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Hi - Fi Phono Preamp Design
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AU
EGIEEIRItJG
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- See
Page
APRIL
1953
35c
19
here are the
30 BEST SELLING RECORDS
OF
29 of
1952*
them used
... and over 43% used
for the master recording
audiotap1 t for the original sound!
Made from
Audiodise
Master
Record, Artist & Label
WHEEL
CRY
YOU
AUF
I
(Leroy Anderson -Decca)
FORTUNE (Kay Starr -Capitol)
TANGO
BLUE
OF
(.Johnnie Ray -Okeh)
ME (Jo Stafford- Colombia)
WIEDERSEH'N, SWEETHEART (Vera Lynn -London)
WENT TO YOUR WEDDING
HALF
W.
BELONG TO
WISH YOU
(Patti Page- Mercury)
-
Hugo Winterhalter-Victor)
HERE IN MY HEART
(Al Martino-BBS)
DELICADO (Percy Faith -Columbia)
KISS OF FIRE (Georgia Gibbs- Mercury)
ANY TIME
(Eddie Fisher -Hugo Winterhalter- Victor)
(Four Aces- Decca)
Yes Audiodiscs and Audiotape are truly a
record -making combination -in a field where tiere
can be no compromise with Quality!
BLACKSMITH BLUES (Ella Mae Morse- Capitol)
JAMBALAYA (Jo Stafford -Columbia)
(Rosemary Clooney- Columbia)
GUY (Doris Day -Columbia)
BOTCH -A -ME
IS
A
(Johnnie Ray- Okeh)
(Frankie Laine -Columbia)
(Eddie Fisher -Hugo Winterhalter Victor)
LITTLE WHITE CLOUD THAT CRIED
HIGH NOON
I'M YOURS
t Trade Mark
-
(Mills Brothers- Decca)
BOOK (Johnny Standley- Capitol)
(Pre 1tS- King-Victor)
WALKIN' MY BABY BACK NOME (Johnnie Ray -Columbia)
MEET MR. CALLAGHAN (Les Paul -Capitol)
GLOW WORM
ITS
-
-a
-
TELL ME WHY
GUY
Of the thirty top hit records of the year, all but
one were made from Audiodisc masters! And that
one
London Record was made abroad.
It is significant, too, that the original recordings
for over 43 per cent of these records were first made
on Audiotape, then transferred to the master discs.
This marks a growing trend toward the use of
Audiotape for the original sound in the manufacture of fine phonograph records.
(Rosemary Clooney- Columbia)
WERE HERE (Eddie Fisher
MUCH
AS
Like Audiodiscs and Audiotape, this record speaks
for itself.
4600y."11Flo
aty
IN THE
SLOW POKE
ilip;iirr
- .
-
I'M YOURS (Von Cornell Coral)
I'LL WALK ALONE (Don Cornell- Coral)
TELL ME WHY (EddieFisher-HugoWinterhaUer- Victor)
TRYING (Hilltoppers
-Dot)
PLEASE,
MR. SUN
According
to
-
(Johnnie Ray Columbia)
AUDIO DEVICES, INC.
Retail Sales, as listed in THE BILLBOARD.
444 MADISON AVE., NEW YORK 22, N. Y.
Export Dept.: 13 East 40th St., New York 16, N. Y, Cablar
áLiLO LßP
JO
Audiodisrs are rnanu fat lured _in th
U.S.A
auctiop.crints
under exclusive license /rom P}'RAL, S.A.R.L., Paris
www.americanradiohistory.com
"ARAB"
--I
Successor to
ßñ101
-Established
1917
o
ENGINEERS
AND
INCLUDING
1
I
,
PHYSICISTS
ENGINEERINIG.j
- - - -N\
attending the
NATIONAL
CONFERENCE
C. G. McProud, Editor and Publisher
Edgar M. Villchur, Contributing Editor
Harrie K. Richardson, Associate Editor
Henry A. Schober, Business Manager
Eve Drolet, Production Manager
Edgar E. Newman, Circulation Promotion S. L. Cahn, Advertising Director
H. N. Reizes,,Advertising Manager
Elizabeth Beebee, Circulation Manager
Howard A. Chinn
H. Thorpe Covington Special Representative
677 N. Michigan Ave., Chicago 11, III.
John D. Colvin
Sanford R. Cowan, Mid -West Representative
67 W. 44th St., New York 18, N. Y.
C. J. LeBel
I. P.
AIRBORNE
ELECTRONICS
Representatives
Editorial Advisory Board
Dayton, Ohio
May ii -13
`
West Coast
J. W. Harbison
Galloway
816 W. 5th St., Los Angeles 17, Calif.
Maxfield
¡
on
i
James C.
George M. Nixon
CONTENTS
APRIL, 1953
-
Vol. 37, No. 4
INQUIRIES
-
2
Audio Patents Richard H. Dorf
8
Employment Register
10
Letters
12
New Literature
14
Audiology-W. R. Ayres
16
Editor's Report
19
High- Fidelity Phonograph Preamplifier Design-R. H. Brown
21
High Futility-Col. J. L. Dickey
23
Feedback -Degenerative and Regenerative Rudolph L. Kuehn
24
Thomas R. Hughes
Theater Sound in a Small Package -Part
26
An Auxiliary Mixer for TV Studios-George A. Singer
28
A Three -Channel Tone -Control Amplifier -Joseph F. Dundovic
Handbook of Sound Reproduction -Chapter 10; Part 2-Edgar M. Villchur 29
34
Feedback and Loudspeaker Damping-John A. Mulvey
38
Canadian House of Commons Sound Installation
40
A Note on Volume Controls -Charles Boegli
42
Equipment Report-Collaro 3RC522 Changer
44
The Best British Records of 1952 -H. A. Hartley
46
Coming Events
Record Revue-Edward Tatnall Canby
48
New Products
56
Industry Notes
71
Advertising Index
72
s,
P.
0. BOX 629, MINEOLA, N. Y.
AUDIO ENGINEERING (title registered U. S. Pat. Oa.) Is published monthly at 10 McGovern Avenue, Lancaster, Pa. by
Radio Magazine., los., Henry A. Schober, Preeldenp C. a. McProud, Secretary. Executive and Editorial Ornas:
204 Front St., Mineola, N. Y. SubealpUon
0ulted States, U. 8. Possessions and Canada. $3.00 for 1 year,
$5.00 for 2 years; elsewhere $4.00 per year. Single sepia Sat Printed In U. S. A. AU rights reserved. Entire contenta
copyright 1953 by Radio Magasina. Inc. Entered as Second Clue Matter February 9, 1950, at the Post ()Mee, Lancaster, Pa. under the Act of March 3. 1879.
rats-
AUDIO ENGINEERING
APRIL, 1953
j
Radar Laboratories
Microwave Laboratories
Guided Missile Laboratories
Advanced Electronics Laboratories
Electron Tube Laboratories
Field Engineering Department
I
c4'0
/
/
For the convenience of
those attending the Conference,
members of the Hughes
Laboratories Staff will be
available for interviews at
the Convention hotel.
...
COVER
RADIO MAGAZINES, INC.,
1
...... - I
e
-3-
N. M. Haynes, (left), Engineering Division of the Amplifier Corp. of America,
explains the operation of the new Magnematic high-fidelity, push-button controlled, a.c. operated miniature tape recorder to Professor P. P. Kellogg
of the Laboratory of Ornithology at Cornell University. Prof. Kellogg has acquired international fame in the field of bird recording, and is particularly interested in high -quality, highly
portable recorders for this work. These bird recordings
are published by the Cornell University Press for
the scientific study and analysis of bird songs
and bird language.
ARE INVITED
REGARDING
OPENINGS ON
OUR STAFF
HUGHES
i
eeta
``
RESEARCH AND
DEVELOPMENT LABORATORIES
Scientific and Engineering Staff
1
CULVER CITY, LOS ANGELES
COUNTY, CALIFORNIA
t
`
Assurance is required that relocation
of the applicant will not cause disruption of an urgent military protect.
1
1
.
r
T*
type no.
specs.
circuit
I
o
tEAgti'61
RICHARD H. DORF'
diagram
who have dealt with
magnetic recording have lovingly
conceived the perfect scheme for
overcoming the nonlinear frequency characteristics of tape. This scheme involves
selecting a carrier frequency to which the
system will respond and modulating it
(A M or FM) with the audio to be recorded. Upon playback, the idea is to
simply receive the carrier and demodulate
it. Since we are dealing with just one
frequency, the frequency response of the
tape and equipment is unimportant. Assuming the modulator to be linear, the output would be linear and, with direct -coupled
demodulators, we could even record d.c. as
a constant amplitude or freqency excursion
of the carrier.
The resultant euphoria lasts only for a
minute or so, at the end of which we run
rudely into what is formally called the
communications theorem, which says
roughly that you can't put two or more
pieces of intelligence in. the same place (in
the frequency spectrum) at the same time.
In practical terms, modulation produces
sidebands which are equal to the modulating frequencies on each side of the carrier, so that, alas, we are using the full
response of the recorder for only half that
range of modulating frequencies. As an
example, a recorder with response from 50
to 10,000 cps would have the carrier most
advantageously placed (for high -frequency
response) at 5025 cps. The maximum modulation frequency would be 4975 cps, because the upper sideband would be at 5025
plus 4975, or 10,000, and the lower side band at 5025 minus 4975, or 50 cycles.
You would, however, be in a good posiMAx 1'
Triad Power Transformers -like
other Triad transformers -have the
essential information right where
you want it -on the decal.
It simplifies installation- speeds
servicing-makes reordering easy.
Whether used for replacement,
industrial applications, PA amplifiers
or amateur gear, they offer
small size, maximum efficiency,
low temperature rise and low cost.
Also, they are "Climatite" treated,
both coil and core, for protection
against moisture and for elimination
of lamination chatter. Laminations
are painted to prevent rust. Copper
straps are used for static shields,
grounded to case and core.
Leads are color coded, UL approved.
Final tests include checking for
proper operation. Cases are
finished in durable, attractive
grey baked enamel.
OF
US
*255 W. 84th S4, New York 24, N. 1'.
I HEAD
1
tion to get low- frequency response sight
down to d.c.
Donald G. C. Hare has invented a system which uses the carrier modulation
scheme and allows use of most of the highf requency range of the equipment. The
patent is No. 2,623,952, assigned to Magnetic Equipment, Inc., of Greenwich, Conn.
From a purely audio fidelity standpoint,
it doesn't seem quite worth while; Dr.
Hare does not state in the patent what
he had in mind, but for instrument recording, for instance, it is easy to see where
HrLr
g RGINAL
l
g
I
u u L
u u ü`
Fig.
A
osc
P
C
1
perfect low- frequency response plus good
upper range might be useful.
The system uses double -track recording,
both tracks being used simultaneously, with
separate heads for each. The carrier frequency is set at the upper-frequency limit
of the equipment's response. The modulation is FM and trouble with upper side bands (out of the range of the recorder) is
eliminated by using only downward f requency swings. To do this, the input signal
is split, one-half of each audio cycle modulating one of two oscillators.
Figure 1 shows a sample signal to be re(Continued on page 6)
LIMITER
IRECTIFIER
LIMITER
IRECTIFIER
Write for Catalog TR52F
HEAD
TRANSFORMER MFG
4055 Redwood Ave.
2
2
CO
Venice, Calif.
Fig. 2 (above)
and Fig. 3 (below).
AUDIO ENGINEERING
www.americanradiohistory.com
APRIL, 1953
SPECIALIZATION
MAKES THE DIFFERENCE
Specialization may be defined as the concentration of
all effort to a special or specific course of action
Even a mechanical device concerned with the function of record
reproduction should possess all the advantages of such specialization.
Most units undertake to do much more. They change records,
mix records, flip records, reject records, and assume a multitude of other
functions. This is 'generalization' as distinguished from 'specialization'.
The REK -O -KUT turntable, on the other hand, is devoted
entirely to paying records. And every design feature, every fragment
of engineering know -how has been devoted and restricted
to the all -important job of playing records ... to provide the
constant, steady, unwavering record motion necessary for
the faithful reproduction of records free of mechanical distortion.
Specialization makes that difference. And all of the
efforts and facilities of the manufacturer shall continue
to be intensively devoted to that one objective...
that one aim: To make the finest turntables in the world.
There is a REK -O -KUT Turntable for your specific discriminating
requirement. Seven models are available at prices ranging from $54.95.
Sold through leading Dealers and Parts Distributors.
Write for Descriptive Literature
.
TURNTAB LES
REK- O -M.UT COMPANY, 38.03M
Queens Boulevard, Long Island City 1, New York
Export Division: 458 Broadway, New York 13, U. S. A. Cables- Morhanex
n Canada: Atlas Radio Corp., Ltd., 560 King Street, W., Toronto 2B
I
AUDIO ENGINEERING
APRIL, 1953
www.americanradiohistory.com
3
New compact amplifiers -use townoise, long -life, miniature tubes.
Every component is easy to get at for
EASY WAY the BC-2B Consolette handles is due in great measure to the careful
attention RCA engineers have given to
THE
construction details-and to a number of
unique operating features (not found in
their entirety in any standard consolette).
Some of these advantages are pictured on
these pages.
For example, see how easy it is to get at
type
his
BC.-2B
is
the amplifiers and components. Note bow
every inch of wiring can be reached without disturbing the installation. See how
the consolette fits snugly into the control
room -unobtrusively. See how the styling
matches other RCA audio and video
equipments.
Based on more than 25 years of experience in building studio consolettes, type
styled to match RCA video equipment -like
fan.liar video
console.
Accessibility, plus) New hinged control panel swings down;
amplifier home swings up.
inspection and maintenance.
...
BC -2B is in our opinion a high point in
consolette design. The instrument includes
all essential elements needed by most AMFM and TV stations. And every feature has
been operation-proved -many in RCA deluxe custom-built equipment. Type BC-2B
it available at a "packager" price!
For details, call your RCA Broadcast
Sales Representative.
and it's styled to match othe- RCA audio equipment, too
this master switcher, for instance.
-like
www.americanradiohistory.com
xl
A :I
To
external connections are made to two terminal blocks.
get at them, just lift the cover.
New,
reliable interlocking push -button
switches are leaf-type and cam -operated.
Improved, faster - operating
speaker relays eliminate key
clicks and audio feedback.
to'
height, and 30- degee slc ping
Trost and top offer maximu -r sudio
eisio Sty. You
install tFs EC -2B
sight up agairest your rtudío win dow. There are no rear corrections.
ra
RADIO CORPORATION ofAMER/CA
ENGINEER/NG PRODUCTS DEPARTMENT
www.americanradiohistory.com
CAMDEN, M.J.
the
AUDIO "BUGS" know
they're using
I
0
best
co
for quality
Audio Amplifier with "Pros
An Unusual P.A. Amplifier
Audio Modulator
Described in Radio News, Nov
1951. Heart of the amplifier is the
CHICAGO full -frequency BO -6
output unit, with other "Sealed in- Steel " trans, ormers incorporated
in the separate power supply
chassis for top audio results.
An unusually compact 20 -watt
P.A. amplifier of exceptional
audio fidelity. CHICAGO full -
Described in Radio News, June
1951. An efficient audio testing
instrument suitable for precise lab
analysis or for subjective quality
tests. CHICAGO "Sealed -inSteel" input, output and power
frequency range transformers are
used exclusively for exceptional
audio quality coupled with small
site and light weight.
transformers are incorporated.
Wherever audio quality is a "must" -the experts specify and use
CHICAGO "Sealed-in- Steel" Transformers
talk about full frequency
-
Output Transformers
really deliver for you...
CHICAGO
Stabilized D.C. Amplifier
D.c. amplifiers rarely find justification
for use in pure audio work today except
for special purposes, but they are essential
for many types of instrumentation. When
they are used -particularly for amplifying
direct current-they are plagued by output
variations traceable to drift in power -
.2 db 30- 20,000 CPS
.04
q W LEVEL- 15 WAITS
rtsw.a w.sw
or .uY
To unroor
°02
SO
500
o
Mil GM Mel
2M
500
tM
rPEOUEMCY IN C.PS.
200
Ne. 60 -6
Ne. 60 -7
For use in high fidelity amplifiers.
Couples push -pull 6L6's (7500
ohms, C-T) to 6/8 or 16/20 -ohm
voice coil. Center -tapped tertiary
winding provides 15% inverse
feed -back to reduce harmonic distortion to a minimum. In drawn
steel case, 4s/µ" s 3%," x 3I1/µ"
with mounting studs and convenient pin -type terminals.
For matching 600 or 150 -ohm line
to a 6/8 or 16 /20 -ohm voice coil.
Frequency response within plus or
There's
-
minus 1 db. at full rated output
maximum power level, 30 watts.
Mounted in compound -filled
drawn steel cose, 4s/µ"
s 3%," s
31/4". Mounting studs and pin type terminals same as No. BO-6
illustrated above.
Free "New Equipment" Catalog
Get the full details on CHICAGO'S New Equipmen! Line -including "Sealed -in- Steel"
transformers designed for every modern
audio application. Write for your Free copy
of this important catalog today, or get It
from your electronic parts distributor.
a
corded, the square wave at A. The first
half-cycle modulates the oscillator associated with track 1, the oscillator frequency swinging downward and back as at
B. The second half-cycle has no effect on
oscillator I but modulates only oscillator
2, on the second track, swinging its frequency down and back as in C. Thus each
track carries information about odd half
cycles. On the playback the oscillators are
demodulated, then the recovered half -cycles
of audio combined to reproduce the original
modulation.
One circuit capable of doing the job is
shown in Fig. 2. The signal goes into the
primary of a transformer. The center tapped secondary and rectifiers cause only
odd half -cycles to affect the reactance tube
lin each circuit. A playback circuit is
shown in Fig. 3. Outputs of the two playback heads are fed to suitable volume
limiters, thence through frequency-slope
networks to detector rectifiers. The transformer recombines the two signals into
the original one. The slope networks are
simple FM discriminators which operate
in the same way as a slope detector for
ri. FM transmissions. In ordinary receivers FM is sometimes (not often these
days, fortunately) detected by ordinary AM
circuits by tuning the carrier to one side
of the i.f. response curve and relying on
the skirt slope to change the signal amplitude over each modulation cycle. The slope
detector shown here is usable because the
slope can be made quite linear, which is
not true of receivers using tuned circuits.
CHICAGO
Transformer for Every
Audio Application
"Sealed -in- Steel"
Transformers (the world's
toughest) are available in 3
complete ranges for every
type of audio requirement:
CHICAGO
supply voltages.
Robert P. Nelson has designed a simple
compensation circuit for d.c. voltage amplifiers; it is diagrammed in Fig. 4. The
patent, No. 2,620,406, is assigned to Philco.
The amplifier itself has two stages, the
two halves of a 12AX7, V, and V, in the
diagram. The circuit is fairly conventional.
The positive voltage at the plate of V,,
which would appear at the grid of V,, is
balanced out by a suitable tap on the voltage divider Rs-Rs--Rs between B -plus and
C- minus. Output for the amplifier is taken
from the plate of Vs. It is this output d.c.
which is to be stabilized.
Initially R, is set for the desired gain
and d.c. balance (correct voltage on the
grid of V. for bias). R, may have to be
readjusted later.
Next R. is adjusted. R. is part of another
voltage divider used to bias the grid of V,,
which is a compensation tube. It has a
Full Frequency, Public
Address, and Communications. Whatever the application, it's wise to choose
audio transformers for that extra margin of
CHICAGO
dependability under all
operating conditions.
CHICAGO TRANSFORMER
DIVISION OF ESSEX WIRE CORPORATION
3501 ADDISON
STREET
CHICAGO 18, ILLINOIS
Fig. 4
6
AUDIO ENGINEERING
www.americanradiohistory.com
APRIL, 1953
BEST
LONG -TERM
INVESTMENT
IN
TV
STUDIG
CONSOLES
SPEECH
11
range of
of wide
by reason
Versatili'.y
zmplifiers
plug -in
Accommodates
line amplifiers,
2
pre -amp
units, 10 pre-amplifiers,
supply
14 plug -in
1 power
1
monitoring
Ocr.tdtci,cd,úu.f
eat.tezea
amplifier,
p
the
Console with
Buy this GATES
expansion
for
add later
needed
Ten mixing channels
amplifiers
of amp
Provision for ten or lesser number of pre-amplifiers
Provision for single or duplicate line amplifers
Choice of
8 ac 16
watt moritori
7g
amplifier
Complete ren ale line, cueirg, override and auxiliary
Here is a TV speech console that
can grow with your station. Meets ALL large
studio demands for TV (and AM too) yet is flexible
enough for any station requirement.
It features NEW GATES PLUG-IN amplifiers throughout. There's room for 14
but you buy only what you
need and add later as you need them.
-
The NEW GATES CC -1 was designed following months
of study covering all phases of TV programming and
production. It fully meets every requirement for complex
or simplified production techniques.
The NEW GATES CC-1 Speech Console is beautifully
constructed, providing a new high in rigid performance
standards
both electrical and mechanical.
Before you invest, investigate the newest and
latest in speech input equipment
the GATES
CC-1 "PROGRAM MASTER".
:witching facilities
Provision for Patch paiel te nlination of all major
circuits
Duplicate VU r,eters
Group contro
provided
of any
i-
iurrber
of mixing positions
twa SJB and one MASTER gain
cantrofs
Color coded
oatrol facilities
-
-
GATES RADIO COMPANY, QUINCY, ILLINOIS, U. S. A.
MANUFACTURING ENGINEERS SINCE
2700
Polk Avenu, Houston,
AUDIO ENGINEERING
Tete
W
APRIL, 1953
Building, Washington, D.
1.111
International Divisien, 11E. 40th St.,
Canadian Marconi Company, Montreal, Quebec
C.
New York City
7
LETTERS
Binaural vs. Stereophonic -Again
SIR:
On semantic grounds, the suggested definitions of binaural and stereophonic reproduction seem to leave something wanting. If
monaural refers to a single -channel sound
source (the word is not used to mean listening with one ear), then binaural logically means listening to two channels. Since
stereophonic listening also can consist of
listening to two channels (or three or
more), it too should logically qualify as a
form of binaural reproduction. Semantically, therefore, binaural and stereophonic
reproduction should not in all cases be two
different things.
Conforming to the suggested definitions,
however, methods of listening to musical
reproduction can be classed as follows:
1. Single Channel
A. "Point Source" -single speaker (or
one earphone).
Source"-several speakers
spaced apart (or two earphones) on
one channel.
C. "Source- Free" -one or more speakers
on one channel heard with one ear only.
II. Multichannel
multiple speakers
D. "Stereophonic"
spaced apart, each on a separate sound
channel. The respective channels originate from microphones spaced in a manner similar to the loudspeakers.
E. "Binaural" -two earphones on separate sound channels. The respective
channels originate from microphones
spaced a head's distance apart.
A and B are the conventional methods
commonly referred to as monaural. Methods D and E are the present subject of
lively discussion as improved means of reproduction. Method C, although an old
trick, seems to have been overlooked.
Multichannel listening endeavors to restore to reproduced music its original
spaciousness, detail, and arrangement of
instruments. More, it tries to free the music
from its connection with a box against the
tries to restore presence. One
wall
wants to feel surrounded by the music, as
happens at a good seat in a good hall.
Perhaps some readers would like to experiment with listening to orchestral reproduction with one ear completely stopped
up. My own reaction is quite favorable.
While one does not hear violins on the
left and horns on the right, yet the music
does seem to acquire more detail and free
itself from association with a speaker at
the other end of the room. It also becomes
more spacious.
Among friends, reactions have been
mixed. At worst, some experienced a loss
of highs and/or bass One complained of
fuzziness. On the other hand, a musically
trained couple who have a fine hi -fi system
said about as follows : 'The music had much
more detail. Individual instruments were
easier to pick out. We felt as though we
were in the middle of the music and in
fact had to turn the volume down a bit."
B. "Diffused
-
¡VFW
pnagninie "yfird
one -case Portable tape recorder
-it
Now o professional portable recorder and amplifier in a single case, light in
weight, yet ruggedly constructed to take the most difficult remotes.
Tested and Proved -Thoroughly field tested, the outstanding performance
of the Voyager has brought enthusiastic approval of networks to this newest
member of the Magnecord family.
Professional Quality- Frequency response up to
+2db
from 50 to 15,000
cycles per second. The amplifier has bridging input and one low impedance
mike input. 600 ohm balanced output and two speed (71/2' and 15") equaliza-
tion and headphone monitor jack on front. Tape lifter optional.
Successfully Used by Advertising Agencies -Permits unlimited uses
-air
checks, development of spot announcements, program development, and with
an amplifier and speaker, auditions and client presentations. The full sound
spectrum
is
flawlessly reproduced.
HERMAN
deme.uret;on,
yew retevAen Di, a,ory
For
undr "Rcerdor,"
BURSTEIN,
280 Twin Lane E.,
Wantagh, L. I., N. Y.
or
Confusion
SIR:
I)?
10
sE -s
INC.
725
west Ohio Sheet
Chicago 10, Illinois
Last summer Antal Dorati conducted the
Minneapolis Symphony orchestra in a series
of recordings at the University of Minnesota for Mercury. Getting glowing reports
from our critic, I hastened to purchase
"Scheherazade."
[Confitteed on page 571
AUDIO ENGINEERING
APRIL, 1953
IN
TAPEWOUNO CORES
JUST NAME YOUR REQUIREMENTS!
RANGE OF MATERIALS
Depending upon the specific
properties required by the application, Arnold Tape -Wound Cores
are available made of DELTAMAX
.
4 -79 MO- PERMALLOY
...
..
.
SUPERMALLOY
MUMETAL
. 4750 ELECTRICAL METAL .. .
or SILECTRON (grain -oriented
silicon steel).
cores -are manufactured to meet
your individual requirements.
RANGE OF TYPES
In each of the magnetic materials
named, Arnold Tape -Wound Cores
are produced in the following
standard tape thicknesses: .012' ,
.008 ", .004' , .002 ", .001", .0005 ",
or .00025 ", as required.
RANGE OF SIZES
Practically any size Tape-Wound
Core can be supplied, from a fraction of a gram to several hundred
pounds in weight. Toroidal cores
are made in twenty-two standard
sizes with protective nylon cases.
Special sizes of toroidal cores-and
all cut cores, square or rectangular
Let us help with your problems
of cores for Magnetic Amplifiers,
Pulse Transformers, Current
Transformers, Wide Band Transformers, Non -Linear Retard Coils,
Peaking Strips, Reactors, etc.
Address: ENG.
DEPT.
A
THE ARNOLD ENGINEERING COMPANY
SUBSIDIARY OF AI .EGHENY LUDLU
A
STFEL
COR'ORATION
General Office & Plant: Marengo, Illinois
]ISTRICT SALES OFFICES
New York: Empire
AUDIO ENGINEERING
Appe..-carce
ïtcle
APRIL, 1953
www.americanradiohistory.com
Bldg.
Los
Angeles: 3450 Wilshire Blvd.
11
NEW LITERATURE
Auca-Rradly Company, Milwaukee, Wis.
.s offering a new 26 -page bulletin featuring multi-unit control centers. Contained
in the bulletin is a complete description
which covers all aspects of design and
construction. Included also are unit dimensions and ratings, as well as typical applications. An informative feature of the
bulletin is titled "Pattern for Planning a
Control Center," which includes typical
layout charts and floor arrangements.
PERFECT PRODUCTION
Allied Radio Corporation, 833 W. Jackson Blvd., Chicago 7, Ill. is releasing the
"Allied High -Fidelity
lrst issue of the
Auditioner," a 4 -page quarterly publication which contains information about new
REQUIRES
Precision
Prints
audio products and developments, especially in the field of high fidelity. One of
the publication's interesting features is
the "Hi-Fi Clinic," which includes questions and answers about typical problems
encountered with home music systems.
Available free to audio technicians, explaced
perimenters, and hobbyists. To be request
on the mailing list, address your
to High -Fidelity Auditioner, Allied Radio
Corporation at above address.
General Electric Compta, Schenectady
N. Y. announces the 1953 edition of the
GE Instrument Buyer's Guide. Fully illustrated, the 102 -page book contains ratings, ASA accuracy classifications, and
prices of all GE indoor and outdoor po5,
Listings
tential and current transformers. together
of ratio and phase -angle tests,
and
with tables covering the mechanical
thermal limits of current transformers,
GEAPublication
Request
are included.
TRACK PRINTS
OF TOP QUALITY
4626F.
All tracks printed independently on
The Gray Manufacturing Company,
Hartford 1, Conn. recently issued an unusual employee -recruiting booklet titled
"Careers at Gray" to interest experienced
radio and electronic engineers in Joining
the company's staff. Pocket -sized, the publication contains 32 pages describing the
employment opportunities existing at
Gray, also the firm's facilities for designing and building reproduction apparatus, radar equipment, and other advanced
electronic devices. In addition, the booklet
describes in detail the advantages of living in Hartford, carefully delineated as
"The Hometown of Happy Families."
you
Truly an exceptional little book-if
weather
are a competent engineer witha adelightful
eye out for a better job in
Maurer 1 -to-1 optical track printer,
exclusive with PRECISION. Highly
refined optical system eliminates
"contact shifts," gives complete flexibility in printing from "A- or
B-wind" originals. Sensitometric
sound control.
YOUR ASSURANCE OF
BETTER 16mm PRINTS
15 Years Research and Specialization in every phase of
16mm processing, visual and
aural. So organized and equipped that all Precision jobs are
of the highest quality.
including exclusive Maurer
designed equipment -your guar-
Hudson Radio & Television Corp., 48 W.
48th St., New York 38, N. Y. announces a
new 196 -page catalog of electronic equipment. In addition to being a worthwhile
buying guide, the book is so prepared that
it can also serve as a reference manual
for users of electronic components of virtually every type. Included is a cross -reference and guide to JAN equipment of
most leading manufacturers. Emphasizing
the importance of Audio in the over -all
electronic picture, the first section of the
for
catalog is devoted to sound equipment
home and professional use. Will be mailed
on request by mail.
NIF CISION
Radio Shack Corporation, 167 Washington St., Boston 8, Mass. will mail free on
request a new 8 -page rotogravure sales
bulletin which has been published as a
part of the company's 30th anniversary
celebration. Featured in the bulletin are
the first commercially avialable Junction type transistors, and the sale- priced high fidelity tuner and amplifier inventory of
Approved Electronics Company, which
Radio Shack bought out in its entirety.
is given
each film, each reel, each scene,
Newest Facilities in the 16mm
field are available to customers
of Precision, including the most
modern applications of electronics, chemistry, physics, optics,
sensitometry and densitometry-
phase of the complex business of
processing assuring you of the
very best results.
antee that only the best is yours
at Precision!
Individual Attention
each frame
- through
every
-
community, write f,,r it by all means.
enable us to offer service unequalled anywhere!
Our Advanced Methods and
our constant checking and adoption of up- to- the -minute techniques, plus new engineering
principles and special machinery
-a
diPrecision Film Laboratories
vision of J. A. Maurer, Inc., has 14
years of specialization in the 16mm
field, consistently meets the latest demands for higher quality and speed.
12
FILM LABORATORIES, INC.
21
Sanborn Company, 88A Osborn St., Cambridge, Mass. is now releasing a 6 -page
illustrated bulletin which explains the
scope of application of Sanborn equipment
for the recording of a wide variety of
electrical and mechanical phenomena. Included in the bulletin is a chart of various
phenomena which can be recorded with
Sanborn direct -writing recorders, together
with transducer data. Also included are
complete performance data and specifications of Sanborn equipment. Titled "Applicability of Sanborn Direct Writing Recording Systems," the bulletin will be
mailed free on request.
West 46th St.,
New York 19, N.Y.
JU 2 -3970
AUDIO ENGINEERING
www.americanradiohistory.com
APRIL, 1953
of Your Installations
Be Sure
.
..
To You, Belden 's Golcen
Use
Anniversary Means
*Wide 1.7idred
-product pert ormance that
can come only from a "knowhow" that has grown through
actual service since the
inception of Radio.
-an ability to co-operate in pioneering new
wires to meet oranticipate industry's growing needs.
In the years that
follow
This Belden
Program
MULTIPLE CONDUCTOR
You know what you are doing when you use
Belden Multiple Conductor Cables they're aptitude rated. They are designed to provide desirable electrical characteristics, and rigid control
-
CABLE
assures constant quality.
Specify Belden Radio Wires.
Belden Manufacturing Co., 4689 -R W. Van Buren St., Chicago 44, III.
-
Is-
TO III
CONTINUED
No. 6453
APTITUDE RATING
Stranding
.
.
.
.
41x34
Insulation Thickness
1
64"
Jacket Thickness
1
32"
Nominal Diameter
.265'
a
APTITUDE RATING
d
Stranding
APTITUDE RATING No. 8454
Stranding
.
41x34
Insulation Thickness
1!64`
.
.
.
Jacket Thickness
Nominal Diameter
APTITUDE RATING
APTITUDE RATING No.
Stranding
.
.
.
Jacket Thickness
Nominal Diameter
.
.
.040'
.370"
Stranding
e
1
I
64"
APTITUDE RATING No. 8425
1
32"
Strandin3
.
Insulation Thickness
.280"
o
locket Thickness
APTITUDE RATING
No. 8424
Stranding
Insulation Thickness
Jacket Thickness
Nominal Diameter
.
Also
.
.
.
.
4
Insulation Thickness
used
as
26x34
.020"
.040"
.305"
Nominal Diameter
32"
P0T64
26x34
.020"
.040"
.335"
Interconiecting power co
ble for all electronic uses.
.
26x34
Insulation Thickness
.020'
Jacket Thickness
Nominal Diameter
.040"
.355"
Stranding
microphone
roble.
No. 8426
APTITUDE RATING
.
Interconnecting power cable for all electronic uses.
The
na ae;îed LINE
AUDIO ENGINEERING
APRIL, 1953
www.americanradiohistory.com
'64"
SV
Nominal Diameter.) 14x.231"
Underwriters' Type
x34
1
132"
x34
1
1
1452
4
.545"
APTITUDE RATING No. 8888
16x34
41x34
Insulation Thickness
Jacket Thickness
Nominal Diameter
Underwriters' Type
Interconnecting power cable for all electronic uses.
8455
.
Jacket Thickness
Nominal Diameter
26x34
Insulation Thickness .020"
1'32"
.265"
No.
Insulation Thickness
No. 8427
Stranding
.
The NEW
DC-AC CONVERTER
by
15L?L?
W. R. AYRES'
Output Transformer
Design Considerations
DEVELOPMENT Of an audio
power amplifier depends greatly upon
output transformer characteristics,
ur ther the principal equipment objective
be economy or quality. While some pertinent features may be specified readily in
simple numerical form, other characteristics, important to high -fidelity equipment,
are of such involved nature that simultaneous development of circuit and transformer is almost essential. However, experience and analysis demonstrate several
principles upon which important choices
are based, and form a basis for judgment
applicable to either design or purchase.
Basic purposes of the output transformer
are coupling tubes to the load with d.c.
isolation, and transformation of the load
impedance to a value suitable for efficient
tube operation. To avoid adversely affecting amplifier performance, the transformer
preferably would be highly efficient over
the desired band, and would not cause objectionable distortion at low frequencies.
Apparently then, refinements characterizing
high -quality output transformers simply
Permit good circuit performance, rather
than cause it to be good.
UCCESSFUL
Delivers MORE Power
S
for PROFESSIONAL Use
These latest -of -all Carter DC to AC Converters are specially engineered for pro
fessional and commercial applications re.
quiring a high capacity source of 60 cycles
AC from a DC power supply. Operates
from storage batteries or from DC line
voltage. Three "Custom" models, deliver.
ing 300, 400, or 500 watts 115 or 220 V. AC.
Wide range of input voltage, 12, 24. 32, 64,
110 or 230 V. DC. Unequalled capacity for
operating professional recording, sound
movie equipment and large screen TV re.
ceivers. Available with or without manual
frequency control feature.
