trio and the Variations, for two oboes and English
horn, are recorded 50 as to bring out most wonderfully the peculiar high, thin, bright tone color of
this oboe-family combination. As is wholly proper,
the acoustics are such that the three instruments
sound big and full and all-embracing. There is
nothing inherently thin or weak about a trio of
a ny sort, if it is heard in the proper surroundings
of intimacy. One doesn't compose a symphony for
small bedroom, nor does any musician write a trio
for huge concert hall-as we hear them too often
today. The splendid realism of this recording is
musically strictly authentic and for that reason a
lovely sound for any ear that can tell Yankee
Doodle fro m Oh, Suzanna. Early Beethoven,
beautifully written and performed, and the same
goes for the short Rondino for a larger group of
instruments.
Mozart: Divertimento # 17 in D, K. 334.
Vienna Konzerthaus Quartet, J. Hermann ,
string bass, H. & O. Berger, horns.
Westminster WL 5276
Hln·between" music, not chamber music yet not
quite symphonic, and this kind of ensemble m akes
the best sound of all for recording purposes. This
version wisely strengthens the string quartet with
a double bass at the bottom for a more orchestral
sound; with the two horns and Westminster's
usual warm liveness the results are as big and fat
as you cou ld ever want.
The music here is so typically Austrian that all
four availab le LP versions (it's a popular Mozart
work) are made in Vienna. In this version we
find the expected rather serious, very musical
Viennese kind of playing, the tempi always rather
on the s low side. The strings are recorded close,
ih the usual warm liveness, the horns are full
and resonant.
One movement of this work, oddly enough, has
become a familiar salon piece heard in a million
renditions from hotel orchestras and restaurant
wired-music services. You'll recognize it at once.
Brahms: Clarinet Sonatas op. 120, # 1 and
# 2. Leopold Wlach, Joerg Demus.
Westminster WL 5236
The music Brahms wrote for clarinet late in
his life is his very best, combining his expert
sense for musical contruction with an unusually
free wealth of melody- the clarinet seemed to
evoke this in Brahms. Pianist Demus is one of
Westmins ter's special Vienn~se artists, introduced
originally a long with Badura·Skoda in a superb
two-p iano series. He is a brighter, more fo r ceful
pianist than Badura·Skoda and is very much at
home in th is forcefu l Brahms, playing a healthy,
alive performance, energetic but not harsh. But
the clarinet is reserved and a bit colorless, aided
by a reticent recording that actually perserves the
normal solo-piano balance with the piano out in
AUDIO
•
SEPTEMBER, 1954
Latest production w I th
higher sensitivity an,d. im:'proved tone balance:' lncorporates C'raltsn\en's fa inous AFC, Phono Pre-Amp '
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greater speaker power handling capacity. 29¥2/1
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In MAHOGANY Net $66.00 • In BLONDE Net. $72.00
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rubbed finish. Supplied all cut out to house C800A
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All- items. available separately at incliviclual net prices
AUDIO
•
SEPTEMBER, 1954
53
\.
fron t. (Most recording engineers succumb to
temptation and stick a mike under the soloist's
nose, pushing the piano "accompaniment" into the
background.) Westminster is right, even if the
clarinet playing is not persuasive, and the" ·piano
is recordetl with a fu ll and rounded bass and a
smooth over -all naturalness.
Debussy: Three Sonatas. J. Fourn ier, vI. , G.
Doyen , pf., A. Janigro, cello, C. Wanausek,
fl., E. Weiss, via ., H. Jelline k, harp.
Westminster WL 5207
The profusion of n"mes listed above wi ll im·
press you with the ins t rumen ta l variety in these
strange last sonatas of D ebussy, none for cello
and p iano, one for violin and piano, and the third
for t he odd combination of flute, viola, and h arp.
The most colorfu l and easiest to hear is the last·
ment ioned j the violin sonat a is curious ly episodic,
hes itating o'!twardly, with Kreisler·like sweet·and·
sour harmonies. The cello sonata, like m ost cello
works, is not easy on fi r st hearing but may com e
through later.
T he taut , introspective, fragment ary mus ic, like
noth ing else, is tonally opulen t here. T he performance , recorded in Vienna J has a certain softness that is not exactly ideal for the music. But
as far as that goes, few performances ever m anage
to realize the fu ll interest and sustain the odd
mood of these sonatas from beginning to end.
T hey are problem -pieces for the performer, strong
stuff that easi ly falls apart in front of an audience
(or a microphone). T h e basic trouble is the
subtlety of rhythm, decidedly lacking in that
typically Germanic "beat" to hang onto (for both
audience and players) that helps many another
piece through a perform ance. Y Ott won't find
any better solution of the problem on records than
th is one.
Beethoven : Sonata # 9 for Violin and
Piano, op. 17 (" Kreutzer" ); Sonata # 2,
opus 12, # 2. Jea n Fourn ier, vio lin , Ginet te
Doyen, piano.
Westminster WL 5275
T wo leading French artists record Beethoven,
w ith pleasing resu lts. The famous "Kreutzer"
sonata does not have t he fiery violence we are
used to in many a big-name virtuoso perf'Jrmance,
but the melodious aspect is beautifully taken care
of and the rhythm is good. This is a strong per·
forman ce, notably in the lovely variation movem ent . The pianist (lady) is forcefu l and masculi ne,
the violin (man) is somewhat quavery and seem s
the more fe mi n ine of th e two. Close-up violin rec·
ording but the balance of volume keeps it in
proper balance with t he warmly recorded pian o-
qu ite correctly. \Vestminster knows its sonata
reco rding. This is one of a long list of SOJlatas in
the Westminster catalogue.
Mozart: Piano Concerto # 21 i.n C, K.467 ;
# 26 in D, K.537 (" Coronation" ). Jeorg
De mus; Vi e nn a State Opera arch ., Horvath.
Westminster WL 5183
Th is Westminster doesn't come up to the usua l
very high Westminster musical standard for
Mozart, though I should add hastil y that it's far
ahead of a good many similar offerings on other
labels. Demus ;5 a top two·piano Mozart p layer in
his recordings with Badura-Skoda on Westminster
a nd an excellent Brahms-period p layer on his own
(see above) but his solo Mozart is brighter and
shallower than Badur a·Skoda's. It is im peccably
phrased and styled-Demus- is too m uch at home
in Vienna to make gross errors in styJe---but the
mus ical depth seems to me to be laCK ing, the two
concerti are not completely rea lized f<lr-,their full
mus ical values.
.
The perfectly dreadful. cadenzas (Busoni) which
Demus uses merely add to this impression. Why?
Do pianists really think that people who buy
Mozart records will take these horrib ly untast.ful,
out -of-style exhibtions of poor musiciansh ip. inserted in the m idst of such scperb m usic?
-if'
French
Chausson: Poem of Love and the Sea.
French Art Songs. ,Gl 2dys Swarthout ; RCA
Victor Symphony, Monte ux . G. Trovillo. pf.,
B. Greenhouse, ce llo, Gloria Agostini , harp.
RCA Victor LM 1793
Westminster Laboratory Series
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made expressly for professional equipment!
ONLY IF you have invested care
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,
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finest equipment. On these recorl'ls there is n o disto r ti on,
either harmonic or intermodulary. There is no It ec ho", no
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1'esponse, no stylus-bridging of
inside grooves. W-LAB sound
is so clear , so clean, it cannot
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promise that YO Wl' system has
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The first release (W-LAB 7002 )
is Tchaikovsky's Capriccio /talien and Rimsky-Korsakoff's
Capricci o E spagnol, London
Sym phony Orchestra under
Scher chen. With dust-protective cover , and accompanied by
a n en g in eerin g' a n a lys is by
C. G. McProud, editor and publisher of A udio Engin ee1'ing, it
is $7.50.
As Mr. McProud says, " You are
due f 01' a pleasant sil1"prise!"
LISTEN - AND COMPARE!
54
What a sense of style the F r ench have! More
important, even, than content. No other nat ion
can turn out mediocre music of such compelling
and beautiful pr oportion s, no composer can wr ite
p lain hot air and get away with it the way th e
Frenchman does.
Here is a iittle·known wor k for soprano and
orchestra by Chausson t hat is a stunning example
of French vocal wri t ing, and that o ld trouper,
G ladys Swarthout, does a heart· warming job with
it in the best French tradit ion, which bas a lways
been her fort e. The mus ic is a long, tragic-sounding love song, out of t he school of Cesar Franck
but a lso much like the colorful early impressionism
of Debussy and Ravel; it swells and dies away in
a lushly co lored swirl of mystic r omance, th e vocal
line beautifull y placed with its French text aga inst
the
impress ion istic
orchest ral background-it
should send sh ivers down the most callous musical
spine, and I Jove it.
It isn't unti l after wards t h at yo u realize how
little has been said, a ll in all, and you understand
that for all its pers u as iveness, this is something
less tban great mus ic. And yet--does it matter? .
For in France one does not j udge ar t in the
Germanic manner, heavily, for arch itectu_re and
"depth ." In France it ' is lightness t hat counts, in
-music as in food, the perfection of s t y le, the impeccable technique and the unerring performance.
It is the very subtlety of all th is th at brings tears
to the Fren chman 's eyes and to ours as welL
From Couperin to Poulenc, from Gretry to Ber·
lioz and Offenbach, the French have never a llowed
a cr ude or s loppy touch to spoil either the com·
position or t h e perform ance of their mus ic.
\¥bere else, then, could a long-time artis t such
as Swarthout, her g reat voice sti ll functioning
mus ically if not with the power it once had, find
for herself a more perfect medium? The m usic is
not trying on the vocal physiq ue-not for an old
t rouperJ in any case. It is of the sort where style
counts far m ore than lung power, and Swarthout,
a ided by a beautifully p laced c1ose·up mike, is
abso lute ly radiant. Radiant even when, rather
st art ingly, sh e lapses now and then into an o ld
trouper's baritone range. It only adds to the
musical potency. Gorgeously impressionistic orchestral backing from Frenchman Pierre Monte~,
who never did a better job of enlivening lit tle·
known music for you r and my delighted consumpt ion. A good recording.
The art songs on t h e reverse, with piano, are
essentially fi ll to round out the LP, and are vary·
ingly efiective according to the d ifficu lty of the
m us ic. C lose studio recording here robs the great
voice of some of its magic, and technical d ifficulties arise. But the songs with cello and harp by
Bedioz (Romeo and J uliet) and Hahn are lovely.
Singing s t udents will want this s ide for study.
Representative items from the singer's repertory.
Note that the Chausson work is reminiscent of
Ravel's early "Sheherezade" and Debussy's "De..
AUDIO
• - SEPTEMBER, 1954
Audiarama 1954
Presented by THE AUDIO FAIR
This is it!
AUDIORAMA 1954! The sounding board for the newest Hig~
Fidelity equipment . . . the final proving ground for the latest designs in
Audio. Broadcast Engineers, Governmental and Military Agencies, Recordists, Hobbyists, Sound-on-Film Men, Di.stributors, Dealers and Music Lovers
. . . everybody will be there .. . representing every important country in
the world.
Now Hear This
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Never before has such a large showing been presented under one roof.
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Never before have so many of the world's leading manufacturers of audio
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Now -Hear This . ..
Never before has there been such an opportunity to discuss sound equipment with the people who know ... who design and build it.
II You Missed AUDIORAMA Before
You Should Not Miss
AUDIORAMA 1954!
AUDIORAMA 1954 is the one 'must'
event for you if sound has any bearing
upon your profession, business, hobby
or just the enjoyment of good music.
FOUR DAYS-October 14, 15, 1'6, 17
FOUR FLOORS - 5th, 6th, 7th, 8th
Hotel New Yorker -- New York City
EXHIBIT HOURS:
Thursday, October 14-1 :00 P.M. to 10 :00 P.M.
Friday, October 15
-1 :00 P.M. to 10:00 P.M.
Saturday, October 16-1 :00 P.M. to 10:00 P.M.
AUDIORAMA 1954 will present the
largest ~howing .of sound equipment
ever organized under one roof.
DON'T MISS IT!
THERE IS NO ADMISSION CHARCE
You Are Invited . • •
Sunday, October 17 -12 Noon to 6:00 P.M.
AUDIORAMA 1954
is presented by THE AUDIO FAIR
Sponsored
by
Harry N. Reizes, Managing Dir. , Audio Fairs
67 W. 44th· St., New York, N. Y.
An AUDIO FAIR-VIDEO FAIR, INC. Project
AUDIO· •
SEPTEMBER, 1954
l
55
moiselle
period.
newest, neatest, Iigh
lapel mike on the market
THE
TURNER
L·l00
with the adjustable clip
that grips from any angle
~ ,
Elue,"
of
the
youthfu l
impl-essiou ist.
Saint-Saens:
Four Symphonic
Poems.
(Phaeton . Jeunesse d'Hercule . Le Rouet
d'Omphale. Oanse Macabre ) . Orch . Co nce rts Co lonn e, Fou resti e r.
An gel 35058
I-Iere is French style all over again-verbose,
long-w inded m u sic but so hand some ly a nd gracefully built that one cannot really condemn it --for
what it is, mus ic a lot less than great and full of
a considerable volume of warm a ir. Two of th e
tone poems are familiar, the we11 known "Dan se
Macabre" an d the "Rauet dJOmpha let" the other
two are to most of llS in the States quite unknown,
though French undoubtedly keep them in loca l
c ircu lation.
If YOll are look ing for cogency, economy. m od·
esty of e......:pression. if you want depth, sincerity,
don't listen to old Saint·Saens, who turn ed ou t h is
s lick m usic as an apple tree bears app les; he just
couldn..'t help it a nd he didn't worry himself one
bit about it on e wa y or th~ other. Indeed, h e fai rl y
basked in his own prolificness, where Brah ms
torLtred himself over every composition, for fear
it was not grea t enough. Again it is t he im peccable
sense of style a nd musica l consistency that keeps
t h is m usic a live in spite of its noisy, bombastic
big-·time s ty le (nothing impressionist ic abo ut th is),
wh ere the equivalent German tone poems of
Liszt (a much mo re profound mus-ical mind)
sOllnd incredibly banal and blatant for o ur ears
today. Your ·first reaction to Saint·Saens may be
"w hat errant bombast;" but on second p laying it
comes off a lot better. One does not even p lay
some of Liszt's tone poems a second time.
Excellent French pe.r£onnance and superb hi -fi
rec ording by Angel recommend this reco rd to both
tllllsit:ia71s and hi-fi fans, warm air or no.
Oebu~sy : La Mer. Ravel : Rapsodie Espagno le_ Philha rmoni c Orch ., Von Ka raj a n .
Angel 35081
_ _ __ I'
The handiest, low cost lapel mike
for a ll tape r ecording uses . . . it
weighs onl y 1 ounce and has an alliga tor clip th at rea ll y ho lds. T he clip
is r ubber padded and adj ustable ho lds th e mi ke w here yo u put it;
on draper ies, clothing or r ecor der
case. Speec h reprod ucti on i s crisp,
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COMPANY
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A paradox, th is disc, and not exactly a s uccess ful one. The u ltra·Latin music is p layed with an
Austt·ian conductor and a British orchestra and,
h owever n ice th e orchestral sound, the m{,tsic is
r ath er r emarkab ly off-style, we run into th is
phenomenon quite frequently on records-Gennan
music played \v ithout comprehens'ion by French or
Italian groups, French music m ishand led in the
m ost subtle and deva tat ing way by Germans or
Aust r ian s. (On ly a frea k like Gieseking, gre'lt
German player of French music, breaks and proves
the ru le.) An incredi'bly bad Beethoven 8th-or was
it the 2nd-by l\ion teux com es to m ind; J r emem·
bel', too, a recent "1\1eistersinger" overture by the
French conductor P au l Pa.-ay that was the oddest
Wagner I ever hope to h ear. But Debussy and
Rave l ill the tradit ion of Schubert al1d Strauss is
equally odd.
.
I can't describe in a few words just wh at goes
wrong in Von Karajan's beautiful1y accurate
French music. It' s all there, but t he sense doesn't
come through; a thousand and one ·d etails of emphasis, of intended color and mood are misinterpreted, the larger pattern, the whole colorful Lafin
intent , is lost and the music gropes for direction in
the midst of its own lush orchestral expression. Ef·
fect after effect falls fl at , or rises too h igh, or j ust
isn't there. A quite remarkably subtle example of
musical misunderstanding.
Good sound and s uperb r ecording, just the same,
and it may be wel l worth your while to listen here,
as a study in interpretation.
French Music for the Theatre (Oukas :
Sorcerer' s Apprent ice. Faure: Pelleas ct
Melisande. Roussel : The Spider's Feast ).
Detroit Symphony, Paray.
Me.rcury Me 50035
Back in France again-even though the sour ce
is Detroit. Paul Paray is "in" on French music
a nd one can spot h is assurance in these works, in
spite of a kind of g(!)od lnunored eccentricity of
aPJ3roach th at makes every Paray record a new
surprise. The fa m ilia r "Sorcerer" here get s a
weighty, slow-tempo h=-e atm cnt that brings out
the horror-appeal of the famous st ory as ex·
pressed in th e score, plays down the skitt ish
wi ll -o' -the-wisp magician stuff. 1'.'lercury's by-now fam iliar close-up one-m ike recording adds a cer·
t a in a lrrtost harsh rea lism t hat finishes the re·
decoration of the m usic-heavy , crisp, percussion ,
striden tly edgy b rass, s harply clear stri ngs, hi-fi.
Faure's melodiously sweet "Pelleas" music is
'56
the be t item on the record for my ear as Paray
conducts it. T he R oussel "Spider" score is instr:umentall y colorful and neatly modern in its language but somehow I find m y mind wandering
before it gets far. From the period o[ Ravel, Ro ussel's m usic is pale and cont rived a longside Ravel
himself, though expertly enough wri tten.
Faure: Ballade for Piano and Orch.; Impromptu # 3 ; Theme and Vars. for Piano.
Poulenc: Nocturnes; Mouvements Perpetuels. Gran t Johannese n, piano; Netherlands
Philha rmon ic, Goe hr.
Concert Hall CHS 1181
Grant J ohannesen, Ainerican pian ist, is a natura l Romantic. His s ubdued lyricism is just right
for the somewhat perfumed music of Faure. The
fam iliar Bal1ade has had more outspoken performa nces, but this one has a lovely sound and a nicely
soft atmosphere with the conscientious Dutch
backing of t he Net herlan ds Philh armon ic under
the conscientiously com petent Goehr, who h as
done some fine conducting for Concert Hall in
earlier releases.
