Dec - American Radio History

Dec - American Radio History
DECEMBER
1950
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AmericanRadioHistory.Com
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NAME
COMPANY
ADDRESS
L
CITY
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STATE
J
rSuccessor to
,dU D 1
I
UREAU
IRCULATI
Ladd Haystead, Publisher
Luci Turner, Production Manager
Lucille Carty, Circulation Manager
S.
For the Home
S
L. Cahn, Advertising Director
H. N. Reizes, Advertising Manager
Editorial Advisory Board
Representatives
Sanford R. Cowan, Mid -West Sales
342 Madison Ave., New York 17, N. Y.
James C. Galloway, Pacific Coast Sales
816 W. 5th St., Los Angeles 17, Calif.
Technical Book 6. Magazine Co.
297 Swanston St., Melbourne, C. I.
Victoria, Australia
Howard A. Chinn
John D. Colvin
C. J. Le9el
Maxfield
George M. Nixon
CONTENTS
Reproduction
N lu afe
UDII
C. G. McProud, Editor
P.
ide Range
Established 1917
ENGINEERING'
J.
_D1Q
DECEMBER, 1950
Vol. 34, No. 12
Triad Hi- Fidelity
Amplifier
2
Audio Patents-Richard H. Dorf
Letters
4
8
Technicana
10
Editor's Report
Design, Construction and Adjustment of Reflexed Loudspeaker Enclosures
15
-David W. Worden
18
A Continously Variable Loudness Control-E. E. Johnson
Rapied Attenuator Calculation Using the Vector Slide Rule
19
-A. E. Richmond
21
Determining Unknown Impedances in Transformers-Louis H. Hippe
Audio Design Notes
22
Resonant Loudspeaker Enclosures -Bob H. Smith
Kit...
Triad HF10 Amplifier, from a circuit
designed in cooperation with J. N. A.
The
Hawkins, prominent sound engineer, has been
produced especially for those who like to
build their own sound reproducing systems.
When used with the high quality speakers,
tuners, turntables, and pick -ups now available, a system can be built that will meet
the requirements of even the most critical
music lover. The Triad HF -10 kit supplies
the basic engineering and solves the most
difficult mechanical layout problems. With
18 db. of feedback, affording a reflected
impedance of less than 2 ohms to the 16 ohm
speaker tap, within 1 db. linear frequency
response from 20 to 20,000 cycles, and with
a minimum of distortion over this same
range, the HF -10 is worthy of use in the very
finest home music installations.
AUDIO engineering society SECTION
Convention Report
The Audio Fair Review
Audiana -High Fidelity-Lewis S. Goodfriend
Record Revue-Edward Tathall Canby
Pops -Rudo S. Globus
New Products
Employment Register
New Literature
Annual Index
23
24
34
36
36
50
59
61
62
64
Advertising Index
COVER
Mr. Price Fish of CBS General Engineering Dept. is seen with two of the
Fairchild Plc -SYNC Magnetic Tape Recorders installed at the WCBS -TV
Studios (New York). This % -in. tape equipment is the heart of the
CBS -TV "Mag -Neg -Tic" TV recording technique of reproducing
sound from the tape in synchronism with motion picture
film. A Fairchild Plc -SYNC installation at the Hollywood
CBS Studios includes recording and production
editing facilities for the preparation of magnetic
tape sound and TV picture film recordings
for release from New York on the
video network.
*Features...
Wide Frequency Response: Within one db.
from 20. 20,000 cycles.
Low Distortion: Less than 2% from 50.18,000
cycles at full 10 watts output. Less than 1%
from 20-20,000 cycles at 5 watts.
Heavy Speaker Damping: Reflects less than
2 ohms to speaker from 16 ohm tap.
Equalization: Continuously variable to +12
db. or -- 30 db. at 50 or 8000 cycles.
High Cain: 74 db. from crystal microphone
or radio receiver; 96 db. (equalized for
magnetic pickup) through preamplifier.
Low Noise: Hum and other noise 60 db. below
maximum output. A -741 equalizing coil has
70 db. shielding.
Beautiful Appearance: Cray hammertone
chassis with ivory silk -screened lettering,
matching gray Triad transformers.