Response
The frequency range over which relatively uniform transformation may be had
is controlled largely by the source and terminating impedances, the shunt winding
inductance, and the leakage inductance.
With fixed source and load impedances, the
ratio of these inductances sets the ratio of
limiting high and low frequencies ; ratio
values range from less than 200 for lowest
cost equipment, to 10,000 or more in costly
idealizations. Chief determining factors are
the core material, prevailing d.c. magnetization, and the winding configuration. To the
extent that capacitances and changes in
HOW LEADING NETWORKS
CARTER CONVERTERS
Photo shows Tommy Bartlett, star of NBC
"Welcome Travellers" program, aboard
N.Y.C. R.R. "Twilight Limited." His Carter
"Custom" Converter makes recording possible on board the train, from regular train
Current converted to 110 V. AC. Radio networks, stations, program producers use
Carter Converters for all sorts of on -thespot recording.
USE
MAIL COUPON FOR CATALOG
*BQG? MOTOR CO.
2648 N. Maplewood Ave.
Ì
Chicago 47
311 W.
Oakland Ave., Oaklyn 6, N. J.
Distortion
Low -frequency waveform distortion in
iron -core transformers occurs because the
shunt winding inductance is not constant
throughout the signal cycle. Relatively little
quantitative material has been published,
and there is considerable variation among
core materials of otherwise similar character. General trends of the data have been
analyzed, however, and are reviewed briefly
here.
Let X/R equal the ratio of the opencircuit reactance of the transformer primary
winding to the parallel combination of
source and load resistances. X may vary
widely with frequency, flux density, and
changes in d.c. magnetization. With X/R
[Continued on page 69]
tib
Carter Motor Co.
2648 N. Maplewood Ave., Chicago 47
Please send new catalogs containing complete information on Carter "Custom" Con.
verters and other Rotary Power Supplies.
Name
Address
City
14
S
cure permeability may be neglected, coil
turns do not influence the bandwidth in octaves, since both self inductance and leakage
inductance vary as the square of the number of turns. While not affecting the response -curve shape, the number of turns
sets the position of the curve in the frequency spectrum.
Assume a certain ratio of these inductances, and no other reactances of importance, and let g equal the ratio of source
impedance to load impedance. The ratio of
high and low frequencies at which the response is down 3 db is then proportional
to the factor (g +1)' /g, which has minimum value when g= 1. Thus, equal source
and load impedances is the least desirable
combination if wide -range response is a
principal 'object. Core distortion considerations indicate that g should be made low
rather than high ; that is, the source impedance would preferably be very low compared with the load impedance. Most significant reduction of g is accomplished with
negative feedback in the amplifier, which in
turn causes additional complication in the
transformer design.
I
This is the first of a series of short articles covering various aspects of audio
engineering on a not -so- technical level, yet with information which can be
relied upon. During the next few months, Mr. Ayres will discuss resistance coupled amplifier charts, the effect of feedback upon tube characteristics, feedback from the output transformer primary, from the secondary, and from a tertiary winding. Æ would welcome readers' comments, as well as suggestions for
further subjects to be covered in the future. Ed.
stale
AUDIO ENGINEERING
www.americanradiohistory.com
APRIL, 1953
Have you heard the latest...
IN BACKGROUND MUSIC?
-or
An atmosphere to relax and enjoy
the stimulation to work, to think, to
-
play or buy
these are the benefits
of background music. And background
music is now practical anywhere, even
beyond the reach of present wired
services.
With the announcement of the new
AMPEX 450, magnetic tape, musical
wonder of a coming era, has become
the ideal medium for background music. Hourly cost drops to a new low;
quality rises to an all-time high. A wide
variety of music for every purpose is
now available on pre- recorded tape
(see your Ampex distributor). Tape
recordings eliminate needle scratch
and their fidelity is permanent. They
last for any conceivable number of
plays.
On the AMPEX 450, up to eight hours
of unrepeated music is available from
one 14-inch reel of tape, and fully
automatic repetition is available. The
troubles and complexities of record
changers are eliminated. And the
AMPEX requires no standby attention
from an operator.
.4 MPEX
For further information, write to Dept. B
AMPEX
MAGNETIC RECORDERS
background music has
place in your business.
THE NEW AMPEX 450
8 hours of uninterrupted music
(rest periods as desired)
Usable on land, sea or air
No standby operator required
Lowest cost per hour
AMPEX ELECTRIC CORPORATION
934 CHARTER STREET
AUDIO ENGINEERING
a
APRIL, 1953
www.americanradiohistory.com
REDWOOD CITY, CALIF.
15
EDITOR'S REPORT
AUDIO ENGINEERING AWARDS
WITH THIS ISSUE, íE rounds out its sixth year
of
publication, and simultaneously takes pleasure
in making its initial public announcement of the
first annual AUDIO ENGINEERING Awards for technical
excellence. These awards -to be made in three fields
involving audio -will be announced in the May issue,
together with the all of the details of the judging. Announcement of the winners will be made at the same
time to the public prints, to the end that many more
converts to better audio may be enrolled.
Of the three fields in which awards will be given,
there are two which involve audio in a form which is far
from being hi -fi, as we know it, but which depend entirely upon audio for the existence. Until next month,
they shall remain unidentified.
The third field will be of greatest interest to most of
AE's readers since it involves what is, by and large, the
largest source of music for reproduction in the home. By
now this field must be recognized as Phonograph Records, and correctly so.
Since there are many thousands of phonograph records made annually, and since there are only so many
weeks in a year, some means of screening had to be
found. Who better than the individual manufacturer is
able to select the best single record put out by his own
efforts ? No one. And if this is the case, the small manufacturer who turns out one super -excellent record has
as much opportunity to win an award as the massive
organizations who make thousands of titles ; which is,
after all, a very fair arrangement.
To this end, therefore, we set up the following criteria: every manufacturer we could locate was invited
to submit his best record in each of eleven categories
judged from both musical and technical excellence-to
Æ's judging committees. The limitations were few
only those records placed on the market in 1952 were to
be allowed, and only one record was to be submitted in
each category.
In the Classical Section, five categories were established- symphonic, chamber or small instrumental
group, solo instrument, vocal (including chorals, duets,
trios, quartets, quintets, and so on), and operatic
either complete opera or selections. In the Popular
Section, six categories were established-dance, jazz,
vocal, musical comedy, novelty, and folk. Regrettably,
many of the finer jazz discs have been created by small
companies, ofttimes impossible to trace. Where possible,
these have been obtained by outright purchase from retail sources. Preliminary screening-from the technical
standpoint- was applied to the popular group, and final
judging was done on those records which were considered passable technically. All classical records submitted were passed to the judging committee without
preliminary screening.
Going back to the original premise-the list of records submitted by the manufacturers naturally represented the top single product in each of the categories,
from the viewpoint of the manufacturers' authorities,
-
16
and consequently makes a very imposing list of records
in itself-without the. need for any further judging. But
it is still a large list, and careful consideration was
necessary to determine which single record in each of
the eleven categories is really the best
the judges'
opinion -both musically and technically.
Obviously, engineers are rarely qualified to judge
how well a musical selection is performed ; and by the
same token, musicians are all too likely to become so
enthralled by the virtuosity of the performer that they
overlook technical imperfections. Therefore, the judging
committees are composed of two types of people-musical, and technical.
Frankly, this is an experiment. We believe that when
a small manufacturer turns out an exceptionally fine
product, he should be commended, just as the large
manufacturer should. However, in the record columns
the small producer is hidden by the sheer mass of records made and released each month, yet he should get a
fair shake. We hold no brief for either the large or the
small manufacturer over the other, but aim only for
fairness.
We believe, therefore, that the method chosen to reduce entries to a number which it is feasible for a group
of judges to study thoroughly has some merit. It gives
the judges a high level of product to work with, and best
of all, it gives all of us a fine list of records.
As for ourselves, we look forward to a number of interesting sessions -all of which will be over by the time
this is being read. But Read All About It in the May
issue.
-in
1-
LOOKING FORWARD
Don't be too dismayed at the prospect of a May issue
filled with ballyhoo about the awards --we still have
some interesting articles on technical matters. One of
the best of these is Bob Moyer's paper on "The Evolution of a Recording Characteristic" which tells the whys
and hows of this elusive curve-and gives the official
Word on the proper playing characteristic for RCA
Victor records from 'way back. We believe you'll like
this article. Julius Postal entertains educationally-or
vice versa-with the first of a two -part article which we
titled "Simplified Push -Pull Theory" ; his title, "Push Pull Without Tears," somehow didn't seem to be sufficiently dignified for AE's austere pages.
The June issue holds up with a few good numbers,
too. Our choice for the lead article is "The Lateral Mechanical Impedance of Phonograph Pickups," which is
not nearly so deadly as its title might indicate. Actually,
this paper shows the importance of lightweight moving
elements in a pickup, and how various factors affect
performance. It takes two issues for this paper, so it
will conclude in July, which, being well into the summer,
will carry an article on the use of our regular high-quality music system in out -of -door surroundings. Incidentally, in June we expect to have a first -hand, ear-witness
report on British and French audio-since we are
spending most of April in those parts as a "vacation."
AUDIO ENGINEERING
www.americanradiohistory.com
APRIL, 1953
PROFESSIONAL
AUDIO
EQUIPMENT
/MAXIMIZE PLAYBACK
BALANCED COMPONENTS
PICKERING CARTRIDGES
PERFORMANCE
...
are the choice of audio engineers throughout the world. They are universally
acclaimec because of their high output, wide range performance and low distortion.
They are used wherever a tune cartridge is required in radio stations, recording studios
and for Furposes of quality control by leading record manufacturers.
MODEL 410 AUDIO INPUT SYSTEM
...
provide a complete audio control center Model 410 may be used
in any high quality playback system. Three input channels ore provided -one for
magnetic cartridges and 2 "fat" channels for other audio circuits. A 3- position
equalizer network is built into the magnetic cartridge channel and provides accurate
equalixaion for LP, AES and 78 rpm recording characteristics. Separate bass and
treble controls are also provided. These are of the step -type and permit bass and
treble adjustments in 2 db increments. The tone control circuits are intended to
compensate for record characteristics and for listener- environment acoustical
conditions. They are not intended to compensate for amplifier and or loudspeaker
deficiencies. Model 410 is intended for use with the highest quality professional type
is design 'vd to
playback equipment. The output of the Model 410 is fed from a cathode -followe
circuit and will work into any high quality audio or line amplifier having a high
impedance input. It may also be used with a transformer for the purpose of feeding
a 500 of m line. Because of its Flexibility, low noise and low distortion level, it is ideally
suited for bridging and monitoring purposes and for critical listening applications.
THE MODEL 190 ARM
.
Yr.
-
do-
...
MODEL 230H EQUALIZER-PREAMPLIFIER
is designed primarily for use with microgroove
records. Its design has been recognized by
..
Is unique in its accuracy of equalization and
leading audio engineers as that which
incorporates all of the desirable tracking
characteristics. Analysis has Shown that for
maximum performance with LP records the
vertical mass of the moving arm element must
be held to a minimum and further, that the am
must be counterbalanced about the vertical
axis This perm is minimum stylus or tracking
force and provides maximum record life.
The Model 190 Arm embodies these all important
features necessary for proper microgroove
record playback.
frequency response. The intermodulation
distortion is .2 per cent at normal output level
It is intended for use with high quality
amplifiers having gain and tone controls.
When used with the Pickering Model 132E
Record Compensator the 230H is ideal for
radio station and recording studio use and for
applications requiring accurate low noise
and
distortion free playback.
MODEL 132E RECORD
COMPENSATOR .. designed to be used in conjunction with a
magnetic cartridge preamplifier such as the
Pickering 230H or any preamplifier which
provides 6 db per octave bass boost. Six
playback positions are incorporated,
rs
1- European
2- Victor 45
78 rpm Records
rpm and Decca 78 rpm Records
high frequency roll.off,
500 cycle turnover
4 -All Capitol Records new Victor 336h.
Audio Engineering Society Curve
5- Columbia, London and most LP Records
6 -To remove the hiss from old noisy records
Precision elements are used in its construction
to give accurate compensation. The 132E is
inherently a low distortion R -C device.
3 -No
,/
PICKERING PROFESSIONAL AUDIO EQUIPMENT
<<
G'G
0
% (/
CCl//l
G///'
PII,P/l/,P
...Demonstrated and sold by Leading Radio Parts Distributors everywhere.
For the one nearest you and for detailed literature, write Dept. A -2.
PICKERING and company incorporated
AUDIO ENGINEERING
APRIL, 1953
www.americanradiohistory.com
Orpanxide, L. L, Neer
lurk
17
Transistor of point-contact type. Two hair -thin
wires control current flow in germanium metal.
A
It's helping to win
the Battle of the Watts
When you keep down the power needed to send voices
by telephone you keep down the special equipment
needed to supply that power. A great new power
saver for telephony is the Transistor, invented at
Bell Telephone Laboratories, and now entering telephone service for the first time.
Tiny, simple and rugged, the Transistor can do
many of the things the vacuum tube can do, but it
is not a vacuum tube. It works on an entirely new
principle and uses much less power than even the
smallest tubes. This will mean smaller and cheaper
power equipment, and the use of Transistors at many
points in the telephone system where other equipment has not been able to do the job as economically.
It's another example of how Bell Telephone Laboratories makes basic discoveries, then applies them
to improve telephone service while helping to keep
its cost down.
TRANSISTOR FACTS
Laboratories engineer examines Transistor oscillator. It is
used in Englewood, New Jersey, where 10,000 subscribers
can personally dial distant cities. Transistors generate the
signals which carry the dialed numbers to other towns and
cities. Other uses are in prospect.
Created by Bell scientists. First announced
in 1948.
Has no glass bulb, requires no filament current or warm-up period. Operates instantly
when called upon. Uses no energy when idle.
BELL TELEPHONE LABORATORIES
Improving telephone service for America provides careers for creative men in scientific and technical fields.
www.americanradiohistory.com
Hi- Fidelity Phonograph
Preamplifier Design
R. H.
BROWN
A comprehensive discussion of the principles of determining component values to
provide the compensation required, combined with practical pointers on construction.
phonograph pre amplifier circuits have appeared in
the literature but it is difficult for
the individual who is not a full -fledged
audio engineer to find the information
he may need for designing a high-quality preamplifier to meet his individual
preferences, or to make desirable
changes intelligently in equipment already on hand. This article aims to set
forth in a summary fashion basic material which a technically minded audio
hobbyist or an amateur engineer would
need in the design or revision of quality
preamplifying and compensating equipment. Rather than attempt a comprehensive survey of the problems and
theory of preamplifier and compensation
circuit design, attention will be con fined to straightforward basic circuits.
gain provided by V, will be
EVERAL EXCELLENT
S
Basic
Amplifier With Degenerative
Bass Boost
Figure 1 shows the basic circuit
around which most high -quality phonograph preamplifiers are designed. Resistor R. provides degenerative feedback to set the amplifier gain to the
desired value for high frequencies, reduce amplifier distortion in the high frequency range, and extend the high frequency range beyond that which
could be obtained from the basic amplifier without feedback. R. provides degenerative feedback to set the maximum
value of bass boost, reduce amplifier
distortion at the extreme low frequencies, and extend the low- frequency
range below that which could be obtained from the basic amplifier without
feedback. R. may be omitted (made
infinite) when compensation is desired
down to a frequency requiring the full
gain of the basic amplifier. Ce provides
6 -db-per -octave bass boost as figured
from the turnover frequency for which
Ct is selected.
The first step in the design of a preamplifier is to design a basic amplifier
which has sufficient gain to provide
down to the lowest frequency of interest
compensation for the highest turnover
frequency to be used. Information on
electrically correct turnover frequencies
may be found in the literature, and it
will be observed that there are combinaations of listening conditions, listener
preference, and recording characteristics which may require turnover f re* Walla Walla College, College Place,
Wash.
AUDIO ENGINEERING
A;
As
L
1. Basic degenerative- bass -boost amplifie
circuit. V, and V_ and associated components
excluding feedback elements V, R,, and C
comprise the basic amplifier. Triodes are shown
for simplicity.
Fig.
quencies as high as 900 cps. As a 900 cps turnover requires approximately 29
db boost at 30 cps, the preamplifier gain
at 30 cps must be the antilog of 29/20
or 28.2 times as great as in the highfrequency range if bass compensation is
to be provided down to 30 cps for a
900 -cps turnover. Since due to the action of C, the gain only approaches the
full basic amplifier gain as the frequency
is reduced, in order to obtain good compensation down to a given frequency it
is necessary to design for a frequency
one octave lower. Thus for good compensation down to 30 cps for a 900-cps
turnover one must have a basic amplifier with a gain at least 56 times greater
than that required in the high -frequency
range.
A preamplifier designed for use with
a "Williamson" type power amplifier
and a G.E. magnetic cartridge should
provide between one and two volts output for a 10- millivolt input at 1000 cps.
If this preamplifier is to provide good
compensation down to 30 cps for turnovers up to 900 cps it must have a basic
amplifier gain cf between 5600 and
11,200, with R, selected to obtain a gain
of between 100 and 200 in the high frequency range. If no turnovers above
500 cps are to be used, good compensation to 30 cps may be secured with a
basic amplifier gain of between 3100
and 6300. High -level cartridges, such
as Clarkstan and Pickering, require
minimum preamplifier gains approximately only one -sixth as great.
The selection of V,, V., and associated
components is best made from reference
to the resistance -coupled amplifier data
supplied by tube manufacturers. Because
of the unbypassed cathode resistor the
APRIL, 1953
www.americanradiohistory.com
1+ (Rc
, )A,']'
(1)
where Ai is the gain provided by V,
with a completely bypassed cathode.
Cr Cee, Cks, and screen bypass capacitors if pentodes are used, must be selected to provide essentially uniform
gain down to the lowest frequency fL
for which full compensation is desired.
To accomplish this it is desirable to
choose the value of Co (in farads) so
that the product fLCcRU is between one
and two, and to choose Ck, so that the
product fLCks is between one and two
times the mutual conductance of Vr.
In many cases adequate gain may be
obtained without use of Cks. Data required for the selection of a pentode
screen bypass capacitor is ordinarily
not available, but one can usually make
a satisfactory choice by requiring that
the product of the bypass capacitance
(in farads), the lowest frequency of
interest, and the plate resistance of the
tube when triode connected have a value
between one and two. If it is not convenient to use capacitances as large as
those required by the foregoing conditions, the situation may be relieved by
providing around 10 db of feedback
through R..
Once the basic amplifier has been designed to provide adequate gain for the
maximum bass boost desired, the next
step is to select R. so that the amplifier
will give the right amount of gain for
the high frequencies. At high frequencies -(5000 to 10,000 cps) the gain is
given by
A'a.
+R,A'e,J,
ARP =
(2)
R, +R,
where A's, is the gain of the basic
amplifier when a resistance equal to
R, + R. is placed in parallel with Ris.
The gain provided by V. under these
circumstances is equal to the mutual
conductance of V. multiplied by a
resistance equal to the parallel combination of the plate resistance of Vs,
R. + R., R., and Ro.. To obtain accurate
6-db- per -octave bass boost it is necessary for A'... to be large enough to
make negligible the unity in the denominator of Eq. (2) -i.e., for A's, to be
greater than 10R, /(R, +R.). When this
L
I
19
condition is satisfied Eq. (2) becomes
Aa,
R,+ Rs
(3)
( )
Since R1 will usually be chosen from
resistance -coupled amplifier data for
proper biasing of V,, one may write the
following equation for Rs,
Rs= R,(Aar -1),
(4)
where Aar is now the required high frequency gain-i.e., the gain without
bass boost. If the loading effect of R, + Rs
keeps A'aP from being large enough to
render insignificant the unity in the
denominator of Eq. (2), the situation
may be remedied by connecting R. and
Ct to an unbypassed cathode of a stage
following V, (possibly a cathode follower output for the preamplifier).
The maximum gain available from
the amplifier may be designated ALP
and is given by
A'
ALP R,A'
(5)
1
+R,+Rs
+R,
where A' refers to the normal gain of
the basic amplifier without feedback. In
practice the coupling and bypass capacitors often prevent realization of the
full value of AL,.
From the fact that a simple resistance capacitance arrangement which will
provide 6 -db-per -octave boost computed
from a turnover frequency ft must give
a 3 db boost at ft.1 one obtains the following relation for the selection of Ct.
1
1 The boost will be very close to 1 db at
ft, 3 db at fr, 7 db at % ft, and 12 db at
''4 ft.
2
35
30 k.
a0 25
? 20
900
z
g 15
Fw
10
SO,
J
rc s
46%.......___
0
15
20
30
50
70
200
100
500
FREQUENCY IN CYCLES
.000
5.000
Fig. 2. Bass performance of pentode amplifier example discussed in text. Dotted lines indicate
idealized 6 -db- per-octave slope.
It will now be instructive to see how
these principles are applied in selecting
the components for a practical highfidelity preamplifier for use with a GE
cartridge and a "Williamson" type
power amplifier. On consulting the
resistance- coupled amplifier charts in a
receiving tube manual one finds that
a basic amplifier gain A' of approximately 18,000 may be obtained by using
for V, a 6SJ7 with 180 -v. Ebb, 0.5 -meg.
Ri,, 2.4 -meg. screen resistor, 2.0 -meg.
Raj, and 2410 -ohm R, to obtain a gain
of 95; and for V. a 6SJ7 with 180 -v.
Ebb, 0.5 -meg. Re,, 2.2 -meg. screen resistor, 1.0 -meg. Ras, and 2180 -ohm Rks
to obtain a gain of 192.
For 10 -db minimum feedback Au.=
1800 /(antilog 10/20) which is 5700.
From Eq. (5) one finds that this requires 20 megs. for Rs, R. + R. being
negligible in comparison with R,. For
ARP =100, Eq. (4) requires a value of
r
0.241 meg. for R,. This provides at high
frequencies a 45 db feedback in addition
to the 6.8 db of current feedback on V,
due to its unbypassed cathode resistor.
For 900 and 500 cps turnovers Eq. (6)
requires values for Cr of 740 and 1310
14µf respectively.
The actual performance of this preamplifier is shown in Fig. 2. The value
chosen for At, was 35.1 db above that
chosen for Aar, an amount just equal to
the boost required at 15 cps by a 900
cps turnover. The necessity for designing to a frequency one octave below the
lowest frequency to which full compensation is desired is illustrated by the
900 cps turnover curve in Fig. 2.
In a preamplifier designed for use
with a high-level magnetic cartridge, a
value of but 15 for Au, would be adequate. One could use the basic 6SJ7
amplifier discussed above with 33,700
(Continued on page 65)
r
3b
2,000
PER SECOND
TO POIEER SUPPLY
W
AD
11E
1
3,000
15,0001N
33.000
SOV
52
5,7107.
' N
=
100-15OV
AT
1.8 MIL
TO PIN
10f
6317
To PIN
S OF
6SN 7
TO CATHODES
OF OUTPUT
'USES
62^000
A
012
MEG
EFE
004306
-
00
DO3/206
53
I
2
SINFGA
S2- TREBLE
002506
1.
5
11l.002006
00150
h'
2 7,000 FOR PICKERING
(II REG
FOR GEN ELEC.
5100
2100
FOR
FOIN
6.200
UDAN
CARTRIDGE
CARTRIDGE
CARTRIDGE
RtXERING CARTRIDGE
FOR OEN ELEC CARTRIDGE
CAPACITOR VALUES IN of
SPECIFIED
OTHER
UNLES
SE
2
3
ROLL -OFF
FLAT
3
SS- BASS TURNOVER
1.
962OC TAUE FRON 3.000'V
CWOCTAVE FRON 1.000-
212
6 <620C TAVE FRON 2.500%
3 6 a62OCTAVE FRON 1090.
6 12 db/ OC TAV E FRON 2000%
300'1.
2
001.
500..11a6
500 ti
s
6
650
830
MAN BOOST
s.
R.
ALL SWITCHES NUS BE SNORTING TYPE.
TOLERANCE.
a,.!5%
RESISTORS ARE L 10%.12 WATT UNLESS
SPECIFIED OTNERWI E.
Fig. 3. Complete schematic of author's preamplifier with six bass turnover conditions and six roll -off positions.
20
AUDIO ENGINEERING
www.americanradiohistory.com
APRIL, 1953
=It
High Futility
-
An Essay on Scale Distortion
JOE
Although the essay -as
DICKEY
-is
a rarity in technical literature,
a form
the ideas presented herein are of sufficient value to provoke considerable thought in the minds of music lovers and audio hobbyists.
ONE OF THE NICER
things about audio
is its universal appeal. Across the
nation there is a growing thirst
for "high fidelity." It is particularly
heart warming to the sound engineer to
see the base of interest in his field being
broadened. At the same time many
hobbyists are fascinated by work in a
tangible field, the bulk of which is within
their means and understanding. In short,
it appears that we are enjoying a renaissance in sound to the delight and good
of all.
It is important to note, however, that
every musician or music lover who may
be attracted to better audio does not
retain his initial enthusiasm. It is surely
true that some lack basic interest. In
addition it must be assumed that an important segment of the artistically progressive and technically curious simply
experience a measure of disappointment
which no amount of "changing output
transformers" can gloss over. Emphasis
on the material side of the problem appears as so much planned frustration
and only widens the gulf between the
objective and the result. The search for
high fidelity finds only its enigma, "high
futility."
The situation calls for an examination
of the concept of reproduced music. In
order to simplify the inquiry, the "little
black box" idea may be applied to the
"electronics" of high fidelity. In other
words, it is a basic consideration of
this study that all limitations stemming
from the electronic portion of the system (including the loudspeaker and its
enclosure), have been overcome. In order to complete the background, it is
desired to introduce the definition of
scale distortion as follows : "the reproduction of sound at a level which differs
from that at which it was originally
made."
At the outset we need to note that it
is unlikely that the conditions, setting,
and environment of any particular event
of importance could be recreated for the
reproduction of the sound associated
with the event. Nor may we assume that
we would wish it so. Reproduced sound,
by its very nature, means a separation
in space, as well as in time, between
performer and audience. Our desire is
to call forth musical, or other events
for our pleasure under conditions of our
choice. It is not at all unusual to enjoy a "symphony concert" in the subdued quiet of a small living room or to
delight in the spectacle of a teen -age
daughter studying Latin to the accompaniment of the "Hit Parade." The
point is that in most cases music is reproduced in the home under conditions
which differ greatly from those usually
associated with the program and it is
therefore neither possible nor desirable
to eliminate scale distortion. One might
say that the treatment of scale distortion
is a personal matter and represents the
adaptation of the available to the needs
or the general to the specific. Everyone
knows that volume controls correct for
inequalities in station signal strength,
and tone controls give "more bass." But
is it appreciated that the volume control
represents the privilege of introducing,
or partially correcting for, scale distortion? Is it fully understood that the true
role of the tone control is to effect second order, (but still not complete), correction of scale distortion?
Before running head -on into the subject, some review is needed in order to
establish a proper point of departure for
our qualitative analysis. In particular
we need to note a few pertinent points
concerning the human ear and room
acoustics. With respect to the ear, the
more important points are: the varia-
The Listening Pattern
The selection of a typical family listening pattern is probably our most difficult choice. Careful observation of our
M. Villchur, "Handbook of
1 Edgar
sound reproduction, Chapter 6," AUDIO
ENGINEERING, Nov., 1952.
2 Loc. Cit.
3 Loc. Cit.
Range and Power Con + Frequency
siderations in Music Reproduction, Technical Monograph No. 3, Jensen Radio Mfg.
Co., Chicago, Ill., 1944.
5 Sound Absorption Coefficients of Archi-
tectural Acoustic Materials, Bulletin IX,
Acoustical Materials Association, Chicago,
Ill., 1947.
"Sure
*75 Roseneath, Newport, R. I.
AUDIO ENGINEERING
tions in loudness with changes in frequency (the familiar Fletcher- Munson
effect) ;1 variations in pitch with
changes in intensity ;2 the non -linear response of the ear which causes amplitude
distortion to be generated at the higher
listening levels ;3 and masking effects
which cause certain normally perceivable sounds not to be heard in the presence of other sounds' With respect to
room acoustics, the more significant
points are: the variations in the effectiveness of sound absorbing material
with changes in frequency s variations
in transmission efficiency with changes
in frequency ;6 reverberation time;7 and
ambient noise levels.8 Each of these
items has been treated quite objectively
as may be seen by a reference to the
notes.
With an understanding of these several separate effects we may turn our
attention to the subject itself. The
mathematical work required to correlate
the above factors in a comprehensive
treatment of scale distortion is a prodigious task. Fortunately for us, an understanding appropriate to our inquiry
can be had for a reasonable expenditure
of effort. A particularly attractive
scheme is to study a typical situation.
it's tough on plaster, but you
hear the bass!"
should
APRIL, 1953
www.americanradiohistory.com
6 Harry F. Olson, Elements of Acoustical
Engineering, page 429, New York, D. Van
Nostrand Co., 1947.
7 Ibid., page 399.
8 Jensen Technical
Monograph No. 3,
Op. Cit.
21
own listening habits, as well as those of vided there are no unusual disturbances
our friends, will most likely reveal that such as resonance effects in heating
music, regardless of type, generally ducts, noisy fluourescent lighting fixforms a background for some other ac- tures, etc. By applying the masking level
tivity. These activities may include contour to the absolute hearing response
housework, dining, or the evening paper. Curve, one obtains the effective hearing
They may range from a high level contour for an average listener in the
(noise, that is) cocktail party to the room being studied. For a frequency of
serene joy of the children sleeping. It
1000 cps and a total room noise of 40 db,
seems clear enough that our choice of the masking intensity is 22 db. When
listening conditions has the greatest of listening to the full orchestra with a 70all influences upon the requirements we db dynamic range the softest passages
set for our sound system. It can hardly fall some 40 db below the average level.
be overemphasized that subjective con- Now, if the listening level has been set
siderations determine these choices. The at a level of about 85 db, which is close
first determinant is volume and the sec- to the loudness experienced by a person
ond is tone. It is not until these two occupying a choice seat at a concert, we
basic selections are made -the first usu- see at once that the softest passages
ally introduces scale distortion and the which are 40 db below the 85 -db average
second partially corrects for the un- -will be reproduced at 45 db, which is
desirable effects of the first -that the 23 db above the noise mask and will be
other forms of distortion which plague heard. But suppose the listening level
reproduced music are even noticed, has been set arbitrarily at 55 db for reamuch less considered. Thus in providing sons of choice. The softest passages will
the music we want it is not enough that then be reproduced at 15 db, which is 7
the sound system simply transmit db below the noise mask and thus not
melody, harmony, and rhythm. Nor is it perceivable. A complete analysis would
sufficient that the system transmit tones require measurements and determinaover a wide band with negligible distor- tions throughout the audible range, but
tion, although it should be stated that the point seems clear enough. The failan electronic system which is free of ure of perception as outlined above is
the more usual forms of distortion is artificial in that we have created the
a basic requirement. In this connection, problem by our listening habits. Since
today's quality equipment is a revela- it does not appear likely that the solution to those who remember the early tion to this problem will come about by
"high- fidelity" systems that would have changing our outlook on music in the
failed completely but for the bass (high home, we must look to other means for
cut) tone control.
a solution. It is obvious that increased
Objective measurements will show quieting of the room by eliminating the
that a lot of listening is done at a level sources of noise would reduce the maskof about 55 db above the usual reference
ing effects. Though desirable, this
of 10-1" watts per square centimeter. change is impractical for the average
This is true regardless of the type of home due to architectual difficulties. The
program material; i.e. the listening level simple expedient of adding acoustic mais determined more by the situation than terial tends to deaden a room by absorbit is by the substance of the program. ing the sound as well as the noise and
In order to see the extent of the prob- thus reduces the reverberation time
lem we need only note that even a string
which is already too low, as will be
quartet is unrealistic at 55 db and cer- shown later. There is no entirely cortainly a symphony orchestra just does- rect solution to this problem, but there
n't show up in one's living room without are considerations which tend to lessen
considerable adjustment. For our pur- the undesirable effects.
pose the symphony provides the better
example, although the same parameters The Program Source
exist in the problem of reproducing any
other type of program.
Suppose we examine the program
A 70 -piece orchestra has an average source and see what the situation is inpower output of about 0.1 watt with /s sofar as standards are concerned. The
sec. interval peaks of 70 watts. The full 70-db dynamic range is not translower limit to the dynamic range is, say mitted on current AM radio because of
a soft violin with a power of 7 micro - two factors : an average modulation 30
watts. This represents dynamic peaks of db below 100 per cent would reduce the
about 30 db, with a total dynamic range geographic coverage to the extent that
of 70 db. Let us now turn to the acousti- the station could not operate in comcal setting in which the music, not the
petition; and average wire lines carryorchestra, finds- itself. If background ing program material cannot handle a
measurements were made in the living range of 70 db by reason of noise level.
room of a typical home, the readings
In the case of recordings, the full 70 -db
would likely indicate a total noise level dynamic range is seldom recorded beof 40 db on a cool night, with the win- cause the louder passages would
dows closed. Spectral distribution of the excessive displacement of the styluscause
and
energy might not be known but could be uneconomical
usage of recording space
assumed to be such as to provide an on
average, or normal, masking level con- withthe one hand, and a bad situation
respect to surface noise on the
tour." This is a valid assumption proother. The net result of these limitations
is a reduction of the dynamic range of
" Jensen Technical Monograph No. 3,
Op. Cit.
programs to a value consistent with
-
22
wire lines, modulation capabilities, and
recording media. It should be noted and
appreciated that compression of the dynamic range is a distinct help in minimizing the loss of perception due to the
combination of scale distortion and ambient room noise. By and large it was
because of these underlying reasons that
the attempt in the early thirties to apply
volume expansion to AM radio and the
phonograph was doomed to failure. With
the advent of wide range (dynamic)
programs on FM, better record materials, and a better choice of the recording characteristic it is even conceivable that some compression will be
introduced in home systems in order to
prevent loss of perception when listening at low volume levels.
Considering the volume control, if
taste were as simple as figuratively
walking toward, or away from, the
orchestra, then a simple potentiometer type control would satisfy all needs.
Furthermore, tone controls, once set to
account for peculiar conditions of the
system, could be left untouched. This
approach to the problem, though psychologically proper, is not very popular and
for good reason. As noted earlier, home
listening is generally characterized by a
depressed level. With most individuals,
the loss of low and high frequencies that
attends the use of an uncompensated voltage-divider type of control is disconcerting to say the least. For the critical listener, the necessity for restoring
tonal balance is great enough to mother
the invention of the tone control, had
it not been chanced upon early in the
game by those who simply "liked their
music the way they liked it." In order
to simplify the operation of sound systems and lessen the chance of an incorrect setting of the tone control, loudness
controls have been incorporated into
many systems.10 Insofar as our analysis
is concerned, these two methods of improving the situation that results from
scale distortion are one and the same.
If microphone placement is such that
the sound level is about 85 db average
in reasonably strong passages, and one
desires to listen at a level of 55 db, then
20 db of bass compensation is required
to correct for scale distortion at 50 cps.
The additional gain could easily be built
into the system, but the problem is not
that simple. When dynamic peaks raise
the level to 85 db the compensation
should be zero, but the 20 db of compensation is still present. The situation
that occurs during soft passages is even
worse for then 30 to 40 db of compensation is required, depending upon studio
technique. Under this condition the 20
db of compensation provided for an average level of 55 db falls short and the
bass is absent. There is only one practical solution to this problem and that is
1
(Continued on page 68)
'o David Bomberger, "Loudness control
for reproducing systems," Aunlo ENGINEERING, May 1948.
AUDIO ENGINEERING
M
APRIL, 1953
M
www.americanradiohistory.com
Feedback -Degenerative and
Regenerative
1
RUDOLPH L. KUEHN
An analysis of the various forms of feedback, with particular attention to conditions which cause oscillation, and a mathematical presentation of the condition which must be present to cause oscillation.
that feedback is a,
common as the measles. By the
brief analysis presented here it is
hoped that a clearer understanding is developed of the electronic phenomena.