But Johannesen is out of his element in the
snazzy Poulenc piano wOl·ks. The Nocturnes, to
be s ure. ar e brooding and nigh t · filled and they
appropri ate a goodly portion of Chopinesque
schmaltz; but th e intention, I anl sure, was halfhumoro us, seriously sat irical in the pl-evailing
French m anner of the 20's and 30's; Joh annesen
plays them, each and everyone, most soulfully
and e......:pressively. Musical, but seriously out of
style.
T he proof is in the little Mouvement Perpetuels
-for if the Noct urnes we re, by the ir very ti t le
enti tled to at least some romance in t he p layng,
the Perpetual ~Iotions are· the purest nose-thumbing French vu lgarit y ! This piariist's solemnly
lyric treatmen t of their strided little dissonance5
is somethi ng hard to believe. As welt play Pine
Top's Boogie in the s ty le of Victor Herbert!
Poulenc : Les Mamelles de Tiresias. Solos,
chorus, orch . Ope ra-Comique de Paris.
Cluyt ens.
Angel 35090
French opera! I-Iere is where you' ll find the best
evidence of the French love of consistency and
sty le. The recordings we've had. to dat e, of Frenchperform ed French opera are far ahead of any th ing
we can do in th e States, with our ·-inev itable mixt ures of artists from every , country, conductors,
orchestras, stag.e designers each with his own background . In France, opera is given by Frenchtra ined artists who sing toget her with simila r tone
and style, who have had the same training. feel
the same way. Try the wonderful "Tales of Hoffm a n" of Offenbach in the Opera-Comique performance on Columbia (SL-106) or tbe "Carmen"
of th e same group (SL- 109)-or try this modern
French work. As the ads say. you' ll be amazed.
Delighted, too.
Pouienc, now in respectab le middle age, was
once t h e deli g htful bad boy of t he gaudy French
1920's and 30's. In those days, avan te g arde art
was not only r adical, nose· thu m bing, eccentr ic,
s hockin g-it was a lso wonderfully al ive, fu ll of
hum or and e......:tremeiy ski llfu l beneath its cacaphon o us exterior. Now t hat the shock-power has worn
off, th e h umor and the skill are apparen t .
"Les Mamelles" has not on Iy a title that had
best b e left untranslated but a text wh ich, li ke so
m a ny French effusions , while perfectly acceptable
in its own language and h ig h ly amusing to boot,
is un thinkable in English. We just don 't have t he
vocab ulary [or it. This is a high-handed and giddy
far.c'e about a man whose wife decided to be a
fe m inist and ou tlaw the making of children amo ng
her kind, whereupon her husband, dressed in skirts,
finds a way to prod uce vast numbers of children
of t h e m ost a mazing k inds, fu ll grown and r eady
to go to work for him, a ll without the aid of the
fe male sex. The bio logy of th is is somewh at obscure, the im plicat ions for an an alytical m ind very
F reudian and weigbty. But the m usic blithely
ig ilores a ll s uch considet·at ions and weaves its
light-footed and melodious way thro ugh a passel of
surrealist high-jinks. a kind of m odern Offenbach
effect.
.,-'
For Foulenc, the music is unexpec tedly lyric and
lovely. The man is a born opera com poser, though
little h ave we know n it. T hose who have enjoyed
his recent Concerto for Two Pianos (RCA Vict or
LM 1048) or the Concer'to for Organ, Strings and
Tym pani, with E. Power B iggs (Gol. M L 4329)
will h e much p leased with this music-as w ill a ll
who appreciate f;-ne singing, beautifull y apt vocal
writing, and Frenoh opera in gener a l- the Opera·
Comique in particular.
AUDIO
•
SEPTEMBER, 1954
ShOftT TilDe Is Here Again!
See Leonard's AUDIO MART Ex·
hibits at: The National Home
Furuishings Show, 34th Street
and Park Avenue, New York,
Sept. 9-19, Booth #71
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Super bly sty led, simple in design,
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is comprised of the University Wide
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34 V2 " H x 40 112" W x 24%" D
and may be used either as a "H iBoy o r " Lo-Boy" to suit any room
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. available in
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"The Hidden Soul of
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Sensitivity: FM : 5mv for 20 db
quieting . . . AM: 5mv
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MC . . . AM: 530-1650 KC
Frequency Response: ± 1 db 5015.000 cps
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. . . AM: Hi gh impedance
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Audio Output: RM : 4 volts . . •
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AUDIO
•
57
SEPTEMBER, 1954
I
ere.
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1. Tape from Tubes.
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58
HUMAN BEING who has anything else
to do (like playing r ecords and figuring out what's good about them) could
ever keep up with all the straws that fly in
the Audio wind these days. A department
like this one just keeps its eyes and ears
open for what comes along, and maybe its
main value is in flagging down these items
(to change · my metaphor to railroading)
which flash by for an instant-yet in that
instant show up as important as all get out.
Such items don't come by .every day and the
huge number of big-talk items that go past,
signifying nothing really very new, is something hard to believe.
Reminds me of that N ew Yorker cartoon
of last summer with the East-of-the-Curtain
family watching a TV commercial-uFolb,
be sttre to go 1'ight ont and b.n y one, now."
They do.
lf we all went right out and took every
word about the new audio sensations seriously we'd be in a pretty pickle. Most of us,
however, know the American language
pretty well. We hang onto ourselves long
enough to think twice, if not thrice, before
getting steamed up. Except, once in awhile,
when something really significant turns
up . .. .
Like, for instance, the casual clipping
somebody sent me a few days that still has
me gasping. It was an article on Interpretation of Old Music (Lan'g ) and right up my
musical alley . . . ,but on the back of the
last page was a part of a column by R. D.
Darrell on tape duplication that made me
sit up with a bang. He was writing up a
Ilew electronic tape playback head developed
by Dr. Melvin Skellett. If what he says is
from the horse:s mouth, this is a really big
thing and I have to flag it down quick and
pass it on to you, though it's not my scoop.
You see, though magnetic tape bas' removed that major obstacle to ideally perfect
sound reproduction, the mechan ical motion
of the cutting and playback stylus-reducing
the problem of mass in effect to zero-the
playback tape still must Do W O1'k as it generates tiny voltages in the head's wire coil.
Because of this, tape playback speeds have
been limited, in spite of much improvement.
The work done (derived from the forward
mechanical motion of the tape and acting as
an infinitesimal brake on the tape transport)
gets involved with distortion especially when
tapes are played at high speeds.
I'm not enough of a electronics man to
catch the details but I get the idea and so
must you. Why high tape speeds? For tape
duplication. The higher the usable playback
speed the faster can tape duplicates be made.
As long as the tape playback head is essentially a generator, producing varying
signals according to the varying strength
of the passing magnetic fields on the tape,
complications are bound to develop, not
on ly when the generator is run at high
speeds and the work is done too fast. Distort ion.
Na Wark
The new tape "head" which Mr. Darrell
describes is a tube, instead of a coil. If I
am right, it operates in very much the same
manner as a TV picture tube (though he
doesn't say so) : a beam of electrons is deflect ed by the passing taped magnetic fields.
A wholly different principle, and its most
direct di fference is that it no longer involves
the generation of a current, however tiny,
and so it does no work. Instead, the only
"work" that is accomp lished is the mere
deflection of an electron beam-which takes
enormously less effort than the generation
of an actual current. This, I would guess, is
a form of amplification, a control circuit that
does not itself provide the energy for the
tiny signal current.
.
Therefore-no distor t ions due to the speed
of tape passage which, I gather, could
ideally be as fast as th!,! speed of light without bothering the internal operation of the
system. As fast as the beam in a TV tube.
Superb transients in practice, tape may be
whisked past this playback head as fa st as
is physically possible without the slightest
effect upon the quality of the transferred
signal. Terrific.
Quality, you see, may be vastly improved
by this new system. The whole problem of
reverse induction of an opposing current
that occurs in any generator and tends, in
tape as elsewhere, to louse up transient response, is eliminated in this head. The electron beam deflects instantaneously, weightlessly, and if I understand this thing, without resistance. Transients, no matter how
fast, are passed on perfectly.
Now some readers ' may be saying' that
tape is ·supposed alr.eauy . to have removed
all the important impediments to the transferal of a sound signal. Not all. Yes, the
relatively huge impediments ohhe' mechanical stylus and the record groove ~re gone,
and tape sounds just that much the better
for it. But we still have electrical troubles
in the system, on a smaller scale, and we
still have the mechanical speaker to content
with. Even taped sounds are far from perfect.
Indeed, what is remar kable, it seems to
me, is the fidelity with which we can play
plain old discs right now, in spite of the
presence of three major mechanical motorgenerator elements-cutting head, playback
head, and loudspeaker-plus a fourth element, the plastic of the record itself. (Not
to mention, of course, the infinite mechanical complexities of speaker enclosures and
room acoustics-to wh ich we may also add
the earlier complications introduced by the
microphone-generator.) All these major
complexes of physical mass and working-
AUDIO
•
SEPTEMBER, 1954
current distort the pure signal before it gets
to us from th e LP record. They have been
reduced to a fabulously low point.
Present-type tape reproduction reduces
them significantly more, even so, by r~mov­
ing the mechanical element in disc cutting
and playback. Given otherwise equal situations, we can still detect the AB difference
between a tape playback and a disc-though
it is astonishingly slight.
With the new electron-beam tape playback, one more remaining tiny source of
distortion is removed with the elimination
of the playback-generator in the usual playing head. The difference at ordinary tape
speeds surely cannot be audibly noticeable,
though the removal of background head
noise and the lower-level recording are
tremendous advantages. Most of us, I suspect, could not possibly tell a standard topquality tape playback from the same via
the new head, nor will most trained audio
ears spot the clearer sound that should result nor the better signal-to-noise ratio.
Good tape is mighty good these days.
But that's not the whole story.. As you can
understand, first, the difference in speededup playback, for mass tape copying, becomes vital, and indeed this would seem to
offer a major missing link in the teetering
balance between discs-for-the-publi.c and
tape-for-the-public in the years to come.
The subtler advantages inheri:!nt in the
system, 'notably the low recording level required, should supplement this and, as I see
it now from tbe outside, could eventually
affect every kind of tape playback from
super-professional copying all the way down
to the lowly home playback unit than can
make ' or break the market for tape in the
home.
.
'
l owe my entire information at this moment to the alert Mr. Darrell and am happy
to throw him the credit for this article's
inspiration. As of now, I am not clear on
several points of detail-I couldn't wait. I
am not clear from him as to whether there
is any application of thi,s new principle to
tape reco'rdillg, though as best I can figure
it th ere is not. (The beam deflection principle is not reversible as is that of the motorgenerator now used for recording and playback.) This is strictly a playback head, a
revolutionary one; but indirectly it will affect recordin g', as already noted.
I also don't know what stage of development has been achieved in the new tape playback "tube" nor how many practical bugs
in' performance 'and pr.oduction have yet to
be overcome. Probably many. But it's
enough to know that th e thing exists and is
revolutionary in principle. We'll probably
hear more-about. it" and , I suggest you: keep
a corner of the mind on the a lert for it, if
and when.
2. FM Sensitivity
Since I got a Fisher Model SO-R FM-AM
tuner I have learned sO'me surprising things
abou t EM listening, as of now. During the
summer I was in the eouritry ' with this
remarkable tuner, r oughly 100 miles from
N ew York City and 30 miles from any other
reasonably big town-which, in New England, is real isolated. In that country spot I
discovered how important FM sensitivity is.
Too many people still think that FM
reception is for the big cities only, that you
can't get stations more than twenty or thirty
miles away, that except in the city you are
limited to whatever tiny local FM outlet
that may be on the air four or five hours
a day, evenings-so why bother with FM ?
That is certainly true if you have an FM
set of average sensitivity and even more so
if yours is one of those turned out at a low
price a few years back, or is the FM section
AUDIO
•
SEPTEMBER, 1954
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of many a medium priced commercial radio.
At noon on one summer Monday, when
a good proportion of FM stations could be
counted on to be off the air (many operate
evenings only) I turned on my Fisher with
its simple folded dipole plastic-and-wire
antenna stuck up on the wall with thumb
tacks. I logged t~vetlty five FM stations
that came in well enough for entirely comfortable radio listening, and didn't count a
half-dozen others that could have been followed through the white-noise hiss if something important had to be heard. (Even a
loud FM hiss is less obscuring and less
tiring on the tZar than the irregular popping
of AM static in summer.)
You'll note in the audio hi-fi catalogues
that tuners are now pretty regularly given
sensitivity ratings in the specs, usually so
many microvolts for 30 db quieting of the
FM inter-station hiss. (Some ratings are
for 20 db quieting). I was astonished to find
what a wide range of sensitivity is still
fo und among the new FM and FM-AM
tuners, from a listed 10 microvolts all the
way down to 2, which by my arithmetic
would be five times as sensitive. (Anyway,
a lot more sensitive.) In the city, sensitivity
is not overly important. But if you want
some superb country listening at great distances, then the new sets, with very high
sensitivity are definitely for you. Among
these, tht; Fisher ranks very near the top
and I must say from some months' personal
experience that it is a superb instrument of
its sort, though possibly its competition
which I haven't happened to try is just as
good.
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Another crucial factor, in case you haven't
paid much attention to it, is AFC, automatic frequency control, present on almost,
but not quite all of the newer FM tunet's.
AFC is the gadget that conqllers the old
and distressing tendency towards drift that
used to bother u~ so in FM and, indeed, did
a lot to give early FM a bad black eye with
the automatic-loving public. AFC draws
each station in, so to speak, and hangs onto
it either way, as you move the dial pointer
away from dead-center. (Some FM circuits do !lot reqni1"e A FC-National's, for
e.m1'l1ple. En.)
AFC, of course, must be "defeated," as
the quaint engineering terminology has it,
when you don't want it to hang on too
tenaciously and thus cover up small stations
that nestle close to big ones. Most sets have
an AFC "defeat" switch, for this purpose.
The Fisher goes further with an AFC
"volume control" as well, which regulates
the degree of tenaciousness from zero to a
lot. Very useful. With the AFC control
full on, the tuner will hang onto a station
for a good tJalf-incb either way, right over
and on top of several neighboring ones ;
when it finally lets go with a pop, it latches
onto the next station. But from that extreme, it can be regulated to fit exactly the
strength of the stations you customarily
tune in. Thus in the <:ountry where many
stations are weak and lie close together, a
very small amount of AFC will hang onto
anyone of them, to keep you in tune, but
will allow you to break away to the next
station a fraction of an inch beyond and
latch onto that for best steadiness. It works
even for groups of extremely weak stations
with scarcely any signal at al l. If you run
into a periodic fading situation, where first
one, then another station is stronger you can
always "defeat" the AFC entirely and keep
tuned in one spot. (An good tuners now
are very steady, once warmed up.) Yes.
definitely, I suggest variable AFC for good
country listening. (Adj1~stable AFC is also
available on the new Pilot AF-860 tHner.
En.)
Incidentally, one lovely present virtue of
FM listening in New England was an unexp~.c ted pleasure-automatic commercialcanceling. No-this is not a feature of
Avery Fisher's versatile tuner. It's built
into our local stations thanks to the prevalent WQXR network tie-ins that cover this
Eastern a rea with FM from New York
City, via micro-wave links.
New Yorkers wi ll be sick with envy
when I say that, up in Connecticut, I can
listen to vVQXR's entire musical program
via FM and every commet'cial is neatly removed! Oh, those lovely, long, palpitating
heavenly FM silences, all 60-db-down of
them! The local benefactor, (probably unwi lling) is FM statioi1 vVRRH of Beacon,
N.Y., which rebroadcasts the New York
program minus the WQXR commercials
that, Heaven be blessed, didn't pay for our
area. Now, everybody, go quick and get a
super-sensitive, variable-AFC FM tuner
and set yourself up quick for blissful FM
listening. Static-free, and hi-fi too. Worth
moving to the country for, I'd say.
Incidentally, too, for the first time in
history I was able to hear my own FM
program, 100 miles away on N ew York's
local FM station WNYC; also heard it at
the other end of Connecticut, some 125
miles from th e city. Judging by my mail,
very few listeners to WNYC live further
than 30 miles Ot' so away, and the station
assumes its main audience to be strictly ill
the city of New York itself. Think what
will happ en, then, when FM sensitivity
really increases all along the receiver line.
It's bound to occur, and FM has here Olle
more hopeful prospect for the future, con·
trasting with the somewhat dismal past.
3. The Real, Honest-toGoodness Organ
One of the most exciting records I have
played in a long time is "The King of Instr uments," a 12-inch LP record that features an illustrated lecture on the new
developments in the so-called "classic"
organ by the man who practically singlehanded brought about the present revolution in organ building in this country now
in its full tide, Mr. G. Donald Harrison of
Aeolian-Skinner. (Available from AeolianSkinner Organ Co., Boston 25, Mass., $5
postpaid.) This disc is required listening, to
my mind, for all readers of the recent di squisition "Plans for a Pipeless Organ"
which I wrote in this magazine last January,
and for all who have any interest in the
workings of a true organ, or in the construction of any and all electronic instruments of
organ-like character.
The account is by Mr. Harrison himself,
who lectures to us, his words frequently
supplemented by the most enchanting fragments of organ playing I have ever heard.
Though Harrison is not exactly a master
of mike technique and his speech is obviously read, and sounds so, the wide-awake
mind will be entirely willing to concentrate
on his words for their sheer interest. He
takes us through the main divisions of organ
tone on the first side and the beginning of
the second, then launches into the special
Qt'gan "stops," their construction and use
( illustrated, of course) and finally goes into
the mixtures and mutations, where colorblending of whole groups of pipes is used.
Here was the most important meat of the
whole lecture for my ear.
"Matching"
I had not been clear before, but am now,
as to the difference between mutations, ex-
AUDIO
•
SEPTEMBER, 1954
tra-color pipes used to add color to individual solo stops, and the mi xture ranks which
are. designe4 . to brighten up a whole keyboard full of musical sound. These last,
astonishingly enough, are tailored individllally by pitch to the bwilding itself; added
to their own keyboard, they reinforce- different partials and at different volumes all
the way from bottom to top of the scale
according to the acoustical qualities of the
building, compensating for weak spots,
resonances in the hall and so on, to "match"
the orgap tone to'its acoustical surroundings
and pn;!sliIc$! an even and balanced scal e
througH,f,q tl he J?itch range. M?ve the organ
a!ld you ,.~<\§t;:r:e"rnatch the mIxtures to the
new locat.ion. -,ILyou want to know why the true or
wind organ is not likely to be replaced by
any electronic equivalent except for practical compromise purposes, you will find the
reasons implied here. Mr. Harrison doesn't
say it itl' so many words; but his careful
and detailed exposition of the business of
acousti.cal sound-making via organ pipes
brings out the·· enormous complexity of
organ tone and, even more, the tremendous
subtlety of the tone-mixing process in organ
building and organ· registration. Absolutely
fascina ting.
