Mar
111
www.americanradiohistory.com
AmericanRadioHistory.Com
Wherever Magnetic
EVER CROWING PREFERENCE for Audiotape is
largely a matter of experience.
Professional recordists started the trend to
Audiotape because they knew, from long experience with Audiodiscsa, that Audio could always
be depended on for consistent, uniform quality
to meet the most exacting requirements.
And the trend is continuing, in every field of
sound recording, because experience with Audiotape
proves its unequalled uniformity of output and
freedom from background noise and distortion.
The superior magnetic and mechanical properties of Audiotape are the result of experience, too
more than a decade of engineering and production know -how by the only company in America
devoted solely to the manufacture of fine sound
recording materials discs, tape and film.
That's why the Audiotape line has grown so
large and so fast. In addition to the standard 1/4"
tapes, Audio is now supplying a wide variety of
special sizes up to 8" in width for specialized
applications of sound reproduction. The new
Audiofilm*, developed for the motion picture and
TV industries, is a typical example.
Whatever your magnetic recording requirements
for standard or special tapes remember that
you can always depend on Audiotape. Get in touch
with your nearest Audiotape distributor, or write
to our New York office.
THE
-
-
-
-
-
-
-
Trade Mark
AUDIO DEVICES, INC.
444 Madison Ave., New York 22, N.Y.
lrpoll
Dept.:
ROCKE
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INTERNATIONAL, 13
fett 40th
St
t
_
.
->. N.Y.
Successor to
1
j1DIÓ
At Precision today
Established 1917
we're processing
the finest
SCIENTIFIC FILMS
for nationwide
ENGINEERING
L
showings
C. G. McProud, Editor
Luci Turner, Production Manager
Lucille Carty, Circulation Manager
S. L. Cahn,
Advertising Director
II
H. N. Reizes, Advertising Manager
Editorial Advisory Board
Representatives
I
Howard A. Chinn
John D. Colvin
C.
J.
J. P.
Sanford R. Cowan, Mid -West Sales
67 W. 44th St., New York 18, N. Y.
James C. Galloway, Pacific Coast Sales
816 W. 5th St., Los Angeles 17, Calif.
Technical Book G Magazine Co.
297 Swanton St., Melbourne, C. I.
Victoria, Australia
LeBel
Maxfield
George M. Nixon
CONTENTS
MARCH, 1951
i
Vol. 35, No.
3
Letters
Audio Patents- Richard H. Dorf
Technicana
Editor's Report
Filter Design Simplified-Berthold Sheffield
Positive Feedback for A -F Curve Shaping-Part 2-L. P. Haner
A Continuously Variable Equalizer- Wentworth D. Fling
New Broadcast Lightweight Pickup and Tone Arm -L. J. Anderson and
C. R. Johnson
2
4
6
AUDIO engi
For your 16 mm. scientific
film requirements
use Precision ...
Over a decade of 16 mm. industrial film printing in black
and white and color.
Fine grain developing of all
negatives and prints.
Scientific control in sound
track processing.
10
13
15
16
100% optically printed tracks.
Expert timing for exposure
correction in black & white or
18
color.
Step printing for highest pic-
g society SECTION
Loudspeaker Damping- Albert Preismau
Record Review -Edward Tatnall Canby
Pops -Rudo S. Globus
New Products
Employment Register
Industry People
Industry Notes
Advertising Index
22
24
24
ture quality.
Special production effects.
Exclusively designed Maurer
equipment.
Personal service.
32
45
46
47
48
. no wonder more and more
of the best 16 mm. films today
are processed
COVER
A few of the sixteen Ampex tape recorders -part of the facilities of the Audio
Video Recording Company-are shown in montage with the disc microgroove master cutters. This installation is at 1650 Broadway in New
York City. Complete facilities provide for original recording and
production editing on tape and for dubbing and mastering
on disc. Equalized lines connect to major studios in
the city for program feeds. Photo by Jack Sharin.
AUDIO ENGINEERING (title registered U. S. Pat. 0R.) is published monthly
at 10 McGovern Ave., Lancaster, Pa.,
by Radio Magazines, Inc., D. S. Potts, President and Publisher: Henry A.
Schober. Vire- President. Executive and
Editorial Offices: 342 Madison Avenue, New York 17. N. Y. Subscription rates --United
States, U. S. Possessions and
Canada, $3.00 for 1 year, $5.00 for 2 years: elsewhere $4.00 per year. Single copies
35e. Printed in U. S. A. All
rights reserved. Entire contents copyright 1950 by Radio Magazines, Inc. Entered as Second
Class Matter February 9,
1950 at the Post Office, Lancaster, Pa. under the Act or March 3,
1879
AUDIO ENGINEERING
at...
au
PRF OISIO\
FILM LABORATORIES, INC.
21 West 46th St.,
New York 19, N.Y.
JU 2 -3970
MMUS
MARCH, 1951
1
www.americanradiohistory.com
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LETTERS
the performance
of any 12" speaker with a
We CHALLENGE
86-_0/
5Ú4G Shortage
Sir:
Stupidity is common these days, one can
see it even in high places, alas, but for an
example of absolute asininity I have yet to
see anyone attempt to equal your sensational
contribution. To print not once, but twice,
the exact designation of a radio tube in
critically short supply strikes me as a superb
example of a lack of the slightest trace of
common sense. By printing in two issues
the name of the tube, together with appro-
1-
ROYAL EIGHT"
SAYS- PERMOFLUX'S MR. HY -FY
This averaged
priate comments indicating its scarcity, you
have, as a child of ten could predict, increased the shortage fiftyfold. Did you think
you were doing a service, by warning
readers in plenty of time to let them stock
up? Rot! For every bonafide user, there
will now be a hundred who place orders,
thinking to use the big bottles in their auto
radios, the family portable, or perhaps to
design a nice new circuit around it. And
even those who do need this particular
type of tube legitimately, now, being warned
will place orders with ten distributors,
rather than with one, and will hold onto
each and every copy they are able to obtain!
Nothing you can do now will undo the
damage you have done. Just class yourself
with the idiot who yells "Fire l" in the
crowded theatre, or "Atom Bomb !" when
a paper bag breaks during subway rush
hour. No words can begin to express my
contempt for such a lack of intelligence.
I defy you to print this, and let the reaäers
Poore
ratuNi Nav
d
laboratory response
curveof
the Permoflux
87_8_1
hot it compares
less
withh the
of size or Price.
nest speakers
Hi -Fi Fans the country over
have accepted this challenge -have
asked their "soundman" for a demonstration -then,
have installed a Permoflux Royal Eight" in their
own audio equipment. Now they possess a magnificent speaker at a reasonable price which reproduces sound with superior sensitivity and fidelity as
well as tonal qualities which YOU too will want to
add to perfect the excellence of your own equipment.
Send for beautifully illustrated catalog No. J201 to
address listed below for further information including a full page devoted to correct baffling of
Royal Eight" and other size speakers.
regardegard_
!
! !
judge!
John H. Cone, President,
ADvice, A unique and
lhec4 These [ohm/.e Fatums
specialized Service
for Advertisers
2327 Arthur Street,
Los Angeles 65, Calif.
Permoflux's exclusive slotted, treated cone
gives the following results which makes
their speaker comparable to any 12' speaker:
Soft- suspended cone and extra -large spider
provide extended low frequency response.
Deeper, curvilinear cone greatly extends
high - frequency response.
High permeance yoke increases output.
ohm -10 watt voice coil.
8
Big speaker performance in a small frame
allows smaller more economical baffle.
Here's BIG SPEAKER performance -clean,
brilliant, musical reproduction but at a sensible price level. Your customers will approve and buy. Order one'for test today
your money refunded if you do not agree
that it is truly outstanding in performance.
-
PE RMO FLUX
ROYAL EIGHT" WITH
THE FAMOUS
BLUE
CONE
DEALER'S PRICE
Inquire about Permof ux's Complete
Royal Blue Line 6' to 15' Speakers
$13.30
10 -DAY TRIAL -MONEY BACK GUARANTEE
PERMOPWX CORPORATION
4902 W. Orend Ave., Chicago 39, Ill.
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Pleas., tend
(81-8-I)
Chock
Money order enclocad
Name of Favorite Distributor
Address
Zone
In the January issue Sarser and Sprinkle,
in their article on "The Musician's Amplifier Senior," refer to a statement of mine
concerning the acceptability of IM distortion as high as 10 per cent when using
frequencies of 400 and 4000 cps.
To avoid any possible implication that
this value is acceptable for amplifiers, I
would like to point out that the 10 per cent
figure pertains only to disc reproduction,
and then only when using frequencies of 400
and 4000 cps. It is also assumed that the
amplifiers do not contribute appreciably to
this value. As pointed out in another article
( "Analysis by the two -frequency intermodulation method of tracing distortion encountered in phonograph reproduction,"
RCA Review, Vol. 10, No. 2, June 1949)
a different distortion value will result for
any change in IM frequencies. Personally,
I like to have the IM distortion of the amplifiers that I use for recording and reproduction below 1 per cent whenever possible.
H. E. Roys,
Sound Engineering Section,
Engineering Products Dept.,
Radio Corporation of America,
Camden, N. J.
Your Name
LPN
Intermodulation
Sir:
State
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
MARCH, 1951
preliminary survey of commercial and educational studios
..
wherever you'tgo
\
INDIANA UNIVERSITY AT BLOOMINGTON now has a professional -quality
recording laboratory in continuous operation.
.
there's
PRESTO!
Made possible by pooling the resources and knowledge of the Department of Radio,
School of Music and Audio-VisuabCenter; this new lab is the result of painstaking
care in every detail of planning, purchasing and construction.
equipment best suited to the quality and budget
requirements. The basic machines are Model 8-DG disc recorders, installed with a
specially designed relay control system and operational status lights on each unit.
These are supplemented by an 8 -D disc recorder, a PT -900 portable tape
recorder for studio and on- location use, and a rack containing two 41 -A limiting
amplifiers and two 92 -A recording amplifiers.
PRESTO was selected as, the
The recording room
showing
The selection of PRESTO equipment was preceded by a study of the facilities of
established commercial recording studios, contacting other Universities with similar
programs and visiting the Library of Congress recording laboratory. The continuous
use of the equipment these past months verifies this selection:
at Indiana U.,
recorders and
rack mounted
PRESTO disc
reproducers, PRESTO
amplifiers and the famous PRESTO
PT -900 portable tape recorder.
Visit
PRESTO at IRE Show
Third Floor-Grand Central Palace
RECORDING CORPORATION
March 19 -22
In
Canada: Walter
P.
Downs,
L
"d., Dominion Square
B
Paramus, New Jersey. Mailing Address: Box 500, Hackensack, New Jersey
dg., Mant eal, Canada
Overseas: M. Simons & Son Co., Inc., 25 Warren Street, New York, New York
www.americanradiohistory.com
AmericanRadioHistory.Com
J
ISZ
RICHARD H. DORF
Record
Turntable
111Atillg
WH
ILE TRACKING ERROR 1n
phonograph
pickups is hardly to be considered
one of the major causes of distortion in playback, it is a minor source,
especially with short arms. Most of us tend
to think of it as just one of those unavoidable things that probably could be eliminated
only by some contraption resembling a
recording lathe.
Archie E. Coppleman of Los Angeles
presents the solution to tracking error in
a patent of the typical "Why didn't I think
of that ?" kind, No. 2,522,997. The basic
thinking behind the invention is illustrated
in Fig. 1. Instead of a rigid arm, the assembly might consist of two rods, connected
at the outer end to a pickup mount and at
the inner to a plate. All four connections
are rotatable in the horizontal plane. The
rear plate is hinged for vertical movement
to a support block which is fixed to the
wood or metal baseplate of the entire rec-
ord- player assembly.
Now, as any lever mechanic will tell
you, if you move the pickup mount across
the disc toward the center, the mount wi
1
*Audio Consultant, 255 West 34th Street,
New York, N. Y.
Figure
Pickup support
shaft
Yoke
Figure 2
remain in the same angular position with re-
spect to the starting point. In Fig. 1 we have
shown it at the start (solid lines) perpendicular to a diameter of the disc, for
perfect tracking. At the inner position
(dashed lines) it is still perpendicular to
that same diameter line A -A'. The rub,
so far, is that it has moved rearward ; if
a new diameter is drawn through the new
pickup position (line B -B') we can see
that tracking is very poor.
The inventor's answer to this dilemma
appears in Fig. 2. A third rod has been
added in the center, and this is connected at
the outer end to a short shaft which supports the pickup. The rod is held in a yoke
which is the termination of the two rods
of Fig. 1. The short shaft is free to move
to some extent lengthwise but is prevented
1
load such as a speaker or cutter head,
not just into an ideal resistive load. McINTOSH 50W -2 and 20W -2 amplifiers
perform substantially the same under
dynamic conditions into a speaker load,
as into a pure resistive load.
r4
Full dynamic range can be realized
only if the noise is low. McINTOSH
amplifiers are designed so that the noise
Type AE -2
$74.50
Type 50W -2 $249.50
least cost.
Service is simplified by
plug -in circuits. Size is small because
AUDIO power peaks reach 200 to 400
times the average power of speech
The unique design of Mcand music.
INTOSH amplifiers provides adequately
of the high efficiency.
Performance of the control unit should
compare with the amplifier. The McINTOSH AE -2 8 -stage Amplifier- Equal-
for such peak power requirements.
A bass drum delivers 140 decibels
threshold at 20 cycles, and a
cymbal delivers 120 decibels above
threshold at 20 kc. McINTOSH amplifiers, delivering full -rated power at all
frequencies from 20 cycles to 20 kilocycles with less than l on distortion,
satisfy this requirement of dynamic
range.
above
The ear is extremely sensitive to distortion. For completely enjoyable reproduction, intermodulation at peak
Mcan.
powers must not exceed
INTOSH amplifiers type 50W -2 and
20W -2 meet that requirement for 100 watt and 40 -watt peak powers. respectively, regardless of the frequency combination within the band of 20 cycles to
20,000 cycles.
1
$149.50
components Irmsl are 80 to 90 decibels
below full rated output, which is an
inaudible noise level.
Factors of economy should not be
The efficiency of McINTOSH amplifiers almost equals class
overlooked.
B.
Here
tion:
is
another important specifica-
Be sure to choose an
works properly with
4
a
amplifier that
variable impedance
with the highest theoretical efficiency
possible. They are the most economical
on tubes and power requirements -the
most watts at the lowest distortion at the
izer provides stable, distortion -free performance that matches the performance
of the 50W -2 and 20W -2 amplifiers.
Engineers agree that McINTOSH amplifiers reach the practical limits of low
distortion and high efficiency. Music
lovers agree that the theoretical advantages are fully reflected in superlative audio reproduction.
For further
information write or telephone:
Mclutooh
Engineering
Laboratory
110 KING
Snqn
+/+.
AUDIO ENGINEERING
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AmericanRadioHistory.Com
I+nn
Inc.
vLVn f/allla, r+D.
MARCH, 1951
Figure
3
from circular movement so that the pickup
will not turn over on its back.
At the rear of the pickup, the two outer
rods operate just as they did in Fig. 1.
Figure 3, however, an underneath view of
the rear support plate, shows that the inner
rod also drives a toothed rack bar back and
forth. The rear of the rack bar is held in
place by a small support roller and the
toothed front drives a small gear. The gear
is attached to a short shaft which goes
through the plate and turns a small disc
on its upper side. As Fig. 4 shows (this is
a sketchy drawing of the top of the support plate), the new center rod is connected
to a pivot on the outer area of the small
disc.
Now for the sequence of events. At the
beginning (solid lines in Fig. 2) the assembly is entirely straight and the pickup
is on the center of the recorded area. If it
THE FIRST CHOICE OF RADIO ENGINEERS
FLEXIBILITY
In rack or console, or in its really portable cases,
the Mognecorder will suit every purpose. PT6
Series shown is the most widely used professional tape recorder in the world, and is available with 3 speeds '(33., 7' i,' 15") if preferred.
Figure 4
is placed nearer the inner diameter of the
disc, the outer rods keep the pickup's relative angle the same, as in Fig. 1. But in
addition, the little disc atop the rear support plate is turned by the rack bar and
gear, and the center rod, which is eccentrically pivoted to the little disc, goes forward.
This pushes the pickup outward, having
the effect of making the entire assembly
longer and putting the pickup on the same
diameter line (such as A -A' in Fig. 1) as
it was when it started. And the result is
perfect tracking. Similarly, if the pickup is
placed at the outside of the record, the outer
rods do their work the same way, and again
the center rod pushes the pickup outward
to take its correct position.
The idea here seems quite ingenious and
shouldn't be difficult to manufacturethough, as you have probably noticed-lit
isn't easy to explain. If it could be made
cheaply enough, but with good enough
bearings and without bad mechanical resonances, a pickup like this might well give
us at least some improvement in reproduction and record wear -and would undoubtedly give some manufacturer a wonderful promotion angle.
AUDIO ENGINEERING
F I D E L I T Y
Lifelike tone quclity, low distortion meet N.A.B.
standards
and 'at a moderate price! P163
Series shown in rack mount also offers three
heads to erase, record, and ploy bock to monitor from the tape while recording.
-
FEATURES
10' 2" ree sand offers 3 heads,
positive timing and pushbutton control. PT7
Series shown in complete console model is also
available for portable or rack mount. For outstanding recording equipment, see the complete
PT6, PT63 and PT7.
Magnecord line
PT7 accommodates
-
WRITE FOR NEW CATALOG
Magnecord, Inc., Dept.
INC.
360 NORTH MICHIGAN AVENUE
CHICAGC
1
ILLINOIS
A -3
360 N. Michigan Ave., Chicago 1, III.
Send me latest catalog of Magnecord
Equipment.
Name...._._ ...__.._...._
_.__...w._.___.
Address_.._..__....___ _..____......._.__._._...._.
City...._..__.._
MARCH, 1951
www.americanradiohistory.com
AmericanRadioHistory.Com
Zone.
. State
5
Here's Sun Radio's
Big New Catalog
Electronic Supplies
Of
Fig.
1.
The
basic
bridge circuit
used with its associamplifier and
ated
cathode follower.
Wien
consists of twu halves telescoped together,
with the core supported by and embedded
in plastic. This type of construction reduces
microphonics and the small size minimizes
hum pickup.
DESIGN of a new magnetic record reproduce head is the subject of an
article by M. Rettinger in the J. Soc.
Mot. Pic. Telev. Engrs., October 1950.
The equation for the inductance of the
head is given and the manner in which the
inductance decreases with increasing thickness of both front and back gap spacers
is plotted. The stacking factor for various
lamination thicknesses is plotted and discussed as is gap leakage for various front
gap spacers. The insertion of a back gap
in the recording head is shown to be of
importance because of a "shearing" of the
hysterisis curve and the attendant reduction
in d.c. magnetization. Also discussed is the
variation in output of the head used for
reproducing as the back gap is varied, as
the ratio of front and rear gap are varied,
and as the face (front -gap thickness) is
worn by use. By the use of the material
presented a head has been designed with
a width of 0200 inches that may be used
for both recording and reproducing and
when used with film running at 18 in. /sec.
has a response from 30- 18,000 cps. The
test bias current was 68 kc. with only 0.016
ma required, while the recording signal
current was 2 ma. The output from a fully
modulated track is 2 mv.
Physically the new head, known as the
MI -10795 record -reproduce head, is only
in. in diameter and mounts with a single
stud. It is housed in a mumetal shell which
TIIE
Designed to Meet YOUR Requirements
brand new concept in electronic components catalogs. 132 large, easy -toread, easy-to -use, 8 1/2 x 11" pages containing all the information you want on
A
every item you need. Listing electronic
components only, there's no need to wade
through page after page of radio sets or
other consumer products. Complete listings for the engineer, research worker,
teacher, broadcast station, repair and
maintenance man. Be sure you have this
new catalog on your desk when you need
it. Write or come in today for a FREE
copy.
.0.
lo STEPS
AUDIO EQUIPMENT CATALOG
Also be sure to get your copy of the new
100 -page 1951 edition of our manualcatalog, "Audio Equipment ". A gold mine
of practical information on high -fidelity
home music installations. You'll also
like its listing of our great line of highf idelity equipment, in logical, easy -tofind sequence. It's absolutely FREE.
Dept.
ST.
BARCLAY
6
NEW YORK 7, N.Y.
7 -1840
BLOCKS NORTH OF CHAMBERS STREET
Open Doily 9 -6, Sat. 9 -4:30
Established 1922
bt
C -D
8 ELECTRONICS CO. INC.
TWO
The use of a Wien bridge to control the
frequency of oscillation in audio oscillators
is not new. However the bulky components
and poor mechanical stability have frequently made other audio oscillators more
desirable for applications requiring a high
degree of frequency stability. Mr. C. H.
Young in the Bell Laboratory Record describes "A Precise Decade Oscillator" based
on the Wien bridge as the controlling element. The usual formula for the balance
frequency in the Wien bridge circuit, Fig.
1, as given in any textbook is
1
f -2nRC
However this expression may be rewritten
in terms of conductance, G, and elastance,
S, which give for the balance frequency
f=
tOSTEP5
100 CP5
10 GP S
EACH
EACH
D2
D3
;
0 STEPS
GPS
EACH
t
i
D4
+150
+2 TO -2
¡
GPS
TO t.2
GPS
PI
P2
0
1111111
Silvered mico High-0
Low temperature
Coeff cent
D I
D2
03
D4
1
(
GS)
The usual designs have varied S, which
requires the use of a large bulky capacitor
with its attendant mechanical instability.
If instead the conductance is varied in
h
FREE
122 -124 DUANE
Stable Oscillator
250 p mho (4000 n) per step
25 p ,Mo(40,00011) per step
2.50 mho (400,0001 per step
0.254 rho ( 4 MR) per step
Pt
P2
+250
Output
'
r
Ampl.
t.Op mho(IMR)
0.3A who
(
Ted
3.33 MR)75ee
I
Overall Amplifier Gain
65 moi.
Fig. 2. The oscillator with the arrangement of each decade and the values per step. The bridge
arm is now shown in the cathode of first amplifier and the other arms have been rearranged for
-
convenience in illustration.
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
MARCH, 1951
8452
8453
MULTIPLE CONDUCTOR
CABLES
8454
,Sold Exclusively Through Recognized Wholesale Distributors
8424
8426
Drawn
Patented
AUDIO ENGINEERING
8427
MARCH, 1951
www.americanradiohistory.com
AmericanRadioHistory.Com
7
AN MITI
STUDIO MICROPHONES
at P.A. PRICES!