In general, the block diagram for feedback is given in Fig. 1. If a voltage proportional to the output current or voltage of an amplifier is fed back in series
with the input voltage so as to decrease
the amplification the method is called
negative, inverse, or degenerative feedback. The resulting amplifier has certain properties which may be desired
despite a loss in amplification.
For simplicity, a sinusoidal input voltage E, and an absence of harmonics due
to nonlinearity in the tube and related
circuits are assumed. The input to the
amplifier proper is the vectorial sum of
E, and the feedback voltage, thus Es =
E, +Etn. The complex voltage gain of
ONE MIGHT SAY
101O
E,
Fig. 2. Block schematic of connection for cur-
rent feedback.
gain depends on the absolute quantity
I1 -BAI. For very large values of negative feedback the expression I1- ßA is
very nearly -PA and E, AE,/-M
so that E. /E, = A' a -143. To an arbitrary degree the voltage gain may be
made independent of supply voltage
changes, tube parameters, and characteristic curves by a high value of inverse
feedback. Without considering the involvements of the theory, it is enough to
state here that feedback reduces the nonlinear distortion produced in an amplifier for a given output by the ratio
I
1
output current and to maintain it constant. Therefore, with voltage negative
feedback the effective internal series
impedance is made smaller by the feedback ; whereas, with current inverse
feedback the effective internal series
impedance of the amplifier is made
larger by the feedback. Thus it can be
seen that at constant input voltage E,
the former approaches the behavior of
a constant -voltage source, while the
latter approaches that of a constant current source. In multistage amplifiers
or in any situation where the amplifier
must be terminated for power transfer
it is necessary to know the effective internal impedance for optimum matching.
Cathode -Follower Analysis
The cathode- follower is a form of inverse feedback amplifier (see Fig. 3).
This arrangement has two major advantages over the conventional ampli-
/(1 -M).
For any resistance- capacitance coupled amplifier the amplification remains
constant for a certain large range of
frequencies, but falls on either side of
this range. This so- called mid -band
range usually extends from below 100
cps to above 5000 cps. In the mid-band
Fig.
1.
General feedback configuration as applied to an amplifier.
the amplifier is given as A = E,/E4, and
the feedback ratio is ß = Ern /E.. It is
seen. then, that Eta = ßE. = ßAE4, and
E4= El/ (1 -ßA), and Es= AE,/(1OA). From the last expression the following is obtained:
A
E.
E, =1 -ßA
`q
which is the over -all complex voltage
gain with feedback.
Now it follows that if ßA is real and
negative, then A' < A and the amplifier
is degenerative. If ßA is real, positive,
and less than unity, then A' > A and the
amplifier is regenerative. The voltage
gain approaches infinity if ßA is real
and approaches 1. If ßA =1 the amplifier is unstable and begins to oscillate.
This latter condition is the Barkhausen
criterion for sustained self- excited oscillation of a single tube circuit under
the initial assumptions above. Generally
speaking, the magnitude of the voltage
*
437 Broad Ave., Palisades
AUDIO ENGINEERING
Park, N. J.
frequency range the output voltage is
180 deg. out of phase with the input
voltage. The angle of phase shift of the
output voltage relative to its mid-band
phase is given as
y = arc tan wrsC,
where C1 is the parallel load capacitance
and rig is the effective output impedance
of the stage (defined as the impedance
that the plate circuit offers to an external voltage applied between the plate
and the cathode).
If the voltage to be fed back is such
as to make ß independent of the value
of the load impedance (which can be
had by a simple voltage- divider across
the load), then the condition is known
as voltage feedback. If, however, the
circuitry is as represented in Fig. 2, then
the ratio of Erb to the output current,
1., is made constant by the feedback impedance Zfb. This is known as current
feedback. In the case of voltage inverse
feedback, E. decreases as Zi. is decreased
and Ell) also decreases; but the decrease
in Efe tends to increase the output voltage and to maintain it constant. With
current inverse feedback I. increases as
Z,, decreases, and Etn increases; but
the increase in Ern tends to decrease the
APRIL, 1953
www.americanradiohistory.com
E
Fig.
3.
Typical
arrangement of
follower.
a
cathode
fiers which place the load impedance in
the plate circuit:
1. One of the load terminals may he
grounded.
2. The impedance presented by the tube
to the load is small enough that it can be
easily matched to a transmission line.
The voltage developed across the load
Re opposes the applied signal voltage so
that the circuit exhibits negative feedback characteristics. If the equivalent
impedance and the transconductance are
not too low, the voltage developed across
the load will be almost equal to the applied signal voltage but never larger.
The equivalent impedance is formed by
the load in parallel with the term
rp /(1 +lt), where IL and ro have their
customary significance.
Oscillators
It was shown earlier that
eral requirement for oscillation
Consider the simple feedback
Fig. 4. In the general case the
is
true:
the gen-
is ßA =1.
circuit of
following
(Continued on page 58)
23
1
Theater Sound in
a
Small
Package
THOMAS
R.
HUGHES
Part 3. Concluding the description of a unique loudspeaker housing with details of the
dividing network and the methods of testing and adjusting for optimum performance.
IN THE TWO preceding articles the
theories and construction of this
loudspeaker system have been developed. This concluding article covers
the electrical system and controls for
providing complete satisfaction.
As previously stated, the tweeter may
be any good make of horn tweeter. with
a horn that cuts off well below 1000 cps.
Some manufacturers have versions that
are inexpensive ($17 to $35) and suitable for our purpose. As stated earlier,
we are not so concerned with the angle
of spread of sound from the tweeter,
where it is to be used in the corner of
a living room. The rated impedance is
most desirable at 12 or 15 ohms but it
may be 8 ohms. In any case,' it is simpler
if it has the same impedance as the
woofer used.
Within the woofer's operating range,
its voice coil impedance does not range
much above its d.c. resistance value.
while the impedance of the tweeter
varies over a larger range. in relation
to the frequencies it is generating. So
we can design the components of the
dividing network for the impedance of
the woofer and forget about the tweeter,
as long as it is not over 100 per cent
from that of the woofer, and we can
match impedances by using add'tional
resistors, if desired.
Many good articles in the literature
have covered the details of designing
and constructing dividing networks.
These articles give charts for estimating
the number of turns of wire to wind on
each coil and the dimensions of the coil
spools, etc. So we will not take up space
with such details here.
For winding coils, remnants of No.
16, 17, or 18 magnet wire can be obtained from motor winding shops and
can be spliced together with a thin copper sleeve, sweated over butted ends.
Thin "spaghetti" can be slid over the
sleeve, after soldering, for insulation.
The voltage is so low that insulation is
not a critical item in these coils.
Surplus capacitors can generally be
used by paralleling different sizes to
get the right capacitance. These can be
the oil-filled paper type with working
voltages at 25 or 50 volts, if obtainable.
If the higher voltage types have to be
used they will be much larger in size
* 3721
Calif.
24
Hilferest Dr., Los Angeles 16,
and higher in cost. There are some
electrolytics for sale in "bathtub" cases,
so beware of them. The regular oil filled paper types have no polarity marking of terminals but the electrolytics
either have a positive and negative mark
or the terminals have different colored
insulators. And, of course, the electrolytic is much smaller.
We used the series -filter system for
our dividing network, since authorities
seem to agree that it is the most desirable. It requires coils and capacitors
of different sizes for the two legs or
circuits. The coils may be bolted to the
sides of the speaker cabinet -in the
upper compartment allotted to the
tweeter. Place them several inches apart
on adjoining sides, so that their axes are
at right angles, and use brass or aluminum bolts.
Preliminary Listening Tests
get used to richer notes packed with
harmonics you were missing before. So,
even the playing of your most familiar
records can be disconcerting. Thus we
repeat : your first decisions are going
to waver back and forth and you had
better not make any.
In the end, the thing you will have
to decide (maybe with the help of
others) is whether you have a satisfactory balance in volume levels between
the two drivers. We mentioned, in an
earlier issue, that a University 4408
tweeter so closely balances the output
of our horn -loaded woofer that they are
just connected directly to each leg of the
dividing network. If one of your drivers
overbalances the other it can be fed
from a potentiometer connected across
its leg of the network, as described in
articles on dividing networks. This may
be a 10 -watt wirewound resistor with a
sliding clamp contact for takeoff adjustment. Its resistance may be from 100 to
200 per cent of the voice coil impedance
rating of that driver in ohms. It's a
good idea to measure the d.c. resistance
of voice coil and resistor with an ohmmeter, as an approximate check.
Connect the two coils and two capacitors together in proper relation with
joints soldered in a temporary manner
for testing. Then place the tweeter about
8 or 10 feet away from the main cabinet for the first hour or two of listening.
By this means you can tell what you are
getting fróm the different components. Means of Comparing Speakers
It is much easier to judge, if you have
You are going to find that it is no
an audio oscillator, but a frequency test easy matter to decide whether you
record can be played on your record should be satisfied with the balance or
player to check the response at cross- not. You play an album of records and
over between the two speakers. Using
then you change it one way. Later on
an output meter across the speaker ter- you play some other records and decide
minals or a microphone placed in front it still isn't right. But remember that
of the speakers is of little avail because in recording you have differing characof the vast difference in the character teristics in microphones and their placof the two speakers and differing spread
ing, not to mention difference in recordof sound dispersion.
ing equipment and operators.
If this is your first experience of trySince your main concern is with the
ing out two speakers and a dividing region that the crossover falls in, it is
network, you may be highly confused at a big help to compare your balance with
first. Things do not happen like you ex- the output from any single cone speaker
pected and you wonder if you are a com- of fair quality. This is just one of the
plete flop. But just be patient and make reasons you are going to need the conno decisions until you have grown ac- trol hookup we use. Another good use
customed to listening to them for sev- for this hookup is to prove to the family
eral hours. If you are getting response and friends that you aren't going slowly
from each speaker you know that there off your nut, when you try to explain the
is nothing open -circuited and it is going
purpose of this new system and what is
to take time to appraise the balance.
different about it.
If this is your first experience of lisWhen a real music lover comes to
tening critically to two horn -loaded visit you and listens to a good over -all
speakers, you not only have the sur- system for a while, he will soon make
prises of where the sound is going to comments or ask questions about the
hit you from but your ear will have to means of obtaining this realism. As the
AUDIO ENGINEERING
www.americanradiohistory.com
APRIL, 1953
reader doubtless knows by now, it is
fruitless to start an explanation of
speaker systems. But it is a simple matter to demonstrate all aspects by flipping
the switches in our control hookup.
All that is needed to complete the
hookup of these controls and the dividing network (as shown in Fig. 10)
are four DPDT toggle switches, a phone
plug jack, and an L or T pad. The pad
may be 12 or 16 ohms, assuming the
impedance of the drivers is in that region. All of the equipment shown in
Fig. 10 is installed in the upper compartment with the tweeter and we have
switch handles protruding into one of
the side openings of the bass horn, next
to the wall, where curious hands are not
likely to discover them. The jack also
opens into this passage as does the handle of the T pad.
Switches 1 and 4 are used most so
they were placed on the ends of the
line of switches, so their handles are
easily found by feel. Switch 2 is thrown
to the position which inserts the pad
only when another speaker is to be
plugged into the jack. Most of the time
the pad is out of the circuit. But the
pad must be used to attenuate the response through the dividing network,
when Comparing our horn -loaded speakers with ordinary box- mounted cones.
To check the balance between woofer
and tweeter (after the connections of
Fig. 10 have been made and an attenuating potentiometer for adjusting the
tweeter -woofer balance has been inserted) a normal cone speaker, around
10 or 12 inch diameter, is plugged in.
Then adjust the pad while operating
switch 1 back and forth until the volume
is the same in either position. Now play
several orchestra or choral records
through the new system and at points
where you doubt your judgment switch
to the other speaker and see if there is
any great difference.
We want to emphasize that the balancing is to be done on the passages
around the crossover region. Do not try
to judge the system on solo flute or
violin music, for example. The comparison speaker will be of little use two
octaves away from the crossover.
pad to attenuate the tweeter or woofer
response for comparison, it will be necessary to flip switch 2 back and forth with
the other switch. By this means you insert the T pad with its attenuation, for
the horn -loaded speaker, and drop it out
for a straight through run to the corn parison speaker, with its poorer efficiency.
This arrangement provides a versatile
sampling hookup. The quality or response of over -all systems can be corn pared or either treble or bass response
can be sorted out for comparison with
that of another speaker. If you are trying to explain to someone that a cello or
Ezio Pinza excite a broad band of harmonics, you can cut out either driver
and show that there is still a considerable complement of harmonics issuing
from the other. On the other hand, you
can show that a lyric soprano has no
lower harmonics while a mezzo- soprano
has to have woofer response for rounded
notes. It is uncanny what can be done
with it.
Les Paul started the novelty of recording several sound tracks on one tape
with different modes of playing the same
steel guitar. With his record of "Little
Rock Getaway" you can completely
erase the highest or the lowest sound
tracks with switches 3 or 4, because
there are no stray harmonics of these
tracks on the other side of the crossover.
We can take certain records of Lily
Pons and erase Pons and leave the orchestra still playing along fairly effectively.
When we are trying to point out to
untrained ears how the efficient response
of the little woofer will etch the sharp
intensity into cello or English horn passages, their attention is likely to be distracted by the sharp excursions of some
flute or violin. So we can cut off the
tweeter and focus their attention on the
feature we are trying to demonstrate.
Then there is the fellow who thinks
his pet speaker is just as good as yours
and he has infinite faith in his hearing
and memory. Tell him to bring his own
speaker and his pet.records over and you
can really give him a comparison. When
he hears his own records he cannot
claim any fakery in the litre up, if his
speaker is shown up.
Confidence in Appraisal
Listening at all the different horn
mouths of the new speaker system will
show you that all kinds of thin squeeky
noises come from the tweeter and choked
squawks come from the lower horn in
some alternate passages. These things
happen when the dividing network cuts
the broad band of harmonics of a note
(in the crossover range) into shreds
and you were listening to the narrowest
of the shreds. Several feet back, this is
not apparent, but if you really want
to hear it you can flip either switch
3 or switch 4 and sample it readily.
Then, if you think it shouldn't sound
that way, plug in the comparison
speaker. Then when you flip the switch,
the sound will come out of the comparison speaker and you can see how it
sounds there. If you have to use the T
AUDIO ENGINEERING
Hold That Distortion
All of the foregoing discussions of the
virtues of this speaker system are predicated on the assumption that high -quality music signal is being fed into the
dividing network. There is the old
argument between techincal experts
whether one should improve the speaker
system or the other sound equipment
first. We believe that the speaker is the
end to start on because you can do a
lot of see-sawing around in the feeding equipment without being fully conscious of results unless you have a sensitive speaker system.
It is about like the old tale of the man
who found a horseshoe and bought a
horse to put it on. Our new speaker
system will mercilessly display the defects in records and equipment. The
first thing you have to do to soothe it
is get rid of record surface noise with
a magnetic pickup and a new changer
one of the better modern changers, with
only a few grams needle force and a
hall -bearing arm swivel, so it is free
from the different forms of distortion
contributed by drag of arm on groove
-
-
walls.
If you have not done this already, you
have no idea how different the records
can sound. Fifty per cent of the sur-
face noise and distortion from inexpensive pickups is from vertical vibrations
and is mostly eliminated by change to a
modern magnetic or variable reluctance
pickup. The reason being that they produce practically no response from vertical vibrations. The other fifty per cent
still remains from lateral distortion of
stylus movement caused by a heavy arm
with stiff swivel joints, working against
the whip of eccentric or warped records.
After the man got a horse he had to
get a stable and a riding habit. So a
preamp stage ahead of the amplifier
will be necessary, unless it already has
one. Then we start in on equalization
because the speaker system shows that
up. There are almost as many ideas for
attacking this problem there are ideas
for speaker enclosures but we have not
experimented with these to the same extent. Success in the matter is not difficult. however.
The amplifier is the oldest member
of the team, having started its career
before the loudspeaker. So there are
no secrets about amplifiers and plenty
of satisfactory performers can be had
-
(Continued on page 701
10. Schematic of the dividing network to show the four switches used in making comparisons between the over -all system and other speakers, and for checking performance of
the individual components.
F'g.
APRIL, 1953
www.americanradiohistory.com
25
An Auxiliary Mixer for TV Studios
GEORGE A. SINGER
a commercial unit which combines good engineering with
practical consideration of the requirements of modern studio operation.
A description of
a
of the more
elaborate television shows require
an extensive and flexible audio
system. In particular, a much larger
number of microphone inputs are needed
in television than are required for a
similar radio show. There are two basic
reasons for the use of more microphones
in a television production. First, the
microphone has to be kept in close
proximity to the actor to reduce noise
pick -up from the audience or changes
of props. As the scene shifts, the microphone has to follow the action or when
this is not practical-as is frequently
the case-other microphones, distributed at strategic locations, have to be
used to pick up the sound.
Unlike radio it is not usually possible for the actor to step up to the microphone to deliver his lines, then to step
aside to make room for the next actor,
thus reducing the number of microphones required.
The second reason for the need of
additional microphone input facilities
in television is the fact that frequently
more than one set or staging area is
used in a single studio. Each area requires its own complement of microphones. However, usually only one area
is in use at a time, and it is therefore
possible by providing suitable input selector switches to reduce the number
of microphone mixer channels needed.
Many of the television stations which
have been on the air for some time are
faced with the need of expanding their
audio facilities. Similarly, the many new
stations which are now springing up all
over the country will require or are at
least planning for more microphone inputs than the standard broadcast studio
console affords.
PRODUCTION TECHNIQUES
Engineering
Products Department,
RC.-1 l'ictor Division, Camden, N. J.
1. Over -all view of the BCM -1A Auxiliary
Mixer which may be used to extend the number of microphone inputs of a conventional
studio console.
Fig.
fier chassis are secured by vibration
mounts to eliminate microphonics.
Following the preamplifiers are the
ladder type attenuators AT, to A7'..
These attenuators have 20 steps of 2
db each except for the last three steps
which taper to infinity. The lever key
switches S. to S. connect the output of
the mixer attenuators to either the program bus or the audition bus.
To make convenient external connections for special applications, the
inputs and outputs of the selector
switches and amplifiers have been
brought out to terminals on the audio
terminal block, as shown at the top of
Auxiliary Unit Needed
There is, therefore, a definite need
for a unit which may be added to a
studio consolette to provide additional
microphone switching, amplifying, and
mixing channels. Such a unit should of
course not only match in styling the
other studio equipment but also be convenient to use and easy to install.
With these considerations in mind,
the BCM -1A Auxiliary Mixer was designed to supplement the facilities of
the type BC -2B Studio Consolette.l The
new unit is shown alone in Fig. 1, and
in its normal operating position alongside the consolette in Fig. 2.
As shown in the block diagram of
Fig. 3, the Auxiliary Mixer provides
four mixing channels. The input selector
switches S, to S. permit a selection of
any one of three microphone inputs for
each of the four preamplifiers, making
available a total of twelve microphone
inputs.
The preamplifiers employ two stages
of amplification with inverse feedback
to reduce distortion and stabilize gain.
Low -noise tubes are used to obtain a
high signal -to -noise ratio. The ampli1 P. W. Wildow and G. A. Singer, "New
AM -FM -TV studio consolette," AUDIO
ENGINEERING, September, 1951.
l....o 111.paib,
Fig. 3. Removing the top and tilting the front
panel forward provides easy access to the interior for maintenance. The bottom of the
amplifier chassis is accessible simply by raising
a
Auxiliary
Mixer as set up for
use with the BC -2B
Consolette -which it
matches in finish and
design -for side -byside operation in the
Fig. 2. The
studio.
e
26
hinged framework.
Fig. 4, which shows the internal appearance of the mixer with the top removed and the front panel tilted forward.
Flexible Mixer Circuit
The mixing circuit itself was designed
so that the mixer busses of the auxiliary
mixer can be paralleled with the mixing
busses of the consolette. This was accomplished by making the output impedance of the auxiliary mixer the same
as the resistance of the load resistors in
the mixing circuit of the consolette.
These load resistors are removed when
AUDIO ENGINEERING
www.americanradiohistory.com
APRIL, 1953
the two units are connected together.
In addition, the auxiliary mixer circuit
was designed so that its proper load
impedance would be that of the mixing
circuit of the consolette.
The imposition of these conditions resulted in an output impedance of 370
ohms and a load impedance of 255 ohms.
It is therefore necessary to use a matching pad when the output of the auxiliary
mixer is fed into a 150 or 250 microphone input of either the consolette or
another amplifier.
The program- audition switches art
also equipped with contacts for interlocking circuits which activate the
speaker muting and studio warning light
relays of the consolette.
Thus there are two ways in which
the auxiliary mixer can be connected to
the consolette:
Paralleling of the mixer busses.
The program and audition busses of
the auxiliary mixer are connected directly to the corresponding mixer busses
of the consolette. Eight connections are
required between the interlocking circuits of the two units. This type of
installation results in 12 mixing chan nels-8 of which are microphone mixing channels -and a total of 18 possible microphone inputs.
2. Using the Mie 1 mixer of the consolette as a sub-master gain control.
In this type of connection, the program bus of the auxiliary mixer is connected through a matching pad to the
Mic 1 input of the consolette. The audition bus of the auxiliary mixer may be
connected through a matching pad to
an external monitor amplifier if so de1.
i ii iiii iiii
MICE,
MIC
Fig. 4. Block diagram of the Auxiliary Mixer
sired. No interlocking connections are
required for this case since the program- audition switch of the Mic 1 channel in the consolette controls the speaker
muting and warning light relays. The
Mic 1 mixer attenuator of the consolette may be used as a "sub- master" gain
control for the auxiliary mixer. This
type of installation reduces the number
of possible microphone mixing channels
by one. The added feature of a sub master gain control, however, simplifies
operation as it makes possible to fade
four channels in and out simultaneously.
Typical Application in Studio
The audio facilities of a typical TV
studio are illustrated in Fig. 5. The
studio is divided into three staging
areas. Each of these areas contains four
microphone inputs to the auxiliary
mixer. In the main staging area #2,
are an additional three or four microphone inputs leading directly to the consolette. (The microphone 1 input is
shown dotted because it cannot be used
if the output of the auxiliary mixer is
fed to the Mic 1 input of the consolette.)
(Continued on page 61)
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Fig. 5. Typical studio layout which employs the capabilities of the Auxiliary M ixer to augment the number of microphone inputs available for instant use.
AUDIO ENGINEERING
APRIL, 1953
www.americanradiohistory.com
27
A Three -Channel Tone -Control
Amplifier
JOSEPH F. DUNDOVIC
Presenting
a
are provided
tone -control arrangement wherein steeper low- and high -boost curves
without appreciable interference throughout the mid -range frequencies.
Fig. 1. Simple tone -control circuit common)
used to provide boost of both low and high
frequencies.
described
here may be considered somewhat
elaborate, but it does produce results which cannot be duplicated by any
of the more conventional circuits. It
is the final result of extended experimentation to obtain the desired effect
in the simplest possible manner.
Most tone control circuits use some
type of R -C network to attenuate or
boost either or both ends of the audio
4119 Irving Avenue North, Minneapolis
THE TONE CONTROL to be
12, Minn.
frequency spectrum. However, the problem in audio equipment is generally a
deficiency rather than an excess of lows
and highs. Two of the responsible factors are the limitations of the equipment,
and the need for compensation for the
Fletcher- Munson effect at low volume
levels. Hence this article will deal only
with the "boost" type of control.
A circuit which is representative of
many of the common tone controls is
shown in Fig. 1. Briefly, the voltage
divider, consisting of the resistors R,
and R,, attenuates the signal applied to
the grid of the amplifier tube. The
capacitor C, shunts R, for the high frequencies, and the amount of shunting
action is controlled by varying the resistance of the series potentiometer
resulting in a variable high-frequency
boost. For the bass boost, C. is introduced in series with the lower leg of
the voltage divider by increasing the
resistance of its shunt potentiometer
R4. Since C, has a greater impedance
at the low frequencies, the effective attenuation at that end of the spectrum
is reduced.
The main drawback of the tone con-
2. The author's tone -control amplifier
mounted on a small chassis for use with other
equipment.
Fig.
trol of Fig. 1 is the shallow slope of
the attenuation curves. For example, in
order to obtain an appreciable boost
such as 20 db at the frequencies around
20 cps, frequencies well into the middle
range of 500 to 1000 cps are also
boosted. The result is the familiar
"boomy" effect generally associated
with juke boxes. Likewise, when the
high -frequency boost extends into the
middle range, a pronounced distortion
of the original tonal balance is observed.
Fig. 3. Schematic of tone -control amplifier
28
A more desirable characteristic may
be obtained by a tone control which reinforces only the very ends of the audio
range, below 100 cps and above 3000
cps. In these regions the limitations of
the loudspeakers and other auxiliary
equipment between the listener and
original performance combine to cause
a sharp drop in output.
A three -channel tone control amplifier which accomplishes the above aim
is shown in Fig. 2, with the circuit
diagrammed in Fig. 3. It is designed
to be inserted between a tuner or phonograph preamplifier and the average
audio amplifier input stage. The insertion gain is 6 db, corresponding to a
voltage -gain factor of two. Thus, with
both boost controls fully retarded, the
middle- frequency amplifier tube section V,. has a gain of 6 db, and is flat
over the entire audio range.
The tube section VIA serves as a preamplifier for the low- and high-fre(Continued on page 60)
of Fig. 2.
AUDIO ENGINEERING
www.americanradiohistory.com
APRIL, 1953
i
Handbook of
Sound Reproduction
EDGAR M. VILLCHUR
Chapter 10 -Part
2. Loudspeakers.
Continuing the discussion of the basic principles of one of the most important elements of a sound system, with a few hints on optimum conditions for speaker operation.
Harmonic Distortion
Non- linearity in loudspeaker, is normally much greater than that of any
other component in the reproducing
chain. While amplifier advertisements
vie with one another in comparing fractional distortion percentages at rated
output, the best commercial speakers
available cannot even approach such excellence. The manufacturer's published
distortion vs. frequency and output
curves of a speaker in the 150 dollar
class is shown in Fig. 10-7. This
speaker is probably one of the top quality units available, but if its distortion
curve were presented as a performance
index of the most humble of amplifiers,
that amplifier would undoubtedly be
scorned by the audio market.
A major source of harmonic distortion is the non -linearity of the cone and
voice -coil suspensions, particularly at
large excursions. As these suspensions
are stretched their restraining forces
increase instead of remaining constant.
-beyond a certain point the suspensions
will not give at all without tearing
and cone displacement ceases to be proportional to the magnetomotive force.
Harmonic distortion is also produced
if the excursion of the voice coil takes
it into a region where the total magnetic
flux through which it moves is reduced.
The instantaneous voice coil displacement no longer follows the signal because the magnetomotive force at the extreme positions is reduced.
These mechanical sources of distortion generally affect both halves of the
cycle equally and the generated harmonics are therefore of odd orders, predominantly the third. Any method for
reducing voice -coil excursion without
decreasing output will reduce harmonic
distortion. The 'more efficient the coupling to the air the less will be the displacement required of the voice coil for
a given radiated acoustical power; the
type of speaker mounting used is thus
extremely important relative to distortion.
Both of the above types of non-linear ity are most prominent in the bass fre-
-
*
Contributing Editor,
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FREQUENCY N
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67891000
CYCLES PER
2
3
456
SECOND
-7. Harmonic distortion of a high quality coaxial speaker, compared to that of an
equivalent -quality amplifier.
Fig. 10
quencies due to the increased excursion.
Voice -coil displacement for the same
signal amplitude increases as the frequency is lowered, and below the frequency of ultimate air load resistance
displacement increases inversely as the
square of the frequency. At a given frequency distortion increases with signal
amplitude, also because of the increased
excursion.
Subharmonie Distortion
Figure 10-8 illustrates how flexing
of the cone in response to voice -coil
motion may produce subharmonics.
When the voice coil moves forward,
a stiff rim suspension may cause
the
cone to bend in either direction. When
the voice coil moves forward a second
time, however, the cone is already in
transverse motion, returning from its
first position of flexure, and the resulting momentum added to the flexing
force causes it to bend the opposite way.
The cone thus completes one cycle of
motion during the time required for the
voice coil to complete two. The frequency of flexure of the cone is one
half that of the frequency of vibration
of the voice coil.
Subharmonic formation is relatively
minor in loudspeaker performance, and
is discouraged by a highly compliant rim
suspension and by cone design which
discourages flexure.
Intermodulation
The fact that amplitude distortion is
produced by a loudspeaker means that
intermodulation will also exist, providing that the different frequencies involved are passed through the same distorting system. In the case of the
speaker this intermodulation may be illustrated physically. When the voice
coil is driven by a low- frequency note
into a position where the suspensions
exercise more than normal restraint on
motion, or where the magnetic field is
- --- FUNDAMENTAL
-
--- SU9NARMONIC
FLETO.
AUDIO ENGINEER -
INa.
AUDIO ENGINEERING
Fig.
10-8. Formation of loudspeaker subharmonics.
APRIL, 1953
www.americanradiohistory.com
29
.
1
-
.5
W
:rig, `
i. ,iii
000.......---ar
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I111
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10-9. Manufacturer's published onaxis frequency response curve for a
high- quality speaker,
Fig.
compared to curve
for equivalent -quality
amplifier.
MAKER
+s
20.
....0
me
.0000
FREQUENCY IN CYCLES PER SECOND
weaker, the peaks of the low- frequency
signal will be flattened. But the restraint
of the suspensions will also limit the
excursion of high -frequency vibrations
at this moment, and any high -frequency
signals will be reproduced with less amplitude during the peaks of the low frequency signal. Since the peaks are
usually flattened during both halves of
the cycle, the higher-frequency signal
will be amplitude modulated at twice
the low- frequency rate. The sidebands,
or sum and difference frequencies associated with such modulation, may be expected to be at frequencies equal to that
of the higher frequency plus and minus
twice the lower frequency.
A second type of intermodulation that
occurs in speakers is caused by the Doppler effect. If the cone is stimulated by
a low- frequency signal it will at times
be approaching and at other times receding from the listener. A high -frequency note superimposed on this slowly
oscillating cone will have its pitch, relative to the listener, alternately raised
and lowered. This constitutes frequency
modulation of the high note by the lower
frequency, creating sidebands. The Doppler type of intermodulation will be
greatest when a cone with large excursion in the bass is simultaneously used
to reproduce the upper treble. The effect,
however, is much less serious than that
of amplitude modulation, and like the
latter it is alleviated by reduced voicecoil excursion.
Speaker systems which assign different portions of the sound-frequency
spectrum to separate voice coil and
cones discriminate against intermodulation between the distorted signals of
each portion.
cated under the same acoustical and
electrical conditions that existed when
the curve was made.
The frequency response of the best
speakers is, as might be expected, far
more erratic than the response of electronic amplifiers. Figure 10-9 is the
manufacturer's published on -axis frequency- response curve for a typical
high -quality speaker, compared to the
curve for an equivalent-quality commercial amplifier. It is common practice
for speaker frequency response to be described numerically, as the upper and
lower frequency limits which the speaker
reproduces. Variation within these
limits is sometimes as much as plus or
minus 10 db or more.
From the point of view of listening,
more variation in the tonal color of reproduction may be expected in changing
from one make or type of speaker system to another than in changing any of
the other audio components. In speakers
of the same general price range this is
usually not so much a function of the
range of frequencies reproduced as it
is dependent upon the emphasis and deficiencies at different points on the response curve. The greatest evils of this
erratic response are associated with
bass resonance, tending to produce
boominess, and cone break -up resonances in the low highs, tending to produce shrillness. At its worst, accentuated
resonant response creates a situation
where signals anywhere near resonance
set the speaker to sounding its lone,
prolonged note in chorus. Low-f re-
quency signals may become loud thumps
or roars whose pitch is difficult to
distinguish.
For the speaker to radiate low frequencies efficiently, large masses of air
must be moved. The excursion of the
cone has a limited range, and so systems
designed for good low -frequency performance generally take full advantage
of what motion there is by having a
large cone area in contact with the air.
(Several twelve- or fifteen -inch speakers in parallel may even be used for extreme low- frequency reproduction.) A
large cone and extended travel calls for
a large voice coil. The voice coil must
be long enough to utilize efficiently the
entire magnetic field over the extended
path, and of sufficient radius for rigid
coupling to the cone. Thus the mass of
the moving system, when designed from
the viewpoint of low- frequency reproduction, will be comparatively high.
This is not particularly disadvantageous
in the low range.
For high -frequency reproduction it is
especially important that the mass of the
moving system be low. Small, rigid
cones or diaphragms and small, light
voice coils are therefore suitable. The
excursion of the voice coil will be
greatly reduced, because of the inverse
relationship between frequency and displacement, and also because of the fact
that typical program material has somewhat less energy content in the high frequency range. The magnetic field can
therefore be concentrated over a smaller
area, and the required size of the magnet structure is less.
The contradictory requirements of
low- and high- frequency reproduction
may be compromised in a single speaker
unit, or two or three speakers can be
used, each designed for optimum performance within its frequency range.
Horn loading is often used for the high
range because of the reduction in size
and weight of the vibrating diaphragm
made possible by the more efficient
coupling to the air, and because the
size of the required horn is conveniently
small.
Transient Response
The accuracy with which a speaker
can follow sudden starts, stops, and
changes of the electrical signal is directly
proportional to the damping and to the
evenness of the frequency response.
Frequency Response
The frequency-response curve of a
speaker is commonly plotted as sound
pressure created by the speaker (in
dynes /cm2 converted to db) vs. the frequency of a constant-amplitude signal
input. It is a very difficult measurement
to make, since it involves the acoustical
conditions of the space into which the
speaker radiates. Speaker frequency-response curves are often more indicative
of general trends than exact performance, and can only expect to be dupli-
30
U
v ù
10 -10
A
left. Impedance and damping characteristics of undamped speaker (8- inchl.
The oscillogram represents back e.m.f. produced by the voice coil for instantaneous d.c. stimulation, removed after the first quarter- cycle. IBI right. Same as (Al, using edge- damped
loudspeaker (12 -inch W. E. 728131.
Fig.
AUDIO ENGINEERING
www.americanradiohistory.com
APRIL, 1953
High -frequency transients will, of
course, require good high -frequency
response, though the transient may be
associated with lower frequencies.
A type of transient distortion commonly associated with loudspeakers is
hangover, the tendency of the speaker
cone to continue to vibrate after the
signal has stopped. Hangover is especially likely to occur at a signal frequency to which some part of the mechanical or acoustical system of the
speaker and enclosure exhibit sympathetic resonance, and where, as a result,
there is a peak in the frequency -response
curve. The effect is that of smearing
one note onto the next, destroying the
clarity and distinctness of the various
voices of the program material.
Mechanical, acoustical, and electrical
damping all reduce hangover. Figure
10-l0 illustrates the effect of internal
speaker damping, achieved by coating
the rim suspension with a viscous material. (Mechanical friction changes
with velocity, while the viscous friction
of the coating tends to be independent
of velocity, as pure electrical resistance
is independent of current.) Acoustical
and electrical damping, upon which most
speaker systems primarily rely, involve
characteristics of the associated mounting device and amplifier as well as of
the speaker itself. Low amplifier output impedance presents a heavy electrical load to the speaker as a generator,
quickly bringing unauthorized motion to
a halt. High magnetic flux in the voice
coil gap, which produces a strong back
e.m.f., aids this damping action.
Power Capability
Speakers are rated as to their ability
to handle steady power within given
distortion percentages, and also as to
their power capacity for peaks of short
duration. These ratings refer only to input electrical power and not to output
acoustical power. If the input power is
quite a bit less than the maximum power
rating of the speaker, distortion is less,
indicating that the use of a speaker
system over -rated as to power is ad-
be subject to sound radiation from all
10-11. Typical speaker frame and voice coil suspension. (Courtesy Stephens Mfg. Corp.)