If you have been inclined to scoff at the
revivat·,9t ·. the older organ practices, the
"Baroque". -or "classic" org1m, Mj:: Harri'son's talk 'will give you the straight dope
most revealingly. The most dramatic musicat examples in the whole record are where
a passage Of music is played first with the
carefully calculated acoustics of the "classic"
organ tone, then with a typical "Romantic"
19th century registration-to show how with
the first, every detail of the masic is audible
and clear, where in ' the second the same
notes come forth in a grand and confusing
blur, musically meaningless. That, my
friends, is what organ design, organ building, and organ playing is all about.
(Since this review was written, Vol. 2
of the King of the Instruments series has
been received. This record-available from
the same source all\d at the same pricecontains three chorals by Bach, and six
other classic organ selections by Davies,
Bach, Alain, Langlais, and Sowerby. Quality of reproduction is excellent, and the
music will be reviewed in the November
issue. ED. )
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NEW LITERATURE
(from page 12)
• Duotone, Inc., Keyport, N. J., is distributing to jobbers and dea lers a new
catalog which cross-references more than
400 cartridges, together with the type of
stylus re'quired for each. Other cross-references include styli of virtually all
manufa cturers. A
stylus replacem e nt
guide lists the cartridge manufacturer's
stylus number, point size, material from
which the point is made, an illustration of
the stylus, Duotone's replacement number,
the ca rtridge number, list price, and a n
illustration of thfr ..cartridge. Request for
copy must be accompa nied by a remittance
of twenty-five cents to cov·er handling.
• National Cine Equipment, Inc., 209 W.
48th St., New York 36, N. Y ., has recently
published a 28-page catal9g which grea tly
eases the selection of equipment for the
production ' of 16- and 35-mm TV and motion picture films. Included among the
catalog listings are professional lighting
equipment, cameras and accessories, synchronizers; recorders, animation equip- .
ment. booms, so.und ·equipment, and v a rious other devices and accessories. :Augmenting the descriptive p a ges is an extensive price list on equipment rentals, in
which the company specializes. Copy must
be requested on company letterhead.
AUDIO
•
SEPTEMBER, 1954
New 224·Page
1955 Catalog,
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FM TUNER _______ ~ $39.95
AM TUNER _______ $29.95
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a nd n on-broadcast purposes. The b a sic
u nit · consists of a continuou s t a pe r e prod u cer a nd a lO -w a tt high -fid el ity a mplifier .. Optiona l equipm e nt inc lude s a hi g hfide llty speaker s y ste m and an a uto m a tic
Program Ma ster. The l a tt er prov ides a utom a ti c control f o r
any d esire d
oper a tin g
s c h e d u l e . Eight-hour ree l s m a y be pla Y'e d
at pre -determ i ned interva ls, for specifi e d
per iods of time, or for continuous cycl es
df eight h o u r s each. Initia lly, an a ssortm ent of 20 r eel s of 8 hou rs each of u nr e p e titive music will be ava ila ble. Magn e c ord, In c. , 22 5 W. Ohio St., Chica g o , 1 0, :m.
62
in s ize a n d less exp en s ive tha n the comp a n y's reg u l ar lin e of e n c l os ures, the
J u ni or s offer t h e sam e hi g h s t a nda rds of
workma n s hip a nd qua l i ty. Three-q u a rterm c h lumbe r -cor e p lywo od i s u sed t hrougho u t , corn e r s a r e mite r e d a nd s p li n e d , and
sh e lves a nd pa n e ls ·a r e r e m.o.v able. E quipmen t cabinets a nd s p eal{ e r e n c l osures a r e
a v a ila ble fini s h e d or u nfinis h e d . T ec hnical
inform ation a nd p r i ces w i ll b e s uppl i e d
on r ~ q u es t.
• Ta.pe Prot ector. The prob l em of k eeping
r e cording tape n ea tl y a nd tightly wo u n d
on its r eel i s s ol ved by the n ew Pro-T ex
into c rys tal inputs thro u gh u se of a c om p a nion p reamplifie r , the B e ll Mode l 2246 .
The unit i s availa b l e fo r ope r ation at
e ithe r 3. 75 or 7. 5 ips. :.Ree l c apacity i s
5 in. A djus t a b l e s upport l e g 13 compensa t e
for v a riation s in t u rnta ble h eight. Fre q u en cy r esp on se of the 7.5 - ips mode l is
50 t o 10, 000 c ps. Both mode l s a~' e e q u iwe d
w ith d u a l -tra ck h e ads. B e ll S o und Syste ms,
I n c., 555 M a ri on R oad, Co l umbus 7, Ohio.
AUDIO
•
SEPTEMBER, 1954
• Audio Generator. An extended fr equency
r a nge, an improved a mplifier, and the
addition of an o utput attenuator an d volt meter are important n ew features of the
General Radio Type l304-B beat-f requen cy
a udi o g en er a tor. Output fr equency extends
f rom 20 to 40,000 cps in tw o r a nges witli
a calibration accu racy of ± (1 % + 0.5
cyc le ). Frequency stab ili ty i s excellent
with the drift from a cold start les s than
7 cps in the first h our of op era tion a nd
essentia ll y complete within two hours.
The NEW MciNTOSH
200-watt POWER AMPLIFIER Model K-l07
The o utput amplifi er u ses a n ew s in g leended pus h-pull circuit a nd s u pplies one
watt into a 600-ohm l oad with l ess tha n
0. 25 per ce nt distorti on b e twee n 100 a nd
10,000 cp s. The n ew l 304-B provides a
calibrated output vo ltage WIth o utput
level b eing indi cated by a m eter an d an
atten ua tor se tting in b oth volts an d dbm.
Gener a l Radio Company, 275 Massac husetts Ave ., Cambridge 39, Mass.
• Variable Tinle Delay. The Echo-Vox is
a portab le instrument d esigned to provide
a wid e and continu o u s ly v a ri a bl e . time
delay at a udio frequ en c ies. Among its
appli cati ons is that of prope rl y phasing
speal{ers in a uditorium s, sta dium s , a nd
other large areas wh er e ob j ect iona ble
ec h oes exist. It may a l so be used to
ach ieve the opposite effect w h e re condit ions are such tha t introduc tion of s li g ht
Designed for high -fidelity theater sound
reproduction, and for disc recorders, the
K-l07 also has industrial applications
wherever variable frequency and / or variable voltage is desired in operating
shakers, motors, etc. The K-l07 consists
of two units; A-l09 Ampl ifier Chassis and
D- I06 Power Supply Chassis, both intended for rack mounting . The Amplifier Chas sis includes a meter for monitoring
cathode current of the impedances. Three
models are available which differ only in
output tubes.
SPECIFICATIONS
Fr~quency Response: 20 to 20,000 cycles
±
. 2db .
Power Output: 200 wa tts, continuous .
Distortion (harmonic): less than 1 % at full
output from 20 to 20,000 cycles .
.
Hum and Noise : At least 80 db below 200·wotl
level.
MciNTOSH
Model C-108
Input: . 5 meg impedance with provi sion for
te rminating 600-ohm line. ·Full power output
attained with .S-volt signal.
Output tmpedances:
Model K· I07F - 150 or 600 ohms , balanced
or unbalanced , isolated from ground.
Mode l K·I07G - 16.5 ohms (57 1; ' volts), 25
ohms (70 .7 volts), 66 ohms (115 volts),
and 100 ohms (141.4 volts) .
Model KI07H - 4, 8, 16, and 600 ohms
(centertap of 600 ohms is grounded within
amplifier) ~
Tube Complement:
AmPlifie r (11 12AX7 , (1) 12AU7 inverter,
(2) 6AV5 dri vers, (2) 6BX7 drive cathode
fo llowers, and (2) 8005 cathode/plote
loaded output employing Mcintosh un ity·
coupled circuit.
Power Supply-(4) 5U4 in high voftage bridge
rectifier and (1) 5Y3 low voltage rectifier .
Power Requirements: 108/ 117/125 volts, 60·
cycles AC , 300 to 600 watts.
~::rf~et:o~!~h Je~~r:~)
........
..$'49450
PROFESSIONAL AUDIO COMPENSATOR and PREAMP
A compl ete front end providing ex treme flexibilit y with ease of
operation. Has 0 5-position input switch for AM , FM , Phono, Micro·
phone, TV, Tape, or other sound so urce . A bu ilt·in rumble filter
minimrzes turntabl e noise. Fi ve sliding switches are used ·ind ivi du·
all y or in combination , permitti ng ' at least 11 turnover points · from
'280 to 1350 h eles. Another se ries of .five ' s,liding switches, allows
at least 11 roll·off characteristics to ma tc h record treble curves. In
add ition to a con ve ntion a l vo lum e control, th ere is a 5·position
aural com pe nsator which maintains proper bass and treble loud·
ness at low volume levels. Powe r is obtained from the ma in
amplifi e r or from a separate suppl y.
50
Complete with tubes in attracti ve ly styled cabinet .... ..............
l ess Cabin et ......................................... _
.. ................................................ 88.50
$96
ec ho enhances the acoustica l properties
of the area. Input imp eda n ce is 600 ohm s.
O utput impedance affo rds a choice of 600,
8. a nd 3.4 ohms. Singl e-ech o time d elay is
continuo usly variable f r om 100 to 500
m illisecond s. Ma ximum p ower ou tput is
25 w at ts for speaker drive. K a y E lectric
Compan y , Pine Brook, N. J.
• :PM Booster. Entirely automatic in operation, the new Electr o-Voice Model 3005
FM booster increases signa l str en gth
m or e than 10 times (20 db) throu gho ut
t h e 88 -to -l 08-m c FM spectrum. Use of the
unit does not e nta il any addition a l con trols. Integral therma l r ela y is provide d
so that the booster can be turn ed on or
New ELECTRO-SONIC " New ELECTRO-YOICE
Electrodynamic
PHONO
CARTRIDGE
The pr i nciple of the
0' Arsonv'a l movement..ap.
plied to cartridge des ign. Has flat response
from 20 to 10,000 cycles, and with some rise,
to 20,000 cycles, dep en ding upon re cord mo·
terial. Has no inheren t resonances in the audio
range. Output impedance is extremely low. High
stylus compliance provi des good tracking with
as little as 3 grams, minimizing record and
stylus wear. Intermodulation distortion is well
under 1 0/ 0 , A matching input transform er is
require d . The Model ESl· 201 permits cartridge
to be used with any preamp designed for mag ·
ne tic pickups . Th e Model ESL·211 is recom·
mended where th e cartridge is to replace a
crystal .
PICKUP CARTRIDGE
ESL-l0l-Sopphire .003" (78 rpm) .......... $14.95
ESL-Ill-Sopphire .001 " (m icrogroove) 14.95
ESL- 121-Diomond .001 " (microgroove) 29.95
ESL·131-Diomond .003" (78 rpm) ............ 29.95
INPUT TRANSFORMER (shie lded)
ESL.201-Secondory: 50 or 200 ohmL.
ESL-211-Secondory: 90, 000 ohms ..... .
SuperCardioid
Model
666
'r"
'
DYNAMIC
MICROPHONE
''',
.\
.
A wide·range, undirectional
microphone with a single moving element and featuring un ,
usually high front-to·back
discrimination . Frequency re·
i'
sponse is uniform from SO to
13,000 cycles . The output
impedance is !i0 ohms with
internal provision for easily ad justing to 150 or 250 ohms . Output is -57 db
(Ref. 0 db = 1 mw/ l 0 dynes/ cm2).
The Model 666 is ideal for TV, radio, recording
and other applications colling for hig h quality,
and can be used with boom, floor and table
stands, and other microphone mounts . Weigh s
only 1 1 ozs.
Complete with Stand Coupler and 20·ft., 2· con.
.
La
m
f;Jl
..
~~~~:~t~~ ~.~ :~.~.~ =~ ~.~~.~ M~.~.~.~.~.~ ~
00
b ..
...
.. .............
Model 366 - Boom Shock·Mount...._..... 24.00
Model 420 - l oble Stond ............... __......._..... 12.00
$147
off a t the FM tuner. without circuit modifi cations. Hi-lo g a in s witc h p ermits limiting the gain of the unit when strong signa ls are encountere d. Both input a nd
output have 300-ohm impedance. For f ull
information write Electro-Voice, In c.,
Buchanan, Mich., requesting Bulletin 202.
( Continued on page 68)
AUDIO
•
SEPTEMBER, 1954
63
DAMPING
OF CABINET PANELS
"
(from page 34)
201 M
U·47M
TELEFUNKEN
wo.rid ISp~I' nest
MICro h.0n
e~
~
DOES THE WORK OF
5 OR 6 ORDINARY MICROPHONES
Extremely smooth frequency res ponse, wide dynamic range,
complete absence of distortion and no ise. Readily chang ea ble
field pattern. Small outside switch provides either highly
directional or non·d irectional characteristic.
The pencil·type microphone 201 M es pecially suited for
broadcasting TV, recording, and motion pictures Is Indif·
ferent to chariges of temperature and hum idity conditions.
Its construction ensures continuous dependable operatIon at
175° F. without affecting Its performance.
MODEL U·47M
Condenser Microphone,
power supply, cables
and plugs. .
Complete
$39 000
Specifications-U 47 M
Frequency response .• .. . . . . . . . . . . ± 3db 30-16,000 cps.
Output impcdan .. ... . ... . 30/ 50, 200/ 250 ohm. , bal.
Field pattern . . . ' .: . . .• .... . .. non-direc tional or cardioid
Output lovel at 1000 cps.
Matched with 200 ohmscardioid 2.8 mV per dyn e/ cm 2 (-49 db)
non·dlr. 1.7 mV per dyn e/ em" (-53 db )
Residual noise leve l equivalent 24 db loudness
Non·linear distortion ......... . . . . . .. . . less than 1 %
PARTIAL LIST OF USERS
RCA Victor
Cinerama, Inc.
Reeves Sound Studios
20th Century Fox
De.. a Recording
Ampex Corp.
See us at the AUDIO FAiR
Suite 851 , Hotel New Yorker
AMERIC'AN ELITE, INC.
1775 Broadway· New York City· PLaza 7-7491
Sole Importer, and U.·. S. Agent.:
64
where A, is the first and A Nthe tlth amplitude.
It is, of course, also possible to excite
the panel acoustically with a loudspeaker
placed near it, and to record the output
from a vibration pickup fastened to the
panel as the frequency is varied. This
might be termed a steady-state transmi ssion measurement (with and without the
damping material applied to the panel) .
Or the vibration pickup may be fas tened
directly to a wall of the cabinet with the
speaker excited sinusoidally by an oscillator. Fig~{re 2 shows a measurement
made in this manner, first without amI
then with the damping material appli ed
to the interior of the enclosure. Since the
vibration pickup was inertia-operat-ed,
its output was first transmitted to an integrating network to obtain a measure of
the change in panel deflection amplitude.
Measurements on various types of
woods show that the logarithmic dec re, ment of % -in. panels is as follows:
P:l~OD
~~~~od
Lg~t~~f~~iC
:~~
The superiority of the plywood as a
materiO
a l with high internal damping is
r ead ily evident from these figures , which
pertain to untreated surfaces. W hen a
mastic compound is applied to them and
permitted to harden, the values can be
still further increased.
The above tests require cOl)siderable
laboratory facilities, and hence cannot be
readily carried out by the average music
lover, home owner, or hi-fi enthusiast. A
number of less complicated tests have
b~en 12roposed to show up the resonant
VibratIOns of a speaker cabinet pane1.
Thus, ripples in a' glass of water set on
the enclosure can be generated, and fine
sand, salt, or sugar crystals sprinkled on
the panel can be made to form patterns,
so-called K undt's figures. However, relatively large panel amplitudes are requi red to achieve noticeable results with
these tests. A rather simple procedure
consists in placing two pencils on the
panel, and a light tin can fi lled with lead
shot on top of the pencils. When the
Fig. 3. This chart
shows the accelera·
tion required at various frequencies to
produce given cone
excursion amplitudes.
Accelerations are
very large and the
movements "hit" cabinet panels very·hard,
so that panel resonances produce maximum effects.
20
i5
t
'"...J
t:;
o
•••
NO DAMPING MATERIAL
-
WITH DAMPING MATERIAL
OL-~
__
~
__
~
__
~~~~
1200
__
~
1270
FREOUENCY IN CYCLES PER SECOND
Fig. 2. The effect of resonance on a panel is
much decreased when damping material is used
as a filler.
speaker is driven with an oscillator, the
lead shot will rattle in the tin pan very
audibly when the undamped panel is set
into vibration at the reson~mt frequencies. After properly damping the panel ,
and properly energizing the speaker
aga in witll the same current used previously, no rattling of the lead shot should
occur.
Fig1tre 3 shows the acceleration for
various cone amplitudes. It is seen, for
instance, that at 100 cps, a: cone vibrating with an amplitude of 0.1 in. undergoes an acceleration of 100 G's. Since a
modern dive bomber can rarely exceed
10 G's without shattering, the acceleration for loudspeaker diaphragms is very
large indeed.
For the same reason, there are great
forces acting also on a speaker enclosure
which is closely coupled to the speaker.
One means of reducing the transmission
of these forces into the speaker panels is
to employ a damping material such as it
rubber or cork gasket ' between the
speaker and the cabinet. If 'the speaker
is not very heavy, the gasket may be
cemented to both the speaker and the
cabinet, and the speaker thereby more
effectively isolated from the cabinet.'
1 RCA makes a speaker cone with a rubber damping ring. This ring should not be
used for cementing the speaker to the cabinet, because the ring is intended for anoth er' purpose.
D • AMPLITUDE IN INCHES
z
0
fi
'"...J
10
..'" /
..
I/
V
0
0
/V
V/
V
100
/V
/
.
/
0001"
001"
/
;r;
0:
01'
1"
-.';100
~/
00001"
V
/
/
vII
/
V
1000
10,000
F • FREQUENCY IN. CYCLES PER SECOND
AUDIO
•
SEPTEMBER, 1954
AUDIO TIME
(from page 44)
Records and Record' Manufacturing is
the title of the' Friday afternoon session,
which is scheduled to include the following papers:
" Quality control in record manufacturing, " by
E. H. Uecke, Capitol Records, Inc.;
" Record quality and its relation to manufactur·
ing," by Dr. A. Max, RCA Victor Division;
" Geometrical considerations of the record groove
and reproducing stylus," by William S. Bach·
man, Columbia Records, Inc.;
" Speculations on the cause and prevention of
needle wear a nd noise in the phonograph
playback process," by Dr. Frederick V. Hunt,
Harvard University; and
"An evaluation of record stylus pressure considerations," by Dr. A. Max, RCA Victor
Division.
The Saturday sessions are primarily
devoted to subjects which are of greatest to the layman, Pick11ps, and Loudspeakers, The tentative list of papers for
the morning session is as follows ~
"A discussion of present day developments in
magnetic phonograph pickups," by Walter O.