11.
at
and DISTANT PICK-LP
CLOSE TALKING
YOU CAN SHOUT RIGHT INTO IT, or STAND AWAY
In either case, Quality will be perfectly natural. CotpJt change reduced to
...
minimum by the Automatic Volume Control effect achieved
bi
spec al constructio
AMPERITE
7WAYS
boom
DS
`LEADS
response
pR0OV.
BLASd
or stand
always
2
oit
Na
is
much
K;ss
perfect.
mike with
WESt
awl diaphragm
response.
than
frequency
e9 ° °1
LESS
q F` pt
the.
Portable Mixer
peaks
as
RESPONSE 1000
range
c
effteict
2
vo6o
5
edo,construction.
and
COMP ACI
.
Modes:
RUGGED.
R3LG -20C ohms
-imp.
RBHG
CHANGES
etc.
-h
DNAFFECtE itiowwind,
s,
List $42.00
in clini
AMPERITE CARDIOID
DYNAMIC MICROPHONE
List 332.00
Models PGH-PGL
..
Model KKH, with hand
volume control
.
List $12.00
List $18.00
AMPERITE Company,
In
8
Broadway
New York 12, N.
Canada: Atlas Radio Corp.,
Three subminiature non -microphonic
tubes in low -level preamplifiers feed high level mixers and a master gain control. A
second stage feeds a push -pull transformer,
coupling to a pair of AAGC -controlled
miniature driver tubes. These in turn are
resistance coupled to the 1S4 output tubes
which deliver at maximum + 18 dbm in the
band 100 to 4000 cps with only 2 per cent
distortion. This provides an additional 10
db over the normal telephone line requirement of +8 dbm.
A built -in phase shift oscillator provides
four frequencies for line equalization. A
VU meter is included on the panel for use
both with the oscillator in line equalization
and for monitoring. It is also arranged to
check the self- contained batteries.
The brief case is designed to carry the
amplifier, together with three KB -2C microphones, a headset, spare batteries, and
spare tubes without crowding.
Amperite "Kontak" Mikes
Model SKH, hi -imp
An article in RCA Review for September
describes a portable three -position
mixer and field amplifier. This unit, described by J. L. Hathaway and Ralph C.
Kennedy, operates on batteries and fits
conveniently into a briefcase, but has most
of the important features of a studio mixer amplifier.
1950
special
«
achieved
561
A thermistor (labeled RV) is used in one
bridge arm to maintain the bride close to
balance while the two -stage amplifier supplies the maximum gain permissible if
noise and switching transient problems and
component stability problems are to be
avoided. Ordinary two deck wafer switches
are used in the construction of the decades.
The frequency range of the instrument
with the values as shown in Fig. 2 is from
100 to 2212 cps. This range was one desired
by the group developing the instrument, and
can be extended with an appropriate choice
of G and S.
With precision wirewound resistors used
throughout, the accuracy of the oscillator
after warmup is ±(0.02 ±0.02 cps). If one
of the continuously variable dials is used
as a calibration control and the oscillator set
to frequency by comparison with a standard,
the remaining dial readings may then be
approached with an accuracy of 0.01 cps.
This, of course, holds over a small range
of the order of ±5 cps. It can thus be used
as an interpolation device when used in conjunction with calibrated standards.
The oscillator is followed by a phase inverter and push -pull feedback amplifier
which is transformer coupled to the load.
The maximum output is about one watt
with less than 0.5 per cent harmonic distortion. The potentiometer in the two continuous adjustment positions are 10,000
ohms each and the remaining resistance is
fixed. If accuracy is to be maintained all
values should be held to a close tolerance.
DISIOR11011;
v
, haul
frequency
6
below
decade conductance switches we have a
new solution to the problem, and have
eliminated the major difficulty of the system.
The effect of the introduction of large
variations in impedance and phase angle is
overcome in large part by making the
source impedance very small as compared
to the minimum bridge impedance.
Y.
Ltd., 560 King St., W., Toronto 28
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
MARCH, 1951
All -New RCA Pick -up and Tone Arm
installed on a 70 -D turntable.
The
'74)0417.),
PICK-UP. one arm, all speeds!
RCA's All -New Tone Arm -with magnetic lateral
plug -in heads -fits all standard turntables. Only
two heads are needed for all speeds.
...
This versatile pick -up and tone arm combination
installed on your turntable ... can play every record and
transcription in your library. Just plug in the head for
the right record groove -and spin the platter. It's as easy
as that.
Designed for studio-quality at all standard speeds, this
unique system has outstanding features over previous
types. For instance, plug -in magnetic heads need no adjustments for stylus pressure. Visibility of the stylus (from
the top of the head) permits accurate groove-spotting.
Anti-friction pivots and low inertia provide easy tracking
on eccentric and warped records. Lower weight assures
better record service- longer stylus life. Tracking error of
the arm is less than 4 degrees.
Arm assembly MI -11885 is complete with tone arm,
mounting plate, hardware, and the filter modification kit
MI-11874 (for 70-series turntables).
You use plug -in head MI- 11874-4 with the 1 -mil stylus
for fine -groove records. You use plug -in head MI- 11874 -5
with the 21/2-mil stylus for standard transcriptions and
78 rpm records.
Order from your RCA Broadcast Sales Engineer, or
direct from Dept. O -7, RCA Engineering Products,
Camden, New Jersey.
AUD/O BROADCAST EQUIPMENT
RADIO CORPORATION
of AMERICA
ENGINEERING PRODUCTS DEPARTMENT, CAMDEN, N.J.
In Canada.
R
C
A VICTOR
Company Limited, Mont.eal
EDITOR'S REPORT
AN EXPLANATION
CII:\NGES in the physical appearance of
AUDIO ENGINEERING may be noticed by readers
MINOR
beginning with this issue. For example, the manner of binding is changed so that the magazine is held
together by staples directly through the center, rather
than through the sides as heretofore. In technical terms,
the magazine is now saddle -wired instead of side- wired.
In addition to offering a slight economy in preparing
each issue, the magazine will lie open at any desired
place more readily.
Text pages are now being set with slightly less leading between the lines in order to permit more words per
page, so that while the total number of pages may remain the same, there will be more editorial material
than heretofore or, conversely, the same amount of
editorial material can be squeezed into a smaller number of pages. The saving in space is actually eleven per
cent. To compensate contributors for this change, rates
for articles have been increased by twelve per cent-not
with any idea of being generous with an extra one per
cent, but to make the rate per page come out at an
even number of dollars. Thus, in spite of more words
per page, contributors will still receive the same rate
per word, with a slight advantage due to the space occupied by photos and drawings. Contributors are not
to take a cut to accommodate these economies.
By this time it is obvious that we are leading up to
an explanation of the reasons for these steps. It is no
news to any of Æ's readers that costs are continually
increasing -paper, typesetting, printing, every element
which goes into the making of a magazine. The obvious
cure would be to increase advertising rates -which has
already been done. However, due to long -term contracts
for space, the increase in revenue is not felt for nearly
a year after a rate increase goes into effect. So far, it
has been possible to make both ends meet without a
boost of subscription rates, which again would not provide any immediate increase in revenue. A rise in second -class postage rates -which seems imminent -would
have to be passed on to subscribers by an increase in
rates on new subscriptions.
It may not be common practice to discuss the business
of publishing with a magazine's readers, but-as we
have observed before-)E's readers are different. They
look upon ìE as their magazine; they are in a sort of
partnership with us in getting these pages out every
month.
;
10
THE CANBY SHOW
Plagued by production problems, the embargo on
mail and express shipments, and a host of unanticipated
delays, the Edward Tatnall Canby show has gotten off
to a slow start, but is gradually picking up momentum.
This is the first mention of the program in 2E, but the
original announcement which was mailed to broadcast
stations just in time to join in the Christmas rush described the series as consisting of about half and half
musical illustration and informal comment. Those readers who hear Mr. Canby regularly over WNYC, New
York's municipal station, can readily imagine just what
the program is like. Those who have never heard him
are assured that this new transcribed show is much like
his column in the magazine. He talks about records,
illustrates his points with comparisons from different
new records-phonomontages, he calls these comparisons-and introduces each week several of the outstanding new releases in the field of serious music.
This new electrical transcription series, produced by
Æ, has already been booked by a number of stations,
and days and times of the broadcasts will be listed next
month. In the meantime, look for announcements of
this program or ask your local station about it. The
platters are now coming off the assembly line once each
week, and distribution is improving.
This may appear to be a strange venture for a magazine, but Mr. Canby's followers are myriad, and they
will welcome the opportunity to hear his weekly program in addition to reading his monthly column with
the latest news about records.
THE I R E SHOW
Another kind of show-coincidental with and part of
the convention of the Institute of Radio Engineerswill hit the boards in New York on March 19 and last
for four days. As usual, everything new in radio will
be shown, and thousands of visitors will drag their weary
feet through the three floors of exhibits at Grand Central Palace. Some rest for the feet may be achieved by
attending the technical sessions-with Thursday March
22 being billed as "Audio Day." Morning and afternoon
sessions devoted to audio will be held in the Blue Hall
on the third floor adjacent to Audio Center, where
most of the audio exhibits will be.
See you there?
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
MARCH,
1951
ACKNOWL!DGEd BY
NGINEERS
AS THE'FINEST A AILABLE!
superiority of diamond styli to
styli of other materials has been thoroughly established.
The
1
Exhaustive tests prove resistance to
abrasion of diamond styli is mbny
times greater than that of the Next
hardest material.
!
i
Great resistance to abrasion means a
iminimum of record wear, longer'record life and concert hall quality music
all the time.
Pickering pickup cartridges, equipped with diámond styli, may cost more than cartridges with
other stylus mater als but the useful life of a
diamond stylus cartridge is so much greater
than is represented in the cost differential that
from all practical viewpoints- length of service,
Pickering
listening pleasure, and record life
diamond stylus cartridges cost less.
-
The diamonds used in Pickering cartridges are
whole diamonds, not splints. They nre wel cut,
gem -polished to high accuracy and precisely
mounted to ride free and smooth in the groove
walls, recreating all the fine tones and nodulations pressed int) modern recordings.
Pickerirg Diamond Cartr-dges
unchallenged. They Mee- every exacting requirement of the most critical record playing
enthusiast who insists upon the finest musical
reproduction; who wants the realism and brilliance of a live performance and who is anxious
to maintain the useful life of his record collection.
The supremacy of
is
Address Department A
AUDIO ENGINEERING
MARCH, 1951
www.americanradiohistory.com
AmericanRadioHistory.Com
11
IT'S "LOADED" WITH
BETTER TELEPHONE SERVICE
(t-
Twenty of the Bell .System's newest small loading coils-like the one at the l
are housed in the long black case, mounted in u cable splice. This type of installa.
tion permits the economical extension of city cables to senr out -of-couve subscribers.
M ANY more wires can be crowded into
a cable sheath when the wires are fine.
But normally, wires don't transmit as
well when they are fine and closely
packed.
Bell engineers long ago learned to
make wires do better work by loading
them with inductance coils at regular
intervals. The coils improve transmission and let messages travel farther.
But originally the coils themselves
were large, heavy and expensive. The
cases to hold them were cumbersome
and costly too.
So year after year Bell scientists
squeezed the size out of coils. To make
magnetic cores of high permeability
they developed Permalloy. Tough but
extra -thin insulation permitted more
turns to a core.
New winding machines were developed by the Western Electric Com-
pany. Coil size shrunk to one -fiftieth.
Some like the one shown above
-can be mounted right in cables
themselves.
The 15,000,000 coils in the Bell
System today mean thinner wires,
more wires in a cable -more economical service for you. They demonstrate
once more how Bell Telephone Laboratories work continually to add to
your telephone's value.
-
BELL TELEPHONE LABORATORIES
\,,,,o
WORKING CONTINUALLY TO
KEEP YOUR
TELEPHONE
www.americanradiohistory.com
AmericanRadioHistory.Com
SERVICE BIG
IN VALUE
AND
LOW IN
COST
Filter Design Simplified
BERTHOLD SHEFFIELD
Presenting a method for calculating the constants for low- and
high -pass filters which eliminates the need for a large number of formulas.
Part- 1.
Fig. 1. (A) Half section. 161 Two half sections
in proper position before combining into a T
section. ICI Full T section consisting of the
elements of 1BI,
part and
parcel of the training of every full
fledged communications engineer. It
is therefore always regretted that the
design formulas which were so painfully developed in theory classes are forgotten by the time they are needed in the
field. Worse yet, the basic theory was
only partially comprehended in many
cases, and handbooks must be consulted
with caution. It is the purpose of this
article to remedy these defects and to
reduce filter theory to an unforgettable
simplicity. The reader will, at a moment's notice, be able to design filters of
any category, includini low- or high pass, T or pi, constant k or ni- derived
types. Reference texts will not be reFILTEE DESIGN is considered
RCA Institutes, Inc., 350 West 4th St.,
New York 14, N. Y.
*
Note: The basic idea for this article was presented as part of a course on networks given by
Mr. Albert Boggs at the Polytechnic Institute
of Brooklyn in 1947. Permission has been granted
to the writer to disclose this material.
quired. Contusing new formulas will not
have to be learned.
The basis for this simplification of
filter design lies in the synthesis from
half sections whose elements do not have
the fractional magnitudes customarily
assigned in conventional filter theory,
i.e., the arms will be represented by the
symbols Z, and Z5, as shown in Fig. 1.
Two identical half sections are readily
combined into a full T or Pi. By this
device it will be found that in any half
section the reactance X of either arm
has the magnitude of the termination,
Ra, at the cut off frequency, fe, of the
filter section ; i.e. XI,. Xe = Ra. Brief
theoretical considerations, as well as illustrations, will clarify the applications
of these simple formulas.
In order to demonstrate the validity
and value of this simplified method, it
must be shown first that the image impedances obtained by half section theory
are the same as if they were obtained
from a full -section T or Pi. This is carried out for a T by comparing the image impedance in Fig. 1 (A) at terminals A -B of the half section with the
image impedances of the full T section,
Fig. 1 (C). The full T section is constructed by butting the shunt ends of
the half sections as in Fig. 1 (B). The
image impedance is defined by'
'For a definition of image impedance see,
for example, F. E. Terman, Radio Engi-
neer's Handbook, p. 204.
o
(A)
131
(B)
Z,T
Fig. 4.
o
(C)
Fig. 2. (A) Half section. IBI Two half sections
for combining into a Pi secsection consisting of elements
of (B).
in proper position
tion.
ICI
Pi
Z1=
(1)
\/Zola
at terminals
A -B with terminals C-D
open as shown in Fig.
Where Za = Impedance
1(A).
(Z, Z.)
Za= Impedance at terminals
A -B when terminals C-D
are strapped together.
Za= Z,
Substituting these values in formula (1)
gives the image impedance
Zt= \/(Z, +Zs) Z,
This expression becomes more useful
if it is written:
1
T
L
>-z,T
LEI
o
o000-------o
2lT-O
a-Zir
El?
-\ZZ a
Zi
(Z, +Z2)
MIZ,Z.(1
Low -pass filter, constant -k type, half
section.
=
+t)
Z, Za -\1 1
(2)
+¡Z,/
`Za
The image impedance for the full T of
(A)
z,*
(A)
ZT
'ad4L
(
B)
`T
500
os.
ohm
load
Tzf
(A)
.5h
.5h
(B)
(B)
Fig. 3. (A) T section with elements as obtained
using half- section theory, with large Z used to
identify elements. (B) T section with conventional element values, using small z to identify
elements.
AUDIO ENGINEERING
500 ohm
bad
4111
(C)
(A) Basic half section. IB) Low -pass
half section. IC) High -pass half section.
Fig. 5.
MARCH, 1951
www.americanradiohistory.com
AmericanRadioHistory.Com
(A) Low -pass half sections before connection as T filter. I B) Low -pass half sections
of (A) arranged as T -type, low -pass, con stant-k filter with cut -off at 159 cps.
Fig. 6.
13
(B) and
2
(C). Its value for both
2
cases is
Zs =vZ0Z.
elements of the conventional T of Fig.
3 (B) with the elements of Fig. 3 (A),
whereby
VZ,Zs
-11
=
+Z.
z,=
It will be observed that the element
sfr=
Fig. 7. (A) Low -pass half sections before conas Pi filter. (B) Low -pass half sections
arranged as Pi -type, low -pass, con 159
This result is the same as formula (2),
aZ,
A
Fig. 8. (A) High -pass half sections before connection as a T filter. (B) High -pass half sec-
Zs
I
Z' +
(
tions of (A) arranged as T -type, constant -k
high -pass filter, with cut -off at 159 cps.
2z
Z'
2
Z
2,Z+N1 1
'
+(Z')
values of the T section of Fig. 1 (A)
differ from the conventional T as treated
in standard texts. To show that these
two T sections are equivalent, it is necessary only to convert the respective element values. For example, the image
impedance of the conventional T, Fig. 3
(2a)
Comparison of expressions (2) and
(2a) shows the equality of the image
impedances of the full T of Fig. 1 (C)
and of the half section of Fig. 1 (A) at
the Series end A -B.
In a similar manner one may prove
that the half section of Fig. 2 (A) presents the same image impedance at shunt
end terminals C -D as the Pi of Fig.
TYPE
(B)
PRACTICAL FILTER
TEE
In
Z
JL
PRACTICAL
:f1
ZT
L
PRACTICAL
L
1,
mc
l
mc
zmc
Zm,-msl
A
-- ee[
TT
WI
Ñ
(m
N
ñ
Tmc
,-m
mc
-,1,-mrla
1,
4,0-,.).,
,
1
UT.,
Z
L
L
F
T
,&,,,_,.)
T I(
T
Lt.
,-f
mr
L
_L
c.t,1?.
%
11,
N
/`a'-mrI)
- Í`
mL
ml
c
zm
mL
mL
mL
.mc
mc
if
c
4.1
m
=
Ai'-m,,
L
%
=m
c
L
L
m
L
m
zm
CHART
c
L
ñ,
m
mc
T
r\
¢
L
(
c
m
2
mc
m
_
,-
mr
N
á
ó
I(
m
m
l
m
14
X,.
R
-
-.
Zsr =TL /C V1 -r0'LC
(4)
This formula shows immediately that
the image impedance has a real value up
to the frequency where rd'LC =1. For
values of a,'LC greater than 1, Ztr is
imaginary. The terni (,'LC =1 defines
the resonant frequency, fr, of the L and
C elements of a half section.
Cut -off Frequency
Much confusion is caused for the newcomer by the meaning of cut-off frequency. Cut -off is defined as that frequency for which there is no output from
an ideal dissipationless filter. If a filter
is operated under ideal conditions, it
must be terminated in its image impedance at every frequency in its operating range. That this is a physical
impossibility is seen from equation (4),
since Zir varies between
/C and
zero as the frequency is swept from
zero to cut off. At this latter frequency
a,'LC =1, which is the series resonant
frequency of the two arms of a half
section. For a practical value of termina-
VL
m
I
Design formula: In any half section at cut -off frequency
X1 -
z,
+Zs,
Z.= 1 /(jwC)
I
2m
m
zm
x
1
and in the low pass half section of Fig. 4
2,= jo,L, and
1
mi.
c
proving that the conventional T and the
modified T produce identical results. The
relations for the Pi sections are proved
in a similar manner.
These considerations permit the application of formula (2) to low pass
filter design, i.e. since
cl-
J
c
-
Fig. 9. (A) High -pass half sections before connection as a Pi filter. (B) High -pass half sections of (A) arranged as a Pi -type, constant-k
high -pass filter with cut -off at 159 cps.
1
T1 c
FE-C..(Tr'
PI
2L2L
ZLfm
Im'1,
Shunt
m- derived
FILTER
i
gml,-nr)
merles
-derived
PI
HALF SECTION ARRAY
1
Zl
®
TEE
L
2
Z
(3)
SECTIONS
FILTER
L
L
(z,)'
+
This is converted to formula (2) for
the modified T section by replacing the
HALF SECTION ARRAY
ry
®
®
is
2
BASIC HALF
SECTIONS
Constant- k
VZ,Z! + Z,'
..iT- s/Z,Z, "f 1 +Zt -Z!T
Fig. 1 (C) is obtained in the same manner, i.e.,
Zsr =
(2Z,)(2) +(2 4')
=
cps.
2
Formula (3) then becomes
nection
of (A)
stant-k filter, with cut -off at
Z, or z,= 2Z,
Z
termination
[Continued on page 341
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
MARCH, 1951
Positive Feedback for A -F
Curve Shaping
L. P.
HANER
Part 2. Describing a 15 -watt power amplifier with unique high fidelity characteristics for use in a home entertainment center.
6H
and is set up to provide boost or attenuation rates as shown in Table III.
6H
+320
TABLE III
22,000
+250
15,000
To
Main Power
Switch
115V.
*200
68,000
AC
Fig. 10. (Upper)
Power supply for
input
63V
20
A.C.
PREAMPLIFIER SECTION POWER SUPPLY
BASS CONTROL I below 500 eel 1
CONNECTIONS
db. change
4 5 6
Ow octave
2 3
1
+7
+5.6
+ 4 2
+ 2.8
+1.4
0
-1
-2
-3
-4
-5
I
+5
K
NC
+ 4
L
I
+ 3
+ 2
J
M
N
P
P
P
P
P
0
A 8 NC C
I B NC C
A NC NC B
NC
I NC NC 8
I NC NC NC A
NCNCNCNC I
NCNCNC
NCNCNC
I
I
NC NC
I
NC
NC NC NC
NC NC NC
I
I
D
E
F
G
H
TAE PRE-AMPLIFIER Shown in
R
S
T
+1
0
-1.2
- 2.4
-3.6
-
4.8
-6
Fig.
8
is basically similar to the standard
G -E pre -amplifier for its mag-
netic reluctance pickup. Two 6SF5's are
used instead of the 6SC7. A 500-1.tµf
capacitor is placed across the series resistor in the record turnover point correcting network to raise the high -frequency response. Fig. 6 gives a comparison of this pre-amplifier with the
normal G -E pre-amplifier.
In the course of work settling upon a
pre- amplifier design, several circuits
were built. Among these were resistance- capacitance and resistance- inductance -capacitance input networks for
providing the necessary 6 db per octave
boost below the turnover frequency of
records. One circuit involved a 3 -step
arrangement for different turnover frequencies. Another circuit used negative
feedback with 3 steps for 350, 500 and
800 cps turnover frequencies. The best
all around compromise seemed to be the
circuit shown in Fig. 8, when used with
the accompanying tone compensator.