Fig.
netic field in the gap relative to the
mechanical impedance of the moving
system, and the length of wire in the
voice coil. Speaker efficiency is also
highly dependent upon the acoustical
coupler -horn couplers may increase
efficiency to from 25 to 50 per cent. A
common "intuitive" fallacy is the assumption that large speakers require
more electrical driving power than small
ones for the same acoustical output. The
opposite is usually true.
Although speaker efficiency has no
direct bearing on performance (especially when internal viscous damping is
used) the same construction features
that make for high electro-mechanical
efficiency create good electrical damping. An efficient speaker system also
allows the amplifier to operate at a
lower electrical power level for the same
sound power. Good mechanico-acoustical efficiency is always advantageous, as
a given amount of acoustical energy
can be radiated with less voice -coil excursion and therefore less distortion.
Speaker efficiency may be simulated
by an apparent loudness created by
resonances and distortion in the midfrequency range.
Radiation Pattern
The radiation pattern of a vibrating
loudspeaker cone is determined by the
combination of effects of the circular
ring elements composing this cone. (See
Chapter 3.) A given point in space will
vantageous. When several speaker units
are connected together in a properly
matched multispeaker system the power
capacities of each unit are added together for the total power rating.
Speaker Efficiency
therefore, has a very directive radiation pattern concentrated around the
axis at the high frequencies. The use
of small treble speakers, or of separate
small cones or diaphragms for treble
reproduction, broadens the high -frequency radiation pattern.
High- frequency sound radiated from
the center ring elements of the cone
travels along two paths, that of the air
and that along the sides of the cone itself. The velocity of travel in the paper
cone is on the order of two times the
velocity in air, and so the phase of sound
from the outer rings -relative to that
from the center
affected by both the
angle of the cone and the velocity of
sound in the particular cone material.
Factors which tend to delay radiation
from the rim relative to that from the
center broaden the radiation pattern.
Shallow cones therefore have a broader
pattern than deep ones of the same
diameter. The flared cone, due to increased rigidity, has a sharper pattern
than that of the conical cone. The use
of corrugations and of relatively soft
cone material, both of which slow up
sound propagation, broaden the angle
of sound radiation.
Special procedures and devices to
broaden high -frequency radiation are
often employed. More than one high frequency speaker may be used, and the
units arranged in an arc. A second
method of diffusion is to load the high
frequency radiator acoustically with a
multicellular horn whose individual
mouths are fanned out. Whatever
method is used, the results are stated
most rigorously by a polar graph which
relates angle of radiation, frequency.
and the sound intensity level.
-is
LOUDSPEAKER CONSTRUCTION
The efficiency of a speaker is defined
as the output acoustical power divided
by the input electrical power. Direct radiator loudspeakers have efficiencies
ranging from about 2 to 7 per cent. For
an input of 10 electrical watts a 3 -percent efficient speaker will radiate 0.3
acoustical watts, while a 6-per -cent
efficient speaker will require only 5
watts of electrical input to produce the
same acoustical output. It is evident
that the power rating of the speaker
must be considered in terms of speaker
efficiency; an efficient 10 -watt speaker
may be able to handle more acoustical
power than an inefficient 20-watt unit.
Important determinants of speaker
efficiency are the strength of the magAUDIO ENGINEERING
of the adjacent vibrating ring sources.
The additive or cancelling effects of the
sound from these sources will be affected not only by the relative position
of each ring, but also by the time delay
involved in the travel along the cone
from the voice coil to the ring element.
The smaller a speaker cone is in relation to the wave length being radiated
the less cancellation will result from
radiation from different points on the
ring elements, and the broader the radiation pattern will be. A large speaker,
The Speaker Frame
The main requirement of a good
speaker frame is rigidity and absence of
resonant behavior. To these ends it is
heavy and sometimes made of cast
metal. A typical commercial speaker
frame (with voice coil suspension in
place) appears in Fig. 10-11.
Rim Suspensions
Fig. 10 -12. Voice coil and seamless molded
cone for use in woofer. (Courtesy Stephens
Mfg. Corp.)
APRIL, 1953
www.americanradiohistory.com
The most common type of rim suspension is that employing a corrugation
in the one -piece cone, as in Fig. 10-12.
Another effective but expensive method
makes use of a separate rim of kidskin,
cloth, or soft leather.
31
i
Voice -Coil Suspensions
be taken in lower resistance or in re-
'
The type of centering suspension in
current general use is the corrugated
disc illustrated in Fig. 10-11. Formerly
the most popular type was the slotted
disc, whose appearance gave the voice
coil suspension the name of "spider."
Cones
Although cheaper cones are sometimes made by rolling and glueing a
paper development of the cone form,
the best type is moulded in one unbroken
section. (See Fig. 10 -12.) A mixture
of pulp and water is drawn through a
master screen in the shape of the cone,
leaving a deposit of pulp which is removed when dry. Hard, springy cone
material may create an impression of
greater volume due to more accentuated
break -up resonances and increased distortion.
Voice Coils
The design of voice coils is concerned
with factors of mass, resistance, and
efficient and linear use of the narrow air
gap.
Low resistance is most important in
low- frequency speakers, for reasons of
efficiency and electrical damping (the
d.c. resistance of the wire appears in
series with the source impedance of the
amplifier), and copper wire is therefore
commonly used. The added mass is not
an important consideration in woofers.
Speakers which must also reproduce
high frequencies, however, require as
light a voice coil as possible, and therefore often make use of higher resistance
aluminum wire for their voice coils.
The most efficient use of the air gap
is made by square wire or by edgewise
wound ribbon wire. The dividend of additional use of the available space may
duced thickness for the same resistance.
The excursion of the voice coil must
not take it into a region where the magnetic flux through which it moves is
reduced. If the voice coil is made longer
than the gap length the average field
strength affecting the voice coil will
be the same, because as one end of the
coil moves into a weaker part of the
field the other end is moving into a
stronger field area. Uniformity of gap
flux may also be maintained by a system which makes the voice coil shorter
than the length of gap. If the excursions
of the voice coil are small it will remain
within the strong uniform section of the
field at all times.
The system which uses the smaller
voice coil is more appropriate for high frequency reproduction, and the one
with the larger voice coil is suited for
low frequencies. These two systems,
contradictory to one another in a
speaker with a single voice coil, may
both be used in a dual or multiple unit.
Multispeaker Circuits
Speakers may be connected in series,
parallel, or series -parallel, and the total
nominal impedance is calculated by the
same method that is used for simple
resistive networks. For example, two
8 -ohm speakers in series must be fed
from the 16-ohm amplifier tap, and a
second such 16 -ohm speaker combination, connected in parallel with the
first, brings the total impedance down
to 8 ohms again.
Where remote speakers are used it
is occasionally desirable to furnish separate volume controls for the individual
speakers. This may be accomplished by
an L -type level control, illustrated in
MOW
C
P
C
R
WHERE
I
,59440
....,..
rw.1«
SEVERAL
r
24,
C
1592
/59000
CROSSOVER
TWEETER
1Z,.....
Z,.,
...,
TIMES VALLE OF
R
FREQUENCY
EDANCE
AT
WHERE
L
IN
Z.....
.......
r
Z.H.H.
WOOFER
IMPEDANCE AT
INDUCTANCE
IN
MILLIHENRIES
/11
A
S
2
V
IMF
AM
112500
z25Z
zr
r
AMPLIFIER
I
Fig.
10-13.
c(
L -type level control for attenuat
ing volume at speaker.
Fig. 10-13, in which the two sections
are tapered in such a way that the
impedance presented to the speaker
source remains relatively constant. Attenuation is accomplished by wasting
power in the control, and its power
rating should be as great as that of the
amplifier. A simple heavy -duty potentiometer, with a resistance several times
the nominal impedance of the speaker,
may also be used, but at the expense of
impedance mismatching.
Bass- treble combinations, poetically
referred to as "woofer-tweeter" systems,
require some sort of dividing network
to separate the different portions of the
frequency spectrum. The simplest of
these networks is shown at (A) in Fig.
10-14. The tweeter is protected from
damage by low- frequency signals, but
treble signals are fed to both woofer
and tweeter. Cone break -up and inter modulation in the woofer is thus discouraged only to the extent that part
of the treble signal is by- passed through
the tweeter.
The more complicated but more effective inductance -capacitance networks
of (B) and (C) in Fig. 10-14 produce
a much greater separation between bass
and treble. Here a roll-off is introduced
at the top of the woofer range and at
the bottom of the tweeter range, at the
rate of 6 db per octave (in terms of
power) for the single capacitor- inductor
network, and 12 db per octave for the
double element network. The crossover
frequency is that frequency at which the
value of the various elements, including
the speakers themselves, cause the input
power to divide equally between the two
speakers. Since the power to each
speaker is halved at this point, the attenuation in both treble and woofer
circuits is 3 db.
The equations for calculating the values
of L and C for given crossover frequen-
1
q/
10-14. Dividing networks for two- and
three -way speaker systems.
32
î
Ztmceter
2niL = Z woofer
270C=
The impedance of the combination is
treated as the impedance of one speaker,
if woofer and tweeter have the same
value, or as the average between woofer
and tweeter impedances if these differ.
(Continued on page 63)
C
Fig.
II
e
cies appear below the diagrams. The
equation for the R -C network is a mathematical statement of the fact that the impedance of the capacitor is equal to that
of the sneaker at crossover. The impedance of the combination is treated as the
impedance of the woofer.
The equations for the single element
L -C network are derived from expressions which state that the impedance of
the capacitor is equal to that of the
tweeter at crossover, and that the impedance of the inductor is equal to that
of the woofer at crossover:
CROSSOVER
CROSSOVER
«
CAPACITANCE
L
en
AUDIO ENGINEERING
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APRIL. 1953
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37th
1953
www.americanradiohistory.com
STREET
NEW YORK 16, N.
Y.
Feedback and Loudspeaker
Damping
JOHN A. MULVEY*
The author proposes a solution to the problem of obtaining a feedback signal
which is equivalent to the movement -generated e.m.f. of a speaker voice coil.
articles on
positive current feedback used to improve loudspeaker damping have, to
this reader, been most engrossing. In
spite of studies made of the articles and
arguments on this subject he has, until
quite recently, felt much in the dark
when it came to feeling able to claim
much of an opinion of his own on the
relative merits of such a system. It
seemed that such a subject should be
resolved into simpler contradictions
than any presented so far in order to
make one feel he has made a wise choice
of one opinion or another.
This need has led to this attempt to
reduce the subject into simpler terms
by digging into the fundamental aspects
of the subject. The author feels that the
analysis which is here presented can
show some things not apparent in foregoing discussions, and finally may offer
amends to those who think they disagree,
as well as to make some proposals that
the engineers more actively engaged
may find promising.
According to Lenz's law, the voltage
induced in a coil due to its passage
through a magnetic field is always of a
polarity such as to produce a current
which would oppose the motion. In other
words, an e.m.f. due to coil motion in
a field tends to stop the motion. This
presumes, however, a closed circuit at
the coil ends, for this e.m.f. can only act
if it can act to cause or influence current through the coil. When such a coil
is a voice -coil there is always such a
closed circuit existing. The path is
around through the windings of the output transformer secondary. This closed
THE RELATIVELY RECENT
+3080 S. W. Spring Garden Road, Portland 19, Ore.
circuit can nearly constitute a short circuit for the coil, permitting much
current to flow with just a small movement- generated coil e.m.f. The more current which flows as a result of this e.m.f.
the better will be the dynamic braking
of the movement, that is, the quicker
will the movement cease. But even with
a short -circuited coil moving in a magnetic field the cuurrent through it is
definitely limited. It is limited by the
resistance of the coil itself. A method
to overcome this limitation and further
enhance the dynamic braking action is
most desirable. Such a method, to be
successful, would have to permit a
greater current flow than a short -circuited arrangement would allow. At first
any such method might seem impossible
for it would seem that nothing could allow more current than a short circuit.
But on second thought it should be realized that a second source of voltage in
series with the voice -coil could be provided to increase the current above what
simply a short- circuited voice -coil would
allow. This suggests a circuit employing
as a second source of voltage one greater
but proportional to the movement -generated e.m.f. and in phase with it having
also a lower source impedance, as in
Fig. 1. So far we have spoken only of
movement-generated voltages. In the
case of a loudspeaker, where it is voice coil current which causes the motion in
the first place, movement- generated
e.m.f. is still present and acts to oppose
the voice -coil current. In this way it influences the actual current and always
acts to stop the motion the same as if
some physical force was causing the
motion. However, generally under these
circumstances the movement-generated
A
Fig.
34
E,
MOVEMENT - GENERATED VOLTAGE
EE
SERIES GENERATOR
1.
(A) Theoretical circuit, and (B) practical circuit of feedback obtained from current
in a voice -coil.
VOLTAGE, WITH OUTPUT
GREATER BUT PROPORTIONAL TO AND IN
PHASE WITH E,
e.m.f. itself causes no current to flow.
It only acts to influence the voice -coil
current which is moving the voice -coil,
by subtracting from the voltage causing
it. This is true all the time except dur-
ing "hangover" periods. During these
periods the physical forces of inertia or
suspension compliance cause the movement-generated e.m.f. to exceed the driving voltage and so cause its own reverse
current to flow. Notice here that this is
a "reverse current," one of opposite
polarity to that originally causing the
motion. This reverse current then will
act on its own and damp the motion
and so limit the hangover effect. Since
positive feedback-whether voltage feedback or current feedback-tends to increase the output signal, at this time if
positive current feedback were introduced it would increase the current
limiting the hangover effect so as to
squelch it quicker.
From this the main point may be apparent but it is simply that positive current feedback does not oppose voice -coil
movement until the movement-generated
e.m.f. exceeds the driving voltage and
produces a reverse current. At this time
there is a phase reversal which, in effect,
changes positive feedback to negative
feedback. If this point is not made clear
there is yet much room for controversy.
It should be noted that the comparison
was said to be only an effect similar to
inverse feedback. The e.m.f. generated
by a coil moving in a magnetic field is
inverse feedback. Any voltage which
aids that voltage is, with regards to it,
a positive feedback voltage, but with
regards to the total effect it is a negative
feedback voltage. There is a good comparison in the rather familiar circuit of
an amplifier using a positive feedback
loop connected to the cathode end of an
unbypassed cathode resistor. The feedback voltage is definitely positive with
respect to the signal voltage appearing
across the cathode resistor, but just as
definitely negative with respect to the
over -all effect.
But the story doesn't end here. To
some, the advantage of improved damping during hangover periods will be
thought to be too highly paid for by the
inherent disadvantages existing the rest
of the time, since the rest of the time
the in -phase feedback is regenerative.
[Continued on page 62]
AUDIO ENGINEERING
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APRIL, 1953
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orchestral works having wide dynamic range. Besides offering unparalleled output at all audio frequencies (see graphs),
this new tape retains all the physical and magnetic properties
that have made "Scotch" Brand No. 111A the recognized
standard of the recording industry: high tensile strength,
freedom from elongation, stable anchorage, low noise level,
excellent uniformity, ease of eraseability.
Freedom from squealing, cupping and curling is assured
thanks to exclusive "Dry Lubrication" feature. High- Output
tape is guaranteed 100% splice-free (up to 2400-foot reels)
The term "SCOTCH" and the plaid desi gn are registered trademarks for Sound Recording Tape made in U.S.A. by MINNESOTA MINING &
MFG. CO., St. Paul 6, Minn. -also makers of "Scotch" Brand Pressure-Sensitive Tapes, "Undereea1" Rubberized Coating, "Scotchlite" Re.
inactive Sheeting, "Safety- Walk" Non -slip Surfacing, "3M" Abrasives, "3M" Adhesives. General Export: 122 E. 42nd St., New York 17, N. Y.
In Canada: London, Ont., Can.
36
AUDIO ENGINEERING
www.americanradiohistory.com
,
;e.aasaa°
APRIL, 1953
1
output
or harmonic distortion!
..n.
n..nNIM.
.......n....1...
.n=1.C...n1.....n1111.
.._................
a
n.n.n11
1nn..nnn.
.nn=.
.n.
...inn...
an?iuaiuuni7
....
=pnN..MIi
...
nn...n.n.
.0
..G......
1..n
...nn.n...
... m.
.... ........
OUTPUT VS D STORTIOn
...n...11111111
62
lNIiimenumrrtnn*mmmiMmumumme.I.
No
120A TAPE
'
.M11111111n=.U1ENfi..n.nIIMi
z
.111111M1
.
MIMI=
10000
1000
EóD
iiiiiiñi.°.i
.fi
20000
EREOUENCY IN CYCLES PER SECOND
A
L
PERCENT HA
6
8
10
ONIC DISTORTION
The frequency response characteristics of both No.
120A and No. 111A tapes are virtually identical
at
tape speed. These curves were made with each
tape set at optimum bias and an input level 15 db
below 1% 3rd harmonic distortion.
15 ips
This graph shows the 8 db increase in output of
High- Output Magnetic Tape No. 120A over No. 111A
at any given distortion level. When compared with
other brands of magnetic tape, the difference in output
is as much as 12 db.
A?EE BaDAtertells
the full story of the tremendous
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Available now on: 120 -AP 1200 -foot Professional Reel
120 -A 2400 -foot on NARTB hub or reel
High-Output and
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AUDIO ENGINEERING
APRIL, 1953
www.americanradiohistory.com
37
Canadian House of Commons
Sound Installation by Tannoy
Low -level sound system provides exceptionally good dis-
tribution of sound to all members with
minimum of
a
un- naturalness often encountered in high -level systems.
IN
RECENT YEARS there has been noticeable a growing tendency toward the
use of so- called "low -level" sound
reinforcement systems, in which a large
number of speakers are situated strategically throughout the area to be covered, and operated at moderate volume,
as opposed to the "high- level" system
in which all sound emanates from a
single speaker or group of speakers
more -or -less centrally located. An outstanding example of this new trend
in the United States is the sound system installed in New York City's new
Port of Authority bus terminal-which
i
MINIM
IMANWE
Fig. 2. Guy R. Foun-
tain, founder and
chairman of Tannoy,
Ltd., discusses remote control panel
with
son
Michael
Fountain
_
lardik;
OEM=
will be described in its entirety in a
future issue of Æ.
Also closely adhering to this advanced
approach toward realism in sound reinforcement is a system recently designed, manufactured, and installed in
the Canadian House of Commons by
Tannoy Products, Ltd., London, England. Similar in principle to the systems
Tannoy created for the Houses of
Parliament in London, the equipment
permits any member of the House to
speak and be heard by all other members as though he was but a foot or so
away, without any intervening disturbance.
Fig. 1. Control panel and main equipment of
Tannoy low-level sound reinforcement system
in Canadian House of Commons.
This effect is achieved by dividing
the chamber into 23 separate zones, with
each zone having its individual micro-
Fig. 3. Rear view of
low -gain
amplifying
equipment in Cana-
dian
House
of
Commons.
i
:
.w....,.
z
e;ri
;.......
38
phone, as well as control over reproducers in the immediate vicinity. Over
500 high-quality miniature speakers are
installed throughout the chamber.
Those for the members are housed in
attractive oak recesses on the individual
desks, while the galleries are supplied
with small metal- enclosed units mounted
between theatre -type seats.
The entire system is controlled by a
single operator seated at a master control desk so situated that the entire
House may be observed. Upon observing a member indicate a desire to speak,
the operator has only to press a key
controlling the zone in which the member is located. This action connects the
desired microphone to the system, and
at the same time reduces the output
level of the speakers in the immediate
vicinity to avoid feedback howl. Volume
output of the remaining speakers
throughout the chamber is unaffected.
When another member of the House
rises to speak, the operator depresses
a switch button controlling this new
zone, and thereby cancels out all of the
previous connections while simultaneously re- setting for the new zone of
transmission.
Main equipment for the system is
housed in a special room adjacent to
the assembly chamber, with all functions operated by remote control. In the
event of equipment failure, provision
is made for automatic substitution of
any unit, so that operation remains continuous and uninterrupted.
In the paragraphs which follow are
described some of the installation's tech [Continued on page 59]
AUDIO ENGINEERING
www.americanradiohistory.com
APRIL, 1953
puts
other
tape
recorders
in th
PRESTO
SHADE.
PRESTO
RC-il
introduces a precision -engineered tape recorder
with a radical new type of construction!
Featuring a self- contained capstan drive unit, the PRESTO
RC -11 provides durability, flexibility and rapid maintenance
heretofore unheard of in tape equipment. Motor, fly wheel,
capstan shaft, pressure pulley and solenoid are all pre- mounted on
a cast aluminum sub-assembly
a complete working unit
quickly removable for service or replacement.
...
ribbed, cast aluminum panel designed for rack or case mounting supports all
other components. Overall durable construction gives additional reinforcement
and protection during shipping and adds years to the life of the machine.
A heavy,
The
"unitized"
In terms of performance and operational ease, the RC -11 also steps
out front. This new recorder, with complete push button operation,
automatic microswitch in case of tape breakage and a reel capacity of
101/2 inches, is an engineer's delight.
construction of the
Presto RC-11
...allows a complete flexibility in the manufacture
of various types of instruments. By the simple rearrangement of components
The combination of advanced design and engineering in the RC.11
puts ordinary tape recorders in the shade ... makes this instrument
an investment, not an expenditure. Ask your PRESTO distributor for full
information on this important development in tape recorder
design
the all new RC -11.
...
the RC -11 becomes a high
fidelity recorder, a dual
track. bi- directional recorder or reproducer or a long -
RECORDING CORPORATION
playing reproducer with
automatic tape reversal.
ARAMUS, NEW JERSEY
Export Division:
Canadian Division:
WORLD'S
LARGEST
MANUFACTURER
OF
25 Warren Street, New York 7, N. Y.
Wolter P. Downs, Ltd., Dominlon Square Bldg., Montreal
PREcN
www.americanradiohistory.com
RECORDING
EQUIPMENT
AND
DISCS
A Note on Volume Controls
CHARLES
P.
BOEGLI
The author shows that it is not always satisfactory to place
a high- resistance potentiometer just anywhere in an amplifier circuit if specified performance is to be obtained.
audio amplifier is generally made
up of several stages arranged in
cascade so that the input signal is
fed through one after the other, being
amplified on the way, finally appearing
as an output voltage at the loudspeaker
terminals. Somewhere in this unit, it is
usually necessary to provide a control
over the gain of the entire amplifier, so
that input signals of the given voltages
can be made to yield output voltages of
the desired magnitudes. This is most
often accomplished in high- impedance
locations, by means of a simple potentiometer ; the output from the plate of one
stage is connected to the top of the potentiometer, the other end of which is
grounded, and the grid of the following
stage is fed from the slider. The purpose
of this note is to mention some considerations that appear to be generally
overlooked in providing a "volume"
control of this type.
Since hum and noise are most apt to
assume noticeable proportions in the input stages of the amplifier where signal
voltages are quite low, the volume control should generally be located after
the first few stages. In this manner, the
signal is maintained at the maximum
value compared to the noise through
these critical stages and becomes attenuated only when it has reached a
value quite large in comparison to noise
voltages. On the other hand, should the
volume control be located too near the
output tubes, the possibility is increased
that the signal will attain sufficient magnitude before reaching the control to
cause unnecessary distortion in previous
stages. Placement of the control at a
point where the maximum signal level
is from 2 to 4 volts will usually lead to
a fairly satisfactory design, suffering
neither from distortion nor excessive
noise. It goes without saying that the
control must not be placed inside the
feedback loop, if any are employed in
the circuit.
The only disadvantage to locating the
control otherwise than at the input to
AN
R
C
E
G
OUTPUT
Ee
I
TOTAL INPUT CAPACITANCE
OF STAGE
2
T1
l
Fig.
EOUVALENT
RESISTANCE OF STAGE
R
1.
Low -pass filter existing between
stages of an audio amplifier.
two
* Cincinnati Research Company, 6431
Montgomery Road, Cincinnati 13, Ohio.
40
the amplifier is that the voltages of the
signal sources used with the amplifier
must
a degree, at least-be controlled. Thus, with the volume control
at the input we need concern ourselves
only with the minimum input required
for full output, but if the control is situated later, the maximum input also becomes important. An input stage handling a minimum of 0.5 volt may well
be designed to carry a maximum of the
order of 1.5 volts; obviously, if a tuner
supplying 6 volts is connected to such
an input, overloading will result. The
best arrangement would therefore seem
to be one in which the volume control
is placed near enough to the output
stages to maximize the signal-to -noise
ratio and close enough to the input
stages to prevent serious distortion, and
in which individual pads are used on
the various signal sources to bring their
outputs to approximately a uniform
level, preferably slightly over the minimum required to drive the amplifier
-to
fully.
Effect on High -Frequency Response
The high-frequency response of an
amplifier (utilizing a good output transformer) is largely determined by the
cutoff frequencies of the series of low pass filters incorporated into it and made
up of the output resistance of one stage
and the input capacitance of the next,
as indicated in Fig. 1. When one stage
feeds directly into the next the problem
of attaining good high -frequency response is fairly well defined, and the
solution consists simply in keeping the
output resistance of each stage as low
as possible. Low-mu triodes with plate
resistances of the order of 10,000 ohms
are excellent in this respect and may be
used with plate-load resistances of almost any size without adversely affecting high- frequency response. With high mu triodes and pentodes the plate -load
resistors, as well as the grid resistors of
the following stages, must be kept small
in order to realize good high-frequency
response. But what occurs upon the introduction of a volume control ?
Obviously, when the slider is at the
top of the control, the situation is the
same as if no control were present.
When the slider is near the bottom, also,
the following stage is fed from a very
low impedance so that the high -frequency response is even better than
when the slider is at the top. In less ex
treme positions, however, if the volume
control resistance is quite high, there
may be a substantial loss of high frequencies-and it is precisely these positions that are most important.
Reference to Fig. 2 will make this
clear. R. is the output resistance of the
preceding stage and R, is the volume control resistance. The symbol a represents the position of the slider and
measures the fraction of the voltage appearing at the top of the control that
is applied to the following grid. Now
Ro, the resistance into which the following grid looks is aR, in parallel with
R.+ (1 a)R,, which is found to be
R
°
-
(a
aR,R.+
a')R,'
R. +R,
We are interested in the manner in
which Ro varies with a. Hence, differentiation of the above expression with
respect to a yields
R,R, +R' -2aR1
(2)
da
R. + R,
The resistance Ro is a maximum at the
value of a found by setting the right
side of Eq. (2) equal to zero and solving
for a:
dRo
R,R.+R,'-2aR'=0
a R.+
R,
(3)
2R,
When a assumes this value, the maximum output resistance
R, +R.
Rom
-
For example, if we had a low -mu triode stage with an output resistance of
10,000 ohms connected to the top of a
1 -meg. volume control, there would be
some point at which the next stage
would look back into as much as
10,000 + 1,000,000
= 252,500 ohms
4
and if the input capacitance of the following stage were sufficient to cause a
[Continued on page 60]
Fig. 2. Equivalent
a
circuit of a stage followed by
volume control.
AUDIO ENGINEERING
www.americanradiohistory.com
(4)
4
APRIL, 1953
.
ilnlm
Of course he's using Soundcraft Recording Tape
>l%
... tt s wi.a
-- V®F
-
Perfect reproduction that's the
reason why more and more engineers
today demand Soundcraft
Professional Recording Tape.
Soundcraft is the only professional
tape that is Micro- Polished. The only
tape that is polished, buffed and
re- polished by a special process to
produce a surface that is mirrorsmooth, completely free of even the
most minute irregularity. The results
of Micro -Polishing are apparent
to any sound engineer:
Lower distortion
Uniformity of output
Improved high frequency response
Better head contact
Less friction, longer head life
- s-
Soundcraft Professional Recording
Tape incorporates all the features
developed by Soundcraft research
engineers during the last two years:
pre -coating to insure better adhesion,
prevent curling and cupping
dry lubrication to eliminate squeals.
The 7" reel has the 2V' hub,
eliminating torque problems and
resulting in better timing. All this,
plus a splice -free guarantee on all
1200' and 2500' reels.
Why settle for less than the best?
Next time, insist on Soundcraft
Professional Recording Tape.
It's Micro -Polished!
-
"
'PATENT APPLIED
FOR
WRITE FOR
FREE
"""
INFORMATION -DEPT.
www.americanradiohistory.com
SOUNDCBAFT
B
CORP.
10 East 52nd Street, N. Y. 22, N. Y.
Equipment Report
THE COLLARO 3RC522 RECORD CHANGER
A review of the details of construction and operation of a modern
automatic record changer relatively new to the American market.
this reviewer sees a new type
of automatic record changer, his first
reaction is that it couldn't possibly
work-yet all of them seem to, and quite
efficiently. The Collaro -one of the latest
makes to reach the U. S. market in any
quantity-is no exception. It is available in
four different types, and can be supplied for
any frequency from 40 to 60 cps, and for
a.c. voltages of 100/125 or 200 /250. The
EVERY TIME
accommodation for different frequencies is
accomplished by a change of motor pulley.
Both mixing and non-mixing types in both
one- and three -speed versions are available.
The principal questions concerning the
performance of automatic record changers
are those about rumble, hum pickup, and
speed constancy. The secondary questions
about simplicity of operation, minimization
of roughness in handling records, ease of
changing from one type of record to another
or from one speed to another, and other
considerations are also worthy of attention.
Since the changers are equipped with
adapters to permit the use of any of the
standard phono pickups, no problem is encountered in this direction, since reasonable
flexibility of adjustment is provided to permit accommodation to various weights of
pickup.
Test Observations
The instrument submitted for test was a
three -speed "mixing" model designed for
33 1/3, 45, and 78 r.p.m. and for 7-, 10-,
and 12 -inch records. The intermixing feature applies only to the latter sizes, since a
separate lever located at the right side of
the top panel must be actuated to cause the
pickup to set down at the 7-inch diameter.
With the intermixing models, the pickup
set -down position is determined by the size
of the record just lowered to the turntable
-the 12-inch discs tripping a lever at the
42
rear as they drop into the playing position.
The operating control knob is also located
at the right side of the panel, and is used
for starting, stopping, and rejecting. As
soon as the last record on the stack is
played, the pickup arm lifts and motor
power is cut off automatically. If it is desired to replay the last record, the operating
knob is moved to START and the changer
completes its cycle, plays the record, and
again stops.
Record handling is quite gentle, with
the drop being occasioned by a small lever
within the center spindle. When all of the
records in a stack have been played, they
may be removed by swinging the balancing
arm out of engagement with the spindle
and simply lifting them up and off. Cycling
time is approximately 12 seconds for LP's,
10 for 45's and 5 for 78's. The cycling action is completely disengaged from the
mechanism except during a change cycle,
being actuated by a rubber pulley which is
moved so as to contact the inside rim of the
turntable, from which it receives its power.
All of the rubber -tired pulleys in the drive
mechanism are automatically retracted
when the changer is switched off, thus
avoiding the tendency to form flat spots
which might cause wow or flutter. The pickup leads are shorted by a muting switch
during the change cycle or when the unit
is switched off.
For users who employ different pickup
cartridges for microgroove and standard
records, a small lever on the pickup arm
changes the needle force allowing heavier
force for the 78's and reducing it for the
LP's and 45's. Further adjustment inside
the arm permits setting the force to the
optimum value for each pickup. The pickup
arm may be clamped to the rest when the
instrument is being moved-thus making
it acceptable for portable use without any
-
additional modifications. The instructions
specify that the arm should be clamped
whenever the cartridge is being changed, in
order to eliminate the possibility of damage
to the arm mechanism.
Once the change cycle is completed, the
pickup arm may be operated by hand as
freely as on a single -play turntable, except
for the inner half -inch of playing surface.
If the arm should happen to be moved sideways too far by hand, no damage is incurred because of the manner in which the
arm is attached to the mechanism-a pair of
spring -loaded rollers engage slots in the
actuating lever. When the arm is moved too
far, the rollers simply slip out of the slots.
They can be restored to normal position,
however, by moving the arm inward to the
spindle, then back to the arm rest.
Mechanically, the changer is well constructed, easy of access, and relatively
simple. The motor is equipped with self -
oiling bearings, and is built with die -cast
end bells which minimize acoustic noise.
The instructions accompanying the unit
are sufficiently lucid that any reasonably
handy user could effect any necessary adjustments. The minimum size of the mounting board is 12% by 15 inches, not less than
inch in thickness. Minimum clearances
above and below the board are 454 and 2%
inches, respectively. Six springs are used
on the three mounting bolts -the lighter
ones being placed below the board. When
transporting the unit, it is recommended
that the screws be tightened to prevent
damage.
The turntable rides on a ball thrust bearing, and is expectionally steady. Tests with
piano recordings at all three speeds showed
no noticeable wow, though no absolute
measurements were made. Tests with recordings of solo violin, string groups, and
soprano vocalists- considered best material to check flutter -indicated "clear as a
bell" performance. Warped records played
satisfactorily when placed directly on the
rubber covered turntable, but not when
combined with other records.
For 45's, die -cut fibre spiders are used,
being inserted in the large center hole and
left in place permanently. Small extrusions
on the spiders provide engagement between
discs so that there is no slipping throughout
an entire stack of records.
Hum pickup was no greater than with the
single -play broadcast -type turntable with
which the unit was compared, and while
the rumble was audibly satisfactory, it
measured 4 db higher than with the comparison turntable. These tests covered a
total of about 30 hours of normal playing
with all three types of records, and with-
out any failures of
during that period.
operation whatever
AUDIO ENGINEERING
APRIL, 1953
www.americanradiohistory.com
EXCLUSIVE
"ADJUSTA- PANEL"
ON EVERY MODEL
America's Finest
HOME MUSIC AMPLIFIERS
CROSSOVER CONTROLS
t
The star of these amazing ompli'iers is
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8
COMPLETELY NEW HOME MUSIC MODELS
4 7eatscu Remote eo cewl
There is absolutely nothing to compare with the brilliant, fullbodied, "live" tones of the Classic 25 by Newcomb, its unique
"Audi- balance" feature or its beautifully finished complete remote
control with the "Adjusta- panel" to extend shafts for easy cabinet
mounting. All eight models have this exclusive "Adjusta- panel"
feature. A crossover selector simplifies attainment of correct
playback response, includes foreign and domestic frequencies as
well as the A.E.S. recommended curve. The A.E.S. standard is
provided on all eight models. "EletcherMunson" compensated
volume control maintains perfect aural balance on all eight models.
The tremendous range of the Classic 25 power amplifier extends
from below 10 to over 100,000 cycles, a by product of perfection
through -out the audible range from 20 to 20,000 cycles. Response
is flat from below 10 to above 30,000. All eight models feature
frequency response ±1 db from 20 through 20,000 cycles or
better. All models but one include a built in, compensated preamplifier to meet needs of wide variety of magnetic and crystal
pickups.
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Exclusive Newcomb features make all eight of these new amplifiers easier to install and make possible savings in cabinetry and
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AUDIO ENGINEERING
Hollywood 38, California
APRIL, 1953
www.americanradiohistory.com
43
The Best British Records of 1952
A compilation of the author's preferred selections from the catalogs of English
record manufacturers, chosen for good performance and technical excellence.
THIS YEAR'S review your correspondent has had a very tough assignment.
The shortness of the list is no indication of the amount of work involved, for
indeed the work has been heavier than
ever. The list is short because it seems the
time has come to delete all 78's unless of
exceptional interest or merit. This year
only a few appear ; next year there will
be none. This doesn't mean that the 78 is
dead in Britain, but it is fighting a losing
battle.
The year was notable for the fact that
in October the E.M.I. combine entered the
LP market, with the Decca Company two
years ahead. In the six months' period between E.M.I.'s announcement and their
actual production of LP's, the Decca Company really got busy, and new recordings
and dubbings of old poured off the presses.