Stanton, Pickering & Company, Inc.;
"Phonograph pickup measurements," by John M.
Salani, Electronics Products Division, RCA;
"Advantages and problems of full frequency
phonograph recOl ds," by Paul Weathers,
Weathers Industries, Inc. ;
" A twin le\rer ceramic cartridge," by B. B.
Bauer, L. Gunter, Jr., and E. Seeler, Shure
Brothers, Inc.;
"Amplifiers for music reproduction," by Hermon
H. Scott and Herbert P. Kent, Hermon Has.
mer Scott, Inc.
W-2 with Peerless transformer or W·3 with
Acrosound transformer (be sure to specify)
Includes Williamson type a mplifier. separate
power supply and WA-P2 preampliggjp~~a ~x~~t.~ngn~~~~gbt. ~9 . P.OU.~dS:
•
W-2M with P eerless transformer or W-3M with
Acrosound transformer (be sure to specify)
includes "Villiamson type amplifier and
separate power supply. Shillping welgbt
29 pounds. Express only. . . . . . . . . . . .
•
\V-4 with Chicago "super range" transformer
includes single chassis, main amplifier and
power supply with W A-p2 preampli·
fler kit. Shipping weight 39 pounds.
'
Express only. . .. .. . . . . . . . . .. . . . .. . .
W-4M with Chicago "super range" transfonner.
Single chassis, main "mplifier and
power supply. Shipping welgbt 29
pounds. Express only .. . , . . . . . . . . . . .
•
WA·P2 preamplifier kit only. Sbipplng
weight 8 pounds. Express or parcel
post.. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
•
$69 50
$49 75
$59 50
$39 75
$1975
Here is the famous kit form William type hi gh fidelity amplifier that
has deservedly earned highest praise from every strata of Hi·fi music
lovers. Virtually distortionless, clean musical reproduction, full range
frequency response and more than adequate power reserve.
OUTPUT TRANSFORMERS - Three trul y fine OUtput transformers
available for your selection. Peerless and Acrosound transformers speci·
fied for twO chassis combinations W·2 and \'V'·3 (mai n amplifier and ,
power supply). New Chicago "Super range" transformer used· in low
priced single chassis Williamson type model (W·4) . Response charac·
teristics of all models virtually equal.
NEW PREAMPLIFIER - The exciting new W A·P2 preamplifier pro·
vides full control t\:lrough irs 5 individually ,controlled input circuits ,
4 position turnover and roll·off sw itches - separate bass and treble
tone controls. Attractively styled , beaUtiful appearance, baked gold en·
amel finish, functional in design. Wi ll operate with any Heathkit Wil·
liamson type amplifier.
BUILD IT YOURSELF - Combined with brilliant performance of these units
is the amazi ngly modest investment required and the fun of biIilding it yourself.
Detailed step-by-step construction manual complete with illustrations 'and pictorials
insures success for even the most non-technical a udio enthusiast.
Comp/ele specification and schematic sheet available "po"
The afternoon program is :
" Correlation of listening tests with transient
measurements on loqdspeakers,JJ by Murlan S.
Corrington, RCA Victor T elevision Division'
"Acoustical calibration of loudspeakers at th~
higher frequencies," by John K. Hilliard, Altec
Lansing Corporation;
" Recent developments in high fidelity loud.
speakers," by Dr. Harry F. Olson, John Pres.
ton, and Everett G. May, RCA Laboratories
Division;
.. An
electt'ostatic
loudspeaker
development,"
Arthur A. J anszen, Engineering Consultant.
Two additional papers are scheduled
but titles were not available at pres~
time., One, t~ be. given at the Saturday
mornmg sessIOn is by Theodore Lindenberg, of Pickering & Company, Inc.;
the other is to be given at the afternoon
session by Paul W. Klipsch, of Klipsch
& Associates.
.
Model SC Corner Style $450 fOB lawrence
YOU'VE NEVER
HEARD
ANYTHING TO EQUAL
AUTHENTIC bass response . . . ability to
handle the full dynamic range of records,
FM, and tapes . . . multi·cone directradiating system for optimum vibrating
surface at every frequency ... . these combine to permit listening at satisfying volume for an entire evening without fatigue.
Professional critics have been unanimous
in their enthusiasm for this radically
different speaker. Fifteen minutes' listen·
ing will convince you. Write for Free
Booklet "Listening Tests and what
they prove:'
PHONO EQUALIZERS
(from page 25)
is to be stressed that this particular
treble equalizer is designed for use with
the GE Variable Reluctance pickup. This
type of equalizer can be used with the
Audak and Pickering pickups, although
the values of the components used will
have to be changed. These values can
best be found by experiment as described
earlier in this article and in reference 4.
All the resistors and capacitors in both
equalizer circuits should have values
within 5 per cent of those stated in Fig.
S for optimum results.
AUDlO
•
SEPTEMBER, 1954
Model 5W Wall Style $450 FOB Law.e"c.
6S
VARIABLE DAMPING FACTOR CONTROL
I
(from page 33)
to your friends
a copy of
AUDIO.
Don't give your copy away. Let us
send one to each of your friendsno obligation, of course. Fill out
this coupon and send to
RADIO MACAZINES, INC.
P. O. Box 629
Mineola, N. Y.
Please send a free copy to
the names given below ...
o with my compliments
o omitting my name
SOigned ......................... .
Address ....................... .
City and State
Name ................... . ..... .
Fi,'m .......................... .
Address ....................... .
City and State .. . .. ... . ... ... . . .
Name .. .... ......... .. ... .. ... .
Finn . ...... .. ................. .
Address ...... ..... . .. . ........ .
City and State
Name .......... . .............. .
Firm ............... . .. . ..... . . .
Address ....................... .
City and State ................. .
with a fairly average DF of + 30 01'
about 40 db harder than is possible with
a DF of + 3 (representative of triodes
with no negative feedback)-with no
increase in distortion! VIre repeat: this
is a typical speaker system, not specially
selected. The reduction of distortion
. below 200 cps is even more drastic for
contours of high distortion. The value
of 5 per cent was selected as the maximum that can be tolerated in a highquality system.
Fig'ul'e 7 shows the acoustl:cal transient response of the speaker system to
a square pulse (dashed line) for different damping factors . The ringing (hangover) is at 55 cps. As the DF is increased the wave-train decays mOl'e
rapidly, the amplitude of the ringing
decreases, and overshoot decreases.
The effect of DF on the sound pressure response of a typical IS-inch coaxial
speaker housed in an 8 cu. ft. bass-reflex
enclosure is shown in Figs. 8, 9, and 10.
The response curves were taken with
a 10 ft. axial free-space between speaker
and microphone at a reference level of
5 watts at 300 cps. The impedance curve
of the speaker system is superimposed as
a dashed curve on Figs. 8, 9, and 10 to
visualize the effect of impedance as discussed earlier. It may be seen clearly
in Fig. 8 that with a low positive DF,
the response curve follows the impedance
curve. Figure' 9 shows that with a high
DF, the response curve has an inverse
I'elationship with the impedance curve.
Fig~we 10 is included for comparison
and shows the response curve of the
speaker fed by a commercial laboratory
standard amplifier that has a fixed DF
of + 10. Note the similarity between Fig.
10 and Fig. 8. Incidentally, the harmonic distortion generated at 30 cps by
the speaker measured 95 per cent in
Figs. 8 and 10 and only 20 per cent in
Fig. 9 for equal sound levels. The curves
of Figs. 8 and 9 were taken with the
300-cps RC filter out of the circuit.
Fig~~re 11 shows that the essential effect
of the 300-cps filter on sound pressure
response is to raise the over-all level
and improve sound output below 25 cps.
and Cs below the fund amental resonance
if extremely high DF is employed.
4. Drastic reduction of low-frequency
distortion caused QY any non-linearities
in the speaker system if extremely high
DF is employed.
5. Increased power handling capacity
of the speaker system by eliminating
low-frequency resonance peaks. The
maxim of the chain and its weakest
link holds true. If the speaker system
has a resonant peak, the system will be
over-driven at the ' frequency of the
peak before being over-driven at other
frequencies. A reduction or elimination
of peaks by adjusting the DF to reduce
the Q of the fundamental speaker and
enclosure resonances to 1 or less will
Il1crease the over-all power-handling
capacity of the system.
BIBLIOGRAPHY
P. G. A. H. Voigt, (letter) Wil'eless World,
Dec. 1947.
T. Roddam, "Output ' impedance control ,"
Wireless World, Feb 1950.
]. Moir, "Transients and loudspeaker damping," Wireless World, May 1950.
T. Roddam, "More about · positive feedback," Wireless World, July 1950.
A. Preisman, "Loudspeaker damping,"
AUDIO ENGINEERING, Mar.-Apr. 1951.
R. L. Tanner, "Improving loudspeaker r esponse with motional feedback, Electronics, March 1951.
]. Moir, "Loudspeaker diaphragm control," Wireless World, July 1951.
W. Clements, "New approach to loudspeaker damping," AUDIO ENGINEERING,
Aug. 1951.
.
J. P. Wentworth, "Loudspeaker damping
by use of inverse feedback," AUDIO E NGINEERING, Dec. 1951.
U. J. Childs, "Loudspeaker damping with
dynamic negative feedback," AUDIO ENGINEERING, Feb. 1952.
U. ]. Childs, "Further discussion on positive current feedback," AuilIO ENGINEERING, May 1'952.
W. Clements, "It's pos itive feedback,"
AUDIO ENGINEERING, May 1952.
F. Langford-Smith (ed.) "Radio Desi,qner's
Handbook," 4th Edition. 1952. Wireless
Press, Sidney, Australia and RCA Tube
Department, Harrison, N. J.
~
Name ................... . ..... .
Firm ........................ . . .
Address .... . ...... . .. . . . ...... .
City and State ...... . .. .. . ..... .
Name .............. .. ...... . .. . .
Firm ..... ..... ... .. .. . .. ..... . .
Address ....................... .
City and State .. .. '" ........... .
66
Summary
In conclusion, let us summarize the
benefits of adjusting the DF to optimize
the performance of each speaker system.
1. Improved transient response from
damping the low-frequency speaker and
enclosure resonances by reducing the Q
to 1 or less.
2. Flatter low-frequency response·
from complete damping of speaker-sys,tem resonances.
Fig. 12. ' Bogen DB20DF-A complete self3. Extended low-frequency response contained amplifier incorporating damping facby cancelling the droop caused by CB
tor control.
AUDIO
•
SEPTEMBER, 1954
IMPROVING fM RECEIVERS
(from page 42)
tained. This latter is especially useful if tubes in the V1Clllity of the oscillator
TV set is to be incorporated into a which take a little longer for thermal
home music system, where the higher equilibrium, about 5 minutes. The last
fidelity can make intercarrier buzz very source is the heating of the power transannoying.
former and other massive components
Realignment should not be required . on the chassis, which may take as much
after installation of this circuit, provided as a half hour to come to equilibrium.
From the above discussion, the apno adjustments have been tampered with.
In fact, the diodes should be cli scon- proaches to the drift problem become
nected during alignment in order to get clear. Drift due to the heating of the osusable readings. Needless to say, its ef- cillator tube itself is obviously unavoidfectiveness goes up with increasing sig- able, but due to its short time constant
nal, and the signal voltage at the primary it is not too objectionable. However, the
with the device disconnected should be writer has found that the use of a polyat least 1 volt for good operation. Some styrene socket for the oscillator tube can
noise wil1 remain with this device in make this drift practically negligible.
operation, but it is most likely FM noise
The second source of drift-heat from
and therefore unavoidable ; all random other tubes-is also to some extent innoise has an FM as well as an AM com- herent, but can be minimized by the use
ponent.
of a more open layout on the chassis. As
with the above source, nothing much can
be done with an existing set, but these
Drift Reduction
are points to watch if you build your
The final requirement of an FM set, own.
freedom from drift, is not as essential
The third source of drift, the slow
as the first three but is nevertheless im- heating of massive components, is ' the
portant for easy, trouble-free operation. most bothersome, since due to its long
In fact, it is so important that many of time constant it requires continual rethe more expensive hi-fi tuners feature tuning for a long period. However, uncomplicated circuits to obtain it. How- like the previously described two causes,
ever, even in expensive sets there is this type of drift can be easily eliminated
much that can be done- to reduce drift on an existing set, as in most sets the
to tolerable proportions. Since drift is only component producing such drift is
inextricably tied up with the general de- the power transformer. Therefore, the
sign of the set, much of what is said here obvious cure is to mount the power supapplies primarily to the design of new ply on a separate chassis, which can
sets, but there are many improvements easily be done even by the average home
that can be made to existing ones.
experimenter. Even high quality sets can
To begin with, let us examine the be improved by this measure. Also, if the
mechanism of drift. The most prevalent set is a complete receiver instead of a
and most annoying type, warmup drift, tuner, it will be helpful to move the
is caused by the increase in dielectric power output stage as well.
constant due to temperature rise of the
Consideration must be given to drift,
few pieces of dielectric which are part not only in the design of a set as covered
of the oscillator tuned circuit. This in- above, but also in its installation. The
cludes the oscillator tube base and socket cabinet or other enclosure used should
as well as the insulation of the tuning give ample clearance at top and sides to
capaci tor.
permit free circulation of air and the
r~e dielectric receives heat from difback should be left open. If a separate
ferent sources with different time char- power-supply chassis is used, as recomacteristics, The first source is the heat- mended above, it should be mounted seping of the oscillator tube itself, which arately, away from the tuner enclosure.
comes to equilibrium in a minute or so. By the same token, if the tuner is
Second is the heat produced by other mounted in a console with other equipment, it should not be mounted near the
amplifier, and particularly not above it.
the superior t ransient
response of
Jim Lansing Signature
extended range speakers
a,
Ul
"'
"H-OI
co
~
0",
c ...
~o
o
":.
Fig. 3. Taking output of an FM tuner across
the de-emphasis capacitor allows the capacitor
to swamp the capacitance of a reasonable
length of line. A blocking capacitor should be
placed in the high side of the line at the first
amplifier grid since the detector output contains a d.c. component.
AUDIO
•
SEPTEMBER, 1954
Output Connection
Many times one of the better tablemodel AM-FM sets satisfies all the requirements for hi-fi FM reception with
the exception of its audio section, and
thus would be useful as an inexpensive
tuner for an economy system. Many
schemes have been proposed for bringing
out the audio, but the simplest and also
probably the best way is to conect the
audio output across the de-emphasis capacitor, as shown in Fig. 3. Here the
low-quality audio stages are bypassed,
A combination of tight electrical and rigid
mechanical coupling account for the exceptional transient response .of Jim lansing
Signature units.
Tight electrical coupling resulis from high'
flux density and close voice coil tolerances.
Rigid mechanical coupling is achieved by
use of a 4" voice call with a 4" dural
dust dome attached directly to it. Thus,
cone area between coil and suspension is
kept relatively small; compliance between
coil and dome Is eliminated.
Structurally, when a 4" voice call and
dome are used with a curvilinear cone,
a shallow piston assembly Is made possible. This shallow form factor permits a
better distribution of highs than would a
deep cone.
•.. before it TALKS
... is the way our doctors put
it - "Our chances of curing
cancer are so much better
when we have an opportunity
to detect it before it talks."
That's why we urge you to
have periodic health checkups that always include a
thorough examination of the
skin, mouth, lungs and rectum
and, in. women, the breasts
and generative tract. Very
often doctors can detect cancer in these areas long before
the patient has noticed any
symptoms.
For more life-saving facts
phone the American Cancer
Society office nearest you, or
write to "Cancer"-in care of
your local Post Office.
American Cancer Society
67
LISTEN!
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The Baroque: (double spiral loaded ) 40" w ide , 38"
high, 22" de ep. Two 12" and one 10" cones, one
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Response 25 to 20 ,000 cps. Tremendous to Iisten to
-matchl ess. Li sts at $525 .75 .
FOi' oUr complete line and the names of our dealers
and representatives, write for illustrated brochure
on HIGH FIDELITY to :
ISOTONE ACOUSTIC SPIRALWAYS, Inc ..
BAROQUE
,
666 East 164th Street, Bronx 56 . N. Y.
IF YOU ARE MOVING
Please noti fy our Circulation Department a t least 5 week s in a d va nce. The Post
Office does not forward magazines sent to wrong d estinations u nless you pay additional posta g e, a nd we can NOT d uplicate copies sent to you o nce. T o save yourself, u s, and the Post Office a h e adache , won't you p le a se . cooper a te ? Whe n notifying u s, please give your old address and new address.
and the relati vely large de-emphasis capacitor swamps out the cable capacitance
and thus minimizes the effect of a long
cable. ( Of course, if the cable ' ca pacitance is large, this capacitor should be
reduced in value to compensate.)The volume control in the receiver
will, of course, be inoperative, but if t h e
amplifier has one that does not matter.
When the set is used as a tuner, the
audio stages should be disabled by cutting loff their B-voltage. This scheme
is also applicable for connecting TV sets
to a hi-fi system, although in a TV receiver B-voItage should be ~~ft on the
audio stages, since that current drain is
r equired for proper operation of the rest
of the circuit and drift is not such a
problem, especially with an inter carrier
set. H owever , the speaker voice coil
should be shorted fo r silence.
NEW PRODUCTS
(from page 63 )
• Exte,n ded-Bange Miniature Oscillator.
D e spite its small s ize the n ew Wavefor ms
Model 512 oscillator p e rforms virtu a lly
a ll of t h e fu n ctio n s n ormally expected
only of m u ch larger cou nterparts. F req u ency range is 0.9 cps to 500 k c, cover ed
in fi ve d ecade ran ges with an a dd i t ional
b and spread range for ease of t u ning at
hi g h freq u encies. A 4-ste]) a ttenuator
provides calibrated ou tpu t f r om 50 volts
Circulation Department
RADIO MAGAZINES, INC.
P. O. Box 629, Mineola, N. Y.
ELECTRONIC MUSICAL INSTRUMENTS
By Richard H. Dorf ·
In one big volume, you can now learn all about the intricacies of commercial electronic organs, including the Allen, Baldwin, Connsonnata, Hammond, Minshall-Estey,
Lowrey Organo, and others, together with many smaller instruments. Constructional
details on the author's Electronorgan and the simpler Thyratone show you how to build
one of these fascinating instruments for yourself. A compilation in book form of the
author's articles in Radio Electronics, brought up to date and wit h many additions.
Ready about October 16, price $7.50 (Foreign, $8.50) .