*Prices
Hí10 kit -- Includes S -31A, R -14A, A -741, and
-10X Triad transformers, chassis, prints and
assembly instructions.
list Price $39.85
HF -10A kit -Same as above except for substitution of HS.81 output transformer for
S31A.
List Price $57.75
C
See your dealer or write for Bulletin HF -10,
and Catalog TR-49A which describes
the complete Triad line.
AUDIO ENGINEERING (title registered U. S. Pat. OR.) b published monthly at 10 McGovern Ave., Lancaster, Pa.,
by Radio Magazines. Inc.. D. S. Potts. President: Henry A. Sehober, Vire-President. Executive and Editorial Offices; 342
Madison Avenue. New York 17, N. Y. Suh;cripUon rates -United States. U. S. Possessions and Canada, $3.00 for 1
year, $5.00 for 2 years; elsewhere $4.00 per year. Single copies 35e. Printed in U. S. A. All rights reserved. Entire
eoRtents copyright 1950 by Radio Magazines, Inc. Entered as Second Class Matter February 9, 1950 at the Post
Mee. Lancaster. Pa. under the Act of /*larch 3, 1879.
AUDIO ENGINEERING
DECEMBER, 1950
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AmericanRadioHistory.Com
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REK -O -KOT
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RICHARD H. DORF"
(or should we
say "capacitor microphones" these
days ?) ate among the best available
when they are designed correctly. They
were used for a long time in broadcasting
and are now reappearing in improved versions. One of the headaches connected with
their use, however, is that a "head" amplifier must almost always be placed within a
few inches of the microphone because the
small microphone capacitance would be
swamped by the capacitance of leads of
any length.
One solution, of course, is the use of a
cathode -follower at the end of a cable,
since ordinary cathode followers can decrease the effective input capacitance by as
much as 100 times. Even this is not sufficient, however, for with the conventional
pentode cathode follower using a 0.5 -meg.
grid resistor-without any cable to speak of
between microphone and grid -and a 25 -1.40
microphone the lower cutoff frequency (3
db down) is about 150 cps. Higher grid
resistor values make for unstable operation.
The "supercharged" cathode follower illustrated in Fig. 1, however, lowers the cutCoNDENSER MICROPHONES
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2
V, is connected across the output of the
cathode follower V,. Since it is in phase
with the V, cathode output voltage the total
feedback of the circuit is greatly increased.
For the circuit shown the effective input
impedance (at the grid of V,) is
R, =1
1
G
where G is the incremental gain from input
to output. If Ri is to be large, as is desired,
G must be very high, close to unity. And
if the gain of V, is infinite then
G=
µ
µ
-1
The insertion of V, makes for very large
incremental gain, which makes the net feedback also very great. Thé effective input
impedance thus is very much higher than
for a conventional cathode follower and the
effective input capacitance is correspond-
ingly reduced.
The inventer's experiments and calculations show that with the 25 -µµf microphone
working into a conventional pentode amplifier with a grid resistor of 0.5 meg., the
lower -frequency cutoff is 13,000 cps. With
an ordinary pentode cathode follower and
the same grid resistor, cutoff is at 150 cps.
With the supercharged circuit the response
is flat to 20 cps. Addition of a shunt grid
capacitor of 1,000 µµf, such as might be
present due to a length of connecting cable
between microphone and grid, resulted only
in a loss of 1 db below 10,000 cps.
The supercharged circuit, therefore, is increased by a factor of about 300. Points A
and B must be at the same d.c. potential.
That at A is adjusted by breaking the connection between the points and setting R,.
Heterodyne Oscillator
Fig.
1
off to 20 cps and even allows a 1,000-µµf
length of connecting cable to appear between
microphone and grid with negligible effects.
It is the invention of Paul S. Veneklasen
and is assigned to the United States as represented by the OSRD. The patent number
is 2,508,586.
The first 1620 in Fig. 1, V,, is a conventional cathode follower except that there
is also a plate load resistor R,. The plate
output of V, is fed in the conventional way
to the grid of V,, whose plate load resistor
is R,. The grid of Vs is directly coupled to
the plate of V,; V, is a second cathode follower. The output-that is, the cathode -of
Audio Consultant, 255 West 84th Street,
New York.
