september - American Radio History
SEPTEMBER
19
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AmericanRadioHistory.Com
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Left-over moisture is no problem when
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C
The worst of the summer months have passed -but the humidity lingers
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For an ordinary lacquer recording disc absorbs moisture much more
readily than it will give it up. And "left -over moisture," absorbed during
the summer, can spoil many a recording months after the humidity has
fallen below the danger point. So why risk "grey rings" and high noise
level, when you can be sure of faultless recording with humidity-resistant
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AUDIO ENGINEERING
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SEPTEMBER, 1949
www.americanradiohistory.com
AmericanRadioHistory.Com
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*SIGNAL -TO -NOISE RATIO: The
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DISTRIBUTED
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2
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
SEPTEMBER, 1949
D. S.
Potts, Publisher
C. G. McProud, Editor
Louisa 8. DeSoto, Edit. Prod. Mgr.
ENGINEERING
Established 1917
Representatives
Editorial Advisory Board
Sanford R. Cowen, Mid West Sales
342 Madison Ave., New York 17, N. Y.
James C. Galloway, Pacific Coast Sales
816 W. 5th St., Los Angeles 13, Calif.
Dale International Publications, Ltd.
106 Bolsover St.,
London W. I, England
Technical Book & Magazine Co.
Melbourne, C. I.
297 Swanston St.,
Howard A. Chinn
John D. Colvin
Successor to
L. Cahn, Adv. Director
H. N. Reines, Adv. Mgr.
L. B. Devine, Asst. Circ. Mgr.
S.
David Saltman, Production Manager
E. E. Newman, Circulation Manager
RADIO
C. J. LeBel
J. P. Maxfield
George M. Nixon
Winston Wells
S. Young White
CONTENTS
Victoria, Australia
SEPTEMBER, 1949
Vol. 33, No. 9
Editor's Report
4
Letters
6
Book Reviews: Radio and Television
Mathematics, Elenients of Sound Recording
8
Modern School Sotfttd SystemArthur W. Schneider
11
Test Record List
14
New Developments in Logarithmic Amplifiers-C.
I. LeBel
15
Problems in Audio Engineering -Lewis S. Good /riend
Record
18
Revue- Edward Tarnall Canby
20
Audio Engineering Society Section
Convention Highlights
21
21
Employment Register
Lateral Feedback Disc Recorder-G. R. Yenzer
22
New Products
28
New Literature
35
Advertising Index
40
COVER
Light pattern of new Cook Laboratories frequency test record, showing
flat recording characteristic up to 20 kc. Frequency bands are
shown on the curve at left. Insert is a photomicrograph
of the 20-kc grooves.
raxouwcv--.
-
York, N. Y., by Radio Magazineç, Inc., D. S. Potts,
AUDIO ENGINEERING (title registered U. S. Pat. Off.) Is published monthly at New
342 Madison Avenue, New York 17, N. Y. Subscription rates
President: Lawrence LeKashman, Vice Pres. Executive and Editorialfor Offices at elsewhere
$4.00 per year. Single copies 36c. Printed in U. S. A.
2
years:
United States, U. S. Possessions and Canada, $3.00 for 1 year, $5.00
Entered as Second Class Matter July 29, 1948 at the Post Office,
All rights reserved. Entire contents copyright 1949 by Radio Magazines, Inc.
New York, N. Y., under the Art. of March 3. 1879.
AUDIO ENGINEERING
SEPTEMBER, 1949
www.americanradiohistory.com
AmericanRadioHistory.Com
3
EDITOR'S REPORT
TV AUDIO PERSPECTIVE
THE CONVERSION
of television receivers to high
fidelity standards entails a number of considerations
which were not immediately apparent when the
original idea came to mind. Chief among these are the
relation between the size of the performers' images and
the audio level at which the sound is reproduced. Even
with a high quality amplifier and speaker system, with
the naturally fine quality resulting from a correctly designed and aligned FM channel, it is apt to be noted
that when the sound is reproduced at what is a normal level for radio programs the overall perspective seems
to suffer slightly.
It does not seem quite realistic for a baritone who
appears to be from four to six inches in height to fill
a living room with a volume of sound which might be
expected from the singer himself, if he were present. Yet
in a purely aural program, this discrepancy does not
exist, and either singer or orchestra may reasonably be
reproduced at concert hall volume. This effect is more
and more noticeable with the smaller direct view tubes,
and will undoubtedly be an unconscious factor in upgrading the buyer of a replacement TV set to one with
a larger screen. With the 10- and 12-inch tubes being
electrically interchangeable, one manufacturer has already discontinued production of sets using the smaller
size, and the increased picture size is now obtainable for
only a slight increase in cost. Manufacturing economies
due to mass production will naturally lower the cost of
the 16 -inch tube and the additional equipment required
to operate it properly, so that it will become the most
popular size for home receivers, particularly in the console model&
Another difficulty presently noticed is the increase in
studio noises that becomes perceptible when the audio
bandwidth is increased. The continuous movement of
technicians, cameras, microphone booms, and other paraphernalia incident to the production of a TV program
necessarily creates some noise, mainly in the low- frequency range. Consequently, improved low end response of
the receiver audio system and loudspeaker tends to increase the effect of this noise. The condition is not serious,
and even now the better programs are reasonably free
of disturbances of this nature. However, it is true that
larger and better -baffled speakers do make such noises
more noticeable. Greater experience in the production of
programs will minimize this trouble.
Television sound is improving perceptibly- almost
week by week-and program production is making great
4
strides. To reproduce the sound in the home with a maximum of realism, it is becoming more and more obvious
that high -quality audio channels are desirable-including the speaker. The addition of two tweeter horns or
small cone speakers at the upper corners of the picture
area will help the illusion that the sound is coming from
the screen, especially when the large speaker is somewhat
removed from the picture tube, as it is in many consoles
and combinations. While this would increase the cost
somewhat -necessitating the additional speakers and
some means of dividing the frequency spectrum to keep
lows off the high- frequency speakers
would improve
the illusion appreciably.
-it
COMING ATTRACTIONS
We are especially fortunate in being able to offer an
important paper by W. L. Black and H. H. Scott on the
subject of "Audio Frequency Measurements." This paper
will run in two parts, the first appearing in the October
issue. Mr. Black of Bell Telephone Laboratories, and
Mr. Scott whose work on the Dynamic Noise Suppressor
is well known, collaborated on this paper, which was
originally presented at the joint IRE -RMA Spring Meeting in 1948. The subjects covered include the measurement of gain, frequency response, single- frequency harmonic distortion, and noise. The treatment is considered
authoritative, and should become a permanent reference
in the audio field.
Also in the October issue is scheduled an article on
the conversion of one of the more popular TV receiver
chassis to give improved audio quality. The changes are
relatively simple, and are desirable if larger speakers
are to be used with the existing chassis. This model, the
RCA 630TS, was sold in tremendous quantities, as a
complete receiver, and a nearly identical unit is still extremely popular in kit form as supplied by a number of
sources.
CONVENTION TIME
With the beginning of the fall season, it appears that
conventions are with us again. Most important to the audio field is the first annual convention meeting of the
Audio Engineering Society, coupled with The Audio
Fair, of which more elsewhere in this issue. This convention takes place in New York City on October 27, 28, and
29.
The "Greatest Show in Amateur Radio" also comes to
New York this fall, with the ARRL Hudson Division Convention being scheduled at the Ninth Regiment Armory
for October 7, 8, and 9.
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
SEPTEMBER, 1949
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SEPTEMBER, 1949
www.americanradiohistory.com
AmericanRadioHistory.Com
Oceanside, New York
5
e8DDk fil2a,tLecv.a
Radio and Television
Mathematics,
by
Lernhard Fischer, Vice -President in Charge
of the Training Division at the American
Television Laboratories, Hollywood, Calif.
The Macmillan Company, New York. $6.00
A practical handbook which consists essentially of nearly 400 problems typical of
those encountered in simpler design work
on radio, television, and audio equipment.
The author has selected one problem of
practically every type of calculation and
carried it through each step to its solution,
making the process thoroughly understandable. These problems cover the field from
basic circuit components to the more specialized elements in television and electronic
control apparatus.
The discussion of the use of the j- operator
particularly clear, and should prove valuable to the beginner in radio mathematics,
although its presentation is thorough and is
couched in terms which -while readily understandable -are completely accurate. The
formulas required for the various problems
are grouped in one section so that they may
be referred to easily after the instructional
portion of the book has been studied, and
the section of extra problems for practice
provides the reader with sufficient exercise
to familiarize him with the methods of solution.
is
When you find your records sounding fuzzy and worn after a few
playings, in spite of the most modern equipment...
DON'T LOSE HOPE...
Saltre/4
a
Elements of Sound Recording,
by John
G. Frayne and Halley Wolfe, Electrical Re-
Piled& VidaEvery disc bearing the Presto label
has long- wearing qualities built
search Products Division, Western Electric
Company. 686 pages. John Wiley & Sons,
Inc., New York. $8.50.
This book is somewhat remindful of the
earlier "Motion Picture Sound Engineering"
which was produced by the Academy of
Motion Picture Arts and Sciences im 1934,
and which has since been the standard
into it. It will give you 100playings
or more on modern .equipment.
reference work in film recording and the
equipment used in making sound pictures.
However, "Elements of Sound Recording"
is completely up to date, and should definitely be in the library of anyone involved in
any phase of recording.
RECORDING CORPORATION
PARAMUS, NEW JERSEY
Although "Elements of Sound Recording"
-
has a strong leaning toward film recording
with sonic eighteen chapters devoted to this
subject
is still valuable to both disc and
magnetic recordists because the principles
Mailing Address:
P. O.
Box 500, Hackensack, N. J.
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In Canada: Walter P. Downs, Ltd.,
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World', Largest Manufacturer of Instantaneous Sound Recording Equipment
and Disc,
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The authors start with a discussion of
the nature of sound. and continue with basic
chapters on electrical, mechanical, and acoustical circuits with a clear presentation of
the analogy as a means to the solution of
problems arising in the study of mechanical
elements. Tubes, audio amplifiers, network
theory, attenuators, filters, and equalizers are
given short descriptive treatments which are
suitable for reference use.
underlying all types of recording are essentially similar. The book is important as a
general text, and will be of continuing use
as a reference work.
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
SEPTEMBER, 1949
7erc Quality and Performance
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SEPTEMBER, 1949
www.americanradiohistory.com
AmericanRadioHistory.Com
7
WHY WOR-TV
CHOOSES FAIRCHILD
The month of September sees another great landmark in the advance
of television. WOR -TV goes on the air. Taking its cue from over a
dozen years of operating Fairchild equipment at WOR, key station
óf the Mutual Broadcasting System, WOR -TV, one of the most
modern installations, again selects Fairchild.
They know, as do many of the AM, FM and TV stations in the
United States and abroad, that Fairchild recording and playback
equipment is professional equipment. They know that a 14:25 transcribed show, spinning on Fairchild Synchronous Turntables will
sign at exactly 14:25 on the nose. Not 14:29 or 14:21. Exactly 14:25!
TRANSCRIPTION TURNTA8LE
On the
familiar
cording
and film
right is shown
a unit
to WOR -TV, to restudios, radio stations
companies.
Direct to center gear drive.
Instant speed change during
operation.
No slippage coupling.
Highest signal to noise.
No tattletale wow or flutter.
Lip Synchr
Removable front access panel.
Adjustable feet for levelling.
Knee and toe space for
operator.
Increased operating efficiency.
Reduced operating costs.
FAIRCHILD UNIT 524
CUING AMPLIFIER
Unit 635 was selected by WORTV to be installed inside the Turntable cabinets. It is a compact 2
stage push -pull power amplifier. It
supplies a local audio signal to a
loudspeaker or to a number of
headsets in order to monitor or
cue a disk. It bridges across any
low impedance line. Specifications:
±
11/2 db, 70- 15,000 cps.
Gain Control. Tone Control.
Three watts output to a loudspeaker.
cZaffivó
Hobbyist's Plea
ir:
While it appears that your magazine fills
the bill for the professional engineer, it also
goes a great way toward satisfying the needs
of the purely amateur builder who builds
either for the fun of it, or who starts by
attempting to get quality he cannot buy easily and still ends up building forever for the
fun of it. This area -inadequately covered
by the other radio monthlies where perhaps
it more properly belongs -could be covered
by AUDIO ENGINEERING without detracting
from its maturity.
I would like to see a through -going set of
closely knit articles elaborating the basic
fundamentals of audio design and application written for the technically minded layman. Most important, the relevant problems
should be considered individually over time
in a strictly logical fashion.
Without denying the great value of many
separate articles which have appeared from
time to time, I would still argue for a step by- step, highly co-ordinated presentation of
these topics which must be considered in
the design and physical layout of a modern,
high -quality set of audio components. That
such a program would involve repeating
ground already covered in one issue or another is justified to my mind.
Concretely, here is my suggestion. Set
aside the last article each month with a
series of topics to run the gamut of "audiana". Then repeat the cycle in a more advanced way, with more formulas, more details. If perfectly serious, it would hardly
hurt the feelings of your best equipped
reader; indeed, it may help others come that
much closer to his standards.
This is just the sketchiest of ideas. A
year or so of such articles would provide a
base for further expansion, a reference for
more technical specialized articles, and a
centralized set of fundamental notes for
future review. Is there any one place where
the relevant information is systematically collated? There are, of course, many excellent
engineering design texts, and many discussions of practical considerations. But not in
one, nor even in just a few places.
M.
Unit 622 obviates the expensive multiplicity of
equalizers literally forced upon the owner of
sound equipment by the ever increasing number and types of pickups. Operates independent of source impedance; provides equalized
line level output from the turntable; Fairchild
Unit 622 is in use with all modern pickups in
professional services. Vertical; lateral; standard and microgroove pickups -high impedance and low impedance -ONE EQUALIZER
FOR ALL. WOR -TV uses it.
(Note: If Mr. Schwartz is not alone in this
idea, we would be in favor of following his
outline, which accompanied the letter, and
which would be an excellent guide. Ed.)
PI
Hobbyist
Sir:
Your magazine arrived on August 9 at
4 p.m., and before 8 p.m. I had built the
Tubeless Hi -Fi Tuner described. I had been
looking for a good tuner for some time, and
fortunately was able to get the required
coils here in Canada.
I am well pleased with the tuner, although
it separates two local stations -1010 and
1050 kc-with difficulty. However, the other
three come in fine.
Write for complete details and descriptions.
RECORDING EQUIPMENT CORPORATION
8
Schwartz
810 Avenue C,
Bayonne, N. J.
PREAMPLIFIER-EQUALIZER
154TH ST. AND 7TH AVE.
H.
r
WHITESTONE,
L.
I., N. Y.
AUDIO ENGINEERING
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Sinclair Hemingway
189 Millwood Rd.
Toronto, Canada
SEPTEMBER, 1949
f
Magnetic
Mas
The Arnold Engineering Company
offers to the trade a complete line of
Magnetic Materials
PERMANENT MAGNET MATERIALS
Cast Magnets, Alnico
1,
II, III, TY, Y, VI,
XII,
X -900
Sintered Magnets, Alnico II, IV, Y, VI, X -900, Remalloy"
Vicalloy'
Remalloy* (Comol)
Cunico
Cunife
Cast Cobalt Magnet Steel
HIGH PERMEABILITY MATERIALS
Dcltamax Toroidal Cores
Supermalloy* Toroidal Cores
Powdered Molybdenum Permalloy* Toroidal Cores
'Manufactured under licensing arrangements with
r
//)'720Ó/7
Permendur*
WESTERN ELECTRIC COMPANY
g ay oÌ t ese /I/1ogì
e
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THE ARNOLD ENGINEERING COMPANY
SUBSIDIARY OF ALLEGHENY LUDLUM STEEL CORPORATION
147 EAST ONTARIO STREET, CHICAGO 11, ILLINOIS
AUDIO ENGINEERING
SEPTEMBER, 1949
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9
ar
THE QUALITY OF DISC REPRODUCTION?
Ili rnnolulation distortion -present in many
rpea of record reproducers to far greater degree
than suspected- causes "fuzziness" in reproduce
tion, particularly at the higher frequencies. Low
intermodulation distortion is essential for clean
7
I
1
t
INTERMODULATION
DISTORTION
HOW THESE 9 FACTORS AFFECT
reproduction.
?
2
TRANSLATION
FREQUENCY
The reproducing equipment must provide the
correct frequency compensation for the recording
characteristics most commonly used. Since different recording companies use widely varying characteristics, a correspondingly wide choice of
equalization characteristics must be available.
COMPENSATION?
When record groove velocity decreases (as the
stylus moves doser to the center pin) a loss in
high frequency reproduction occurs. To keep this
"translation loss" to
minimum. stylus tip
radius, stylus force and mechanical reactance
must be in correct balance.
LOSS?
8
SCRATCH
A choice of scratch equalization is also necessary
to meet the surface noise conditions of all records.
"Rolloff" of reproducing curves must permit
maximum scratch reduction while retaining as
much as possible of the original material on the
record.
EQUALIZATION?
hile low stylus force is desirable to lengthen life
of records.
frequently
inability of the
the
to track properly
properly at
high frequencies. This, in turn, produces high
intermodulation distortion. Stylus force should
he kept to the lowest value consistent with proper
N
3
STYLUS
FORCE?
4
MECHANICAL
5
OUTPUT?
6
ARM
NOISE
tracking.
The signal-to -noise ratio must not be impaired by
induced noise pick-up in the reproducer or equalizing circuits. Design of the equalizer and repeating coil should minimize hum pick-up from motor
fields or other sources.
PICK -UP?
Fora given stylus force. low mechanical impedance
in the reproducer stylus improves tracking at
Loth low and high frequencies. Both ends of the
recorded spectrum are therefore reproduced with
less distortion.
IMPEDANCE?
UNWANTED
9
n
On lateral recordings, the pick -up unit should not
reproduce the unwanted vertical output which
can result from surface irregularities, turntable
vibrations and riding up of stylus on groove walls.
Conversely, on vertical recordings, the pick -up
unit should not reproduce the unwanted output
caused by lateral stylus motion.
The reproducer arm should not have resonant
points within the spectrum of frequencies norm.
ally reproduced. If the resonant frequency of the
arm is within the range of frequencies on the
transcription or record, the resonant vibration
of the arm will cause a spurious response.
How does the 109 Type Group stack up
against these reproducer requirements?
Western Electric has just issued a 12 -page bulletin
explaining in greater detail the importance of these
nine factors in high -quality reproduction -and showing
just why the design of the 109 Type Reproducer Group
results in outstanding performance.You'll want to have
all these facts when you select reproducing equipment!
CALL YOUR LOCAL GRAYBAR
REPRESENTATIVE
FOR A COPY OF
THIS NEW BULLETIN OR MAIL COUPON
BELOW
RESONANCE?
Western £Jectric
- QUALITY
COUNTS
DISTRIBUTORS: IN THE U.S.
IN n:ASADA-.Northern
Graybar Electric Co.
420 Lexington Avenue,
New York 17, N. Y.
-
Gentlemen: Please send me a copy of Bulletin
T2551, "109 Reproducer Group."
Name
Title
Company
Street Address
City
State
A.-Graybar Electric Co.
Electric Company, Ltd.
L
10
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SEPTEMBER, 1949
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ARTHUR W._SCfiNEIDER*
1..».
Archbishop Stepinac High School. Eggers and Higgins, Architects; George A. Fuller Co., General Contractors.
publicRecent educational advances practically demand the availability of flexible, high- quality,
rethese
fulfills
School
High
Stepinac
address facilities. The system installed in the new Archbishop
quirements with outstanding success.
in the city of
White Plains, in Westchester
County, New York, is perhaps the
most beautiful and most efficient High
School built in this country to date.
This school for boys was named after
Archbishop Stepinac of worldwide
fame, and is dedicated to the advancement and education of boys throughout
the world. In its planning every advantage was taken of up-to -date materials, functions, and equipment.
The sound equipment was supplied by
the Commercial Radio -Sound Corporation, whose engineers designed a
modern, all- inclusive sound system. It
is the purpose of this article to describe
the functions, design, and installation
of the entire system.
Figure 1 shows the overall block
schematic of the system. It will be
noted that there are actually many
separate systems, each an operating
unit of apparatus in itself but which,
together with the main control rack,
constitute a complete integrated and
flexible system capable of facile operation from the master control station
located near the Principal's office.
These systems are basically as follows:
RBCENTLY DEDICATED
1.
Two -channel main classroom system
2.
Auditorium system
3.
4.
5.
Gymnasium system
Cafeteria system
Studio classroom system
Studio Classroom System
The studio classroom system, as
shown on the block diagram and in the
photograph of Fig. 2 with Father Hargrave at the controls, is a 30 -watt
amplifier providing two studio inputs, Cafeteria System
The cafeteria system is a 30 -watt
talkback, and facilities for amplifying
the signals from an AM /FM radio amplifier with one input brought out
receiver. Located in the control room to a microphone station. This system
is used for locally originated programs
is a small metal cabinet containing the
tuner and power supply. This tuner is from a portable phonograph turntable
used for feeding programs into the or for use by the instructor in charge
studio classroom, and can also be used of the cafeteria. The equipment is lofor feeding an auxiliary program to cated in a metal cabinet with flush
trim, the appearance of the complete
the main rack.
Monitoring facilities are provided unit being shown in Fig. 3.
Eight speakers, located in the side
which, together with the talkback facilities, permit complete control by the walls of the cafeteria, give adequate
instructor of "mock" and "real" broad- distribution of all programs without
casts. It is also to be noted that it is an excessive level in any part of the
room.
possible to feed the program originating in the studio from this unit to the Gymnasium System
The gymnasium system is rather
main system. Magnetic recording facilities have been provided for instruc- unique in view of the fact that it makes
tional uses, as well as for recording use of a multiple- speaker installation
talks of visiting dignitaries so they because the problem of illusion is not
may be played back at a later time a serious one, and because the system
through this or any of the other sys- is used mainly for instructional purposes. However, since it is contemplated
tems, or through all of them simultathat one of the principal uses of this
neously.
Fig. 2. Father
Hargrave at the
controls
of the
studio - classroom
amplifier, which
approximates all
the functions of a
normal broadcast
mixing console.
*General Manager, Commercial Radio -Sound
Corp., 570 Lexington Ave., New York.
www.americanradiohistory.com
AmericanRadioHistory.Com
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Fig. I. Block schematic of the entire High School sound system.