SAVE $1.00 with this special pre-publication offerIf your order is received before Octobe r 16, you may have your copy at the
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$7.50. All orders must be accompanied by check o r money order at this
reduced rate .
t o 5 mv. with a maxim u m power of 2
w a t ts in to a GOO -ohm load . So u rce imp edance is under 50 oh ms and distortion is
less than 0.1 per cent over most of th e
a udio r ang e. Vernier drive provi des 14i n s. of scale l ength p e r range. Ou tpu t
r emains constant within 0.5 d b throu ghou t
th e tuning range. The 512 m eas u res 7 'h. "h
x 6'4 "w x 8"d an d w eighs 12 Ibs. T echnica l
shee t may be obtaine d from W a veforms,
Inc., 333 Sixth Ave., N ew Y ork 14, N . Y.
Customary discounts to dealers and distributors
RADIO MACAZINES, INC., Book Division,
P. O. Box 629, Mineola, N. Y.
Please send me ........ copies of Dorf's ELECTRONIC MUSICAL INSTRUMENTS at the special pre-publication price of $6.50 each ,
(Foreign, $7.50 ). I enclose chec k 0 money order 0
Name ... . .... . .. . . .. ....... . . . . . . .. . . . . . . ... . . . ... .. . .... . . . .. .
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• H i gh-Accuracy V'.rVK. All freq uen cies
f rom 10 c ps t o 4mc a re covered b y t h e
n ew Hewlett-Packard Model 400D vacuum- tub e voltmeter which m easu res vo ltages from 0.1 mv t o 300 volts w i t h a c ·
c u racy of 2 per cent up t o 1 mc. I np u t
im p ed a n ce is 1 0 m egohms , s o tha t f or all
practical p u r p oses circuits u n der tes t are
not load ed. Ran ges a re s elected b y a pa nel
swi tch w hich c h a nges s ensitiv ity in 10-db
step s. This, p lus calibra tion of the 4-in .
m e t er directly i n d ecib e ls, p ermits direct
r eadings with o ut ca lcula tion or conver s ion b etweeen mi nus 72 dbm a nd plus 52
dbm. R eadings a r e a lways on t he upper
portion of the scale where m axi mum acc u racy is obtained . A n ew c ircuit further
s implifies op e r ation by v irtua Uy eliminating switchin g tran sien t s . In a ddition t o
AUDIO
•
SEPTEMBER, 1954
fea turing gain, resp o n se, a nd o u tp u t leve l,
t he 400D a l so m easures hum a nd n o ise
d ir ectly, serves a s a n a udio l e v el met e r
a nd h igh-g a in broa d - ba nd amplifier, a nd
i
[na~ b e u ::;ed for m easuring coil " Q ", capa Clta n ce a n d r eso na n ce. F or comple te d etails w r ite Hewlett-Pack ard C o., D e pt. P,
395 P age M ill Road, Palo A lto, Calif.
• Medica.l Microphone System. Deve lop e d
s pecia lly f or resea rch a nd fo r diagn osis
a nd t each ing of cardiology, t h is n e w Altec
La nsin g d evel opmen t i s a specia lize d v e rs ion of t h e co mpany 's cond e n ser-ty p e
" L ip stik" m i croph on e. A ll ty p es of h eart
s o unds may b e pi c k ed up a nd fe d int o a
r ecord e r , h ead set, or lo uds p eaker . The
micr oph one is d esigne d to acco mm od a te
a s t andard Rieger Bowl es stethoscope
h ead. Shor t ti m e stab ili ty of th e unit
is 0.1 d b, a n d ov e r l on g pe rio d s of time
maximu m d evi a tion is 0. 25 db . Other f eat ures which m a ke the s y stem pa r tic ula rly
desirable to t h e m e dical profess io n i n-
Here, in kit form, is the finest com-..
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workmanship is metiCUlous. Both
circuit with modifications for incr eased, undis~ tort ed power output. Uses famou s-make, speunits are matched to provide you I cially wound , quality output tran sform er. All
with the maximum of listening plea- i sockets, terminal strips and conn ect ors are
Tt~_~~is~is, re~~~~~et~~ii~~: $49.95
Simple, .step-by-ste·p pictorial .} ~~bt:~
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last.det~iI. - '
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KIT with CATHODE FOLLOWER OUTPUT.
Provid es compl ete equalization f or virtually all
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channel s for radio or TV tun er, cryst al or magnet ic pickup, t ape recorder or oth er signal
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and att enuation control s. Cathod e foll ower output permit s remote ~ ontro l op eration without
hi gh f r equ ency loss.
MODEL TM-20P
..................... Net Pri ce :
•
$'19 95
TAKE CARE
OF YOUR REC ORD S
Your records represent an Important investment.
and they deserve the best treatment possible if you
are to have the many hours of enioyment you are
ent itled to, unmarred by increasing noise and distor ...
tion. Records may be irreparably damaged by continuing to use worn styli in playing the m-though
I.hey may still be "unbreakable."
cl ude t h e ste r ili zatio n fa c to r- it b ei n g
possib le to ste r lize t h e mi c r oph on e in d ry
hea t at 35 0 d eg. F .-as w e ll as wide fre q u e n cy ran ge a nd u n u s u a l sensitivity .
Norm a l h ear t sou n d s produ ce app roximate ly 0.1 vo l t o u tp u t. Designa te d T ype
M-1 6, the sys t e m already is i n u se in a
n um b er of prom i nent med ical cente rs,
a mon g
th em
Georgeto\vn
University,
Washingto n , D. C., w h ere D r . Pro c tor H a r vey h as made a ser ies of t a pe recor d i n gs
of var i ou s h ea rt so u n d s for teaching p u rposes. D escriptive litera ture i s availab le
u pon r eq u est to Altec L ansing Corpor a ration , 161 Sixth Ave., New York 13, N . Y .
• Hi-Fi Converte r. I n resp on se to t h e
uniqu e r eq u ire me n ts of h igh-fi d eli ty m u s i c
s yst em s , Carter Motor Compa ny, 2648 N .
Maplewood Ave., Chicago 47, I ll ., is n ow
producin g a s p ec ia lly - des igned con verte r .
Desi g n ated t h e T ype DR1025C5PX C u s tom
Con verter, th e u nit is d esigne d to d e liver
125 v.a. c. w i t h 120 v. d. c . input at a l oad of
only 50 watts. D u e to exceptional r e g ula tion, the o u t p u t voltage drops o nl y to 105
volts with 1l0- vo lt d.c. inp u t at f ull 25 0watt l oad. Th e se a .c. li mits co incide with
eq uipm e nt r atin gs. A fr eq u ency control
with f r eq u e ncy m e t e r i s included, allowi n g t h e u ser to a d j u st exactly to 60 cps.
for r ecord p laye r s and t a pe r ecorders. Filter is availab le to give n oi se- free t un er
l'eception. Effici e ncy is a p prox.im a tel y 60
per ce n t at 250 w a tts. T h e converter is
b uilt on a 5 00-watt fra m e to g i ve a l ong
life of tro u b le -free operati oll. Req u ests f or
com p lete infor mation s h o uld b e dir ected
to Dept. 6 a t the above a elel l·ess.
AUDIO
0
SEPTEMBER, 1954
In this booklet the author gives the results of comprehensive tests on the various types and materials
of styli-information which should be in the hands
of eve ryone who plays phonograph records _ His tests
are t he result of thousands of. hours of playing-during which time he wore out hund reds of LP records
and dozens of styli_
You will want this book as a guide to the proper
treatment of your records-how to t ake care of
PRIC E
$1.00
Book Division',
Rad io Magazi'nes, Inc.
P. O. Box 629, Mineola,
Sirs: Enclo se d is m y
them, how to clean them, how to store themeverything you need to know to give you satisfactory
record reproduction. Order it now!
N. Y.
0
ch e c k
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The Wear and Car e of Records and Styli, b y Harol<rl D. W e ile r
Name (print carefull y )
Address
City .
Zone
Sta te
.
69
/lc'UJ4fJund
Utt't4 - ~tltealt
RECORDS
(from page 56)
Modern in the Raw
Charles Ives: Symphony #2. Vienna Orchestra, F. Charles Adler.
SPA-39'
Charles Ives: "A Set of Pieces" for Orch.
and Piano, Milhaud: Fantasie Pastorale.
Ste ll Ande rsen; Vienna State Opera arch .,
Ste rnbe rg.
Oceanic OCS 31 (10" )
TRANSFORMERS
lor the ultimate in
High Fidelity amplification
TO-300 for Ultra· Linear circuits $24.75 net
with KT ·66's, 807's, etc.
TO-31 0 ~~r 6~~r~~~:~ear operation 18.75 net
39.75 net
Charles r yeS, the ins urance m a n from D anbur y,
Conn ., wh o is n ow the very idol o f a considerablesegmen t of American musical opin ion, was a very
strong man who, quite independently (he lived off
ins urance) , com posed very odd music in the early
years of. this century that seems, now, to haveforecast all sort s of modern t rends. It d id, withou t
a do ubt ; polytonality, p'iano t one·clusters, A m eri.
can folk·s t y le sym phonic t hemes, v iolent d issonanceand a lot more.
B ut as music, Mr. r yeS' compos itions are poles
away from t he F rench ideal of cons istency-rYes,
of a ll American composers, is the most chaot ic as
to s ty le, ingred ients, organization, aim or whathave-you! I yes is a lways e."<citing to h ear ; he·
was too tron g a man ever t o be uniformly dull.
Bu t t he hodge·podge of this and th at, the bewilder.
ing mixture of "modern " and ultra-old-fashioned,.
of A merican gospel hymns and pseudo· Wagner, of
crum bling d issonance and saccharine consonance.
is hard to believe. T he plain fact is tha t I ves was
hoth a revolution ary and a pur veyor o f u ltra.
conventional p latitudes; he was a p rophet of th ings
t o com e and s imult aneo usly a m irror o f the ti mes
he lived in, m usically speaking. It's not popular to.
say so now, b ut I'm s ure an y experienced ear wi\l'
find a lot m ore undigested Wagner, Brahms,
Mahler, Strauss, Liszt in I yes than the m odern.
The very trade-m ark of I ves is-in e."'<treme con tras t to all things French-the absence of anT
consistency, of any sty le, t he admi ttance of anything anywhere, anyhow, if it struck his fancy.
Strong stuff-especially in relation to t he con·
sisten t pla ti tudes o f imitation t hat h is respectable'
American contemporaries of 1900 we re t urnin g
out , accordi ng to the then ru les! You ' ll be ar.
rested by m any a moment in the early 2nd Sym.
phony (1897-1901), sometimes for its beauty and
originality, more often fo r its stomach.shiftingleaps from one thing to another, from passages of
Wagnerian schmaltz, without a second's pause
into New England Square dance t unes. The finaL
passage, after a Mahler · like deve lopment right out
of Germany but based on HO h S uzanna," outdoes
t he end of t he "Meistersin ger" overture (and
imitates it very neat ly) on "Colum bia, the Gem
of the Ocean." Whew! An excellent job of record.
ing, particularly effective on side 2.
T he "Set of Pieces" b y Ives typ ifies h is later '
work, alternating the most extreme dissonance
the m.ost violent whanging of clum ps of keys o~
t he pIan o ( very prophetic) with some firs t .rat em ovie m usic r ight in t une with the 1950's, a half.
cent ury ahead of its time. Yes, we Owe a lot t o
I ves, but we need strong stomachs to take hisoysters-and·sugar, clams-and-choco late-cake concoct ions.
l'vlilhaud? He's French. The t riRi ng little Fan.
tasie, probably t ossed off in an odd moment , is a
getn of utterly consiste nt, beautifully written dullness. Charming , like strawberry souffle, after Ives.
I hate to say so, b ut I thin k I' U take the clams.
for Ultra·Llnear 100 watt
9 50 t
TO-350 ampliftors with 6146 tubes 4.
ne
Prices slightly higher in West
It t a kes more than a tap ped o ut put transfo rm e r t o ma ke an Ultra-Linea r amplifi e r. 11
ta kes t he exclus ive pa t e nted Ac rosou nd Ul t ra-Linear t ransform e r desi gned for this appi icatio n and c rafted to the most ri go rous
specificati o ns. Whether you buil d your own,
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or b uy a m a nufact ured a mplifi e r you ca n
have gen u ine Ac rosound Ultra-Linear circ uitry, the fi nest avai la ble. Fun t ransform e r
,data and h igh f ide lity circuits are a vailable
on request .
AC'RO PRODUCTS CO., 369 Shurs Lane, Phila. 28, Pa.
Authoritative and
Enlightening ...
AUDIO
Acknowledged the Leading Publication
in the Fileld 01 Sound Reproduction
If you are novice, hobbyist, experimenter, or engineer ... if
you are a lover of music ... and in pursuit of sound, undistorted . .. AUDIO will be your faithful, reliable companion
all the way. You will find no more pleasure able and stimulating reading than there is in AUDIO; absorbingly interesting material, valuable and authentic data, workable detailed instructions... all comprehensively and yet
practically presented.
"Whflt to Do" and "How to Do" will guide your every move
through this thrilling experience we call Audio.
Each new issue brings New Ideas, New Slants, and Latest
Developments ... month in and month out ... twelve times
a year.
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---70
----
I
I
I
I
I
I
J
I
I
Arias Sung and Acted. (From Aida , La.
BClheme, Madame Butterfly, I Pagliacci •.
Rigoletto, La Traviata.) Joseph Cotten _
.Dennis King, Deborah Kerr; Bjoerling, War~
reno Merrill , Albanese, RCA Victor arch .,.
Weissman.
RCA Victor LM 1801
This unique RC A experiment in opera (see.
A u dio, April) a s lightly d izzy idea but interesting
in the workin g out : the t ext of each aria is first
act ed by t he pr ofessional act ors, then sung by t he
sin gers. T he result is q uite st range, for what
comes thro ugh m ost for cefulI y is the u tter remote.
ness of the operatic and dram atic ways of telling a
story, though both are intended for the stage. It
is, in fact , rather a shock t o hear t h ese words acted
in st age (or rad io·TV. fi lm ) style, natura listic,
slangy, mod ern, of today. S om ehow one expects
AUDIO
•
SEPTEMBER, 1954-
the spoken words to have the never-never-land
flavor of the operas themselves. Even opera in
English, when sung, manages to preserve the ol~­
style melodra m atic manner thanks to the musIc
itself. B lit minus the music, the whole operatic
illusion vanishes and with it a good deal of the
atmosphere that makes sense out of the stories.
Frankly, I doubt if most operatic libretti could
stand up to plain acting, even those derived from
actual stage plays-for these are usually changed
to fit the opera conventions. Nevertheless, this is
an interesting experiment, equ ~l1y interesting for
the opera specialist and those who don' t konw what
opera is a ll about. The budget perform ance,
doubling up on the roles, is competent in the musi·
cal end if lacking in vocal variety; the acting is
straightforward and professional but without
particular distinction.
LOUDSPEAKER
PERFORMANCE
FOR ALL YOUR REQUIREMENTS IN MAGNETIC HEADS
• The perform ance of magnetic
recording equipment depends on the
quality of the magnetic head-which
records, reproduces or erases. Brush
offers a complete line of heads, outstanding for precision a lignment
and balanced magnetic construction .
For assistance in application, call on
Brush's unequalled experience in this
field. Write Brush Electronics Company, Department ZZ-9,3405
Perkins Avenue, Cleveland 14, Ohio.
BRUSH ELECTRONICS
INDUSTRIAL AND RESEARCH INSTRUMENTS
PIEZO.ELECTRIC MATERIALS
ACOUSTIC DEVICES
MAGNETIC RECORDING EQUIPMENT
U LTRASON IC EQU I PM ENT
indi¥tut~ Ute
n
-_.
---- ---IUili'l,nill
COMPANY
formerl,
Tht Brush Dtvtlopmtnt Co.
Brush Electronics Company
;s an oPerating unit of
Cltvitt Corpora tion.
Performance
jJinmtco/tCttfWe
~i~e¢
WEATHERS FM
CAPACITANCE CARTRIDGE
Until recently the Weathers
cartridge has been used chiefly by
professional audio engineers and
technical hobbyists. Now all
music lovers can experience its
full range, flawless reproduction.
Enjoy the freedom from record
damaging pressures and heat
generated by conventional pickups
which are 6 to 15 times heavier
than the Weathers 1 gram pickup ..
Thrill to the difference that
this outstanding pickup can make
in yOU?' high fidelity .system. Ask
your dealer for a demonstration.
Compare the Weathers with
gny other cartridge,
regardless of price:
GREATEST COMPLlANC·E:
14 x 10 -6 centimete rs per dyne
LOWEST DYNAMIC MASS:
1 milligram
WIDEST RANGE :
15 to 20,000 cycles ± 2 db, equalized
LOWEST TRACKING PRESSURE :
1 gram vertical stylus force
LEAST CROSS MODULATION DISTORTION:
Well under 2%
Includes a sable brush ahead of Ihe stylus to clean
away damaging dust and d i rt . . . and a permanently
installed movable g uard which prevents da mage to
the stylus plate.
Ask your dealer about these other
quality Weathers products:
Reproducer Tone Arms
Stylus Plates
" De bonnaire" Hi Fi Re cord
Player
High Fidelity Music Record
Oscillator
Power Supply
Pre-Amplifier
Stylus Press ure Gauge
Write for free catalog and technical information .
• 66 E. Gloucester Pike. Bafrington, N. J.
AUDIO
•
SEPTEMBER, 1954
(from page 23)
The first step is to cut away the spider
while the periphery of the cone is still
intact, to minimize the dangers of dislodging the suspension. Next, the entire
ga::,ket should be pried off with a knife,
leaving the cone glued to the frame. The
cone rim may now be cut away at the
inner corrugation in sections, so that
four parts of the cone extend to the
frame and are still glued in position.
These parts will hold the cone in a centered position while the four pieces of
chamois are glued in position as previously described, evenly spaced in the
middle of the gaps. After the glue has set,
the remainder of the cone rim may be
removed and the usual four large pieces
of chamois cut and fitted into place. The
gasket may then be replaced as before,
and the job is completed.
If the work was done carefully, the
speaker should now provide good reproduction, often with more "presence" than
much more expensive single-un'it speakers. One especially useful purpose for
such speakers wher e cost may otherwise
be excessive, is as a matched binaural
speaker sy~tel11. Recently the writer used
two of these speakers for a binaural
broadcast by the :r<M and AM transmitters of station KF AC of the Los Angeles
Philharmonic. The sound r eproduction
was beautifully reafistic. For ordinary
monaural use these speakers give clean,
quiet reproduction, although they do not
have the efficiency or high power capacity of more expensive systems. While
they may not stimulate the neighborhood
dogs to the same extent as some of the
more expensive high-frequency horns,
they nevertheless supply rather satisfying music with exceedingly clean reproduction of low bass. In some of the
recent high-quality recordings there are
low-frequency sounds that can be felt
more than heard. The true effect of these
is lost in many speakers, but one of the
chamois-"ftoated" units will supply them
with clarity.