One of the common troubles in beat frequency test oscillators is "pulling" between the oscillators when they approach
the same frequency. The result is that the
beat value is usable only down to a certain
minimum frequency, below which the oscillators suddenly lock. The usual solution is
separation of the oscillators, thorough
shielding, and sometimes by adding buffer
isolation between each oscillator and the
mixer.
Ivor R. Worsley of London, England,
has designed a beat -frequency oscillator for
which the necessary space and cost have been
reduced and which has a special arrangement to reduce the effects of pulling between
oscillators. The patent, No. 2,510.165, is
assigned to International Standard Electric
Corp. The circuit is shown in Fig. 2.
The factor making for the reduction of
space and cost is the use of a triode -pentode
tube, such as the 6F7 (the inventor did not
mention this tube). The triode section of
the tube is used for the fixed oscillator and
[Continued on page 47]
AUDIO ENGINEERING
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AmericanRadioHistory.Com
DECEMBER, 1950
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AUDIO ENGINEERING
DECEMBER, 1950
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3
LETTERS
We CHALLENGE the
performance
of any 12" speaker with a
Ground Loudspeakers
Sir:
It was with great interest that we found
in AUDIO ENGINEERING, October 1949, an
article on Ground Loudspeakers.
We avail ourselves of this occasion to
draw your attention to the fact that ground
loudspeakers have been developed and installed in the Olympia Stadium in Berlin
by Telefunken as early as 1936. A description of the ground loudspeakers, the performance of which was fully satisfactory,
is to be found, for instance in the periodical Telefunken-Hausnlitteilungen No. 79
(1938) pages 66 and 67.
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PVVYY1,
ROYAL EIGHT"
SAYS PERMOFLUX'S
MR. HY-FY
bnias raacvouer
TELEFUNKEN
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Proves
that it
co
tess of
with.
sizee or Price. the
Choral Recording
Sir:
For a long time there has been a con-
est speak__
Hi -Fi Fans the country over
have accepted this challenge -have
asked their "soundman" for a demonstration -then,
have installed a Permoflux Royal Eight" in their
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well as tonal qualities which YOU too will want to
add to perfect the excellence of your own equipment.
Send for beautifully illustrated catalog No. J201 to
address listed below for further information including a full page devoted to correct baffling of
Royal Eight" and other size speakers.
Cheek These
troversy between engineering balance and
the proper acoustical balance of orchestral
and choral groups. Unfortunately this controversy stems from the failure of engineers
and conductors getting together on intel pretation of individual selections.
We are currently specializing in large
a capella and choral groups including the
famous St. Olaf Choir of Northfield, Minn.,
the Concordia Choir of Moorhead, Minn.,
The Notre Dame Cathedral Choir of Paris
(France) recorded in the cathedral itself,
The Cathedral Choir of the First Presbyterian Church of Hollywood, and many
others. These choirs consist of about sixty
Exclusive
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Soft- suspended cone and extra -large spider
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High permeance yoke increases output.
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Zone
voices, and we have found in many instances
that it is necessary to rearrange the music
for proper recording balance. There is a
vast difference between a concert arrange-
ment and a recording arrangement, which
few engineers or musical directors recognize. As a result there is always the tendency to run into shattering or complete
loss of balance on high -volume passages.
It is practically impossible to record consecutive thirds in women's voices and maintain proper diction or definition. However, if a simple expedient of inversion is
applied to the music itself the results are
very gratifying. The foregoing, of course,
is just one of the many problems to be met
on individual selections, and impossible
to get across to some musical directors for
it is treading on sacred ground, so to speak.
Any good director can usually be interested
in the laws of acoustics in recording if properly approached. Here the engineer should
be thoroughly versed in musical terminology in order to get his point across. A
good approach is to point out that film,
radio, and phonograph recording has a distinct technique of its own to be met and if
the director is given an opportunity to see
what happens when these problems are
not met, he will correct the situation.
On the surface, this report may sound
ambiguous, but the writer has spent years
in research and study from the viewpoints
of musicianship, scoring, and engineering,
and has given many courses in colleges
throughout the country in acoustic balance.