The amount of new stuff made available to
us was truly fantastic, and made your reviewer's life far from easy. As might be
expected, this colossal burst of activity
was not without effect on the records themselves, and a large proportion did not come
up to the standards laid down for these
annual lists. Whether these faults were due
to hurried recording or hurried processing
is not known, but that the faults are there
is undeniable. On the other hand the year
produced some notable discs, and the
characteristic ffrr string tone, which is
not favored by many of us, seems to be on
the wane. Hurried production resulted in
a large proportion of records being pressed
too thin and coming out conical. These
could be spun on the table like a top, and
when put on a record-changer, literally
nothing happened at all. Reviewing was
done on a normal simple turntable and
several records were unplayable. These may
have good music on them, but there was no
means of extracting it with a lightweight
pickup.
When the E.M.I. LP's arrived it was
seen that the processing had been well
done. The records were flat, clean, and
provided with the nice tapering rim which
is the hall -mark of a well -made record,
although with few exception, the quality
of recording was far from satisfactory.
A check -up on the source of the performances soon revealed that these LP's were
simply dubbings from 78's, sometimes of
pre -war vintages. Some of the old 78's
were masterpieces in their day, but time
and technique marches on, and the shortcomings were painfully obvious to anyone
with good equipment and a critical ear.
Some, of course, were dubbings from quite
recent 78 recordings, but this did not ensure
satisfactory results. A few LP's were somewhat better than the original 78's, but in
general something was lost in the transfer
to LP.
At any rate, many of these records could
not go into your list, and many hours of
listening to E.M.I. LP's have resulted in
152 Hammersmith Road, London, W. 6,
England.
H. A. HARTLEY
OR
F
44
ORCHESTRAL
Beethoven
Berlioz
Creatures of Prometheus. L.P.O. Ivan Beinum)
Symphonie Fantastique. Concertgebouw O.
Ivan Beinum)
Harold in Italy. R.P.O. (Beecham)
(781 Overture: Le Corsaire. Philharmonia O.
Kletzski)
Mer. Suisse Romande O. (Ansermet)
Nocturnes. Suisse Romande O. (Ansermet)
L'Apres -midi d'un Faune. Suisse Romande O.
(Ansermet)
(78) Eventyr. R.P.O. (Beecham)
Symphony No. 4. Concertgebouw O. (Szel I)
Faust, Ballet music. Paris Conserv. O. (Fistoulari)
Lon. LL577
Lon. LLP489
Col. ML4542
Br. Col. LX1533
I
Debussy
Delius
Dvorak
Gounod
La
.
Lon. LLP388
Lon. LL530
Lon. 13503
Br. Col. LX893I 2
Lon. LLP488
Lon. LLP180
.
Handel
Concerti Grossi, Op. 6. Nos.
O. (Neel).
Haydn
Massanet
Meyerbeer
Symphony No. 49. London
Le Cid. Ballet music. L.S.O.
Les Patineurs, Ballet music.
Divertimento No. 2. K. 131.
Mozart
Ponchielli
Ravel
Rossini
Schubert
5
6
6. Boyd Neel
Mozart Players.
(Irving).
L.S.O. (Irving).
London Mozart
Players.
Symphonies Nos. 31 & 39. L.S.O. (Krips).
Gioconda, Dance of the Hours. Paris Conserv.
O. (Fistoularìl.
Bolero. Paris Conserv. O. (Winch).
Rapsodie Espagnole. Suisse Romande O. (An-
sermet).
Alborado del Gracioso. Suisse Romande O.
(Ansermet).
Overtures: Semiramis, Scala di Seta, Gazza
Ladra and William Tell. Concertgebouw
O. Ivan Beinum).
Symphony No. 7 (or 9). Concertgebouw O.
(Krips).
Strauss, R.
Tchaikovsky
Vaughan -
Williams
Symphonie Domestica. Vienna P.O. (Krauss).
Swan Lake (complete). L.S.O.
Fistoulari)
Overtures: Hamlet and 1812. L.P.O. (Boult).
A London Symphony. L.P.O. (Boult).
Fantasia on a theme by Tallis. New S.O.
1
.
(Collins).
Lon. LPS396
Lon.
Lon.
Lon.
Lon.
LL586
LL651
LL651
LL586
Lon. LL542
Lon. LLP180
Lon. LLP446
Lon. LL530
Lon. 13503
Lon. LL358
Lon. LL619
Lon.
Lon.
Lon.
Lon.
Lon.
LLP483
11565'6
LL582
LL569
LL583
CONCERTI
Piano
Beethoven
Concerto No.
in C. Guida and Vienna P.O.
Lon. LLP421
Lon. LLP417
Rachmaninov
Concerto No. 4 in G. Backhaus and Vienna
P.O. (Krauss).
Concerto No. 3. Lympany and New S.O.
1
(Bohm).
Lon. LL617
(Collins) .
Violin
Beethoven
Concerto in D. Campoli and L.S.O. (Krips).
Concerto in D. Ricci and L.P.O. (Boult).
(Two quite different interpretations. You pays
your money and takes your choice. Both good
Lon. LL560
Lon. LL562
recordings).
Oboe
Marcello
Concerto in
mande O.
C
Concerto in
D
mi. Reversy and Suisse Ro-
Lon. LS591
(Ansermet).
Bassoon
Vivaldi
mande
O.
mi. Helaerts and Suisse Ro-
Lon. LS591
(Ansermet(
AUDIO ENGINEERING
www.americanradiohistory.com
APRIL, 1953
i
Here is the
first basic advance
in tone arm design in
many decades!
The GRAY "Viscous- Damped"
108 -B Tone Arm
Gives you perfect contact and tracking on all records at
lowest stylus pressure virtually eliminates tone arm reso-
-
nances- cannot damage record if accidentally dropped.
The entirely new suspension principle of
the Gray 108 -B makes it hug the grooves
..
.
-
prevents stylus skidding on worn records
overcomes groove -jumping caused by floor
vibrations. Its "viscous- damped" design provides perfect tracking, virtually eliminates
tone arm resonances, and prevents any possibility of record damage if the arm is dropped.
The 108 -B satisfies every requirement of
high fidelity reproduction. A plug -in feature
permits instant change from 78 -rpm to 33%.
rpm or 45 -rpm, with automatic adjustment to
the correct stylus pressure. See and try this
"viscous-damped" arm soon solve all your
transcription problems with this revolutionary,
-
versatile arm!
Gray Re carch 8 Development Co., Inc.
Hilliard Street, Manchester, Conn.
Please send me your Bulletin RF-4 on the new Gray
"Viscous- Damped" 108-B Tone Arm.
NAME
AND
DEVELOPMENT CO., INC.,
HILLIARD STREET, MANCHESTER, CONN.
ADDRESS
Divi.ion of The CRAY MANUFACTURING COMPANY-Originators of the
Cray Telephone Pay Station and the Gray Audograph and PhonAudograph
AUDIO ENGINEERING
APRIL, 1953
www.americanradiohistory.com
CITY
STATE
45
only two being listed for you. As they are
obtainable under your Columbia label,
American Columbia numbers are given. It
is possible, of course, that many records
originally recorded in England, or under
British auspices, already appear as LP's
in either the Columbia or RCA -Victor lists,
but the task of ferreting these out is too
gigantic to contemplate. Such must have
happened during the past few years, for
there is the celebrated case of the Berlioz
Requiem recorded in Paris under Columbia
auspices which came out in your country
and has never appeared in Britain in any
form at all; on the other hand, the Ravel
"L'Enfant et les Sortileges," again recorded in Paris, appeared as an LP with
you and on 78's here. The 78's were good,
and they were listed in an earlier article,
but the LP is far better. Yet both were
taken from the same tape.
As a contrast, the Columbia tape recording of the complete Meistersinger appeared
in Britain on thirty -four 78's and sounded
beastly. You can judge the American LP
version for yourselves. Here all the professional reviewers loudly praised the Decca
version as superb recording. Your correspondent found himself in a minority of
one, and he still thinks it far from good.
The celebrated Mercury recording of
"Pictures at an Exhibition" was transferred to a ten-inch H.M.V. LP (losing
something in the process). One of our more
learned record magazines came out with
this in the review of the H.M.V. version:
"This recording is the answer to criticisms
of shallowness of tone on LP attributed
to narrowness of the groove (the italics
are mine). I do not think there has ever
been before such realistic reproduction as
we hear of timpani and big drum
in
fact the recording makes one sit bolt upright with amazement from the first trumpet notes.... Sensational recording. .
I am eager to know what this system of
recording will yield in less picturesque
music." That reviewer was unaware that
the H.M.V. company were not responsible
for what is undoubtedly a fine piece of
technical effort. So the list that has been
prepared for you was put together the hard
way-by getting the records themselves,
playing them on good equipment, and listening. The result, as you can see for yourselves, is meagre.
Every record originating in America has
been omitted because you can get them at
first hand. The list is intended to show
which records originating in Britain are
worth getting as real high- fidelity discs.
The few 78's that are included have been
...
COMING EVENTS
INSTRUMENTAL
Chamber Music
Beethoven
Brahms
Schubert
Archduke Trio. Trieste Tno.
Piano Quintet in F mi. Quintetti Chigiano.
Quartet No. 13 in A mi. Op. 29. Vegh
Quartet.
Beethoven
Sonatas Nos. 14 and 31. Guida.
Sonata No. 29. Guida.
Piano
Schumann
Bach,
J. S.
Sonata No.
Bach,
J. S.
Handel
Moussorgsky
Scarlatti
28 -May
1- Seventh
Annual
NA-
TIONAL ASSOCIATION OF RADIO AND TELEVISION BROADCasTEMS' convention and
1953 BROADCAST ENGINEERING CONFER-
Burdette Hall, Philharmonic Auditorium, Los Angeles.
April 28-May 1 -1953 ELECTRONIC COMPONENTS SYMPOSIUM. Presented through
ENCE.
443
LLP150
LLP422
H.M.V. C4159
Br. Col. LX1532
Lon. LLP530
Lon.
Lon.
(781 Sonata No. 22. Solomon.
1781 Sonata No. 5 in E. Gieseking.
Pictures at an Exhibition. Katchen.
Longos Nos. 10, 142, 223, 292, 294, 325,
382. Long.
Carnaval. Nikita Magaloff.
Lon. LS524
Lon. LS528
Violin
in C. mi. Renardy.
1
Lon. LPS423
Piano 6' Violin
(78
1
Sonata No.
3
in
Menuhin & Kentner.
E.
H.M.V.
DB21435.'7
Organ
(78) Eight little pieces for mechanical clocks.
Haydn
H.M.V. C4177
Jones.
OPERATIC
Debussy
Pelleas &
Delibes
Lakme
Melisande
(complete).
Mollet,
Lon. LL592 5
Mozart
Danco etc. Suisse Romande O. (Ansermet)
(complete). Opera Comique, Paris.
Le Nozze di Figaro (complete). Schwarzkopf,
London, Kunz, etc. Vienna State Opera and
Lon. LLA -12
Col. SL114
Puccini
La
(complete). Rome Acadamia di
Lon. LLP462
Phil. O. (Karajan)
Boheme
3
Sta. Cecilia.
Strauss,
J.
Wagner
Madame Butterfly (complete). Tebaldi and
Rome Acadamia.
La Tosca
(complete). Tebaldi and Rome
Acadamia.
The Gipsy Baron (complete) Vienna State
Opera & P.O. (Krauss)
Parsifal (complete) Bayreuth Festival (Knappertsbusch I
Lon. LLPA -8
Lon. LL660 /1
Lon.
LLP418 /9
Lon.
LLPA -10
put there because they seem to your compiler to have intrinsic merits which should
not be overlooked, but individual arias from
operas are not now included since the LP
opera makes the collection of them unnecessary, or so it seems to the writer.
Much thought was given to the problem of
whether to include "recital" records or
not. Some people like these, some do not,
and a private census of the people who
might buy such records showed that the
majority don't, so out they went.
Perhaps before this time next year this
scheme may have to be substantially modified or perhaps even abandoned altogether.
There seems no prospect whatever of individual small recording companies spring-
ing up as they do in your country-possibly the market here isn't big enough.
Whatever may be the cause, what remains
is that occasionally a few independent 78's
come out, usually of very poor technical
cooperation of AIEE, IRE, RTMA, and
WCEMA. Shakespeare Club, Pasadena,
California.
May 7- Forty -fifth Meeting of the
August
quality.
The following abbreviations are used:
O simply means "orchestra ". L.S.O. is
London Symphony Orchestra. L.P.O. is
London Philharmonic Orchestra. R.P.O.
is Royal Philharmonic Orchestra. Lon. is
London (i.e. British Decca). Col. is American Columbia. Br. Col. is British Columbia. H.M.V. is His Master's Voice. The
conductor's name is given in brackets after
the name of the orchestra.
All records are LP's except where otherwise specified.
SHOW
War-
wick Hotel, Philadelphia, Penna. Featured subject: Sound Reproduction. Side
18-21-1953
SHOW.
May
ELEcTRoxrc
PARTS
Conrad Hilton Hotel, Chicago.
20-22-SOCIETY
OF
PHOTOGRAPHIC
Third Annual Conference,
Hotel Thayer, West Point, N. Y.
ENGINEERS'
AND
sponsored
3-
1INTERNATIONAL
SIGHT
AND SOUND EXPOSITION, combined with
the CHICAGO AUDIO FAIR. Palmer House,
Chicago, Ill.
October 14-17 -Fifth Annual Convention
of the Aunio ENGINEERING Soanrr, and
THE Aunto FAIR. Hotel New Yorker,
New York City.
.
AUDIO ENGINEERING
www.americanradiohistory.com
ELECTRONIC
CONVENTION,
Francisco, California.
September
trip to RCA Laboratories, Princeton,
N. J., on May 8.
May
19- 21-WESTERN
jointly by WCEMA and Western Sections of IRE. Municipal Auditorium, San
9-
ACOUSTICAL SOCIETY OF AMERICA.
April
Lon. LL599
Lon. LL501
Lon. LL587
APRIL, 1953
HARVEY
the House of Audio
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AUDIO ENGINEERING
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FM -AM TUNER -Model AF-723
Designed for high quality reception of both
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continuous treble attenuaing controls: 'on /off' switch and volume
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APRIL, 1953
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LUxemburg
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47
EDWARD TATNALL CANBY*
and I have some
more to say on the subject -perhaps
revising some earlier ideas expressed
here. As said many a time before, this department reserves the right to climb onto
limbs, speculatively, and the further right
to climb delicately off again if need be, to
"changer d'avis", as the French so elegantly put it.
My last, in the December issue, was
written the day I arrived in St. Louis for,
among other things, an extended look into
the details of the two-channel process, at
Washington University where I'm currently
attached to the Music Department. Those
indefatigible pioneers in the binaural tape
field, the Magnecorder people, had followed
up their initial interest with the loan of a
recorder without which, needless to say, investigation would be slightly theoretical.
Now, a good many very uncommercial tapes
and a number of months later, I'm feeling
an awful lot clearer about the whole business though my efforts have not, alas, been
of the sort that could pay Magnecorder
back as handsomely as deserved in terms of
gorgeous binaural recordings!
BINAURAL AIARCIIES ON
Eavesdropping
Indeed, as some old readers will guess,
my approach to the recording problems was
deliberately informal. I wanted to be able
to fuss around with a minimum of trouble.
that the college band, sight -reading for their coming basket -ball session,
would be as good a test audio source as,
perhaps the St. Louis Symphony. It was,
if one forgets about music. An amateur
trombone, out of tune and a measure late,
is as good a binaural point-source as Harry
James or Yehudi Menuhin in person I
picked up the band and a Hindemith Clarinet Sonata and the college organ (that one
is a wow of a recording) and a woodwind
quintet playing for fun and a tea party-to
catch voices talking in a general scramble
-and ended up my first session working
with the cast of a college play, as adaptable
a source of sound as I've ever had.
And all of this was played back on
speakers and via phones in a great variety
of places and to many people. Direct comI figured
!
*780 Greenwich St., New York 14, N. Y.
48
parisons were made constantly between
two -channel and one- channel reproduction
(one track through two speakers or both
phones of a set) at every phase of the experiments-which was certainly the best
check we could have as to what was going
on. Especially the speaker comparison, between two speakers on the same channel
and on two channels. That comparison,
strangely enough, I had never been able to
hear before and it is a vital one that every
one of us who is interested in two -channel
work (or 3- or 5- channel) should make
constantly. Most revealing.
Brain Twisting
That was, shall we say, the physical exercise part of the job (Magnecorder did
more for my muscles than Charles Atlas
ever could, begging their pardon. Suffice
it to say that my office was on the third
floor, no elevator....) But alongside of
the tape puttering, I began sounding out
People Who Ought to Know in the University-which has a raft of them. Physics
department, Electrical Engineering. We
would listen, then go out for three -hour
lunch and cover all the menus with how does -it -work binaural doodles.
Most important contact, however, was in
the Institute for the Deaf, a fabulous place
where binaural hearing was practically invented. Those people were not aware that
there was any great problem, in the dim distant audio world, as to how to get a
binaural effect, but they certainly knew a
great deal about how two ears work better
than one. The Lord had worked out the
two -eared process quite some time before
binaural tape. Science had got to the bottom
of a good deal of the Lord's intentions
quite a while back, too. They referred nie
to the Literature, which I haven't absorbed and probably never will -it's tough
stuff. The one thing that is dreadfully clear
was that from the ear men's viewpoint
there just isn't any argument. it's all very,
very simple, relatively speaking.
There came a memorable day when I
finally saw a blinding flash of light or
something. I haven't recovered since. I
think I catch on now, as I say, and maybe,
Literature or no, I can give you non-
Literature readers some useful hints in
plain ordinary Amurrican.
Bistereonauralphonie
Yep-it has to do with Binaural versus
stereophonic. It seems, as you probably are
well aware by now, that we have two quite
distinct kinds of hearing involved in the
present two-channel developments. Whether
they overlap at all is still somewhat of a
question. It seems to nie a good guess,
anunr conflicting opinions now raging,
that they don't There are those who feel
that two loudspeakers can give a partial
true-binaural effect -one sound to each ear.
I certainly had thought so. I'm still not
clear on the point. Rut I can only say two
things. First, the Higher Scientists gave
nie to understand in most emphatic ternis
that there can be no binaural effect at all
worth mentioning via two loudspeakers. I
repeat, no effect. The observed phenomenon are accounted for purely as stereophonic-which I will get to in a moment.
I'm not quoting this directly, but that is
what my two attentive ears and one brain
took in. Dr. Ira Hirsch, one of the top
hearing experts, who has done extensive
work in this field (including construction
of as nearly perfect a binaural "head" as
could be devised, with mikes imbedded in
ear -like channels) was the main source for
this deduction on my part.
Secondly, I can give you, too, my own
private evidence. to supplement what I seem
to have understood from the experts ; i.e..
my observations of the phenomena of twospeaker reproduction are accou stable very
nicely in stereophonic terms without necessarily any binaural effect. Moreover, there
are what I might call "anti- binaural" observations which indicate to me that the
loudspeaker effect, such as it may be and
however good it may he, is specifically not
true binaural.
True Binaural
There is no argument about the "binaurality" of headphone reproduction, with
two mikes, say, not over fifteen inches
apart (the ears are flexible) and the usual
complete dual system. Perhaps not literal,
especially as to accurate direction, since
standard mikes are not really very much
AUDIO ENGINEERING
www.americanradiohistory.com
APRIL, 1953
coast
At the recent Audio Fair -Los Angeles, (as in
New York) hundreds waited in line before each
Audax CHROMATIC performance (every 20
minutes) best described by the following excerpt from the Audio Fair Review in AUDIO
ENGINEERING.
"If we
had to name the most popular display of
the recent N. Y. Audio Fair, the top honors
would most certainly go to the Audak Company. Maximilian Weil, AUDAX president, long
known for his virtuosity in the creation of fine
Electronic Music reproducers
had the violinist David Sarser, (Toscanini's NBC Symphony), and the cellist, Sebe Sarser (New
York City Opera Co.) in person, play for the
AUDAX audience. Intermittently, they would
put down their bows and the performance was
then carried on by the new AUDAX CHROMATIC pickup, playing a disc -recording of the
same composition.
So startlingly realistic was the reproduction by
the new AUDAX CHROMATIC reproducer that,
invariably, the audience broke into spontaneous
applause. Adding to the demonstrations dramatic proportions, was the fact that the musical
instruments used by the artists were Stradivari,
valued at well over a hundred thousand dollars.
to
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like standard ears -in-heads. But the two ness of the reception is enough to give us
the undeniable binaural effect, not unlike
the undeniable 3- dimensional effect of a
stereo photograph via a viewer.
The big argument comes with speakers.
Binaural effects depend strictly upon the
selective reception by the two ears of different signals. With earphones, as in normal hearing, the separation is 100 per cent
or so. But is there (a) no separation or
(b) some separation with loudspeakers?
That is a very big question, and it is the
basic clue as to whether there is any truly
binaural effect at all with loudspeakers.
The answer is pretty technical. All I
can say is that I heard much about sound
pressure being substantially equal on both
sides of a head for most significant frequencies regardless of direction; therefore
two loudspeakers, to right and to left and
equidistant, will be heard equally loud at
significant frequencies by both ears -hence
no separation. Both ears hear both speakers.
Like two eyes looking at a pair of stereo
photos without a viewer. True? Not true?
I'm not sure-but it is a point that is vital,
if we are to explain two- loudspeaker "binaural" scientifically. I say, again, that my
St. Louis experts gave rile to understand
that there is no significaut'separation of the
right and left sounds with speakers off in
room, to right and left. (If they were six
inches or even two feet from each ear there
might be separation -but this is not what
we are considering.)
Stereophonic
Suppose, for the argument, that we accept the idea that there is no binaural action at all when two speakers reproduce
two channels. What else is there involved?
A lot.
The stereophonic principle, involving the
hearing of sound by two ears together, can
account by itself for the well known observable effects when we have two -speaker
reproduction at its best. The way I see it,
stereophonic reproduction via speakers is a
sampling of the "curtain of sound" in front
of you-or the mikes, as picked up. If
we could set up a thousand -odd mikes in
parallel rows and feed them through a
soundproof curtain to a thousand -odd correspondingly placed speakers, we would
have a sort of "half tone" reproduction of
the total sound, spaced out neatly according to its multiple source. The multitude of
tiny dots in a printed picture are in a way
similar to this. Sample the light intensity
in terms of black and white at many points
and reproduce the same-and you "see"
the original picture.
Moreover, even though the picture dots
be large, crude and few in number, we can
still reconstruct the sense of a photo. The
coarser the dots, the harder it is to see the
picture and the more indistinct is the detail.
Our ears are a lot more easily satisfied,
in this sampling process, than our eyes. We
use more imagination with our ears, even
if we are in the long run less accurate as
to shapes and directions. Sample a "soundpicture", the area of sound -source in front
of you, with as few as a half dozen mikes,
six points, and the reproduction via loudspeakers in the same relation will be (distortion allowing) very nearly perfect.
Even with as few as three points, middle
and the two sides, we can pick up and reproduce a sound -picture that is remarkably
accurate in its directionality. We can mentally spread out a whole orchestra and
hear the first violins on the left, the heavy
brass at right rear. We scarcely miss the
lack of an up- and -down dimension. The well
known three -track stereophonic demonstrations, via wire and film recording, of the
Philadelphia orchestra illustrated this most
effectively back in the early thirties.
Two -point Sampling
What then, if we sample space at only
two points? (Remember that the ordinary
one -point sampling of the usual record or
broadcast still gives us a vast number of
clues as to space and distance, even though
we have actually only one perceivable dimension-front -and -back.) Two-point sampling falls somewhere between the accuracy
and clarity of direction that three -point
sampling gives us, and the pleasant but indefinite illusion of space heard via the one point system. It clearly can be an improvement, technically, over the one -point sound.
If we get as much as we do, with one
mike and one speaker, then two points,
nicely spaced, should, we can easily deduce, add in addition a somewhat greater
sense of side -to -side "shape" in the whole.
round picture. (Not all the instruments of
an orchestra will be inches from one mike
or the other; many will be in between.)
Not too accurate-for there is the vast
complexity of reverberation to count in;
sounds reaching the two mikes are reflected,
in most good musical situations, from all
sorts of directions in addition to the direct beam. When this side -to-side clarity is
added, we can more accurately imagine the
actual shape and position of the sound
source, around and between the points of
sampling. We fill in the details via imagination.
This means that reproduction of two
sound pickups via two speakers can allow
us to "place" the music distinctly better
than we can when (for fair comparison)
two speakers reproduce only one track, together. And that, in turn means a greater
sense of presence, realism, and an improvement in musical clarity, in separation of the
various sounds as they come from vaguely
different spots, instead of all from the one
source.
Moderate Improvement
Now, 1 suggest you read that last bit
carefully and ask yourself -is not this exactly what we experience in actuality when
we hear a so-called "binaural" reproduction
via two loudspeakers? Is not this fully sufficient to account for the observed phenomena?
If you have made the fair test between
one -channel and two -channel sound via two
speakers -using two speakers in both cases
-you will, I am sure, agree. The effect may
be better or worse according to circumstance, hut substantially it fits this description, in character and in degree. There is,
at best, a notable but still a moderate improvement. The improvement over equivalent one -channel reproduction (same music,
same speakers) is not a thing you can put
in percentages; it depends on your subjective feeling. But, with constant experience,
constant demonstrations of both ways, AB
tested, I think you'll find it satisfying, exciting, but still -moderate. Three -channel
reproduction -or 5- channel, as in Cinerama
-would do a great deal more for you via
loudspeakers.
That is stereophonic reproduction, the
sampling -of -space system. Ideally, N channels, optimally, perhaps five channels, minimally for rough accuracy of spacing, three
channels. Absolute minimum, for moderate
general improvement in presence and a
vague general sense of direction-two chan-
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APRIL, 1953
nels. Two points of space sampling, to give
cues to the entire space -picture.
I find no good reason to think that the
binaural, sound -separation effect is involved
here at all. Here we have always both ears
hearing both (all) points. That's why
Cinerama (and Fantasia) don't involve earphones.
Li
s-a
LISTENERS AND
CRITICS ALIKE
APPLAUD THE
ØW
Big Clue
-I
can't quite stop
But -editor permitting
here. There are anti-binaural indications to
in
-loudspeaker
sound. I've
me,
this two
been listening hard.
What are the essentials of the real, twoeared binaural hearing, as differing from
the one -eared "broadcast" and recorded
sound? (Also the one-track sound of the
hearing aid.)
Briefly, in speech and everyday noise, the
two -ear separation and the directional clarity it affords us allow us to sort out sounds,
as we can sort out colors with our eyes.
That sorting ability gives us a far better
grip on the mass of sound and we can
relegate that which we do not want into
our subconscious. In a crowded cocktail party or a dinner -table multiple conversation, we can be attentive to the sounds we
want, put the others into the background
of our minds. Without the directional ability to sort out sounds and separate them,
we are far less able to do this-and the result is confusion, a general blur, inability
to understand one speaking person against
the competition of others. The difference
between binaural and monaural hearing is
sensational in this sorting -out respect. (\Ve
can also compare this to the stereoscopic
effect of, say, a tree with millions of leaves ;
on a flat picture they blend and merge, but
in perspective-with two-eyed separation
they stand out in their individuality.)
And music? The same basic sense for
sorting, for reducing confusion, for eliminating unwanted interference, makes binaural hearing of music vastly more clear
than the same music heard via one channel.
Liveness, the general blur of delayed echo
coming from all directions, is much more
apparent with the non -sorting, monaural
sound. We most go out of our way to
reduce it-via close -up mikes, dead studios,
etc. A voice at ten feet in a "bright" room
sounds entirely normal via two ears, but
recorded monaurally, it is dismally off -mike.
Too far away-too much room confusion
added to the direct sound.
Now for the pay -off, as I've found it.
Even though directional effects are not entirely accurate via binaural headphone
reproduction, the 100 per cent separation of
the two sound pickups definitely gives these
same binaural effects. Confused, mixed
voices are startlingly more clear, more
easily understood via binaural phones than
via monaural phones or speaker reproduction. I tried that, with a tape of muddled,
mixed party conversation. Via speaker, I
got only a few words from the confusion.
Via binaural phones I could follow almost
every conversation verbatim and could concentrate on any one of them, at will.
I also recorded speaking voices ten and
fifteen feet from the mikes in live halls.
Via monaural speakers or via monaural
phones they sounded typically off-mike. Too
far away. But via binaural phones the same
voices were entirely natural, with no sense
of too -great distance. I've done this over
and over again, to complete satisfaction.
Voices recorded close, sounding just right
monaurally, as for standard radio, are much
too near via binaural phones. Unpleasantly
close.
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The saine principles apply in music. Binaural phones allow you to move your
mikes very much further away than for a
proper one -channel standard set -up. Good
standard recording mike placement is in
most case far too close via binaural. Too
close for two ears.
In other words, the binaural effect is
consistently and accurately present via binaural phones, in terms of liveness, clarity,
separation of wanted and unwanted sounds.
Even such noises as that of passing busses,
very distracting and painfully obvious in
monaural pickup, are easily relegated to the
background via binaural. I have watched
a woman listening via phones to a speech
where a bus roared past outside. Via the
single monitoring speaker on the Magnecorder (one channel only) the speaking
voice was almost drowned out. Yet the
lady behind the phones was not even consciously aware of it. She lived right there
and merely put that bus where she always
put it binaurally-out of mind.
Do these true binaural effects occur when
two loudspeakers are used? That is an
acid test.
I have tried and tried and tried, corn paring one -channel and two-channel sound
via speakers. The answer, in my experience,
is a dramatic NO.
Off -mike voices remain off -mike when
reproduced via two channels on speakers
though the source of the voices can definitely be heard in space between the speakers. That is the stereophonic reconstruction
of the sound- picture by your ear and mind.
The liveness, however, does not change.
Confused recorded conversation is just as
confused via two -track sound as via one track- though the placement in space and
the realism is heightened.
Music recorded off -mike-that is, too far
away for good monaural sound-remains
too far away via two -channel, though,
again, the placement of the sound source
may he dramatically improved. The liveness does not change.
Therefore. I deduce, there can be no appreciable binaural effect, via loudspeakers.
The specific binaural phenomena are miss-
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.
But what of the wonderful sense of
placement in space that two-speaker reproduction via two channels can give?
What of the magical effect when a grand
piano-or a speaking voice or an orchestra
-suddenly seems to "appear" in the space
between the two loudspeakers-or around
and behind them? That effect has been
taken by many as proof that the music is
binaural. I thought so, too. If you can
place the sound in space between the loudspeakers, you must be getting a directional
effect from the two tracks, via some degree of sound separation from the two
speakers, to their respective right and left
ears. So I thought.
I believe you will find that this is not the
case. The space placement is thoroughly
and adequately accounted for by the stereophonic space sampling of your ears -they
gather enough sound clues from the two
points of sampling to reconstruct the actual
aspect of the sound -space as picked up.
That is the entire explanation. It fully
covers all the aspects of "binaural" sound
you have heard of, with one minor qualification, to follow.
If, then, the more specific binaural effects
of liveness-which are so dramatic via earphones and natural hearing-are not found,
by direct comparison, in the two-speaker
set -up, then we must conclude that the ear
is not concerned at all with binaurality. If
there is some percentage of actual separation of the two sounds to the two ears,
then it cannot be much, nor very effective.
And that is that.
Dual Point-Source
One final note. I made a boner in my last
on this subject. There is a third effect of
a sort, the literal substitution of a point source speaker for a point- source sound.
I called that "stereophonic "; it is not,
strictly.
Record two actors three feet from two
mikes, at thirty or forty feet separation.
In effect, each voice is on one track only.
Doesn't carry to the other. Then play these
tracks back through two speakers. Wherever you put them-there will be the voices.
Point -source two- channel recording. But
never will you hear either voice in space
between the two speakers. Each voice is
"inside" its own speaker box.
This point- source effect, has figured quite
a bit in "binaural" sound recently. A table
tennis game for instance. A piano at one
mike and a singer close to the other. There
may be some sound merging, and thus the
stereophonic "iii-between' effect gradually
may be introduced, as well.
Emory Cook's "Mosque" two- channel organ records, termed binaural, are essentially
point source dual recordings, I'd say. The
two parts of the organ were in two corners
of the huge hall and mikes were placed
fairly close to each, maybe 30 feet, and
perhaps 90 feet or more apart. (So I hear)
That, I'd suggest, is neither stereophonic
nor binaural! But the effect, mind you, is
gorgeous via speakers. Each speaker reproduces its own organ and they blend externally, as they did in the original hall,
more or less.
All these effects may be put to excellent
use. It's just a matter of getting them
straight. And to point up that big difference
between binaural and stereophonic. I only
suggest, for your edification, that if the
Lord had figured we needed more than two
ears, given complete sound separation, he'd
have given us more. He didn't figure on
sound reproduction, I guess. We can use
his way -true binaural. Or we can fake up
that "curtain of sound" in front of our
listening ears, via sampling at various
points. To match the good Lord's system
we then need N points, and economy gives
us "only" two. We ought to have at least
three.
But we'll never, never need three ears.
SPECTACULARS
Strauss: Ein Heldenleben.
's0 (A) Minneapolis Symphony, Dorati.
t Mercury MG 50012
g (Bl
Vienna Philharmonic, Krauss
London LL 659
It takes a long tme to listen to these two
mammoths and make a comparison A lot of
music. For excellence in the recorded medium
I'll choose the Mercury- Dorati version, but not
without comment. I underline, above, intentionally. Do we want concert -hall realism or
phonograph realism?
Mercury's version is done via the now well
established one -mike technique, with a Telefunken. That technique is fairly straight- forward
in theory; one finds, in a good hall, that point in
space where the direct over -all sound, from the
source, nicely balances the liveness, the reverberation. Sometimes that point is quite critical- too far away and you're off-mike, too close and
the instruments are solos instead of ensemble.
They don't blend.
This record has hit the over -all sound to perfection. But the balance among the instruments
-which must be adjusted to the single mike
is, shall I say, phonographically effective but
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I
-
APRIL, 1953
musically slightly cockeyed. Brass and percussion
are very loud, sharp, close, and clear, overriding
the strings as is seldom the case in a concert
hall hearing.
Wrong? Not at all-in this case. The sharp
brass sounds and the equally clear drum sounds
are wonderful -via good reproducing equipment.
Moreover, these sounds are musically very important in the score itself and their technical
exaggeration, though perhaps a concert musician's
ear would not approve, on the whole does the
music much good. We must adjust our music to
the new medium. This is a real "hi -fi record ",
The London version, probably done with more
than cue mike, has a more conventional brass
balance of tone, though paradoxically, here the
strings (as in many Londons) sound unnaturally
close. An excellent ensemble -but less trans paret, the bass more tubby than the Mercury.
Inner grooves do not hold up quite as well, either.
Credit that to Mercury's Margin Control, I'd
guess.
Standards are high these days! Ten years ago
either of these discs would have been miracles
unbelievable.
on both sides, but the Chopin is no hi -fi record.
the Tchaikowsky is -so much so that you might
be tempted to say it is "better recorded." I
suspect the difference is all in the music. The
Chopin is quiet, mostly strings; the loud parts
are heavily stringed-and loud strings, with their
multiplicity of violent IM effects, are extremely
hard to record clean (and get clean onto a disc).
Thus the Chopin occasionally sounds shrill and
a bit distorted. But, on the reverse, Tchaikowsky's clean, varied orchestration, full of line brass
and percussion, makes
a superb sound.
Musically a most sympathetic and warm playing of both pieces, by an orchestra that knows
its ballet, even if its ensemble is not as perfect
as in some of the fanúer orchestras.
Dvorak: The Golden Spinning Wheel:
The Midday Witch; as Waltzes, op 54,
#1 and #4. Czech Philharmonic, Prague
Soloists Orchs., Talich.
Urania URLP 7073
e
Two rare bits of Dvorak and no less attractive
(as we might expect) fur the mere fart that :he
first is seldom heard. the second just about unknown, until now. That is, to U. S. concert
audiences. (The two dances are familiar and
lovely.)
The fat, resonant big -orchestra sound of these
is one that we don't seem to get in this country.