Adjustable tone compensation is considered essential. The basic circuit utilized is supposed to provide a maximum
of about 28 db boost or attenuation
Wilmington, Delaware.
AUDIO ENGINEERING
Z
NC
Z
AA BB NCCC
Z BB NC CC
AA NC NC BB
U
NC
V
Z NC NCNCAA
NCNCNCNC Z
NCNCNC Z DD
Y
X
X
X
X
W
amplifier.
(Lower) Connections of circuit points to ob-
tain indicated
TREBLE CONTROL(obove500cps
CONNECTIONS
OD change
Per aclave 7 8 9 10 11 12
Z
equalization.
Numbers refer to
switch arms, letters to contacts
on switch decks.
NC NC BB
NC NC NC Z
NCNCNC Z
NC NC NC Z
NC NC NC Z
Control
+ 7
db per octave
+ 5.6 below 500 cps
Bass
EE
FF
GG
HH
above and below 500 cps. Only about 20
db maximum boost or attenuation was
obtained when this tone compensator
was connected thru this positive feedback power amplifier as it was finally
set. Two 11 -point switches are used for
the bass and treble controls. This provides 5 points on each side of normal
+
4.2
+
+
2.8
1.4
0
"
-2
-3
-4
-5
"
"
"
"
+5
+4
+3
+2
Treble Control
db per octave
above 500 cps
+1
- o1.2
-- 2.4
3.6
4.8
The basic circuit for the tone compensation was obtained from an article
published in Electronics, Dec., 1948, entitled "Versatile Tone Control," by Wm.
B. Lurie. With careful shielding of the
switches and leads, excellent results have
been obtained. A good feature of this
system is that all compensating networks
and switching takes place at low impedance, being in the output of a cathode
follower. Signal level is kept up to a
safe level by level- restoring amplifier
stages properly located. Little hum and
tube noise is, therefore, encountered in
the output of the system.
Figure 4 shows the nature of the
family of curves which are available
with this tone control. Figure 9 shows
the normal and maximum curves which
[Continued on page 33]
Fig. 11. Block diagram of system switching.
MARCH, 1951
www.americanradiohistory.com
AmericanRadioHistory.Com
15
Fig.
(left). Fairchild Unit
1
627 equalizer which employs the circuits described. Fig. 2
variable equalizer chassis.
(right). Internal appearance of
A Continuously Variable
Equalizer
WENTWORTH
FLING
D.
Electrical details of a non -passive equalizer which offers a
wider range of frequency correction than is usually available
III
I
COM M CN IC:\T IONS,
BROADCAST -
and recording industries have
been using equalizers for many.
many years and they've been unhappy
about it. Telephone lines have frequency
losses which must be compensated for;
dramatic programs require special effects; pre-emphasis for noise reduction
and diameter loss compensation is necessary in record making, and frequency response must be adjustable for record
playback. Every broadcaster and recordist is familiar with equalizers and
their limitations in application.
Until recently, no genuine all- purpose
Vice-Pres. and Gen. Mgr., Fairchild Recording Equipment Corp., Whit estone,
New York.
ING,
I
equalizer has been available cornIllercially. The nearest approach to versatility was an L -C resonant -circuit
6J5
INPUT
INPUT
PAD
65G7
REACTANCE
TUBE
HF
LF
BOOST
BOOS
650/
AMPL
ATH.
. F OL.
I_-
REC T
6E5
ND CA
OR
6SN7GT
-
I
UNIT 627
cc
10000
CYCLES PER SECOND
Fig. 3. Low- and high- frequency boost circuits provide response curves of this
type, but frequency peak may be set at any intermediate value desired.
16
OUTPUT
PAD
NON
ROLL
OFF
gram of variable
equalizer.
1000
pUTPUT
/\
TYPICAL VARIABLE EQUALIZER
-
AMPL.I\ IAMPL
OFF
HIGH A LOW FREQUENCY BOOST
100
6SN7GT
LOW
ROLL-
Fig. 4. Block dia-
I
FREQUENCY
which could either boost or attenuate at
both ends of the spectrum. One reason
for the lack of equalization versatility
has been the tendency among broadcasters to depend on passive circuits
those including only elements of L. C,
and R, and not incorporating vacuum
tubes.
Vacuum tubes with resistance -capacitance circuits are capable of producing wider and more flexible equalization effects. This is demonstrated by
the new and interesting unit' diagrammed herein. It can produce roll -off or
boost, or a combination of the two at
both ends of the controllable range. The
frequency at which the response curve
begins to change is continuously variable at each end. Through separate controls for high- and low-frequency channels, a maximum boost of 16 db and a
i
Fairchild Unit
627
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
MARCH, 1951
6J5
C98IL
3
C6
7000
II
CLOCKWISE
Pt
60011 1-PAD
F.
VI
V2
R4
°007`8251(
t
4
1
.00áá
R9
C.5
P2
60011 7-PAD
¡¡
l/
Meg
C11
LI
.05
R2
UTC
a
S-23
.0025IF
Ç5
C23
25
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R14
o
R6
R7
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6SN7
Rs
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FULL
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15000:600=
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o-Z
R46
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20
C16
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C14
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.0024
R32
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R12
6SN 7
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R35
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22A-
R22C
33v;
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f
R27
R30
R31A
Selec
Spec
R29
R
CONTROLS
26
SW-
High Roll
Low Frequency
Low Boost
R22A,B,C
R18
maximum attenuation of 25 db at the
equalization peak is available. The mid frequency level can be held constant
from input to output so that the unit
causes no insertion loss whatever. As
can be seen in Fig. 3, the boosts are comparable in steepness of slope to those obtained with passive L -C equalizers. The
fact that the turnover frequencies are
variable continuously rather than in
steps represents a large additional operational advantage.
The unit contains six tubes and
mounts on a standard 19 -inch rack, taking up vertical space of 7 inches. Eight
controls are on the panel. An indicator
tube aids the operator in setting the input level at a point consistent with optimum distortion -less conditions. The
completed continuously variable equalizer is pictured in Figs. 1 and 2, and
the circuit is block -diagrammed in
R30
R28
8A-7,
R21A,B,C High Frequency
R34
High Boost
Unit 627 Variable Equalizer.
Fig. 5. Complete schematic of Fairchild
Fig.
Low Roll
I
R46
n
R
20
R
C20
25
T2
B+
+yC27b
down to below 2 cps (down 3 db at 1.6
cps), but each of the others causes a
drop in low -frequency response. This
is illustrated by the curves of Fig. 6.
[Continued on page 29]
tance coupled to V,. The coupling capacitor is not fixed, however, different
values being selected with the LOW ROLL
switch. With the 1 -p.f capacitor in use,
transfer to the grid is nearly uniform
J
a LOW FREQUENCY ROLL
TYPICAL VARIABLE EQUALIZER
UNIT 627
HIGH
o
-10
j
a
o
á
-20
-30
-40
4.
Circuit Description
A 600 -ohm line is connected to the
variable input pad and a line-level signal
applied. A low-frequency roll -off circuit
precedes the first stage. Between its
plate and the following grid a 6SG7
reactance tube is in shunt with the signal
to provide high -frequency roll -off. A
variable attenuator enables the output
level to be adjusted to provide operation
as a zero gain device. The high- and
low -frequency boosts are provided by
a pair of parallel -T networks in a feedback loop around V, as seen in the
261,
t
s
FREQUENCY - CYCLES
is loaded.
The transformer secondary is capaci-
AUDIO ENGINEERING
PER
.
6
,
i000
10,000
SECOND
Fig. 6. Low- and high- frequency roll -off curves obtainable with the equalizer.
HIGH
a LOW
TYPICAL
FREQUENCY CUT-OFF
VARIABLE EQUALIZER
UNIT 627
schematic, Fig. 5.
Three input terminals are provided.
though the unit is designed for unbalanced -line operation, to conform with
good practice of carrying audio on two conductor shielded line to minimize the
danger of developing a hum loop. The
secondary of the input transformer T,
s
100
Curve No.
Low Roll
Low Freq
Low Boost
I
2
Curve No.
High Roll
3
I
2
3
22
50
90
13
13.5
s
5.748,
13
100
s
5
re1
1000
3
10
2
1
5.8
9
10
High Freq
High Boost 7
7
5
12
11
r
s
s
7
10000
FREQUENCY - CYCLES PER SECOND
Fig. 7. By combining effects of roll -off and boost circuits, additional curve
shapes may be obtained easily.
MARCH, 1951
www.americanradiohistory.com
AmericanRadioHistory.Com
17
New Broadcast Lightweight
Pickup and Tone Arm
L.
J.
ANDERSON
and C.
R.
JOHNSON
A discussion of the effects of tone arm on the overall performance of a pickup designed for broadcast station use.
used for the 78- r.p.m. home records, the
total force which may safely be applied
to the stylus will be still further reduced.
The fact that the stylus pressure must
be low also makes it necessary that the
mechanical impedance of the moving system of the pickup be low as viewed from
the stylus tip. If it is not, the pickup will
not track well and records will wear
rapidly. On the other hand, the force
must not be too low or the pickup will
skip grooves when the turntable is
subjected to mechanical excitation such
as might be caused by building vibration.
A truly universal pickup is no longer
possible without considerable compro1. New pickup and arm designed
for playing both fine- and standard groove records in broadcast station use.
Fig.
lightweight pickup and tone
arm (MI -11874 and MI -11885 respectively) have been designed to
fill the need for a high -quality broadcast
pickup combination for playing fine groove records, both 33 1/3 and 45 r.p.m.
The most popular application of this
new design will be in combination with
the present Universal Pickups for
broadcast station installations with RCA
70 -D Transcription Turntables, thus
providing broadcasters with transcription pickup facilities for handling all
three speeds-33 1/3 and 78 r.p.m. with
standard groove, and 331/3 and 45
r.p.m. fine groove. Existing turntables
are easily adapted, and present filters
in these turntables may be utilized by a
simple addition of a few small components such as resistors and capacitors.
-though designed
to operate as a unit
-be separable to the extent that for each
type of record a pickup having the optimum stylus size be available.
The tone arm should have bearings
with low coefficients of friction, and the
inertia about both horizontal and vertical pivots should be low so that excessively large forces will not be applied to
the stylus when wavy records or records
with eccentric grooves are played. Care
must also be taken to place tone -arm
resonances below the audio range, but
not in the range where the system may
be excited by the wavy starting grooves
which are present in some 78- r.p.m. records.
Figure 1 shows the complete pickup
and arm mounted on a conventional
broadcast turntable, along with the Universal Pickup. Figure 2 shows two views
The new
Design Considerations
The introduction of fine- groove records made of relatively soft materials,
coupled with a desire of the user for
extended frequency range and lower distortion, has emphasized many of the
problems inherent in the design of pickups and tone arms. Stylus pressures
must be low to assure both long record and stylus life; since the fine -groove
stylus diameter is about one -third that
Audio Engineering Section, Radio Corporation of America, Camden, N. J.
18
Fig. 2. Pickup heads compared to a
standard steel scale to show their size.
er
Fig. 3.
Fig. 4. Curves showing correct length
of arm as a function of center distance
and radii of records.
Essential tone arm and disc
dimensions.
mise because the difference in groove dimensions between 78- r.p.m. records and
fine -groove records is so great. A stylus
which will play 78- r.p.m. records satisfactorily will ride the top edges of the
cut on fine -groove records, and a pickup
stylus specifically designed for fine groove records will ride the bottom of
the groove in the 78- r.p.m. records. Both
conditions result in noisy reproduction
and possibly poor tracking. It is, therefore, desirable that the pickup and arm
Fig. 5. Curves showing tracking error
for
a
straight arm.
and I 11.0 in. 2) d = 12 in.
and l= 12.8 in. 3) d = 16 in. and i = 16.7
in. r, = 8 in. and r, = 2.5 in. for all three
conditions.
1) d
10 in.
AUDIO ENGINEERING
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AmericanRadioHistory.Com
MARCH, 1951
CUTAWAY VIEW
ADVANCEp
FOR
U1
rRa HIGH FIDELITY
`
The Jensen G -610 is designed to achieve the highest possible
quality of sound reproduction, and yet be a compact unitary assembly.
This 3- channel system in one package has the widest frequency range
and the lowest distortion available today. Typical of the advanced know how in acoustics represented here are such features as very low crossover
plus compactness, due to articulation of mid -channel horn with lowfrequency diaphragm
the unique precision compression driver unit
built -in ruggedness and reliability combined with precision construction throughout. Write for data sheet 160.
...
enge fl
vr and Contrat
Crossoe
a separate
Network is
with Ping"'
an
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t for speaker
DIVISION
and impeectiondance-odiasting
neededl.
/rpnsformer (if
OF THE MUTER COMPANY
6601 SOUTH LARAMIE AVENUE
AUDIO ENGINEERING
MANUFACTURING
COMPANY
MARCH, 1951
www.americanradiohistory.com
AmericanRadioHistory.Com
CHICAGO 38, ILLINOIS
19
(left). Experimental light- weight tone arm. Fig. 9 (right). Experimental arm of box section.
rrs +ls Ds
error is a function of the effective tone -
Fig. 6
of the commercial version of the pickup,
which is available with two stylus radii
-1.0 and 2.5 mils -both of diamond to
assure long life. A total force of 8 grams
is required for the 1.0 -mil stylus and 12
grams for the 2.5 -mil stylus. The pickups
may be interchanged readily, and the
difference in the required stylus force
is obtained by internally weighting the
pickup which has the 2.5 -mil stylus. No
change in tone arm balance is required
when the pickups are changed.
.10
.5
db
o
-5
-10
15
S
.
FREQUENCY
.1
.
G
,
100
-
CYCLES PER SECOND
arm length, the distance from the center
of the turntable to the vertical axis of
rotation of the arm, and the position of
the pickup on the record. The effective
length of the arm is the distance from
the stylus tip to the vertical axis of rotation for the arm.
Increasing the length of the arm will
make decreasing values of tracking error possible. Since there are obvious
physical limitations to the arm length.
the expedient of turning the pickup at an
angle to the arm is an excellent means
of reducing the tracking error. The
scheine is to so select the effective arm
length and pivot position that the angle
of error at the outside of the largest,
and the inside of the smallest records
to be played will be equal. The head is
then offset by this angle and as a result
the tracking error at the extremes will
be zero, and as will be shown, the error
at intermediate points is also small. Fig-
Fig. 7. Torsional resonance in tone arm.
Tone Arm Design
Although the design of the pickup itself is important if good quality and
tracking are to be assured, this paper
is principally concerned with the requirements of the tone -arm design. The
arm used with the lightweight pickups
is the result of a long series of experiments with arms of different types
arms which were spring balanced instead of counterweighted; in which ball
bearings were extensively used; and
in which the arm section was rigid and
the pickup head pivoted -but all were
discarded for one reason or another and
the problem resolved itself into refining
the design of the more or less conventional tone arm.
-
Tracking Error
Error in tracking occurs whenever
the record radius through the stylus
point does not coincide with the path
along which the stylus is driven by the
record modulation. The distortion introduced is a function of the wavelength of
the recorded signal and becomes increasingly serious for high frequencies and
the inner record grooves. The tracking
20
CR
Il2
F
ILz
m,
2
Fig. 8. Equivalent
circuit of pickup and
tone arm.
ure 3 shows the essential tone arm and
disc dimensions.
1= the distance from the stylus
to the vertical axis of rotation for the arm.
D= the distance from the center
of the turntable to the vertical axis of rotation for the
arm.
r, and r, = the radii at which the tracking error is to be made equal
for a straight arm.
ß= tracking error (90 °
From the cosine law for a triangle
r,r +ls Ds
Cos a,=
2
r,l
(1)
cos as =
If
a, is then assumed to be equal to as,
equations (1) and (2) may be solved
for
l= VDs f,fs
(3)
This function is plotted in Fig. 4 and
the only restriction. for practical purposes, in the selection of D and l is that
D should be larger than r,.
When the proper arm length has been
calculated or selected from the foregoing, the offset angle ß to make the
tracking error zero at both the inside
and the outside of the record may be
calculated from
16= (90 °°
a,)
.
(4)
+l
ß=90°COs-'
D'
2r,1
(5)
Figure 5 shows a plot of the above for
several conditions. If the head is offset
by the angle shown for the end points of
the curves, the maximum tracking error
will be the difference between the
highest and lowest points. For the worst
condition shown this is less than 5 deg.
The radius at which the deviation will
be a maximum may be determined by:
d cos a, r4 - 1s +T1s
dr
`
.._
2
_
.
..._
15db
.
S
I
3
3
loo
FREQUENCY
S
7
S
loon
CYCLES PER SECOND
'
-
,
,0000
Fig. 10. Torsional resonance in experi-
mental tone arms.
1) Tone arm with plate welded to bot-
tom. 2) Tone arm with 1 /8 -in. wall. 3)
Tone arm with 3/32-in. wall. 4) Final
design.
AUDIO ENGINEERING
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AmericanRadioHistory.Com
(2)
2 rsl
MARCH, 1951
shown in Fig. 7. This model employs
an arm built of a box section of thin
aluminum alloy in order to keep to a
minimum the moment of inertia about
the vertical and horizontal pivots. In
addition to the usual resonance at about
25 cps, another disturbance takes place
around 160 cps. This is due to a torsional resonance in the arm. The equivalent circuit and the responsible elements
are shown in Fig. 8; rl', Ill, and Cl' are
respectively the torsional resistance, inertia, and compliance of the arm referred to the stylus tip. The remaining
elements involved in the performance
are: CR, mechanical compliance of the
[Continued on page 39]
11.
Lightweight tone arm
and pickup in
final form.
Fig.
r= \/l : D!
(7)
The value a, at this value of r will be:
a, =cos
,
lightweight tone arm and the response frequency characteristiè of this arm is
(8)
l[v1 D'J
Attention..
Audio Engineers!
The maximum tracking error which
will result when the head is offset an
The effective
angle 13 will be (a,
length chosen for the first experimental
arms was 16.7 in., resulting in a maximum tracking error of 3° 40'.
a,).
Tone Arm
"Audio" is 60% of Radio. IRE
fully recognizes its importance! The new IRE Audio
Professional Group, under Leo
Beranek, Chairman, has more
than a thousand members.
One of its activities has been
the scheduling of audio papers
and sessions at the IRE Convention.
R
Test records having discrete frequency bands resulting in point-by -point
data are generally not suitable for exploring tone -arm performance because
2.5 MIL STYLUS
12 GRAMS
Throughout the meeting many
papers are of interest to Audio
Engineers. But Thursday particularly is "Audio Day" with
the morning and afternoon
sessions listed below designed,
timed and placed for you.
They will be in Blue Hall on
same floor with Audio Center.
AUDIO Technical Session
O
t
).5
t
3
100
3
.f
3
t
12.
a. f
, 3000
FREQUENCY - CYCLES PER
Fig.
"A
RGNAMS,
MIL.
Single -Ended Push -Pull Audio Amplifier"
-A.
Morning)
Peterson and D. B. Sinclair
"The Application of Damping to Phonograph Reproducer Arms"
-W.
30000
S. Bachman
"Transient Testing of Loudspeakers " -O. H. Mawardi
SECOND
"A Practical
Typical response of pickup,
tone arm, and filter.
Speech- Silencer for Radio Receivers " -R. C. Jones
Symposium: LOUDSPEAKERS (Afternoon)
of the sharpness of the arm resonances
encountered. Therefore, continuous
curves were taken on all tone arms by
the following method: A disc record was
cut from the output of a beat- frequency
oscillator when the oscillator was driven
through the frequency range by mechanical linkage to a continuous curve recorder. The testing then consisted simply of playing back the disc, using the
arm and pickup under test, and recording the output on the curve recorder
which was used to drive the oscillator
when the disc was cut. The result is a
continuous record of output vs. frequency. Final data were taken by the
Variable Speed Turntable method for
greater accuracy.'
Figure 6 shows the first attempt at a
"Amplitude and Phase Measurements on Loudspeaker Cones"
-M.
S. Corrington
"Design Elements for Improved Bass Response in Loudspeaker Systems"
-H.
T. Souther
"Direct- Radiator Loudspeaker Mounting " -H. F. Olson
"Physical and Electrical Constants of Direct -Radiator Loudspeakers"
-L. L.
Beranek
Registration- Non -members $3.00
AS EXHIBITED AT THE Radio Engineering Show
Grand Central Palace
See
the Exhibits
-
Audio Center
and Theatres
3rd Floor.
1H. E. Haynes and H. E. Roys, "A variable
speed turntable and its use in the calibration of disk reproducing pickups. Proc. IRE,
vol. 38, no. 3, March 1950.
AUDIO ENGINEERING
(
March
19 -22
1951
MARCH, 1951
www.americanradiohistory.com
AmericanRadioHistory.Com
The 1951 National Convention
and Radio Engineering Show
of the
INSTITUTE OF
RADIO ENGINEERS
The Waldorf- Astoria Hotel
and Grand Central Palace
New York City
21
AUDIO
engineering society
Containing the Activities and Papers of the Society, and published monthly as a part of AUDIO ENGINEERING Magazine
OFFICERS
President
Bob Hugh Smith Western Vice. -Pres.
Colvin
Lawrence Shipley Central Vice. -Pres.
C. G. McProud Executive Vice -Pres.
Norman C. Pickering
Secretary
Ralph A. Schlegel
Treasurer
john
Audio Engineering Society,
Box F, Oceanside, N. Y.
D.
.
Loudspeaker Damping
ALBERT PREISMAN
1. A discussion of theoretical considerations of loudspeaker characteristics, together with a
practical method of determining the constants of the unit as a preliminary step in obtaining satisfactory performance.
Part
in the
design and application of loudspeakers is the adequate damping
of their motion. Thus, owing to the
masses and compliances involved, the
sudden application or removal of current
in the voice coil tends to produce a
transient oscillation of a damped sinusoidal nature.
In particular, the sudden cessation of
current in the voice coil may find the
loudspeaker continuing to vibrate in the
manner described, so that the sound
"hangs over ". Any one who has experienced this unpleasant effect will seek
ways and means to eliminate it.
In the case of a horn type loudspeaker, the horn imposes in general
sufficient mechanical loading to damp
out such transient response of "hangover", and also serves to limit the exursions of the voice coil so that it does
not operate into the nonlinear portion
of the air -gap magnetic field. The damping also serves to minimize nonlinear
compliance' of the suspension system by
limiting the amplitude of oscillation.