It is a highly specialized field of research,
and is extremely fascinating. To both the
engineer and the musical director it opens
horizons in music that have not been
touched.
Eddison von Ottenfeld, Mus.D.
Vonna Records,
12129 Hartsook,
North Hollywood, Calif.
Address
Lc7
i
State
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
DECEMBER, 1950
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OLENU0ER CORES
COMPLETE LINE OF CORES
TO MEET YOUR NEEDS
* Furnished
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four standard
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obtain nominal inductances as high as 281
mh 1000 turns.
sizes to
toroidal cores are given
* These
various types of enamel and
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2
For high Q in a small volume, characterize( by low eddy current
and hysteresis losses, ARNOLD Moly Permalloy Powder Toroidal
Cores are commercially available to meet high standards of physical
and electrical requirements. They provide constant permeability
over a wide range of flux density. The 125 Mu cores are recommended for use up to 15 kc, 60 Mu at 10 to 50 kc, 26Muat30to75kc,
and 14 Mu at 50 to 200 kc. Many of these cores may be furnished
stabilized to provide constant permeability (±0.1%) over a specific
temperature range.
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DECEMBER, 1950
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TAPE RECORDER
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Designed for applications where operating TIME
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For example, you can start or stop the tape in 0.1 second.
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A synchronous capstan makes it practical to hold
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...
for which proAnd with synchronizing equipment
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...
Many more important features, too.
Self-centering "snap -on" hub adaptors assure perfect
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('pZC ,Aauj
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'exciting
test
-
aë`
current
Another in
a
series which
demonstrates
PEERLESS
transformer
superiority!
I.
PEERLESS
S
o
Since the 1949 Audio Fair,
tests on transformers shown
all over the country have
demonstrated Peerless
superiority ...Now Peerless
emphasizes another very
important property of
Comvl,tar
t.t
tt.ttrte
transformers as shown by
the "exciting current test."
No
Competitor No.
NEI
1
An
2
output transformer's
ability to deliver plenty of
clean, low- frequency power
(the goal of every music
lover) is inversely proportional to the amplitude and
distortion of its exciting
current.
Competitor No. 3
PEERLESS superior low frequency power handling capacity is illustrated in these
comparative oscillograms.
Write for complete data.
PEERLESS
Electrical Products
Competitor No.
4
Division
1E1
Loren L. Ryder reporting in the International Projectionist, September 1950,
magnetic tape recordings with motion picture films is covered by Walter T. Selsted states that large savings in the production
in J. Soc. Mot. Pict. Tel. Eng. for Septemcosts of motion pictures are being effected
ber 1950. The equipment was designed to through the use of magnetic recording film
work with the Ampex model 300 and con- systems. Production, scoring, and dubbing
sists of a synchronizing signal generator recordings are largely magnetic-to- magnetic
and differential speed
detector and power
Audio and 60- Modulated
18Kc.R ection Filter
18 Kc.Carrie from
amplifier. The synPlayback O tput
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Input 600n
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II
II
ulated by the sixty
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Synch. Motor
Synch. Motor
IB Kc. 60- Audio
frigid mounted) Rotors (free Stotor)
for the motion picture camera. The
N2
18Kc.
DC
60- 10 Watt
18 K
60- 'u -c'
Selective-Lrmiler
audio input and the
mp
Pot.
60- Detector
60Amplifier
10 Watt
modulated 18 kc are
then recorded on the
From
V 60PrOjeCtorSupPly
tape.
tD C
In the playback the
Auto
18 kc is filtered from
50 Wait
Synch.
60- á,115V,
Manual
V F.0
Power
the audio output and
Indicating
50 Watt
Amplifier
fed to an 18 -kc limiter
Meter
To Playback Capstan
Manual
amplifier, 60 -cps deDrive Motor
Speed
tector, and 60 -cps 10Control
watt power amplifier.