It might be pertinent to note here a
limitation of these speakers. Even
though the chamois is careftt:lly fitted,
considerable "breathing" occurs around
the peripher~ of t~e cone .. ·This fac t
precludes thetr use 111 any kli1d of horn
enclosures .
71
ABOUT MUSIC
(from page 14)
IF
YOU'RE
INTERESTED
IN
.HIGH
FIDELITY•••
then
YOU1LL WANT
TO KNOW MORE
ABOUT THE
High Fidelity ·
RECORD
C~ANGER
Mail This Coupon Today
r----------------I
I
I
ROCKBAR CORPORATION, Dept . M /- !
215 East 37th Street, New York 16, N. Y.
Please send me literature des cribing (OltARO
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High fidelity RECORD CHA·NGERS .
NAME ..........................................
ADDRESS
CiTy.... ...................................ZONE . ...... STATE
L __________________ •• J
72
composing machine will cost approximately
$500,000.
The composing machine is the logical
point of convergence for the hundreds of
experiments in sound produced electronically, by obj ects other than musical instruments, or by unorthodox methods. Germany
in the late Twenties produced at least two
sonic explorers. Paul Hindemith anticipated
John Cage in a film score composed by
preparing the rolls of a mechanical piano.
Ernst Toch had four speaking voices recite
the names of four cities in clifferent rhythms
and later re-recorded the odginal at a
hi gher speed.
Some of the more recent of a series of
excursions into a new acoustical realm include those film shorts made in Canada
with sound tracks produced by directly
engraving patterns on the celluloid strip
in the manner of a stencil. But the sounds
created here are rather limited, curiously
resembling a recording of someone blowing
bubbles under water. In 1951, the New
M usic Society presented a piece by J ohn
Cage for twelve radio receivers. Twentyfo ur "operators" were stationed at their
dials-two per dial: one for selector, the
other for volume-while beer jingles, soap
operas, news programs and quiz shows unwittingly played roles in Cage's new opus.
At times a voice stood out above a subdued
hubbub; at other moments Cage brought
in the t·lt/ti at full volume. At one point
in the proceedings all twelve sets were
down to a pppp when Cage signaled one of
his operators to ride gain. The station happened to be WQXR and for a good thirty
seconds or more some "real" music floated
out of the chaos. Someone in the audience
( I think it was Fred Grunfeld) got up and
shouted "Bravo!"
In P aris men like Pierre Schaeffer and
Pierre H enry have been developing what
they call "musique concrete." Schaeffer,
the composer of such works as Ell/des fo r
turnstiles, railroad trains, and saucepans,
says' that the essential c\jfference between
"concrete" music and music as we know it
lies in the fact that the latter is based on
notes and the former on sounds. Last year
the National French Broadcasting and
Television Studios in the French capital
sponsored a ten-day demonstration of the
most r~ent creations of "musique concrete,"
"electronic music," and "music in spatial
Vladimir
Ussachevsky's
projection."
"Music for Tape Recorder" was auditioned;
Schaeffer and Henry discussed their latest
activities; and the audience listened to a
lecture on the new "sound alphabet" illustrated by a drop of water, "the sound of
a gong without the impact by which the
sound is produced," the click of a Chinese
block, etc.
A statement made by Varese some time
ago might easily apply to these new directions : "Whole symphonies of new sounds
have come out of the modern industrial
wo rld and have been all our lives a part
of our daily consciousness."
The above experiments, however , are as
primeval as E rli ,on's tinfoil phonograph of
SIMPLIFY
CUSTOM
INSTALLATION
.The 4200 Sound Effe~t5 Filter and
4201 Program fE.ci'Jal,i~er are now
' available in c6mp~>nent 'form, as
t . illu5trat~d, for Jpl:' ,~ust~m :puilder;
. In addition to, the ;fJexibility of in:, , stallatieo, '~11 th~~f~~~~res.and chQr-
·I:7:~~~~e~;~!{~~~:Zo~~:~:
model may be .optoined separately.
Cqmplete wi l:<i n~rinstruction5 ·
.included.
DIS T RIBUTOR
Hycn, Sales of California
11423 Vanowen St., North Holly\'/oo d. Calif .
REPRESENTATIVES
Beebe Associates
1155 Waukegan Road, Gtenview, tllinols
Burl ingame Associates
103 Lafayette Street. New Yo rk City
Harrison J. Blind, 1616 Cord 51.
Indianapolis 24, Indiana
G. M. Howard & Associates
:734 Bryant Street, San Francioeo 7. Calif.
EXPORT DIVISION
Morhan Exporting Corporatio n
458 Broadway New York 13, N. Y., U.S.A.
Cable: " MORHANE)( "
AUDIO
•
SEPTEMBER, 1954
1877 when compared to the potentialities
of the composing machine. When the long
engagement between music and electronic
is finally consumated in marriage, the results, in the words of the American composer Roger Goeb ( one of the leading
exponents of the electronic "one-man
band") "would take music (new music)
out of the category of theatrical enterprise.
out of the category of the museum-like
strictures of Carnegie Hall, and would
place it directl y to the audience via recordings, radio, television, and in the neighborhood theatre. Music would be in the same
position as painting, sculpture, and poetry :
the artist dealing directly with his audience."
Whether the audience will take to music
minus the performer remains to be seen.
The theatrical aspects of Heifetz tossing
off a Paganini Caprice, Rubinstein delivering a "jack-in-the-box" performance of '
the Rachmaninoff Concerto No.2. Toscanini accidentally breaking his baton in
two while conducting Tchaikovsky's Manfred and sending the free half flying across
the stage like an arrow-such dramatic
supplements of concert-going seem to be
no less popular. More important than the
nineteenth-century virtuoso hangover of
contemporary concerts, however, are the
obvious stimulating featur-es of contact
between artist and public.
But when the composing machine becomes
a reality-and at the moment this is primarily a Question of money-will the performers or the listeners run for cover)
LETTERS
(from page 8)
I
as possible in the first stage to which it
is connected in order to avoid cumulative
hum-and-noise contributions.
It is our recommendation that the total
shunt capacitance be kept under 300 ,...,.d
through the use of cartridge lead lengths
under 3 feet using standard shielded lead.
and under 10 feet using low-capacitance
lead. If it is impossible to stay within those
values a preamplifier such as the General
Electric Model UPX-003A should be installed close to the cartridge and the preamplifier output run to the control amplifier.
This system has the advantage, not only
of avoiding any possibility of resonance in
the system, but also of boosting the signal
level before running it any appreciable distance through ambient noise signals. If an
exceptionally long run were necessary a
cathode follower could be added to the
UPX-003A output.
The capacitance encountered in most normal installations, that is, commercially
available record changers and manual turntables, will stay within the 300 J..I.J..I.f and the
inherent damping of the cartridge will
ensure that no appreciable peaks occur.
Incidentally, the value of shunt capacitance
which we recommend as the optimum is
140 J..I.J..tf, although values up to 250 J..I.J..I.f may
improve . response, depending upon the
amount of loss in the capacitance and the
type of material of which the record is
made. The same results will not be obtained with all types of lead, even if the
same total capacitance is retained, but
these are very minor considerations which
will cause little or no audible variation .
N. S. CROMWELL, Supervisor
Audio Products Engineering
General Electric Co.,
Electronics Park, Syracuse, N. Y.
AUDIO
•
SEPTEMBER, 1954
ASCO has HIGH FIDELITY ...
IN MINIATURE!
Here within a function ally beauti·
ful roll·top enclosu I'e iR a higb
fidelity instrument combination of
top quality . . . yet RDlail enougb
to be molded with in the DlOst compact interior. Adrled to a speaker
system, the result Is superior
music reproduction.
Featuring the New
BOGEN DB·15 Hi-Fi Amplifier
and the
BOGEN RECORD PLAYER
complete package
(ready to operate)
$179.50
The BOGEN Record Player, manually operated,
with au to stop and start is d esi~ned to play
33, 45. and 78 RPM records. The Bogen DB·15,
in a class with the most expensive amplifiers,
yet of moderate cost. features :
• Rated power 15 watts at V2 % harmonic dis·
tortion.
• Frequency response: 20 to 20,000 cps within
.5 db.
• Two-section equalizer, allowing the choice of
20 combinations of low frequency compensation
and high.frequency roll-off.
• Separate equalized inputs for magnetic cart·
ridges, tuners, tape recorders, or ot her program
sources.
Bogen Record Player
(with GE cartridge)
Bogen DB-15 Amplifier
548.80
598.60
Enjoy the finest today-send check or money order.
Requests fo r further information will be gladly filled.
ASCO SOUND CORP.,
115 West 45th St., New York City
73
APPLICATION
FOR
MEMBERSHIP
AUDIO engineering society
P. O. Box 12, Old Chelsea Station, New York 11, N. Y.
I d esire {
admission in to
advancement in
} the Audio Engineering Society. Grade desired
.... ... ... ... ....... .. .. 'p;in'i
Born at
~~. T;,p ~ 'N~~; ' i~ 'F ~i/
................. ... .. .. , .. ..................... , .. ....... ... .. , ... ........ .... .... .... ...... ..... . .
..... .... ..... .. C5ii y.. · .. · .. ···· ··· ·· .. ·· .. · .. · .. ·· si~i ;'" ' '' ''' ''' '''' ' ''' ' '' ' G'~',;,;t~y''' '''''''' ' '' '' 'D~'t~'"'''''''''''' "Ag~''''''' ' ' ' ' '''' '
Residence
........ .. ... si;;;i ... .. ........ .... ... ...... ...... ........... .... . Gii y' .. ..... ....... ..... .. ... ........ .. ... ...
St~ i~ "
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St~i ~"
Mail Address
Occupation ... .. .. ..... P'';;;ii~~' .... ... .... ... .. .... .. ...... .... .. ... ... .. .. .. ... ... .. ....
Present Duties
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..... ... .N';;"~ ' ~'';d "idd;;s~ ' ~i ' c,;~~;;~ ............. ... ... .. ..
... .... ....... .......... ... ......... ................. ............ ...... .... ., .. .
Past Experience .. . . . . 'Gi~~ ' C~;"'pd~i~~; ' y~~~~: '~~j' P~ji;i~'~s" " """ " " "" " " " "" " """""" " """ " """"""""" " """"" """" ' "
Member of Other Societies 'Gi~~ 'jv~;;'~;
'';; Abb;~~i,;t;~~;: ~~d G;~d; ' ~i ·M;';'b~~~;' ip ··· · ········· · · ··········· _... ... ........ ........ .... .. ........ ..... .. .
EDUCATION
PRO",
SCHOOL A'IlENDED
DEGRE E
COURSE
TO
ADMISSION REQUIREMENTS
A Member, according to the constitution, may be any penon active in audio engineering who has an a cademic degree or its equivalent in scientific or
professional experience in audio engineering or in a closely related field or art. Su ch a person shall, upon election, be entitled to all the r ights and privileges
of the Society.
An Associate Member may be any person interested in the objectives of the Audio Engineering Society and, upon election , shall become entitled to aU
the rights and privileges of the societY except the r ight to vote or to hold office or chairmanship of standing committees.
A Student Member may be. any student interested in audio engineering and enrolled in a recognized school, college or university. A student member is
not elig_ible to vote or to serve on committees except in his own local chapter.
Three references are required with application for the member grade two for associate membership -a nd one for student m embership. References should
be familiar with your work; they need not be members. Yearly dues are $7.50 for member, $6.00 for associate and $3.00 for student, each of which is halved
if the date of application is between April 1st and September 30th.
Payment must accompany application, and application must be signed to expedite handling.
R E FERENCES
T itle
Company and Address
Name
01
Positio n
1. .... . ... . .. . ........... .. ................•... • .•..............•......... ..• ... . . . . ..
2. . . . . • ..... . ....... .. .••. . . . ........ . ......... . .......• . . . . .. ...... • .... • . . . .•. . .. • . •.•.•. • .......... . .......•.•. . .. . .... . ...... . . . ... .. . • . .•.•.....••
3.
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Sig~~i~~~' ~i 'Aj,j,iida'~ i
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PLEASE DO NOT WRITE IN THIS SPACE
AK~~~dn
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ment to
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Date
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Put
Papers
I
74
AUDIO
•
SEPTEMBER, 1954
Oddities, But Interest, in Audities
SIR:
I'm afraid M r. Saul J. Whi te has got
himself sartoriall y imbrangled* in his last
paragraph of "Too Much Music." The
whodunit to which he alludes is "The Nine
(not seven) Tailors (not T aylors)" by
Dorothy Sayers (not Agatha Christie) .
When I read th e book I, too, raised a
dubious eyebrow about the possibility of
killing a feller with pur e decibels-but it
wasn't a bad yarn.
But he draws a perfect score for misquotation, what?
L. F . SOUTHWICK,
R.F.D. 1, Yale Avenue,
Wallingford, Conn.
* Miss Sayer's own word for "confuse,
disord er, 'op. cit."
SIR;
"Audio Audities" by Saul J. White is
a refreshing bit of tart erudition in your
otherwise reserved publication.
I am r eminded of myoid college professor
who, after a heavy mathematical session,
would wave his arm at the blackboard covered with bewildering formu lae and solutions, and say, "Now let's send that to the
beauty parlour and have it manicured and
perfumed so that you romantic gentlemen
can be better seduced by it."
Then would follow ten minutes of the
most fascinating popular summation which
indeed threw a new light on what was up
to that point a dull theoretical subj ect.
Sugar-coating of mathematics has its place,
especially after a grinding classroom session, or after a dull day on the job. It is
highly relaxing to read as interesting and
speculative a situation as described in "The
sound that goes nowhere,"
SOL G. MARCUS,
331 Bay Street,
Toronto, Ont., Canada
frequency Runs on FM
SIR:
While Mr. Benson (J uly Letters) is
somewhat out of range of KPFA (94.1
mc, Berkeley, Calif.), you may be interested
to know that we have provided the service
he requests for FM listeners in much of
Northern California. We schedule an hourlong "Test T.ones" program on a Saturday
:afternoon once a month, featurin g fr equency
runs and sweeps fo r measuring response,
and reference tones and silent periods for
m easuring distortion ' and signal-to-noise
-ratios. Actual transmitted values are announced so that ' it is possible to check
through an entire a udio system, Typically,
the frequency runs are correct within 0.5
-db from 30 to 15,000 cps; distorti on is 0,5
per cent; and noise is 67 db below 100 per
cent modulation. And many are the disillusioned hi-fi owners who thought their rigs
were flat to at least 100,000 cps.
PARTRIDGE
OUTPUT TRANSFORMER
CORE DESIGN
For use in
HIGH QUALITY A.F. REPRODUCING EQUIPMENT
The P artridge UL2 p.p. transformeris spe cifically designed [or rea lly high quality aud io
equipment. Extended frequency range and
low harmoni c distortion enable a large measure of N.F.B. to be taken from the secondary circuit and applied three or four stages
back .
SOME
SALIENT
REFERRED
CHARACTERISTICS
PRIIIIA RY LOADING,
Standard
models cover requirements of a ll popular tubes.
Each half pritnary is brought O l l t separately to
posts anel is tappeil at 430/0 of t h e turns.
POWER RATING, P cak 50 watts at 60 c/s or
14 watts at 30 cIs fo r less than 0-5 %
dis tortion without reedbuck.
harmoni c
LEAKAGE INDUCTANCE: 10 mH.
SELF CAPACITY, 500 pF (ull primary.
Duty Paid
• • • • • •
•
$25
• • • •
ALSO AVAILABLE
TYPE C.F.B.
(al so available a ... TICFB willi each half p rima ry tapped
at 430/0 of tllrns. See Ju.n e issue "'Audio Engin eering") .
Leads tlt e way in. ' C' Core techniqu e. PouJer up to 60 w(l lIs
from 22 cIs to 30 Kcls . Distortion leo-.s t!tOIl 1% witll
no N.F.B.
$40 Duty Paid.
Th ese three models arc avail a ble
NO\V for your usua l jobber. If in
d iffic ulty, write u s direct-w e' ll ~ c c
you nrc sup plied without d elay.
F ull es t t echni cal d ata rush ed nir
m ail t o you ·on request.
TYPE W .W.F.B.
Built to the fClmol~.s Williamson .f!; peci}ica tion. and avail~
able i.n. a wide range of impedance... Secondary windings
brought oul to eight sep orote sect ions of eq ual impedan ce.
$26 Duty Paid.
PARTRIDGE
TRANSFORMERS
TOLWORTH
.
·
SURREY·
•
LTD
E N GL AN D
AXil M 1Mivf.i~ltIIWi
MAD E I N ENG LAN D
Regd. Trade MarK
AXIOM 150 Mk II
A 12-inch twin-cone full r ange high fidelity reproducer,
wi th a power handling capacity 01 15 watts.
BRIEF SPECIFICATION
AUDIOPHILE
Frequency Coverage - Funda menta l Resona nce
F lu x D ensity N.ett Weight - - - - -
$43.50
BRUCE ]. H ARRIS,
,II
Chief Engineer KPF A,
2207 Shattuck Ave.,
Berkeley 4, Calif.
(1IV O1tld that many more cities had s1lch
11seful service for serio ItS listeners. ED.)
A medium power FREE SUSPENSIO N high fidelity
P .M. reproducer faT the professiona l enthusiast.
AUDIOPHILE
'Early Magnetic Recorders
$52.30
BRIEF SPECIFICATION
Freq uency Covera ge - Fundamental Resonance
F lu x D ensity N ett Weight - - - - -
- - - 20/20,000 cis
- - - 20 cIs
17,000 gauss nominal
- 91b. 60z. (4'2 kg,)
SIR :
I noted with interest in th e May issue
tbe article entitled "T::pe Recorder Weighs
A Ton" in which was desc ribed an early
BBC tape r ecorder used in the 1930's with
the appellation "one of the earliest tape
-recorders."
In the 1901 edition of the Proceedings
of th e Smithsonian Institution, there is a
report on what is probably the earliest
AUDIO
•
SEPTEMBER, 1954
Exclusively distributed by:EAST: Goody Audio C. ntr. Inc.,
2.35, West 49th St., New York 19. N.Y.
WES'f : Hollywood Electronics.
7460, Melrose Avenue, los Angeles 46. Cal.
SOUTH & SOUTH-WEST : High Fidelity SSS,
606. Peachtree St., N. E., Atlanta. Ga.
CAN ADIAN SALES OFFICE :
A. C. Simmonds & Sons ltd .
100. Merton St.. Toronto 12.
coo
s
GOODMANS INDUSTRIES LTD
AXIOM WORKS,WEMBLEY. MIDDLESEX
ENGLAND
75
,
AUDIO __
SAVE
I •• , . " . , . t
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AUDIO is still the only publication
devoted entirely to
•
•
•
•
•
•
•
Audio
Broadcasting equipment
Acoustics
Home music systems
Recording
PA systems
Record Revues
(Please print I
Name . . .. . . . ..... . . . ... .. . . . . . . . .