However, if the horn design is limited by such considerations as maximum
permissible mouth area and is operated
at a frequency not too low to be transmitted by the horn taper yet low enough
so that appreciable reflections occur at
the mouth, then the horn may cease to
act as a mechanical resistance, but instead become predominantly reactive,
and thereupon cease to damp a resonance in the speaker unit occurring in
this frequency range. In such an event
other means of damping will be of value
ONE OF THE CONSIDERATIONS
Radio Engineering
Washington, D. C.
Capitol
and is mainly reactive at the lower
frequencies. Hence mechanical damping
of the unit is small in magnitude, and
"hangover" effects may be particularly
noticeable.
A reflexed cabinet may help to load
the loudspeaker, or at any rate to produce a two-mesh mechanical network
exhibiting two resonance peaks, neither
of which is as high as that of the unit
by itself or in a flat baffle. Nevertheless, the damping may still not be sufficient to produce "clean" low- frequency
tones.
Hence, in general. it is advisable or
at least desirable to provide sufficient
damping of the direct -radiator type of
unit by means of its electrical characteristics. so that whether it is operated into
a horn. reflexed cabinet. or simply a flat
baffle, it will be adequately damped.
An important point about electrical
damping is that it represents high
rather than low efficiency of operation.
just as a horn does. On the other hand.
were some material such as viscaloid
employed to provide the required clamping, the electrical input power would in
part at least be converted into heat energy in the material instead of into
acoustic energy, and thus represent a
Mc
Ma
Ce
f
Institute,
Responsibility for the contents of this
paper rests upon the author, and statements contained herein are not binding
upon the Audio Engineering Society.
22
to the designer or applications engineer.
In the case of the direct- radiator
loudspeaker unit, the air load is small,
Fig.
1.
Equivalent circuit of loudspeaker
unit at low frequencies.
decrease in efficiency. It will therefore
be of interest to examine damping produced by the electrical characteristics of
the system.
Motional Impedance
When an alternating current flows in
a voice coil, it reacts with the constant
magnetic field to produce an alternating
force which causes the voice coil to
vibrate at the frequency of the current.
In so doing, the voice coil cuts through
the magnetic lines, and generates a
counter electromotive force, c.e.m.f.
The action is exactly similar to that
of the rotating armature of a d.c. motor
-the
armature generates a c.e.m.f. by
its rotation in the magnetic field. Con-
Z,
e
Fig. 2. Mechanical characteristics of
speaker as seen
from voice -coil
terminals.
sider the case of the loudspeaker voice
coil. The electrical c.e.m.f. which is generated, tends to oppose the flow of current in the coil, just as if its impedance
had gone up. After all, one ohm of intpeclance simply means a one volt drop in
the unit for a one -ampere current flowing through it; i.e., volts per ampere.
In the case of the loudspeaker. the force,
and hence motion and c.e.m.f., are proportional to the voice coil current, so
that a ratio is involved which is an ap-
parent impedance.
Hence, when a loudspeaker voice coil
AUDIO ENGINEERING
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cme-
MARCH, 1951
permitted to vibrate. its impedance
apparently goes up. The increase in the
impedance owing to its motion is known
as the MOTIONAL IMPEDANCE, and it is
measured in ohms just as the electrical
impedance of the voice coil is measured
is
in ohms.
Several characteristics of the motional
impedance can be readily analyzed qualitatively. In the first place, the lower the
mechanical impedance, the more readily
does the voice coil vibrate, and the
higher is the induced c.e.m.f. for a given
current flowing through it; i.e., the
higher is its motional impedance.
A second point to note is that the
greater the magnetic flux density, the
greater is the induced c.e.m.f., and the
higher is the motional impedance of the
voice coil. Finally, we note that if the
total length of voice -coil wire is increased, there is more conductor cutting
the magnetic field, 'and hence more
c.e.m.f. induced. Therefore the motional
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Model 510C
Model 510S (with switch)
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Code: RUTUF
Code: RUTUS
.
BULLET"- Specially designed to provide quality music and speech reproduction at
moderate cost. A streamlined unit that lends itself
to fine -quality, low -cost installations where durability is an important factor. Features high output, good response, high impedance without the
need of a transformer.
The "GREEN
Code: RUDAL
MODEL 520
Fig. 3.
Circuit of Fig. 2 with addition
of generator.
The "RANGER "
impedance increases if the length of
voice coil wire is increased.
The actual quantitative relations are
as follows:
Zme_(Bl)7x109
Z,
(1)
Model 505B (Medium Impedance)
Model 505C (High Impedance) .
MODEL 505
The "DISPATCHER "
where Zm, is the motional impedance in
electrical ohms; B is the magnetic flux
density in gauss;
length of voice coil
conductor in cm., and Zm is the mechanical impedance in mechanical ohms
I.
(dynes/cm/sec.).
Loudspeaker
Low -Frequency Resonance
The mechanical impedance Zm of the
loud speaker unit varies considerably
over the frequency range. However, in
a direct radiator its value and effect at
the lowest audio frequencies is of greatest importance, particularly with regard
to "hangover' effects, and hence will be
analyzed at this point.
At the lowest audio frequencies, the
loudspeaker unit acts mechanically as a
simple series resonant circuit. This is
illustrated in Fig. 1. The masses involved are those of the cone, Me., and of
the air set in motion by the cone Ma.
The latter is a function of frequency,
but can be assumed fairly constant over
MODEL 520SL -7
r
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-
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Complete dis-
patching unit. Designed to handle
the most severe field requirements
of paging and dispatching systems. Ideal for police, railroad, taxicab, airport, bus,
truck and all emergency
communications work.
Operates both micro phone and relay circuits.
High output, high speech
MODEL RS
intelligibility. Unit is
preassembled.
Code: RUDAN
Model 520SL-20 20cesIC . . . Code: RUDAF
CONTROLLED
RELUCTANCE CARTRIDGE
-
Available for service installation. Ideal for
replacement of crystal cartridges in Shure
cases of Models 707A, 708 and carbon cartridges in the 100 and "CB" series. Can also
be used in most semi -directional microphones
where space permits. Supplied with rubber
mounting ring.
Code: RUTUC
Specific in/emotion provided on request.
Patented by Shure Brothers, Inc.
SHURE BROTHERS, Inc.
Microphones and Acoustic Devices
[Continued on page 37]
AUDIO ENGINEERING
-
Recommended for those applications where long lines are used and a rugged
hand -held microphone is needed. Ideal for outdoor
public address, mobile communications, hams,
audience participation shows, etc. Designed for
clear, crisp natural-voice response of high intelligibility. Has heavy -duty switch for push -to -talk
operation.
225 West Huron St., Chicago 10, III.
MARCH, 1951
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Cable Address: SHUREMICRO
23
EDWARD TATNALL CANBY
How to Widen the Orchestra
continued apace, chez
this department, on the further implications of the "Hole in the Wall"
way of explaining our listener- reactions
to reproduced music. (Æ for Oct.; this department, Jan. 1951.) It's inevitable, this
pondering. Every person who listens to
reproduced music for itself must form
some conception, conscious or unconscious, of the sense of presence which
his loudspeaker provides
for him -he
must mentally visualize, somehow or
other, the actual existence of the music
before his ears. And once one begins to
think consciously about what one is or isn't
visualizing, once a mental investigation
in medias res gets underway (i.e., once
we begin thinking about while it's actually
happening), we are bound to discover
that a conception such as that of an
imagined hole in the living room wall
through which the music enters is necessary. And useful, too, if one is curious as
to an explanation of what is or isn't
natural in sound reproduction. I'm always
curious.
A considerable interchange of mail with
an engineer correspondent from Vancouver, B.C. bears directly on this tantalizing business of imagined sound source
as one listens to reproduced music. Like
many another engineer, this one had been
working on the problem himself ; he, too,
had conceived of the hole in the wall independently (as no doubt have others of
us in one way or another) and we had
actually had some discussion of it before
either of us ran into Mr. Voigt's article
in the October lE last fall.
PONDERING
has
-
Runt Orchestra
There's one significant addition, howwhich the Vancouver hole- in -thewall research makes to what has already
been said, that widens the extent of the
conception and hence its usefulness. Widen,
quite literally-for that is exactly this engineer's argument.
How can one increase the seeming
width of the apparent sound source, the
orchestra or what-have -you, as imagined
in space "behind" or on the other side
ever,
*279 W. 4th St., New York 14, N. Y.
24
of one's living room wall? For, as my
friend Mr. Gordon points out, one must
be able to imagine an orchestra in its
natural width at whatever distance the
recorded liveness suggests. If not, then
the orchestra sounds pigmy or undersized, and the visual conception distorts
the music. (If, as I suggested in January,
high fidelity is faithfulness to the imagined original, then an imagined pigmy sized runt -orchestra is clearly an inadequate mental image and so it is a distor-
tion ! )
Which prompts me to observe immediately that one can well think of the
"hole in the wall" in another way : After
'all, one does not "hear" an actual hole
in the wall ; one hears sound which appears to be "behind" the wall. The "hole"
is a purely intellectual rationalization
a common -sense explanation of the fact
that one is apparently listening right
straight through solid plaster and brick.
There has to be a "hole." And so we im-
-
agine one.
Area of Binaural Tolerance
-
How, then, to widen the hole-how to
make the sound source -the orchestra
seem as wide as it should be? My Vancouver correspondent has a most interesting hypothesis there which I'll take
the liberty of paraphrasing, at my own risk,
hoping to do it no injustice. With a point source speaker the listener can, with his
binaural sense of direction, attribute (imagine) the source only within a very narrow angle, an angle which includes the
speaker cabinet and little more. The area
of our two -eared listening tolerance-the
angle of width plus the depth that we can
imagine
quite small. Any musical source
that ought to sound wider than this included
angle is distorted in the hearing. Made
pigmy. This seems to me a very sound idea.
If one can increase the Area of Binaural
Tolerence (i.e., imagine a larger width
and so, combined with the imagined depth,
a larger imagined area) -then one has a
more natural imagined effect. This, as you
will realize, is exactly what any system of
reflection or other wide- source arrangement
does; my "French doors" of January were
[Continued on page 26]
-is
Pops
RUDO
GLOBUS
pathos of a viciously distorted life, the
extraordinary fulfillment of a creative
life, and the stupidity inherent in the suicide
of a whole aspect of our collective lives.
There will be several points which emphatically repeat the conditions already
stressed in this column; they are being
stressed once more because of the repeated failure of a few members of our
kind to accept the facts of life. My reviews
this month are a necessary part of this piece,
for they exemplify in a concrete way the
dull, apathetic and mediocre way in which
the recording industry has collaborated in
murdering a thing of great beauty. The
question will legitimately be asked as to
why a piece such as this is included within
the covers of a magazine directed toward
those whose interests are classified under
the broad category of "audio engineering."
The answer is radically simple : nobody can
make a recording, build instruments directed
towards the reproduction of the recording,
or analyze the efficiency and adequacy of
"techniques" unless he is fully aware of
the purpose behind his work. So sit tight
what follows will not make pretty
reading.
The newspapers, wire services, syndicated
columns and magazines carried a brief item
this past month, noting the critical physical
condition of one "Pee Wee" Russell. The
circumstances surrounding the discovery of
the noted jazz clarinetist were veiled in ambiguous and meaningless language. Found
unconscious on a street in Los Angeles,
Russell was removed to a hospital where the
tall hulk of a body is being carefully preserved in a state called "life." Alcohol,
malnutrition, and a few other choice causations are mentioned briefly. Numerous
groups of the jazz faithful have organized
various local benefits to supply an ingredient
called "money" to assist the various wonder
[Continued on page 39]
15 Palm Lane, Westbury, N. Y.
.
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
S.
THIS MONTH'S COLUMN arises out of the
MARCH, 1951
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AUDIO ENGINEERING
MARCH, 1951
www.americanradiohistory.com
AmericanRadioHistory.Com
RECORD REVUE
[from page 24)
Preferred
another way of saying that I had achieved
a larger imagined area "behind" my wall.
My Vancouver correspondent has gone so
far as to put this theory of Area of Binaural Tolerance to the test in an actual
working model, a reproducing system gets
its wider area in a manner that is well
worth a moment of thought. (The basic
idea has been suggested to me several times,
but this correspondent has developed a complete system and has got full protection
on it already.)
Haphazard reflection along a wall, from
a corner, or sound distribution via multiple
openings in some of the new horn -loaded
enclosures, or distribution from multiple
speakers -these are ways of achieving the
desirable wider sound source and the larger
imagined original which is the thing we
want. This particular system is different.
The method, fully protected as I say, is
simplicity itself.
The speaker, mounted rear-to- the -listener, operates directly into a concave reflector of particular dimensions determined
experimentally. Simple laws place a virtual
image of the speaker facing towards you,
at a distance and considerably enlarged
right through an imaginary hole in the
wall behind the reflector. The whole thing
(bad pun) is a unit and has the virtue,
obviously, of being independent of local
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room conditions.
As far as the ear is concerned, the
speaker is on the other side of the wall and
enlarged. It reproduces concert sounds,
sending them back (apparently through the
"hole," complete with liveness distance effects that put the orchestra even further
back in that nice, wide imagined area, the
Area of Binaural Tolerance, which the
"distant" speaker gives you. Ought to sound
good, I'd say. A thought- provoking idea,
anyhow.
NEW RECORDS
SUPER -MISCELLANEOUS
Twilight Concert; Program #2.
Columbia Symphony Orch. Rodzinski
Columbia LP:
ML 4337
"Abram Chasins and Constance Keene"
Mercury LP:
Brahms; Chasins)
MG 10061
A Promenade Concert.
London Symphony, Weldon
M -G -M LP:
E -525 (10 ")
LP being what it is, (you can't put less
than, let's say, 12 minutes on a 12" side
or the customers grouse. .
.) the miscellaneous pot -pourri of items is becoming
increasingly popular with the record companies. Package deal. The higher brows
frown, but without much doubt these
records offer the hi -fi man a highly convenient gathering- together of a lot of different music treated with a given recording
technique, all on the one record. Good idea.
The first Twilight Concert struck me
as one of the finest recordings Columbia
had made to date. I don't have it at the
moment for direct comparison ; number 2
is a dilly also, but not exactly in the
spectacular category. The recording is very
live, with a rather soft, un- brassy quality
that I find very pleasing.
But- here's the interesting question.
Compare this with M -G -M's Promenade
Concert. The M -G -M disc is the ultimate
.
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AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
MARCH, 1951
in an engineer's dream of brassy, sharp,
clear -cut recording. With full NAB roll off it remains brilliant, edgy, almost (but
not quite) distorted. Sounds like a bit more
pre- emphasis than the Columbia LP curve
demands. On the other hand, in direct comparison, the Columbia Twilight disc, same
conditions of playing, is distinctly duller in
the highs and a decrease in the roll -off
brings them out so that they are not unlike
the M -G -M disc. Could it just possibly
be that Columbia is quietly beginning to
use somewhat less than the full official LP
pre- emphasis in their recent recordings?
I've been suspecting that possibility for
some time, and if so, welcome it as a wise
step. General engineering opinion will agree,
most likely.
-it
(But then again
all may be an
acoustical effect. Never can tell. Try these
two for yourself.)
Musically the Twilight disc, conducted
by Rodzinski, is on a high level of performance for such a venture. The M -G -M
disc is average -acceptable playing but
nothing super.
Strange that two-piano music records so
well. The Mercury disc, Brahms on one
side, some fairly serious and fluently, easily
modern works by the pianist himself on
the other, is a nice example of it. Only the
high hiss level is to be deprecated.
"The Only Good Doctor
Is A Hoss Doctor!"
-
Leroy Anderson, Classical lake Box: Kabalevsky, The Comedians.
Boston Pops Orchestra, Fiedler.
RCA Victor LP:
LM 1106
his patients can't fool him! ", he added to make
his point. The noted humorist's trenchant remark
may be applied today to the skilled technicians in
the recording field who have for many years used
the tape and discs perfected in Reeves Soundcraft
Laboratories. We haven't fooled them -nor have we
tried. Perfection, nothing less, has won us the confidence of this exacting industry.
From Reeves Soundcraft Laboratories come magnetic
tape offering users ten distinct features that add up
to higher efficiency and fidelity; an assortment of
recording discs to answer every requirement -all
backed by the greater integrity and experience of
the Reeves name, foremost manufacturer of recording and electronics accessories.
"...
Some category-but Anderson's wonderful tomfoolery merits a separate listing of
this disc. Froth, corn, but of the most delightful variety and highly musical to boot.
The Jukebox number mixes "Music, Music,
Music" with a most amazing assortment of
ultra -familiar classics, the while imitating
an elderly jukebox, complete with music
starting several grooves in, nickels swoosh-
ing into slots and even a needle stuck in one
groove! It remains to remark that technically in this disc and the Twilight Concert
Columbia and RCA come closer together in
recorded sound than I can ever remember.
Same apparent pre- emphasis, too, as one
listens -which is surely interesting.
* * *
RCA's new "Treasury" series, replacing
the former Heritage records on 78, comes
in 45 and LP and is an excellent idea. The
first twelve discs are carefully processed
re- issues of old Victor records as far back
as 1904, grouped in convenient and reasonable categories -"Composers' Favorite Interpretations," "Caruso Sings Light Music,"
"Golden Duets," etc.
But most important facet of the enterprise is that it is not restricted to the old
operatic acoustics; the first series gets up
as far as the early 1930's (Lotte Lehmann
in "Rosenkavalier ") and RCA plans soon
to bring out many notable electrical sets of
the 30's and 40's in the 33 -45 format. Fits
the RCA situation perfectly, since at a
time when numerous musically fabulous
RCA recordings were appearing the technical end of the company was perhaps a wee
'Soundcraft tape is made in all types and
lengths to accommodate all tape recorders.
Soundcraft recording discs
available in a variety of
sizes, single and double face.
bit backwards in comparison to competition;
material from that era is not suitable for
up -to -date LP and 45 quality standards as
we all know -and yet musically the stuff is
wholly satisfactory and indeed in enormous
CORF'.
REEVES
demand.
Doubtless other companies will begin
soon to find ways and means of issuing the
great recordings of the 1930's on LP;
Decca, Vox and others have already made
a stab at reissues, without, however, being
entirely honest about the quality end. RCA,
AUDIO ENGINEERING
Will Rogers
TWENTY YEARS OF LEADERSHIP IN SOUND ELECTRONICS
10
EAST 52nd
EXPORT-REEVES EQUIPMENT
MARCH, 1951
www.americanradiohistory.com
AmericanRadioHistory.Com
STREET,
CORP., 10
NEW YORK
22,
N. Y.
EAST 52nd STREET
NEW YORK
22,
N. Y.
27
AITE(rcif°^°".
via its special label, is making the case absolutely clear, and it couldn't be a better
case, for all music lovers.
Incidentally -here's one occàsion when
the issuance of both 45 and LP versions is
well justified. On 45, the old records are
are available singly as in the original (I
hope, anyhow) ; on LP. they are conveniently bunched, patched when possible.
The two forms are equally legitimate.
*
*
*
Where to turn next, what with hundreds
AMC
of LP records to consider? Here's a brief
cross section of items from some of the
of the small LP companies whose output
may not reach your notice.. Some of the
finest recordings of all comes from these
small outfits-which seems to be typical of
the Age of LP.
n
Mendelssohn, Symphony #1.
Stuttgart Philharmonic, Van Hoogstraten.
Renaissance LP:
X -28
Hindemith, Concertmusic for Brass and
Strings: Concertino for Horn and Orch.
Vienna Symphony, Haefner. Franz Koch,
Horn.
Anon. Speaking Voice.
Period LP:
SPLP 515
Two brilliant orchestral recordings. imported as usual from Europe via tape and
pressed here, thereby avoiding the tenfold
cost of musicians in this country. The early
Mendelssohn symphony is overly long but
surprisingly exciting even so; not very
well rehearsed, by the sound of the playing.
Beautiful recording, but strings are rather
close, brass at a distance. The two Hindemith works are really superbly recorded,
with better balance and liveness than the
Mendelssohn above, a soft, undisturbed
quality that still leaves excellent "edge"
on the brass. Dissonant music, especially
the Concertmusic, but of a satisfying sort.
The horn recording is extraordinarily good
-the horn being notably hard to capture.
This is top rate recording. Don't jump
when a woman's speaking voice suddenly
enters!
evitd,
.usatAtvut
Bruckner, Te Deum.
Chorus, Orch., soloist, Salzburg Festival,
1949.
Festival LP:
FLP 101 (10 ")
I.
C. Bach, Sinfonia Concertante in E flat;
K.P.E. Bach, Sinfonia #1 and #3.
Vinenna Symphony, Guenther.
Bach Guild LP:
BG 504
Especially now, when material shortages may make
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quality pays extra dividends. Equipment failures can
mean the loss of thousands of dollars. Altec superiority,
in
engineering, large safety factors, conservative rat-
ings and the use of quality components, is the best
Two more taped imports. The Salzburg
Bruckner is a huge work, with a huge recorded sound, ultra-hi -fi tape; soloists are
too close (very realistic !), chorus and
orch. in background -but still, it's an impressive sound. The music of the Bach
sons, in what to most of us is a Mozart Haydn style, is most welcome, and nicely
recorded here. But watch for Westminster's
duplication of the two K.P.E. Bach works,
made with the same orchestra.
possible insurance against these costly breakdowns.
Invest wisely. Buy the amplifiers that give the greatest
value. Buy Altec amplifiers. They
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perform.
Handel, the Complete Water Music,
National Gallery Orch., (Wash. D. C.),
9356 Santa Monica Blvd., Beverly Hills, Calif.
161 Sixth Avenue, New York 13, New York
Bales.
WCFM LP:
Dorothy Eustis plays
Bach- Father and
#2
Son.
Artist LP:
#501 (10 ")
Schubert, Three Violin Sonatas op. 137.
28
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
MARCH, 1951
M. Mischakoff, vl. Erno Balogh, piano.
Lyrichord LP:
U. 7
The little companies do what they can
to record in this country-on a small scale,
necessarily. The Handel is a long-overdue
venture, bring the other fourteen movements of music to us in a rather wooden
but presentable performance, nicely taped
and LP'd. The Eustis Bach piano is one
of those accidentally ( ?) natural recordings
-sounds just like someone playing in her
own living room ; no studio effect nor concert stage either. The Schubert sonatas are
wide- range, with fine liveness, but the
violin is a bit close and edgy, the piano
excellent in tone but a trace too much in
background. This'll hold up to any big company work nevertheless, and that easily,
mark my words.
Small- company LP is a real challenge
to the industry now, and those readers who
live away from big cities and hear only the
big -company stuff that's widely distributed
in smaller towns had better keep their
eyes and ears opened wide. If you have
trouble in acquiring any of these-write
1E and we'll be glad to help you.
t; e Aze$-
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Tchaikowsky, Symphony #4.