This approximately
60-cps signal drives a rigidly mounted synwith only the negative for release printing
chronous motor, the rotor of which drives having a photographic sound track.
the rotor of a second synchronous motor
In practice, two recorders, each loaded
with 2500 feet of film, are assigned to each
with a free stator. The second stator is fed
from the 60 -cps supply driving the projector. production, eliminating loading delays and
minimizing run -outs. The recorders are
If there is a difference between the output
fully automatic, being turned over and
from the tape and the projector supply, the
"killed" by the cameraman as he operates
second stator will rotate. The second stator
the camera. Synchronization is also autooperates a d.c. potentiometer controlling a matic. When
trouble appears the equipment
variable-frequency oscillator. The oscillator is exchanged.
output is near 60 cps and is corrected by
Such use of magnetic film has eliminated
the two -motor differential system to syn- much of the film costs formerly required in
chronize the tape. The tape drive capstan dubbing and editing, since the magnetic film
is driven from the oscillator through a 50is never cut and may be used indefinitely.
watt amplifier.
1 -inch
a
comparative square wave
a>_a
Motion Picture Tape
The accurate synchronization of
115
-240 -0
ïl
Tape -Movie Synch
Sixth Avenue
New York 13, N.Y.
9356 Santa Monica Blvd.
Beverly Hills, Calif.
Australia Audio
Phono -Tape Adapter
The Italian journal Radio for September
carries the description of an assembly
to adapt a phonograph-radio into a tape re1950
corder.
Using no motors, the unit derives its
power from the phonograph drive spindle
through a variable speed system. The tape
speed is about 15 in. /sec., and the tape is
driven in both directions to provide a total
recording time of 15 minutes. The radio phonograph amplifier is used for both record
and playback, while the assembly contains
the bias oscillator. The general claim for
the adapter is its low cost, which is made
possible by the elimination of any motors.
The quality is said to be adequate for music.
The importance of high quality audio
equipment in radio broadcasting is the subject of an article by J. E. Teller in the
Amalgamated Wireless Technical Review
(Australia) Vol. 8 No. 4, June 1950. In
this 30 -page paper Mr. Telfer discusses the
fundamental requirements of studio design
and broadcast audio facilities. Various
pieces of equipment are described and illustrated. Many of these are of Australian
design and others are American.
One important phase of the discussion is
the comparison of the land line facilities
in the United States and in Australia. In
the U. S. the four major networks employ
130,000 miles of telephone circuit, while in
Australia only 8,000 miles of land line are
used. However, the Australian lines cover
[Continued on page 481
AUDIO ENGINEERING
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DECEMBER, 1950
r
A SIMPLE
ACOUSTIC CALIBRATOR
for
Your Sound -Level Meter
THE G -R
Type 759 -A and -B Sound Level Meters have built -in calibrators
for their electrical circuits; no means are
readily available, however, to check the
condition and calibration of their as-
sociated microphones.
The new Type 1552 -A Sound -Level
Calibrator is introduced as a simple,
convenient and accurate method for
calibrating both the microphone and
the over -all system. Essentially it consists of a small, stabilized and rugged
loud -speaker mounted in an enclosure
which fits over the microphone in the
sound -level meter. The acoustic coupling between the calibrator and the
microphone is fixed and can be repeated
accurately. Any audio oscillator with a
harmonic content of less than 5 %,
supplying 2 volts at 400 cycles, can be
used to operate the calibrator. A 500TYPE 1552 -A Sound -Level
ohm potentiometer is -. uired as an
output control if the o;illator is not
equipped with such a coisrol. An accurate vacuum-tube volt ter is needed
across the
to measure the volta
calibrator.
The level at which tlt: calibrator is
used is such that its op3ation is not
affected by ordinary bsck2round noises.
This simple device is an :d:al means not
only for assuring consiste:cy of calibration and locating defec :ivemicrophones,
but also for inter -stag ardization of
several sound level meters
The audio oscillator, v -t voltmeter and
i
potentiometer shown in the set-up photograph
you need these
are standard G -R items.
or if you do not know about the complete
line of G -R noise and vibration measuring
and analyzing equipment. WRITE FOR THE
If
"NOISE PRIMER ".
Calibrator
The Sound -Level
designed for use
Microphone.
$4'.00
GENERAL RADIO COMPANY
90
West St., New York
AUDIO ENGINEERING
6
920 S.
Calibrator was
primarily with
the Shure Brothers Type 9898
microphone as used on the G-R
Type 759 -B Sound -Level Meter.