I2
AUDIO ENGINEERING
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SEPTEMBER, 1949
system will be in connection with meetings, banquets, athletic exhibitions,
and so on, a multiple installation was
decided on, employing twelve loudspeakers flush in the ceiling and arranged on nine circuits. When tested,
this system proved to be completely
satisfactory. It is possible to place the
microphone on any side of the room,
using with it appropriately located
speakers selected by the nine switches
shown in Fig. 4, so as to provide for
many varieties of lanquets or other
setups. It is also possible to cut off
the central speakers should the gymnasium be used for wrestling bouts,
prize fights, or other exhibitions. It
is to be noted from the block diagram
that master control can feed the speakers with any desired program, or that
a program originating in the gymnasium may be fed to the main control
for redistribution.
Auditorium System
The auditorium system employs a
Fig. 3 (right). Cafeteria system amplifier housing, closed. Fig L (left). Cafeteria
system amplifier, showing various input controls as well as speaker selectiig
switch es.
gymnasium, and cafeteria. It is to be control panel. This includes two Daven
noted that these last three microphone step -by -step attenuators and two ilcircuits were put in as an emergency luminated VII meters. Behind the panel
measure in case any one of the three are the two preamplifiers whose internal
systems involved should fail. For ex- controls are used to equalize the gain
ample, if the amplifier in the cafeteria of each channel. Below this panel is
confour -input amplifier permitting
plug the the classroom distribution switch panel
trol of each microphone circuit inde- should fail, it is possible to
selecpendently either from the amplifier microphone into an outlet in the cafe- with fifty special three-position
telephone-type
location in the projection booth or teria which connects directly to the tor switches. The three
below are used to
from a remote control station located main rack, and set the selector switch on key switches shown
With
of programs
input.
distribution
rack
cafeteria
the
main
to
control
the
in a locked box in the rear of the
audiAuditorium. This four-unit mixer -and- the cafeteria output switch set to the to the cafeteria, gymnasium, and
these switches
master is the RCA MI -4273 type, feed- same channel, it is possible to continue torium. Pilot lights over
with programs in the cafeteria just as indicate that the local systems are in
ing a MI-4288 power amplifier.
easily as with the local system. In this use, and are energized by the 6 -volt
four
This amplifier, together with
back from each
microphone receptacles located on the manner, a main amplifier is used to filament circuit brought
The lower porstage, feeds two MI- 1469 -1425 mul- provide program from and to the cafe- of the local amplifiers.
cabinet is taken up with two
ticellular units located behind decora- teria. Similarly, direct microphone cir- tion of the
-12245 power amplifiers, to-watt
MI
used
in
the
auditorium
and
70
be
cuits
can
of
the
in
the
center
protive grilles
with
the necessary terminal
gether
the
gymnasium.
scenium arch. As with the other sysThe next panel on the rack is the strips for connecting the rack to all
tems, it is possible for master control
Three power switches
to feed the speakers with any desired voltage- amplifier, VII-meter, and gain- external circuits.
program, or it may pick up the locally
originating program and feed it to the
other systems.
Master Control
This is a rack type of construction
selected for its flexibility of operation,
ease of installation and servicing, and
lower fabrication cost. The rack is
shown in Fig. 5. Located in the top
panel is a six -inch MI -12435 accordion edged cone speaker together with a
three -position selector switch on the Fig. 5. Main amplifier
left and a monitoring volume control rack assembly -master
on the right. The next panel has the
control -with the author
AM-FM radio tuner, and below it is (left) and Father King,
the input selector system. Each of the
school Principal.
selector switches is an 18-position, twocircuit, non -shorting switch, especially
designed for this application, and can
connect any one of the program sources
to either of the two channels. These
sources are: rack input receptacles 1
and 2, the Principal's microphone, music room, band room, auditorium system, gymnasium system, Chapel microphones 1 and 2, studio classroom
system, and separate direct microphone circuits from the auditorium,
AUDIO ENGINEERING
SEPTEMBER, 1949
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Fig. 6. Cardinal Spellman addressing assembled guests
at the dedication cerem-
onies, with two system microphones at right and left. Radio station microphones
are in front.
-a
are provided
main key- operated
switch and two auxiliary switches
which are used to energize the two
channels. The type of equipment selected was chosen with the service aspect in view. The voltage amplifiers
are of the plug-in type, and the 70 -watt
power amplifiers are serviced from the
rear-the hinged chassis permitting
complete accessibility without disturbing the amplifier. The 24 -volt plug-in
power supply is used to energize relays in the auditorium, cafeteria, and
gymnasium systems. These relays are
those that cut off the local program
and permit the program from the rack
to come through and bypass the local
amplifiers. The separate loudspeaker
JPAI &coìtd
and other types
of records designed for various
testing purposes are indispensable
to the audio engineer for checking
pickups, equalization, and overall performance of a disc reproducing system.
They are practically the only measuring device which will include the performance of the pickup, and may be
said to be as useful as a gain set or a
volume indicator in other branches of
audio work.
A number of test records are available commercially- doubtless there are
many more which may be obtained
from various sources from time to
time-but those listed below are standard items, and are readily obtainable.
Their uses include the checking the
mechanical performance of record
changers as well as the most common
tests on frequency performance of
pickups, equalizers, and amplifiers, and
in making various acoustical measurements. Unfortunately, no manufacturer
lists a complete "warble- frequency"
record for loudspeaker testing over a
wide range of frequencies, although a
FREQUENCY RECORDS
14
control provided in the Principal's office permits manual selection of either
Channel A or Channel B program, as
well as control of volume. The pilot
light located on this panel is controlled
by a button located on the input selector panel, and the operator at master
control can signal to the Principal
when the circuit is complete for hint
to address selected groups.
The antenna system supplied is a
rather unique one. On a single mast
approximately fifteen feet above the
roof level there are two 300-ohm FM
dipoles, each of which feeds into a
special antenna coupling transformer.
The 300 -ohm balanced antenna line is
transposed into a 50-ohm unbalanced
coaxial line. RG -58/U cable is used to
carry FM signals from the antennas to
each of the two receivers, where a similar transformer is used to transpose
the signal back to a 300 -ohm balanced
circuit. Inasmuch as the antenna runs
have to be in conduit and the FM signals are low in level, this type of transmission circuit was decided on.
For AM signals, a 60 -foot flat top
antenna approximately fifteen feet
above the roof is used. It is coupled
into an antenna transformer to transpose the signal to a 70 -ohm balanced
circuit. This is fed into a distribution
transformer at the first receiver and the
output of this distribution transformer
[Continued on page 89)
fiat
few such records are in existence, and
may be found by diligent search.
At the time of compilation, this list
is believed to be complete for lateral
phonograph records and transcriptions,
as far as possible comprising those records which are regularly in stock. The
audio engineer or experimenter may
well want several of them on hand to
be able to make complete checks of
his equipment.
RCA VICTOR
12 -5-5 (Old No. 84522A) 12 -inch, 78 rpm.
Shellac, DF with 12.5.7 on reverse. Glide
frequency record, 10,000 to 30 cps. Crossover, 500 cps, 1.5 db below CV portion.
Essentially CV above 800 cps, with 3-4 db
dip at approximately 8,000 cps. Buzzer signals at 10, 9. 8, 5, 4, 2, and 1 kc, and at
500, 200, 100, and 50 cps.
12 -5 -7 (Old No. 84522B) Reverse side of
12.5 -5. Two modulated bands: at 78 rpm,
2300 and 1000 cps for 1:00 and 2:15 min.
respectively; at 33% rpm, 1000 and 400
epa for 2:26 and 5:15 min. Frequencies are
held constant to within 0.2 per cent instantaneous.
12-5 -9 12-inch, 78 rpm. Shellac, DF, same
on both sides. Four bands, each one minute.
(1) Unmodulated; (2) 400 cps at 5.9
cm /sec; (3) 1000 cps at 9.6 cm /sec; (4)
Unmodulated. Frequencies held constant to
within 0.2 per cent instantaneous.
12 -5 -11 12 -inch, 78 rpm. Shellac, DF, same
on both sides. Test record to check operation of changers. Contains a landing area
with no lead -in spiral, at least one unmodulated normal pitch groove at the outside,
and a steep blank spiral into a normal pitch
groove at the inside which joins a lead-out
and eccentric groove.
12-5 -13 10-inch, 78 rpm. Shellac, DF, same
on both sides. Same as 12.5.11, except for
checking operation with 10 -inch records.
12 -5 -1S 12-inch, 78 rpm. Unfilled Vinyl, DF.
same on both sides. Four warble frequency
bands of thirty seconds each, with sweep
rate of approximately 5.5 cps. Frequencies
are: 500.2500 cps; 750-1250 cps; 1250 to
1750 cps; 1800-2600 cps.
12 -S -17 10 -inch, 78 rpm. Shellac, DF, same
on both sides. Same as 12.5.15 except that
each band is seven seconds in length.
12 -5 -19 (T- 24841) 12 -inch, 78 rpm, Unfilled
Vinyl, SF. Frequency bands, CV above 800
cps; turnover 500 cps, with level at 500 cps
1.5 db below normal level of approximately
8.6 cm /sec. Bands: ten seconds each, 10, 9.
8, 7, 6, 5, 4, 3, Z and 1 kc, 800, 500, 300,
200, 100, and 50 cps; 1000 cps down 2 db
from normal, and 10 kc band at inside of
record.
12 -5 -21 (T-2913) 12 -inch, 78 rpm. Unfilled
Vinyl, DF, with 12-5-23 on reverse. For test-
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[Continued on page 401
SEPTEMBER, 1949
New Developments in Logarithmic
AmpliFiers
C. J. LeBEL*
Fig. I. Meter scales which result from logarithmic amplifier and linear
vacuum tube voltmeter.
A description of a novel method of converting an audio signal
to an output voltage which is proportional to sound level.
A LOGAIITII'IIC AMtLIFIF.a the output voltage is equal to the logarithm of the input voltage, independent of frequency or input voltage.
The logarithmic effect may be secured
in the amplifier stage itself, or in the
interstage coupling circuit. While the
definition applies to both a.c. and d.c.
amplifiers, basic fields of usefulness
seem to lie chiefly in the former.
We can think of a logarithmic amplifier as a device with an output in
db for a normal linear (voltage) input.
Applied as a converter between any
linear -scale indicating or recording device and a source of voltage, it enables
an ordinary v -t voltmeter or oscillograph to read db on a linear scale.
A good example of this lies in the
measurement of acoustical reverberation time. A studio or auditorium is
filled with steady sound, the tone is
shut off, and the sound decay is measured. Reverberation time is defined
as the time for the sound intensity to
drop 60 db. As a practical fact, it is
recognized that only the first 30 or
40 db of decay are important, and that
any echoes, slap, or other non-uniformities during this interval are very
significant. A decay curve, which has
very pronounced irregularities in this
most prominent portion, is likely to
prove characteristic of studios 'which
are bad sounding or difficult to use
properly. While 100 db per second recording speed will care for the basic
sound decay, a much higher speed is
necessary to reproduce the fine structure-perhaps 1000 db per second. Direct writing oscillographa are available
that will follow a 200-cps sine wave
fairly well; combined with a 50 dL
N
!
*Audio Instrument Co., 1947 Broadway,
New York 23, N. Y.
AUDIO ENGINEERING
tion, but rather that it supplement the
VU meter at lower levels. The same
logarithmic unit may be used to feed
a recording oscillograph (via a suitable
amplifier) for an accurate permanent
chart of program levels. For training
purposes a chart record of this type
should be invaluable.
A similar application is that of
measuring or recording any phenomenon which is varying over too wide a
range to be handled properly by an unaided linear-scale device. Continuous
measurement or recording of noise
without frequent use of a range- changing switch calls for a scale range of
30 to 50 db, which can be provided most
easily by a log element. If multichancilloscope.
nel recording is necessary, such as in
machine noise analysis with quarter octave band filters, an arrangement of
this sort will provide high-speed recording at less than a third the cost
of, and at a tenth the size and weight
of a whole group of high -speed level
recorders.
Securing the Logarithmic Effect
A wide variety of nuans is available
for securing a logarithmic characterMAGNETIC FLUX
istic. The earliest and virtually the only
Fig. 2. Magnetic structure of meter method repeatedly mentioned in the
with shaped pole pieces.
literature is the use of variable bias
on the grid of a variable -mu tube, a
Observing and recording program species of a -v-c circuit. Perhaps the
levels form other applications of loga- best work on this type of circuit was
rithmic indications. The standard VU done by F. V. Hunt in a paper pubmeter will indicate maximum level lished in the 30's. He fed the amplified
very well, but it shows nothing about signal back to the grid through a recthe lower levels to which many pro- tifier. For a wide db range he used
grams drop much of the time. The several tubes and rectifiers, with one
new technique provides a volume in- taking over as the previous tube reached
dicator with 50 db range -one which cutoff. By virtue of careful selection
will indicate minimum as well as max- of tubes and individual circuit adjustimum levels. It is not suggested that a ments to fit the tubes a wide range of
levels could be covered. On the other
50 db meter be used for peak indica-
logarithmic element, they make possible
recording at 5000 db per second with
ample margin of safety. High -speed
level recorders heretofore generally used
have had a nominal writing speed of
not over 600 db per second. Being
servo systems, and using tapped potentiometers for the logarithmic effect,
some question may be raised whether
their true following speed was not
considerably under 600 db per second.
By using a sufficiently slow sweep
rate, a cathode ray tube with a P -7
slow decay phosphor, and a timing
circuit to control the loudspeaker, it
is possible to examine reverberation
characteristics on a cathode ray os-
SEPTEMBER, 1949
www.americanradiohistory.com
AmericanRadioHistory.Com
15
hand, the accuracy of result depended
entirely on tube characteristics, so
that a change in tubes had to be
accompanied by considerable testing
and adjusting.
Another method of indicating in db
is to feed the amplified and rectified
Fig. 3. Circuit using Maxwellian distribution of emission velocity for logarithmic amplification.
tiplier setting at the bottom of the
meter scale by as much as five to ten
db, a good indication of the possible
error.
Another method that crops up periodically, involves the use of the Max wellian energy distribution of vacuum
tube electron emission. A resistance of
ten megohms is placed in series with
the control grid (Fig. 3) and the input
signal of the logarithmic tube is rectified so that the grid is driven only
positive. Considerable effort was spent
on this old idea, only to abandon it
finally for these reasons:
1. The linearity of the logarithmic
relation is only approximate; the curvature is enough to require a special
meter scale.
signal to a d'Arsonval meter movement
whose distribution of magnetic flux
in the air gap is non -uniform, as shown
in Fig. 2. this can be achieved by using
especially shaped pole pieces, a method
employed in several v -t voltmeters. The
scale law can be followed exactly, but a
20 db range seems to be the maximum
obtainable. This construction has been
used for indicating meters, but not
for recording meters, due to practical
difficulties. A meter movement of this
type is satisfactory for steady signals,
but not for transients such as reverberation, speech, music, or noise, because the damping factor changes
with meter reading. At the lower part
of the scale, the movement is over damped and very sluggish; at the upper
part of the scale the damping is insufficient and the pointer will overshoot
badly. On program material a reading
taken at the top of the scale will fail
to check one taken with another mul-
greatly attenuates the higher frequencies. For example, an attenuation of 3
db is reached at only 1000 cps, and
it increases rapidly above that frequency. If this happens in the indicating
vacuum tube voltmeter, it is not serious; but if we try to use such log
circuit to feed an external a.c. oscillograph- amplifier, the attenuation is excessive.
4. The input- output curve changes
rapidly with small changes in tube
heater voltage, and careful stabilizing
is necessary.
On these grounds it was felt necessary to abandon the method, and look
for another.
Logarithmic Materials
The preferred method is to use a material whose resistivity varies inversely
with the current through it. The preferred relation is E = If log I, where
E is the voltage drop across the material, I is the current through it, and k
is a constant which depends on the
dimensions of the material and its
specific resistance at a given current.
Since d.c. amplifiers are a nuisance,
it is highly desirable that the mateFig. 4. Output waveform of logarithrial be usable in small cross-section,
mic circuit at various output voltages so that the shunt capacitance will not
with sine wave input.
be high enough to prevent its use on
a.c. if desired. Incidentally, any logarithmic material distorts the waveform,
2. To achieve this slightly curved
relation over even a moderately wide for it takes the logarithm of the input
db range calls for the use of a very voltage instantaneously throughout the
large grid resistance-of the order of voltage cycle. The distortion varies
ten megohms -and hence about three with input; at low input the wave aphundred volts driving voltage. To secure pears semicircular, as shown in Fig. 4,
this undistorted output from an am- whereas at high input the wave becomes
plifier stage takes rather special de- practically square.
When we come to study materials,
sign or high plate voltage.
we find that many semi -conductors
3. The high grid resistance combines with the grid capacitance of the have logarithmic characteristics, with
tube to form a low -pass network which great differences in the range over
which they exhibit the effect accurately. In the worst materials the log
Fig. 5. Error produced by slight curvature in logarithmic relation.
range will barely cover 10 db; in the
best it will extend over 50 to 70 db.
Some varieties of copper oxide and silicon carbide show interesting properties
in this respect.
It is desirable to adjust the circuit
characteristics so that the log relation
is followed perfectly. A slightly curved
characteristic (Fig. 5) will require a
hand drawn meter scale, or result in an
error of as much as 5 db if a linear
scale meter is used.
Operating Conditions
When using a perfectly logarithmic
material, the relation E = IC log I
requires that the circuit be such that
the current is not significantly affected by the varying resistance of the
material. A series resistor must be used,
with a value which is high compared
to the resistance of the log material
at the minimum working voltage. If
16
AUDIO ENGINEERING
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SEPTEMBER, 1949
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Fig. 6 (left). Oscillogram of radio program, showing ease of observing range of levels covered. Fig. 7 (right). Acoustical decay curve, with dotted line showing mean slope of sound level from maximum to noise. Time indicated (.34 sec)
represents drop of 40 db, but reverberation time is based on drop of 60 db. Thus, reverberation time is 0.51 sec.
carried too far, this leads to extremely
high circuit loss, and a series resistance which is so high that stray capacitance has some effect at the higher
frequencies.
Rather than use excessive series resistance, the characteristic may be linearized at small inputs by applying
suitable bias. The bias voltage should
be accurately stabilized, for too much
bias is as bad as too little.
Using the Logarithmic Effect
In using a logarithmic circuit a number of problems must be overcome to
retain the accuracy of the relation.
These revolve around the input amplifier, the output circuit, the meter
circuit, and use with external oscillographs.
Any amplifier used between the voltage to be measured and the logarithmic
circuit must be extremely linear in its
input -output voltage relation over the
complete working voltage range, or the
overall log-law conformance is injured.
When we ask instrument linearity of
an amplifier circuit over a 40 or 50 db
range, we call for rather high grade
design. It is simply not possible to take
any amplifier off the shelf, and expect
it to fulfill the linearity requirement;
an amplifier of instrument quality is
called for. Commercially, this practically compels combining log circuit and
input amplifier in a single unit.
If an external circuit is to be fed
from the output of the log circuit, an
isolating amplifier must be used to
avoid shunting the log output with a
load and injuring its accuracy. This
amplifier must be linear over the full
voltage range, or the log accuracy is
destroyed. More difficult yet, it must
be done over a wide frequency range,
for the output of the log circuit is a
square wave. If the fundamental frequency is 15 ka, then the output amplifier should be good up to 100 or 150 kc.
Finally, the voltmeter which measures the output of the log circuit must
be of the vacuum -tube type, to avoid
AUDIO ENGINEERING
loading, and must be of wide frequency
range to retain accuracy as the waveform changes with level.
The wide range of system levels to
be handled imposes strict requirements
on circuit noise. For example, a logarithmic meter designed for a 50 db
range, and with a full scale sensitivity
of one -tenth of a volt, reads a voltage of
70 db below one volt, or approximately
-68 dbm in a 600-ohm circuit, at the
lowest part of the scale. This will
show up poor filtering or unremoved
line fluctuation in very strong fashion.
Again, we find it expedient to build
input amplifier and log circuit as a
unit.
with Oscilloscopes
and Oscillographs
Use
In view of the wide frequency range
and instantaneous action of a properly designed log circuit it may be
desirable to feed its output into an
indicator with faster response than that
of even a good volume- indicator meter.
Since the log circuit output amplifier
delivers a.c., it may be fed into a
standard cathode-ray oscillograph to
read instantaneous peaks visually, or
to be photographed on a moving film.
Fig.
8
Bias
circuit
for logarithmic
element.
10,000
LOG.
ELEMENT
INPUT
-
OUTPUT
0
BASIC CIRCUIT
22,000
OUTPUT
INPUT
BIASED
If the material is not varying at so
rapid a rate that a cathode ray oscillograph is necessary to follow the variation, the much more convenient direct
writing oscillograph is available. At
least a half dozen manufacturers can
supply these units, which can follow
a sine wave of up to 100 or 200 cps
with good fidelity. They can therefore
follow a signal variation within Al
seconds with ease, and write the result
directly on a paper chart. If program
level is to be followed, the signal may
be rectified and applied to the oscillograph galvanometer. The same method
may be used when recording acoustical
reverberation curves. The recording
speed can be reduced by shunting a
capacitor across the galvanometer
coil if it is desired to match the speed
of a VII meter for program recording
or similar purposes. Figures 6 and 7
show examples of log amplifier applications with two types of measured
sound levels.
There is an intermediate class of
recording where the speed of the direct- writer is too low, and the speed
of the cathode ray tube is not necessary. For such work photographic recording oscillographs of the Duddell type
are made by a number of manufacturers, recording up to 10 kc, on film
or paper of any length from a few inches
to hundreds of feet.
Both direct- writer and Duddell type
oscillograph are inherently fairly linear,
and a logarithmic circuit is necessary
to enable them to record any phenomenon varying over a wide range of
amplitude. Incidentally, the same log
action will protect the oscillograph or
indicating meter from violent overloads, for when a strong signal has
passed through the log circuit, the galvanometer sees not the overload, but
the logarithm of it. Thus a ten -fold
signal overload becomes a two -fold ratio at the output of the log circuit, and
a hundred -fold signal overload becomes
CIRCUIT
[Continued on page 45]
SEPTEMBER, 1949
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LEWIS
S.