Boston Symphony, Koussevitsky.
RCA Victor 45:
WDM 1318 (5)
This work is a piece of high- intensity
writing and is apt to get bleary and
hysterical when a tired orchestra plays
it for the hundredth time. Paradoxically,
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Koussevitsky's somewhat heavy touch
and the comfortable resonance of traditional Boston Symphony Victor recording combine to keep things well in
hand. The result isn't bad at all. I'd pick
the Koussevitsky 4th (as I picked his 5th
some years back) for all who like Tchaikovsky when he's quiet but distrust any
kind of musical hysterics. An excellent 45.
Wagner, Siegfried, Act. 3, Scene 3.
Eileen Farrell, Set Svanholm; Rochester
Philharmonic; Leinsdorf,
RCA Victor 45:
WDM 1319 (51
There hasn't been much Wagner hereabout lately. Biggest recent news was the
reissue on LP of the several Traubel
Wagner albums, originally issued on 78.
This album adds a third speed to Wagner's
power plant (I can't help
whenever
I listen to a total Wagner recording like
this -the works
get involved in power
analogies!). Not top performers, as in
some of the great Wagner recordings of the
past ; but these do a sincere and musical
job with the difficult third scene. Svanholm is dramatically moving, but wobbles
a bit to much for comfort, nor has he the
steely brilliance of a Melchior. Farrell has
a beautiful Wagnerian voice, her only
difficulty being a lack of the superhuman
breath capacity Wagner takes. Good or-
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MARCH, 1951
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.9/4
r
QUALITY
fit r/
XV
No. 1401
High- Frequency Roll -off
encitc
M A
N
G
$345óo
T I C
E
TRAY
LESS
TAPE RECORDER
FOB. N.Y.
A precision built and thoroughly tested instrument, capable of recording
the full range of audible sound with full dynamic sweep and freedom from distortion.
Only the most expensive professional equipment rivals the tape handling ability of the Con -
-
certone recorder
and none equals its versatility and simplicity of operation. Especially
designed for the most discriminating user, the basic recorder comprises a 14" x 22" rigidly
ribbed, cast, aluminum plate carrying the tape mechanism, dual track heads. a shock mounted
chassis containing erase amplifier, record amplifier, and playback preamplifier, a power supply chassis, mounting lugs for auxiliary equipment, and all necessary switches and controls,
ready for use. Weight: 30 lbs. Easily connected to your existing high fidelity amplifier system.
Monitoring directly from the tape while recording gives a constant check and control on what
is being recorded while it is being recorded. A much prized program is never lost unknowingly,
any departure from proper operation is immediately heard.
High speed rewind in either forward or reverse direction, firm, positive braking and fully interlocked controls assure rapid handling without damaging tape. A special circuit controlling a
cathode "eye" gives accurate indication of the proper record level for best results. A special
locking button prevents accidental erase of recordings.
The Concertone magnetic tape recorder uses any standard reel from the tiny five inch to the
arofessional NAB 101/2 inch reel, together with instantaneous choice of 71/2" or 15" per second
tape speeds, permitting matching frequency response and length of program to operating cost.
High speed rewind, forward and reverse
2500 feet in 60 seconds.
Single or dual track optional.
Size: 22"
14" x 5" mounting depth
below panel.
Frequency response:
2 db from 50 to
12.500 cycles at 15" /sec.
-±- 2 db from 50 to 7,000 cycles at
7.5" /sec.
Total harmonic distortion: Less than 2%
at normal maximum signal level.
Playing time: Up to 2 hours on dual track.
Broadcast studio quality complies with
NAB standards.
-
Separate heads for high frequency
erase, record and playback.
Simultaneous monitoring from the tape
±
while recording.
Prealigned heads quickly interchanged
for single or dual track.
Instantaneous choice of 7.5 or 15 inch
per second tape speeds.
Plays standard 5 inch, 7 inch and NAB
101/2 inch reels.
CARRYING CASE
NO. 501
CONCERTONE TAPE
RECORDER ACCESSORIES
This handsome fitted
custom case quickly and
easily converts the basic
REEL ADAPTERS
recorder
- Accurately machined
to hold NAB
reels on
RMA spindles
standard
300
-
eight inch high fidelity
speaker mounted in detach.
able cover. Convenient to ga
carry; 24" x 15" x 12 ". Weight: 15 lbs.
8950
V
Low inertia 2500 foot reels,
flanged on both sides. Conform to NAB
No. 802
250
recommended standards
a
amplifier x603, and
10%" REELS
NAB
into
portable use. Supplied
with built -in monitoring
of
recorder
401
complete system for
No. 801
101/7
CONSOLE TRAY AS ILLUSTRATED
14.95
TERMINAL VALUES ON QUALITY
PLASTIC RECORDING TAPE
DOMESTIC
PROFESSIONAL
$1.35
2.10
4.20
600 FT
1200 FT
2400
FT.
600
1200
2400
$1.65
2.70
5.40
FT.
FT.
FT.
Terminal Radio Cor
Distributors of Radio and Electronic Equipment
8 5
C
O
R
T L
A N D
T
S
T R
E
E
T
Worth
30
quency at which the response is down
3 db is that at which the capacitive
reactance and the resistance are equal.
Below that point there is some curvature, after which response drops off at
a steady 6 db per octave. With the values
selected for the Low ROLL switch, the
turnovers take place at approximately
100, 200, 350. and 600 cps for positions
2, 3, 4, and 5.
The plate of V, is coupled to one
grid V4, a dual triode operating with
the two sections in cascade. A non-frequency- discriminating feedback is applied between the two stages to improve
characteristics and stability. The output
triode plate is loaded by an audio
choke and coupled through a blocking
capacitor to the output transformer and
the output pad.
N
4
E
W
Y
O
R
K
7
,
N
E
W
.
The high frequency roll -off is controlled by the reactance tube, Vs. When
the tube is adjusted to plate- current
cut -off, the circuit has no effect on the
main audio line, with which it is in
shunt.
As R46 is adjusted, however, and plate
current begins to flow, the tube becomes
active and the continuously variable roll off characteristics shown in Fig. 6 are
obtained. The figures on the curves indicate the settings of the roll -off control. Maximum attenuation of 16 db at
10.000 cps is possible with the circuit as
it was designed.
The principal reason for using a tube
for high- frequency roll -off may be seen
by referring to Fig. 5. R47 and the
series-parallel network of R4e, R4e, and
R49, make up a voltage divider across
the B- supply. By adjusting R4e, the
cathode may be made more or less positive, determining the plate current and
the degree of roll -off. Note that between
cathode and ground there are two
terminals to which an external control
may be connected.
One use for this feature is in diameter
equalization for recording. The highboost controls can first be adjusted to
give the maximum emphasis required at
the innermost diameter. A variable resistance with its slider mechanically
linked to the cutting lathe is then set
initially for small enough resistance so
that, when connected to the EXT terminals, the roll -off will approximately cancel the boost. Then, as the cutterhead
moves inward, the resistance automatically increases to lessen the roll -off
and allow the net response to rise and
compensate for the diameter loss.
Boost Circuits
The basis of the bass and treble boost
circuits is the parallel -T network. It is
is the equivalent of a Wien bridge and
the values are calculated in the same
manner for a null at any given fre-
Y O R K
-3311
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
MARCH, 1951
quency. An important difference is that
one end of the generator and one end
of the load may be connected to a common point, usually ground. The boost
circuits are employed in a negative feedback loop around V,.
In Fig. 5, the two sections of
are
used with the boost networks. The grid
of one triode is fed signal from the output of V,. The first section of V, is a
cathode follower, loaded by a series combination of RJ0 and R/8. The latter has a
resistor R18a across it which is especially
selected at the time of factory test to
give, in combination with R/8 the low boost calibration.
The resistances of the "T" are variable on a ganged shaft so that the frequency of null can be shifted between
20 and 100 cps. The broadness and degree of the null are controlled by R80.
This control directly affects the voltage
passing through the "T" by regulating
the a.c. potential difference between
the input and ground points. It has,
however, no substantial effect on the
over -all level of the signal, as would be
the case if the more obvious method of
grounding the vertical leg of the "T"
and placing the input on the potentiometer arm were used.
The output of the low -frequency
parallel -T is fed directly to the input of
a similar network "tuned" to "resonate"
or reject continuously between 4,000
and 10,000 cps, according to the settings
of its three ganged variable resistors.
The amplitude of the high -boost peak
is controlled in the same manner as is
the low -boost circuit. Here, the second
section of V, is used to isolate the
high- and low -boost controls. The transformer T, adds a 180 -deg. phase shift
to offset the phase inversion caused by
the second section of V,.
The curves of Fig. 3 show what frequency response can be obtained with
typical settings of the low- and high boost controls. Maximum peaks at either
end of the range approximate 16 db.
Figure, 7 indicates how fairly steep
low-frequency cut -offs may be obtained.
For curve 1, the Low ROLL switch is in
position 1 for a gradual roll -off beginning at 100 cps. In addition, however,
the LOW FREQ and Low BOOST controls
are set to boost frequencies somewhat
below 100 cps and so to offset the early
part of the roll -off. When the roll-off is
allowed to begin, the result of the net
effects of the two, the steep slope at the
lower end of the boost circuit's peak
takes over and gives a cut -off effect.
Figure 7 also shows three examples
of variations at the high frequencies.
In curve 3, the HIGH ROLL control is set
for a point near maximum roll -off. The
HIGH FREQ control, however, is set for
boost to offset the early roll -off. As a result, the effective frequency at which
roll -off begins is shifted at will, and the
operator has the valuable advantage of
varying both the slope at the roll -off and
the frequency at which it begins.
V
AUDIO ENGINEERING
SELECTED
for
Hallicrafter -Built SCR-399
Again E -V serves in vital communications! The 600 -D Dynamic Microphone (T -50) is standard equipment
on the famous SCR -399. It insures
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clearly. It is an example of E -V
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E
Substantially Flat
Frequency Response
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Extra Rugged -Withstands
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PHONO -PICKUPS HI -FI SPEAKERS SELF -TUNING TV BOOSTERS
MARCH, 1951
www.americanradiohistory.com
AmericanRadioHistory.Com
31
NEW PRODUCTS
Pour-Position Kier. Flexibility of any
audio system may be greatly expanded by
means of the Audio -Mix, claimed by the
manufacturer to meet the most exacting
demands of multi -microphone recording on
tape, wire or disc. Low in price and simple
in operation the Audio -Mix has ample
gain for microphone and all types of
of particular value in voltage doubler circuits and as bleeders. Available in 2- and
3 -watt sizes with resistances ranging from
one to ten megohms. Type T resistors are
processed at high temperature to insure
high stability with minimum effect due to
aging and humidity. Resistance change due
to either of these will not exceed two per
cent. Manufacturer is Resistance Products
Company, 714 Race St., Harrisburg, Penn.
Tape Recorder Kit. A unique tape recorder kit is now being marketed by Judge
Industries, 676/8 Romford Rd., London,
E.12. As shown, the assembled unit attaches to a standard 78- r.p.m. turntable,
the spindle serving as the shaft for the
cent at full output; hum level, down
db. Included in the circuit is the Scott
dynamic noise suppressor. Loudness control compensates for reduced sensitivity
of the human ear to low frequencies at low
levels. Pre -amplifier is operated entirely
on d.c. and has 500 -cps turnover frequency.
Effective turnover frequency adjustable
between 250 and 1000 cps by means of bass
control. Descriptive bulletin may be obtained by writing direct to Herman Hosmer Scott, Inc., 385 Putnam Ave., Cambridge 39, Mass.
Self- Looking Set Screw Demonstrator.
The improvement in holding power of set
screws to be obtained by the use of the
new Zip -Grip self -locking design is shown
leer
84
phonograph pickups. Built -in attenuators
permits balancing of high- and low -output
signal sources. Frequency response is 2020,000 cps. Size of the Audio -Mix is 8 x 6 x
6 in. and weight is 4% lbs. For full technical description write direct to Pentron
Corporation, 221 E. Cullerton St., Chicago
16, III.
D.O. Power Supplies. Precision control
of d.c. output is featured in a new series
of general -purpose low -voltage power supplies recently introduced by Opad-Green
Co., 71 Warren St., New York 7, N. Y.
Available in ranges of 0 -8, 0 -12, and 0 -28
vdc, all models in the new serles have
continuous output ratings of 10 amperes.
Both d.c. voltage and current may be read
directly on two 3 -in. meters. The units are
designed for operation from standard a.c.
line voltage and bench space requirements
are 8 x 16 in. Descriptive bulletin GPA1
will be mailed on request.
Attenuator Units. Adding to its line of
precision attenuators. Daven announces
Model 650 r -f attenuation network, and
Model 795 carrier -frequency decade attenuator. Model CIO is ;i mod.rately- priced
tape supply reel and a takeup reel. The
recording head is mounted adjacent to the
turntable, and two idlers perform the dual
function of maintaining tension and serving as guides. The arrangement provides
for the use of existing turntables, requiring only the addition of a single dual triode as the amplifier and oscillator. The
kit also provides for the home construction of the recording head, and necessary
parts are included.
New Tape Mechanism. The Sonar model
PTM tape mechanism employs the latest
in electrical and mechanical design, and
when combined with the Sonar PRA amplifier is said to provide a frequency response from 30 to 15,000 cps at a speed of
7% in. per sec. This is comparable to most
machines operating at 15 in. per sec.
The PTM employs three motors, and
uses a magnetic clutch and braking sys-
unit with zero insertion loss and flat frequency response from d.c. to 225 mc.
Range is 100 db in 1 -db steps. Operation is
by means of push- button -type unit with
conventional rotary- decade -type switches.
Model 795 is a box -type unit with conventional rotary- decade-type switches. It permits extremely accurate measurements
from d.c. to 200 Ice. Switch stops prevent
return from full to zero attenuation when
adjustments are being made. The Daven
Company, 191 Central Ave., Newark 4,
N. J. will supply further information on
request.
Noise- Suppressor Amplifier. Although it
represents many improvements over the
original Model 210 -A, the new Scott Model
210 -B amplifier is announced at a considerably lower price. Specifications of the
Model 210 -B, as supplied by the manufacturer, are: Frequency response, virtually
flat from 12 to 22,000 cps; harmonic distortion, less than 0.6 per cent at full 20watt output; intermodulation, less than 0.1
32
conclusively by the use of the new demonstrator model just developed.
These set screws have a unique arrangement of thread which provides a definite
"contra- thrust" action even though the
screw is not set up against the shaft
solidly. When augmented by the additional
pressure of the screw against a shaft,
Zip-Grip set screws do not loosen even
under appreciable vibration, as shown by
the demonstrator.
Engineers, purchasing agents, and manufacturing executives having vibration
problems for which self- locking set screws
or adjusting screws may prove the answer
are invited to request a Zip -Grip Demonstrator, addressing the manufacturer -Set
Screw & Mfg. Co., 342 Main Street, Bartlett, Ill.
High- Voltage TV Resistors. Designed
especially to withstand the high d.c., pulse
and transient voltages encountered in TV
power supplies, RPC Type T resistors are
tern which requires no mechanical adjustment. Separate heads are used for
erase, record, and playback, permitting the
choice of optimum head construction for
each application. This unit will accommodate both RMA and NAB tape reels
from 3 to 10% inches in diameter. Fast
forward and rewind time for 2500 feet of
tape is 58 seconds.
The six -tube PRA amplifier has an illuminated VU meter, built -in loudspeaker,
and monitor jacks. It provides for low -.
impedance microphone inputs, as well as
bridging standard circuits; the output impedance is 600 ohms, at +8 dbm.
For complete information, write Sonar
Radin Corp., 59 Myrtle Ave., Brooklyn 1,
N. V.
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
MARCH, 1951
f
JENSEN
POSITIVE FEEDBACK
[from page
LEAK
LIVINGSTON
MARKEL
MASCO
NATIONAL
PENTRON r
NEWCOMB
e
a
fl
W
151
UNEXCELLED BROADCAST QUALITY AT 7.5" PER SECOND
may be used as the amplifier was finally
adjusted.
This tone compensator makes it possible to compensate for unbalanced program source material. It also provides
a means of adjusting for hearing characteristics. The curves in Fig. 1 provide
an idea of the type and amount of compensation that is needed. It is interesting to note how the frequency- response
curve obtained at the PREAMP INPUT,
shown in Fig. 3, compares with cURve -3
in Fig. 1. Apparently, some of this desirable basic characteristic is lost in
actual playing, shown in Fig. 7. The adjustable tone compensator makes it possible to adjust this curve to produce the
most natural sound for the particular
volume level desired.
The charts in Fig. 10 provide the
key to connections for wiring the compensator. All compensating network
parts can be mounted on the 11- position
6 -wafer rotary switches.
Sonar
TAPE RECORDERS
RECORD l'LAIItAC6
AMPLIFIER
TAPE
FREQUENCY
RE-
SPONSE-30 to 10,000 cycles
db with less than 2%
total harmonic distortion. Overall usuable response flat from 27
±2.75
-
to 15,000 cycles.
RESPONSE
AMPLIFIER
20 to 20,000 cycles ±2 db zero
db level. Output leu than 2%
total harmonic distortion.
WOW AND FLUTTER
0.25% at 7.5" per second.
FORWARD AND
FAST
MODEL RPA1
FAST REVERSE-58 seconds
for 2.500 feet of tape. 40 seconds
for 1,250 feet of tape.
will accommodate
REELS
I0,A ", 7 ",
and 3" reels.
-
NET
$429.00
Dynamic Noise Suppressor
The system for dynamic noise suppression as originally developed by H.
H. Scott has been studied with much
interest by a large number of investigators. Several variations are possible.
This circuit is a composite of several
circuits that have been variously published. This one works as well as any
that have one high -frequency gate and
one low- frequency gate that have been
heard by the author. However, this
noise suppressor is seldom used and is
only included here because it is built
into the system and is therefore available for use. If this system were to be
rebuilt or duplicated, the dynamic noise
suppressor would be left out. Most new
record material has a low scratch level
that is much less objectionable than
the losses incurred in the dynamic noise
suppressor.
Two separate power supplies are used
with this system. One, shown in Fig. 2,
supplies filament and d -c voltages for
the power amplifier. The other, shown
in the upper section of Fig. 10, supplies
power to the preamplifier section and
the wire recorder oscillator.
Figure 11 is a block diagram with an
interconnection switching schematic. A
double -pole 6- position 3 -wafer switch
is used to select and interconnect the
various units as desired.
MODEL MPA 3 CHANNEL MIXER
AND THIRD HEAD PRE-AMP
Mixer pre -amp makes possible mixing three microphones, low
impedance as well as monitoring from the third head. Having
its own illuminated V.U. meter, the third head can be individually controlled. May be mounted on top of RPA -I
Recorder. Available with PTM Mechanism in durable and
attractive leatherette. Also for rack mounting.
$170.00
NET
TAPE MECHANISM MODEL PTM
Simultaneous use of three heads, full width
track, erase, and playback, permits listening
to recorded tape a fraction of a second after
it is recorded, insuring perfect recordings.
Three heavy torque, dynamically balanced
motors. Electro- Dynamic braking system -ex clusive with SONAR
guaranteed to require
no adjustment. Will accommodate 10 %a"
(NAB or RMA), 7 ", f ", and 3" reels.
-is
NET less carrying case
carrying case
101/2" NAB Reel adaptors (per pair)
$209.00
30.01)
9.00
LEONARD RADIO is proud to announce that it has been selected
by SONAR as their exclusive metropolitan distributor.
Visit our sound studios to see and hear this truly
nt.
remarkable in& tr
Open Mondays through Saturdays 9:00 AM to 7:30 I'M.
Conclusion
The finished home entertainment center is shown in Fig. 12.
A General Electric 1201 -D speaker
(W2) is located in the left section, and
AUDIO ENGINEERING
LEONARD RADIO, INC.
69 Cortlandt Street, New York 7, N. Y.
MARCH, 1951
www.americanradiohistory.com
AmericanRadioHistory.Com
33
a 1939 Jensen extended -range 12 -inch
speaker (WT) is located in the right
section of the cabinet. A University
tweeter (T) and a 5 -inch television set
speaker are located in the center section.
The baffle extending across the cabinet
is made up of a 44-inch laminate of
Celotex. It is inclined to point upward
at about a 30-degree angle. The back is
covered by a sound absorbing curtain.
This spacial arrangement of speaker results in a stereophonic effect that is
pleasing. All who have heard it prefer
the effect produced by the widely spaced
speakers better than when a single
woofer and tweeter are used.
An RCA 45 -rpm changer is located
in a bookcase nearby. Results from it
compare favorably with the 45's played
with the GE pickup.
At maximum gain, the hum through
the power amplifier alone is inaudible.
However, slight hum is experienced
through the preamplifier section, especially when the magnetic reluctance
pickup is connected.
Results from this system have been
gratifying. Listening fatigue seems nonexistent. However, a super-critical attitude towards music sources has been
developed. Record sources have improved greatly in the past year. Now,
the hope is that radio material will likewise improve thru the use of more live-
HARVEY'S
Still Available at
including lower
FILTER DESIGN
crossover frequency, redesigned high frequency chamber. Has
Famous AUDIO -Torium
extended
HARVEY'S well -known AUDIO -Torium is a
musical paradise for high fidelity sound
enthusiasts. In this complete, carefully plan.
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SEE
incorporate
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HARVEY'S
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[from page
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ronge. 60° horizontal,
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crossover 1000 cycles, impedance 16 ohms,
power rating 30 watts. 15" diameter.
604B speaker, less network...
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N1000B network
$ 19.00
KIT
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Write to Harvey Today
If you would like to receive future HARVEY
Sound Equipment Bulletins . . . or if you
want detailed information on specific products
or if you want assistance in planning your own installations
please write
today to DEPT. AE -3. No charge or obliga-
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tion.
Telephone:
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visit our
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Come in and
ment... all
items and many more
on
The fomous Williamson HR -15 amplifier
orking
,a;\010
display
at all times.
1!!'
circuit...
now available with the original Partridge transformers built to Williamson's specifications. Build
this kit in 3 hours or less, and enjoy sound of a
quality you never heard before. The HR15 is o
2- Chassis power amplifier for use with tuners or
other front ends having own volume and tone con-
trols. All American triodes, 2.6SN7GTY, 2 -807,
or 66G6G in PP output, 5V4G rectifier. Response
.5db, 10- 100,000 cycles. Output impedances
1.7 to 109 ohms in 8 steps. Absolute gain 70.8
db. 20 db. of feedback around 4 stages and the
output transformers. Kit is complete with Tubes,
Punched Chassis, Pre -wired Resistor Board, Sockets,
Genuine Partridge Output Transformer, and All
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available separately_..