It cal be used on other microphones
such as the Brush BR2S Sound Cell
Micsaphone and the Western
Ele.-ic Type 633 -A Dynamic
Michigan Ave., Chicago
DECEMBER, 1950
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5
1000 N. Seward
Cambridge 39,
Massachusetts
St., Los Angeles
38
9
EDITOR'S REPORT
MONITORING SYSTEMS
E IMPORTANCE of monitoring systems is often
overlooked by the design engineer or by the purchasing department when a recording studio installation is being laid out. It is not enough that just any
loudspeaker system be located somewhere in the monitoring booth, with the hope that it is capable of reproducing the material so that it is possible to determine
accurately the balance of an orchestra or between the
orchestra and a singer, for example. Monitoring systems -from the point where the amplifier is tied to the
recording system clear to the acoustic output of the
speaker into the air-are of tremendous importance,
and influence the quality of the entire product.
As an example, assume that a monitoring system is
deficient in bass. In order to obtain well balanced reproduction, the musical director may insist upon additional
equalization of the low frequencies or a change in microphone placement, with the result that the product has
too much bass if reproduced on a standard system. This
will not show up on playback because the same system
is used both times, and the increased bass level on the
recording will appear to be correct when reproduced
on a bass -deficient system.
Obviously, the same condition can obtain with high
frequencies, but an even worse loss may be caused by
the presence of an untoward number of people in the
monitor room during the recording. If a microphone
setup is made with only the musical director and the
engineer in the monitoring room and the balance is apparently correct, it should be apparent to anyone that
the influx of a number of people who presume to have
an interest in the recording will most certainly affect
the acoustics of the room. Changes in balance to
compensate for changes in monitoring conditions will be
reflected in the recorded result.
For a variety of reasons, radio stations provide a cliTII
alp Editur0
tit*
10
ents' booth in many cases, and it is usual for the number
of persons in the monitoring room to be restricted.
Where such restrictions cannot be imposed, it seems
desirable that a location be chosen for the loudspeaker
where changes in room acoustics will have a minimum
effect. This suggests that the speaker be mounted forward and above the mixing console, where it would be
impossible for anyone to come between it and the en-
gineer or the producer.
If a recording system is set up with variable equalization available to the engineer, it seems logical that the
tap -off for the monitoring system should follow that
equalization. Between the tap -off point and the recording cutter, the only equalization that should be permitted
-in addition to the decompensation required for the
pre -emphasis-is that which is fixed or semi -fixed for
compensation of the cutter, or for processing losse,..
Similarly, no variable equalization should be permitted
in the monitoring system, except that which is adjusted
with the aid of a soldering iron. If level adjustments
are available at the console, some loudness compensation
should be added automatically. Since the final product is
dependent on what is heard in the monitoring room at
the time of recording, the monitor system is of prime
importance, and should receive at least as much attention as any other part of the installation.
Both amplifiers and speakers should be set up on the
basis of a standard playback curve, and should be most
carefully maintained in accordance with those curves if
there is to be any standardization of the product. The
Standard Playback Curve recently adopted by the
Audio Engineering Society is ideal for the electrical
circuits. The choice of speaker, housing, and location
should be made after thorough tests, and after the
acoustic output of the speaker in its selected location is
carefully assessed. Only by attention to every detail can
a consistent product be expected from any recording
studio.
Beyond that
.
..
ftiff
of Aixdiu Enginueri ng
gun a urrg Merry Tiristmas
an.d a liäppg Nrui War.
anò
AUDIO ENGINEERING
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DECEMBER, 1950
I,Ii1111//111]
stylus /
pickups
ACKNOWLEDGED BY ENGINEERS
AS THE FINEST AVAILABLE!
superiority of diamond styli to
styli of other materials has been thoroughly established.
The
Exhaustive tests prove resistance to
abrasion of diamond styli is many
times greater than that of the next
hardest material.
Great resistance to abrasion means a
minimum of record wear, longer record life and concert hall quality music
all the time.
Pickering pickup cartridges, equipper with diamond styli, may cost mor? than cartridges with
other stylus materials but the useful life of a
diamond stylus cartridge is so much greater
than is represented in the cost diferential that
from all practical viewpoirts- length of service,
Pickering
listening pleasure, and record life
diamond stylus cartridges cost less.