Our big ensembles are more pretentious in tone;
our littler groups can't achieve the tonal mass.
Acoustics
count heavily in the gorgeous old
halls that abound in Europe. This record (the
two tone poems) is very live, with a strange
"double" echo, about a half,second late; that is
quite pleasing; the sound has fine presence, big
bass and good highs, and the music, while
rambling, lives up to the usual Dvorak reputation
for lyric charm and warm, colorful harmony.
Some exotic effects in the "Witch."
The two fill -in waltzes are in closer acoustics;
recording distorted in loud parts. Inner groove
trouble, perhaps.
°Mendelssohn: Midsummer Night's Dream;
incidental music. Robin Hood Dell Orch.,
Reiner.
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Unusually good musical performance
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Respighi: Fountains of Rome: Pines of
Rome. Vienna State Opera Orch., Quadri.
tt Westminster WL 5167
A competing version of this has not yet reached
me-but this offers enough for comment, as the
first in Westminster's new "
" technique
($1000 to you if you can find a name for it)
-the company's bid for notice in the developing
spectacular field, once pretty much monopolized
by London.
It's a fine recording, no doubt, and truly more
"naturally balanced" in detail than either of
the Strauss records above, from the musician's
viewpoint. Excellent big liveness, with good sharpness in the detail. But I have one serious corn plaint -too much pre- emphasis of the highs.
Compared directly to the Mercury and London
offerings above, this Westminster is noticeably
shriller and louder in the highs. :\ change in
equalization is definitely needed. (The album calls
for NAB roll -off for best results on high- fidelity
equipment.) Even with proper equalization, this
steep high boost, combined with high -level groove
cutting, is bound to cause some distortion trouble
in many a home system. I found a noticeably increased distortion in the loud parts as compared
with the other two discs, above. (Mercury, you'll
note, calls for AES on its album cover.) Before
Westminster settles on a name and throws out
that One Grand, I'd strongly suggest it reconsider its high end, and settle on something less
steep -say the AES curve.
Musico- ornithological note: the famous recorded nightingale who sings in the "Pines" is
expertly inserted here, to any ornithologist's delight. How? The bird, immersed in shimmering
strings, is so faint that you can just hear
and thus is startlingly realistic! First time, I
thought it was outside my window. That's the
way we normally hear birds: at a distance, not
"close -up" as in most bird song records. Natural
balance! This is what I call enlightened recording technique.
it-
°''Chopin:
Princess
Levine.
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Sylphides. Tchaikowsky:
Aurora. Ballet Theatre Orch.,
Capitol P 8193
Les
A lot to be learned from this disc as to what
sound. Same recording, we assume,
makes hi -fi
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APRIL, 1953
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53
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Debussy: Petite Suite. Ravel: Le Tombeau
de Couperin. NBC Symphony, Reiner.
RCA Victor LM 1724
RCA's "new orthophonie sound surely makes
up for certain oft- mentioned deficiencies of the
dim, distant past (a few years ago) -there were
never such clean, sharp highs as these, and no
tonal "ceiling "; I came close to putting a small
"b" beside this item, too--"heavy bass; use
300 -cps turnover " -believe it or not. The days
of thin bass seem over, as well.
The Midsummer Night recording omits the
lovely choral parts, seems to me a lot less melodious and fresh than the sturdy Fricsay LP
from Decca (DL 8516) though this one probably
has better quality. (If you don't like these two,
you have no less than ten LP versions of some
or all of this music to choose from. Don't ask
only got one lifenee to
compare them
time .
!) The Wedding March, however, is
tremendous. Fast, loud and brassy, with all the
interludes.
The French music is acoustically more on the
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small- studio side, which is quite correct. Again,
not as warm as the old Mitropoulos version, from
discs, of the Ravel (Col. ML 2032) and Urania
has a nice Petite Suite. Neither one of those
ha, the new orthophonie sound, alas.
Volume Controls
Rheostats
today!
Strauss: Le Bourgeois Gentilhomme 4Der
Biiger als Edelmann). Vienna PhilharLondon U. 684
monic, Krauss.
This really delightful bit of period music, semiorchestra
of soloists) with
style
(small
chamber
a fine whiff of the 17th century, of Moliere's
rewritten
by Strauss
musicplay and Lully's
so
r r
"=
w
4e
¡r
-
performance here but
supposed reputation for humor
this strikes me as not as rich
the Straussian satire as that
Columbia LP,
the earlier
I think comes from disc orig-
is given a good Viennese
in spite of Krause
(see album notes)
an exploitation of
on
by Reiner
(ML -2062) which
inals.
in
RADIO'S MASTEN
POTENTIOMETER and VOLUME CON -
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TROL
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are
l
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45 EXTENDED PLAY
OG,IMOTIE
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Summary of
Whether you buy, sell, or specify, you will find this
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Contents
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Control
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RADIO'S
MASTER.
The 45 longish -play disc discussed in these
columns not só far back has been spreading
rapidly. Most of that spread has been in the
expected and conventional semi-pops and light
collection area -witness in particular RCA's own
Extended -Play catalogue. I'm not the one to
quarrel wth the economics of this. 45 probably
scoops in the cash in this form and, I'll admit.
it is bringing some astonishing sounds to the
nation's juke boxes -enough to stop any longhair musician in the midst of his dog -wagon cup.
of coffee. (Von can get a whole Beethoven sonata
in the original--not jazzed -for two nickels!)
But, semi -pops or no, fact remains that 45 -ext.
opens up an attractive area in the so- called classical field. Urania seems to be the most alert,
right now, to this interesting opportunity and
the Urania 45 series, nicely packaged with full
album notes, is an intelligent culling from the
existing catalogue, removing one -sided LP works
to independent existence, excerpting salient items
from longer pieces, etc.
In common with other Uranias, a lot of these
are of so -so quality (they come, I bear, from
earlier German radio tapes) with considerable
distortion in the louder parts. Here are the better
ones from the first list. All are worth a try
De
Falla; Three -Cornered
Hat Dance.
45 UREP
AUDIO ENGINEERING
629, Mineola, N. Y.
Please send me, without cost or obligation, the VOLUME CONTROL and ATTENUATOR Booklet reprinted from Radio's
Master.
P. O. BOX
Name
Address
City
54
Contradictum -after my objections to Reiner's
Mendelssohn, above? Not quite. Mendelssohn
and Strauss are worlds apart; Strauss was a
rapier composer, sharp, brilliant; Reiner is a
conductor to match. Mendelssohn needs a sweeter,
warmer treatment -Fricsay's.
An excellent disc from the standpoint of quality, which is good enough reason for considering
AUDIO ENGINEERING
www.americanradiohistory.com
11
Strauss:Wiener Blut: Overture, Waltz and
Duet.
45 UREP
5
Wagner: Tannhauser; Elizabeth's Greeting, Evening Star.
45 UREP 13
Prokofieff: Love for Three Oranges Suite.
45 UREP 7
Berlioz: Roman Carnival Overture.
45 UREP 9
Beethoven: Piano Music (Polonaise, Vars.
on Turkish March,) Steurer.
45 UREP 15
APRIL, 1953
1
f
ODDIANA
Early Italian Music. Leopold Stokowsky &
His Symphony Orchestra, Brass Choir,
-
Chorus.
RCA Victor LM 1721
"Freely transcribed by Leopold Stokowsky"
how that takes us back to the pre -war days of
Bach-Stokowsky and the rest of those hyphenated
horrors! Not that Stoky didn't spread a taste
for the old masters, and it must be admitted
that he represented, in a backyards sort of way,
a budding interest in "our great musical heritage"
on the part of the larger musical audience.
In reasserting, here, his old self as classical
popularizer, Stoky mainly shows us how tastes
have changed
bit. Same old pompous, heavy.
weight ultra -slow style of playing, with the well remembered swellings and dyings -away, calculated
to flutter the naive musical heart. (Evidently, in
his mind, nobody played anything fast until
Alter Bach.) But here we have new appeal
instead of the old -time full symphony orchestra
we have chorus, organ, brass, approximating
more nearly the original forces. A big concession
to our recent feeling that music ought to be heard
as intended, un- doctored. Well
only a little
doctored.
Best item (and only one I can listen to without getting the creeps) is the Gabrieli "In
Ecclesiis ", with large organ, mixed chorus, boys'
chorus, brass choirs. -Stoky gets over the feelhug of ultra-magnificence of sound that undeniably was intended in this display music for St.
Mark's cathedral in Venice.
-a
-
...
Colosseum justice, it is an excellent recording.
The answer, aside from more competent performers, is I'd say in that this is a radio performance, not a public concert. Audience or no,
a performance set up primarily for radio runs
a lot better chance of becoming a good record
than a public concert.
Cavalli, another 17th century Italian ex-
perimenter, writes a really dramatic oratorio, with
all the elements that went later into the great
Handel works and the like. A serious lack here
there is no text and we are in the dark as to
what's happening. An excellent performance, with
good singers, chorus, solos, plenty of life and a
minimum of fancy affectation. The music, under
these circumstances, tells its own story most
effectively.
-
Sorry, Wrong Number. by Lucille Fletcher,
Agnes Moorehead, supporting cast.
Decca DL 6022
A concentrated bit of horror for you if you
world's largest
selections of Professional
and Home Quality
Audio Components
-
Pussonally, I'd
call it pretty far- fetched and definitely morbid
don't let the kids get it. But this was a famous
radio thriller and with reason. Lady, in bed with
her telephone, gets a knife in her, after two LP
sides of hysterics.
feel inclined to witness murder.
From Barrelhouse to Bob. Piano stylings
by John Mehegan, with narration. C.
Mingus, bassist.
Perspective PR
1
J3 Scarlatti (A.) ; Cantata "Sulle Sponde del
Tebro". Mozart: Marcia #2; Recitativo
and Rondo "Mia Speranza ", K. 416.
Teresa Stich -Randall, Scarlatti Orch. of
Naples, Baumgartner.
Colosseum CLPS 1035
-
Here's another approach to the old music
The Italians have their own
peculiar way of "modernizing" as far as I can
see, which involves instead of the slow- as -molasses treatment, a kind of breathless exaggeration, with much gusty sighing and carrying -on,
at the proper tempi more or less; the instruments
are often technically correct for the music, as
here in the Scarlatti, but the perforniance is
something else again.
This album is labelled LIVE MUSIC- a
new twist on the old practice of taking down
a public concert for issue
on records! It reflects, I think, the unfortunate aspects of that
easy practice. Not only subdued coughs, which
arc unimportant. More significant is the division
of interest which brings us in America a soprano
who may have had local interest for the Italian
audience but is not at all suited to the music,
either Scarlatti or Mozart -the latter being
wholly beyond her vocal powers. Moreover, she
is the type who suddenly sings very loud, then
as suddenly dies away; concert conditions made
an impossible situation for the recording engineer, who took what came his way: result is
poor balance, much sudden blasting, acute aural
indigestion for the record listener.
And yet -these are worthwhile pieces, decidedly. The Mozart is a stunning Italian -style
aria of great virtuosity, the Scarlatti, by the
early pioneer of opera- oratorio in the 17th cen.
tury, is an equally fine work, dulled by the
singer's gusty vocal treatment, in spite of good
typically Italian.
instrumental playing.
We've had enough
of this
Cavalli: 11 Guidizio Universale ( "Universal Justice "). Chorus, soloists, orch. of
"Societa del Quartetto".
Colosseum CLPS 1032
This, a Vatican Radio production, h also
labelled LIVE PERFORMANCE-but, to do
AUDIO ENGINEERING
-I
it-
Schubert: Quartettsatz (movement from
a quartet) in C minor. Wolf. Italian Serenade. Koeckert Quartet.
Decca DL 4044
This is as strikingly fine playing of Schubert
you'll likely bear-and the piece is an unforgettable one, full of Schubert melody and that
strange eerie tension, midnight witchery, that
was so much in style at the time, early 19th
century. An ideal quartet sound, too -full, rich,
not too sharp yet plenty clear. The Wolf work is
good too, though not up to the Schubert. If
you want just one sample of quartet playing, try
this, by all means.
as
Music of the Arab People. Toraria Orch.
of Tangiers.
Esoteric ES 2002
Another of Jerry Newman's peripatetic rewith Telefunken and Ampex 401 -A.
Authentic enough, this -the Arab version of
cordings,
local cafe music, sung in odd Eastern ways and
played on traditional instruments. A Western
"beat ", steady and pounding, but otherwise
very Eastern. The relationship of this to Spanish
gypsy music is clear enough to any ear. Super
hi -fi, but take it in small doses!
get and use
the 236 -page
buying guide
complete music systems
all famous -make amplifiers
speakers & enclosures unlimited
widest selection of tuners
all phono components
tope and disc recorders
tantalizing half -
baked music on LP. Let's stick to more careful
work, with the recording as the primary consideration, not a mere incidental.
The old truth remains, in spite of LP -the
recorded listening medium is unlike that of the
live concert, and it is basically unsuited to the
preserving of publicly heard music in concert
form. The psychological difference between once only, on-the -spot listening and listening via rec.
ords (with repeats ad infinitum) is permanently
immense. A good recorded concert is a freak of
luck, and every performing musician knows it.
Better not to tempt fate, for a little cash saving.
s
This young gent tells about the big men of
ragtime, blues, etc. while strumming soft piano,
then plays in their style, one by one. A bit
confoosin'
thought at first these were historical recordings. He does 'em all himself.
Improvisations, "after" the original. He writes
a good script, but he can't read
sounds like
junior high school stuff. Diction lessons -or
somebody else's voice-is the answer. An interesting use of the LP medium.
A Tribute to Lotte Lehman (Songs of
Schubert, Mozart,
Brahms,
Schumann,
or
Franz,
with piano).
RCA Victor LCT
1
108
No amount of hi-fi could Lace made Lotte
Lehmann more intelligible than she is, in her
own way, in these wonderful reissues of 78's
from 1935 to 1940. Lehmann flatted plenty of
notes and she wobbled on more. Outwardly, her
middle -aged voice was nothing much. But
you can break through the language barrier, so
to speak, get the sense of the tunes, the harmony,
the words, you may discover for yourself why
this lady has been one of the greatest conveyers
of musical emotion in our time. Nobody else
can touch her, especially in the Schubert.
Play this disc with flat highs-no roll -off at
all; otherwise they'll sound strictly sofa- pillow.
The originals were probably flat in the high end
and for some reason RCA has got them onto LP
everything in microphones
IF IT'S ANYTHING
IN AUDIO, IT'S
IN STOCK AT
ALLIED
-if
ALLIED RADIO
833 W. Jod,son
B
vd.. Dept.
17 -D -3,
Chicago 7,111.
disc in the same way.
APRIL, 1953
www.americanradiohistory.com
55
NEW PRODUCTS
Step -Type Proqueney Oscillator. Choice
of seventeen fixed frequencies is obtainable at the turn of a single knob with the
new oscillator manufactured by Pulse
Techniques, Inc., 1411 Palisade Ave., West
Englewood, N. J. Although it weighs only
7 lbs., the instrument offers a standard of
accuracy, stability, and low distortion
which is well within accepted require-
meats for lan"ratory and lirdu.l ion line
and
testing of amplifiers, filters, recorders,
similar devices. Portability makes it ideal
for field maintenance and testing. A unique gain -stabilizing circuit holds amplitude variation within 0.2 db over the entire frequency range. Use of toroidal coils
assures frequency stability well within
1 per cent. Signal -to -hum ratio of 60 db
prevails at all output levels, and known
resistive output impedance is provided
through use of a "T" -pad attenuator. Distortion is less than 0.7 per cent. Frequencies provided on standard model cover the
audio range, although other frequencies
are available and any 17 will be provided
on request.
Recording Head Demagnetizer. Excessive noise level in tape recordings caused
by accumulation of permanent magnetism
in the recording heads can be prevented
through use of an a.c. magnet assembly
now available from Audio Devices, Inc.,
Sound System Control Consolette. Complete control of an extensive sound system
is afforded by the new RCA Type MI14937 control consolette. Designed for use
in schools, hospitals, hotels, and industrial
plants, the unit is designed to provide recorded programs, radio programs, or live
material of local origin to selected areas
or to all areas reached by the sound sys-
Attenuation Network. A direct -reading
precision attenuation network designed for
operation over the 0- to -1 -mc range, the
new Daven Type 790 is particularly useful
in gain and loss measurements on filters,
transformers, and amplifiers. Non- inductively wound, the 790 is mounted in series
on an alumilited panel and housed in an
attractive metal case. Each decade dial
-
10 steps of attentuation. Each
iprovides
ndividual decade is shielded in a brass
housing, and all decades are grounded to
the front panel. Among the 790's outstanding features are: extreme accuracy over a
range extending into the low r -f spectrum; wide range of attenuation in small
db steps; stops and detents are positive
tern with which it is used. Up to 20 rooms
or areas are served by the consolette in
its standard forni, but it can be expanded
to handle up to 60 circuits if required.
Provision is made for adaptation of the
program channel for intercom use when
desired. The consolette may be mounted
on a standard desk or table, or on any of
several RCA cabinet bases to form a com-
plete program control center. Full information will be supplied by Engineering
Products Department of the RCA Victor
Division, Radio Corporation of America,
Camden, N. .1.
and prevent over -travel. Both balanced
"H" and "T" networks are available, as
are networks for various impedance requirements. Full technical information
may be obtained by writing direct to The
Daven Company, Dept. AT, 191 Central
Ave., Newark 4, N. J.
Mixer-Preamplifier. The new Masco
Type EMM -6 mixer greatly expands the
usefulness of tape recorders and other
single -input devices, by permitting the
simultaneous use of up to four microphones, plus radio tuner and phonograph.
Matched Hi-Pi Radio -Phono System.
Tuner, three -speed record changer, amplifier, speaker, and magnetic cartridge are
all included in the new packaged home
music system recently announced by
Meissner, Mt. Carmel, Ill. All units are
matched in attractive gold -finish styling.
In addition to major components, the
system is supplied' complete with all
t711111111
The amplification provided on all six inputs, of which four are mixing channels,
plus a cathode -follower output, allows
placement of the unit up to 400 feet from
the amplifier or recorder it is feeding. Output is 1.0 volt r.m.s. Harmonic distortion
is less than 0.75 per cent. Response is 50
to 15,000 cps ±'l db. Three 12AX7 tubes
are used, plus selenium rectifier. Mark
Simpson Mfg. Co., 32 -28 49th St., Long
Island City 3, N. Y.
Magnetic Record -Reproduce Heads. Improved uniformity, wider frequency response, and extended life are features of
a new line of magnetic heads now being
produced by Stancil- Hoffman Corporation,
921 Highland Ave., Hollywood 38, Calif.
York 22, N. Y.
Madison Ave., New
Designed to remove any residual magnetism from recording heads of tape recorders, the Demagnetizer has extended pole
pieces to fit the contours of all heads
currently available. Use of the device requires only a few seconds. It is supplied
complete with cord and plug for connection to standard a.c. outlet. Since high
noise level may be caused by factors
other than residual head magnetism, the
unit is sold with the provision that it can
be returned for credit if results are not
444
satisfactory.
Tiny Mercury Batteries. Rapidly expanding use f junction -type transistors
in hearing aids and other miniature electronic equipment has resulted in the introduction of a new line of low -voltage,
miniaturized mercury cells and batteries
by P. R. Mallory & Co. Inc., Battery
Division, North Tarrytown, N. Y. Known
respectively as "Energy Capsules" and
Power -Pak batteries, the new units are designed to meet the specific requirements
and characteristics of transistor operation,
including increased energy per unit volume, long service life, constant discharge
characteristics, and extended shelf life.
Batteries are coated with a "shrink -on"
plastic to provide a tight, leakproof seal
between cells. They maintain a substantially constant voltage and current
output level over wide temperature ranges
at drains ranging from 10 microamperes
to 10 ma.
56
mounting hardware, matched knobs and
escutcheons, shock mounts, and cabling,
plugs and jacks for interconnection.
Changer is equipped with muting switch
for silencing the system during changing
cycle. Tuner features high -gain front end,
with frequency response fiat within -!- 2
db from 50 to 15,000 cps. Ten -watt amplifier has separate bass and treble controls
providing both boost and attenuation.
Amplifier frequency response is fiat within
± I db from 20 to 20,000 cps. Speaker is
rated at 20 watts and uses two coaxiallymounted cones driven by a single voice
coil. The new system will be merchandised
through radio parts distributors. A
brochure, describing the system in detail,
is available from the manufacturer.
The new heads have the same
appearance as the Model TD -704, t "rnierly
AUDIO ENGINEERING
www.americanradiohistory.com
APRIL, 1953
1
1
manufactured by Indiana Steel Products
Company. Stancil- Hoffman has taken over
all of this company's magnetic head activity. The excellent qualities of the new
heads result from improved production
procedures which have been originated by
Stancil- Hoffman. Standard heads record a
track 0.2 in. wide. Full technical particulars will be supplied on written request.
Smallest Transformer. Designed primarily for use with transistors, a new line
of iron -core ultra- miniature transformers
recently introduced by Standard Transformer Corporation, 3580 Elston Ave.,
Chicago 18, Ill., are described as the
Hear It BETTER Now
PEDERSON PRT -1
PREAMP TONE CONTROL
$99.50 net
A precision built all- triode equalizer
PRT -1 is ideal for use with any power
preamp, the
amplifier. All
equalization and tone controls are of the preferred
step type. Low distortion and wide band operation are
made possible through an entirely new circuitry utilizing a cathode coupled, grounded
grid dual triodes in each isolated tone control stage. Treble control: 10 positions; Bass
control: 11 positions; Low frequency phono equalizer: 6 crossover positions; High fre6X4; Size: 151/2" x 91,4" x
quency equalizer: 5 roll off positions; Tubes: 5 12AXT's,
534 "; Weight: 13 lbs. Cabinet in blond or mahogany, $12 net.
1
PEDERSON W -15
WILLIAMSON AMPLIFIER
$129.00 net
Featuring a new high in performance, the W -15 gives
you the exact crcuitry laid down by Williamson PLUS
every laboratory technique developed in the Pederson
Laboratories. Power output: 15 watts; Frequency response: X0.1 db, 10 cps to 35 KC; ±2 db, 5 cps to 150 KC; Hum & noise level: 90 db
below; Sensitivity: 1.5 volts; Power consumption: 105 -125 volts, 60 cps, 130 watts;
Tubes: one 6J5, two 6SN7GT, two KT66, one 5V4G. All coupling condensers are oil
impregnated, plastic cased, molded paper type. All transformers are specially built to
specifications by Triad. Size 13 -7 8" x 7'2" x 734 "; Weight: 33 lbs.
world's smallest of their type. Weighing
less than one -tenth of an ounce, the new
Stancor units measure as little as 14 x
% x % in. and are no larger than the
transistors they are designed to power.
While they are intended essentially for
transistor audio applications, they can be
used wherever low power is involved. Useful below 1 mw power level, they are
wound on molded nylon bobbins, with
special nickel alloy steel laminations.
Various types are available for input, interstage, and output or matching applica-
GARRARD RC -80
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$41.45 net
The world- famous Garrard has been acclaimed by music
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including switch -off at end of last record.
Complete with automatic 45 RPM spindle and 2 empty cartridge shells.
...
tions.
LETTERS
BOZAK B -199
WOOFER
$38.72 net
(Continued from page 10)
"Now," I mumbled, looking over my amplifier controls built on the pattern of a
B -29 control panel, "what compensation do
I use for this ?" Something induced me to
read the back of the record case, and there
it all was: the family trees of everyone
concerned with the recording, a plain statement-in English-that it took the AES
curve, everything excepting barometric
pressure and temperature at the time.
Wouldn't it be marvelous if every recording company could be induced to publish this information on the sheath-or even
better, on the record? There are so many
companies recording, and many of the records are from abroad.
Pouring the first signal into a new amplifier with a pair of 3C33's in push-pullparallel (country home, no doubt. ED.)
and getting a sine wave that looks like a
Japanese pagoda struck by lightning is a
blow from which one can recover, with
patience. Having a record with an unknown
compensation curve is definitely not a joy
forever. I hope we can enlist ETC in such
a campaign, for he impresses one as a person who won't believe things even after
he has proved them.
You don't have to be nuts to be a 101 per
cent audiomaniac, but it helps immensely.
Offering
a new sense of orchestral fullness, the B -199
gives you true pitch and unmuffled tone. Output: 12
watts, peaks to 18; Impedance: 8 ohms; Frequency response: 40 -4500 cps; size: 1234" x 5 -7 8 "; Weight: 8 lbs.
BOZAK B -200X
DUAL TWEETERS
$22.72 net
Here is listening pleasure entirely free of the
usual shrill tones. A unique system of rubber damping gives you an amazing degree
of smoothness. Power output: 5 -8 watts;
Frequency response: 1500-13,000 cps; Impedance: 16 ohms: Weight: 4 lbs.
Write for Free Hi Fidelity Booklet, Music of the Masters
_
b//I
DWIGHT B. JONES
Night Managing Editor,
The Pioneer Press,
St. Paul, Minnesota.
AUDIO ENGINEERING
69 CORTLANDT
ST.,
NEW YORK 7, N.
cti4 /r%/tt
>Q
Y.
Dept. A 43
CORTLANDT 7 -0315
The House Built on Service
APRIL, 1953
www.americanradiohistory.com
57
.
R
µjWC
FEEDBACK
New Portable
(from page 23)
Battery -Operated
Spring -Motor
Tape Recorder
z
`4 --µrv+Z
1
- \µ +-2A
A
+i1wL- C) ,il
R
RC
``
- C -
gm
gm
Q
-
This is the circuit requirement for oscillation.
-
Z
Ev = -µEt
rp +Z
P
+L
1
1Z/
which is simply applying the normal
tube and circuit parameters to the Bark hausen criterion. In this particular case
-
Ca
0-0
I,
I1
--,ssa2--Er
-II
-ypT
Ir
e
co.
Eft, =EP
Fig. 5. A simple, tuned -grid, tuned -plate
jwMIt.
- jw31
Ep-- (R+jwL) /,. -R +jwL
Ea
ß
Also.
Similar analysis may be performed for
any configuration. One other is here
given as illustrated in Fig. 5. This becomes at once evident as a tuned-grid,
tuned -plate oscillator.
+jwL)(1 /jwC)
Z =(R
R+
j (o.)1,
Now substitute ß and Z into the Bark hausen criterion:
For all field recording without AC power!
Smaller and lighter than a portable typewriter, the Magnemite° actually makes
field recordings that can be played on any
studio console equipment. Completely
self- powered, the Magnemite" does away
with bulky and cumbersome generators,
Z,=1(WLP-wCP)
wL+wC)j
R+1
Z' -
F
R
+
jwL
µ
+g"'
(R`+ jwL) .1
IaC
jWM-R+jwL+ R+ ( WLµ
storage batteries and rechargers.
Just check these unusual features:
1
Noiseless and vibrationless governorcontrolled spring -motor assures constant
µ
+
1
j wLp+wLP-1w
1
y(
1\WLp-ruCv)
g
tape speed.
j
wC
-WC)
Completing the general Barkhausen criterion, we have:
1
jrWLv\
WCv)
Cv+Cv+Cfrv)
((
w
\WLv
um..
Zs= )1(0)14v
gn,(1/jwC)
µ
os-
cillator.
1(WLv-W
Cv+Can)
-
Cv+CaP)
100 operating hours per set of inexpensive
flashlight-type dry cell batteries.
Earphone monitoring while recording, and
earphone playback for immediate quality
1
j (WLP+wLP-(»Co)
1
-gl't
I
check.
toLp_
`\
Operates in any position, and is unaffected
by movement or vibration during operation.
1)
WCr'
a choice of 5 different models for
any recording need. High fidelity units,
meeting primary and secondary NARTB
standards, which record and play back
frequencies up to 15,000 cycles, are available for broadcast stations, critical music
lovers, and scientific research. For investigation, missionaries, reporters, and general
dictation while traveling, there are units
which play up to 2 hours per reel of tape
1
1
1
CP+Cgp )
Q
1
WLP-W
CP+CPP
Co= CP+Cv+COP
and:
Requires no more desk space than a letterhead, measuring only 11 x 81/2 x 51/2 inches.
There's
\
1
WLP-W
- WCP
where
Warning indicator tells when to rewind,
and shows when amplifier is on.
Broadcast models weigh 15 pounds. Slow speed models weigh only 10 pounds.
I
WLp
1
1
WLg
1
1
(.4
CD+CDP
g' j
WLp+Lg-WCo
wLP+WCP
=0
WCv
WLP
-'-.
Write to Dept. A today for complete descriptive
tiferature and dint fa eon p"i..
AMPLIFIER CORP.
of AMERICA
Re
R.
©
M
L.
Er
Es
r,
A
398 Broadway, N. Y. 13, N. Y.
/rade
58
Mark Reg
Fig. 4.
IAI A simple feedback amplifier,
and
tB), its equivalent.
AUDIO ENGINEERING
www.americanradiohistory.com
APRIL, 1953
i
The generalized criterion used above
depends on the assumption of circuit
linearity and inductances of zero resistance for simplicity. It can be shown
7
that
1
Z,+Zs +Zs
+9,n Z,(Z. +Zs)
Zs
1
Zs +Zs
SELECTS
_0
DIACOUSTIC DEPENDABLE
DIAMONDS*
is required for oscillation.
for
HOUSE OF COMMONS
R.
nical features which are considered of
unique interest.
The system contains 23 microphones,
all being of the single-element unidirectional type. Each has its own preamplifier. Three spare preamps are provided
as standbys. Both inputs and outputs
can be connected as desired by remote
control, the outputs being fed to relays
which are interlocked with the speaker
muting circuits. The same relays also
operate indicator lamps, showing the
state of the equipment at any time.
Output of the selected preamplifier is
fed to a buffer amplifier through the
main control panel. The buffer incorporates frequency correction circuits, and
also acts as a driver for the power
amplifiers.
Output of the power amplifiers is connected to 19 speaker groups comprising
a total of 550 speakers. The speakers
are fed through the muting panel which
provides level adjustments for the various groups, dependant upon the microphone in use. Also included in the output circuit are volume indicators showing power being delivered to the loudspeakers.
Full monitoring facilities are provided at the control panel, while the
main equipment room contains, in addition, a comprehensive test unit permitting all aspects of the system's performance to be checked without interrupting operation.
Individual level controls are provided
for each microphone in addition to a
conventional master volume control.
Although the entire system was designed with superb audio performance
as its chief objective, primary consideration was also accorded the need for
esthetic value in appearance, and the
fact that it must not interfere in any
manner with normal parliamentary procedure.
How effectively these objectives have
been achieved is well proved by the
large number of engineers, sound technicians, and architects who have inspected the installation with the thought
that it may influence their own future
activities.
AUDIO ENGINEERING
Sozotee
elagaiddecer
C.A. - G. E. and other Reproducers
Standard or Microgroove
Díacoustíc Revolving Resharpen Service for
Sapphire§
Cutting Stylíí
Custom Made and Guaranteed UnJer Capps Patents
Literature and Prices on Request
Viacoadtic
4a6rcatonv
Since 1928
P.
0. Box "P"
Phone STate 4 -0881
Encino, California
'Genuine
cSynthetw
WHITE SOUND
WITH
THE
Ng& "RovourmteditAINitm
...
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WHITE SOUND AMPLIFIERS
White Sound's new circuit has established a
New High in the realistic reproduction of
music. The finest electronic components, precision engineering and White's new design
combine to give you Ultra High Fidelity.
Cross -Coupled Amplifier Circuitry
Balanced Drive Tapped Screen Output
Balanced Impedence Phase Inverter
1020
Model
- --
Ultra High Fidelity
E:e(isaeoef Non -resonant
Cross -Over Circuit
at the Input of
Cross -Over (24db./ Octave)
Dual Channel Amplifier.
Model 1010, 10 wa_s. Model
Model 2010, Dual Channel
the Model C -101, Cross -Over
1020, 20 watts
Amplifier with
Network.
WHITE CABINET SPEAKERS
A True Exponential Horn (within 1%c)...
Coupled to Speaker through a New Unique
Nine foot
Phasing Device and Sound Trap
Horn compactly Curled into Non -Resonant
Response: 15- 18,000 cps
Cabinet
White Cabinet Speakers offered in 4 Sizes
Model 3122
15- 18,000 cps.
.,.3 Finishes...5
Prices.
For Complete Information, see your Distributor
or Write to Department H -3
105 W. MADISON ST.
w HI
I
T
APRIL, 1953
..
www.americanradiohistory.com
SOUND,
INC. CHICAGO
2,
ILLINOIS
59
Plug -in Broadcast
VOLUME CONTROLS
(from page 40)
PROGRAM /MONITOR
AMPLIFIER
3 -db drop at 1000 kc without the volume
control, there would actually be a drop
of 3 db at about 4000 cps at this position
of the volume control.
We find, consequently, that the resistance of the volume control is rather
stringently limited by the capacitance
into which it must work. As an example,
suppose we had a 12AY7 stage with an
output resistance of 20,000 ohms working into a 6SL7GT with an input capacitance of 100 µµf. At best, there will
be a drop of 3 db at 80 kc. Suppose further that we cannot tolerate a drop of
more than 3 db at 50 kc in this particular stage. Then the maximum output resistance at any position of the control
must be 32,000 ohms. To find the maximum permissible volume control resistance we use Eq. (4) with 20,000
ohms for Rs, 32,000 for Rom, and solving
for R, we obtain R, = 108,000 ohms, and
a 100,000 -ohm control would be .used.
Suppose we are more exacting and
state that the high -frequency response
with the volume control must never be
any poorer than without it. This is the
same as saying that Rom in Eq. (4) must
be the same as R.:
DESIGN -simplifies maintenance.
VERSATILE -Fulfills all medium and high -level
PLUG -IN
audio
system requirements. Up to 8-watt output when used as
a Monitor Amplifier.
EXCELLENT FREQUENCY RESPONSE- Features low distortion and noise level.
COMPACT...YET HIGHLY ACCESSIBLE.
The G -E Plug -in Broadcast Audio line includes:
BA -1 -F
BA -12 -C
BP -10 -B
PRE -AMP
PGM /MON AMP
POWER SUPPLY
For information write: General Electric Company.
Section -14.13. Electronics Park, S-: ron,se. New Pork
R, + R.
4
)ELECTRIC
GENERAL
BRITAIN'S
FINEST
LOUDSPEAKERS
WHARFEDALE
SUPER 12 CS /AL
single extended range
speaker that outperforms
many multi-speaker
combinations!
A
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voice coil
...extended
range without
"peaking"
Cloth
suspension
complete range of speakers
reduced
is available for every
resonance
application ... all built by
improved
Wharfedale Wireless Works
transients
under the personal
direction of
Bakelized
G. A. Briggs,
cone apex
. amazingly
world- renowned
clear "highs"
audio engineer
Costs only
;61.95 net
Send your name
for free fact sheet
telling why it will perform so well in your home.
NON-TECHNICAL
SIMPLE LANGUAGE
Ampl fiers $2.95
Practical
Informative
Only books of their kind
written expressly for the
layman. Simple, easy-tounderstand
language.
Many illustrations and
diagrams. At your jobber
or send check or money
order.
Speakers- Baffles
Acoustics -- Frequency
response, etc.
60
(5)
To realize this performance in the case
just described we should have to utilize
a 60,000-ohm control. That these values
are much lower than those commonly in
use will readily be recognized.
The installation of a volume control
thus appears to be somewhat more involved than simply inserting a 1 -meg.
potentiometer at the amplifier input. In
particular, the use of relatively low
values is indicated in cases where the
control is working into appreciable capacitance.
...
A
loudspeakers
- Ra
Ri= 312,
Amplifiers
Phasa Splitters -Push
Pull- Negative Feedback
--Tore Compensation
Circtits, etc.