- /'
Rn
=240
as used
$22.50
e,omrnyi ijca,
Ro = V
NOTE: In view of the
rapidly changing market <conditions, all
Atfc
prices shown are subta
thong. without
natice end ore
F.O.B., N.Y.C.
Net,
34
. .. ..
.
..
C=
V WwcC
= XLXO
=1, hence XL= Xa
Ro=vXLXO=VXLS=VXOs
eda'LC
' For example, L. J. Giacoletto, "Optimum
resistive terminations for single section constant-k ladder -type filters". RCA Review,
Vol. VIII, Sept. 47, #3, page 460-479.
103 West 43rd St., New York 18, N. Y.
.
(5)
Equations (5) and (6) are combined to
give the promised simplifications, as follows:
lUxemburg 2-1500
jct
=VL%C
and ,,,,'LC =1,
(6)
where fo = cut off frequency of ideal
filter, and
$75.00.
PARTRIDGE OUTPUT TRANSFORMER,
in above Kit,
VISIT THE
tion, engineering texts recommend the
maximum real magnitude of the image
impedance, i.e. './L /C. Numerous researchers have shown the error of this
choice.2 With this termination a T -type
low -pass filter does not cut off when
a,'LC =1. In fact, the insertion loss of
such a single- section filter is only approximately 3 db at the so- called cut -off
frequency. The reader can prove this by
substituting + jRp and jRp respectively
for the Z, and Zs elements of a full T.
Thus the term "cut -off frequency" has
been carried over from the ideal filter.
With the above facts in mind, it is
seen that the element values of a half
section are specified at once, given the
so- called cut -off frequency and the desired termination. For example, if the
termination
-
...
"Custom Match
for Direct
Comparison"
any combination of components and
equipment, from the least expensive to the
"best in the entire world."
1a11
frequency
WILLIAMSON HR-1 5 AMPLIFIER
the products of 59 leading manufacturers, everything you could possibly need
or wont, from a needle to a cabinet. And
from our working display, we can instantly
.
H. Shepard, Jr.
U. S. 2,313,098, "Methods and Means for
Reproduction of Sound Frequency Vibrations," F. H. Shepard, Jr.
Speaker and net-
work
from it.
R. T. Bozak, speaker engineer and
manufacturer. also provided many helpful criticisms and suggestions and helped
in listening and comparison tests.
Frequencies," F. H. Shepard, Jr.
U. S. 2,313,097, "System for Compensating
Anode Supply Potential Variations," F.
604B
ALTEC
The basic idea for using positive feedback in an audio amplifier for high fidelity came from Frank H. Shepard, Jr.,
an electronics consultant, whose patents,
filed in 1940 and 1942, suggest this application (see references). His advice
and counsel over the whole period of
amplifier development were of inestimable value both in the development of the
amplifier and in judging the results
PATENT REFERENCES
SPEAKERS
Everything for the High
Acknowledgments
U. S. 2,313,096, "Reproduction of Sound
QUALITY UNITS AT "SOUND" PRICES!
Fidelity Sound Enthusiast
music programs, high -fidelity recorded
tape material, and wider frequency
range on chain transmission lines.
..
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
MARCH, 1951
This results in the simple equation
R° = XL = Xe, which specifies the basic
elements of many filter types. The reasoning for evolving high- pass, tn- derived
and band-pass filters follows along the
same lines. Numerical examples will
serve to illustrate the application of this
simplification of the basic design formulae.
Let it be assumed that it is desired to
find the elements of a constant -k low pass, T -type filter, to operate between
500-ohm loads and to cut off at 159 cps.
Referring to the basic low -pass half
section, Fig. 5 (A), since it was stipulated that XL = Xe = R0 at the cut off
frequency f0, the values of the elements
signs may be checked by referring to
any standard text.
The above filter half sections are
readily arranged in the form of a Pi
having the same insertion loss characteristics as the T, as shown in Figs. 7 (A)
and 7 (B). The filter becomes a highpass T or Pi by the simple device of
interchanging elements. Figures 8 (A)
and 8 (B) show a high -pass T, and Figs.
9 (A) and 9 (B) show a high -pass Pi,
both having the same cut-off frequency
and losses.
m- Derived Sections
The element values of a series in-
derived section, it will be recalled, are
obtained by equating the image impedances of two sections of which one
uses the standard constant -k filter elements, while in the m- derived type the
series arm is arbitrarily altered by the
factor m. When the image impedance
equations are solved, it is found that the
ni- derived section requires a shunt arm
consisting of two elements. This is illustrated in Figs. 10 (A) and 10 (B).
The arrangement of the m- derived
half- section elements is easily remembered since the series arm has the factor
in as multiplier, while the shunt arm has
ni as divisor; further, the second shun:
are obtained from
Jfoa1inJction
500
R0
10r
( Za
)2,r
=0.5 henry per
24
and C
per
F
section
for all TV Cameras
section
"BALANCED"
TV TRIPOD
Pat. Pending
tripod was engineered and designed expressly to meet all video
camera requirements.
This
1,
Previous concepts of gyro
and friction type design
have been discarded to
achieve absolute balance,
,5(n
2(mtyt
.5h
jjsm
effortless operation,
super- smooth tilt and pan
~(iXE=2)n
2
action, dependability, rug-
(C)
gedness & efficiency.
(A) A constant -k and an m- derived
half section with identical mid -series image imFig.
10.
pedances ZIT.
B) Element values of an mderived section having the same image impedance as the T end of the section which it
faces. ICI Low -pass constant -k half section
and its related low -pass m- derived half section.
I
3
Below:
portable
wheel
dolly with
balanced
TV Tripod mounted.
Complete 360° pan without
ragged or jerky movement is
accomplished with effortless
control. It is impossible to get
anything but perfectly smooth
pan and tilt action with the
"BALANCED" TV Tripod.
11. IAl A constant -k and an m- derived
half section having identical mid -shunt image
impedances Z,. (BI Element values of mderived section having same image impedance
as the Pi end of the section which it faces.
Fig.
The filter arranged as a T consists of
two half sections placed with their pillars
in parallel, Fig. 6 (A), and appears in
its final form in Fig. 6 (B). The correctness of this and subsequent filter deAUDIO ENGINEERING
Quick -release pan handle adjustment locks into position
desired by operator with no
"play" between pan handle
and tripod head. Tripod head
mechanism is rustproof, completely enclosed, never requires
adjustments cleaning or lubrication. Built -in spirit level.
Telescoping
handle.
extension
pan
Write for further particulars
AmERfl
ECJU5mEf1T
Io00
arg
pgp90i11P9
se.
9EW 4ORA
MARCH, 1951
www.americanradiohistory.com
AmericanRadioHistory.Com
35
0.3h
Togo,L
0.5h
8gt
L
0.55
0.3h
L
mL
mC.r.l.2pf
m(I-mt)
0.534h
5
CT pt
500
mL .3h
ziT
1.2
h
pf
0.8h
!1
ohms
1.2p11
4
l
4
T
2p e
ohm
Load
T.2pf
(A)
0.213
0.8
0.213
h
1.2
of
500
500 ohm
0.3h
ohms
Load
0.534h
500
ír
2
(A)
500
(4,-"2)c
0.5h
.3h
Tm
ohms
0.534
Zirm
mL
VC
Il
2 pf C
0.213{íf
(t_mz)C
0.5h
1.2pf
mC
z,T
ohms
0.2130
°o
0.35
1h
500
0.534 h
3.2pTT3.2pf
ohm
Load
I
(B)
Fig. 12
IB with f. - 159 cps. Fig. 13 (right). Assembly of filter with same character
but employing shunt m- derived terminating half- sections instead of series.
(left). Filter sections (A: combined to make complete filter
istics
as Fig.
12,
element has the reactance characteristics
of the series arm times (1 ní2). For example, a low -pass constant -k half section
and its related low -pass tn- derived section appear in Fig. 10 (C).
Similar considerations are involved in
determining the elements of the basic
shunt tn- derived section which is used
for joining Pi configurations of con stant-k filters. This is shown in Fig. 11.
It is very important to observe in Fig.
11 (B) that the image impedance at
terminals 1 -2 is that of a Pi for all
values of in. However, the image impedance at terminals 3-4 is that of an titderived T (Zinn) and depends upon the
value of m. It may face either a load or
another section having an image impedance Zinn. The configurations of low and high -pass constant-k and tn- derived
half sections are shown in Chart I.
Design Example
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This 12 -in. high fidelity unit has a twin -curvilinear diaphragm (British patent No. 451754). A carefully designed magnet assembly using anisotropic material provides a total flux of
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The combination of these features gives this precision -built instrument an oustandingly wide coverage from 40 to 15,000
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SPECIFICATION
Frequency Coverage
40, 15,000 c.p.s.
Overall Diameter
12 in. -31.3 cros.
Overall Depth
6 in. -17.6 cros.
Fundamental Resonant.
55 c.p.s.
Voice Coil Diameter
1314 in. -4.4 cros.
Voice Coil Impedance
15 ohms at 400 c.p.s.
Maximum Power Cap.
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Flux Density
14,000 gauss
Net Weight
12 lbs. 13 ozs.
(5810 ors.)
Finish-Grey Rivelling
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Manufactured by:
GOODMAN
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36
E M B
L
E
Y
S
I
N D U
S
T
R
MIDDLESEX
I
E
S
L
I
M
E
I
T
E
D
N G L A N D
A typical design example follows to
illustrate the application of the in formulas. Assume it is desired to improve
the insertion loss characteristics and
matching properties of the low -pass T
filter designed at the beginning of this
article, by adding a half section of inderived configuration. If ni is chosen as
0.6, the filter will cut off very sharply at
a frequency 25 per cent above idealized
cut-off, in this case at 198.75 cps. It is
important that the image impedances be
the same at the junctions of all sections.
The filter sections and the complete filter
are shown in Fig. 12.
On occasion it is more economical to
employ a Pi type constant -k section. In
the present case, for example, it is possible to reduce by one the number of inductors required. Such a design demands shunt m- derived sections as terminations in order to produce the proper
image impedances at the junctions of the
half sections. This is shown clearly in
Fig. 13.
A subsequent article will present
further applications of these simplifications to the design of crossover networks
and to band -pass filters.
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
MARCH, 1951
LOUDSPEAKER DAMPING
(from page
narrow frequency range involving the
resonant frequency of the unit.
The compliance C, represents that of
the suspension, both of the rim of the
cone and of the center spider. It is apt
to be nonlinear, particularly for large
excursions, but is reasonably constant
for moderate and small amplitudes of
vibration.
The resistive factors are that of the
and that of the air set
suspension
in motion by the cone, R. The latter is
particularly variable with frequency, but
is usually very small at the low frequency at which resonance occurs, particularly if the speaker unit is tested by
itself, or at most in a flat baffle. Values
for several sizes of cones are given by
Olson.'
From Fig. 1, it is apparent that
a
R
impedance is equal to the reciprocal of
the sum of the reciprocals of the individual impedances.
Hence we finally arrive at the conclusion that the mechanical characteristics
of the loudspeaker at the lower frequencies appear at the electrical terminals of
the voice coil as shown in Fig. 2. Here
R,,, represents the electrical resistance of
the voice coil; the electrical (clamped)
inductance of the voice coil can be disregarded at the lower audio frequencies.
The mechanical characteristics of the
speaker appear as a parallel resonant circuit shunted by a certain amount of resistance ; these constitute the motion:
impedance Z,,,, of the speaker, and the
tance. The latter transformation has
been known for a long time in the power
field; years ago oscillating synchronous
motors were used in Europe as electrical
capacitors, since a relatively small armature mass appeared as a surprisingly
large electrical capacitance.
If we substitute Eq. (5) in Eq. (4),
we obtain:
Z..=
1
(1/Rme) +IwCme+ (1/10)Lme)
(6)
The quantities on the right side represent a resistance, capacitance, and inductance in parallel, since the parallel
leading audio engineers choose
for discriminating listeners
For custom installations, audio engineers know they must please the most
the serious
severe judge of high-fidelity
music listener. These engineers know, too,
that only the best engineering resources
can produce such gratifying performance.
-
Z.= (R,+R.) + jw(M,+M.)
+1/ jwC, (2)
Substituting this in Eq. (1), we obtain
. . And that is why leading audio engineers choose from these BROWNING
models for their exacting custom installations.
Zme=
(B1) 2 x10-9
(R,+ R.) + jw(M, +Ma) +1 /jwC,
(3)
If we divide the numerator and denominator of the right side of Eq. (3) by
(Bl)2 x10-9 we obtain
Z..=
1
R.)
(M.+ M.)
(B1)2x10-9 +Iw (B1)2x10 -9
(128+
+
x 10-9
(4)
Let
(Re+R)/ (BO
2
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Armstrong FM circuit; 20 db quieting
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MODEL RJ -12B FM -AM TUNER
1
jwC,(Bl)s
x 10-9 = Gme = 1/Rme
(Ms+Ma)/(B1)2 x 10-9 = Cm,
and C,(Bl)2 x 10-9
= Lme
Armstrong FM circuit; 20 db quieting
Separate
with less than 10 microvolts
AFC on FM
r.f. and i.f. on both bands
Drift-compensated
/OFF
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AM audio 20-6600 cycles ±3 db
Triple -tuned I.f.
(5)
MODEL RV -10A FM TUNER
Armstrong FM circuit; less ti-an 10
AFC
microvolts for complete limiting
2 -stage
.
with ON /OFF switch
Drift Tuned ri. stage
cascade limiter
compensated High impedance output.
where
R,se is the motional resistance
corresponding to the mechanical damping R, and Ra,
Cm, is the motional capacitance
corresponding to Ma and M,
Learn the full specifications for Browning
write for complete perhigh -fidelity
formance curves and data on these
models.
-
and
Lm, is the motional inductance
corresponding to C,.
In short, we shall assume that the mechanical resistance appears as an electhe metrical conductance
chanical compliance appears as an electrical inductance; and the mechanical
mass appears as an electrical capaci-
In Canada, address:
Measurements Engineering Lid.
G,=1/R;
Arnprior, Ontario.
B R
L
' H.
F. Olson, "Elements of Acoustical
Engineering," p. 126. D. Van Nostrand Co.,
New York.
AUDIO ENGINEERING
FM -AM TUNERS
BROWNING
W
a b o
i
O W N
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o
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e s
,
MARCH, 1951
www.americanradiohistory.com
AmericanRadioHistory.Com
,
N G
n c.
I
M a
s
s.
'
ENGINEERED
F
O
R
ENGINEERS
37
«
,4,i
total electrical impedance ZI is Zm, plus
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"balance" to
.
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that is, the electrical LC product equals
the mechanical MC product; either
therefore represents the same resonant
frequency.
It will be of interest to compare the
behavior of the electrical circuit of Fig.
2. For example, at the resonant frequency of the loudspeaker, namely
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We can now analyze the behavior of
the speaker from its electrical motional
impedance characteristics. Thus, just as
Fig. 1 indicated a certain frequency of
resonance, so does Fig. 2 indicate this
fact. Since the two circuits are equivalent, they must have the same resonant
frequency. This can be readily shown.
Thus, from Eq. (5)
1
fr= 2 tr (A1, + M,) C, 2w L, C,,
(8)
the mechanical current or velocity y is
a maximum, and is in phase with the
force F, Fig. I.
This in turn means that the electrical
c.e.m.f. will be a maximum and in phase
opposition with the force F, which in
turn is in phase with the current in the
voice coil. Hence this c.e.m.f. will produce an in -phase or resistive reaction:
the generator will view the voice coil as
having increased in impedance, and that
this increased impedance is resistive in
nature.
Now refer to Fig. 2. At the frequency
of resonance, Lme and Cm, act as an
open circuit shunting Rm so that the
electrical impedance is
Zt=Rve+Rme
(9)
I
I
I
1
I
1
I
INC
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and is a maximum. Furthermore, if the
mechanical resistance (R.+ R.) is
small, y will be a maximum, as will also
be the c.e.m.f., whereupon the electrical
source will see a high resistive impedance Rm,. This checks the inverse relation between Rm, and (R, + R,) given
ill Eq. (5) ; when (R,+ R.) is small,
Rm, appears large since (R,+ R.) appears in the denominator of the expression for Rm, in Eq. (5).
To be concluded in the April issue.
38
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
MARCH, 1951
job. My L. A. correspondent reported that
Russell was working in pictures, seemed
PICKUP and TONE ARM
POPS
[from page 20]
[from page 24]
content and was apparently making an adequate living. The other details were identical
with what has already been reported. So
what The behavior of jazz men is nothing
new. It is commonplace to refer to their life
in the romantic terms of a school girl
novelist :
"Jacko came into the room, swaying from
too many shots of Old Cat. His bloodshot
eyes leered at Mamie and, with a cynical
laugh, he picked up his horn, played a few
bars of Body and Soul and dropped deal
in front of the picture of the great man,
'Ole Spitball'."
Here is the neat little sentimental tradition of Beiderbecke, Jammy Jones and the
whole coterie of the tragic jazz myth
!
drugs in what is, in the final analysis, a
record material; ni,', the mass of the
losing battle.
pickup armature referred to the stylus
Upon receipt of this preliminary informatip ; r,', the resistance of the rubber tion, I contacted a correspondent on the
West
Coast for further information. Old
stylus
tip
;
C,',
bearings referred to the
the combined compliance of the center- "razor blade's" financial impoverishment
was nothing new ; he had the knack of going spring and rubber bearings, referred ing through large quantities of money with
the total mass asto the stylus tip;
the ease of a fancy lawn mower doing a job
on spring grass. The difference in his case
sociated with the pickup body.
simply the fact that no effort was reStiffening the arm without appreci- was
quired in mowing. His was a power -built
ably increasing the mass will raise the
frequency and reduce the amplitude
quite rapidly without impairing the
tracking properties. This was accomMAGNETIC
plished in the second model shown in
RECORDING
Fig. 9. The arm is a tapered rectangular
TAPES TO
box section of .062 in. aluminum alloy.
The response frequency characteristic of
THE HIGHEST
this arm is shown in curve 1 in Fig. 10.
PROFESSIONAL
Box sections were used for the original
STANDARDS
experimental arms because of the relatively high stiffness -to-mass ratios
well
the
Now
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known
which can be obtained.
is
super -quality
Box sections do not, however, lend
available in magthemselves readily to easy manufacture
recording
netic
tapes for commernor to shapes of pleasing appearance,
cial and home reand for these reasons experiments were
corders. The six
continued with a channel structure of
quality
Duotone
assure
features
The
general
shape
large
section.
fairly
finest sound reproof the arm was the same as that shown
duction for profesin Fig. 9 and the wall thicknesses tried
sional
programming
and
the
were 1/8 and 3/32 in. The results are
ultimate in home
shown in curves 2 and 3 in Fig. 10.
entertainment. For
The final design was obtained 112
finest performance
on any tape reshortening the original arm length of
corder, use Duo
16.7 in. to an effective length of 12 in.
tone
professional
The maximum tracking error increased
quality
magnetic
tapes
to about 4 deg -not enough to be serious
-and at the same time the arm length
becomes such as to facilitate greatly its
Low Inertia Plastic
Interchanges with
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Wheel
Other Tapes
Low Friction
Constant Tracking
Final Design
Long Life
Winding
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The final design of the arm and
Minimum BackNo Snarls or Backmounting is shown in Fig. 11. Overall
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Playing tests have shown that this
Made with plastic or kraft paper base in extra long 625
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for the 2.5 -mil stylus and 8 grams for
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standard and special tapes, call or write for illustrated
the 1 -mil stylus. Intermodulation tests
catalog.
yield results which are low to the point
where it is not possible to determine acFamous for Phono
curately whether the distortion is in the
Needles, Recording
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Needles,
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C'\XXV
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In conclusion, the authors wish to
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AUDIO ENGINEERING
MARCH, 1951
www.americanradiohistory.com
AmericanRadioHistory.Com
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Free technical bulletin.
641-43 MILWAUKEE
40
AVENUE
wrapped up in the cloying, hot -breath moats
of a stupid lie. When we make heroes out
of our bad boys, we always mark them with
the stigma of a bad habit, be it alcohol, a
disappointing love affair, or the myriad of
unfortunate and pathetic characteristics that
our comic book intellectuals accord the
"jazz musician". Up to ten years ago, the
tragic flaw might get by because too many
cases fitted into the pattern. But the real
tragedy of the moment has nothing whatsoever to do with Russell's physical condition, or his purported mental breakdown.
The tragedy hinges around the words
"working in pictures."
Excuse me for not being fashionable and
blaming all the horrors of our civilization
on "dat ole demon Hollywood." The motion
picture industry needs musicians and pays
them according to scale. This is a legitimate
way of making a living and does not, in
itself, produce the disastrous emotional distress that is characteristic in the treatment
of the "Hollywood Tragedy." But when a
man of the stature of Russell is not devoting his time to his rightful work, and by
not doing so pointing up the slow decrease
of that work, it is time for some careful soul
searching. I don't want to make too much of
a case out of the Russell episode; listening
to Pee Wee over the past five years, I came
away with the sad conclusion that he was
pretty much finished. He looked bad, he
sounded had ; he played in a haze in which
only small snatches of his earlier brilliance
reached the surface. He belonged and still
belongs to the great fraternity that made out
of the chaotic piecework of early jazz a
strong and noble structure. For this alone,
lie deserves everything from the deepest
respect to the most superficial foot -stomp.
But, let's switch cases for a moment. This
month's reviews include a large batch of
LP's purporting to present great jazz and
great jazz men. They are tired, ignoble, dull
specimens which are marked only by the
sedative content of the stuff being played
and the mood in which it is being spewed
forth. When a man of the stature of Sidney
Bechet is accused of being dull and plodding,
the world has come to an end and its time
to find out why. When Red Norvo, a skilled,
imaginative and productive vibes man sticks
to the rutty mire of stylized and sophisticated "hop," when Art Hodes and Jesse
Stacey play as uninspired a collection of
blather as characterizes the recent recordings, or when Teddy Wilson takes in
the shekels after the sloppy and moribund
performances presented daily on a small
radio station, we think it is about time to
give up jazz and take up knitting.