GOODFRIEND*
Part V. A study of sound generators.
must necessarily
include a study of the principles
involved in the generation of
sound whether from an original source,
or as a reproduction by means of some
form of electro-acoustical transducer,
such as a loudspeaker. In the previous
article, considerable space was devoted
to the wave equation and to its derivation, and before continuing further it
is desirable to derive the simplified
equation for the intensity of a sound
wave as an illustration of the math matical methods used. The general
form of the equation for intensity is
ANY STUDY OF SOUND
1
-21.2
p° C3
x2
a2
Multiplying the numerator and denominator by c/c -which is equivalent to
'Rangertone, Inc., 71 Winthrop St.,
Newark 4, N. I.
r0111
01
multiplying by 1 -gives
21.2 pe
h2
02
v
/\
C
2w2 ps c4 02
ñ2c
c
Then, by substituting
in the numerator,
Per/ pa for
c2
Returning now to the radiation from
a plane piston in an infinite wall, let
us compare the radiation pattern for
the piston to that for an ideal point
source. It will then be possible to ex-
amine the pattern for the loudspeaker.
While the radiation from a plane cirX2 c pat
cular piston in a wall is almost identiThe terms may now be rearranged, cal with that from a point source,
actually there are several differences
giving
in the respective radiation patterns.
2w2 o2
1
72
(Pe2
I
However, these differences are small
a2
ps C
at long distances from the piston and
The part in the brackets is equal to at low frequencies, as shown in Fig. 1.
the effective sound pressure P. We now If the wavelength of the sound being
have a simplified form of the equation radiated is less than four times the
for intensity expressed in terms of two diameter of the piston, the pattern
constants for the medium-density and narrows down and the intensity along
wave velocity -and the effective sound the axis perpendicular to the center
pressure
of the piston is much greater than at
an angle off to one side. For the case
of the loudspeaker it will be noted that
the curve shown in Fig. 2 is similar,
with the loss at 90° being about double
that for the piston of the same diameter. This is the result of a conical
surface radiator in the loudspeaker
and the fact that the cone is not absolutely rigid. However, in working problems in sound distribution it is not
illogical to assume that the loudspeaker
will behave as a 'plane piston, and for
so
a rough estimate of the distribution at
e
low frequencies, the point source treatment may be used. The computation of
the high frequency case is not simple,
and the published curves for the distribution of sound from pistons are of
great value here. In order to overcome
the normal concentration of sound
along the axis at high frequencies,
I=
-
21.2 pe
Pet y2 a2
L
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*AIAA
(above). Polar pressure radiation
pattern for a plane circular piston in
an infinite wall. The piston is small
compared to a wavelength and the
pressure was measured at a long distance from the piston.
Fig.
I
60
(right). Polar pressure radiation
loudspeaker in an infinite baffle.
The diameter of the speaker is small
compared to a wavelength.
Fig.
for
18
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a
90
161,51.14
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90
SEPTEMBER, 1949
audio engineers use multicellular horns
or directing vanes which help to distribute the energy more evenly. In addition it is known that a good lowfrequency unit is seldom efficient as
a high -frequency reproducer. Therefore, a separate high frequency horn
designed to have a high efficiency and
good distribution pattern is not a
whim of the manufacturer or the theoretician, but the logical solution to
two problems.
Acoustical Dipole
If there are two point sources of
sound spaced by an infinitesimal distance and radiating 180° out of phase,
we have what is known as a dipole or
doublet source of sound. For purposes
of analysis it is also possible to use a
small spherical source, but instead of
pulsating, as in the ease of the point
source, the sphere oscillates back and
forth. The radiation from a dipole is
not uniform in all directions, but is
maximum along the axis through the
two points or on the axis along which
the oscillating sphere moves, Fig. 3.
AXIS OF OSCILLATI0I
AND
MAXIMUM PRESSURE
not be dealt with here, as they enter
into audio only in the design of special
instruments.
Mechanical Vibration and Sound
Generators
Having examined the various forms
of radiation most common in the audio
field, let us turn our attention to the
generation of sound waves by considering the application of some perturbing
force to strings, pipes and plates. It
shall be assumed that the reader is
familiar with some of the fundamentals
of physics or will consult a physics
text. The generation of harmonic oscillations may be studied by taking an
ideal, frictionless case of the simplest
mechanical vibrating system, a spring
and a weight, Fig. 4. The spring is
fastened at one end to a wall, at the
other end to a ball which rolls on a
perfect bearing. It is found from physics that if the weight is pushed toward
the wall and then released it will oscillate back and forth, and the frequency
of oscillation is dependent only on the
mass of the weight and the stiffness
or compliance of the spring. (Stiffness k
is the reciprocal of compliance C.)
The equation for frequency is
This is the case of the loudspeaker when
not in a baffle of any kind. The equa-
tions for the radiation from the point
source and the dipole differ in one important respect. Radiation from a point
source varies directly with the square
of the frequency, and that from the
dipole varies as the fourth power of
the frequency. This means that the low frequency response of a loudspeaker
outside of a baffle drops much more
rapidly than that of a speaker in a
baffle.
The phenomenon associated with a
point source can also be associated with
a loudspeaker in an infinite baffle or
a wall. However, if the speaker is in
a finite square, flat baffle there will
be some frequency at which the wavelength of sound is long enough so that
the sound diffracted around the edges
of the baffle travels one wavelength
before reaching the front of the cone.
At this frequency, destructive interference (cancellation) will result. Below this frequency the system acts in
a manner similar to a dipole source,
while above, it will act in a manner
similar to a point source. Further information on this subject will be found
in the references. Although there are
other ts-pes of munnl source., they will
AUDIO ENGINEERING
FRICTIONLESS
BEARING
SURFACE
WEIGHTLESS SPPMJ
K
STIFFNESS
Fig. 4. The ideal, frictionless, case of
a spring fastened
to
rigid wall.
weight and
a
a
Air Column Generator
The next generator to be examined
is the air column. Fundamentally the
where k = stiffness in dynes per cm. air column is
not a sound generator,
m = mass in grams.
but a resonator for the sound made by
This frequency is called the natural a vibrating reed, double reed,
or edge
frequency of vibration of the system, tone. Organ pipes, clarinets,
trumpets
and as defined by the Proposed Ameri- and trombones are a few of the instrucan Standard is "a frequency of free ments that use this method
to produce
oscillation." In other words, the natu- amplification of the sound
generated
ral frequency is the frequency of vibra- by one of the three
methods named.
tion of any system which is excited The usual example-the organ pipe
by a small perturbing force which is will be discussed here.
When a sound
then removed. For the practical case wave travels the length of a tube which
of a plucked string the natural fre- is terminated by a closed
end, it is
quency may be the fundamental or any reflected back to the other
end of the
harmonic, the fundamental being ex- tube. If the wavelength of
the sound is
pressed as
equal to four times the length of the
tube (the tube is then said to be a
/ V1 v/ Tm
quarter-wavelength long) the wave
will be reflected back to the transmitwhere f = fundamental resonant fre- ting end in the correct phase to reinquency in cps.
force the original wave and we have
l = length of the string be- the case of a standing wave in a tube.
tween supports in cm.
It is also possible to have a standing
T = tension along the string wave in the tube for any wavelength
in dynes.
whose frequency is an odd multiple of
m = mass per unit length in the fundamental frequency.
grams.
In the case of the pipe with the far
If a sinusoidal driving force is now end open, standing waves will exist at
applied to either the string system a frequency whose wavelength is twice
or the weight-spring system at the the length of the pipe or at any mulresonant frequency and in phase, tiple of this frequency. Therefore it
standing waves are set up in the sys- may be stated that the tone produced
tem. Actually the term "standing wave" by a closed pipe will contain only the
comes from the case of a wave that is odd harmonics of the fundamental
transmitted down a string, pipe or bar, while the tone of an open pipe will
and is reflected so as to reinforce the contain all the harmonics.
next wave cominç from the transmit[Continued on page 461
1
/
2rß
Fig. 3. The oscillating sphere moves
transversely along the axis, which is
also the axis of maximum pressure.
ting end. When standing waves are
set up in a vibrating system the amplitude of the vibrations is likely to increase, being limited by either the resistance forces within the system or
the amplitude at which the system will
destroy itself.
When the string is excited at some
frequency other than the fundamental
it will produce the fundamental and
the harmonically related overtones up
to and including the exciting frequency,
and some of the higher overtones. In
musical instruments it is phases and
relative intensities of these overtones,
in addition to the sound box amplifier,
that greatly affect the quality or timbre
of the instrument. Without any sort
of sound box the note from the string
would be almost inaudible.
k
m
-
SEPTEMBER, 1949
www.americanradiohistory.com
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19
HONORED FATHER, who is a great
story teller (the kind of story that
grows about 27 per cent at each
telling) accidentally got me started on a
bit of random speculation, which will be
elaborated herewith. His story was about
the nice old gentleman who was a bit harder
of hearing than he quite realized. He was
finally persuaded to acquire one of those
new streamlined hearing aids. It worked
too, and he found himself catching things
he hadn't for years. Didn't like the gadget
too much, though. "Trouble is," he said,
"I come up to meet these nice young women
and all I keep hearing is their tummies
rumbling."
The more humorless among us may want
to question that on strictly scientific grounds
-but
the fact is that hearing aids are
bound to give a slightly distorted earview of the wearer's surroundings. Not only
the usual forms of electronic distortion, if
any, or amplitude distortion (unnatural vol.
urne, as the hearer receives it in the brain;
or perhaps a sound inadequately compensated for the peculiar curve of the ailing ear
-cf. Atmto ENGINEERING, July 1949) but
-and this is my point of departure
hearing aid is a monaural device. That constitutes the most enormous distortion of
normal hearing that I can imagine.
Now I haven't consulted anybody about
this little idea and so if perhaps the hearing aid industry has long since gone into
the problem, my immediate apologies. I
am sure that the rest of us, in any case,
have seldom if ever thought of it. And I
have yet to lay eyes or ears upon a dual
hearing aid, which is what I'm wondering
about. A two -channel, two -miked, two eared device that would give a good approximation of binaural, i.e. normal, hearing.
Ever since, in casually wondering about
binaural problems in the recording of music,
I hooked up a hand mike through an amplifier to one of those huge, padded earphone sets (surplus from Army tanks), then
walked about my quarters, making ordinary
noises like footsteps, tapping things, rattling
china, the mike acting as my ear,
I've been having monaural nightmares. The
shock of this "monaural" hearing (actually,
both ears were hearing, but both heard
exactly the same sounds) substituted directly for the binaural, was hardly believable.
As has been pointed out here before, the
most immediate apparent effect of the substitution of monaural for binaural hearing
is an enormous increase of liveness. (Hence
the dead radio studio, to compensate.) An
ordinary apartment kitchen in operation
with water running, pots and pans clanking
slightly and the like- sounds with this set-
-a
-
279
20
W.
4th St., New York 14, N.Y.
EDWARD TATNALL CANBY*
up as though it were operating in one corner
of an all -tile indoor swimming pool! Tap
two pot handles together and the echoes
resound -this in a room that a moment
before had seemed perfectly "normal" to
your two ears. Dangle yourself and mike
out the window, on a busy city street, and
you hear the most astonishingly cavernous
sound, as though your home opened directly
into Mammoth Cave, somehow equipped
with busses and trolley cars. A few moments
with this experiment, which I advise all
recording enthusiasts to try, will teach
more of the difference between monaural
and binaural sound than a month of Sunday reading.
Unfortunately, I still have my hearing. It
was reasonably normal, at least, at the 1939
World's Fair testing station. I haven't tried
a hearing aid. Don't actually know how it
sounds, to the deaf. Any sound is a lot
better than no sound. But even so, I can
now imagine some of the effects that the
deaf may have to get used to, monaurally!
T can see
that deafness in only one ear
might be compensated for, so that the two
ears were again working in a reasonably
normal manner, so to speak. I can also see
that a binaural effect would be out if one
ear were entirely gone.
Since I am speculating high, I'll by -pass
the slight matter of convenience -of having
to wear a button in each ear-with the
philosophical reflection that after all you
can only look at one side of a person at a
time - Might look a bit silly, I admit, to be
found equipped on both sides. People no
doubt would ask you whether one was for
hearing to the right and one to the left,
and why not one on the forehead for
straight ahead. It would be like wearing
socks of different colors or a wrist watch
on each arm. People might stare. But with
all this, it a binaural aid worked, if it gave
better hearing, I'm betting some brave souls
would try it, and memorize a convenient
spiel to explain a hundred times a day
what "monaural" means.
My speculation, entirely untested, is that
a binaural aid, with two complete channels,
each adjusted and compensated to match
ite particular ear, a common, locked- together
volume control that would maintain the
loudness relation between the two (loudness,
not intensity) might give an extraordinarily
satisfactory sound compared with any
known monaural aid, working by itself.
Details would be quite tricky and, no doubt,
results would vary greatly with the type
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...
what
already noted. Still
say?
Another point that, indirectly, led me to
all of this is the great difficulty with any
other type of binaural sound set -up, the
necessity for separation of the two sound
channels so that each goes only to one ear
and there are no leaks to the other ear.
The only satisfactory way of doing this in
any sort of reproduction is to use earphones.
A system where open speakers are set up
at some point away from you is bound to
introduce a very large leakage, both ears
hearing a good slice of both channels, the
listener then quite literally not knowing
his left from his right. Worse, there are
problems of phasing, since the out -of -phase
arrival of sounds in the two ears has a
vital part in binaural hearing. With earphones all of this is taken care of. Sounds
arrive electrically at the ear itself and the
phasing of the two microphone sources is
preserved. The phones themselves insure
separation of the two channels.
But who wants to wear earphones these
days to lister to music or to watch a movie?
That's going back to the first juke box,
the "phonograph parlours" of the 1890's,
with its dozens of snaky tubes, held to the
ear. Barring some form of stereophonic
sound, there is no 100 per cent solution that
I can see to the problem of separation of
channels except the dual 'phone -and thus
what is a disadvantage for binaural reproduction becomes a fine advantage in the
hearing aid, which can hardly do other
than separate the two channels, exactly as
desired. ft's a natural.
It is to be noted that I have not so far
mentioned the usual feature of any discussion
of binaural hearing, the perception of direction- It is easy to think that the gain
in this respect with binaural over monaural
hearing is the most important noticeable
factor. I assure you it is not. And particularly with the hearing aid. Unless you are
blind as well as deaf, you will seldom be
bothered by any acute failure of direction
sense with a hearing aid, I'd guess. The
tie -up between eye and ear is so sensitive
and quick that binocular vision plus monaural hearing is plenty adequate. (Perhaps
a one -eyed person with a monaural hearing
system might get pretty balled up-but this
begins, somehow, to remind me of the famous
New England cows with the legs on one
side shorter than on the other so they could
stick to the hillsides. Traffic of course, always moved to the right.) No, direction
perception is a secondary matter as one
consciously compares one -eared and two eared hearing. True, the physical basis of
all that happens is in the last analysis a
matter of direction perception. But as we
hear the sound, the conscious effect of mon[Continuevl on poor 3(0
of deafness, as
Y
e
SEPTEMBER, 1949
r
4
AUDIO
engineering society
Containing the Activties and Papers of the Society, and published monthly as a part of AUDIO ENGINEERING Magazine
OFFICERS
C. J. LeBel, President
Audio Engineering Society,
Box F, Oceanside, N. Y.
C.
NI
A.
--nan
Rackey
C
D." ^
Executive Vice -Pres.
S- --=ery
- :
Western Vice -Pre.
John T. Mullin.
Treasurer
Ralp' A. Schlegel
CONVENTION HIGHLIGHTS
A program of considerable interest is Audio Fair Stresses Sight
being planned for the technical sessions and Sound Demonstrations
of The Audio Fair, which will be sponNo exhibit of audio equipment can
sored by the Society for presentation
be
complete without giving the visitors
at the Hotel New Yorker in New York
an opportunity of hearing the equipOctober 27, 28, and 29.
it
Highlighting the many papers to be ment, in addition to that of seeing
this
For
its
operation.
and
observing
on
magnetic
given will be a session
recording which will consider the ex- reason, The Audio Fair was conceived
need, and the
perience which has been gained during as a solution to this
has
recent years in the relatively new re- method of presenting the exhibits
by both manufacturers
lauded
been
in
the
Authorities
medium.
cording
and engineers alike.
field will discuss several phases of the
Departing completely from the more
art with particular stress on problems
which consists
which have been encountered and ap- usual form of exhibit
The
plications to which magnetic recording of many booths in an auditorium,
on a single
be
held
Fair
is
to
Audio
adapted.
has been successfully
New Yorker, with
The present status of magnetic re- floor of the Hotel
having separate rooms in
cording standards will be reviewed, par- exhibitors
their
ticularly as regards interchangeability which to show and demonstrate
sixth floor of
and uniformity of performance, to be equipment. The entire
is to be devoted to the exfollowed by a summary of present the hotel
and
those attending will actuhibits,
standards. In another paper, the effect
able to hear the equipment
of the lack of adherence to standards ally be
already set up and resultant problems being shown.
Banquet Features Loudspeaker
will be aired.
Speed regulation in magnetic record- Comparisons
ing will be discussed from the standThe principal feature of the banquet
points of both timing and flutter, or of the Society, to be held on the eveaverage and instantaneous speed. The ning of October 28, during the contype of drives now in use and projected vention, is a comparative demonstraare to be considered.
tion of loudspeakers presented in true
In addition to rounding out the pro- "A-B" fashion. Using high -quality
gram with a presentation of methods magnetic tape with live recorded proof duplicating magnetic tapes, other pa- grams involving classical and popular
pers on new magnetic developments are orchestral, piano, vocal, and speech
planned.
sections, and using the same amplifier
At another session a symposium on equipment throughout for each test,
audio testing methods is to be held, the speakers on exhibition will be
with both equipments and methods of demonstrated one by one for the edioperation to be described. Among the fication of those who attend the banfactors to be discussed by a panel of quet.
experts will be frequency characterEach person attending will be given
istics and harmonics, intermodulation a card on which the various louda n d cross -modulation measurements, speakers will be listed by an identifyand methods of measuring transient ing letter. This card will provide colresponse means of pulses and square umns for each type of program materwaves.
ial, and the listener may score the
The exhibits of manufacturers at performance as the speakers are demonThe Audio Fair promise to cover the strated. Following the tests, the listenentire field of audio equipment, with ers will be informed as to which
the roster resembling a listing of the speakers are designated by the letters,
major manufacturers.
thus giving the listener an opportunity
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arrive at his own opinion in an
unbiased manner. Since the demonstration is solely for the entertainment of
the listeners, the score cards will not
be collected. Consequently the test cannot be considered a sampling of lietener preferences.
The banquet will also feature the
installation of newly elected officers,
who will begin officially their 1949-50
year of duties in the Society.
to
Employment Register
Positions open and available personnel may be listed here at no charge to
industry, or to members of the Society.
For insertion in this column, brief announcements should be in the hands
of the AES Editor before the tenth of
the month preceding the date of issue.
Address replies to AES Editor, Audio
Engineering, 342 Madison Ave., New
York 17, N. Y.
Technical Public Relations man, with
wide experience in publicity, brochure production, press relations, etc., especially in
audio work. College graduate, 30, married,
presently employed. Will consider part -time
employment. Box 91.
Audio Engineer, with manufacturing,
design, development experience in disc, film,
and magnetic recording and reproduction
and in sales engineering for recording equipment desires to change present position, held
10 years. Age 33, married, university graduate in engineering. Prefer New York area,
but willing to travel. Box 92.
Audio Engineer, BSEE 1936. Section
head at govt lab; 8 years applied research,
analysis, and development in electronics,
electro-acoustics, sound recording and reproduction. Desire position in private industry
in audio or electronics, northeast preferred.
Age 33, married. Box 93.
Music Engineer. Grad. RCA Institutes;
MA in Music (Harvard). Excellent background in audio and music. Seeking position
requiring coordination of technical and
musical considerations. Highest references.
Available Sept. 6. Box 94.
Engineering Student
Graduate.
Trained in audio amplifier and circuit design. Interested in audio-video amplifier and
test equipment design. Box 95.
Engineering Trainee. RCA Institutes
graduate, Age 25. Recording, amplifier, and
transducer interests. Machine shop experience. Box 96.
Recording Engineer. 10 years exp. recording, maintenance, disc and tape. Good
mixer, available after 2 p.m. daily, all day
Saturday or Sunday. Box 97.
21
Audio Engineering Society Section
Lateral Feedback Disc Recorder
G.
How proper
THE VERTICAL -TYPE FEEDBACK RECORD-
introduced in the electrical
transcription field about 1938 i
made possible vertical recorditigs of
wider frequency range with reduced
distortion and provided a higher degree
of uniformity among recorders. This
paper describes the W.E. 2A Lateral
Recorder, developed around the same
general feedback principles as the corresponding vertical feedback cutter.
Although the principles involved are
the same for both types, the lateral development presented an entirely new set
of problems. For example, in the vertical unit the generated forces are chiefly compressive and tensional and are
transmitted from the driving coil to
the stylus by means of a thin cone,
while in the lateral recorder the member which connects the drive coil to the
stylus is subject to forces in shear, and
as a result it was found necessary to
increase its thickness thirty -fold in
order to eliminate spurious vibrations.
As will be seen later, it is imperative
that the vibrations which are produced
by the generated forces be constrained
to the mode for which they are intended.
The requirements for an ideal recorder include not only uniform response
and low distortion through the audible
frequency range, but also the ability to
maintain its performance for long
ER
Bell
Telephone Laboratories, Inc.,
Murray Hill, N. J.
'Recent Developments in Hill and Dale Recorders, by C. F. Wiebusch and L Vieth.
SMPE Journal, Jan., 1938.
use
R.
YENZER
of feedback improves lateral -type recorders.
periods of time despite temperature and
humidity variations and regardless of
whether the recording medium is the
softest wax or the most resistant lacquer. It can be demonstrated that proper
application of the feedback principle
to a recorder element will achieve these
objectives.
Theory
Assume the recorder element to consist of a vertical member attached to
a fixed support by a reed binge and carrying a recording stylus at its free end
(Figure 1). The element can be vibrated by means of an attached driving coil
as in the dynamic -type loudspeaker.
Motion of the element induces a voltage
in a second (feedback) coil which is
proportional to the velocity of the
motion, as in a moving -coil reproducer.
The recorder is connected to an amplifier system as shown, the object being
to move the cutting stylus with a vibrational velocity V whose wave shape is
an exact replica of the wave shape of
a signal voltage E.
A general expression for the relation
between stylus velocity and signal voltage in an electromechanical feedback
recorder system has been previously
developed.' It is desirable to repeat its
derivation here, with the terminology
applied specifically to the lateral unit.
Let
=
E
£2
=
V
=
signal voltage
output voltage of A- circuit
amplifier
stylus velocity (inches per
second)
E4
=
=
Et
=
Es
voltage generated by the
feedback coil
voltage output of the B- circuit
amplifier
E + E4
voltage input to A
circuit amplifier
(1)
=
All of the above are complex quantities.