-
Piano, Pian !Is, Sonic&
Touch and acne -Tuning
-Toning- Ot.il
of sounds,
e C.
ograms
Dept. AE 4
BRITISH INDUSTRIES CORP.,
164 Duane St., N,Y.13, N. Y.
THREE CHANNEL
(from page 28)
quency channels. Its output feeds a lowpass R -C filter network in the grid circuit of Vas, and a high -pass filter in the
grid circuit of V,a. The multiple sections
of these filters produce the desired steep
attenuation slope. Potentiometer R. controls the level of the low- frequency signals fed to V,a, the low- frequency amplifier channel. Likewise, R,. is the high boost control feeding the high- frequency
amplifier, V,a. The plates of the three
tube sections are tied together and are
fed from a common plate resistor,
thereby mixing and adding the signals
from the three channels. Capacitor C.
serves to couple the resulting output signal to the master gain control of the
following audio amplifier.
AUDIO ENGINEERING
www.americanradiohistory.com
APRIL, 1953
1
".I
,D
:35
z5.
III
1
IUI
Fig.
I
Ilk,
I
1
to
;1
/-'
Response
4.
curves obtained with
three -channel tone
II
Rd
-
control
Figs.
PIS!!!!
amplifier
2
and
of
3.
700,7
Ito,
FREQUENCY IN CYCLES PER SECOND
A question might be raised regarding
the problem of the additional phase shift
of 180 deg. in the high- and low -frequency channels, since they both have
one more stage of amplification than the
center channel. It is conceivable that
a condition could arise wherein the low and high- frequency components of the
broad band passed by Vu would cancel
the signals of the other two channels.
This does not occur, however, because
of the additional compensating phase
shift introduced by the low- and highpass R -C filters.
The response curves of Fig. 4 illus-
trate the measured results obtained from
various settings of the low- and high boost controls. Boosts ranging from 6
db to 24 db at the 20- and 20,000 -cps.
spectrum extremes are shown. Note that
practically no increase occurs in the
middle-frequency range between 200 and
1000 cps, even at maximum settings.
Construction of the tone control amplifier is not difficult. It may be incorporated directly into an existing or proposed amplifier, or else built up as an
accessory on a small subchassis similar
to that used for magnetic pickup preamplifiers.
The author has used variations of this
type of tone control for over ten years,
and the results have been very satisfactory. Although it will not work miracles for a poor audio system, the degree
of depth and crispness imparted to music
and speech is remarkable.
PARTS LIST
0.1 µf, 400 v.
Cs
0.25 µf, 400 v. paper
20 -20 µf, 450 v. electrolytic
.05 pf, 400 v. paper
.02 µf, 400 v. paper
500 µµf, 500 v. mica
200 µµf, 500 v. mica
100 µµf, 500 v. mica
470 ohms, Y. watt
47,000 ohms, 1 watt
47,000 ohms, % watt
0.1 meg, % watt
0.22 meg, % watt
0.5-meg potentiometer, audio
Ca, C.
Ce
C,
Ci
CIO
Cu
R,
R.
R,, Ru
R., Rn
Re
Re
R.,
R.
AUDIO ENGINEERING
You can't listen to a radio tuner on
a magazine page. But one glance at
the charts above will tell your audiophile eye- here's high -fidelity!
You're looking at the visual delineation of frequency characteristics of
Stromberg- Carlson's newest equipment. If a sensitive electronic instrument recDrds such wide-range fidelity,
imagine how pleasant it will sound
to your ear!
taper
Rr, R,,,
R.
R. 2200
R,o
R.
V,, V.
AUXILIARY MIXER for TV
The control room and announce booth
microphones, turntable, cue, remote line,
network, and film inputs are handled in
the usual manner.
This is only one of many possible arrangements, but it shows the flexibility
of the auxiliary mixer. The microphone
inputs can also be divided between two
studios which may be used simultaneously-one for program, the other for
audition purposes.
The BCM-1A auxiliary mixer should
be installed adjacent to and to the left
of the consolette. Both units are identical in cross -section and similar in
styling. The auxiliary mixer is 16g in.
in length, and the combined length of
the two units is only 49g inches. All
controls are therefore within convenient
reach. The front panel of the auxiliary
mixer is hinged and tilts forward as
paper
C1, Cr, Cs
ohms, % watt
22,000 ohms, 1 watt
meg,
Y. watt
0.33
0.18 meg, % watt
0.25 -meg potentiometer, audio
taper
12AT7 dual triodes
from page 27)
You can hear for yourself by asking
shown in Fig. 3 to provide access to
your dealer for a demonstration of the
the attenuators and switches for inspection, cleaning and service. The sloping
top cover is removable to expose the
tubes and tube test jacks. The amplifier wiring becomes accessible by rais"CUSTOM FOUR HUNDRED"
ing the pivoted amplifier mounting
SR -401 AM -FM TUNER
frame. Power for operating the speaker
one of the component parts of the
muting and warning light relays is sup"Custom Four Hundred" high plied through the consolette. Only an
fidelity series which carries the
external plate and heater supply is rerecommendation of Leopold
quired for the operation of the auxiliary
Stokowski.
mixer.
t dealer or
For the name of your
for more complete technical data. write
The BCM -1A auxiliary mixer is another example of the building -block type
of broadcast equipment which may be
STROMBE RG- CARLSON
placed in operation at the initial installation or may be added later to existing
L.5mm449,4A4eAq,
equipment as the need for greater faRochester 3, N. Y.
Ave.
1219
Clifford
cilities becomes apparent.
-6/400
APRIL, 1953
www.americanradiohistory.com
61
LOUDSPEAKER DAMPING
(
,,n
fay,' .1)
The basic problem is one of separating
the movement-generated voltage from
the driving voltage so that only and at
all times will the feedback signal resemble the actual cone movement, in-phase
current feedback succeeds in doing this
part of the time only. True it serves
best during those critical periods of
hangover, but hangover is only part of
realism. It follows usually in the wake
of transients which themselves would
be much improved if motional feedback
could be put to work on a full -time job.
Fig. 2. Typical
circuit
3
employed a movement
generated
feedback
voltage.
The use of resistor
R: is optional, since
the feedback could
be applied in any of
a number of ways.
VOICE
AND
E,
L,
Source of Feedback Signal
It is not difficult to produce separate
and independent movement- generated
voltages. Every microphone does it. A
separate winding on the voice -coil former suggests itself but this is only a
partial answer for it will have some
mutual inductance with the voice -coil
that will mean voltage will be induced in
it other than that due to motion. The
apparent solution is to shield the windings from each other magnetically. This
seems a difficult problem since the pickup windings should be as close as possi-
Authoritative and
Enlightening .. .
Acknowledged the Leading Publication
in the Field of Sound Reproduction
If you are novice, hobbyist, experimenter, or engine:... if you
are a lover of music
and in pursuit of sound, undistorted
Audio Engineering will be your faithful, reliable corn panion all the way. You will find no more pleasureable and
stimulating reading than there is in AE; absorbingly interesting material, valuable and authentic data, workable detailed instructions ... all comprehensively and yet practically presented.
...
...
"What to Do" and "How to Do" will guide your every move
through this thrilling experience we call Audio.
Each new issue brings New Ideas, New Slants, and Latest Developments ... month in and month out ... twelve times a year.
BE SURE to get your copies REGULARLY.
AUDIO ENGINEERING
P. O. Box 629, Mineola, N. Y.
MAIL this
Coupon
Enclosed is áCheck
Money
oney
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$3.00 2 years .$5.00. other countries: 1 year..$4.00 2 year...$7.00.
1
L
62
100'
OUT
WHICH
AND
IS
OF
DUE
TRANSFORMER
THIS
VOLTAGE IS
PHASE
TO
THE
WITH
THAT
INDUCTIVE
EQUAL
TO
COMPONENT
COUPLING
OF
OF
L2
ble to the voice-coil from the standpoint
of minimizing time lag between driving
voltage and pick-up voltage. Such a time
lag is due, of course, to sound traveling
at a rather slow speed even through a
solid. If it were not kept at a minimum
serious phase shifts would occur at the
higher frequencies and would limit the
introduction and effectiveness of feedback. Another approach suggests itself
and this is likely the simplest solution:
use of neutralizing voltage. Feedback
windings wound over a voice -coil, or
near one end would be the same as a
transformer ; current through the voicecoil would induce a voltage in them. If
another simple transformer of special
design were used in series with the
voice -coil to allow the same voice -coil
current to produce a secondary voltage
equal to that induced in the feedback
windings it could be used to cancel the
voltage so induced. This transformer
could have a low- impedance primary
since the secondary can consist of many
turns to produce the right voltage. By
this device then, it should be possible
and feasible to use motional feedback
with all the advantages that the principle implies. Figure 2 shows a suggested circuit.
Although the author has believed for
some time now that a feedback signal
due to voice -coil movement would be
considerably better to use than any signal existing within an amplifier itself,
this positive feedback discussion has
helped to stimulate and crystallize thinking on the subject. It can be seen that
theoretically the resulting improvements
of using an independent feedback signal as described would not be limited to
improved damping. It would act to
make the voice-coil and cone follow
more exactly whatever voltage wave shape was applied, and at all times.
It is felt that much credit belongs to
Warner Clements who seems to have
stirred up this thing in the first place
and to Ulric Childs who gave him some
good arguments.
S
of Audio Engineering for
Plus. hint
Name
COIL
FEEDBACK COIL
SPECIAL NEUTRALIZING
NEUTRALIZING VOLTAGE
AUDIO ENGINEERING
www.americanradiohistory.com
APRIL, 1953
1. 1.
MI RE
MN
MOB
B1 INN
1
SOUND HANDBOOK
1
1
(from page 32 )
1
equations for the dual element
L-C network are derived from expressions which state that the impedance of
each capacitor and each inductor is equal
to the impedance of each voice coil at
crossover, multiplied by the square root
1
kit
"Just like being there"
The Clarinet, basic instrument
of the woodwind section, has
2arIC
1
1
1
fundamental response from
83 to 9000 c.p.s.; an overtone
rarge extending to 15,000 c.p.s.
of two:
1
1
a
=V2Z
24L =V2Z
The impedance of the combination is
treated as the impedance of one speaker.
When the woofer and tweeter voice
coils have different values, and the circuit of (C) in Fig. 10-14 is used, the
values of L and C associated with each
speaker must be calculated independently.
In such a case the rated input impedance of the whole network, as in the case
of the single-element network, is treated
as the average between the rated impedances of the two speakers.
Where the upper range is again divided
up between speakers the network of (D)
in Fig. 10-14 is used. This circuit is
derived from that of Fig. 10-15 (C) ; the
input leads to the latter's tweeter are
treated as the source for the new two way system of middle and high range
speakers. Using the same equations as for
the original two -way system the values
for the sub -network may be calculated
independently, on the basis of the new
crossover. The total impedance is still
the average.
The value of speaker impedance used
for all of the above calculations will
probably be fairly close to the nominal
impedance, depending on the crossover
frequency used; the value for Z at particular frequencies may be estimated, requested from the speaker manufacturer,
or measured as in Fig. 10-15. The variable resistor in this test set -up is adjusted until the voltmeter indications are
the same in both positions.
The crossover frequency is selected
on the basis of the characteristics of
each speaker. The advantages of a low
crossover frequency are that intermodulatory products between the bass signals
of probable greatest distortion, and the
higher -frequency signals are avoided,
the woofer can operate over the frequency range in which it moves rigidly,
without break -up, and the radiation pattern of higher frequencies is not restricted by the large diameter woofer.
The disadvantages are that the crossover network becomes bulkier and more
expensive, and that the responsibilities
placed upon the tweeter become much
greater. Crossover points from several
hundred to several thousand cps have
been used successfully. When the crossover point occurs at a frequency region
in which the output of one or both of
the speakers is significantly accentuated
(a common situation where the woofer
is used for low treble signals) this condition may be relieved by a suitable
shift of the roll -off of that speaker
away from the crossover point. This is
achieved simply by calculating L and
C of the affected branch on the basis
of the shifted crossover. Similarly, a
AUDIO ENGINEERING
1
1
1
1
1
1
1
To
1
faithfully capture and repro-
1
he pure, round
duce on tape
1
tones of the clarinet in its complete range requires the finest
1
Modrl 150'
recording equipment.
1
The Concertone 1501 is the only tape
Write for Bul etin 200
recorder under $1000 combining distortion -free full frequency response with all
the tape handling facilities of professional
Manufactured by
Berlant Associates
equipment.
=I
IM B1 EN MI
N
E
W
NM
ri
W
4417 M. Jefferson Blyd., Los Angeles Ig, Calif.
M M M M M
I
L
L
I
A
M
O
S
N
T
Y
P
E
qeatteax
AMPLIFIER KIT
FEATURES
Practically dislarbenless. Harmonic and inlermedulahon distal bon
belt less Ilan one hall of I B;, at 5 watts.
I dl from 10 cycles In 100 kilocycles.
Frequency response
Altec Lansing PEERLESS 9 ACROSOUND Iranslormers available.
First Wlllamson type Amp ifier suppled will matching preampifier.
When selecting an amplifier for the heart of
a
fine high
-
fidelity audio system, investigate the outstanding advantages
offered by the Heathkit Williamson type Amplifier. Here is
an amplifier that meets every high -fidelity audio requirement and makes listenin; to recorded music a thrilling new
experience through naturally clear, lifelike reproduction of
sound
at all
tonal levels
Wide acceptance
of
the Heathkit
Williamson type Amplifier by the most critical purchasers
clearly demonstrates than high-fidelity can be coupled with
low cost. For factual information regarding the Heathkit
Williamson type Amplifier. consult "CONSUMERS RESEARCH ANNUAL CUM JLATIVE BULLETIN 1952 -53."
This outstanding amplifier is offered with the optional
choice of the ACROSOUNDoutput transformer or the PEERLESS output transformer. ACROSOUND features ULTRA LINEAR circuitry, which is the exclusive development of the
Acro Products Company and provides a- greater margin of
reserve power efficiency and increases power output. PEERLESS features additional primary taps to permit the optional
choice of either the extended ower circuitry, now enjoying
current popularity. or al of the advantages of the original
Williamson type circuit.
The construction manual has been simplified to the point
where even the complet a novice can successfully construct
the amplifier without d fficulty. Write for a free catalogue
containing complete specifications and schematics of the
Heathkit Williamson tyre Amplifier.
PRICES OF VARIOJS COMBINATIONS
W.2 Amphrl Kit Incl. Main Amplifier
.,in Peerle.ÿ Outing Transform.
,r, Pm.rr Supply and WA -PI
O
39 situ. Shipped express fÓ9
.hoir.
w -aie Amplifier Kit ylnrl. Main Amplifier
hipping
aid Power SUPp1)Transformer
Weight 29 lbs. Shipped mimeos
only.
W-3 Amplifier
ith Arrosound Opt{tput Trans.
PI Pre.mplIfier °K4) Shipping
Weight 39 lbs. Shipped express
only.
..
$
49
15
Kit Incl. Main Amplifier
w -as Amplifier Kit Ilnri.
+6950
e
Amplifier
-sign Aeroound output Transrç
former nit Poway Sapplr) ship.
HEATH COMPANY
BENTON HARBOR 25, MICH.
APRIL, 1953
www.americanradiohistory.com
ping
WA -1.1
'Nelght
Mahn
eight 29 ah.. Shipped ex-
$.uT
7
Preamplifier Kit only. Shipping
exposa
7 lbs. Chirped
or parcel post.
s19ß
63
10-15. Method of measuring unknown
speaker impedance at a given frequency. The
speaker impedance is numerically equal to the
value of the resistance when the voltage drops
across each are equal.
Fig.
found
only in
T. S. C.11 an exclusive Permoflux
development and the result of many
years of laboratory research -truly a
touch of "Black Magic " -increases
cone compliance, adds octaves of frequency response, and gives startling
realism to reproduction.
Royal Blue Speakers will bring you
undreamed of fidelity-the Royal
Eight comparable to any 12 -inch
speaker and the Royal Twelve superior
to larger reproducers. Hear them both
at your nearest Sound demonstration
room. Look for the Blue cone -the
emblem of high fidelity.
'Treated, Slotted Cone with permanently soft
plastic impregnant.
Folded -Horn Enclosures
Home -level reproduction
at its finest is achieved by
Royal
Blue Speakers in
Folded -Horn
corner
enclosures.
Two
sizes are
available: Model CH -8 for
a single Royal Eight speak.
er and Model CH -16 for
two Royal Eights or one
Royal Twelve. Both sizes
are offered in mahogany or
blonde to suit your taste
and your room decor.
See your
Permollux Distributor or ask us for
literature.
eFLux
(r=)
SOUND IN DESIGN
PERMOFLUX CORPORATION
4901
W. GRAND AVE., CHICAGO 39, U.S.A.
136 SO. VERDUGO RD., GLENDALE 5, CAllt.
Canadron [ or ensee
Campbell Mfg. Co., Toronto. Canada
64
significant "hole" in the response curve
may be filled in by a corresponding
shift in the opposite direction.
An array of speakers assigned to different portions of the frequency spectrum may produce an unbalanced tonal
structure due to varying efficiency from
one unit to the other. Horn -loaded
tweeters used alongside direct- radiator
woofers, for example, normally require
provision for attenuating the treble
signal, and a horn loaded woofer should
be given a correspondingly efficient
tweeter. An L-type level control between
the speaker (normally the tweeter) and
the network feeding it [See (B) in
Fig. 10-14] accomplishes this result
without affecting operation otherwise.
The coils of the dividing network
must have high power -handling capacity, and must not introduce non linearity into the circuit. Non -metallic
cores, which avoid the non -linear and
power dissipating effects of core saturation and eddy currents, are suited to
such requirements, and are made possible by the low values of inductance
called for. Winding data appears at (A)
and (B) in Fig. 10-16.
The capacitors must be non -polarized
since they are in an a.c. circuit, and
should have a working voltage rating
of about 50 volts for safety. Although
non -polarized electrolytic capacitors
(two electrolytics connected "back-toback") have been used in dividing networks, this practice is not recommended
because of the lower reliability of electrolytics from the point of view of accuracy of rated value, changes of value
with time, and failure in service. Good quality paper or oil -filled capacitors are
suitable.
however, the acoustic output of a voice
coil with constant-velocity response
would exhibit bass losses, due to the
progressive drop of air -load resistance
at lower frequencies. The shape of the
acoustic frequency- response curve at
the low end, corresponding to that of
the graph of air -load resistance vs. frequency, would require that compensatory bass boost be introduced, and that
the amplifier have a power capability
sufficient to handle this extra boost.
A revolutionary principle of speaker
design has recently been introduced in
France. The "ionic" loudspeaker is a
direct electro-acoustic device that bypasses the usual electro- mechanical
stage. Agitation of the air molecules is
produced by an electrostatic field rather
than by the mechanical pushing and
pulling of an intermediary cone or diaphragm, and since no mechanical moving parts are necessary the entire suspension system -the weakest link in
loudspeaker design -may be eliminated.
The molecules which are controlled
electrostatically are in an acoustical
chamber which contains the stimulating
electrodes. Since air molecules in their
normal, uncharged state are insusceptible to the influence of electric fields, the
particles in the chamber are first ionized, or given a positive charge. This
is done by heating the chamber, increasing random molecular movements and
inducing collisions which knock off
orbital electrons from some of the molecules. Once there are a few charged
particles, an alternating field of supersonic frequency is able to complete the
ionization process by more of these
electrically created collisions.
USING AWNS FORM SHOWN AND No 17 ENAMELLED WME
USE THIS CHART FOR VALUES BELOW 15 MLLIIENRT
400
g
375
350
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225
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2J. P. Maxfield, et. al., U. S. Patent No.
1,535,538.
IN
USE THIS FORM FOR
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MILLIHENRIES
USING WINDING FORM SHOWN AND
¢
3
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7
15
20
30
40
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MLLINENRIES
Fig. 10-16. Winding data for dividing network coils. Brass screws are used for the coil
form. (From "Crossover Networks for Speaker
Systems," Courtesy University Loudspeakers,
Inc.)
AUDIO ENGINEERING
www.americanradiohistory.com
.,
AINNO
IIII!I11f1.11.I
=.IMM.IPA.
=MI.IA
Experimental Trends in Speaker Design
The logical extension of the use of
negative feedback in amplifiers is to
include the speaker moving system
within the feedback loop. If the source
of feedback voltage is an independent
generating coil in the loudspeaker, inaccuracies in voice-coil motion as well
as electrical inaccuracies in the amplifier will be corrected. Such a design was
patented as long ago as 1925,2 but has
not, to date, been brought to commercial
practicability. A successful feedback
loudspeaker would go, far in bringing
instantaneous voice -coil velocity to a
closer relationship with the electric
signal. (The feedback principle has already been applied, with great success,
to disc recording heads.) Paradoxically,
I
III111.I
-
g 275
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II11 =.1.1I.'
1.
APRIL, 1953
The signal to be reproduced is applied
as an amplitude- modulating voltage to
the supersonic field, and the acoustical
vibrations are coupled to the room
through a horn. The field is of radio
frequency, a fact which introduces an
interesting feature. The output of an
AM radio receiver requires only sufficient r.f. amplification before it is applied to the speaker, dispensing with
the need for a detector and audio amplification stages.
/f
rIVLG WEi
DB10 -1
THE NEW BOGEN
HIGH FIDELITY AMPLIFIER
10 WATTS OUTPUT
RESPONSE FLAT FROM
30 to 18,000 CYCLES
REFERENCES
John G. Frayne, and H. Wolfe, Elements of
Sound Recording, Chapter 30.
Jensen Mfg. Co., Impedance Matching and
Power Distribution in Loudspeaker Systems, Technical Monograph No. 2.
H. F. Olson, Elements of Acoustical Engineering, Chapter 6.
SHOCK MOUNTED
PREAMPLIFIER
C. G. BURKE,
INDIVIDUAL BASS
d TREBLE CONTROLS
WRITING
MUSIC HAS STATED =
......t
PREAMPLIFIER DESIGN
page 220)
-
ohms for R. and 4 megs. for R8 to obtain
good compensation down to 20 cps for a
900 -cps turnover. Actually the 6SJ7 is
a poor choice for V,, for unless d.c. is
used on the heaters one is likely to experience hum difficulties. The 6J7 would
be more suitable in this respect, even
though it will not provide quite as much
gain. The high-level cartridge makes
possible good bass compensation with
a simple preamplifier using a twin triode
such as the 12AX7, 6SL7, or 7F7.
Triodes may be used in a preamplifier
designed for use with a low level cartridge by following the basic amplifier
with an additional stage of amplification
as shown in Fig. 3. With a high-level
cartridge the amplifier noise and hum
level will be about 16 db lower with
respect to the signal level than would be
the case with the same amplifier and a
low -level cartridge.
If the preamplifier is to provide for
switching between various turnovers,
CALL OR WRITE FOR
LITERATURE ON BOGEN
HIGH FIDELITY EQUIPMENT
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Added feature: 13 bands of frequency response, 30-12,000 cps.
TRACKING
PHONOGRAPH'S
PERFORMANCE
one
'52 AUDIO FAIRI
HIT OF THE
MEASURE
PHONO -TEST
AL
OF RECORDED
"The Bogen DB -I0 is a compact little marvel
of tone . . rescurceft I enough to compete over
most of its range with amplifiers costing three
It employs six tubes and is
times as much
has three input channels
rated at ten watts
-one for strong- impulse magnetic pickups line
the Pickering, one for weak impulse magnetic pickups like the
GE, and one fer tuner or crystal
pickup . . . The tome controls
separate for boss and treble are
continuously variable providing
both increase and diminuation,
and are capable of surprisingly efficient rectificati5n of the idiosyncrasies of records .
VIRTUALLY HUMLESS
UL APPROVED
(frn:
IN THE SATURDAY REVIEW
HOME 800K
D -100 is
required)
the
a series of test records
CO....
offered by THE DUBBINGS
Basically
a
Re-recording
Service,
Aim
we have always believed that a need
exists for
Fig. 4. Bask variable -load- impedance bass -boost
amplifier circuit. Triode shown for simplicity.
reliable test disc.
the result of our intensive research...
the selector switch must be of the shorting type to avoid serious switching
transients high -quality capacitors should
be used for Cr, and a 10- to 20 -meg.
resistor must be placed in parallel with
the selector switch for each switch
position. These precautions are required
because of the d.c. potential difference
across Ce. The value of the switch shunting resistors is not critical, but
the combined resistance of all of them in
parallel should be no less than about 40
times Rs.
AUDIO ENGINEERING
a
This new 12" long playing record is
(look for this cover)
ENCLOSED
RITE U.S FOR THE NAME.
(IF YOUR LOCAL. DEALER
ET
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or mail this coupon to
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NAME
DEPT. AE -43
CITY 4,
CHECK
PhONO -TEST
postage
N. Y.
APRIL, 1953
www.americanradiohistory.com
ADDRESS
ZONE
(please
print)
65
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Brook
- Sell
loosen
TEXAS -TV
I
"Southwest Sound Hq."
°
of one
corner
.\
3
of
the
Texas -1T
,i
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be
demon -
Iti Fi demonstration rooms in which all major lines
of sound and
.Orated at the
recording
"flick of
equipment can
a
switch."
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00
Altec 604C Loudspeaker
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TEXAS -TV
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GROMMES
AMPLIFIERS
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The Columbia long -playing recording
characteristic requires a 500-cps turnover with a maximum bass boost of
about 14 db. For this compensation the
capacitor used for Ce should have shunting it a resistor of such value as to provide in parallel with the resistor used
for Ra an effective resistance for the Rs
term in Eq. (5) that will give a value
for AL, which is five times the value of
Aur for the amplifier. To avoid serious
switching transients a blocking capacitor should be placed in series with this
resistor. This blocking capacitor should
be chosen so that the product of its
capacitance (in farads) and the lowest
frequency of interest is at least equal
to the reciprocal of three times the
resistance of the shunting resistor in
series with it.
Variable- Load -Impedance Bau Boost
A simple, commonly-used type of bass
boost circuit is shown in Fig. 4. Rk, R..,
and Ra may be selected from resistance coupled amplifier data to provide the
maximum gain desired at the lowest
frequency of interest. The requirements
on Cd and Ck are the same as discussed
for the basic amplifier in the degenerative-bass -boost circuit. The high -frequency gain is given by the product of
the mutual conductance of the tube and
a resistance equal to the parallel combination of the plate resistance of the
tube, RL, Ra, and Ra. The required value
for Ct may be computed from Eq. (6)
by substituting Ra for R, + Re. The maximum gain should be at least 6 db above,
or two times greater than, that required
for the greatest bass boost desired, if
a 6 db per octave slope is to be followed
to the lowest frequency of interest. A
6S J7 operated to obtain a maximum
gain of 200-46 db -will provide for a
high- frequency gain of about three and
Model 50 PG
.. Moan..
11"»
1.^20 000
Fig. 5. Treble roll -off circuit. R. selected for
cartridge damping and /or to obtain roll -off
rates between 6 and 12 db per octave. RI,
selected to obtain roll -off rates less than 6
db per octave.
full bass compensation down to 30 cps
for a 900 -cps turnover when used in
this simple circuit. There will be, of
Model 210 PA
PRE -AMPLIFIER
Completely variable feedb.M eq.ol.zanon for rprodusino
records
wanly.
Response 6 ta 100,000 CRS. IM distortion luss
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PRECISION ELECTRONICS, Inc.
9101 King Avenue, Franklin Park, III.
course, no degenerative feedback to provide for low distortion obtainable with
the previously discussed system. For a
500-cps turnover compensation may be
carried about one octave lower. or about
6 db more gain may be provided for the
high frequencies.
By following a degenerative-bassboost amplifier with a stage of amplification containing variable load imped-
-
ance bass boost with a very low turnover frequency-50 cps, for example
extra boost for the low bass may be
obtained if desired.
Treble Compensation
For a 6 db per octave roll -off, the
simplest treble compensation is obtained
by selection of the resistance shunting
the magnetic reproducer cartridge.
Neglecting the effects of cartridge internal capacitance (usually negligible in
the audio range), 6 -db-per -octave attenuation will be obtained as figured
from a frequency equal to 6.28 times
the cartridge inductance in henries divided into the sum of the internal resistance of the cartridge and the effective external resistance shunting it.
One can select the roll -off frequency by
adjustment of the preamplifier input
resistance with either a fixed position
switching arrangement or a continuously adjustable potentiometer control.
A more flexible treble roll -off circuit
Fig. 6. Circuits for commonly used roll -off less
than 6 db per octave. (Al is accurate within
± Y4 db to 15,000 cps. (B) is accurate within
± I/4 db to 10,000 cps and gives 1 db less than
ideal attenuation at 15,000 cps.
is shown in Fig. 5. Ra is usually selected
for cartridge damping in accordance
with the recommendations of the cartridge manufacturer. If Rb is zero, an
attenuation at 6 db per octave will be
obtained as figured from a frequency
equal to the reciprocal of the quantity
6.28 times the product of Ra in ohms
and C in farads. Ra should be large
enough so that its parallel combination
with Ra acting in connection with the
cartridge inductance will not cause appreciable additional high -frequency attenuation, unless a roll -off rate greater
than 6 db per octave is desired. To accomplish this the resistance of Ra and
Ra in parallel should be at least 125,000
times the cartridge inductance in henries. Figure 6 gives data for selection of
components for treble roll-off at less
than 6 db per octave as required by
some RCA Victor and some British 78
rpm recordings.
Noise and Hum Reduction
If the preamplifier is laid out and
wired carefully, hum and noise may be
reduced to a negligible level by simple
2 Norman Pickering, "Effect of load impedance on magnetic pickup response."
AUDIO ENGINEERING, Mar. 1953.
AUDIO ENGINEERING
www.americanradiohistory.com
APRIL, 1953
s
means. Resistor noise will ordinarily be
unnoticeable; the ultra -perfectionist may
practically eliminate it by using wire
wound resistors in the plate circuit and
any unbypassed portion of the cathode
circuit of the first stage. Most of the
hiss noise from an amplifier usually
comes from the first tube. Tube noise
varies greatly between tube types, and
between individual specimens of a given
type. Unless a selected low -noise tube
is used, tube noise will usually be less
in a preamplifier employing a triode
in the first stage than in one using a
pentode. If the first stage is to use a
pentode it is well worth while to use
the 1620 or the 5879 for their low
microphonism, hiss, and hum. Where a
low -noise triode is desired one can use
the 12AY7 or a triode- connected 5879.
The most obvious and straightforward
way of eliminating hum arising in the
cathode circuits is to use direct current
heater power. D.c. for heaters may be
obtained from a full-wave dry disc
bridge rectifier with a simple capacitance filter of between 1000 and 5000
microfarads. The rectifier will require
an r.m.s. input voltage about 50 per
cent greater than the required filament
voltage. One should provide a variable
series resistance between the rectifier
and the capacitor so that the filament
voltage may be adjusted to the proper
value. With this arrangement a standard
12.5 -volt transformer may be conveniently used for a 6.3 -volt d.c. heater
supply.
If one is not so unfortunate as to get
a poor tube in the input stage, hum due
Fig. 7. Hum reduction circuit. Neither of the
heater lines may be grounded, and a center tap
on the transformer should not be used. Potentiometer is adjusted for minimum hum.
to a.c. heater operation may usually be
eliminated by the simple arrangement
of Fig. 7. The value of the bypass capacitance is not critical (values less than
sf have been used successfully).
Satisfactory hum reduction may often
be accomplished by eliminating the balancing potentiometer and connecting the
positive bias to the center tap of the filament transformer. When the balancing
potentiometer is used it is well to locate
it and the associated bypass capacitor
near the first stage of the preamplifier.
as it takes the place of the usual grounding of one side of the heater line.
1.0
AUDIO ENGINEERING
IM1I:1IIh:
Ill .I.I\ h:li1
Illustrative Preamplifier Circuit
As an illustration of the principles
discussed in this article, Fig. 3 gives the
schematic of an easily constructed pre-
amplifier designed for use with the author's Ultra- Linear Williamson power
amplifier. This preamplifier has ample
gain for use with a low -level GE reluctance cartridge and carries compensation fully down to 30 cps for the highest
turnover frequency. At maximum gain
settings approximately one -third volt input on the high -level inputs 3 and 4 will
drive the power amplifier to full output.
The author's unit is completely contained within a 10 x 4 x 2% inch aluminum box. In constructing the preamplifier it is important to keep to a minimum
the stray capacitances in the treble compensation circuits and in the input connection to the 12AX7. If the preamplifier is to be used only with a Pickering
cartridge, or any other make of similarly
low inductance, it would be well to
double the compensation capacitor connected to the first 12AX7 grid to 1000
ppf and reduce to one -half the values
given for all the compensation resistors
connected to the treble switch points 2,
3, 4, and 5, thus reducing stray and input
capacitance problems.
In the author's opinion, any adjustment of the system frequency response
beyond the simplest that will compensate for the recording characteristics of
the disc being played will deteriorate the
transient response. As a concession to
situations in which simulated live program loudness is undesirable or unpermissable, the circuit of Fig. 3 has been
designed to incorporate an IRC loudness
control. For this control to function
properly the level control must be set
to give simulated live program loudness
with the loudness control at its maximum setting. Much of the criticism of
loudness controls has come from failure
to do this.
HIGH FUTILITY (from page 22)
bass is absent. There is only one practical solution to this problem and that is
to set the compensation for the average
level so as to obtain a minimum of
scale distortion. While this solution is a
compromise, it is not so bad as may appear at first. If our listening habits are
reasonably firm, the scale-distortion
peaks will vary about the compensated
characteristic just as the dynamic peaks
vary about the average level, and the
peak excursions of scale distortion will
be reduced over what would be true
were there no compensation. Further-
Nouf 4eacht--
more, some compression is almost sure
to be present, and this will be a further
aid.
The situation that obtains for the high
frequencies is very similar to that just
discussed for the low, and, once again,
compensation is needed in order to insure the high frequencies not being lost
at depressed listening levels. In this
case there is a mitigating circumstance
in the characteristic shape of the
Fletcher- Munson curves in that they
more nearly maintain their spacing
while rising. The significance of this
APRIL, 1953
www.americanradiohistory.com
No bigger, no better than the original Audio Anthology
fact it's
just the same size and it's a perfect
companion for the most authoritative book you now have on the subject of home music systems. However, the 2nd Audio Anthology contains all new material- reprints of
over forty of the valuable articles
which have most interested Æ's
readers during the past two and a
-in
half years.
FEATURES
Amplifiers
Preamplifiers
Tone Controls
Phono Equipment
Loudspeakers
Speaker Enclosures
Tape Amplifiers
Details of the modified Universal Tape Recorder amplifier first described in AE in May.
June-July, 1952. This material has not appeared in the magazines, and presents improvements which simplify construction and
better performance.
Board Cover
.
.
Paper Cover
.
.
Customary Discounts to
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$2.00
Di
butors
The first Audio Anthology
is
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AA -1 and AA -2, paper cover
$4.00
P. O.
RADIO MAGAZINES, INC.
Mineola, N. Y.
Box 629
67
that the source material is more likely
to contain the stronger high frequencies
and less compensation is needed in the
system proper. This is most fortunate,
for even the slightest trace of harmonic
distortion will be raised in percentage
by a gain characteristic that rises with
is
SAVE
33°/0
increasing frequency. This is known as
selective distortion. Where compensation is deemed necessary, an attractive
scheme is to lessen the de- emphasis.
This is feasible in FM reception and in
the playback of modern records.
This
is
The Listening Room
our
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1
AUDIO ENGINEERING
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The only publication devoted
entirely to Audio-.
Recording
Broadcasting equipment
Acoustics
Home reproduction systems
PA systems
Psychoacoustics
(Please print)
Name
Address
Potation
Company
Nam./
Address
Position
Company
Nam
Address
When one undertakes the determination of quantitative data on which to
base the design of tone or loudness controls, it is soon learned that there are
other factors to be considered besides
the response of the ear to various intensity levels. For example, few living
rooms are arranged or furnished with
real consideration for the reproduction
of music. It is a matter of slight misfortune that a room we would consider
as comportable for living, is "too soft"
for best music enjoyment. With the
battle lines so clearly drawn, it is easy
to see whose point of view will prevail.