-
The diamonds used in Pickering cartridges are
whole diamonds, not splints. They nre well cut,
gem -polished to high nc:uracy apd precisely
mounted to ride free and smooth in the groove
walls, recreating all the fine tones rind modulations pressed into modern recordings.
Diamcnr Cartridges
unchallenged. They meet ever} exacting requirement of the most :-itical reccrd playing
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to maintain the useful life of his record collection.
The supremacy of Pickering
is
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AUDIO ENGINEERING
DECEMBER, 1950
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Y.
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BROCHURE
No
12
obligation
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DECEMBER, 1950
HIGHEST
FOR
Precision Magnetic Tape Recorder
for
The Jury of
HIGH - FIDELITY
Professional Use
Award for the 12th
Annual Electrical Manufacturing
Products Design Competition selected Ampex Model 300 as an outstanding achievement in product
development, design and engineering.
We at Ampex were more than
delighted to find our name in the
winning group which included four
other manufacturers receiving similar top -flight awards.
During the past several months
Model 300 has, performance -wise,
just about revolutionized magnetic
tape recording standards throughout the world of entertainment as
well as in scientific research. Write
for Model 300 specifications and
the address of your nearest Ampex
distributor.
FOR FULL DETAILS OF AWARD read Oc-
tober (1950) Product Design Issue of
Electrical Manufacturing Magazine.
HIGHEST ACHIEVEMENT
jn
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DECEMBER, 1950
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13
Testing for sound lost between
telephone receiver and ear. Many
subjects were used in these tests.
How to compensate for
a curl
... and
add to
our telephone value
Bell scientists know that the telephone is
not used under ideal laboratory conditions.
There is never a perfect seal between receiver and user's ear. A curl may get in
the way, or the hand relax a trifle. And
ears come in many shapes and sizes. So
some sound escapes.
Now, sound costs money. To deliver more
of it to your ear means bigger wires, more
amplifiers. So Bell Laboratories engineers,
intent on a thrifty telephone plant, must
know how much sound reaches the ear,
how much leaks away. They mounted a
narrow "sampling tube" on an ordinary
handset. The tube extended through the
receiver cap into the ear canal. As sounds
of many frequencies were sent through the
receiver, the tube picked up a portion, and
sent it through a condenser microphone to
an amplifier. That sampling showed what
the ear received.
As a result, Bell scientists can compensate in advance for sound losses -build receivers that give enough sound, yet with
no waste. That makes telephone listening
always easy and pleasant.
It's another example of the way Bell
Telephone Laboratories work to keep your
telephone service one of today's biggest
bargains.
BELL
TELEPHONE
LABORATORIES
Working continually to keep your telephone
Automatic recorder plots sound pressures dèveloped in
the ear canal at different frequencies.
14
service big in value and low in cost.
AUDIO ENGINEERING
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DECEMBER, 1950
r
.20 ediy#t,
eoi2it2uclic41
aid 4djusifneni al
Reflexed Loudspeaker Enclosures
DAVID W. WORDEN
Practical procedure in the planning for a reflexed speaker cabinet,
with constructional hints which will simplify the work of building.
UNI.IKE
TILE
EXPONENTIAL
HORN,
multiple speaker, and large or "infinite" baffle arrangements, the reflexed enclosure is a resonant device. If
the resonant frequency of the enclosure
is made equal to the frequency of the
loudspeaker cone resonance, a cancellation of resonant effects occurs and the
result is smooth response down to a frequency somewhat lower than the loudspeaker would otherwise reproduce.
Furthermore, the speaker diaphragm
works into a favorable acoustical impedance, which means increased efficiency, reduced distortion and improved
transient response. The damping characteristics of this enclosure are inherently rather poor, but a liberal use of
sound absorbents -necessary for good
cancellation of resonant peaks -results
in excellent damping. A further advantage is its compactness and flexibility of
physical shape and size.
The speaker resonant frequency determines the low- frequency cutoff of the
system, since there is naturally a limit as
to how far the response of the system
will extend below this frequency. Hence
the speaker should be chosen which has
a low resonance; if response down to 30
cps is desired, the speaker should resonate at around 60 cps or less. Hence for
best results 12- or 15 -in. drivers are preferred, although the performance of any
speaker will be greatly improved with a
properly designed enclosure.