Let
v_v
A--x
- E, EZ -
(2
and
B= v.xç=V.
(3)
where Ez /Ei and E4 /Es are the voltage
gains of the A- circuit amplifier and the
B- circuit amplifier, respectively, and
V/E2 and Es /V are respectively the
electromechanical transducer conversion factors of the drive coil and the
feedback coil. Therefore,
AB
-
E4
(4)
The product AB thus defines the transmission around the loop formed by the
A-circuit amplifier, recorder, and Bcircuit amplifier. Substituting the value
of E4 from this equation in (1), we find
EI=
E
I_
(66)
which, with equation (2), gives
V= EIA =EIA-
(8)
Equation (6) thus determines the
behavior of the system (stylus velocity
vs. frequency and phase shift vs. frequency) when A and B are known. In
particular, when AB is large compared
to unity, the condition usually present
in the recorder, equation (6) becomes
V
=BE
(AB
»I)
(7)
which indicates that under this condition the velocity depends only on the
signal input E and the factor 1/B
which can be made very nearly constant.
[Equation (3) shows B to consist of
two factors Es /V and E4/Es. For the
former to remain constant and independent of the amplitude and frequency of signal voltage E, the feedback
coil must meet three conditions: It
must be rigidly coupled to the stylus;
Fig. I. Electromechanical feedback system.
22
it must vibrate in a uniform magnetic
field; and it must be unaffected by the
magnetic field set up by currents in the
drive coil. The other factor to be main teinod constant, E4 /Es, represents the
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w
Audio Engineering Society Section
voltage gain of an amplifier working at
low level and presents no problem. It
should be noted that these factors,
which are responsible for the benefits
accruing to the use of feedback, when
once embodied in a physical recorder
are inherently stable, and consequently
the performance of the system should
remain fixed over long periods of time.]
If equation (G) is rewritten to include noise and distortion products as
well as signal, it becomes
V-
A
E
I- AB
r
CLAMP
PLATES
Description
str
sistance of the recording medium) may
their effect is reduced in like manner
when AB is large.
Unfortunately, these benefits are obtained only with precision in design
and manufacture. Examination of
equation (6) reveals that if at any frequency the quantity AB becomes equal
to 1 -F j0, the denominator becomes
zero and the system will sing or oscillate. Nyquist2 shows that for stability
a polar plot of IABI L e and its conjugate from zero to infinite frequency must
not enclose the point 1 L O. Bodes estimates that for each 10 db of feedback in
the useful range one octave must be added to the actual range which must be
explored and controlled to insure stability. He aptly describes the limitation
as tantalizing-"In typical designs the
AB characteristic is always satisfactory
except for one little point. When the
engineer changes the circuit to correct
that point, however, difficulties appear
somewhere else, and so on ad infinitum.
The solution is always just around the
corner." This frustration is magnified
when a mechanical element possessing
both mass and stiffness is added to
Bode's circuit. A moment's reflection
will prove that this is true, for only at
the frequency for which the mass reactance is equal to the stiffness reactance
will the driving force be in phase with
the stylus velocity. As the frequency
is reduced, the stiffness reactance in-
DOWEL
DRIVE COIL
N
a
be considered as noise or distortion, and
ALIGNING
TERMINALS
+I -ÁB (B)
where n and d are the noise and distortion,, respectively, introduced in the
amplifier and recorder without feedback. Hence, when AB is large compared to unity, a considerable reduction
in noise and distortion is effected.
Other forces acting upon the stylus
during recording (such as those produced by the turbulent air of suction
and blowing equipment and reaction
forces due to the mass, stiffness and re-
be intercoupled) are possible. several
are probable, and all affect AB La
STYLUS HOLDEN
The vibrating member as finally
evolved is shown in Figure 2. It consists of a precision casting of magnesium to which the drive coil and the
feedback coil are permanently attached.
At the bottom is a cylindrical cavity
into which the stylus shank can be
cemented and at the top is a fiat
spring or hinge of beryllium copper.
This spring is tightly clamped between carefully lapped plates of nonmagnetic stainless steel which in addition to their clamping function provide facilities for terminating the
coil leads. Breakage of leads is no
Fig. 2. View of vibrating member.
Similarly, as the frequency is increased
above resonance the mass reactance
predominates and the phase between
driving force and velocity approaches longer a problem since they are sup+90 °. Introduction of the mechanical ported throughout their entire length
element has therefore augmented the on a compliant plastic apron securely cemented to the moving element.
original phase shift by 180 °.
Actually, this simple recorder ele- When the vibrating member is attachment, which for convenience has been ed to the magnetic assemblies, the
assumed to be rotating about its voice currents resulting from a volhinge in the plane of the paper (Fig. tage impressed on the drive coil pro1), will undoubtedly change its mode duce forces which swing the member
of vibration as the frequency is in- about its hinge. Due to this motion a
creased, and this change will further voltage proportional to the stylus vemodify the phase shift. Additional locity is generated in the feedback
trouble is likely, therefore, when all coil.
Figure 3 is an exploded view of the
parts of the element no longer vibrate
in unison or when at "one little recorder showing the assembly in
point" in the frequency spectrum the greater detail. Both magnets are covelement vibrates in either or both of ered by plastic jackets to prevent acthe planes perpendicular to the plane cidental contact with magnetic obof the paper, to say nothing of rota- jects which would otherwise cause the
ting about each of the mutually per- formation of secondary poles with rependicular axes. Vibrations in six sultant loss in flux. Precisely located
distinct modes (some of which may dowels automatically align the gaps
Fig. 3. Exploded view of the recorder showing the assembly in detail.
RECI PTACLE
DRIVE MAGNET
ARM
SUCTION TUBE
CLAMPING
PLATES
FEEDBACK MAGNET
ASSEMBLY
02
creases and the phase between driving
force and velocity approaches -90°
Nyquist, Regeneration Theory. Bell
Syst. Tech. J., Jan., 1932.
3H. W. Bode, Relations between Attenuation
and Phase in Feedback Amplifier Design.
Bell Syst. Tech. J., July, 1940.
2H.
AUDIO ENGINEERING
STYLUS
HOLDER
`ADVANCE BALL
MECHANISM
SEPTEUCER, 1949
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23
Audio Engineering Society Section
the reproducer itself. The optical
method of Buchman -Meyer (the socalled Christmas -tree pattern) is quite
popular and the results are dependable
for most purposes. However, unless
rather exacting precautions are taken,
the pattern appears fuzzy and striated
Fig. 4.
Frequency Distortion. Stylus velocity can be determined in several ways.
Methods whereby it is calculated from
observed values of amplitude and frequency are satisfactory only at low
frequencies where the amplitudes are
relatively large and can be measured
by means of a microscope with calibrated eye -piece. Another method, that
of measuring a recorded signal by
means of a calibrated reproducer, is
satisfactory provided care is taken to
correct for all effects introduced by
results, effect of temperature change,
aging over long periods of time, etc.
It was decided to forego the use of
such "swamping" resistance and, as a
result, all mechanical damping is omitted for the useful frequency band. A
non -critical damping member reduces
a peak in the response at approximately
40,000 cycles. This reduction decreases
the phase shift by an amount which is
small in itself but which provides added
phase margin stability to permit recorders and amplifiers to be inter-
Western Electric 2A recorder attached to
of the two magnetic assemblies with
the coils of the moving element, insuring adequate and permanent clearance for the vibrating parts. Precision manufacture allows complete interchangeability of components with
elimination of trouble generally associated with centering moving parts
in a restricted space. After these parts
have been assembled, the vibrating
element is further protected against
dust and magnetic particles by a
transparent plastic closure assembly
at the base of which is attached a
flexible neoprene insert and through
which the stylus holder protrudes.
The advance-ball mechanism (Fig.
8) is composed of two accurately
machined precision castings. The assembly can be quickly positioned for
either increasing or decreasing spiral.
Adjustment of the depth of cut can
be exactly controlled by means of a
smoothly running thumb screw which
can be locked in position if desired.
Either a sapphire ball or a felt pad
can be accommodated.
The suction tube extends above the
head to allow attachment of a suction
hose. It is generously proportioned
and so located that it will remove
wax or lacquer shavings without danger of fouling.
Figure 4 shows the recorder in operating position. Although the recorder weighs 4 -3/4 pounds, the weight
on the lathe is no greater than for the
feedback vertical recorder, since in
the new unit the usual balancing
weight is replaced by an adjustable
counterspring. The mass and spring
24
Measured Results
as the frequency is increased beyond
10,000 cps and therefore becomes difficult to interpret. Another method
for determining stylus velocity is applicable only to the feedback cutter.
The voltage Ea generated in the feedback coil is proportional to the velocity
of the coil. If the parts joining the
stylus bolder to the feedback coil are
sufficiently rigid to prevent any relative motion, and no electrical coupling
exists between the drive coil and feedback coil, voltage Es is also a true
indication of the stylus velocity, V.
In Fig. 5, curves A and B, the stylus
velocity was measured by the feedback
coil voltage method, and in curve C
the stylus velocity was determined by
the Buchman -Meyer optical method.
For the feedback condition a signal
voltage E of 0.5 volts applied to the
input terminals produces a stylus velocity V of approximately 1" per second
maximum velocity and the feedback
coil voltage E8 measures approximately 0.018 volts. The difference between
curve B and curve C,
t i n g at
7,000 cps and increasing with frequency, is the result of relative motion
between stylus point and feedback
coil in this frequency range caused
by multiple bending of the hinge, and
is responsible for the sharp dip and recovery in response in the neighborhood of 11,000 cps. One remedy has
been found to be the addition of mass
so distributed that the new percussive
center causes no reaction at the hinge.
On the other hand, to drive this increased mass would require more current and so reduce the margin against
burnout and amplifier overload. The
dip and recovery in response in the
neighborhood of 11,000 cps has been
completely eliminated in experimental
models by a generous application of
damping material, but the use of sizable damping pads is undesirable for
several reasons: necessity for rigid
shop control to insure uniformity in
a
Scully recording lathe.
values have been carefully chosen to
avoid mechanical resonances when recording at either 33 -1/3 or 78 rpm.
The recorder is connected to its associated amplifier by means of a cord,
nominally 8 feet long, composed of
two twisted pairs each individually
shielded and with a different ]ay of
the pairs to reduce electrical coupling
between them to a minimum. Experimentally, substitution of a 20 foot
length of cord showed no detectable
deterioration in performance. Conductors, shielding, twist, fillers and braid
covering have been chosen to produce
a cable as flexible as is consistent with
the requirements. The cord terminates
in a plug in which the contacts have
been sized and gauged to provide adequate contact pressure without requiring excessive pull-out force.
The amplifier with which the cutter
must be used is a W. E. 115 type having
a two-stage, push -pull, 15 -watt, internal feedback amplifier in the A circuit and
a single push -pull stage of adjustable
gain in the B circuit of Figure 1.
star
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Audio Engineering Society Section
cnanged at will. The response at frequencies between 16,000 cps and 20,000
cps is not under the direct control
of feedback action but remains fairly
smooth; several sharp dips of the order
of 10 -15 db occur for frequencies
between 20,000 cps and 40,000 cps, and
definite cutoff occurs in the neighborhood of 50,000 cps, beyond which the
response is more than 25 db down.
Physical Limitations
As the recording
today, the recorded level of the low
frequencies will be limited by the
amplitude of stylus motion in order to
prevent cutting into adjacent grooves,
the level of medium frequencies will be
limited by the velocity of the stylus so
as to prevent the heel of the recording
stylus from touching the groove wall,
and the level of the high frequencies
will be limited by the acceleration of
the stylus to prevent the radius of curvature of the groove from becoming less
than that of the reproducing stylus. The
amplitude limitation depends upon the
unmodulated groove width and the
groove pitch, while the velocity and acceleration limitations are functions of
the linear groove speed. Figure 6 shows
the maximum level that can be recorded
within these limitations for a pitch
of 88 grooves per inch with the width
of cut equal to the land between
grooves, a linear groove speed of 25
inches per second (approximately 6inch diameter at 78 rpm), and a minimum radius of curvature of .002 inch
in the recorded groove. The power
required of the 115. type amplifier
in order to produce this maximum level
recording is also shown in Figure 6.
As a matter of fact, in actual recording the maximum level is usually made
considerably lower than that shown
because of tracing distortion of the
reproducer.
i
iii
.111''IEIO FEEDBhUCj.
40
35
111111I1111111111I111
I111111 \11111111
1113111III11
131111111
I/111111
CtPTIMUM FEEDBACK,.,,,,l
30
m
c
z
W
art is practiced
111111111M11
1111111I
IIIIIIIIPAIIMEIIIIII11111
i2
25
`IIIII
20
15
w
M111111111111i
111I1I111IIIr,
111I1I111III
5
I1111111111111
FREQUENCY IN CYCLES PER SECOND
Fig. 5. Frequency response of feedback recorder.
It should
be understood that the
velocity curve of Figure 6 is not recommended as a recording characteristic but only a limit beyond which a
recorder should not be required to
To arrive at a recording
characteristic the limit curve would
be modified by the energy distribution
curve of the material to be recorded
and by a factor which would take into
account the manner in which distortion becomes more or less disagreeable
with various frequency and energy
combinations. This is usually determined by experience in the recording
studios and is not properly a consideration in recorder design.
Occasionally, in a preliminary recording of a selection, the distributions of
frequency and energy are such that
the record, although of average loudness, will possess less than the usual
perform.
iiii r
=S:::C:CCP7::11C
o
iíiiiÌ\AMIN
i
i ii i
IMiEIllltllNIMMas1111t=1IMU111NIEN
1111111IIII1.11
111.111=
VELOCITY
ii.N.1111oill.11
iiie
IIIIf
f%\\Illff
.1111=
i iii
i ii
c:
llist aeuossMessNOMasnss011..
assosssssWi
I I11
iiiiiii
11t_ilill%11111111W"liliil
C:..::'.:C:
O
iiiiiiiiiiiiii
10
Fig. 6. Physical
limitations of
recording
a
sys-
tem and power
required to
0.1
drive the feedback cutter.
0.1
FREQUENCY C.P.S.
AUDIO ENGINEERING
SEPTEMBER, 1949
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tracing distortion. Because competition is keen among the recording corn panies to produce the loudest records
consistent with distortion which their
experience shows to be tolerable, it is
common practice to make the final
recording of such a selection at a
higher level to effect a gain in the
signal -to -noise ratio at the expense of
increasing tracing distortion. For this
reason, the recorder should be capable
of meeting the more demanding velocity requirements of Figure 6 rather
than the less stringent ones which
result from a consideration of tracing
distortion alone.
It may be argued that the maximum
level curve of Figure 6 should be based
on a linear groove speed of 20 inches
per second (approximately 5 -inch diameter at 78 rpm) since this speed more
nearly represents the condition at the
innermost grooves of most records. If
this argument is accepted the margin
of reserve power increases by a factor
of 2.4, or 3.9 db.
Amplitude Distortion
The realization of a flat response
curve fulfills but one requirement of
an ideal recorder. Increasing importance is being attached in the audio
engineering fields to amplitude distor-
tion and intermodulation distortion.
Harmonic and intermodulation measurements on disc recorders are seldom,
if ever, published. For this reason, few
recording men know whether a criterion of a good recorder is 5 %, 10% or
20% inherent distortion. One reason for
this lack of information is the difficulty
of performing the measurements, the
customary procedure being to cut a
test record and measure the distortion
generated in a reproducer when the
25
Audio. Engineering Society Section
MEASURED INTERMODULATION
RECORDER
USED
2A
LOW FREOUENCY COMPONENT
FREQ
AMPLITUDE
VELOCITY
.0025"
0.63 /SEC
40
60
D90946
CONTEMPORARY
0.I6 "/SEC
I.0
0.24
1.0
0.39
IO
9.5
9.2
.0025
0.63
2000
0.16
60
"
0.94
^
100
"
1.57
0.24
0.39
40
.0025
0.63
0.94
"
1.57
100
record is played back. The measured
distortion necessarily includes that of
the reproducer, and if the linear velocity of the recorded groove is not sufficiently great, added distortion due
to the finite size of the reproducer
point (tracing distortion). Measurement of harmonic distortion is particularly difficult with a sharply tuned
wave analyzer unless the turn-table has
negligible wow or flutter. On the other
hand, intermodulation measurements
of the two-frequency modulated carrier method4 in which the sum of the
intermodulation products is indicated
on a meter are not greatly affected by
small changes in turn -table speed. For
this reason the intermodulation method
is becoming increasingly popular for
measuring distortion in disc recorders.
Apparatus suitable for performing
these measurements is available in
commercial form .5 Table 1 shows intermodulation distortion measured in the
output of a Western Electric 9B reproducer when reproducing records cut
by a 2A recorder, a W.E. balancedarmature, rubber -line recorder, and another commercially available recorder
(also of the balanced -armature type.)
In each recording the velocity levels
were so chosen that the low- frequency
oomponent fully modulated the groove
of an 88 grooves per inch record in
which the width of cut equaled the
"land" between grooves. The velocity
of the high -frequency component was
then adjusted to be % ( -12 db) that
of the low frequency. The same cutting
stylus (.002" radius, 87° in el u d e d
angle) was used successively in each
recorder. The linear velocity of each
record was sufficiently large to eliminate tracing distortion in the reproducer
output. It was found necessary to employ a moving- coil -type
INTERMODULATION DISTORTION
MEASURED IN OUTPUT OF W. E.
98 REPRODUCER
1.57
40
60
reproducer
+Analysis and Measurement of Distortion
in Variable Density Recording, by J. G.
Frayne and R. R. Scoville. SMPE Journal,
June, 1939.
Improved Intermodulation Measuring
System, by G. W. Read and R. R. Sco-
5An
ville. SMPE Journal, February, 1948.
26
2000
V.
0.94
100
W E.
DISTORTION
HIGH FREQUENCY COMPONENT
FREO.
VELOCITY
2000
I.
Inter modulation measured with the aid
of a reproducer.
TABLE
9.0
52.0
53.0
52 0
0.16
0.24
0.39
in order that the distortion introduced by this means. For each measurement
by the reproducer would not mask that in Part A the intensity of the low
generated in the recorder. In fairness frequency was adjusted to produce full
to the third recorder, it should be groove modulation as in Table I. The
mentioned that when the input was results of this test compare quite closereduced 6 db the intermodulation dis- ly with those of the preceding method
tortion decreased to the more reason- if allowance is made for the rather
able values of 21 %, 24 %, and 23 %,
small distortion contributed by the rewhich is probably comparable to 6% producer in obtaining the data of Table
on a harmonic basis.
I. Part B shows the intermodulation
The limitations in measuring tech- distortion produced by fixed frequencies
nique due to the inclusion of a re- at several intensities. The intermodulaproducer and varying turn -table speed tion test presented in Table II was reare eliminated by the feedback cutter peated using 7,000 epa and then 12,000
provided the feedback coil voltage Es cps in place of 2,000 cps, with almost
is a true replica of the stylus velocity identical results.
V. For then the feedback coil may be Effect of Record Material on Recordo
considered as an ideal reproducer fol- Response
lowing the contour of the recorded
The use of voltage readings Ea to
wave even as the stylus is engraving measure stylus velocity and distortion
it. Obviously, distortion products meas- also makes it possible to compare the
ured in the output Es of this re- behavior of the cutter when recording
producer are independent of variations "in air" to that when recording in the
in turn -table speed and contain no most resistant lacquer medium. It is
tracing distortion. Table II is a tabula- important in all types of disc recorders
tion of intermodulation distortion that this difference in behavior be made
products in a 2A recorder measured
[Continued on page 441
MEASURED INTERMODULATION
DISTORTION
A
HIGH
LOW FREQUENCY
COMPONENT
FREQUENCY
INTERMODULATION
COMPONENT
DISTORTION
FREQ.
AMPLITUDE
VELOCITY
FREQ.
VELOCITY
PERCENT
40
.0025'
.63"/SEC.
2000
.16" /SEC
0.61
60
.94
100
1.57
*
.24
*
0.62*
0.61
.39
B
*WITH THE ABOVE VELOCITY VALUES OF 60'AND
2000., AS A REFERENCE. THEIR LEVEL TO THE
RECORDER WAS VARIED IN 2 DB STEPS:
INPUT TO RECORDER
INTERMOOULATION(
-6DB
.47
-4
-2
.49
%)
.55
0
.62
+2
+4
.83
1.14
+6 (60.
SINGLE
1.70
AMPUTUDE..005)
TABLE II. Intermodulation measured by output voltage of the feedback coil.
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y
TH su
I
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little IMPROVED
_mat
wis
CARDIOID DYNAMIC
MICROPHONE
It Means: Better Performance!
tatdtotd
ttaneVhasee
E.4 M
impedance
Selector
High Output
Level
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7011
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Model
)2d
Built-in Cannon
XL-3 Connector
Wide
Smooth
(9p-12 000
11
Wider Stand d
Stu
A0.10 000
Range Response
q.
Mde17261
cD'
Mountoy,
Exclusive
Acoustalloy Diaphragm
Here you have reason after reason for the
fgrowing popularity of the CARDYNE. More
response imeatures have been added
ithaul
With of W
"On-Ott"
Switch
...
SEND FOR CARDYNE BULLETIN NO. 139
Export: 13
DualTYpe
External
Shock
Mount
Highest Purity
(99.9%) Cast
Case
Enclosed
Magnetic
Assembly
Chromlum Fititsh
AUDIO ENGINEERING
$59.50
mount. List Price
ELECTRO- VOICE, INC., BUCHANAN, MICH.
New York 16, U.S.A., Cables: Arlab
E. 40th St.
Thread
58" -21
k
Sahn
...
output level increased ... to proproved
vide a higher standard of excellence! It all
adds up to greater satisfaction on the job!
The E -V Mechanophase* principle provides
a high degree of unidirectivity at all frequencies ... cuts reverberation and random
nearly
noise pick-up ... stops feedback
doubles conventional pick -up range . . .
response.
close
-up
provides clear, natural
The Acoustalloy diaphragm withstands
severest service. Just try the CARDYNE now!
E -V Model 731. Broadcast Cardyne II.
$80.00
List Price
E -V Model 726. Cardyne I. With MC -3
connector and without external shock
Smooth Firm
Tilt Control
Standard
Finer Quality! Greater Value!
NO FINER CHOICE THAN
**CC.
'Potent Pend.
SEPTEMBER, 1949
www.americanradiohistory.com
AmericanRadioHistory.Com
27
NEW PRODUCTS
Pioneer Ham- R.Press. Added to its
already popular line of screw -type punches,
including the new square and keyed models,
the Pioneer Broach Co Dept. RA, 1424 S.