Address .. . . • . .. .. . . . • ......... . .
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Name . . .
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magnetic reco rder. T he article deals with
a device called the "Telephonograph" invented by the Danish inventor Waldemar
Poulsen. There were two types of telephonograph-one using wire and the other
usi ng tape-both ancestors respectively of
the modern wire and tape recorders.
The wire telephonograph had iron wire
wound on a non-magnetic cylinder which
was rotated like the cylinder of an Edison
phonograph. The signal was applied and
picked up by a coil with needle-pointed
pole pieces. The input signal was produced
by a telephone transmitter in series with
dry cells-vacuum-tube amplifiers (and
vacuum tubes) being unknown at the time,
1898. Similarly, the signal was picked up
by a telephone receiver, and erased by
passing d.c. through the recordi ng-playback
coil.
The band telephonograph looked superficially like a modern tape recorder except
that the tape was a thin steel band much
like that used i41 the later BBC recorder.
This device was used for a time in the
courts of Denmark to record testimony.
The inventor had an ingenious scheme
for using the band telephonograph as a
type of amplifier for use as a telephone repeater. The input sigrial was recorded on
a continuous belt of steel tape. Immediately
beyond the recording head was a pickup
head connected to a recording head on
an adjacent steel band. This arrangement
was repeated several times so that the
original signal was recorded on four or five
tapes. Then the signal was picked up fr om
all tapes simultaneously with the pickup
heads wired in series or parallel depending
on whether voltage or current amplification
was desired. While this may appear to be
getting something fo r nothing, it must be
remembered that the added energy came
from the work expended in moving the
tapes against the magnetic drag of the
recording heads. Immediately following the
second pickup head was a permanent magnet
serving as an erase head to prevent the
output signal froth interfering with the
input.
MARTIN H . M. FRANCIS, Lt.jg, USNR,
USS Midway, CVA-41 ,
Cia FPO, New York, N. Y.
.
~
..
a New . . . . .. ..... a Renewal .... . .. .
R~
Personnel may be listed here at no charge
to Industry or to menibers of the Audio
Engineering Society. For Insertion In this
column, brief announcements should be
sent to Chairman, Employment Register
Committee, P. O. Box 629, Mineola, N. Y.
before the fifth of the month preceding
the date of Issue.
• Positions Wanted
Name . . . . ... . . . . . . . . .
Address
aNew
.... a Renewal
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RADIO MAGAZINES, INC.
P.
o.
Box 629, Mineola, N. Y.
• Technician. Over 25 years in communications, instrument maintenance, electrical - a nd electronic musical instruments,
sound, intercoms, general electrical and
prototype work. Fo!' r esume, address:
Finley L. Berry, 94-30 113th St., Richmond Hill 19, N. Y . .
• Full of enthusiasm and initiative, but
short on professiona l experie nce. This
yea r's E.E. graduate desires s tart in audi\>
industry, preferably recording. Some tape
and disc recording experience, mixing,
editing, etc. Feels well infonned in th is
field but requires position to prove abilities. Any location considered. Thomas W.
Thorniley, 538 W. 19th St .. Sa n Pedl'o,
Ca.lif.
76
folder
Save dollars!-form your own bracke ts, channels,
boxes, and chassis to exact requirements with this
hlgh·quallty brake. Portable, yet rugged-a " must"
for every shop. school, and labora tory~ (l Price :
only $12.95 postpaid, shipped direct from England
by fast Parcel Post. You pay small duty ch2rg.
(about $2.00) on arrival. OR, $14.95 duty· paid ,
F.O.B. Virginia warehouse. Order today or write for
full details.
TELVAC Dept.43'·R Box 6001 Arlington 6, Va .
AUDIO
•
SEPTEMBER, 1954
EDITOR'S REPORT
(f1'911l
page 16)
IT'S SO SIMPLE
Ever since the introduction of L P's
the audio scene, we have been exhorted
to be careful a)Jout the stylus force-that's the correct term, although common
usage is stylus pressure--with which we
played our valuable records. It is certa in
that e ith er too little fo rce or too much
·c an cause accelerated wear , and for a
·correctly shaped stylus the optimum
force is claimed to be 6 g rams. If both
microgroove and standard records a re
'played, it seem,; that the compromi se
:setting for the stylus force is around 8~
g rams.
To make sure that we have the forc e
recommended, we have been 'using a
variety of devices to measure it-spring
balances, relay-spring adjusters, modi'tied . letter scales, and the like, some of
which are undoubtedly ingenious. Howe ver it seems much more simple--a nd
certainly far easier to use-to employ
.a "go/no-go" dev ice much in the same
fashion as we would employ a gauge to
.a manufacturing process.
One device just introduced (see page
.51) is such a "gauge" in that it shows
.accurately when the stylus fo rce is correct. I t does not tell you what the force
is, but shows easily and very simply
when it is exactly 6 g rams-or with a
piggy-back weight, when it is 8 ~ grams.
This device is so simple that at fir st
look one is constrained to say "why
didn't T think of that?" But someone
finally did.
'to
SePt. 30, Oct. 1-2-1954 High-Fidelity
Show, International Sight and Sound
Expusition. Palmer House, Chicago, Ill.
·Oct. 4-6-National Electronics Confen;nce,
Hotel Sherman. Chicago. Papers are
solicited on all ('Iectronics subjects, and
the program chairman would appreciate
5ugestions for titles and authors of suitable papers. \\' rite George E. AnneI',
Elec. Engrg. Dept., University of Illinois,
Urbana. 111.
·Oct. 13-li-195.t Annual Convention. Audio
Engineering Snrit·ty. Hotel New Yorker,
New York City.
'Oct. 14-17-The Audio Fair, Hotel New
Yorker, New York City.
. ·Oct. 22- 24-New England Hi-Fi Festival,
Hotel T ouraine, Boston.
·Oct. 27- 30-30th Annual Convention, National Association of Educational Broadcaster~. Rf)wtnan Room, Hotel Biltmore,
New' York.
Nov. 18-19-Si:-:lh Annual Electronics Conference spollsorerl by the Kansas City
Section of. the I.R.E., Hotel President,
Kansas City, Mo.
Feb. 10- 12. 1955-Audio Fair-Los Angeles,
Alexandria H otel, Los Angeles, Calif.
.AUDIO •
SEPTEMBER, 1954
Just OUT!
A COMPLETE GUIDE TO BETTER
HIGH-FIDELITY EQUIPMENT, CIR·
CUlTS, CONSTRUCTION, SERVICE
and better results!
Get better results from "hi-fi" by having all
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HIGH FIDELITY
TECHNIQUES
by John H. Newitt
Staff, Mass. Inst. of Technology
494 pages, 203 illustrations
Price $7.50
This big new book by one of the nation's
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"low-down " on modern sound reproduction
methods and equipment. It shows exactly how
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all details of circuitry, components and equipment; covers the service angles; compares the
di fferent methods - and is chock full of howto-do-it tips and ideas.
ANSWERS YOUR QUESTIONS ABOUT HI-FI
Chock full of how-to-do-it tips and ideas
flere are just a few of the subjects covered: What to look for in high fidelity
equipment - what to avoid 0 Getting reproduction. to suit your taste 0 Some unusual
" hi-fi" combinations • Hi-fi vs. P .A. type speakers 0 Matching the reproducer to its
environment 0 Loudspeaker construction and performance 0 Adjusting bass-reflex
cabinets 0 Controlling distortion 0 A novel horn system 0 Ba'ffles 0 -Getting rid of
" overhang " 0 The best reproducer enclosure • Choosing a reproducer 0 Selecting
a woofer-tweeter combination 0 Sound-proofing materials 0 How grillwork affects
attenuation 0 Output transformer specifications and what they mean 0 Special hi-fi
circuits • Proper crossover frequencies • Do's and don'ts of volume expansion • Practical ways to suppress noise 0 A good tone control 0 Negative feedback. and how
t o use it 0 Pre-amps and equalizers 0 Amplifier construction hints 0 Judging commercial amplifiers • F-M tuners 0 Minimizing tuner distortion 0 Avoiding chatter
and crosstalk 0 Limiter-discriminator vs. ratio detector FM circuits 0 All about records
and record players 0 Selecting turntables and pick-up cartridges 0 Avoiding reco~d
wear • A comprehensive course in magnetic recording 0 Pick-up resonance, its
cause and cure 0 Choosing a recorder 0 Tips for custom builders 0 Special installa.
t ion problems 0 Typical "hi-fi" installalions 0 Bass-reflex calculations and design
charts 0 Acousticol horn design data • • . and dozens of other subjects .
. Read it for 70 days AT OUR RISK! Use coupon.
,------------------------_
Dept. HF-14 Rinehart Books, Inc., Technical Division
232 Madison Ave., New York 16, N. Y•
Send HIGH FIDELITY TECHNIQUES by Newitt
for IO-day FREE examination. If I decide to keep the book,
I will then remit $7.50 plus postage. Otherwise I will
return book postpaid promptly and owe you nothing. (If
you send cash with order, we pay postage - same return
privilege with money refunded.)
..I
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Address .... ... .... ... ....... .... ...... .. ....... .. ...... ... .. ...... ... .. ..... .. ....... .... .
It
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77
r--- Just
Publisiled! ---. VERSATILE CONTROL UNIT ~CLASSIFIED----.
ELECTROACOUSTICS '
(from pag e 21)
Modifications
The schematic of the amplifier-Fig. 1
-shows fi xed values for the frequencydetermining elements, C, C" a nd R., and for
the values shown, the turnover would be at
approximately 375 cps, and the high-frequency response would be down approximately 6 db at 10,000 cps, which closely fits
the ffrr curve. These values can be changed
to suit the individual preference, or the
ci r cuit can be arranged so that various
values could be sw itched in at will. C. controls the turnover frequency and R , contr ols
the a mount of Rattening or deemphasis at
the low end. The amount of rolloff is controlled by the capacitor C .
For equa li zation to fit the RIAA curve
-which is becoming more and more the
standard in the industry- it is advisable to
decrease the value of C. to .0035 !Jof, chang e
RI to 1.0 megs, and incr ease C, to 470!Jo!Jof.
This should g ive suitable results with almost
any LP record, provided some adjusting of
the tone controls could be resorted to. F or
other equali zation curves, the values shown
in Table I could be substitut ed for those
in Fig. 1.
The Analysis of 'transduction
and Its Historical Background
By FREDERICK V. HUNT,
H arvard University
This important new monograph is the
first work to provide a complete and
orderly history of the evolution,
growth, and modern characteristics of
the major electroacoustical transducer
types.
Featuring
New material on onglOs of electromechanical and electroacoustical energy
conversion.
Results of war research on impedance
..nalysis of transducers.
A new scheme for dealing with antisymmetry in electromagnetic transduction.
New results concerning suppression of
harmo!:ic distortion in push-pull electrostatic loudspeakers.
Rational methods of analyzing the performance of loudspeakers.
300 documented references.
Harvard Monograph in Applied Science
No. 5-Co-published with Harvard
University Press.
1954
260 pages
$6.00
TABLE , .
Component Values for Different
Equalization Curves
Curve
Send for your on-approval
copy today
JOHN WILEY & SONS, Inc.
/1
440 Fourth Avenue, New York 16, N. Y.
,._---------------- ..
:
I
Now Ready for
Immediate Delivery
I
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RIAA
ffrr
Co l 78
RCA 78
Old AES
Col LP
Compr omise
R2
~Lf
1.0 m eg
4.3
4.3
1.8
1.8
0.56
1.2
PARTS LIST
MT ·lM PRESTO·SPLICER
for WELDING TOGETHER
%" Mylar and acetate tapes
without cement or adhesives
• Diagonal cut capable of withstanding 3 pound pul l
• Inaudible with playback amplifier
ga in at maximum
•
F.O.B. Factory
Sample splice and brochure on request.
PRESTOSEAL C~~~·.
3727 33rd st. , long Island City I ,N.V.
78
Co
.0035
.004
.004
.003
.004'
.005
.005
The value for R , is that sp~cified by
the pickup manufacturer a s optimum. A
2-watt unit is recommended to ensure lownoise operation.
The New
$67
C,
470 !Jo!Jof
220
1000
470
620
1000
470
C, C,
C,
See Table I
2400 !Jo!Jof, mica, 5%
Cl
1200 !Jo!Jof, mica, 5%
C,
560 lAI~tf, mica, 5%
CG
270 !Jo!Jof, mica, 5%
C" c" C", C" , 0.25 ~Lf, 600 v, paper
C , C,.
SO !Jof, 25 v, electrolytic
C o, Cll, C.. 0.1 !Jof, 600 v, paper
C"
1.0 !Jof, 600 v, paper
Ct." CI I
4700 !Jo!Jof, 400 v, paper
C"
100 !llLf, mica
C"
0.15 !Jot 600 v , paper
C"
2 /.If. 200 v, paper
L,
0.8 Hy
R,
0.11 m eg, 2 watts
R.
See Table I
R,
15,000 ohms, I watt, 5%
R,
22,000 ohms, 1 watt, 5%
R,
36,000 ohms, 1 watt, 5%
RG
62,000 ohms, I watt , 5%
R,
See text
R.
1500 ohms, deposited carbon, 1%
R,
0.22 meg, 2 watts
RIO
1.0 meg, 1 watt
Rll
0.15 meg, 1 watt
R,.
2400 ohms, 1 watt
Ru, R I ,
10.0 megs, I watt
1.0 meg, 1 watt
R 15, R"
1600 ohms, 1 watt
R", R "
R17J R 32
15,000 ohms, 2 watts
Dual 25,000-ohm potentiR",a, b
ometer, linear t aper
0.1 m eg, 1 watt
1.0-meg potentiometer, linear taper
0.47 meg, 1 watt
R."
Rate,: 10¢ per word per InsertIon for n.ncomm".I.1
ad.ertlsements ; 25¢ per word for comm.rclal ad.cr·
tls.ments. Rat., ate net. and no discounts w111 b.
allow.d. Copy must b••c.ompanlo' by romlttonco ·In
f.II, and mast roach tho Now York oft1co by tho
first of tho month pr••• dlng tho date of I..UI.
THE AUDIO EXCHANGE has the la rgest
selection of new and fully guaranteed used
equipment. Catalog of used equipment on request. Audio Ex~bange, Dept. AE, 159-19 H ill·
Side Ave., Jamruca 32, N. Y. OL 8-0445.
AUDIO EXCHANGE EXCHA..t,\,GES AUDIO
30% DISCOUNT Fnctory-fresh gua l'aneed
LP records. Send 10 cents in coin for complete catalogue
SOUTHWEST RECORD SALES, Dept. A,
4710 Caroline,
Houston 4, Texas
FM ANTENNAS. Broad band Yagis and
standard types. Wbolesale Supply Co., Lunenburg, Mass.
MUSIC FROM A BOX- is tbis your Hi-Fi?
Thirteen years experience in engineering, constructing, and rebuilding borne music systems.
May I belp you? Sherwood Sax, 3638 Regal
Pl., Los Angeles 28, Calif. HOllywood 9·4043
Sell complete file AUDIO ENGINEERlt'\'G
and AUDIO from second issue, June 1947, to
date. No reasonable offer refused or will dona te
to organization. Henry Sbaw, 1811 Roberta ,
Willow Grove, Pa.
WHARFEDALE 5/CS/AL treble speaker,
month old, $18.50. A. M. Vash, Stony BI'ook,
N. Y.
SELLING OUT: Complete Brociner audio
control center consisting of A100 preamplifier
equalizer and CA-2 control amplifier, $60 .
Kelton Diplomat speaker system, $30. All. in
perfect condition. Tony Hofmann, 90-A Kirkland Street, Cambridge, Mass.
SELL two Rek-O-Kut Console model tum·
tables; original value $700 eacb; 6 years old.
Make offer. Also 5 R-J baffles, almost new.
Audio Electronics, Inc., 2516 Highland, Cincinnati 19, Ohio.
CONCERTONE NETWORK RECORDER,
mechanism and amplifier, never unpacked.
New price $795. Must sacrifice $495. B. Kamnitzel', 89-21 153rd St., Jamaica, N. Y.
SELL-Partridge
output
transfdrmer
WWFB and mounted resistor board for Williamson amplifier, used but perfect, $15. Wm.
Tannenbaum, 160 Bennett Ave., New York 40,
N. Y. TO 7-1698 .
HEATHKIT Ultra-Linear Williamson, perfect, $50; CI'aftsmen RC2 amplifier, $20; University 6201, :f30; Permoflux 8T-8-1, $7.50.
Each in excellent condition. Norman Teten·
man, 2350 E. 27th St., Brooklyn, N. Y.
MICROPHONES: SELL two Sbure :11:300
multi-impedance (with 3-way switch for 30/ 50.
150/ 250, and 100,000 plus ohms) bidirectional
broadcast micropbones complete with 20 ft.
3-cond uctor shielded cable; in original boxes .
Used only 22 bours; we replaced with directional mikes. $50 each. BURTON BIGELOW
ORGANIZATION, 274 Madison Ave., :(\few
York 16. N. Y.
Hi-Fidelity plastic-base recording tape, 1200
ft. on 7 ¥., " plastic reel, $2.19 ea., 6 for $12.
Hi Fi Shop, 2 N. Howard St., Baltimore I ,
Md.
R" ,
R ZI
R"
R"
R"
R" , R"
R' I
V" V ,
V" V ,
VI
AUDIO
47,000 ohms, 1 watt
68,000 ohms, 2 watts
560 ohms, 1 watt
0.22 meg, 2 watts
33,000 ohms, 2 watts
18,000 ohms, 2 watts
Two halves of 12AX7
Two h a lves of 12AT 7
12AU6
•
SEPTEMBER, 1954
PROFESSIONAL
DIRE~TORY
HIGH-FIDELITY HOUSE
Offering the World's Finest Home
Music Systems, cre ated by experts
with years of experience.
High Fidelity is our only businessnot a sideline. Complete stock flf every
worthwhile component at all times.
536 South Fair Oaks, Pasadena 1. Cal.
SY 5-4118
RY 1-8171
"EVERYTHING IN HIGH FIDELITY"
From Primary Components
to Completed Custom Aud io Equ ipment
KIE~!und Corp.
820 West Olympic Blvd .· Los Angeles 15, Calif.
Ri chmond 7·0271
ZEnith 0271
Custom-Built Equipmen t
U. S. Recording Co.
1121 Vermont Ave., Washington 5, D .
Lincoln 3-2705
c.