Speak to any of the big people; ask them
how they feel about the business. Their
answers are as honest and legitimate as a
chocolate cigarette. Some of them are making very big money (which they can use
and which gives them a well fed feeling
thrice daily) they give you a lot of optimistic malarky until the fifth drink and
then they are likely to borrow a shoulder
and cry their commercial heads off. At this
point, they don't give a hoot for all our
fancy, sophisticated recording techniques
and they don't care about the whole plethora
of technical arguments which justify what
has been done to music and to the people
who want to listen to it. Ten thousand
microphones will never improve the quality
of the stuff that is being fed into them.
The diamond stylus may save the record
and supply a good response curve; it will
never cover up the absence of value in the
sinewy grooves.
Several weeks ago, I received a letter
from a reader in the middle -west who took
i,si1e with my defense of live music versus
CHICAGO 22,
ILLINOIS
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
MARCH, 1951
canned music and suggested the following
hypothetical case (which he freely admits
is probably out of the question). He suggests the possibility of the perfect recording
and the perfect "play back" mechanism. By
perfect, I assume he means
completely
faithful reproduction of the recorded performance. According to this faithful reader,
there would then be no distinction whatsoever between live and canned music. His
argument continues that even if perfection
itself is impossible, we can approximate the
perfect to such an extent that the difference
between the two would be negligible. Since
recording allows for a greater flexibility in
terms of listener possibilities, placing jazz
within the range of everybody, no matter
what geographical location and what economic status, in the interest of the public
at large we should push the recording industry and the radio industry as worthwhile
replacements for the live thing. He also
suggests that because of the present sophistication in taping techniques, we should play
ball with the radio stations that have discontinued live programming because of the
concomitant efficiency involved. The sum
total of his argument is . . . give the
listener a break
Give the listener a break, indeed There
is no point in repeating previous arguments
which clearly indicate that the listener is
not getting a break. We needn't point out
the problems involved in the manufacture of
the "perfect recording" and the perfect
"play- back" equipment. Nor will we repeat
the psychological problems involved in the
distinction between live , versus canned
listening. Accepting what friend reader hypothicates, we need merely point out that
he has left out the most important part of
the argument
. the stuff that
we are
forced to listen to. He is going on the
assumption (like many of the wise men in
this business) that the musician is merely
a mechanical datum, who either blows,
beats, strums, or bows an instrument, thereby producing sounds. He also forgets the
distinction which has previously been made
in this column between so- called classical
and so- called jazz music. While we might
be more or less inclined to accept his
arguments as being justifiable concerning classical or "scored" music, they
simply point to an ignorance concerning the
conditions behind the making of jazz sounds.
The validity of my arguments are being
proven day after day by the kind of stuff
the jazz musician is playing and recording.
Completely detached from his audience,
determined by various technical conditions,
including time and equipment, no longer
within the stimulating and exciting arena of
the jazz combat, he merely plays notes. As
he becomes further and further separated
from the conditions out of which great
moments of jazz erupt, he becomes duller
and duller, finally reaching the stage
where he approximates a standard announcer reading a standard commercial,
with equivalent amounts of sincerity and
personal participation. The jazz man becomes a typist, copying somebody else's
letter and involving nothing of himself other
than the physical work of hitting a key and
printing a copy of what he has before him.
Even if the perfect record can be made,
even if recording becomes absolutely identical of a perfect standard (whatever that is),
this has nothing whatever to do with the
'creative job of making jazz. When jazz left
the bistro and entered the respectable confines of the private home, the motion picture, recording, television and radio studio,
the creeping paralysis that characterizes it
inevitably set in.
Nobody can put the jazz experience on
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1951
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about
paper. It is a personal thing which requires
complete involvement. All that can be done
is to create a metaphor which approximates
the feeling. Try to imagine what would
happen to your speech, your every day,
individualistic, personal way of communicating with somebody else, if you could only
stand in a room, day after day, and speak
to an invisible audience. It would become
dull, devoid of personal characteristics, and
self- conscious. It would cease to be a living,
vital, and personal experience; good recording techniques and apparatus would only
reproduce the dull, dry, and impersonal
character of this stilted performance of a
dead task. In exchange for the convenience
of our favorite chair, our own highball, and
our hot -rod record player, we have sacrificed the only object that makes these things
worthwhile. As long as the record industry,
the audio industry, the average listener, and
the musician himself collaborates in this
vicious circle, great jazz will simply not
exist. Just before he died, Charlie Christian
gave an impromptu recital in a dressing
room near Times Square for a bunch of
musicians, friends, and admirers. It culminated in some of the most beautiful guitar
work these ears have ever heard. He was
facing an audience, not a mike, and that fact
determined the experience. No recording
studio could house the big notes that came
out of the cigar box that night
no recording studio will ever be large enough.
The Pee Wee Russell's of this world don't
die from cirrhosis of the liver
they die
of malnutrition of the head and heart. No
matter how much money they make, no
matter how 'satisfied the acceptors of
mediocrity are with their playing, they die
a slow death in which all that is left is a
man blowing into a clarinet
. manufacturers of a noise called "jazz," not the
creators of a great moment, which is neither
jazz nor music in general, but the thing in
life called art.
SWITCHBOARD AND SUPPLY COMPANY
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NEW RELEASES
Jelly Roll Morton
The Saga of Mr. Jelly Lord, Vol.
1
Circle L 14001
anthology
Paper cover
$2.00
.
Distributors write for quantity discount
r
A compilation of articles reprinted from early issues of AUDIO ENGINEERING, most
of which are unobtainable.
These articles have been of great interest to readers of AUDIO ENGINEERING over
the past three years. Assembled if one volume the 7 coin P rise the most authoritative
ref erence work for the audio hobbyist.
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42
Some years back, Allan Lomax engineered one of the most fantastic recording
sessions in history. Under the aegis of the
Library of Congress Archives, this session
resulted in twelve albums comprising the
life, history, and music of Jelly Roll Morton.
Only available in a limited edition, the
albums are now being re- released in LP
form, the above being the entire first album.
The dubbing is poor and no attempt was
made to clean up the acetates, a job justified
by the content and form of this recording.
Technically, the LP is poor and the culprit
responsible should hang his head in shame,
especially considering who the culprit is.
With eleven more to go, he should be required by law to treat the material with
the respect it deserves. Jelly Roll must still
exist in some tangible form somewhere in
the universe and, characteristically, will not
be lenient with anybody who fails in the
duty of respect which the great man always
felt his due.
About the 12-inch disc itself
anybody
who maintains an interest in jazz must own
it. It is both the most fabulous history of
one man, a tradition and the history of jazz
which is on or ever will be on discs. Outside of the musical experience, which includes definitive versions of "Mr. Jelly
Lord" and "Tiger Rag," it is by far the
best way to get into the center of the
creative movement in which and through
which jazz emerged. Jelly Roll's constant
patter, especially the detailed description of
AUDIO ENGINEERING
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...
MARCH, 1951
IF
YOU BUY ON SPECIFICATIONS
what is meant to grow up in the ferment
called New Orleans (one of the most touching and magnificent stories in the whole
history of Jazz), is told in a way which
leaves no doubt as to what it meant to be a
jazz man. You will never be able to listen
to the synthetic blather of today after a
complete listen to this disc. You gotta get
it The whole life blood of a great creative
act comes to life (despite surface noise,
fading and poor cutting).
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ULTRASONIC FUNDAMENTALS
By
S.
YOUNG WHITE
of uil rmsunie. during
amerce +r In Ike
last few years makes It natural that the well informed sound engineer should want to learn something of the applications and totentialiues of this
Iles field.
lint Interest in ultrasonic. 15
is of still
ind engineer
notaxing
cunmcd to the
greater insamianee to the indpstrlal engineer for he
Is the one who will visualise Its uses In his own
the
'rile rapid
,
I
-It
pnaeues
Elementary In
character. ULTRASONIC FUNsari. of
DAMENTALS was written originally as
magazine articles Just far the purpose of acquainting
the novice in this field with the eno
possibllll/ee
of
new tool for Industry. It serves the double purpose of introducing ultrasonics to both sound and
The list of chapter headlnge
Industrial engineers.
will Indicate how It can help sou.
CHAPTER HEADLINES
OWertnities pat Ultra,nles.
Too Mach Audle.
Experimental UltraElements et Ultrasonics.
Load.
It Energy to
hit
sonics. Coupling
In Solids.
Ultrasonics
Ultrasonics pat LICulds.
High -PUwm Ultrasuln.
Testing by Ultrasonics.
les.
Apial.
Notes as Using Hlgh -Power Ult
Miens et Ultrare lee to Biology.
Industrial
Economics of
UltrasenIfs.
The applications of ultrasonics have already extended to many industries. and as Its ponlblllthn
hundredfold. To keep
are explored they will increase
abreast of its growth. engineers in all eslda must
know what they may expect from ultrasonics. how It
Is used. how the energy Is generated. and the techniques tr applying ultrasonic treatment 10 many pros rsses.
ULTRASONIC FUNDAMENTAI.S Is not a big
does not cover the entire field of ultrasonics
book
with hundred. of pages of dull reading. But in the
three hours it will take you to read it. you will get
a down -to -earth glimpse into the far -reaching possibilities of a new art.
This is, in its own way, one of the more
interesting recent recordings to come from
the "little companies." Don't misunderstand
by no stretch of the imagination
me
is it good. It has an air of staleness about
it which the brilliant virtuosity of Red
Norvo, Tal Farlow, and Charlie Mingus
can't displace. A little bit about the group,
first. Red Norvo is, for my money, the
greatest vibe man we have. Given the right
conditions, he can outplay and out -think
anybody in the business. An impeccable
technique, a broad range of ideas, and a
genuine excitement when he is working
with the right group, and playing the right
material, make him something beyond a
vibe artist
. an outstanding jazz man.
Tal Farlow is a guitarist whom I originally heard with the Teddie Napoleon trio
(unfortunately not recorded) and who deserves close attention. While fantastic technically, he lacks the cuteness and banality
of such so- called wonders as Alvino Rey
and Les Paul. His single string work and
his chording are marvelously developed and
he has gotten away from the cliche'd riffs
and runs of the characteristic guitar man.
Charlie Mingus is a phenomenal bass man,
tripling as an arranger -composer. He can
get more out of the unwieldy rat trap than
almost anybody in the business. Put them all
together and what do they do? Play a
nauseating and dull variety of stuff in the
tradition of George Shearing. There is no
genuine excitement elicited anywhere in this
12-inch disc ; all there is is a tired, dull,
...
complex mish mash which never gets out of
the set pattern of sophisticated bop. Only
one band (reserved for a thing like "Move")
holds promise. The rest dies a lingering
death. The jacket specifically notes that
great care was taken to preserve the "inti-
mate atmosphere" of the group in the recording. This has been achieved with some
success, at the cost of an overemphasis of
guitar and vibe overtones, which occasionally obscure the intricate patterns of the
liveness, no The
stuff. Intimacy, yes
recording must have been a hard one to
make, given the character of the group, and
Discovery has succeeded to a greater extent
than characteristic of the general run of the
he's
mill. Pay attention to Tal Farlow
quite a guitar man. Now we'd like to hear
him on some really decent stuff.
...
ULTRASONIC FUNDAMENTALS
By S. YOUNG WHITE
36 pages, 40 III., 81/2 x 11, paper cover
$1.75
Book Division, Dept. A
RADIO MAGAZINES. INC.
New York 17, N. Y.
342 Madison A
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Two more records in the Columbia
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MARCH, 1951
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are generally foul in all cases. Technically,
these recordings do not live up to the job
done on the Ralph Sutton Disc. Piano is
occasionally completely distorted, percussion is muted. The spaciousness characteristic of the other discs is missing. Jesse
Stacy, accompanied by George Van Eps on
guitar, Morty Corb on bass, and Nick
Fatool, drums, lazes along through a dull
uninspired session. Numbers such as Lullaby of the Leaves, Under a Blanket of
Blue and Cherry, all of which Stacy has
done magnificently on other occasions, are
pedestrian. The sheer boredom of this
session is becoming characteristic and points
the finger again at what happens to a great
instrumentalist under prevailing conditions.
Heywood has never been, in my estimation, a top man. He burst into fame with
the stylized, tricky recording of "Begin the
Beguine," and has lingered within a stylistic pattern which is cute, but unproductive.
Research Engineers
Electrical Engineers
and Physicists
The Franklin Institute
Laboratories for Research
and Development
have openings for personnel
with 0 -10 years experience.
Advanced degrees are desirable in certain of the positions. Fields of interest
This job is dull throughout, including a
so -so job on St. Louis Blues, When Your
Lover Has Gone, and a bad shot at All the
Things You Are. Tired, uninspired, lacking
any vestige of original ideas, the recording is
technically a perfect match of the musical
deficiencies. This is the age of the cute
boxer and the cute piano man ; Heywood
and Joe Bushkin are both cuties. Skillful,
but lacking power and a knockout punch,
they can be used for background music,
especially before going to bed.
Mathematical
Analysis of Physical Problems, Statistical Theory of
covered are:
Communications, Electromagnetic Theory, Servomechanisms, Electrical Corn puting, Advanced and Fundamental Circuit Development,
Radar and Pulse Circuits,
Operation of G. C. A. or
Wild Bill Davison
Blue Note LP 7001
Sidney Bechet jazz Classics
Blue Note BLP 7002
Hot Jazz at Blue Note
Art Hodes Hot Five
Blue Note BLP 7005
Sidney Bechet with
Tracking Radar, Aeronautical
Radio, Automatic Controls,
Design and Development of
Small Mechanical and Electro- mechanical Instruments,
and Electrical Machinery.
Three LP's featuring Sidney Bechet and
practically every other big man in the business, including Meade Lux Lewis, Sid Catlett, Max Kaminsky, Pops Foster, Wild Bill
Davison, Art Hodes, Teddy Bunn, Fred
Moore and others
all dull, tired, banal,
and terribly recorded. Soprano sax isn't
easy to record, but this is just smeared all
over the place. These are all dubs and
characterize all the worst aspects of the
process. Balance is awry, surfaces poor,
range limited to the hollow of a peanut
shell
why bother. Becket is a genuine
artist and rarely fails to produce great
moments, but even the job on "Dear Old
Southland," a specialty of the house, gives
one a beddy -bye feeling. Abe Kaplan and
Stanley Rosenberg, able mentors of the
...
Send resume of education
and exp.?rence, salary requirements and photograph
to:
...
Personnel Department
THE FRANKLIN INSTITUTE
record department at Rabson's and cognoscenti of all kinds of music, shuffled these
out for me with the despairing look that
comes from knowing what to expect these
days. Why review them ? To point out and
point up the argument at the beginning of
this month's piece. No matter how good
the discs would have been, the musical content is sorely defficient. A blast, a bang and
a couple of old hat tricks don't represent
a decent session in my book.
Philadelphia 3, Pennsylvania
SENSATIONAL NEW BOOK
ELEMENTS of SINGLE and DUAL
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FOOTNOTE
and 1001 APPLICATIONS
To avoid any further confusion, it is nt,t
generally my practice to single out had
recordings for review. The above mediocrities were cited in connection with the initial
part of this month's column, and should Itt
listened to for an empirical lesson in what's
what. The blood bath that would characterize this column if half the records I'm forced
to listen to each month were reviewed
would make Nero look like a piker. Next
month, I'll wash my ears and mouth out
with soap and begin the long over -due job
on the "basic pops library."
by A. C. Shaney
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MARCH, 1951
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A` Berlant lelte'sonC
4917
1
4,4-
W
Los
Angels
6
I,IIo
n
Langevin
AMPLIFIERS
wye
For broadcau, public addre..s, recordi,g, and music
services
cestom designs
-
!or
Langevin
TRANSFORMERS
F.- ,,--
e
Ope
met
or
l
ccre, encased, herrally sealed, high -tem
pare turc. Boil
UIL -T -27
to your own
:
Wanted: Audio Technician, thoroughly
experienced, to be chief engineer of two
professional -grade recording studios. Prefer man not subject to draft. State salary.
Box 201, AUDIO ENGINEERING.
-tudla Engineer: No degree needed;
must be able to expeditiously and completely design high -grade commercial
radio amplifiers and associated equipment for short -run production. Excellent
opportunity for a stable and conservative
personality. Small nationally advertised
Chicago concern. Submit photo with
personal and professional history in replying. Box 301, AUDIO ENGINEERING.
Laboratory Assistant: Must have fair
knowledge of audio engineering, be familiar with laboratory test equipment and
be able to completely build and test special
one -or- two -of -a -type amplifiers. Small,
nationally advertised Chicago concern.
Submit photo with personal and professional history in replying. Box 302,
AUDIO ENGINEERING.
ERRATA
applications.
special
*
pecifications.
The following paragraph was omitted from
page 21 of the February 1951 issue of "An
Effective Frequency Rejection Circuit" by
R. B. Nevin.
If there is any doubt about the noise
frequency that is being rejected, then adadvancement of R, right to the Rke end will
enable identification to be made. R, can, of
course, be divided into a fixed and a variable part, and the junction placed at the
pre-set measured nullpoint, so that over-
shooting this point cannot then happen.
Adjustment of R, affects the signal level
and if this is not satisfactory for any particular application, then the . . . .
(Langevin
aa
`m
AS EXHIBITED AT THE-
ENGINEERING
Radio Engineering Show
Available for the
ment and manufacture of
special electronic desk.,.
For
detailed information on our
services, write to
products and
Antennae, ServoMicrowave ccts. and
other phases of communications
and navigation equipment.
RESEARCH
ON
mechanisms,
PRODUCTION DESIGN OF: Military
and
communications
commerical
and navigation equipment.
-
Supervise
installation and maintenance of
radio and radar equipment. Factory
training will be given. Base salaries
FIELD ENGINEERS
from $4200 to $6900 per year.
25% bonus for time spent overseas.
Traveling and living expenses paid
by Bendix. Insurance plan.
AND INSPECTION ENGINEERS
knowledge of radio,
radar, or TV manufacturing processes. Good knowledge of rodio
fundamentals essential. Base salaries from $3900 to $5880.
TEST
-Practical
-
Knowledge
of radar fundamentals or radio re.
quired. Work closely with engineers
to gather material for instruction
TECHNICAL WRITERS
and maintenance manuals. Base
salaries from $3400 to $4300.
LABORATORY TECHNICIANS
-
Re-
quire knowledge of radio fundamentals and skill in use of measuring instruments and laboratory
equipment. Previous industrial experience essential. Salaries from
$262 to $321 per month.
BASE
SALARIES
FOR
ALL
POSI-
TIONS LISTED ABOVE ARE SUPPLEMENTED BY UP TO 30% FOR
REGULARLY SCHEDULED 48 HOUR
WEEK.
Housing is no problem in Baltimore.
Excellent group insurance and
family hospitalization plan.
Attractive retirement plan for professional personnel.
Write for application:
New
York
City
¡angevin
MARCH
all
salary and experience levels.
Grand Central Palace
MANUFACTURING CORPORATION
37 W. 65th St., New York 23, N. Y.
AUDIO ENGINEERING
..
-At
ELECTRONICS ENGINEERS
March
19 -22
1951
1951
www.americanradiohistory.com
AmericanRadioHistory.Com
Engineering Personnel Supervisor
BENDIX RADIO DIVISION of
Bendix Aviation Corporation
Baltimore 4, Maryland
TOwson 2200
45
AES Sections
CLASSIFIED
Rates: 10e per word per insertion for noncommercial
advertisements; 25e per word for commercial advertisements. Rates are net, and no discounts Will W
allowed. Copy must be accompanied by remittance in
full, and must reach the New York office by the first
of the month preceding the date of issue.
FOR SALE. Feed screws, automatic equal zer mounting brackets for 128N Presto overhead. Advance ball for Presto 1 -C, 1 -D head.
Also other quality recording equipment, pads,
transformers, microphones, Leica camera
equipment. For details write M. E. Boyd, 903
Salmon Drive, Dallas, Texas.
CHIEF Engineer -minor partner position desired in small existing or projected electronic
or electro-mechanical manufacturing firm engaged in defense activity in central U. S.
BS, MS, EE, Professional Engineer. 6 years
development experience. College Professor.
Box CM -1, AUDIO- ENGINEERING.
ALTEC -Lansing 604B speaker and crossover network mounted in 3- cu.ft. cabinet.
Used one month. Perfect condition. $200.
Box CM -2, AUDIO -ENGINEERING.
WANTED. One Amplifier Corp. of America
tape recorder. 7% and /or 15 In. per sec.
speed, preferably #800C, or Concertone tape
recorder. Not over $200. John A. C. Callan,
3819 Military Road, N. W., Washington 15,
D.C.
PROFESSIONAL
DIRECTORIC. J. LEBEL
AUDIO CONSULTANT
Development, Test, Custom Equipment,
Complete Laboratory and Shop Facilities
133 WEST 14TH STREET
NEW YORK
N. Y.
CH 3 -8082
Il,
Custom-Built Equipment
U. S.
1121
Recording Co.
Cincinnati
Meets at WSAI studios. For information, write the secretary, W. E. Mahoney,
1730 Kleemeier St., Cincinnati.
Cleveland
Usually meets the third Wednesday of
each month ; for information, write the secretary, T. E. Lynch, 3120 E. 135th St.,
Cleveland 20, Ohio.
Rensselaer Polytechnic Institute
Meets the first Friday evening at the
Sage building on the RPI Campus, at 7: 30
p.m. Meetings are also held occasionally
on the third Friday. Faculty Advisor: Dr.
R. E. Whallon.
New York
The New York section has finally located
a permanent meeting place -Studio 1,
WMCA, 1657 Broadway, between 51st and
52nd streets. Meetings are held on the second Tuesday at 7: 30 p.m.
RICHARD H. DORF
AUDIO CONSULTANT
Sound Systems
Recording Installations
Product Design
255 W. 84th Street
New York 24, N. Y.
Technical Literature
Phone
Schuyler 4 -1928
RECORDERS
MAGNERASER*
The Perfect Bulk Tape Eraser
-
Provides complete 100% tepe erasure on
the reel
without rewinding. Portable, light
weight, fast, easily operated. Guaranteed to
erase tape 3 to 6 db. quieter than unused
tape! Also demagnetizes record and erase
heads. Size: 4" Diameter; 2" High. Weight
3 lbs. Operates from any AC outlet.
Net Price
$15.00 (Includes II ft. line cord and plug)
Order direct from factory, or send for descriptive rirrulars.
AMPLIFIER CORP. of
398 Broadway,
eoatiya9
AMERICA
New York 13, N. Y.
Trademark Reg.
Minnesota Alumni Luncheon,
together former Minnesotans, isto tobring
held at Le Marmiton Restaurant, 41 be
E.
49th St., in New York at 12: 30 p.m. on
Thursday, March 22, during the I.A.E.