Main St., Los Angeles 15, Calif. has introduced what appears to be the cleverest innovation to date in tools for the small shop
or home constructor. It consists of a frame
made of strong nickel alloy designed to hold
a movable ram on which may be affixed a
variety of punches which mate with dies
seated in an opening on the work table. The
punching operation is then completed by a
hammer blow on the ram. A centering point
eliminates the need for drilling of the chassis
before punching the desired openings, and
dies are available for round holes from
to 1% in., and square and oval holes from
to 7 in. Practically any desired shape
'can
can be obtained by making combination cuts.
The Ham -R -Press is available with throat
depths of 5, 7%, 12, and 24 in. allowing
for practically any size of chassis. Riveting,
slotting, notching, and staking tools are listed
in the literature available from the manufacturer.
Toroid inductors in the miniature
class are available custom wound to any
specified inductance value over the range
from 1 mh to 25 h, with no extra charge,
from The Hycor Company, 7116 Laurel Canyon Blvd., North Hollywood, Calif. These
inductors are particularly useful in audio
filters requiring high values of "Q" and are
wound on molybdenum- permalloy dust cores.
The toroid form of construction reduces the
external field almost to zero, and it is possible to stack a number of these coils together without interaction, as well as to
use them without particular regard to the
proximity of power supply components. Specifications of these coils are supplied in
technical bulletin A -5.
Pre -fluxed Ribbon Solder. Imagine
making a perfectly satisfactory soldered joint
with only a match for heating! With the new
DeLuxe Ribbon Solder this is now possible,
making it simple to solder wires at places
where it is impossible or inconvenient to
carry a soldering iron. To use, a piece of
ribbon solder, % in. or less, is wrapped
around a wire splice, and the joint heated
with a match. For larger wires, it is desirable
to use a candle or a cigarette lighter in
order to maintain heat for a sufficient time.
DeLuxe Ribbon Solder may also be used on
sheet metal or heavier parts, although more
heat' will be required, usually provided in
the form of a torch. Information: Proved
Products Mfg. Co., Drawer 1190, San Fernando, California.
New Speaker Line. Permoflux Corporation, 4900 W. Grand Ave., Chicago, Ill. announces a new line of high -fidelity speakers,
ranging from 6 to 15 in. in the standard
line, and with two sizes-12% and 15% in.
-in the Coronet line. These speakers are
low -distortion, wide -range single direct radiators, covering the range from 40 to 12,000
cps. A new edge damping compound lowers
the resonant frequency and provides increased flexibility with a resulting increase
in power handling capacity at low distortion.
Further information may be obtained from
the manufacturer.
Audio Development Company, 2833
13th Avenue South, Minneapolis, Minn. now
offers a new series of high- fidelity eight watt amplifiers suitable for radio and TV
broadcasters and for other locations where
reliable service must be maintained. Known
as the Type 71 series, these amplifiers are
available with different input and output
impedances, and have a gain of 50 db when
used with matching input, or of 38 db
when used with bridging input. Frequency
response is h'eld to within 0.5 db over the
range from 50 to 12,000 cps, with a nominal distortion of not more than 2 per cent
over the same range. The built -in power
supply is constructed with components having low external fields, and no special precautions need be observed if the amplifiers
are mounted near other equipment.
Audio Development Co.
Proved Products Mfg. Co.
f
Industries
An induction Pickup coil which may
be used for a number of audio applications
is the latest product of A.J.F. Industries,
Inc., 858 Monroe St., Brooklyn 21, N. Y.
This coil which has a d.c. resistance of over
2000 ohms, makes it possible to locate and
measure small electrical impulses, to pick
up a radio program to feed to a p.a. system
by placing the coil near an audio or output
transformer of a small receiver. or to reproduce a two -way telephone conversation
through a speaker system without making
any connections to the telephone circuits.
Another use for the coil is in exploration
of hum fields, such as those which surround
phonograph motors or the transformers and
chokes of a power supply. By connecting the
coil to an amplifier, the amount of hum
pickup may be measured by an output meter,
or fed to a speaker for aural analysis of
frequency and intensity.
A. J.
Pioneer Broach Co.
Permoflux Corp.
RCA Service Co., Inc., Return Apparatus Control, Bldg. 8.2, Camden, N. J.
announces a fast repair plan for RCA Microphones and transcription pickups which
enables the shipping of a repaired micro-
The Hycor Co.
28
phone within four days from receipt, and
only two days for pickups. Also available is
a service for the repair and calibration of
all types of RCA test and measuring equipment. This service should be a boon to radio
stations and other users of this equipment,
since the time usually consumed in a repair
job greatly exceeded these short periods.
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
F.
SEPTEMBER, 1949
NEW WORDS HAVE BEEN ADDED
TO THE BROADCASTING DICTIONARY
-
MAGNECORDED
PROVEN HIGHEST
BROADCAST QUALITY. Thousands of hours
New words and new terms are easy to coin
but it takes popular acceptance to give them
life. That's why you're hearing so much about
"MAGNECORDER," "MAGNECORDED," and
.
of unexcelled performance in radio stations and
recording studios throughout the world have
proved Magnecord portable and studio equipment to be the finest.
"MAGNECORDING." That's why they've become a part of everyday broadcasting speech.
Reasons for the popular acceptance of the
MAGNECORDER are many.
MAGNECORDER
THE ONLY TAPE RECORDER FEATURING UNIT CONSTRUCTION. The several elements that make up the
Magnecorder are available as individual units.
-
As a professional you owe it to yourself to
see and hear actual PROOF of Magnecord
equipment's superiority now. Don't delay. Learn
how a Magnecorder can improve your recordings today!
Buy only those units you need. Combine them
or carry them where you need them as you
need them.
ANOTHER MAGNECORD FIRST
1949
The new, completely portable Magnecorder
PT6 -JA produces truly amazing professional
recordings. Write for specifications.
$499.50
Office
-
(47
360
,INC.
Chicago
N. Michigan Avenue
Plant
-
222
West Ohio Street
World's Largest and Oldest Manufacturers of Professional Magnetic Recorders
AUDIO ENGINEERING
SEPTEMBER, 1949
www.americanradiohistory.com
AmericanRadioHistory.Com
29
NEW PRODUCTS
JIoaiinj
[from page 28J
Many applications for amplifier con-
for all TV Cameras
"BALANCED"
TV TRIPOD
Pet. Pending
This
and
struction involve the use of tap switches, and
in some instances space is at a premium.
Grayhill, Chicago switch manufacturer, supplies a small rotary tap switch, Series 5000,
which has just recently been made available
as a multi -deck unit with a maximum of 10
contacts on each deck, and with continuous
tripod was engineered
designed expressly to
meet all video camera requirements.
Previous concepts of gyro
and friction type design have
been discarded to achieve
absolute balance, effortless
operation, super-smooth tilt
and pan action, dependability, ruggedness á efficiency.
Below:
wheel portable
3
dolly with balanced
TV Tripod mounted.
Complete 360°
pan
without
ragged or jerky movement is
accomplished with effortless control. It is impossible to get anything but perfectly smooth
pan and tilt action with the
"BALANCED" TV Tripod.
rotation. With less than ten contacts, stops
are employed, and rotation is no longer continuous. Any reasonable number of decks
may be addded, with each requiring an increase in length of only 13/16 in. In spite
of its small size, the switches may be had
in either shorting or non -shorting types.
Information and specifications may be requested from Grayhill, 4524 West Madison
St., Chicago 24, Ill.
Recording Microscope. Successful
study of the results of disc recording usually necessitates a good microscope, but they
have been rather expensive until recently,
when the new Model 231 was introduced by
Clarkstan Corporation, 11927 W. Pico Blvd.,
Los Angeles 34, Calif. Containing a built -in
Illllllllllllllllllllllllllllllll'
Quick-release pan handle adjust.
ment locks into position desired
by operator with no "play" between pan handle and tripod
head. Tripod head mechanism is
rustproof, completely enclosed.
never requires adjustments.
cleaning or lubrication. Built-in
spirit level. Telescoping extension pan handle.
Write for further particulars
EQUIPI11Ef1T
.11111ERH
1600 BBOBC'JF4
I
Ills
I I 1.1
I
1
1
1
"EW 9^P., CITY
I'
4l
1
1
I
I
I
C.
I I I
I I I I I
I
I
1
1
1
1
1
I
I
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1
1
1
1
1
I
1
I' IJIIIIIIIIIIIIIIIIII6
NEED BACK ISSUES?
Only a few are available and
the supply is limited
August 1948
September 1948
November 1948
December 1948
January
March
May
June
1949
1949
1949
1949
Payment should accompany order.
1948 issues
30
I
I
I
I
I
I
.I.
1
14 SI
Plug -in subminiature amplifiers are
50c
1949 issues
3 5c
Circulation Dept., Audio Engineering, 342 Madison Ave., New York 17,
I
illuminator, and with a calibrated reticle
and adjustment for powers of 20x and 40x,
this instrument was designed expressly for
use with recorders. The reticle is calibrated
in either 2- or 4 -mil gradations, depending
on the power used, and has the unique
feature of having an eye point 1 in. above
the eyepiece, thus facilitating its use by
those who wear glasses.
N. Y.
.I.1:i111IIIb1111I11II111U11I,IiDI1111I11I11111II111O1I1i111n1I11111I11I11111I11111II1111I1'I011g1i1Ig11I111ubh:
now available in units with voltage amplifications of 10, 100, and 1000, all in similar
forms and small enough for most applications. Amplification is substantially flat
from 20 cps to well above the audio range,
and the tubes and components are completely sealed in compound to provide resistance
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
SEPTEMBER, 1949
to humidity and to mechanical shock. These
MANUFACTURERS OF
FINE ELECTRONICS & INDUSTRIAL EQUIP.
units all contain three subminiature tubes,
with the cathode follower output and the
input being connected directly to the grid
UI.
CORPORATION
I.
THE ARM WITH A HAND
HAS SLIDE -IN
CARTRIDGE HOLDER
of the first cascade amplifier. Further information may be obtained from The Walkirt Company, 5808 Marilyn Ave., Culver
City, California.
The Electronic Workshop, Inc., 351
Bleecker St., New York 14, N. Y. is flow
marketing its control unit, Model C-3, long
used as an integral part of custom systems.
1 he unit includes a continuously variable
volume, bass, and treble controls, with the
tone control settings providing a complete
range frunt
a
A Me quality tone arm that features the
new " ìLIDE-IN" cartridge holder. It Sta
any crr rtridge. lust
quick twist of the.
thumb
screw and the cartridge Is securely
held is place. No need for soldering. Silver
plat+d spring loaded plungers maintain positive electrical contact. The quick act-
positive
adjustment
ing
force.
accurate
ate balance pus proper
Meets all requirements for LP records as
well as standard speed and groove sizes.
Arm made in two sires. for records up to
12" and also up to 17 ". See your jobber or
write for Bulletin No. 172A.
-
16-db boost to a 20-db cut in
both bass and treble. The unit is designed
to work from a 50,000 -ohm source into a
1-megohm load, and has a total insertion
loss of 20 db. Available with or without
switch, the unit is supplied with an attractive
etched plate 11/2" x 21/2". The housing is
11" deep, and will fit into a 2-inch chassis.
Decade resistance boxes are a necessity in many types of audio measurement,
and the unit recently offered by Marna
Electronic Co., 1632 N. Halsted St., Chicago
14, Ill. is particularly useful because of its
power handling ability. The Model 10 resistance box will dissipate a minimum of
CLARKSTAN AUDIO SWEEP
FREQUENCY GENERATOR
CLARKSTAN AUDIO SWEEP
FREQUENCY TRANSCRIPTIONS
`n eitrely new method of making instanta
neon frequency response runs. Audio Sweep
Frequency Transcriptions embody all correction factors in the original recording which
the need for charts and graphs.
.lima
Whew used with an oscilloscope. the Audio
Swap Frequency Transcriptions provide an
A Clarkston development for testina the behavior of audio and other alternating elec-
trical apparatus with respect to frequency
and associated phenomena The generator
operates in the audio range from 40 cps to
10.000 cps. The complete frequency range is
regularly recurrent so that the signal may
be used in conjunction with an oscilloscope.
The Sweep Frequency is governed by 20
synchronizing pulses per second. Where an
instantaneous evaluation of the performance
of amplifiers at various settings of tone control and pickup correction networks is de
tor is
sired the Sweep Frequency G
ideal. A quick performance check on the
following can be accomplished with this
recorders,
film
recorders.
wire
product
, motion picbroadcast and aircraft recei
ture sound equipment. loud speakers. micro
Phones. transformers. filters. pickups. pro
amplifiers and cutting heads. See your jobber or write for Technical Bulletin No. I57A.
Instantaneous response measurement so a
few quick adjustment. on a circuit complete
the yob. Used extensively tor testina audio
amp ifien. loud speakers. microphones acoustical networks, electrical filter networks.
etc. Broadcast engineers can make frequent
quick checks of transmission systems and
comporents. Used for production testing.
Locates distortion. Excellent for laboratories as well as FM stations, motion picture studio and theatre sound equipment.
See your jobber or write for Bulletin No.
...
104.A.
STEADY STATE FREQUENCY RECORDS
Clarkston now offers three new test records
which for the first time conform to exact
specifications. permitting the user to work
in known quantities. The reproduction of
:LARKSTAN RV WIDE RANGE
PICKUP WITH EASILY
REMOVABLE STYLUS
10 watts, and
a'maximum of 30 watts, de-
pending upon the setting, and covers the
range from 10 to 99,990 ohms in 10 -ohm
steps, all with an accuracy of 2 per cent.
Resistors are wirewound using Advance
wire, and they are insulated from the metal
case in which they are mounted. This device should find considerable use in laboratory work, as well as by experimenters
and equipment development engineers.
AUDIO ENGINEERING
This wide range variable reluctance pickup
meers the requirements of discerning r ers
e
and FM specifications. Removable andinterchaageable stylli available with various
tip radii for all types records. LP m r
grocve etc. See your jobber or write for
these fine test records involves no polishing
and employs the very latest techniques
which insures exact duplication of the orig.
final recordings in each pressing. Complete
Decifications of the original recordings are
furnished. See your jobber or write for But.
satin No. 181A.
Bul et.n No. I41A.
O R P O R A T I O N
C
1
1
9
L
O
S
SEPTEMBER, 1949
www.americanradiohistory.com
AmericanRadioHistory.Com
2 7
W
A N G
E
E
S T
L
E
P
S
I
C
O
34,
B
C
O U
A
L I
L
E
F
O
V A
R
R
D
N I A
31
High -Fidelity Tape Recorder. With a
response within ±2 db from 50 to 10,000
cps at a tape speed of 7% in. per sec., the
new Audiograph tape recorder employs both
constant current output and pre -emphasis
equalization, and permits head replacement
without variation in response. Housed in two
carrying cases with a total weight of 80 lbs.,
Quality Electronic
Equipment Deserves
.1 udax
Tradr
\t
ark
reproducers
this unit incorporates more flexibility than
most in its price range. Among its outstanding features are: plug-in equalizers to permit future changes; two microphone inputs
with impedance -change switches; and separate recording, line, monitoring, and playback amplifiers. Full information can be obtained from the Audiograph Co., 1410 El
Camino Real, San Carlos, Calif.
t
TRIAD "H5"
TRANSFORMERS
Volume production of Triad HS (her-
Decade Inductors. One of the difficulties confronting the development engineer
to audio work has long been the high cost
of decade inductors. Using high-Q toroid
coils, the new units offered by The Hycor
metically sealed) Transformers to
JAN specifications has enabled Triad
to lower costs to little more than that
of ordinary
cased types. Triad HS
Series Transformers feature:
Triad Hermetic Seals- sturdy brass studs,
molded In low-loss plastic, eliminate
mechanical weaknesses often found
in other designs.
Wide Frequency Range- Nickel alloy laminations, low capacity and low leakage reactance windings, plus balanced
designs, result in a frequency range
from 20- 20,000 cycles ± 1 db.
Reduced Field Pickup -Triad GP series
cases, drawn from annealed nickel
alloy, reduce stray field pickup by as
much as 95 db.
small Sir. -HS -1 line input transformer with 95 db. shielding and 2020,000 cycle frequency response, in
case only 1,,," x 1%" (base dimensions) x 21/2" high above chassis.
Low oistenien -Triad output coils employ large cores of the best magnetic
alloys, with coils of low resistance
and low leakage reactance, to approach full output at all frequencies
with low distortion. Output transformers may be included in feedback
loops using 30 db of feed -back.
comptte tine -All types of audio coils,
power coils, reactors, supplied in
matching HS Series construction.
Microgroove
DISCS
Standard DISCS
Vertical DISCS
The Standard by Which
Others Are Judged
and Valued
Company, 7116 Laurel Canyon Blvd., North
Hollywood, Calif. cover the range from 1 mh
to 10 h in four decades, all with accuracy
of 2 per cent. Bulletin D obtainable by writing the manufacturer, contains full informat
ion.
Laboratory Bridge. A new universal
bridge for measurement of inductance, capacitance, resistance, and the resistive components of impedance has been made available
It is futile to buy the most modern
records, if you do not give them
the very BEST pick -up to bring
out their built -in excellence!
There is so much in present -day
discs, that even a mediocre pick -up
is bound to bring something out of
them. However, to obtain the fullest
results of which these discs are capable, they must be reproduced with
the finest reproducer for that purpose-the AUDAX.
Remember, two singers may both
be able to hit "high C"
yet one
will please the ear -the other not
at all. There is much more than
mere WIDE -RANGE to quality reproduction. A U D A X reproducers
deliver not merely WIDE - RANGE,
but also all vital factors essential to
highest quality of musical performance and unequalled
EAR -ACCEPTABILITY
...
Write for complimentary pamphlet on
life of permanent points
Write for
Catalog TR-49
AUDAIh COMPANY
500 Fifth Avenue
2254 Sepulveda Blvd.
Angeles 64, Calif.
Los
32
by Freed Transformer Co., 1718 -36 Weirfield
St., Brooklyn 27, N. Y. This instrument,
Model 1150, has a frequency range from
20 to 20,000 cps, and is guaranteed to 1 per
cent accuracy. It is arranged to be used in
most of the conventional bridge configura-
New York 18, N. Y.
"Creators of Fine ElectronicAcoustical Apparatus since 1915"
tions.
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
SEPTEMBER, 1949
Lever Switch. A new key -type switch
requiring only
a
single hole for mounting
has been announced by Switchcraft, Inc.,
1328 N. Halsted St., Chicago 22, 111. Known
as the LEV -R switch, this unit is especially
Really Smooth- Outstandingly Quiet -Fully Dependable
MANY TYPES
AVAILABLE FROM
STOCK
and through
Shallcross
parts distributors
adaptable to all types of low -power switching where good contact is essentiaL Contacts
of silver, rated at 3 amperes, 120 volts a.c.
are standard, with palladium contacts being
available for such uses as low -level communication circuits. These switches are
stocked by most leading radio parts jobbers.
The Telex Earset, weighing only onehalf ounce, is the latest product of Telex,
Inc., Telex Park, Minneapolis 1, Minn. The
construction employs conventional hearing aid type units, but the mounting is unusual
W
-a
Y
in that the 'phone is supported by a lightweight plastic frame, thus eliminating headband and pressure on the user's ear. Available with either high. or low- impedance
units, the Telex Earset offers comfortable
listening level with an input of 0.3 milli watts.
Quick disconnect cable couplings
de-
signed for all- weather and submarine applications will be of interest to users of elec.
trical and sound equipment in places where
there is a possibility of the connections being immersed. These connectors have with.
stood tests with external pressure conditions
ALL STANDARD FIXED AND
VARIABLE TYPES
LADDER AND BALANCED
LADDER CONTROLS
"T"
BALANCED
CONTROLS
"H "CONTROLS
POTEN-10METERS
equivalent to 1150 feet of water, and with
no leakage or seepage. The quick- disconnect
feature is convenient-only a quarter turn
of the shell is required to make or break
the coupling, -and no tools are necessary.
Plugs are made with a wide variety of inserts of the standard Army -Navy type, and
the shells are made in bronze, aluminum alloy, or stainless steel. For further details,
write to Roylyn Inc., 718 W. Wilson Ave.,
Glendale 3, Calif.
The Soundmaster is one of the newer
entries into the field of lower priced tape
recorders. This model has a continuous playing time of one hour with a net frequency
response on playback from 80 to 5000 cps,
AUDIO ENGINEERING
VARIABLE IMPEDANCE
MATCHING NETWORKS
V.U. METER RANGE
EXTENDING ATTENUATORS
STANDARD AND SPECIAL
FIXED PADS
SPECIAL NETWORKS
Perhaps you've noticed how
frequently Shallcross attenuators now
appear in the finest audio or communications equipment? Or how often they
are chosen for replacement purposes?
There's a reason! Improved design,
materials and production techniques have
resulted in a line that sets new, higher
standards of attenuation performance for
practically every audio and communications use.
Shallcross Attenuation Engineering
Bulletin 4 gladly sent on request.
Shallcross Manufacturing
Co.
Callinglale,
Pa.
DEPT.
RESIS7ORS- INSTRUMENTS
SEPTEMBER, 1949
www.americanradiohistory.com
AmericanRadioHistory.Com
A -99
- SWITCHES - ATTENUATORS
33
NEED A LOT OF POWER
IN SMALL SPACE?
±3 db, and
is equipped with a tone control
in addition to the conventional operating
controls. The erasure is by means of graduated permanent magnetic field, and a neon
lamp is used as a volume indicator. The unit
We made this special
transformer for a major
aircraft company
It delivers 480 V.A. in a
4 hour duty cycle with
temperature rise
UNDER 40° C.!
Meets Pro Jan -T -27 Grade 1,
Class A specs
Let Peerless figure on
YOUR
transformer requirements
PEERLESS ELECTRICAL
PRODUCTS
SPECIFICATIONS:
DIVISION
ATEC
Dimensions: 45/4" high, width 4- 3/16 ", depth 244"
Volume: 44.7 cubic inches
Weight: 544 lbs.
3 phase primary, 3 phase secondary
Yconnection
6
1161 N. Vine St..
161 Sixth Avenue.
700 vult test
Frequency: 400.800 cycles
Primary voltage -208, secondary 25
F
301
is self-contained, and provides for phono,
radio, or microphone inputs, and for output
to an external speaker, although a 64" PM
speaker is built in. Information: Pelco Industries, 629 2nd Ave., N. Y. 16.