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Hi-Fi R ecor ds Compon ents
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SPLICES MAGNETIC TAPE
Neatly - QuicKly - Easily
Kit Includes plastic splicer whic h adheres to recorde r or work·
t8ble, generous supply of pre·cut tape splicing tabs, handy blade,
instructio ns and plastic case. Only $1.50 post paid. If your dealer
ca n't supply you, order from • .•
COUSI N O, INC.
2S57 Madison Ave.
Toledo 2, Ohio
Visit AUDIO at the International SIGHT and SOUND
EXPOSITION Palmer House,
Chicago Sept. 30, Oct. 1 and 2
Room 735
AUDIO
•
SEPTEMBER, 1954
!J~P~ ...
Bill B a chman, who devel Qp e d the GE
m agn e ti c pic k u p while w ith Gen e r a l E lect r ic, h as started a n ew t r e nd in a udi o with
d eSi gn of a n ew e lectr ostatic s p eak e r for
t h e Phon ogr a p h Div is io n of Columbia
R ecords, In c.- i t will b e u sed fir s t in the
r evi sed m'o d e l of t h e Columbia "3 60" t a ble
phon ograph ... Dr. W i llia m Shockte y, b est
known fo r his co n tributions to the d e vel opme nt of th e tra n s i stor , h a s tak e n
leitve of a b se n ce f ro m hi s p osition ' as
D l rect or o f t h e T ran s i stor Physics De p a rtme nt of B ell T ele phon e L a b orat o ri es
t o b ecom e Direct o r of R esearch f or t h e
Weapon s Syst e m s E valua tion Gr oup, a
div i s io n of th e D ep a r t m e nt of Defen se.
One of t h e season 's mo s t lavish t r a d e
s h owings was conducted by Th e Magn avox
Compa n y to introduce its n ew hi g h -fid eli ty
comp on e nt lin e a s w ell as assem b led r a di o ph on o-TV receivers. H eld a t New York' s
Park L a n e H o t e l, the m ee tin g was co hos t ed by M agn avox preside n t F rank Freill~ann a nd Leste r J , Sholt y, acco unt executIVe for Maxon, I n c., M agn avox a d ver t i s m g agen cy . . . Equa lly impressi ve was
the buffe t lun c h eon given a t th e Bel mon t
P la za by Charles Ollste,i n , presi d ent of
M a nhattan 's Sanfo rd El ectroni cs Cor porat i on , L es H irte'n st ei n a nd Ray Bellins on ,
sales execs. , to a nno unce th a t t h e firm h as
tak e n over dis tribution of J en sen speak e r s
a nd R egen cy a mplifie r s , in a ddition t o t h e
W e b cor line of pho n os, record chan ger s.
a nd t a p e r ecor d e r s w hic h i t h as h a n d le d
fo r some t im e .
Stanley Kligfeld, writ e r o n hig h fid eli ty
for The Wall Street J ou r n a l, h as resign ed
to h a n g out his s hin g le as a p r actisi n g
at t orn ey . . . L y man E. G . Suiter, fo r merly
w ith the Radio Divis i on of W es tin g h o u se
h as b een a ppoin te d Assistan t to th e V ice ~
P r esident of F ai r ch ild Recordin g Eq ui p men t Com p a n y . . . Henry T. Roberts h a"
b een named v ice-preside n t in c h a r ge of
the Commer cia l M u s ic Di v i sion of Magnecord, Inc.-h e w ill continu e t o act as gene r ,!-I m a n age r to w hic h posit ion h e was a p lJomte d las t May . . . L i nwood G. (Li n)
L assig, for m e rly with J . W a lte r Thompson
Com pan y. h as j oine d t h e New Y ork office
of A I Pau l Lefto n Com pan y . In c. . as
DI r ect or of T echn ical Adver tisin g- baf'k g l'o und i ncludes 14 year s in vari ou s d e pa r tmen ts of R CA Tub e Div is i on.
B ryc e Haynes , vice-p resi d en t of A u dio
D evices, In c., exp r essin g e n t hu s iasm over
an Air For ce contract fo r t h e compan y to
s u pply 15 milli on feet of three -i n c h-wi d e
m agn e tic r ecordin g tape-en ou g h to reach
f r om New York to Sa n F r a n ci sco . Cost of
tape w ill b e abou t $220,000 . .. Max B aume.
fo rme r ly gen eral manager of Brook E l ect r o ni cs, In c. , h as opened s h op as a factory
r epresen tati ve i n New York under t h e fir m
nam e Bau me E l ectroni c Sal es Compan y.
, Freder i ck I. K a n tor h as reti red f r om t h e
re p fi e ld t o becam e sales m a n ager f o r E n core magn etic tap e -m os t of Kan tor's
accoun ts h ave b een t a k e n over by Le onard
Zlowe of t h e Leonar d Zlowe Company . . .
Dea th of Harold Shennan , p r om in e n t
m em b er of t h e A udio En g in eerin g Society
an d pion eer in b i n a u ral r ecordin g, a m at te I' of s in cer e grief throu g h ou t t h e a udi o
in du s t ry. Ger hard G. Schnei der, w h o j oi n ed
t h e com pa n y i n 1934 as a too l m aker. h as
been el ecte d v ice-pres ide n t i n charge of
p ro du ction of Nation a l U nion E l ectric
Corp or a tion . . . William R. Saylor, for m erly in t h e Cambridge office of General
R a dio Com pan y , h as b een a ppointed m a n ager of the firm' s n ew e n g in eerin g and
sales offi ce in Si l ver Spring. Md.
Her bert B orchardt, president of Sonoc r aft, I nc., fo r ecasts g r eatly ex pa n ded u se
of t a p e r eco rder s i n sch ool s an d co llegesexp ects F a ll sales in the edu cational fie ld
t o set n ew records . . . William H . Cllthe,r o,
Jr., pre v iou s l y w ith D avid Bogen Company, h as b een a p pointed manager of
bran c h store oper ation s by Gates R a d io
Comp a n y . . . B ert B erl ant, president of
Berl a n t Associa t es, j n a n effor t t o protect
d eal e r s an d j obb ers agains t p r ice- c u ttin g .
a nnoun ces t h at effecti ve imm edi atel y a ll
Concerton e p ro du c t s w ill b e fa i r - t r a d ed.
a nd that s t r ic t f r a n c hise p olicy in sti gated
by t h e compan y last J a nuary wi ll be
str e n gth en e d .
J immy Carroll, sal es exec i n H arvey
Radio Company ' s Sound De\,ar t m e n t . h as
recover ed f r om maj o r op erat lOn p erformed
during h is A u g u s t v acation. Vacation ? . ..
BUI Mooza, pro m inent New y'ork fac t or y
re presen tative, i s s h owing o n e of t h e
c utest g immicks yet to come a l on g in t h e
fo rm of a r a dio con ceale d i n t h e replica
of a n ol d -fas hi on e d wall- ty p e t e le phon e n o t exactly hi g h fidelit y , but it's pl e n ty
easy on the eyes ; m a nufac tured b y the
sam e outfi t tha t produces t h ose fa n cy
little " s pice b ox es" . . . Don·t fo rget, A udio
F a ir Tim e i s a lm os t h er e-Oc t ob er 14
t hrou g h 17 a t th e H ot e l N ew Y orker -a nd
if the buzz-s aw t e mpo of F air M a n a g e r
H a rTY Reizes' activiti es i s a n y indicatio n ,
w e' re i n for the time of our lives.
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GOLDEN MAHOGANY
~
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MODEL 4
(ORNER HORN
• Performance of unri valled purity and
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it a complement to the fi nest decor.
• Hear. the Brodner Model 4 Horn . You
will agree that its u nobtrusive naturalness
pl aces it in a class by itself.
The midd le range and high treble tones are
dispersed uni fo rml y by a refl ector horn of
unique design. In the bass range, the driver
unit is efficiently coupled to the air by means
of a folded horn utilizing the corner of the
room as a pro l o nga t ~o n of the horn structu re.
literature upon request.
B~OCINER
ElECTRONICS LABORATORY
Dept. AE9, 344 E. 32nd St " New Yo rk 16
:79
ADVERTISING
IN D EX
•
FOR YOUR OWN
HIGH FIDELITY
SOUND SYSTEM
The New WEARITE TAPEDECK
Another example of the ad vanced state of the audio art in E ngland, the W earite
tapedeck fills a long awaited need in this country. The high fidelity enthusiast can
easily adapt his basic tape mechanism to his own quality sound system without
duplicating power amplifier and speaker.
The We.rite tape deck has three 60 cycle AC moto rs : One H ysteresis synchronous
for RECORD and PLAYBACK (speed regulation: 0. 5% ) , and two 4-pole
induction motors for REWIND and FAST FORWA RD.
Other feattlres i1lclllde:
• 3 heads: RECORD, PLAYBACK, and ERASE
• R esponse: 50 to 12 ,000 cycles • Wow and Flutter: less than
0.2 % • Speeds: 3 % and 7Yz inches/sec. • Capacity: 1200 feet
(7Yz" reel) • Dual Track
C omplete with special componenes for construc ting
bias oscillator
........ . .
$225.
$195.
T apedeck alone
Write for complete descriptive data and specifications to Dept. DJ-I
H. A. HARTLEY CO., INC.
521 E a s t 162 n d 5 t r e e t, B ron x 51, N ; . Y.
I'
Aero Products Co. . ......... ".... . 70
Allied Radio Corp. . . . . ............. 59
Altec Lansing Corporatio n . . ....... . . 6142
American EI ite Co. . .... . . . . . . , .... .
Ampex Corporation ........ .. .... ,.. 3
Asco Sound Corp. . .......... , ... ' . . 73
Audak Co. . . . ... .. . .. . . ... .. ... 50. 51
Audio Devices. Inc. . ........ . . Cover 2
Audio Fair The . .. . .. . . .. ...... , .. 55
Audiogersh' Corporation . .. . ......... 37
Bell Sound Systems. Inc. . ..... .. . , ..
Bell Telephone· Laboratories .. ..... ,..
Bozak. R. T . Co. . ... , ......... , .. .
Brociner Electronics Laboratory ........
Brush Electronics Company ..... ,. ....
76
1B
8
79
71
Cinema Engineering Co. . .......... '. ~~
§Ia~~im:;;d IA~verti~~';'~~t~
. : : : : : : : : : : :: 78
deMars Engineering & Mfg. Co.
65
Electro-Voice. Inc. . ..... ...... 1, 40. 41
Electro-Voice Sound Systems ... ,... . . 79
General Electric Co. . ... . ... , ...... , 9
Goodmans Industries. Ltd . ." ....•... 75
Hartley. H. A .. Co .• Inc, ...... ... .. . .
Harvey Radio Co .• Inc . . . . . . . . . ... , ..
Heath Co. . . .. .. .... . . . . .. ... , .. . .
High Fidelity House . .... , . . . ..... . .
Hollywood Electroni cs' . . ... .. ... , . . . .
Hughes Research and Development
Laboratories . . ...... . ........... .
Hycor Co.. Inc. . . .. .......... .... . .
80
63
65
79
79
Isotone Acoustic Spiralways. Inc . . . ,.
68
2'
72
Jensen Mfg . Co. . . . ....... .. ..... ,' 49
~ ~If 'Ze4d4 tk
audio anthology
Kierulff Sound Corp.
. ..... . .. . ..... 79
Lansing. James Boo Sound. Inc. . . .. . , 67
Leonard Radio. Inc. . .... . . .......... 57
Lowell Manufacturing . Co. .. ... .. . ... 7
Marantz. S. B. '.. .... . .. ....... , .,.. 73
Minnesota Mining and Mfg. Co , .. . ... 4. 5
and
the 2nd audio anthology
The original audio anthololY is still
being ordered by people who have
worn out theIr first copy or who have
just learned about the book. ContaIns
reprints of 37 articles which appeared
in AUDIO ENGINEERING from May
1947 through December 1949. An invaluable reference work on audio in
the home.
- - - - - - - - - - - - CUT OUT -
the 2nd audio anthololY continues
from where the first left off and contains reprints of articles from January
1950 through July 1952. In both
books the articles were brought up to
date. corrected where necessary, and
assembled by subject. the 2nd a a may
still be had with board cover.
MAIL TODAY ----~-------
Book Division. Dept. 3V,
Radio Mogozines, Inc.,
P. O. Box 629, Mineola, N. Y.
Sirs: Enclosed is 0
copies
copIes
copIes
check 0 money order for $ ..
of
ludio anthology
of the 2nd audio anthology
of the 2nd audio anthology
Orradio Industries. Inc. .., ...... Cover
3
Partridge Transformers. Ltd. . . ... . .. .
Peerless Electrical Products . .........
Pickering and Company. Inc. . ., . .. ,..
Pilot Radio Corp. . ...... .. ". . ..... .
Presto Recording Corporation . . ... .. ..
Prestoseal Mfg. Co. . .. .. .. ..... .....
Professional Directory .. ..... ... . ,....
75
60
43
39
78
79
Radio Shack Corporation ... . .........
Rauland-Borg Corporation .... . . .. . . .
Record Retailing . ... ........ ... ... .
Reeves Soundcraft Coro. . . ..... ..... .
Rek-O-Kut ' Company. The .. ..........
Rinehart & Company .. . ........ , ...
Rockbar Corporation , ... .. . . .. . .....
61
58
47
15
13
77
72
'" .. Please send me
I paper coved @ $2.00 each
(paper coverl @ $2.00 each
(board coverl @ $3 .00 each
Address .... ... . . . .. .. .. . .. . . ....... .. •.. ....... ... . .............. ...•.••.•.•••
City . . .. ...... ...... .. .. . .. .... . .. ... . Zone ..... . State . .. . ....... . ..• • • ••• • .
17
6
Shure Brothers. Inc.
Name (please print)
80
National Company ........ ....... 10. 11
Tannoy (Canada) Limited .. .........
Tech-Master Products Co. . . .. .......
Television Accessories .. ... . ........
Terminal Radio Corp. . . ....... .... . ..
Turner Company. The .. . ....... , .. . ..
45
69
76
53
56
United Transformer Co. . ...... .. Cover 4
University Loudspeakers . Inc. .. " .... . 35
U. S. Recording Co. . . . ....... . . .. ... 79
Weathers Industries. Inc. . ...... . . . ". 71
Westminster Recording Co. . . . ".... . 54
Wiley. lohn & Sons. Inc. .., ... .. ... 78
AUDIO
•
SEPTEMBER, 1954
irish
BRAND
GREEN BAND
PftD/e".aL
:IE-Xl!Ir EIS·....• ......
.
Ca,::a1.
«
-.:7se .• __
600 feet on plastic reel
..................................................... net $ 2 .10
1 200 f eet on pla stic ree l...
................................................. net 3.30
2400 feet an metal reeL ..... ............................................................ net 7 .71
SPLICE-FREE
Available Wherever Quality Audio
Reproducing Equipment is Sold
ORRADIO I ndustries , I nc .
World' s Largest Exclusive Magnetic Tape Manu f acturer
OPELIKA, ALABAMA
EXPORT DIVISION : Morhan Exporting Corp., New York, N. Y.
IN CANADA : Atlas Rad io Corp ., ltd ., Toronto
E=
. . . . . . . .. ...
. . . .. .. .. . ........
WITH COVER REMOVED
LINEAR STAND. RD MlF AMPLIFIER
SUITED TO 7"flACK PANEL MOUNTING
. ...
LINEAR STANDARD POWER A""PLIrlER
IMu~nlOOP F(E06.'CIQ
....
I~ .t" rE~!!vs~-IA~OU~Tpt)~T~111111
~~
;:::
!
~
a~t+t-+H1+Iti
~~~~II~~~II~~I§~~
!~ ... E
.1
1.0
10
20
PO'....[R OUTPUT- WATTS
INTERMODULATION DISTORTION CURVE
The Linear Standard amplifier climaxes 'a project
assigne<! to our audio engineering group a year .ago. The
prgblem was, why does a Williamson circuit amplifier which
tests beautifully in the laboratory seem to have consider·
able distortion in actual use? It tonk a year to fully deter·
mine~ the .nature and ·cause of these distortions and the
positive correGtive measures. This new amplifier not only
provides for full frequency response over the audio range
but, in addition, sets a new standard for mtnimum transient
distortion.
An inherent weakness of the Williamson circuit lies
in the fact that its negative feedback becomes positive at
subsonic and ultrasonic frequencies. The resultant insta·
bility in use lends to parasitic oscillation at the high end
and large s'ubaudio cone excursions both of which produce
substantial distortions. The Linear Standard Amplifier uses
Multiple Loop Feedback and network stabilization to com·
pletely eliminate these instabilities. The osci llograms below
show comparative perfo rma nce. The flat frequency response
and extremely low intermodulation distortion provided by
36 db fe edback. are self evident from the curves shown.
In addition to providing an ideal amplifier electrically.
considerable thought was given to its physical form. A
number of points were considered extremely important: (1)
Size should be minimum (power and audio on one chassis).
(2) Each kit must have identical characteristics to lab
model. (3) Rugged. reliable, structure is essential •
. This resulted in a rather unique construction employ·
ing a printed circuit panel as large as the chassis with
virtually all components pre·assembledand wired. The
result is that each kit. which comes complete, including
tubes and cover. can be fully pretested before shipment.
Additional wiring involves only the connection of 17 leads
to screw terminals for completion.
LINEAR STANDARD TYPE MlF
AMPLIFIER SPECIFICATIONS •••
Rated Power output: ._...................................................................._........ 20 Watts
Intermodulatlon Distortion :................_ ...._................... 07%-1 W. 1%-20W
Frequency Response (controlled): ..................! db 20 to :!O.OOO cycles
Hum & Noise level:......... _._......._....__:__._... 80 db belOW rated output
Feedback :... _ ..__....___.......... _......__..........._....__.._........,........_......_.............36 db
outpu ~ impedances (not critical) :.........................................................4. 8, 16
also 2. 5. 10, 20. 30 ohms
Tubes:. ___ ........ ____.._.............._ .., 1.12AX7: 2;SAUS. 2·5881. 1·5V4G
Plmensions & Welght:_ ._ .._________ 51/4" x 8" x 17Va" . 24 Ibs.
Net PriceL _ _ _ ~. ________........._••_._. ___$108'.OO
stelSfuncUon
Oow frequenCY)
transient Stability.
. Hlihfr
-OSCilTa*lY.
Av......
t wlrlng
capacity.
100
I
11 11111
UNEAR STANDARD POWER AMPUnER
4OCPS&7KCMIX[04;i
1M CONNECTION
10
. .. . .. . ..
I I11 111 1
\NT[RMOOULATION OlSTORT1C"j
IMUl TROOP r EEOBACK! .
MIOOMUM UNOISlORTEO POWER OUTi'UT
0'08::0217 WATIS
16n CONNECTION
5
0
5
20
100
IKe
10'"
FREQUENCY RESPONSE CURVE
, O<C
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