Even so, it is important to know something of the room acoustics. A typical
living room and dining room combination may have a volume of 3000 cubic
feet, and yet contain sufficient furniture,
rugs, drapes, doors opening into other
rooms, etc., to reduce the reverberation
time to 0.6 seconds. The optimum reverberation time (for music) for a room
of this size is closer to 0.9 seconds, some
50 per cent above the actual value. This
departure from the ideal, though undesirable, is not severe. It must be remembered though, that these optimum characteristics are for live performance, and
for reproduction there is an unavoidable
deviation from the ideal caused by the
characteristics of the studio wherein the
performance is actually accomplished.
The quality of program in the home can
11
Olson, Op. Cit., page 399.
The relation between tonal compensation and reverberation time may be derived from the approximate formula for
12
Potation
Company
acoustic power required to maintain a
given intensity in a room:
Name
Address
(in watts) = 11.6xVxT
where V = volume in cubic feet,
T = reverberation time in seconds.
and
1 = intensity in watts /square cm.,
If Tf is the reverberation time at some extreme frequency, and To is the time at mid frequency, then the compensation that can
be obtained from an increase in reverberaPOWER
Position
Company
Name
Address
Position
Company
tion time is
Nave
Address
Position
Company
Add $.50 to each Foreign subscription
ordered
RADIO MAGAZINES, INC.
P.
:
(in db) =10 log Tf /To
This method for accomplishing tonal compensation is not recommended for home
use for the following reasons : difficulty in
obtaining a sufficient amount; inflexibility,
in that changes are difficult to make; and
the danger of creating an acoustical absurdity in which eerie high -frequency echo
effects may become manifest, or strong
modes of vibration may be set up in a
small room to upset seriously the pattern
COMPENSATION
O. Box 629, Mineola, N. Y.
of low- frequency tones.
68
be enhanced by control of studio rever-
beration time, best microphone placement, and a more objective approach on
the part of performing artists. All of
these factors are receiving consideration
today.
It is generally much easier to calculate reverberation time than to measure
it.11 The coefficients normally used in
computing reverberation time are average, and therefore the calculated time
is probably too high for high frequencies
and is surely too low for very low frequencies. This deviation at the lower
spectrum limit is in the correct direction, however, for optimum reverberation time at, say 50 cps, may be greater
than that at 1000 cps by an amount
consistent with the bass compensation
needed.12 Conditions at the upper end
of the spectrum are not so favorable.
Here the requirement for optimum reverberation time at 15,000 cps is equal
to, or greater than, that for 1000 cps
and the actual time is below the calculated value to the extent that average
absorption coefficients are used and all
factors are not considered. Reverberation time is influenced by absorption in
transmission as well as upon reflection,
and, at average room conditions of 70°
F. and 50 per cent relative humidity, the
transmission of a 15,000 cps sound wave
may be down by a factor as great as 30
when compared to the transmission of
a 1000 cps wave. The necessary power
gain at 15,000 cps can be had in the
amplifier to correct this deficiency, but
its inclusion is questionable because of
the increase in selective distortion and
the psychological effect of the high frequency tones coming from the "box"
instead of being a part of the sound
pattern existing in the room.
There are a few other items which
should be mentioned in order to complete our view of the matter of scale
distortion. We know, for instance, that
the ear is non -linear and different intensity levels produce varying percentages of amplitude distortion and combination tones. Thus a performance may
be "distortionless," or at least tolerable,
as played but when the level is raised by
even a perfect fidelity system, the total
distortion produced in the ear may be
noticeable and even objectionable. The
human ear is sensitive to pitch rather
than frequency, and the pitch of a constant- frequency tone varies with amplitude. The artist will perform so as to
produce the correct pitch initially, but
when the level is changed upon reproduction (the frequency remaining constant), there is a change in pitch and
discords may result. These two points
may seem somewhat academic because
our listening experience with scale distortion is generally confined to lowering the average level of the entire program, rather than raising the level, particularly the selective amplification of a
solo part. It may well be that some of
the underlying reasons for the chronic
troubles associated with the application
of sound reinforcing systems to top quality musical performances is to be
AUDIO ENGINEERING
www.americanradiohistory.com
APRIL, 1953
i
i
found in these two factors. At least we
are on firm ground in drawing the conclusion that a symphony orchestra is
not likely to be composed of one violin,
one flute, one horn, etc., each with a
public address system.
Conclusion
M
4,
In summary, the following factors are
generally bearing upon high-fidelity reproduction in the home: listening level
depends primarily upon acoustic environment, concurrent activities in the
case of incidental listening, and taste;
within the home the listening level is
generally depressed and scale distortion
is therefore present; the more pronounced effects of this distortion are
alterations in tonal balance and failure
of perception at the lower limits of the
dynamic range; compression of the dynamic range, although detrimental to
true fidelity, is a strong factor in minimizing the effects of scale distortion; a
lower ambient noise level will permit
wider dynamic range under the conditions of intentional scale distortion;
and tone, or loudness, controls offer the
only simple means for partially correcting the adverse effects of scale distortions involved in recognized high-fidelthe recognition of a problem coupled
with failure to understand its nature
AUDIOLOGY
as the independent variable,
1. Distortion at a given flux density
varies roughly inversely as X/R for
values of this ratio above about unity.
2. Distortion variation with flux density
for constant X/R is of the general
form y = a + bx" (a straight line on log log paper) in the flux density ranges of
approximately 200 to 8000 gauss for
silicon steel, and 300 to 3000 gauss for
the more common nickel alloys.
3. Distortion falls only very slowly as the
flux density is reduced below about 200
gauss.
4. Direct -current magnetization results
in even as well as odd harmonics, and
may increase the total distortion materially.
For minimum transformer distortion, the
a.c. flux density and d.c. magnetization
would be minimized, and the ratio X/R
made as large as practicably possible. But
there is no useful object in making distortion due to transformer nonlinearity much
lower than that due to other causes at the
low frequency in question.
Efficiency
Losses at mid -frequencies are usually
considered to be due to winding resistances
only. Aptly named "copper efficiency" is
easily estimated in design, and may be
tested by simple resistance measurements.
Notion of the error at low frequencies may
be gained from consideration of a transformer with a 2 -lb. core of high -silicon
steel, operating at 10 watts output with a
flux density of 5000 gauss at 60 cps. Total
core loss would be about 0.4 watt. Were
the copper efficiency (say) 92 per cent, the
true efficiency would be more like 88 per
cent.
While heating is ordinarily not the problem in output transformers that it is in
power transformers, the cost per watt-hour
AUDIO ENGINEERING
leads invariably into "high futility." For
that reason this paper has attempted
to point out some of the basic considerations involved in recognized high-fidelity problems with the hope of fostering
a better understanding of some of the
non-electronic problems.
Perhaps it shall ever remain that a
ticket to the symphony or opera is the
privilege of true entertainment. In a
sense, the audience and the performers
comprise a team and under these circumstances a concert can neither be re-
hearsed nor duplicated (a playback is
an attempt at duplication). While the
technique of recorded sound is no real
match -nor competitor-for the live
performance, it is still a wonderful
scheme for broadening the base of music
appreciation and enjoyment. In the
process of capturing, holding and calling
forth at will our musical choices, some
restraint must be used. If the restraining
forces are applied intelligently and
gently the changes in dimensions which
we find upon freeing the imprisoned
sound may well leave a pattern and texture that is subjectively pleasing. If we
are to reach the goal of having the re;
created seem as the original, the listener
alone can supply that final measure of
understanding which must take over
where techniques fail.
et-loge
HEADQUARTERS FOR
SOUND EQUIPMENT
INDUSTRIAL SOUND
for any and all installations. Continuous music
or business message up
to 8 hours.
.941111!1¡!tl"
I
0
47
Illustrated: MAG NECORD Units PT61,
PT6AH, 814, with automatic switching equipment, custom built by
Air -Tone Sound & Recording Co.
fii4-71"
SOUND AND RECORDING CO.
from page 14)
is much higher.
But from the designer's
standpoint, increased over -all value of an
equipment development through improvement of output transformer efficiency is
often small compared with the increased
component cost. Almost any successful design, whether commercial or laboratory, is
a wisely chosen set of compromises, and
choice of operating efficiency is no exception.
When necessary reduction in physical
size warrants added cost, significant miniaturization of low -level audio transformers
is possible through the use of nickel -steel
cores. But if transformer requirements dictate maximum operating flux densities as
high as several thousand gauss or more at
the lowest intended frequency of operation,
nickel-steel core material is generally inferior to high-silicon steel. Of the latter,
the grain oriented variety is a preferred
type, and is available in woundloops and
as punched laminations, with neither form
always having advantage over the other.
Additional output -transformer miniaturization is possible by improved utilization of
the core window area, or by selection of a
more favorable core shape.
Assuming such improvements have already been incorporated, further size reduction (for a given specification on response
and distortion) can be had only with reduced efficiency. The extent to which one
may exploit this possibility depends largely
upon the associated circuit, and over -all
equipment considerations of size, cost, and
practicability of manufacture.
Particularly for wideband arrangements
in which extensive negative feedback is
employed, there are important transformer
details "not shown in the circuit diagram."
These are complex coupling and capacitance
structures resulting from interleaving of the
various windings, and are not readily
subject to design calculation or adequate
description in simple specification form.
APRIL, 1953
www.americanradiohistory.com
1527 CHESTNUT ST.
PHILA. 2, PA. RI -6 -8388
A MPERITE
Studio Microphones
at P.A. Prices
Ideal for
BROADCASTING
RECORDING
PUBLIC
ADDRESS
"The ultimate in micro-
phone quality," says
Evan Rushing, sound
engineer of the Hotel
New Yorker.
Shout right into the
new Arnperite Micro phone-or stand 2 feel
away- reproduction is
always perfect.
Not affected by
any chmof,r conditions.
Guaranteed to withstand severe "knocking
around.'
Models
RBLG -200 ohms
RBHG
-I- -imp.
List
$42.00
"Kontok" Mikes
Model SKH, lis- $12.00
Model KKH, lis. $18.00
ial
eel
Introdueery Offer'
Write for Special
folder.
illustrated
and 4 -page
AMPERITE eimpany l,c
561 BROADWAY
NEW YORK 12. ts. Y.
Canada: Atlas Radio Corp_ Ltd., 560 King
St.
W., Toronto
69
w o4, ..,
nDFts
Thus one frequently finds that superior
power -amplifier designs have been based
upon simultaneous development of circuit
and output transformer, with each adapted
to accommodate the other.
Manufacture may then consist of duplicating the model declared optimum for the
particular circuit, with just enough tests
along the way to assure the required closeness of duplication. To the manufacturer,
this is an obviously workable plan. To the
casual amplifier construction enthusiast who
wants top quality at moderate power, the
implication is that best results, for effort
expended, may probably be had by purchase
of an output transformer of published overall characteristics. There is often a strong
element of buying on faith, and likelihood
of satisfaction is improved through buying
from one of the now numerous manufacturers who specify the circuits with or for
which their transformers were developed.
1aWC1A2+QS sinACt 1924
RADIO
THE SENSATIONAL
NEW MILLER BAND -PASS TRF
TUNER USING A GERMANIUM DIODE
DETECTOR
NO
NO
TUBES!
POWER SUPPLY!NO HUM!
A SIMPLE 2 TUNED CIRCUIT NEGATIVE
MUTUAL COUPLED BAND PASS TUNER
EASY TO ASSEMBLE & WIRE!
-
spite of its simplicity, low costs .585 kit is not o toy: it
carefully designed High Fidelity Broodcast bond tuner.
Use it with your amplifier and speaker system for truly high
quality reception.
The audio output of the tuner is proportional to the input
signal and will nary from 05V to 5V for stations within o
2025 mile radius when used with a good antenna of from
75 to 100 feet in length. A good antenna is absolutely essen.
tial to the proper operation of the .585 tuner.
585 TRF tuner kit, including
The net pr'
f the Miller
chassis, dial, and tuning condenser. is only S11.40. The additional ports required make it possible to build the complete
tuner at a net cost of less than S15.00.
ask for the new MILLER Order yours
Cot. Ne. SSS Crystal Defector Tuner -Net $11.40
In
CLASSIFIED
Ratm: 10* per word per insertion for noncommercial
advertisements; 25e per word for commerei at
tIsements. Rates are net, and no discounts WI II be
allowed. Copy must be accam ponied by remittance In
full, and must reach the New York office by the
first of the month preceding the date of issue.
THE AUDIO EXCHANGE. INC. buys and
sells quality high -fidelity sound systems and
components. Guaranteed used and new equipment. Catalogue. Dept. AE, 159 -19 Hillside
Ave., Jamaica 32, N. Y. Telephone OL 8 -0445.
WANTED: Used disc recorder with overhead lathe not driven from turntable center.
Box CA -1. AUDIO ENGINEERING.
AUDIOPIIILES WANTED for part or full
time work. Technical or secretarial experience
desirable. Location : North Suburban Philadelphia. Send resume of education and experience to Box CA -2, AUDIO ENGINEERING.
is
t
-
RF TOUA LOCAL RADIO
MILLER
OHS
SU
M
ER
tut
FOR
AND 010E11 MILLER PRODUCTS
RIT
MILLER COMPANY
J. W.
5917 S. MAIN ST. LOS ANGELES, CALIF.
IF YOU ARE MOVING
notify our Circulation Department at least
5 Weeks in advance. The Post Office does not forward m ages irtes sent to wrong destinations unless
you pay additional postage. and we can NOT duTo save yourself
plicate copies sent to you
and the Post Office a headache, won't you
please cooperate? When notifying us. please give
your old address and your new address.
P lease
,
Circulation Department
RADIO MAGAZINES, INC.
.
0. Boa 629 Mineola, N.
P.
Y.
HI -FI WILLIAMSON TYPE
AMPLIFIER e
KIT
U
WANTED : Old -fashioned ear trumpet -the
type used before electric or electronic hearing
aids. Please state asking price. Reply to Box
THEATRE SOUND
CA -3, AUDIO ENGINEERING.
(froni page 23)
at moderate prices. But, here again,
modern tubes, circuits, and output transformers will probably make a better
showing in reproduction of the exquisite
detail in later recordings, as displayed
by the new speaker system.
In the writer's opinion, simplicity is
the watchword-from the diamond stylus right through all stages to the dividing network. Simplest tubes with
self-biasing, no interstage transformers,
simplest power supply with oversize
components, and no special circuits in
Radio Craftsmen tuner, 500 amplifier, Garrard changer, E-V SP-12B speaker ; reasonable.
Stearns, 307 N. Adams, Mason City, Iowa.
the regular line up.
It is hoped that this description may
have been sufficiently full of detail that
any interested hobbyist who wants
speaker performance which, in the
writer's opinion, is well above the average, will be able to duplicate the enclosure type with a minimum of effort.
The pleasure given by a speaker of this
type is usually well worth the trouble
taken to build one-a fact which is attested by a number of the writer's acquaintances who are using the same
type of speaker housing.
The ULTIMATE in Williamson -type amplifiers, $129.50. Send for facts. Nicely Associates, Kenton. Ohio.
IT'S NOT TOO LATE
50 -WATT PRESTO 92 -A Recording Amplifier $200. 40-magnification microscope, Bausch
& Lomb lenses, mount on any disc recorder.
$100. Brush 3-hour wire recorder, original
cost $800, only $185. Reco -Art Company, 1305
nor p.: ^'r
e
Stancor transformers. Easy
with schematic and Instruction, sheet based
Williamson circuit. Frequency response 1 db.
from 20- 50,000 kc at 8 watts.
Using
-
kit.
Comes
on famous
is SPECIAL
Intermodulatlon distortion
3% at 8 watts output.
Total harmonie distortion at PER KIT
$44.95
1000 eyries is non- eristant
Less Tubes
below 10 watt power level.
only
WITH CBS
)
HYTRON TUBES
2G1807
TOTAL
2.6SN7GT
1.5U4G
$52.75
wide. Frequency response: 50 to
cy. Plastie reel included with
600 FT. $1.35
1,200
s/
15% DISCOUNT on cartridges. Highfidelity transformers perfect for Fairchildsbargain. Oil -filled capacitors, filter and coupling, matched pairs. E. Garr Box 101, Riverdale Station 71, New York, iv, Y.
30% DISCOUNT on factory-fresh, guaranteed LP records! Send for free catalog and
literature. SOUTHWEST RECORD SALES,
Dept. AE-2, 4710 Caroline, Houston 4, Texas.
FOR SALE
:
Collins Custom Deluxe AM -FM
tuner. Perfect condition, highest quality.
Charles Garland, 505 Edgewood, Columbia,
Missouri.
SPECIAL PACKAGE PURCHASE: Ampex
portable recorder, 400-A serles, 50 -watt McIntosh amplifier, Electro-Voice 650 microphone with stand. two 15 -in. Lansing speakers,
Permofiux headphones -all for $1200. Mr. J.
Ross, HY 7 -5397 (Brooklyn, N. Y.) between
9 : 30 a.m. and 5:30 p.m.
AUDIO RESISTORS, LOW- NOISE, 1 %,
DEPOSITED -CARBON TYPE. Beautiful appearance, ideal for preamps, phase inverters,
improve existing equipment. Williamson Kit:
NOT SURPLUS. This
First Grade recording tape is
Company, 3221 S. Acoma, Denver, Colo.
Market Street, Philadelphia 7, Pa.
PRICE:
IRISH PLASTIC RECORDING TAPE
BRAND NEW
Send for tape library catalog. Over 61 halfhour programs available. Empire Recording
In.
8,000
lw, 2-20K 1w, 2-.47 meg w, 2-50K 2w,
2.100K w -$5.00. Single resistors : $w 43e.
lw 63e, 2W 884. Shipping charge 15e. Edwin
Bohr, Dayton Pike, Chattanooga 5, Tennessee.
1 -47K
each.
FT. $2.10
FOR YOUR HI- FIDELITY
REQUIREMENTS VISIT OUR
FOR SALE: W. E. 728 -B Speaker $21.
Thordarson T -32W10 Amplifier $21. Charles
Leigh, 162 Passaic St., Trenton, N. J.
NEW SOUND STUDIO.
All
F.0.. Los Angeles. Minimum
$5.00. 25% deposit required with order.
SELL : Allee 603B speaker, perfect condition, best offer. W. Tannenbaum, TOmpkins
7-1698 (N. Y. C.)
OLYMPIC ELECTRONICS SUPPLY
1440 W. Olympic Blvd., Los Angeles 15, Calif.
AUDIO ENGINEERING
70
www.americanradiohistory.com
APRIL, 1953
PROFESSIONAL
DIRECTORY
Custom -Built Equipment
U. S. Recording Co.
1.1urolu :S-270
odusbut Nate
?'644.44.. FREE!
Fred Cantor, lv..11- known, <:,I,
cutive
in high fidelity circles, is newest addition
to list of New York manufacturers' reps
among first accounts are Bozak speakers
and Sound Workshop radio -phonos .
John Bou, long -time associate of Maj. B.
H. Armstrong and president of the Radio
Club of America, on the receiving end of
industry congratulations for performing
major developmental work on new FMmultiplex system -permits transmission
of up to three programs on single FM
channel
"Life" magazine is latest
major consumer publication to plan article
on Audio -piece will be written by Herb
Brean
Bob Catherwood, broadcast pioneer, is
newest tenia mate of Ira Hirschman,
owner of Manhattan's FM station WABFintends to establish the station as the
country's pace setter in stimulating and
satisfying listeners' desire for fine music
on the air ... Robert X. Mitchell has been
appointed to executive sales position by
Sonotone Corporation-appointment represents part of Sonotone's expansion pro gram-in addition to hearing aids, company is now engaged in volume production
of miniature tubes, pickup cartridges, electron guns for TV picture tubes, and
special purpose batteries ...New v. p. of
corporate affairs for Westinghouse Electric Corporation is E. V. Huggins, formerly
Assistant Secretary, USAF-also elected
president of Westinghouse Radio Stations,
-
.
.1
...
"EVERYTHING IN HIGH FIDELITY"
From Primary Components
to Completed Custom Audio Equipment
KIE
F
Sound Corp.
820 West Olympic Blvd.
Richmond 7 -0271
Los Angeles 15, Calif.
ZEnith 0271
In Southern California it's
HOLLYWOOD ELECTRONICS
(in The Audio Mile)
Distributors of Hi Fidelity
Components Exclusively
Webster
7460 Melrose Ave.
3 -8208
+
Hollywood 46, Calif.
Two ways you can
protect your family
against CANCER
...a check
...a check -up
Cancer strikes in one of every two
families. Each year more than
60,000 American children under
the age of eighteen lose a parent
to cancer.
Yet many cancers can be cured,
if discovered in time.
Every man should have a complete
physical examination once a year.
Women over thirty-five should have
a complete physical examination
twice a year. Patients are being saved
today who could not have been saved
even a few years ago.
The American Cancer Society
asks your help.
How soon we find cancer's cause and
cure depends on how soon and how
much help comes from people likeyou.
Send contribution to Cancer,
e/o your local Post Office.
Cancer strikes One in Five
STRIKE
BACK...
Give to Conquer Cancer!
AUDIO ENGINEERING
TERMINAL'S
New, Illustrated, 130 -page
AUDIO
CATALOG
complete guide to the
Finest in Audio Equipment I
Yo
Write or come in for your
Complimentary Copy!
Visit our Audio Dept.
Inc....
CREE
John Silver, formerly general manager
of Communications and Electronics division of Motorola, Inc., has been elevated to
vice- presidency
.
Hari B. Hoffman,
whose radio -TV days date from 1921 (in
'27 he worked under Dr. Alexanderson in
designing first GE TV transmitter), has
been elected vice- president of WGR Broadcasting Corporation, Buffalo, N. Y. .
Joseph M. Benjamin, formerly manager of
government contract department, has been
named vice -president of Pilot Radio Corporation
. Max Baume,
sales manager,
Brook Electronics, Inc., has altered company policy to include factory reps in
selected areas -first appointments are
George Davis Sales Company and E. W.
Brandt Company covering Southern and
Northern California, respectively. . . .
Prank J. Donnola, audio expert for Liberty Music Shops, New York, has assembled truly fine custom -built audio systems
for installation in cabinetry to customer
specifications included are Craftsmen
tuner, and Brook amplifier
Joe Martin,
director of public relations for Association of Record Manufacturers, reports
that the classics are accounting for increasing percentage of total sales . . .
Jerry B. Minter, chief engineer, Measurements Corporation, Inc., Boonton, N. J.
spending evenings at home working on
a gadget which may well have revolutionary effect on the science of disc recording
Sam Girard, head of New York's
Sun Radio & Electronics Company, taking
pride in country's first triple-demonstration-studio sound department at firm's new
midtown headquarters . . . Harry muer,
eastern factory representative for McIntosh, Magnecord, and James B. Lansing,
has expanded sales force to meet demand.
of increased business.
-
...
Open Thurs. eves.
till
9 P. M.
Ample Parking Space after
P.M.
6
Terminal Radio Corp.
L85 Cortlandt St., New York
Ont1CO
7,
EASY -HANDLING
MAGNETIC TAPE REELS
Precision manufactured In
orda' ro
witAhe exacting standards set
6..
et
b
MAC,.
...
.
.
.
ERRATUM
Inadvertently the trade name of
Ree ves
Soundcraft Corporation's
Magna- Stripe sound -on-film process
was misspelled in the caption describing
the cover of AUDIO ENGINEER ING's March issue. At least, it was correct on the cover -but they furnished
the cover art work in complete form.
APRIL, 1953
www.americanradiohistory.com
In's
'
° hand\° b° py1°.
°1
°n ho'P
ß,a''d,
°Y.
1.
2.
ed9
o rs
stay
cos,w.
'sot:,
'tote
4. Slobs ora
s.
tot
g
quickly,
assertible
Components
A.
mooched
llantas
robbing
dia.en to
write°°
1101.
losa
close
Etimi.
It:Wants
° °'
editing notas.
TAPE REELS, STORAGE CANS. AND
CASES POI EVERY PROFESSIONAL
sew
SNIPPING
REWIRE.
ALWAYS IN STOCK
dorripri lise,rmre ford pria lits
COMPCO CORPORATION
Writ, for
Morse/,., layers of sot products for
1251 W.
têt Ardis.
Visual .rdwar.
Ave.
Chicago 47. IIIInels
Sr. Pool
71
ADVERTISING
HERE IS THE SPRING
BULLETIN OF HARTLEY AUDIO
ADVERTISED AND PERFORMING
INDEX
In our March ad we said "For the finest possible results. regardless of expense, we introduce the double Boffle, which, with the two 215's wired in simple
series, will give you for $200 a performance not to be equalled by any speaker ensemble offered elsewhere at prices up to more than $1,000." You might say that
this
is
Asco Sound Corp.
52
15
11
49
Cover 2
51
13
18
65
60
British Industries Corp.
Brush Development Co.
Bud Radio, Inc.
8
53
Carter Motor Co.
Chicago Transformer Co.
Cinema Engineering Co.
Classified
Compco Corp.
Concertone Recorders
The 215. the Boffle, the Hartley amplifiers. are now in stock at headquarters
in the U.S.A. and in the hands of various agents. These are the basic units for a
non -distorting reproducer. but we are now getting around to completing the whole
picture. The first of the newcomers is a record -changer better than you have ever
met. This changer has been most rigorously tested in London and we guarantee
that it meets our fastidious requirements in freedom from rumble, wow, and vibration. It handles mixed 10" and 12" records, operates 45's automatically, and is so
free from "t :p hamper" that it can be used delightfully as a plain turntable unit
for single L.P's. lust slip the record on and slip it off, and the changer will gently
lower the pickup cn to the proper groove of a ten or twelve -inch disc.
14
6
9
70
71
63
Cover 3
59
Daven Co.
Diacoustic Laboratory
Dubbings Co.
65
Gates Radio Co.
General Electric Co.
Gray Research & Dev. Co., Inc.
Coming with this is a new really high -fidelity turnover crystal pickup with
diamond stylus. For long we have tended to believe that high -fidelity and crystals
were not in sympathy, but we are always learning, and this new pickup is astonishing. But, as we believe in freedom of opinion, we shall also be able to supply
interchangeable plug -in adaptors fitted with Audak or Fairchild cartridges.
7
60
45
Hartley, H. A. Co., Ltd.
Harvey Radio Co., Inc.
Heath Co.
Hughes Research & Dev. Co.
72
Leonard Radio, Inc.
57
Magnecord, Inc.
Magnetronics Corp.
10
47
63
1
price will be very
We hope all our mailing list subscribers will have had their new information
by the time this ad appears, but if you are not on our mailing list, a postcard to
our New York address is all that is necessary. There has been some delay in replying to many enquiries for literature, but this has been due to the vast amount of
work resulting from setting up our new headquarters in New York.
50
70
W. Co.
Minnesota Mining & Mfg. Co. 36, 37
Miller,
Meanwhile we draw your attention to three demonstration centers, where
you will be entertained intelligently and artistically. New England music -lovers
should visit us in New York, where we are open all day Saturday for your
convenience.
J.
Newcomb Audio Products Co.
...
43
Olympic Electronics Supply Co.
..
70
64
Permoflux Corp.
Pickering & Co., Inc.
Pilot Radio Corp.
Precision Electronics, Inc.
McSHANE AND COMPANY, 6903 MELROSE AVENUE, LOS ANGELES,
CALIFORNIA, are our sole agents for Los Angeles, but will welcome all enthusiasts
from southern California.
17
35
66
Precision Film Laboratories
Presto Recording Corp.
Professional Directory
THE DIXIE HARTLEY CO., P. O. BOX 1622, CHATTANOOGA. TENNESSEE
demonstrations in any of the following places:
Knoxville, Atlanta, Birmingham, Nashville. Chattanooga, and the Southeast.
Radio Corp. of America
Radio's Master
Reeves Soundcraft Corp.
Rek -O -Kut Co.
Rockbar Corp.
be glad to arrange
H. A. HARTLEY CO. INC.
York 56, N. Y. LU 5 -4239
4, 5
54
41
3
33
Terminal Radio Corp.
Texas TV Stores
Triad Transformer Mfg. Co.
66
AUDIO ENGINEERING
www.americanradiohistory.com
39
71
61
White Sound, Inc.
152 Hammersmith Road, London W.6, Eng.
12
Stromberg Carlson Sound Div.
United Transformer Co.
H. A. HARTLEY CO. LTD.
72
58
Bell Telephone Laboratories
Bogen, David Co., Inc.
It would not be fair to say who, but eminent audio experts, known to you all,
wrote and told us that McShane had produced the hit of the Fair. and people were
queuing up to hear this terrific outfit. It was, we were told, a wonderful performance. and at the price it was miraculous. So, honestly, we mean what we say in
our ads, and what we say in our ads is endorsed by our customers.
521 East 162nd St., New
69
Beam Instruments Corp.
Belden Mfg. Co.
Well, when we wrote that copy the Los Angeles Audio Fair had not started.
Our Los Angeles agent, acting entirely on his own initiative, decided he was going
to prove it to one and all, and the double Boffle with 21 5's "wired in simple series"
was duly demonstrated.
will
55
Ampex Electric Corp.
Amplifier Corp. of America
Arnold Engineering Co.
Audak Co.
Audio Devices, Inc.
just some more advertising guff that doesn't mean what it says.
Supplies will be available shortly and we expect the
favorable.
69
Air Tone Sound & Recording Co
Allied Radio Corp.
Amperite Co., Inc.
WITHOUT DISTORTION
...
'71
2
Cover 4
59
APRIL, 1953
or MINIATURIZED COMPONENTS
/
m nidturîzatian of military and portable civilian gear has required audio
components of smaller and smaller dimension. This is particularly e: aggerated in the case of
transformes for use in transistor circuits. The 'H" series of miniature and sub -miniature units
described below are hermetic military types to cover virtual y all audio applications. For
ever smal er structures our ultra- miniature types are availcble against quantity orders.
The Cons an
from STOCK
MINIATURE AUDIO UNITS...RCOF CASE
Type
No.
H.1
H
-2
H
-3
H.4
H
-5
H -6
MIL
Type
Application
Mike, pickup, line to grid
Mike to grid
Single pl rte to single grid
Single ple to to singe grid.
DC in Pri
Single plate to P.P grids
Single pl 'le to P.P grids,
Pri. Imp.
Ohms
5),200
TF1A1OYY
TFIAI1YY
Sec. Imp.
Ohms
CT, 500
CT
82
TFIAI5YY
15,000
TF1A15YY
15,000
TFIAI5YY
15,000
15,000
TF1A15YY
- Response
2db. (Cye.)
in
DC
Pri., MA
50,000
135,000
60,000
60,000
Max. level
dbm
50- 10,000
50
250 -8,000
50- 10,000
+21
16.0C
0
+
6
13.5C
4
200 -10,000
+14
13.5C
0
50-10,000
+
5
15.5C
4
200- 10,000
+11
16.00
95,000 CT
95.000 split
-1-
DC in Pri
N -7
H -8
H -9
H -10
Single or ,.P. plates to line
Mixing and matchirg
82/41:1 nput to g-id
TFIAI3YY
TFIA16YY
10:1 sing e plate tc single
TFI415YY
Reactor
TF1A20YY
23,000
150'600
150.600
TF1A1OYY
1
grid
H -11
150,600
CT
),000
4
600 CT
1 meg.
0
meg.
0
1
List
Price
0
0
$16.5(
5
200 -10,000
50- 10,000
+21
16.5C
+
200 -3,000 (4db.)
200 -3,000 (4db.)
+10
15.50
16.50
15.00
8
+10
300 Henries-0 DC, 50 Henries -3 Ma. DC, 6,000 Ohms.
RCOF CASE
Length
Width
1
Height
1
Mounting
Screws
13/32
1 1/8
4 -40 FIL.
7/8 Dla.
Cutout
Unit Weight
12.00
25/64
61/64
1.5 ox.
SUBMINIATURE AUDIO UNITS...SM CASE
Type
No.
14-30
H-31
Pri. Imp.
MIL
Type
Application
Input to grid
Single plate to single grid,
Sec. Imp.
Ohms
Ohms
50"
TFIAIOYY
RC in
Pr _, MA
- Response
2db. (Cyc.)
SM
CASE
H-32
H -33
11/13
1/2
29/32
H -34
4 -40 F11.
H -35
o:.
8
Sirle
plate to line
Single plate to low
impedance
Sin ;le plate -o low
imredance
Reactor
+13
+13
$13.00
13.00
List
0
150-10,000
0
M0-10,000
200
3
?70-10,000
50
1
330- 10,000
+13
+15
13.00
13.00
.5
3)0- 10,000
+
13.00
DC,
4400 ohms.
10.000
TF1A13YY
10,000''
TFIAI3YY
30,000
TF1A13YY 100,000
60
TF1A20YY
Price
62,500
90,000
TF1A15YY
3:1
Length
Width
Height
Screw
Unit Weight
Max. level
dbm
100 Henries -0 DC, 50 Henries -1
M..
6
11.00
ULTRA -MINIATURE UNITS TO SPECIFICATIONS ONLY
ultra- minia-ure unit! are uncased types of extremely small size. They are made to customers' specifications
only, and represent the smallest production transformers in the world. The overall dimensions are 1/2 x 1/2 x 7/I6"
...Weight approximately .2 ouxoes. Typical special units of this size are noted below:
UTC
type
K -1
6949
100,000 ohms to 100
20,000 ohms
type
6
M -14679
Type M -14880
Type
M
ohms...6 MW...100 to 5,000 cycles.
...6 MW...300 to 5,000 cycles.
ohms to 10,000 ohms...6 MW...300 to 5,OOC cycles.
30,000 ohms (.1 Ma. DC) to 3,000 ohms...6 MW...300 to 5,000 cycles.
25,000 ohms (.5 Ma. DC) to 1.000 ohms...6 MW...300 to 5,000 cycles.
Type M-14678
14381
(1
Ma. DC) tc 35 ohms
200 ohm term nation can be used for 150 ohms or 250 ohms, 500 ohm termination cas be used for 600 ohms.
can be used with higher source impeiances, with corresponding reduction in fregic icy range. With 200 ohm source,
loaded response is -4 db. ac 300 cycles.
secondary impedance becomes 250,000 ohms
can
1
5
0
V A
R
Le used
I
C
K
for 500 ohm load
S
T
RE
EXPORT DIVISION: 13 EAST
E
40th
T
... 25,000
...
ohm primary impedance
/J
NEW
STREET, NEW YORK 16, N. Y.
www.americanradiohistory.com
... 1.5
YORK
Ma. CC.
1
3
CABLES:
N.
Y.
'ARLAE
'
Shocking
N_
Since Daven originated the first pie -type
wire wound resistor more than a generation ago,
it has pioneered many innovations in the production of resistors.
Today, only Daven uses a stranded lead wire
to connect the resistance wire to the solder ter-
-r
minal of the Super Davohm Precision Wire
Wound Resistor.
As a result, no matter how much strain,
stress, heat or pressure is applied to the solder
terminal, no accompanying shock is put upon
the fine resistance wire itself, but is absorbed by
the heavy lead wire without adversely affecting
the resistor in any way.
Therefore, Super Davohm Resistors are substantially more rugged than conventional resistors and are able to withstand unusual vibration,
rough treatment and abnormal shocks.
This exclusive Daven feature, plus the many
other quality aspects of Super Davohm Precision
Wire Wound Resistors, makes Daven the leader
in the resistor field.
The Super Davohm line includes resistors
made in accordance with MIL-R-93A specifications, as well as sub -miniature units to give you
the most complete selection of resistors available anywhere. Deliveries can be made to meet
your requirements.
Write for assistance with your problems,
and ask for a copy of Daven's complete, new
brochure on Super Davohm Precision Wire
Wound Resistors.
THE
VENc°
185 CENTRAL AVENUE, NEWARK 4, N. f.
www.americanradiohistory.com

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