Phil -teal Relaya are made in such a
variety of types that they are capable of filling almost every requirement for low -power
switching. One of the latest is the interlocking type shown. When the lock -up relay
coil is energized, the switching contacts are
Hollywood 38. Cal.
New York 13. N. Y.
RAZAR & HANSEN LTD.
Clay St., San Francisco 11, Cal.
Exclusive Export Agent
STEPHENS
Manufacturing Corporation
8538 Warner Dr., Culver City, Calif.
Presenting two leaders
in the
11, IlL
1950
Pre -recorded Tapes. Apparently the
first to announce the availability of commercial recordings on magnetic tape, Amplifier Corp. of America has contracted with
representatives of Vox and Polydor, prom-
RED LINE
MODEL
MODEL
106AX
102FR
SUPER CO- SPIRAL
SPEAKER
Especially designed for the high fidelity
enthusiast, it raises the present standard
of reproduction for beyond the abilities of
ordinary speakers. and brings to the discriminating listener a new luxury in listening pl
Handles a full 20 watts of input power; employs a seamless, molded
curvilinear cone of advanced design with
the unusually low free space resonance of
45 cps. Reproducing range is 30 to 14,000
cycles, feat
5 db from 50 to 9500 cps.
Utilizes 4 pounds of the new super powerful Alnico 5 orange streak magnet material.
The unique Silver Spiral differential diffuser
is employed with over 90" of high frequency dispersion. Nominal input impedance ange from 8 to 16 ohms. Diameter
15,8", Baffle Opening 131/2"; Depth Behind Mounting Panel 81/2"; Weight, 25
pounds.
.
DO
TOY KNOW THAT!
The TRU -SONIC C -1C Microphone System is
COAXIAL TWO -WAY SPEAKER
This unit is a vastly improved model of the
famous
P -52A
Coaxial Speaker, which was previously recognised as the standard of excellence by
which other speakers were judged. This unit is especially designed far high quality monitoring for broadcast stations, mcaion picture film reproduction, AM,
and especially FN reception. Combines in a single assembly a newly developed low resonant 41 cps law
frequency unit of the new "LX" cone type, and a high
frequency reprodscer of the multicellular type utilizing 8 individual :ells. The complementary 1200 cycle
crossover network prevents distortion by channeling
the proper portiens of the signal to the individual
driver units designed to reproduce them. High power
handling capacit- of 20 watts input. Widest angle
high frequency d spersion in any Coaxial speaker of
40' x 8U '; input impedance 16 ohms; Frequency Response flat
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the
34
actuated, and a mechanical latch holds the
relay in the operated position, even after the
control circuit is opened. When the second
relay is energized, the action of its armature
releases the latch, restoring the circuit to
the non-operated position. A complete catalog of relay types is available from Phillips
Control Corp., 612 N. Michigan Ave., Chicago
inent European recording studios, for exclusive rights to their libraries, which feature internationally famous orchestras and
solo artists. The first catalog is now available, listing the selections and performing
artists copied onto 4-in. tape for reproduction at the secondary standard speed of 74
in. sec., and may be obtained by writing
direct to the Recording Division, Amplifier
Corp. of America, 398-4 Broadway, New
York 7, N. Y.
An amplifierless PA system is the
newest product of University Loudspeakers,
Inc., 80 S. Kensico Ave., White Plains, N.Y.
Known as the Powrmike, this device consists
of the microphone of special design, and an
efficient horn speaker. The only power source
required is 6 volts, d.c., which may be supplied by a "hot shot" battery or by a storage
battery when used in mobile work. The output is approximately 1.5 watts over the
voice spectrum and the Powrmike cannot
be overloaded, nor does it have any "hiss"
characteristic. While the system is not intended as a substitute for a conventional
Pa system, it has exceptional value for reinforcing speech without the need for bulky
amplifier systems.
AUDIO ENGINEERING
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AmericanRadioHistory.Com
SEPTEMBER, 1949
NEW
LITERATURE
Thordarson
transformers, Catalog
400H, listing the entire line of transformers,
chokes, and audio components, available
from Thordarson Electric Mfg. Division,
Maguire lmdustries, Inc., 500 W. Huron St.,
Chicago 10, Ill.
A
capacitors, together with the
C -R bridge, L-C Checker, and interference
Filter Selector. This six -page folder lists
Duranite Molded paper tubulars, several
types of electrolytics, oil -filled tubulars, mica
capacitors, and other components. Ask for
Form SC-549, Aerovox Corporation, New
Bedford, Mass.
`%-
d
OF THESE MICROPHONES
SUPER -CARDIOID
HAS THE
PICKUP PATTERN THAT
,3/p
OJ
REDUCES FEEDBACK BY
Federal Miniature Selenium Rectifier
Handbook, a 48 -page aid to engineer's man-
ufacturers, and other users, describes basic
theory of selenium rectifiers and carries
THE FAMOUS
UNIDYNE
"55"
DYNAMIC
Unidirectional Microphone. This superlative
dynamic microphone is a Multi- Impedance
Microphone -you can have either High, Medium, or Low Impedance simply by turning
a switch! Because it is a Super -Cardioid, the
"Unidyne" kills Feedback energy by 73 %-
making it possible to use under the most
through to the design details and applications
of 23 types. Available (25e) from jobbers
or from Federal Telephone and Radio Corporation, 900 Passaic Ave., East Newark,
Multi- Impedance Switch
for Low,Medium or Hi5h
difficult acoustic conditions. The "Unidyne"
is probably the most widely used microphone
throughout the world. Recommended for all
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impedance.
J.
The new Yeoman line of transformers is
N.
described fully in the latest calalog issued
by Audio Development Company, 2833 13th
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incorporates the high standards of performance of the Quality Plus series, but the use
of open frame construction and the elimination of terminal boards reduces the cost of
manufacture, resulting in lower prices.
Electronic and electrical components
Killen are needed for quality construction
are described fully in Catalog #300 which
may be obtained from Cambridge Thermionic
Corporation, 445 Concord Ave., Cambridge,
38, Mass. The products listed include ter-
minal lugs and boards, swagers, hardware,
insulated terminals, and a series of coils
and chokes, as well as unwound forms for
special applications.
Microphones. Bulletin 154, illustrating
and describing the new Model 911 Crystal
and Model 611 Dynamic Microphones; and
Bulletin 104, with concise information and
list prices on the entire line of microphones
and accessories. Electra- Voice, Inc., Buchanan. Mich.
Soldering Guns. Descriptive catalog
bulletin covering the Weller Soldering Gun
line, which includes four models for every
soldering requirement. Weller Manufacturing Co., 808 Packer St., Easton, Pa.
Preferred Tubes. A new issue of the
RCA Preferred Tube Types List, Form PTL501A, has been brought out with revisions
to keep abreast of advances in the electronic
field. Commercial Engineering, RCA Tube
Department, Harrison, N. J.
Transformers. Complete catalog of new
equipment transformers for audio and power
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18, HI.
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SEPTEMBER, 1949
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THE
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36
causes) a very great increase in confusion,
a decrease in the ability to sort out sounds.
If the change in liveness is the first thing
to be noticed, the increase in confusion with
the monaural system is surely the most
vital point. Hearing aids with one channel
(the other ear being too deaf to help) bring
a tremendously confused sound to the
wearer when things get at all complicated
A hearing aid at a tea party must be an
instrument of torture for the wearer--ao
wonder he so often leans towards you, or
thrusts his mike in your face -not to get
more volume, but to achieve greater separation between your voice and the surrounding
confusion! If you normal- hearing engineers
want to see for yourselves, try my microphone
and earphone experiment in the middle of
a crowd of talking people -then be sorry
for the monaurally deaf! And the tragedy
of it is, as I see it, that probably not one
in a hundred thousand hearing aid wearers
knows why there is such confusion. Most
probably blame it either on the machine,
which is not to blame. Or much worse, on
themselves. It's bad enough to have to wear
such a gadget but to find yourself at sea
and confused in spite of it is pretty hard.
Must be slipping, such an unfortunate soul
is likely to think. My nerves are shot .. .
everything seems to echo and reverberate
and I can't tell one voice from another.
Bad. What's the matter with me? Mister,
you need another ear.
This being a record column, maybe we'd
better end on that subject for the record.
It is hardly necessary at this point to mention the tremendous importance of these
same effects, in reverse, when music is
recorded. We have found highly ingenious
ways to fool the ear into accepting an utterly
artificial, multi -mike monaural sound as a
good faked binaural one. Good enough.
But somebody, every day, turns up with the
odd notion that reproduction from records
is supposed to be like the original sound
When that person is a recording engineer,
things go haywire and fast. When he is a
listener, perhaps the consequences are
less-but there are a lot of listeners to add
together and the net quantity of confusion
as to how reproduced music should ideally
sound is terrifying. No monaural sound will
ever be like a binaural one, nor will we
have exact reproduction until someone figures a way to feed two ears at once and
separately without tying wires to each.
Final word: what does a monaural hearing aid user hear when he listens to monaurally recorded music? Perfect reproduction
of course- the same that a color -blind man
with one eye would see in a black -andwhite movie.
J. LEBEL
C.
AUDIO CONSULTANT
Sound Recording Instrumentation
370 RIVERSIDE DRIVE
NEW YORK 25. N. Y.
Winston Wells
Designer and Consultant
Acoustical, Electronic and Nuclear
Research
307
Eut
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MU 4-3487
New York 17, N. Y.
Custom -Built Equipment
U. S.
1
121
Recording Co.
Vermont Ave., Washington
5, D.
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7, N. Y.
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RATES FOR
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Orders Are Accepted
for 12 Insertions Only
HERMAN LEWIS GORDON
Registered Patent Attorney
Patent Investigations and Opinions
Recent Recordings
ELECTRONICS COMVAN
122 -124 DUANE
New York
(from page 20]
aural sound is the first great increase of live ness and secondly, (we hear effects, not
.
Automatic Frequency Control
Suuá
PROFESSIONAL
DIRECTORY
RECORD REVUE
7
-1840
ST
after Paganini.
Concert Hall LP CHC
Liszt, Six Grand Etudes
IO
Werner Building
Washington 1. D. C.
NAtional 2497
100 Normandy Drive
Silver Spring. Md.
SHepherd 2133
Robert Goldsand, Pianist.
AUDIO ENGINEERING
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AmericanRadioHistory.Com
SEPTEMBER, 1949
Villa Lobos, Quartet
eiro)
#6 (Quartetto
Brasi1
Concert Hall LP CHC 19
Stuyvesant Quartet.
Beethoven, "Spring" Sonata for violin E piano.
Concert Hall LP CHC 17
Joseph Bernstein, Ella Goldstein.
Cho ce
The LP record, a bit surprisingly, has
turned out to be the salvation of the small
company in the classical field -at least most
of 'em are making like salvation. LP processing is reasonably available now, some
through Columbia, a good deal elsewhere;
packaging and shipping costs are greatly
lowered, a vital matter with small companies.
And sales must be good, judging from what's
appearing. A good many small company LP
recordings don't even get around to appearing on 78 at all. Concert Hall so far has
issued only unlimited edition LP's, as above;
an interesting arrangement is that whereby
this company has taken over rights to recordings made by other companies-- especially interesting since the International Records
items to date, including the Liszt Etudes and
the Villa Lobos Quartet above, are better
sounding than almost anything of Concert
Hall's own! Indeed, they are about the finest
jobs of their type I've heard anywhere, with
wide range, low distortion, a beautiful liveness, a cross between Mercury (domestic)
and English Decca ffrr. All of these LP's
seem more stable, less finicky in the playing
than many a Columbia LP. Part of the reason, I'd guess, is wider groove spacing, somewhat shorter play; another aspect is considerably less pre -emphasis of the highs
these running more or less like their 78-rpm
counterparts, not far from flat as my ear
judges it. Surprising the difference between
optimum control settings for these and the
average Columbia LP.
The Liszt piano is a gorgeous, big, sonorous sound, not unlike the best of RCA Victor's Horowitz -type recording. The Villa
Lobos quartet is similar, a big, resonant
sound with ultra clear details. The Beethoven, recorded by Concert Hall, is quite different, with dullish highs (they are present),
rather close and dry acoustics. Not bad,
though, for the music. Surface noise is fairly noticeable in all of these, partly due to
lack of Columbia's pre- emphasis.
-
of ÓZÓ Tubular Resistor Values
N
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of other Stock
i
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have been produced and used over more years
than any other make. And records show that
Mendelssohn, Octet for Strings, Opus 20.
Polydor -Vox LP PLP 6510
quite often a stock unit as the perfect answer to
many an industrial need ... for application, for
performance, for economy, for quick delivery. For
example: there are 626 Vitrohm tubular stock
and
values in fixed and adjustable types
promptly available! It pays to
many others
for your requirements.
check into them
Contact your local Ward Leonard
Authorized Industrial Distributor.
Send now for handy
Stock-Unit Catalog D -130
Pro Musica Chamber Group.
Schumann, Trio
#
I
in D Minor, Opus 63.
Polydor.Vox LP PLP 2030
Trio de Trieste (violin, cello, piano).
Mozart, Piano Concerto
#
in B flat, K. 450.
Vox LP VLP 6580
15
...
Andor Foldes; Lamoureux Orch., Bigot.
Vivaldi, Gloria Mass for solos, chorus, orch.
Polydor -Vox LP PLP 6610
S. Zanotti, sopr. A. Giordano, mezzo.
Choral Academy of Lecco, Orch. of Teatro
Nuovo, Milan, cond. Perdollo.
Here is a batch from another sudden
convert to LP -Vox has for the moment virtually deserted the 78 field. These are typical
of this company, which now farms out its
recording here and there over the face of
Europe. Vex's music has always been extremely interesting, its recording technique
and pressing highly variable, according to
the "farm" of the moment! The tendency
is towards excellent acoustics, fine balance,
only fair recording; or irregular recording
with some wonderful sounds, marred by defects such as sudden blasting peaks.
These LP's vary most astonishingly in
these respects. The Mendelssohn Octet and
the Mozart, from France, are similar-rather
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BASIC DESIGNS ARE RESULT -ENGINEERED FOR
R, 1949
www.americanradiohistory.com
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YOtiJ
37
You Haven't Really Enjoyed
Your Favorite Records Till
You've Heard Them Thru The
SOMERSET
NOISE SUPPRESSOR
Pre -Amplifier
This complete unit includes
pre-amplifier with adjustable
Two stage
pick -ups.
equalization
for magnetic or crystal
Three tube dynamic Noise Suppressor that reduces record scratch to the vanishing
point at low levels, but reproduces essential overtones at all levels.
Built
in
power supply to operate from 115 volt AC line.
No technical skill required for installation or operation.
Write for booklet AA giving full explanation and specifications.
SOMERSET LABORATORIES, INC.
1701 Palisade Avenue
Union City, New Jersey
A MPERITE
Studio Microphones
at P.A. Prices
.s.
RECORDING
PUBLIC ADDRESS
"The ultimate in microphone quality," says Evan
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Shout right into the new Amperite
Microphone -or stand 2 feet away
-
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Models
The only type microphone that is not
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"Kontok" Mikes
Model SKH, list $12.00
Model KKH, list $18.00
In Canada: Atlas Radio Corp., Ltd., 560 King St. W., Toronto
38
-
-if
Vivaldi, Concerto Grosso in D minor, Op 3,
*I I.
Ideal for BROADCASTING
reproduction
dead, with weak highs, only fair presence,
but excellent musical balance some distortion towards ends of original 78 sides. For
some inexplicable reason the Mozart 78 sides
have not been patched in the LP and there
are several old- fashioned breaks while the
records "change "! Moreover, the grooves are
wide pitch, only six 78 sides to the entire
LP. (But, after all, Mozart didn't write any
more.) No records, these for a hi -fi enthusiast, but remember, there's music on them
and it's perfectly audible, hi -fi or no. People
will like them.
The Vivaldi Gloria Mass comes from Italy.
Musically it is extremely interesting to anyone who goes for such works as the Bach
Mass, the Handel Messiah, Mozart Requiem,
etc., since this work and indeed anything
for chorus by Vivaldi has been unheard of
in these parts. It's a brilliant piece, easy to
catch onto, almost juicy in the Italian manner. The performance is so-so, with a lot of
throaty Italian singing, Listerine style; but
the singers like the music and that helps mo
end. And as to the recording -most interesting technically! With a 5000 -cps cutoff
(the usual plush home console machine) it
sounds perfectly swelL With an 8000 cutoff
it still sounds extremely good, with more
brilliance, a few slight buzzimesses. But
open 'er up to 10,000 and the most excruciating distortion shrieks at you! It's razor edge, just the kind of thing that drives the
anti -hi-fi listener mad. A rather unusual example of excessive distortion limited almost
entirely to the extreme upper frequencies.
(Note
you play this with 5000 -cps cutoff, cut down on the low emd too, for balance. With attenuation of the lows, the music sounds surprisingly good.)
As for Schumann, there's no indication
where this big, diffuse, highly Romantic
piece was recorded; it's quite unlike any
of the above Vox imports. Here the bass is
tremendous, the highs rather spineless, so
that the piano bass and the cello, for once,
actually drown out the violin! Might be in
part the mike set -up. A large bass attenuation will change this remarkably; the cello
suddenly gets back where it belongs and
the violin comes forth. It's a nice piece and
the sound is big and full, if again nothing
for the hi -fi fan to rave over.
Mercury LP MG 10002
Mozart, Divertimento in D major, K. 251.
Dumbarton Oaks Chamber Orchestra,
Schneider.
This is a reissue, by still a third company in the LP field, of a recording issued
last year on 78, originally recorded on 16inch, 33 -rpm discs. This is one of the short
series of domestic-made jobs done for Keynote, then absorbed by the Mercury label;
technique was one-mike, with Fairchild cutters, giving beautifully clear, wide-range
sound. The LP version seems as good as the
78 was, especially since the 78's had rather
bad surface noise to mess up the higher
tones.
There seems to be little doubt, incidentally, that LP records re- recorded from tape
or 16 -inch originals are consistently better
than those copied from 78-rpm masters.
Those companies, like Mercury, fortunate
enough to have either of these types of original are in a fine position for LP's. Tape
originals will doubtless soon supersede the
still omnipresent 78 recordings now being
made in Europe -the Vox series, for instance, and the British Columbias, copied
not too successfully here as LP's. Big question? What will the forthcoming English
LP's from Decca (London) sound like
copied from 78's?
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
-
SEPTEMBER, 1949
Tchaikowsky, Overture "1812," Opus 20.
a) Mercury LP.MG 15000 (1/2 IO"
b) Capitol 78 EBL 8022 (2
Orchestra,
Amsterdam
Concertgebouw
Mengelberg.
Here's a fine kettle of fish! These two
are, to the best of my knowledge and ear,
taken from the same original German recording. Capitol, some months back, announced a suit against Mercury for infringement of rights to German recordings, and
this is an illustration of what gives. No word,
to date, of the results; in any case what
seems to have happened is that Mercury, on
the other side of the Iron Curtain, got rights
to the Czech Ultraphon catalogues-which
included many German recordings via previous exchange arrangements. (The whole
of Europe has been networked for decades
with such arrangements and the Nazi period
followed by the war and the Liberation,
plus the present East -West split and the assorted MG control, has made an incredible
stew of the whole business.) Capitol, going
in from this side of the Curtain, via Germany itself and the U.S., got direct rights
to the German records at the source! The
astonishing thing is that the recording was
made in Holland (presumably), no doubt
through still another inter- country arrangement, probably invalidated by now.
Be that as it may, the recording of the
"1812" is typically wide -range, with the
sharp, rather tinny brass and strings we now
are getting to know in these older Telefunken
jobs. Not quite distortion -free compared to
newest wide -range recording, but still quite
amazing. Capitol's version is, I'd say, somehat filtered, to smooth things out a bit.
Mercury's sounds more like a straight rerecording, with more in the high end, but
not as smooth. Otherwise, granting the difficulty of directly comparing an LP and a
78, the two are neck and neck.
Imagine the confusion when, this fall,
Capitol brings this out on 45 and as an LP!
Strauss-Chasins, Waltz- Fantasy, ( "Music of
Fm Ike first
studi
quality reproduction
in
automatic record
a
citan sr for all types of rec-
Chasins
Mercury LP MG 10005
and Constance Keene,
pianos.
.
Slightly misleading title here. This is
two -piano music that is about 50 per cent
Strauss, the rest Chasins. Themes are from
Strauss, but the harmony is a special sophisticated dinner music sort, quite unlike the
original Strauss, far more elaborate, and the
"continuity" is entirely Chasins, moving
from one idea to another in pot -pourri style
somewhat like a Gilbert and Sullivan operetta overture. An ingenious job, I'll admit,
and not at all bad listening, though Johann
most assuredly wouldn't know what to make
of it. The piano playing is terrific, the arrangement for the two pianos extremely
skillful. (One number is a similar fantasy
cn themes from "Carmen" by Bizet. Fine
background music, too.
The recording is spacious, the two pianos
a bit in the background, avoiding thus a
lot of "ping ". Funny how much better twopiano recording sounds than one-piano. This
is evidently domestic Mercury, not European.
It's as good piano as has been done here.
i1% /Vdesign plug -in pick -up
heads permit use for the first time
of highest quality pickups as used
by many broadcasters.
ords RCA Victor 7" 45
RPI< Columbia 7" LP,
Colu Ibia 10" and 12" LP
331/3 1PM, Standard 78
R PN 10" and 12" records- all played autotuati
Controls are marked for simple selection, according to type of records to be played. Records
may also be played manually. Quiet jam -proof
mcehanism. Webster Chicago 356 -27PS supplied
with special matched pair type W Pickering cartridges balanced to give only 17 grams stylus
pressure on standard records and 6.7 grains on
l.P microgroove records. Special Pickering cartridges have built -in precision sapphire styli for
standard and microgroove records.
iCKERIt
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yti for years of finest reproduction with
Price
ear
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AC.
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A
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The degree of noise suppression is controlled by a calibrated indicator. The built in equalized preamplifier with equalization
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The Somerset noise suppressor preamplifier has a self-contained power supply
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[Iron: page 14]
feeds the two radio receivers through
coupling transformers. This type of
transmission for AM signal was chosen
because the balanced transmission Mr-
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es COI
of Rodio & Electronic Equipment
N.T. Phone -WOrth 4 -3311 Coble-TERMRADIO
4NDT ST. -NEW YORK 7,
AMMO
SEPTEMBEF
1949
www.americanradiohistory.com
AmericanRadioHistory.Com
39
wow cacG& Ph,ÚZC[pk:
C!
Stable logarithmic amplification is for the first time
commercially available in these two new designs.