Convention. Dr. Henry Hartig will be
toastmaster. Reservations in advance
through
Arthur G.
CBS, 485 Madison Ave. New YorkPeck,
N. Y. or phone
Plaza 5- 21000, ext. 249.22,Cost
is $2.75 per
person, which includes gratuities
and
checking.
fifth anfnnual Spring Technical Conference
on Saturday, April 14, at the Engineering
Society Headquarters in Cincinnati, with
Television as the theme.
Dallas -Port Worth Section, I.R.E. will
hold the next Southwestern
I.R.E. Conference on the campus of Southern
Methodist University, Dallas, with the Student
Branch acting as joint sponsor, on April
20 and 21. In addition to a number of important papers, the meeting will feature
an Industrial Exposition and a banquet
with "Texas- style" eating.
British
and Birmingham,
t
leLdon m
April 30 to May 11 will Engand,fr
embrace more
than one million square feet
of
Olympia Hall, in London, will be exhibits.
the center of displays of musical instruments,
home entertainment units, and electronic
and special sound equipment combined.
This show will cover virtually the whole
range of British industry-agricultural,
industrial, marine, electronic, and many
other branches.
Dayton Section, I.R.E., together with
the Professional Group on Airborne
tronics is sponsoring the National Elecference on Airborne Electronics at ConBiltmore Hotel on May 23, 24, and the
25.
Subjects covered will range from antennas and components to radar and airborne
Audio Fair
REGISTRATION LIST
Only 50 copies of complete
Audio Fair - 1950 Registration
available for non- exhibitors.
$35.00 prepaid
AUDIO FAIR
342 Madison Ave.,
New York
17, N.Y.
AUDIO ENGINEERING SCHOOL
Practical engineering training in Audio fundamentals,
Disc, Film. Magnetic Recording, and Audio frequency
meuuremenn.
Studio training simulates Broadrut, Motion Pictures,
Telerision, and Commercial Recording work.
Approved for Veterane
Hollywood Sound Institute, Inc.
1040 -A North Kenmore, Hollywood 27, Calif.
Specify if Veteran or Non- Vatern
B
TV.
YOUR 1950 BOUND VOLUME is ready
You will like
the convenience
Vermont Ave., Washington 5, D. C.
LIncoln 3.2705
46
FOR ALL TAPE
Additional Meeting Data
the permanence
Allied Record manufacturing Co., Inc.,
,f Hollywood,
California, and K. R. Smith
Co., Inc., of New York became associated
:,s of February 1. Mr. Smith, who pioneered the development of electrical
transcriptions, will continue to head the
New York plant, which will be operated
as the K. R. Smith Division of Allied
Record Mfg. Co. Move said to provide
fuller and faster processing service for
the recording and transcription industry.
International Rectifier Corporation adds
a second story to its plant located at
6809 S. Victoria Ave., Los Angeles 43,
Calif. Firm manufactures selenium rectifiers and photocells in modern completely
air -conditioned plant.
Newcomb Audio Products, Hollywood,
announces the appointment of Art Cert
as manufacturer's representative
in the Metropolitan New York Territory,
widening rep's coverage which now includes Eastern Pennsylvania, Washington, D.C., Delaware, Maryland, New Jer& Co.
the handsomeness
the wearability
of the
AUDIO ENGINEERING
1950 Bound Volume
Order now-Limited Supply
$8.95
Radio Magazines, Inc,
342 Madison Ave., N. Y. 17, N. Y.
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
MARCH, 1951
all of New York State and Long
Island.
Permoflux Corporation, 4900 W. Grand
Ave., Chicago, has just appointed J. Y.
Schoonmaker Co., 2011 Cedar Springs,
Dallas, Texas, as their jobber sales representative covering the territory of Arkansas, Louisiana, Mississippi, Oklahoma,
and Texas. New rep will promote sale of
the famous Permoflux Royal line of
speakers as well as head sets and other
electron i, -luipnnnt.
sey, and
BARKER
SOUND
UNITS
TELL
9oubssillit People--
THE
TRUTH
Ray F. Crews has b,cu appointed Vice
President in Charge of Sales for the Fairchild Recording Equipment Corporation
. J. W. Duffield
of Whitestone, N. Y.
appointed eastern regional sales manager
for General Electric's Tube Divisions,
with headquarters at 570 Lexington Ave.,
New York. Duffield will be responsible for
the sale of replacement tubes and associated electronic items in all states on the
eastern seaboard from Maine to Florida,
as well as in Tennessee and Alabama.
Allen Easton has been appointed
chief of the Microwave Section of Radio
Receptor Co., Inc., 84 N. 9th St., Brooklyn 11, N. Y. manufacturers of electronic
and radio equipment since 1922. Mr.
Easton, who was formerly chief engineer
of Teletone Radio Corp., will be responsible for development of new products for
government and industry.
Edwin Dorsey Foster, U. S. Navy
(Ret.), has been appointed Director of
newly established Mobilization Planning
Department of RCA Victor Division of
Radio Corporation of America. Formerly
Chief of Naval Material in the office of the
Secretary of the Navy, Vice Admiral
Foster will guide RCA Victor's resources
in development, engineering, and production facilities to fulfill all requirements
which may be placed upon the company
by various Government agencies.
William Hargreaves appointed Vice President in Charge of Engineering, Transicoil
Corporation, 107 Grand St., New York 13,
N. Y. Mr. Hargreaves, well known in the
industry, has been associated with development of servo motors and other equipis
ment produced by Transicoil. Companysecexpanding its facilities by adding a
ond floor, thus doubling its floor space.
Marvin Friedman appointed Production Manager and Secretary of Andrei
St., Brooklyn,
Products Corp., 55 S. 11thleading
quality
N. Y., one of country's
tool, die, and jig plants now utilizing its
technology for the production of radar
and electronic equipment.
Braes D. Henderson appointed general
purchasing agent for Westinghouse Electric Corp. simultaneously with appointment of Wesley H. Lees as general traffic
manager. Both have been with company
for years, working up through various
divisions and degrees of responsibilty,
thus bringing thorough familiarity with
company to new jobs. . . Gordon C. LeRoy, 29 Bancroft Dr., Rchester 16, N. Y.
appointed sales representative for Insuline Corporation of America, 3602 35th
Ave., Long Island City 1, N. Y., to cover
radio parts jobbers in upper New York
W. P. L'Hommedien just apState.
pointed assistant Pacific Coast District
manager for Westinghouse Electric Corporation with headquarters at San Francisco. With Westinghouse for 44 years,
Mr. L'Hommedieu will assist W. J. May tham in handling special staff assignments that will include study of manpower, methods, and organization procedures.
Theodore A. Smith appointed Assistant
General Manager of RCA Engineering
Products Department, taking over duties
of W. W. Watts who has been granted a
leave of absence to serve with Maj. (len.
William H. Harrison, Defense Pr,loction
Administrator in Washington. A. R. Hopkins was appointed General Sales Manager of the department at the same time,
and Barton Krenser became General ProdJohn A. McCone, Unuct Manager.
der Secretary of the Air Force, has been
designated the Air Force civilian member
of the Department of Defense Research
and Development Board, replacing Assistant Secretary of the Air Force, Harold
8. H. Coombs will head
C. Stuart. .
electronic sales engineering department
of H. E. Ramsford Co., manufacturer's
agent in Western Pennsylvania and West
Virginia. Coombs comes from Sales Manager's Staff of Allen B. Du Mont Laboratories' Instrument Division, and will handle similar equipment with Ramsford
Company, Du Mont agents for past ten
.
The ideal loudspeaker is probably one
which corrects all preceding defects from
studio microphone to final output stage
and delivers perfectly re- constituted sound
to the listener's ear.
We have not reached that far yet. In
fact, we doubt if we ever shall. But we do
know that our units get very close indeed
to telling the truth about the input they
receive. And that is a lot farther than most
speakers go, for very good reasons.
Many hundreds of our friends now enjoy
the ever fresh joy of hearing favorite music
and artists sound NATURAL, and can appreciate clean detail, transients clear cut,
full frequency range without break or
change of texture. Some of them in your
country tell us we have in our dual drive
with built -in cross over and our graded
compliance cone a combination which beats
all, even at many times its price, which is
.$60 or $42, according to magnet size.
Why not write for details now?
BARKER NATURAL SOUND REPRODUCERS
BCM /AADU, LONDON, W.C. 1, ENGLAND
DU¡
HEARD
HAVE YOU
OF
THE SOUND
i
59
FRT0TV
SERVICEMEN
THE LAST WORD IN
.
TV 'TENNA INSTALLATIONS
coca
.
TV- ANTENNA
INSTALLATIONS
.
pocket size reference mare-al
edited by outstanding authorities. Packed
with vitol information on all types of
antennas, Helpful Hints, Do's and Don'ts,
Dimension Guide, Channel Frequencies,
Proper Feed Methods and many other
A fact -filled,
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NEWCOMB SOUND
Iwo
BETTER
.
Manufacturers of public address, mobile,
phonograph, musical instrument and wired
music amplifiers
Portable systems
Portable phonographs and radios Transcription
Rack and panel equipment.
players
Write todayl Circle items of interest and
indicate whether you ore a Dealer, Parts
Jobber or Sound Specialist.
NEWCOMB AUDIO PRODUCTS CO.
DEPT. T, 6824 LEXINGTON AVE.
HOLLYWOOD 38, CALIFORNIA
LIMITED QUANTITY
PUBLICATION PRICE 50c. AVAIL
ABLE WIT'1011T OBLIGATION
IF YOU WRITE IMMEDIATELY.
-MAIL
rs.
MARCH, 1951
www.americanradiohistory.com
AmericanRadioHistory.Com
HIS COUPON
TODAY-
SNYDER MFG. CO., Dept.
.
22nd
A
B
Ontario Sts., Piila. 40, Pa.
Please send free copy of TV'TENNATIPS
.
e
AUDIO ENGINEERING
subjects.
Name
Address
L
City
Zone.
..State
J
47
ADVERTISING
INDEX
PRICE ALTERATION IN THE
HARTLEY- TURNER 215 SPEAKER
Diminishing supplies of steel strip in
Britain have now got into the black market,
and we don't buy there. We have, therefore, changed the cone cradle of the 21 5 to
an aluminum casting. This costs us more,
there is more machining, and all our other
raw materials have skied. The inevitable
consequence is that the 215 will now cost
you $48.00 (plus 15 °o duty at your end).
We are sorry about this, but as very many
people have told us that the 215 gives a
better performance than many American
speakers at three times the price, we hope
that this modest increase will not put you
PARTRIDGE
THE AUDIO TRANSFORMERS
that pass all tests
Air -Tone Sound G Recording Co.
38
Allied Radio Corp.
Altec Lansing Corp.
Amperite Co., Inc.
41
Ampex Electric Corp.
Amplifier Corp. of America
Astatic Corp.
Audak Co.
Audio Devices, Inc.
Audio Fair
Audio Instrument Co
49
28
8
...
43, 44
46
29
25
Cover 2
45
43
Time, no less than
test, has proved Partridge Audio Transformers to be the most efficient and reliable
in the world.
* WILLIAMSON
Output
of which
TRANS-
FORMERS,
there is no U. S.
equivalent (vide "Audio Engineering" Nov.
1949) built to the original specification,
comes to you for $21.00, mail and insurance
paid.
*type,PARTRIDGE without
CFB :o
Watt output
accepted as
rival. Series leakinduct. 10 m.H; primary shunt induct.
130 H, with 'C' core construction and
hermetically sealed
you for $30.00,
mail and insurance paid.
age
Barker Natural Sound Reproducers
Belden Manufacturing Co.
Bell Telephone Larboratories
Bendix Radio Division
off.
We are not calling it the 216 because
there is no change in performance. It
still the 215, now the favourite among
American connoisseurs, but it is a better looking 21 5, and a more robust 215. Also,
the non -magnetic cone cradle means some
increase in flux density, so it is more sensitive. All this and Heaven, too, for only
$48.00 (plus that darned import duty).
Speakeasy prices pro rata.
And what is a 21 5? A recent British
customer says this: "Yesterday took delivery of my first H -T speaker. What did
find in the box? Rather a large magnet
for the chassis size, an iron frame, and a
most unusual cone arrangement. Being myself a manufacturer,
was impressed with
the finish and accuracy of the unit.
"By the time had screwed this into my
cabinet, the orchestra at the Albert Hall
was tuning up for the Promenade Concert.
Before the concert started, was more than
satisfied with my new reproducer. Candidly
heard top
had never heard before. A
music stand was shifted a little, and the
impression was that a steel strip was moved
within my lounge. Within a few minutes,
very quietly, a man ran off a few notes on
an oboe just behind my chair. He definitely
had a real oboe in the room with me.
"Then the concert. This is quite beyond
description. The timps were just perfect
not too heavy, but they were there. The
slight adjustments to their pitch were all
so apparent. The flutes and French horns
were just magnificent. No other word will
do. And then, finally, the applause. The
whole thing was something quite new to me
after having searched for quality for a number of years.
"Yes. Several whole L's for just a magnet, a steel pressing, and a curious cone
assembly, but the research that was also
packed into that carton is something which
shall never know about. It is, however,
NOT a speaker. It is surely a reproducer.
It is a very beautiful musical instrument.
It is a human voice. It is a really amazing
47
7
12
45
-to
37
Fullest data, including square save tests, distortion curves etc.. together with list of U. S.
stockist, re,hed Air .tfail to sou.
Equipment Co.
Chicago Transformer Co.
Classified Ads
35
JUDGE FOR YOURSELF
Dorf, Richard H.
Duotone Co., Inc.
46
Electro -Voice
31
Franklin Institute. Tha
44
Berlant Associates
Browning Laboratories,
is
.
45
Inc.
Camera
26
46
39
I
I
General Radio Co.
Goodman Industries Ltd.
Cover 3
36
at the
RADIO ENGINEERING SHOW, N. Y.
STAND 263) March 19th -23rd 1951
Our full range is being shown.
NOTE: We despatch
by insured mail per
return upon receipt of your ordinary dollar
check.
th
-
PARTRIDGE
TRANSFORMERS
ROEBUCK
LTD.
TOLWORTH
are invited fo handle
transformer that the S
is ea g, to buy
remember. immediate delivery from are
stocks in New York!
Jobbers
ROAD,
SURREY,
ENGLAND
I
I
I
I
I
-
H. A. HARTLEY, CO., Ltd.,
152, Hammersmith Road
London W. 6, England
48
Hollywood Sound Institute, Inc.
34
46
Institute of Radio Engineers
21
Jensen Manufacturing Co.
19
Kellogg Switchboard and Supply Co
42
Langevin Manufacturing Corp.
LeBel, C. j.
Leonard Radio, Inc.
45
46
Magnecord, Inc.
McIntosh Engineering Lab, Inc.
5
Par-Metal Products Corp.
40
Partridge Transformers
Permoflux Corp.
48
2
Radio Corp.
'
FX
STANDARD
OF
THE
GREAT RADIO
SHOWS
11
to 40,000 cps at 30 inches
per second tape speed
1
3
46
9
Reeves Soundcraft Corp.
Rek -O -Kut Co.
27
Shure Brothers, Inc.
23
41
to 15,000 cps half -track of
71/2 inches per second rape
speed
AMPEX ELECTRIC CORPORATION
San
Snyder Manufacturing Co.
Sun Radio G Electronics Co., Inc.
47
Terminal Radio Corp.
30
Recording Co.
United Transformer Co.
University Loudspeakers, Inc.
reL'0rGler
40
of America
U. S.
tape
4
47
Ltd.
no ot4ee
33
Newcomb Audio Products Co.
Pickering G Co., Inc.
achievement."
technical literature.
48
Harvey Radio Co., Inc.
Precision Electronics
Precision Film Labs, Inc.
Presto Recording Corp.
Professional Directory
I
One subscriber to our technical data service said he had had more useful information for his dollar than a year's subscription
to several technical journals (but not A.E.,
we hope). Send your dollar bill today for
"New Notes" and a regular mailing of
Hartley, H. A., Co. Ltd.
6
46
Cover 4
38
Carlos, California
BING CROSBY ENTERPRISES, INC., Hollywood
AUDIO -VIDEO PRODUCTS CORP..New York City
CRAYBAR ELECTRIC CO., All Principal Cities
TERMINAL RADIO CORP., New York City
RADIO SHACK CORPORATION, Boston
NEWARK ELECTRIC CO., Chicago
WESTREX CORP. (Export), New York City
AX -34
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
MARCH, 1951
This Heterodyne -Type V -T Voltmeter has an
Input Voltage Range of 1,000,000 to
This wave analyzer offers the simplest, most accurate and most direct method of measuring the
amplitude and frequency of the components of any
complex electrical waveform.
It is ideally suited to measurements of distortion
components in:
* Audio -Frequency Equipment
* Broadcast Transmitters
* Broadcast Receivers
* Telephone Systems
* Public Address Equipment
* Hearing Aids * Amplifiers
* Oscillators
* Vacuum -Tube Circuits
Essentially it is a heterodyne -type vacuum -tube
voltmeter with a highly -selective i-f filter using
three quartz bars. At only 60 cycles from resonance
the attenuation is down by 75 db. yet tuning is very
easy as it has a 4 -cycle flattop characteristic at
resonance. Standards for both voltage and frequency
are built into the instrument and can be used to
check its calibration at any time.
The input impedance is constant at 1 megohm; a
built -in 100,000 -ohm potentiometer is provided
for use where absolute voltage levels need not
be measured.
For complete information write us, without obligation.
90
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AmericanRadioHistory.Com
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38
ON
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Ultra compact audio units are small and light in weight, ideally suited to remote amplifier and
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UTC
being -} 2 DB from 30 to 20,000 cycles.
True hum balancing coil structure combined with
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Type
No.
A -10
A -11
A12
A -14
A -20
A -21
A -16
A -17
a
Application
high conductivity die cast outer case, effects good
Secondary
Impedance
Primary Impedance
MA unbalanced D.C.
Single plate to two grids.
8
A18
Split primary
A -19
A24
80,000 ohms overall,
2.3:1 turn ratio
80.000 ohms overall,
2.3:1 turn ratio
15,000 ohms
Single plate to two grids 8 15,000 ohms
MA unbalanced D.C.
Single plate to multiple line 15,000 ohms
50,
125/150. 200,'250,
333, 500/600
A -25
ohm
A -27
A30
A -32
r
14.00
18.00
TYPE A CASE
15.00
Single plate to multiple line 15,000 ohms
50, 125/150, 200,'250,
unbalanced D.C.
333, 500/600 ohm
Push pull low level plates to 30,000 ohms
50. 125/150. 200;250,
multiple line
orate to plate
333, 500/600 ohm
Crystal microphone to mul- 100,000 ohms
50. 125/150. 200.'250,
tiple line
333. 500 /600 ohm
Audio choke, 250 henrys ,,, 5 MA 6000 ohms D.C. .65 henrys
10 MA 1500 ohm D.C.
Filter choke 60 henrys
15 MA 2000 ohms D.C. 15 henrys
30 MA 500 ohm D.C.
8 MA
A26
List
Price
Low impedance mike, pickup, 50, 125/150, 200/250, 50 ohms
$15.00
or multiple line to grid
333, 500/600 ohms
Low impedance mike, pickup, 50, 200, 500
50,000 ohms
16.00
or line to 1 or 2 grids (multiple alloy shields for low hum pickup)
Low impedance mike, pickup, 50, 125/150, 200/250, 80,000 ohms overall,
or multiple line to grids
333, 500/600 ohms
in two sections
15.00
Dynamic microphone to one 30 ohms
50,000 ohms overall,
or two grids
in two sections
14.00
Mixing, mike, pickup, or mul- 50, 125/150, 200/250, 50, 125/150, 200;250,
tiple line to line
333, 500/600 ohms
333, 500/600 ohm;
15.00
mixing, low impedance mike. 50. 200/250, 500/600 50, 200/250, 500/600 16.00
pickup, or line to line (multiple alloy shields for low hum pickup)
Single plate to single grid
15.000 ohms
60.000 ohms, 2.1 ratio 13.00
Single plate to single grid
As above
As above
15.00
"
.
14.00
11/2"
:11/2"
x 2" high
maimmiIs
15.00
15.00
10.00
9.00
=Emma
_
ar
1It!11 021
.TC OUNCER components represent the acme in compact quality transformers. These units, which weigh
sle otnce, are fully impregnated and sealed in a drawn aluminum housing 1/e" diameter...mounting
:pposite terminal board. High fidelity characteristics are provided, uniform from 40 to 15,000 cycles,
acept for 0 -14, 0-15, and unite carrying DC which are intended for voice frequencies from 150 to
=,0)0 cycles. Maximum 'eve! 0 DB.
List
Type
No.
0 -1
0-2
Mike, pickup or line to
2 grids
0-3
Dynamic mike to
0 -4
Single plate to 1
Plate tb grid, D.C. in Pri.
Single plate to 2 grids
Plate t7 2 grids,
D.C. it Pri.
Single plate to line
Plate to line, D.C. in Pri.
Push pull plates to line
0 -5
0.6
0.7
OINCER
CASE
Cia.
x
11/2" high
Application
Mike, pickup or line to
1 grid
0 -8
0-9
0.10
0.11
0 -12
0.13
0 -14
0.15
Sec. Imp.
Pri. Imp.
grid
grid
1
50, 200/250
500 /600
50, 200/250
500/600
50,000
Price
$13.25
50,000
13.25
7.5/30
50,000
60,000
60,000
95 000
95,000
12.00
10.50
10.50
12.00
12.00
200/250, 500/600
200/250, 500 /600
50, 200/250, 500/600
13.25
13.25
13.25
50, 200/250, 500/600
13.25
12.00
9.50
13.25
13.25
15,000
15,000
15,000
15,000
15,000
15,000
30,000 ohms
plate to plate
50,000
Crystal mike to line
Mixing and matching
50, 200/250
Reactor, 300 Hys. -no D.C.; 50 Hys. -3 MA. D.C.,
50:1 mike or line to grid
200
10:1 single plate to grid
15.000
50,
50,
50,
200/250, 500/600
6000 ohms
42 megohm
1 megohm
150 VARICK STREET
EXPORT DIVISION:
I3
EAST
40th STREET, NEW YORK 16,
N. Y.,
www.americanradiohistory.com
AmericanRadioHistory.Com
CABLES:
"ARIAS"
1MMMEM/
,ú.t.c..cwi,á ncw`e
0 -2
...no
Rob
0-7
MEN
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:mu.c: <ux: n. nsúr
C-9
aima
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as
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