MODEL 121 LOGGER
Logarithmic voltmeter with 50 db linear
meter scale; output may be used to feed
direct writing recorder (via
suitable
amplifier) for acoustical reverberation tests.
Input impedance-50,000 ohms; output impedance-1000 ohms.
MODEL 140 DISC -NOISE METER
Overlod -proof amplifier voltmeter for
quality control of lacquers. phonograph records, transcriptions. New stable logarithmic
element. 20-db linear meter scale. Minimum
reading 75 db below 7 cm /see. velocity with
pickup cartridge supplied.
100 BRIDGER- Connects a vacuum -tube voltmeter, distortion meter. and /or
oscilloscope to a high -impedance circuit, such as an amplifier or counter, without loading
it and changing the operating characteriatics. A shielded cable may be used for eliminating
hum without loading the circuit under test with the cable capacitance. Using an improved
cathode follower and a specially designed double -shielded cable, the Bridger often an
input impedance of 100 megohms in parallel with 6 mmf at the end of a three -foot shielded
cable, and an output impedance of 200 ohms.
MODEL
MODEL 106 VOLTAGE DIVIDER -Extends input -voltage range to 250 volte when slipped
on tip of the cable-probe of Bridger. Input impedance 50 megohms in parallel with 6 ma:
voltage ratio 10:1.
Miniature Preamplifiers For Use With 640AA Condenser Microphones
Model
No.
12
14
16
Output Z.
Length.
I dyne /cm2
ohms
inches
250. bah
250, bal.
500, unbal.
9%
6%
135
v
135
v
41.1
300
-40
-60
dbm
dbm
1.5 mv.open cet
Diameter, all models
-
I
Requirements
Plate I
Fil. E
Power
Output for
Plate E
2.2 ma
2.2 ma
3.0 ma
Fil. I
1.25
1.25
6.3
70 ma
10 ma
v
m
200
1% inches
YOUR SPECIAL PROBLEM can also benefit from our wide acquaintance with new methods
and unusual techniques, In many cases we can provide hitherto unavailable results at
very reasonable cost.
AUDIO INSTRUMENT COMPANY
1947 Broadway
New York 23, N. Y.
NEW... Improved
r
12ÁT
Wiring Eliminates Leakage
PTK
TYPE
h"E1
MEASURING
2A
(KITRANSMIS
SET
Range: 111 db. in 0.2
steps.
Frequency resp.: 0.1 db.
from 0 to 20 kc.
Accuracy: 0.1 db.
Impedance, load section: 4, 8, 16, 50,
150, 200, 500, s
600 ohms.
Impedance, transm.
set.: 50, 150, 200,
500 d 600 ohms.
Reference level: 1 mw.
into 600 ohms.
Circuit: "T",
unbalanced.
Attenuators: 10x10,
10x1 L 5x0.2 db.
Load carr. cap.:
Transm. sect. 1 w.
Load section 10 w.
school.
In order to cover this large number
of people gathered in front of the school
for the dedication ceremonies, two multi- cellular speakers were installed on the
parapet and were fed from one of the
nearby classroom circuits. During the
dedication of the Chapel, the voice of
the Cardinal and the choir were picked
up over the microphone inputs indicated on the block diagram as Chapel
Mike #1 and Chapel Mike #2. Thit
program was distributed through the
selector system to the outdoor speakers,
the classrooms along the first floor, the
gymnasium, and the auditorium.
This description of one type of elaborate system is offered to show how a
specific requirement for sound service
may be fulfilled by designing into the
system all of the necessary facilities for
flexibility and complete coverage. While
systems of this magnitude are encountered rarely, the same principles obtain
in smaller layouts, and those facilities
which are not required may simply be
omitted. The system described is functioning to the satisfaction of the Principal and staff, and is proof that time
spent in the original design and installation is more than repaid by the performance and convenience of the finished product.
TEST
RECORDS
[/rum page 141
A precision Gain Set with specially developed
wiring that permits no troublesome leakage
and provides improved frequency characteristics. Available completely assembled, or
in kit form -which permits the sale of a high
accuracy instrument at a low price.
WRITE FOR DESCRIPTIVE BULLETIN
Manufacturers of Precision Electrical Resistance Instruments
P
40
cuit provides an efficient method of
coupling unaffected by noise pickup.
Located over the clock in each of
the classrooms is an accordion -edge
speaker mounted in a flush baffle. The
size of back box was designed to provide an acoustic volume suited to this
mechanism to provide the best overall response.
As a side light to the technical aspects of the equipment, it is interesting
to know that practically all the facilities
of the system were used on the day of
dedication at which time His Eminence
Cardinal Spellman, together with other
dignitaries of the Church, educational
and political worlds, dedicated this
A
L
I
S
A
D
E S
PARK,
NEW
J
E R
S
E
Y
ing record changers; consists of three modulated bands of 936 cps tone for "wow" check.
Inside eccentric groove is equal to largest
known to be used on a Victor record.
12-5 -23 (T -2914) Reverse side of 12.5.21.
Modulated bands joined by spirals to indicate limits of standard records. Modulation
is at 400 cps at level of approximately 5.9
cm /sec., and spirals provide checks for 10and 12-inch records, and center eccentric
is standard.
12 -5 -25 12-inch, 33% rpm. Unfilled Vinyl,
SF. Frequency bands: 400 and 4000 for intermodulation test purposes, followed by
frequencies of 12, 11, 10, 9, 8, 7, 6, 5, 4, 3,
2, and 1 kc, and 700, 400, 300, 200, 100,
70, 50, and 30 cps. Crossover frequency
500 cps, with CV portion above crossover
AUDIO ENGINEERING
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AmericanRadioHistory.Com
SEPTEMBER. 1949
-3
and
held to -*O, -1.5 db to 10 kc, and
-2.5 db at 11 and 12 kc respectively.
Vinyl,
DF,
7
-inch,
45
rpm.
Unfilled
12 -5 -29
with 12-5-31 on reverse. Consists of 20-sec.
band of 1000 cps at 4.4 cm /sec, unmodulated section, 1:30 min. of 400 cps at 2.6
cm /sec, unmodulated section, and 20 sec.
of 1000 cps at 4.4 cm /sec. Last music
groove for check of record changer operation has diameter of 4.250 in.
12 -5 -31 Reverse side of 12 -5.29. Frequency
bands of 1000 cps, 10, 9, 8, 7, 6, 5, 4,
3, 2, and 1 kc, 700, 400, 300, 200, 100, and
50 cps, followed by another band of 1000
cps. Crossover frequency, 500 cps. Levels
shown on curve of Fig. 1.
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III
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11;111IIM11II1IM111111111
ryes
IIVIROW.MC
IN
CM
SCCINNO
MI
Fig.
I
RCA -Victor Test and Technical Purpose
records may be obtained by ordering from
Custom Record Sales Section,
RCA -VICTOR DIVISION,
155 E. 24th St.,
New York 10, N. Y.
Ihr
COLUMBIA
10004M 12 -inch, 78 rpm. Shellac. Frequency
bands of 1000 cps, 10, 9, 8, 7, 6, 5, 4, 3,
and 2 kc 1500, 1000, 800, 500, 300, 200, 150,
100, 70, and 50 cps. Crossover frequency,
800 cps. Frequencies announced.
10003M 12 -inch, 78 rpm. Shellac. Same
frequency bands as 10004M, but with crossover frequency of 300 cps.
YTNY -170 -4 16 -inch, 33% rpm. Same frequency bands as 10004M, but with crossover frequency of 500 cps. (Standard groove
dimensions for transcriptions.)
RD -103 12 -inch, 33% rpm, LP Microgroove.
Frequency bands of 10, 9, 8, 7, 6, 5, 4, 3,
and 2 kc; 1500, 1000, 800, 500, 400, 300,
200, 150, 100, 70, 50, and 30 cps. Levels as
shown at (A) in Fig. 2. This record is essentially flat over constant- velocity portion,
with crossover at 500. cps.
RD 130A 12-inch, 33% rpm, LP Microgroove. Frequency bands same as RD 103,
except levels arranged so as to reproduce
±2 db of "flat" on correctly equalized LP
reproducing system. Levels as shown at (B)
in Fig. 2.
TURNER 87
One look at the Turner Model 87 and you sense immediately
here's a microphone masterpiece. Every detail of its attractive
gunmetal case and polished chrome screen reflects the precision
and care behind its manufacture. The Turner Model 87 is a single
ribbon velocity type microphone with the Figure 8 Polar Pickup
pattern so desirable in highest quality recording, public address
List price $47.50
and studio broadcast work.
POLAR PICKUP PATTERN
figure 8 pattern illustrated by the
diagram shows the attenuation of
sound arriving from sources at 90°
from front or rear of microphone.
The
IIIIIIIII
11111111111I1111111
M1
11111IM
a11i11M
Write for Bulletin giving complete details
11IIII1115!:::::\P!'
II :IIIIIIIIIIIII
IIIIII<c!7
r!.ínl111111
1111
TURNER
11!:t lle:ai11I111M11111i1111
,._ac
oet
'wan
mil
The shorter
way of saying "Sound Microphone Performance"
me*
Fig. 2
281 12-inch, 33% rpm, LP Microgroove. Gliding tone frequency record, from
10 kc to 50 cps; marking tones at 10, 8,
5, 4, 3, 2, and 1 kc, and at 500, 400, 200,
150, 100, 70 and 50 cps. Levels are approximately same as on RD 103.
Columbia Test Records may be obtained
from any local Columbia distributor, or
from Columbia Records, Inc., 799 Seventh
Ave., New York 19. N. Y.
XERD
THE
929 17th Street
COMPANY
Cedar Rapids, Iowa
Licensed under U. S. patents of the American Telephone and Telegraph Company,
and Western Electric Company, Incorporated. Crystals licensed under patents of
12-
the Brush Development Company.
inch records pressed on a mixture having
AUDIO ENGINEERING
N-E-,
IN CANADA:
Conadion Marconi Co., Lfd.
Montreal, P. O., and Branches
EXPORT:
Ad. Auriema, Inc.
89 Broad Street, New York 3, N. Y.
LONDON GRAMOPHONE
Album No. LA 32, consi-ting of three
TURNER
SEPTEMBER, 1949
www.americanradiohistory.com
AmericanRadioHistory.Com
41
MODEL
B
a shellac content of not less than 22 per
cent, which results in a surface hardness
essential for long life. This is the same
material on which London Decca records are
pressed, and surface noise is held to a
minimum.
T -4996 (A) Glide-tone record, covering
the frequency range from 14,000 to 3000
cps, with a break at every 1000 -cps point.
Levels are shown on Fig. 3, and are in
accordance with recording curve employed
on Decca "ffrr" records.
T-4996 (B) Reverse of above. Glide tone
record, ranging from 3000 to 10 cps, with
breaks at 2000, 1000, 400, 250, and 100, cps.
Levels are as shown on Fig. 3.
T -4997 (A) and (B) Glide-tone record,
same on both sides, covering the frequency
range of 14,000 to 10 cps, with breaks at
every 1000 -cps point, and at 900, 250, 100,
-201 LOUDSPEAKER
A two -way direct radiator system
is
distinguished by its
OUTSTANDING BASS
DISTINCTLY NATURAL TREBLE
AND
UNSURPASSED TRANSIENT
RESPONSE
The one above all others on all
points vital to good listening.
SPECIFICATIONS
RACON
-
TWEETER
Response: 40- 13,000 cycles
Coverage: 100° at 13 kc
Pal ems
Highest Music Quality
At
Impedance: 8 ohms
Input Power: 12 watts
Enclosure: 32" diam. utility design
hemisphere
Pending
low Cost!
Qualify loudspeakers designed and m nufnetured by
It. T. BOZAK,
90
Mo ntrose Ave.,
Buffalo
14, N. Y.
MODEL
CHU -2
Clean
Output to
$37.50
List Price
15,000 Cycles!
Wide Distribution Pattern!
World -Wide Popularity
Since the inception of AUDIO ENGINEERING in May 1947, engineers
and audio hobbyists have subscribed in ever -increasing numbers, not only
in
the 48 states and in all of the major foreign countries but in such
places as Tasmania, Transvaal and Trinidad.
Each month
AUDIO ENGINEERING covers the latest developments and
practices in recording, reproduction
and instrumentation for the entire
audio field.
.
Subscribe Now -Don't Miss an Issue! Back numbers are hard to get!
.. -- ...,... -.... ^
gm*
AUDIO ENGINEERING
342 Madison Avenue, New York 17, N. Y.
e.. -,...
--
awn
-.....t
Sirs: Here is my
check (or
money order) for $
Enter my subscription order i
to AUDIO ENGINEERING for the next
issues. Subscription Price: In U.S.A. Canada 1
and Pan American Union-12 issues $3 -24 issues $5. All others $4.00 per year. Please check one:
New Subscription
Renewal
,
i
Add the Racon tweeter to your radio or
phono amplifier to s-t-r-e-t-c-h the range
of your 12 -15" cone speaker to the upper
limits of today's wide range music. For
the first time, enjoy the rich brilliance
and life -like realism of concert hall
music!
Smooth, clean response to 12,000 cycles,
with usable output to 15,000 cycles. High
frequency horn logarithmically expanded
as two horns for wide, uniform distribution pattern. Satisfactory match assuted
with amplifier output impedances from
4 -15 ohms. When used with crossover
network, will handle amplifiers rated to
25 -30 watts.
Cast aluminum throughout. Easy flush
mounting. Cutout template provided
with free wiring diagram and instructions to build your own 1,000-cycle crossover network.
Listen to the Racon tweeter at your
nearest distributor, or write for free
Catalog A
list Price $22.50
All bacon products are gucronteed for IA months.
Recen LC Crossover Network, Model CON-20
)I
Name
(please
print)
1
Address
City
Zone
i
Firm Name
r-rrrewr64-...r.a..er-ers..-...r-
42
EXCELLENCE
1
1
Occupation (give title and department)
ore.
ACOUSTICAL
I
State
IMO
-- I1.rr-rr,r.-,.--
1
Imp
.
1
52
East 19th Street, New York 3, N. Y.
AUDIO ENGINEERING
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SEPTEMBER, 1949
f
New
and 50 cps. Level is constant from 14,000
to 400 cps, with levels below 400 cps same
as on T -4996. (Fig. 3).
T-4998 (A) Frequency bands of 14, 13,
12, 11, 10, 9, 8, 7, 6, and 5 kc at constant
leveL
T-4998 (B) Reverse of above. Frequency
of 4000, 3000, 2000, 1000, 400.
250, 100, 55, and 30 cps, with levels as
shown by the dotted curve of Fig. 3.
bands
1111II1111111I=1111111M
II®1111111MI/!:í IIIIII
111
111
1PA/5111111II MINIM 11E1
II%..IUUIuuu
FO
Transformer
E11 II111111 111111
/.%11111111111111M1111111111
II
11
ÏM11
11
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11I1111111I=
Series
Fig. 3
Album also includes stroboscope disc for
both 78 and 33% rpm for power frequencies
of 50 and 60 rpc.
CLARKSTAN
1000A 12-inch, 78 rpm. Vinylite, SF. Sweep
frequency record for oscillographic observation of equipment response. Range-70 to
10,000 cps, flat within 11 db. Sweep repetition rate, 20 per second. Crossover 500 cps.
1000D 12-inch, 78 rpm. Vinylite, SF. Sweep
frequency record similar to above, but covering range from 5000 to 15,000 cps, flat
within ±1 db, for observation of response
in high-frequency ranges. Sweep repetition
rate, 20 per second.
100A 16 -inch, 33% rpm. Vinylite, SF. Sweep
frequency record similar to above, but covering range from 60 to 10,000 cps, and
recorded with NAB characteristic. Sweep
repetition rate, 20 per second.
All three above records have synchronizing
pulses at beginning of each sweep, and with
marker pulses at 1, 3, 5, 7, and 10 kc. Clark stan frequency records may be obtained from
most radio jobbers, or from Trionic Co. of
America, 11927 West Pico Blvd., Los Angels 34, California.
STANDARD RADIO
Frequency Test Record, l6 -inch, 33%
rpm. Vinylite, SF. Frequency bands of 1000
cps, 10, 9, 8, 7, 6, 5, 4, 3, and 2 kc, 1500,
1000, 800, 500, 400, 300, 200, 150,
100, 70, 50, and 1000 cps. Crossover at 500
cps, with constant velocity recording above
this frequency. intended for use by broadcast
stations, recording studios, and professional
users, and groove dimensions are standard
for transcriptions. Obtainable from Standard
Radio, Inc., 1 E. 54th St., New York 22, or
140 N. LaBrea, Hollywood 36, California.
COOK
10, 10 -inch, 78 rpm. Plastic. DF. Side
A: Frequency bands with voice announcements. CV above 500 cps with 3 db knee at
crossover. Velocity of stylus is 9 cm /sec,
±1 db. 1000 cps, 20, 17, 15,12, 10, 9, 8, 7,
6, 5, 4, 3, and 2 kc, 1500, 1000, 700, 500,
350, 250, 125, 62.5, 40, and 35 cps, followed
by 1000 cps band.
Side B: Band 1 (for 33.1/3 rpm) : LP spot
check with standard LP preemphasis-100,
1000, 3000, 6000, and 10,000 cps. Band 2:
100 and 7000 cps intermodulation test, with
7000 cps 12 db lower than 100 cps, on flat
basis. No preemphasis. Band 3: Slow sweep
frequencies, from 1000 cps to 35 cps, with
350-cps crossover.
Both sides are cut with V -tip stylus, permitting use with either 1- or 3 -mil reproducer.
Cook Laboratories, 139 Gordon St., Floral
Series
Provides Famous
ADC Quality
at Low Cost
The unvarying
formers has been
engineers through
dependability and
high quality of ADC trans-
recognized by electronics
the years. This record for
close tolerances over wide
frequency ranges results from:
e Training and experience in transformer design.
A careful system of production testing.
Modern production methods.
Use of only quality materials.
NOW! ADC has designed a new line of transformers
to meet a present day industry need for high trans-
former quality at lower prices.
Industrial Series
Yeoman Series for
Quality at Lower Price
The Yeoman series of low-priced transformers
includes a number of new designs not previously
offered by ADC, and some features of both the
famous ADC Quality Plus and Industrial lines.
Substitution of open frame construction for
hermetic seals and flexible leads for solder terminals are among design changes made in the
interest of economy.
The industry will find many uses for the
accurate, dependable, trouble free performance
of ADC transformers in the Yeoman price range.
This new transformer line covers all types of
applications; i.e., input, output, bridging, power
transformers and chokes.
Quality Plus Series
For full information about ADC transformers,
Write Today for your new ADC catalog.
GdGQ DEVELOPMENT CO.
"Audio Develops the Finest"
4851 13th Ave. South, Minneapolis 7, Minn.
Park. N. Y.
AUDIO ENGINEERING
SEPTEMBER, 1949
www.americanradiohistory.com
AmericanRadioHistory.Com
43
shows the stylus velocity of the 2A
recorder in cellulose nitrate relative
to that in air as measured by readings
of feedback voltage Es. This relationship was found to be independent of
the linear groove speed.
Perhaps one of the most important
yet least appreciated factors in recorder
performance is its response to a suddenly applied impulse, or its transient
7
DISC RECORDER
[from page 26]
as small as possible to insure that the
frequency response of the cutter will
not vary with discs of differing hardness nor change as the diameter or
depth of cut of the recorded groove
changes. The expanded scale of Figure
0
STYLUS VELOCITY IN CELLULOSE NITRATE
LACQUER RELATIVE TO STYLUS VELOCITY
INAIR AS MEASURED BY READING OF E3
I
1.0
2.0
i
FREQUENCY IN CYCLES PER SECOND
Fig. 7. Effect of record material on recorder response.
FULL POWER
ALL
THE
WAY
with the new
MODEL II
AMPLIFIER
SPECIFICATIONS:
Power:
Size:
watts anywhere
from 30 cycles to
IS k.c. with only
1/2% TH and N.
19.6
7
" :II " :6 "hi
Gain:
High
imp. input
volts in produces
20 watts out.
11/2
Wt.:
171/1
Output imp.:
8
-
20 Ohms
AUDIO PACIFIC CO.
You Are
Invited
To
$60
users
lbs.
net
30 W. Colorado St.
Pasadena 1, Calif.
Attend The first Annual
AUDIO FAlli
Hotel New Yorker, New York City, October 27, 28, 29
An event of utmost importance
to Broadcast Engineers, Recordists, Sound -on -Film Men, Public
Address Men, Audio Hobbyists
and Distributors and Dealers.
F.S
44
Sponsored
by
the
Presenting for the first time,
under one roof, an industrywide display of audio equipment, components and accessories.
AUDIO ENGINEERING SOCIETY
response. Speech contains many transients, and in music many instruments
are more readily identified by their
characteristic transient attack than by
their harmonic content. It is important,
therefore, that these transients should
undergo as little change as possible
in the recording process. In general
this requires a wide frequency band
of uniform response and a phase shift
which is linear with frequency throughout the band, not only to prevent degradation of the components of the
transient itself, but also to insure that
individual elements of the recorder do
not vibrate independently at their own
natural frequencies when subjected to
this form of shock excitation and so
introduce extraneous frequencies which
help mask the original impulse. The
transient response of the feedback cutter system was studied by observing the
oscilloscope tracing of voltage Ea while
the stylus was recording a square wave
of 400 -cps repetition rate. The record
was then played back with the reproducer output connected to the scope.
Both patterns showed steep sides and
fairly sharp corners, indicating satisfactory high- and low- frequency response with linear phase relationship.
Superposed on the horizontal top of
the patterns was a transient wave of
approximately 11,000 cps with a small
initial amplitude and having a decrement sufficient to reduce the amplitude
of the wave train to substantially zero
in 1/1600 second (,4 cycle of the 400
-cps repetition rate). It seems reasonable to assume that such a transient
will not seriously affect an otherwise
high -quality recording.
That the behavior of the recorder
would be satisfactory when subjected to
a sudden impulse or transient could
have been predicted by a consideration of data taken under steady -state
conditions. Figure 5 shows the response
to be flat over a wide frequency band.
The phase shift corresponding to the
no- feedback- condition curve can be
calculated and then modified according
to equation 6 (feedback results in improved phase linearity as well as improved response). Phase calculated in
this manner checks quite accurately
with measured results over the frequency band where feedback is controlling
and indicates a favorable condition for
transient response.
Conclusion
The data presented above on frequency response, reserve power, intermodu-
ration distortion, effect of varying record material, phase and transient response attest to the benefits of properly
controlled feedback in a disc recorder;
benefits which are permanent and independent of temperature and humidity
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
SEPTEMBER, 1949
variations as well as the deterioration
of damping members.
It has also been demonstrated that
the recorder possesses another inherent
advantage -the ability to permit rapid
evaluation of response and distortion
while in actual use by examination of
the feedback voltage, Es. This can be a
valuable tool with which to investigate
and correlate recording parameters as
well as facilitate routine checking of
the complete recording channel.
It is hoped that the recorder will be
instrumental in establishing new standards in the disc recording field.
Logarithmic Amplifiers
[from page 17]
only a four -fold increase at the output. These are within the capacities of
most oscillographs.
Circuits
Some of the circuits are new enough
to warrant discussion, and some are well
known to the art. The means of applying bias to the log element is perhaps
the most important. The log element
alone may be used in a simple circuit,
at the expense of some curvature of the
log characteristic at low input levels. If
we apply bias, it has to be d.c. To ensure
the right polarity of bias for the right
signal polarity, it is necessary to use
two matched log elements appropriately
biased, with the inputs to the two
elements through oppositely phased
rectifiers as shown in Fig. 8. The outputs of the elements are paralleled
through the rectifier resistances (which
are low by comparison). The bias voltage should be set very carefully for beat
results, then stabilized.
The most convenient output circuit,
with a log element which gives a
large enough output voltage, is a cathode follower. The one shown in Fig. 9
STEPHENS TRY-SONIC
HIGH FREQUENCY CELLULAR HORN
with 20-watt electro- dynamic driver
LIST PRICE $110-
Audio engineers and all
music lovers instantly recognize this
as the prize audio bargain of the year
a superior "tweeter" for homes,
sound studios, schools, labs and small
theatres! Convert your PM or dynamic speaker to an 800 -cycle cutoff
dual speaker system of incredible
range, fidelity and tonal quality. So
far as we know, this type of unit
has never before been available at
below regular price. Write, phone
or wire your order today, while the
...
supply lasts!
YOU SAVE
$80.50
Limited quantity! shipped anywhere in the world.
Add postage for 26 lb'. 'hipping weight.
-
SPECIFICATIONS: Strp6rn, Tru- 5.nic mold 824H horn
fig-tration; 40x80 degree dispersion; eight 800 -cycle cells
800 cycle, 2x4 con -
4 "x4
-
"x1l" (intercept
20 degree solid angle. Stephen' Tun-Sons model Eli high frequency unit
futl 20 watts above 800 cycles; II ohm aluminum voice coil; electro- dyynagiic
unit has 3 Ib. copper coil (150 ohms), field dissipation 15 watts. Extra deta'!t:
21 lbs. Color
gray.
overall size
15
L. 1454" W. 8^ H. Net weight
Horn and driver completely assembled; mounting brackets at front and rear.
-
-
-
FREE! Write today for your copy of the 108 -page Radio Shack
Catalog for 1949, and monthly Audio Comparator Newsletter.
WHEN IN BOSTON
DON'T FAIL TO VISIT
THE RADIO SHACK
6J5
300
Boston's famous RADIO SHACK brings you
an EX[L USI VE SPECIAL PURCHASE
V.
"AUDIO COMPARATOR"
ot
INPUT
CUTPUl
Fig. 9. Cathode follower output stage.
has an output impedance of 1000 ohms,
low enough to feed a shielded cable
without attenuation of high frequencies. Lower impedance may be secured
if necessary by raising the transconductance of the tube.
The input amplifier which drives the
AUDIO ENGINEERING
SEPTEMBER, 1949
www.americanradiohistory.com
AmericanRadioHistory.Com
45
log element is a standard instrument
amplifier, with heavy negative feed-
NEED RECORDING
back for stability, and an'exceptionally well filtered power supply.
TAPE IN A HURRY?
Pr cautlons
emergency use, we will
rush ship (by Air if outside
N. Y. area) up to 20 reels
from oui New York stock at
prices listed for such quantities.
For
It might
be well to emphasize some
basic precautions. They have been given
before, but they will bear repeating.
THESE
IN
DISPLAYS
FOUR HUNDRED
RADIO PARTS
STORES
from coast to coast, and also Honolulu and Anchorage, Alaska, making it
easy for you to pick out the "XL" for
your microphone and radio equipment.
The XL Series is growing in popular-
ity wherever quality radio equipment
is used. Prices are reasonable.
Among the 400 radio parts firms where
you may buy "XL" fittings are: Concord
Radio, Chicago; Southeast Audio, Jacksonville; Springfield Sound, Springfield,
Mass.; Eugene G. Wile, Philadelphia;
Carolina Radio Equipment, Raleigh,
N. C.; Harrison Equipment, Houston;
Satterfield Supply, Madison, Wis.; W. D.
Brill, Oakland, Calif.
The slightest degree of nonlinearity
in the amplifiers is cumulative, and can
result only in a non-linear scale. Worse
than that, every time a tube is changed,
the scale law will change -an unbearable situation. To avoid this, check the
amplifiers carefully for nonlinearity,
with a gain set and a v -t voltmeter.
The possession of a good logarithmic
material is only a part of the design
problem, for one must retain the linearlog relation in the rest of the circuit
after achieving it in the log element.
Finally, the log element should be so
proportioned that the maximum output
voltage is of the order of a volt. Too
small an output will require more amplification in the vacuum tube voltmeter and in the output circuit, amplification which will handle a 15000
cps square wave without distortion.
This is costly and unnecessary, for the
log output can be made as much as a
volt without trouble.
It is. believed that the stable logarithmic system, perhaps combined with
an oscillograph, has very interesting
possibilities in audio instrumentation.
CALL
OR WRITE
today for complete
Recording Tape price
list and a Free supply of
Program Identification
Labels.
AUDIO & VIDEO PRODUCTS CORP.
i
650 BROADWAV, N.Y,19,H.Y.
TAPE
SPLICER
FOR MAGNETIC
RECORDING
TAPES
The new CARSON s.uE SPLICER: 1. Holds
tape In correct alignment; 2. Makes a diagonal splice
for no playback splice noise; 3. Uses
razor blade
or similar cutting edge for all cutting operations;
4. Allows all operations to be made with the tape
in one position; 5. Uses any kind of cellulose adhesive tape; 6. Is small enough to be mouhted on
your recorder ready for Instant use; 7. Permits anyone to easily and quickly make good splices on either
paper or plastic tape.
CARSON TAPE SPLICER
Postpaid In U. S.
SPLICER -With blades and splicing tape
-
NEW XL -4 INSERT
Box 6960. Washington 20, D.C.
PROBLEMS IN AUDIO
4
10 -amp.
contacts
2
Face
a
View
Pin Side
Shown in the new XIA -249
latest edition of the
four -page XL Bulletin
which lists prices of
the XL-3 types as well
as the XL-4. The New
CEDR -9 will be sent
with the XL, if you
prefer, so that you
may pick out the
radio parts store
nearest you carrying not only XL
plugs but other
Cannon Electric
fittings.
-
Address
Department I-109
SINCE 1915
CaaAoai
Ja
QQOQ
"-/-HIG7/¡'vaor
Division of Cannon Manufacturing Corp.
3209 HUMBOLDT ST., LOS ANGELES 31, CALIF.
IN CANADA A BRITISH EMPIRE:
CANNON ELECTRIC CO., LTD., TORONTO 13, ONT.
WORLD EXPORT (Excepting British Empire):
FRAZAR & HANSEN, 301 CLAY ST., SAN FRANCISCO
46
$1.60
$2.00
MAGNECESSORIES
I
If the source of the sound which
the pipe amplifies or resonates, contains numerous other frequencies, but
none that are harmonically related,
then only the one frequency will be
amplified. This is the case with the
organ. In either the reed or the fluepipe organ, the tones produced by the
reed or edge contain numerous tones,
some that are harmonically related and
others that are not. However, because
the pipe is a selective device it will deliver a fairly pure harmonically related
series of tones.
The final two cases of sound generators that will be considered in this
article are the circular membrane and
the circular plate. There have been
numerous analyses made of plate and
membranes of various shapes. However,
they are extremely complex and result
in a series of equations for each case
which express the frequency of the fundamental and the series of overtones
for the different modes of vibration
of the plate and the membrane.
Basically, if a stretched circular
membrane is struck in the center, a
two dimensional wave will be gener-
AUDIO ENGINEERING SCHOOL
practical
A
Engineering
eourse
In
Sound
termodulatlon Analyzer and other eapt. Recording
Studio assimilating Broadcast. Motion Picture and
Commercial Sound Recording. II. M. TRENTAINE.
I
r, -Dir
s
Approved !
r
Veteran< and Foreign Visas
HOLLYWOOD SOUND INSTITUTE Inc
1040 -A
Kenmore
No.
Hollywood
27, Calif.
ADDRESS CHANGES ...
Subscribers to AUDIO ENGINEERING should notify our Circulation
Dept. at least 5 weeks in advance
regarding any change in address. The
Post Office Dept. does not forward
magazines sent to a wrong address
unless you pay additional postage.
We can not duplicate copies sent to
your old residence. Old and new addresses MUST be given.
.
AUDIO ENGINEERING
RADIO
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
Andin
Fundamentls: FILM, MAGNETIC and DISC Recording: Transmission Measurements: Monitoring and
Mixing. Laboratories contain. Transmission Sets,
Oscillators, Distortion Sets; Harmonic Analyzer: In.
342
MAGAZINES, Inc.
MADISON AVENUE
New York .7, N. Y.
SEPTEMBER, 1949
ated and the air in front of the membrane will be set in motion thus causing a spherical wave to be generated
in the air. This is the situation that
occurs when a drum is struck. However the form of the enclosure of the
drum also affects the modes of vibration
thus determining the overtone structure. The frequency spectrum of the
stretched circular membrane may be
expressed by the general equation.
C
R
where C
R
T
m
=
y
j
I
\
I
HE PROFESSION, ;liA HONORED NAME
ALTEC
T
m
Right -The Altec Lansing
A -323C Amplifier
constant determined by
the overtone to be found
and the mode of vibration.
radius of membrane in
a
=
cm.
= tension on membrane in
dynes per cm.
= mass in grams per square
cm. of area.
In the references, the book by Dr. H.
F. Olson contains an excellent list of
the numerical values of the constant C.
For the clamped circular plate which
appears in audio work as the diaphragm
of the carbon microphone, the telephone
receiver, and certain types of loudspeakers, the derivation and the resulting equations of its fundamental frequency and overtones are even more
complex than those for the membrane.
The general form of the equation is
Ct
/
R2 V p
Left -The Altec Lansing
FM-AM Tuncr
Air -101
ENGINEERED FOR THE HIGHEST POSSIBLE
PERFORMANCE REGARDLESS OF COST
This superb two -unit
Altec Lansing combination was designed in accordance with a single directive: "They are to be
the finest. No component,
no circuit, is to be chosen
with price in mind. They
must be able to realize
the full resources of the
finest AM and FM programs; they must be
capable of receiving and
delivering these resources
undisturbed to the finest
loudspeaker in the world,
M
quality reception. The
distortion-free circuits of
the FM section re-create
all of the life -like repro-
duction possible with
FM. The A -323C Amplifier transmits to the loudspeaker the signal deliv-
ered by the tuner,
changed only in power
level. This two -unit corn-
PROGRAM
(1--02)
where C = constant determined by
the overtone to be found
and the mode of vibration.
R = radius of the plate between clamps in cm.
p = density of the plate in
grams per cm.3
M = Young's modulus of elasticity in dynes per cm?
a = Poisson's ratio.
t = thickness of plate in cm.
Again the reader is referred to Dr.
Olson's book for the values of the constants.
Having discussed the general background of sound generators, two special cases will be left for the next and
concluding article. These are the generation of speech sounds and the generation of sound by musical instruments.
READING LIST
Acoustics. -Wood, Alexander, lnterscience
Publishers, Inc., New York, N. Y., 1941.
Elements of Acoustical Engineering. -Olson,
Harry F., D. Van Nostrand Company, Inc.,
New York, N. Y., 1947.
Theory of Sound.-Lord Rayleigh (John
William Strutt) Dover Publications, New
York, N. Y., 1945.
Vibration and Sound.- Morse, Philip M.,
McGraw-Hill Book Company, Inc., New
York. N. Y., 1945.
AUDIO ENGINEERING
the Altec Lansing 604B
Duplex." The AM section
is an improved tuned radio
frequency circuit recognized as the best for high
bination is available with
special accessories to permit rack mounting for
professional monitoring.
Phonograph and television inputs and required
switching are provided.
Technical folder describ.ng
ALC -101 Tuner and A -3230
Amplifier sent on request. Waste
Alter Lansing Corporation, 1161
North Vine Street, Hollywood
38, Calif., 161 Sixth Avenue,
New York 13, N. Y.
EQUALIZER
Cinema Type 6511
.
e.e e
i1
-
°11= 1621r.IiESPIEMI
IIIII /NIIIIWá1II
RIIIII
+,
,
,
IIIIIMI-
MINIM
WI
The chart above i lustrates the maximum equal'zation and attenuation
offered in Cinema's New 6511 Program Equalizer. Low insertion loss, constant
"K" circuit means extremely flexible click -less control, in 3 db steps. It's the
answer to poor acoustics.
SPECIFICATIONS:
Constant "K"
Insertion Loss
10 db
Circuit
Panel
31/2" Rack
Controls
-
Low -f knob; 3db steps; 9db
equalization, (peaked at 100 cps) 9db attenuation. High -f knob: 3db steps; 9db
equalization (peaked at 5 KC). 9 db often-
Mounting (W.E.Std.)
uation.
Write for Bulletin C-1000 for Additional Data.
CINEMA ENGINEERING COMPANY
1510 WEST VERDUGO AVENUE, BURBANK, CALIFORNIA
Export Agent.: Fraaar
SEPTEMBER, 1949
www.americanradiohistory.com
AmericanRadioHistory.Com
&
Honren, Lid.
301 Clay Street
Son Francisco,
Calif., U. 5. A.
47
sw.11
BETTER ELECTRONIC EQUIPMENT
Ready NO II'
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toea STANDARDIZED
ULTRASONIC FUNDAMENTALS
READY -
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NEEDS
Par -Metal
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Equipment
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Write for Catalog.
PAR -META
L
31.62 -49th ST., LONG ISLAND CITY 3, N.Y.
Export Dept.: Rocke International Corp.
13 East 40 Street, New York 16
THE HARTLEY - TURNER
SPEAKER
IS FORGING AHEAD.
The 215 Speaker Is making its way all over the
United States and Canada too. The price interns
but the performance settles the matter. Practically
every null is bringing new testimony from delighted
users that the speaker they have sought for years
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Pelee which on the face of
It seems absurd for such performance.
It Is our settled policy not to allow the distribution out of our hands. This company has been built
up in
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are hand -made and our technical advice and service h
not "laid on" In a mans-production way. Each one
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So where we
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have found
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-
representative.
These representatives are gradually being found.
and when found we tell them who has written to
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local sound expert you will know we have not yet
got together. We are glad to hear from dealer. who
want an exclusive agency and we are glad to hear
from the user himself if he knows the right man
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Send
dollar bill today for the complete guide to
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New Notes in Radio ", including
service of technical data sheets dealing with every
aspect of the subject. Literature is free for the asking.
$50.00
14.00
32.00
H. A. HARTLEY Co., Ltd.
152, HAMMERSMITH ROAD,
LONDON, W. 6, ENGLAND
48
Allied Radio Corp.
48
47
Alfec Lansing Corp.
38
Amperife Co., Inc.
Ampex Electric Corp.
Arnold Engineering Co.
9
Audak Company
32
Audio Development Co.
43
Audio Devices, Inc.
Cover 2
Audio Engineering Society
44
Audio Facilities Corp.
36
Audio Instrument Co.
40
Audio Pacific Co.
44
Audio & Video Products Corp 46
Bozak, R. T.
42
Camera Equipment Co.
Cannon Electric Dev. Co.
Cinema Engineering Co.
Clarkstan Corp.
30
46
47
31
Daven Co., The
PRODUCTS CORPORATION
By S. YOUNG WHITE
The rapid increase in the use of ultrasonic. during
few rem makes It natural that the well Informed sound engineer should want to learn something of the applications and potentialities of this
amazing new field. But interest in ultrasonics is
not confined to the sound engineer
in of still
greater Importance to the industrial engineer for he
is the one who will visualize Its uses In his own
the last
Cover
3
-it
processes.
Elementary
DAMENTALS
in character,
ULTRASONIC FUN-
was written originally as a series of
magazine articles Just for the purpose of acquainting
the notice in this field with the enormous possibilities
of
new tool for Industry. It serves the double purpose of introducing ultrasonics to both sound and
industrial engineers. The list of chapter headings
will Indicate how it can help you.
CHAPTER HEADLINES
Too Much Audio. Opportunities in Ultrasonics.
Elements of ultrasonics. Experimental Ultra.
sonic,. Coupling Ultrasorlie Energy to a Load.
Ultrasonics in Liquids. Ultrasonics In Solids.
Tenting by Ultrasonics. Nigh -Power Ultrawnia..
Notes on Using Nigh-Power ultrasonics. Applleations of Ultrasonics to Biology. Economics of
Industrial Ultrasonics.
The applications of ultrasonics have already extended to many Industries, and as Its possibllitlm
are explored they will increase a hundredfold. To keep
abreast of Its growth, engineers in all fields must
know what they may expert from ultrasonics. bow
is used, how the energy Is generated, and the technique. of applying ultrasonic treatment to many pro-
it
-it
cesse..
ULTRASONIC FUNDAMENTALS is not a big
book
does not rover the entire field of ultrasonics
with hundreds of pages of dull reading. But In the
three hours it will take you to read it, you will get
a down -to -earth glimpse into the far- reaching toralbiiities of a new art.
ULTRASONIC FUNDAMENTALS
By S. YOUNG WHITE
illustrations. 81/2 x
$1.76
paper cover.
Book Division, Dept. A
RADIO MAGAZINES, INC.
342 Madison Avenue
36 pages, 40
Electro- Voice, Inc.
27
Fairchild Recording Equip. Corp.
Freed Transformer Co., Inc.
8
7
New York
Gordon, Herman Lewis
36
Hartley, H. A. Co., Ltd.
Hewlett- Packard Co.
Hollywood Sound Institute
48
46
LeBel, C. J.
36
Magnecessories
46
Magnecord, Inc.
29
Par-Metal Products Corp.
Peerless Elec. Products
Pickering & Co., Inc.
Presto Recording Corp.
48
34
Professional Directory
36
196 PAGES
Racon
42
Radio Shack, The
45
Everything in
Radio and
I,
N. Y.
1
ALLIED'S NEW
1950
CATALOG!
5
6
Shallcross Manuafacturing Co.
Shure Brothers, Inc.
Somerset Laboratories, Inc.
Stephens Manufacturing Co.
.
33
35
38
34
Sun Radio & Electronics Co.,
Inc.
36
Tech Laboratories, Inc.
Terminal Radio Corp.
Triad Transformer Mfg. Co.
Turner Company, The
United Transformer Corp.
U. S. Recording Co.
17,
I
Cover
Ward Leonard Electric Co.
Wells, Winston
Western Electric Company
40
39
32
Electronics
4111g1
fe114
RADIO'S
LEADING BUYING GUIDE
GET
Service Technicians and Engineers: ALLIED's 1950 Buying Guide brings you all
the new releases and money- saving values -from the world's largest stocks of
teat instruments, amplifiers, P.A. systems and equipment, tubes, parts, tools,
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expert shipment. Send today for your
FREE new 196-page ALLIED Catalog.
41
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36
37
36
10
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AmericanRadioHistory.Com
-
SEPTEMBER, 1949
r
...FOR
TOUGH
THOSE
'i'44g" PROBLEMS
TRY
DAVEN!
Whether you use switches for industrial applications, communications or laboratory
a Daven -constructed unit will give maximum performance. Many years of
engineering experience and skilled workmanship have been combined to make a
truly superior switch.
work
WRITE FOR YOJR COPY
OF OUR NEW
SWITCH BULLETIN
Daven switches are the rotary selector type-outstanding in design and capable
of withstanding the most critical tests. They are preferred by engineers who want
the best.
Some outstanälñg
fees are
Low and uniform contact resistance.
Minimum thermal noise.
High resistance to leakage.
Trouble -free operation and long life.
Roller -type positive detent action.
Depth of unit not increased by addition of detent.
A full line of sta!
CIA
make
break
make
break
C2B
C7A
C8B
DIA
D7A
D9A
1
10
E3A
E4B
E7A
E8B
before
before
before
before
break
make
break
make
DAVEN can adapt
a
standard switch for your special requirements.
Our engineers will he glad to offer suggestions on your problems.
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Diameter
Site
3/4..
13/4"
2
I
5
make before break
break before make
make before break
break before make
Single deck switches are round.
Poles
Deck
Per
15
47
make
Deck
Maximum
31
make before break
make before break
make before break
break before make
break before
F2B
switches are available.
1laximum No
of Positions
(per pole)
Operation
Type
D
P
2
1Y4"
13/4"
21/4..
14
4
21/4
9
5
5
5
21/4"
21/4"
47
2
23
23
2
12
4
30
4
I
Multi -deck switches are square.
23/4"
23/4.
tin
AIL'
PRODUCERS OF PERMALLOY DUST TOROID COILS AND FILTERS
S FOR O. R A DECADE
20I
NNE
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MIEN
BROAD BAND
SHARP CUTOFF
1}¡"
FILTER
HClA, C, D
Die. y ITV High.
II»
IN
U
In
.,rowcL-erars
4
Iw
sr
HQA
Emu
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Lx
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NARROW BAND
Hm
SHARP CUTOFF
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FILTER
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111111ÌAINI\INI
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UNCASED TOROIDS
,00
ATTENUATES
HOC
10KC TO 30
MEGACYCLES
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¿Co
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01111010101 *1 0 MAL)
,00
- ME
ii
art
-
LC
VIC
W FREQUENCY
11/2-
LOW PASS
L.
x
10
NM
MI
HOD
930C
11/4" W. x 11/2" H.
FILTER
SUB- OUNCER
TOROID FILTERS
Filters employing SUB.OUNCER toroids and
special condensers represent the optimum
in miniaturized filter performance. The band
pass filter shown
weighs 6 ounces.
150 VARICK STREET
write :or catalog PS-409
NEW YORK 13, N. Y.
EXPORT DI'.ISION: 1. EASE 13 h STREET. NEW YORK 16, N. Y..
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AmericanRadioHistory.Com
CO
rozour0C.
CABLES: "ARLAW'
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