The reflexed enclosure is nothing more
nor less than a cavity resonator of the
type developed by H. Helmholtz. Referring to Fig. 1, it consists of an enclosed volume of air V coupled to the
outside by means of a mass of air M in
an open tube, or port. The magnitudes
of V and M determine the resonant frequency. The operation is analogous to
that of a parallel tuned circuit.
The volume, V, and the mass, M, of
air in the exhibit acoustical reactance
(capacitive and inductive, respectively)
just as do their electrical counterparts.
Also, similarly, the Q of the circuit is
determined by the amount of resistance
Engineering Department,
Vultee Aircraft Corp.
*
AUDIO ENGINEERING
Consolidated
present, the acoustical resistance being
supplied by sound absorbent lining inside
the box and by curtains of burlap or
similar material stretched across the
port. The impedance of such a parallel
tuned circuit is maximum at resonance.
The speaker is also a resonant device.
The moving parts (cone and voice coil)
and their suspension are mechanically
equivalent to a weight acted upon by
a spring. Such a system behaves like a
series resonant circuit, which shows
minimum impedance at resonance. Hence
if the two systems be connected together
and adjusted to resonate at the same frequency, the impedance "peak" of one
fills the "valley" of the other and the
combination tends toward constant impedance over a broad range of frequencies. If the resistive element, Q, of one
of these circuits is adjustable, the cancellation of resonant effects can be
brought about more closely.
The simplified equivalent circuit of
the combination of speaker and enclosure is essentially as shown in Fig. 2.
for more than 20 deg. or so around 60
cps. The phase shift is due rather to the
nature of the resonator, which may be
considered as a closed organ pipe with
lumped constants; the enclosed air, V,
must always be a node and the air, M,
a loop. (Note that no overtones are
possible, in contrast with the organ
pipe.) One quarter wavelength then must
exist between node and loop, which
means 90 deg. phase shift. This is sufficient to give an additive component, even
if the signals from port and cone are
equal; however, near resonance, the
stiffness of the enclosure limits the cone
amplitude to a very small value, and the
radiation is almost entirely from the
Rs
o
Sgnol
Source
-.I.-Loudspeoker -- ..-Enclosure
Phase Effects
The question is often raised as to the
phase of the signal issuing from the port
relative to that from the speaker. The
popular belief that phase shift in the
reflexed box is due to internal reflections, and hence to greater path length,
must be discounted in view of the fact
that -with the usual box dimensions
path length could not possibly account
-
R
Enclosed Cr
.
M
(Irldur,ve)
(CopoUhve)
V
Fig. 2. Simplified electrical equivalent
of loudspeaker mounted in reflexed
cabinet.
port. Furthermore, the output of a loudspeaker contains, near resonance, a
strong component at 90 deg. with respect
to diaphragm velocity, which would be in
phase with the enclosure output. Thus
the phase relations are favorable regardless of the shape or proportions of
the box.
The large reduction in loudspeakergenerated distortion is due to the restriction of cone amplitude mentioned
above. Henney1 shows the maximum
distortion in an open -back cabinet of 43
per cent to be reduced to a maximum of
12 per cent in a reflexed enclosure.
This represents a reduction in distortion
of over 72 per cent.
Design Procedure
Fig.
Reflexed enclosure reduced to
1.
Helmholtz resonator equivalent, with
electrical circuits corresponding to the
acoustic network.
DECEMBER, 1950
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Lord Rayleigh presents the following
formula for the frequency of resonance
"Radio Engineers' Handbook," 3rd. Ed.
McGraw -Hill Book Co., New York.
15
(Theory of Sound, Vol. 11), for an enclosure of the type shown in Fig. 3.
f
A
2
r\11 (L +
%
V,r A)
(1)
where
f = resonant frequency, cps.
c= velocity of sound, in. /sec.
r = 3.1416
A = area of cross section of port,
sq. in.
V = net internal volume of en-
closure, excluding volume of
port, speaker, sound absorbents, etc., cu. in.
L= port length, in.
The velocity of sound is approximately
13,560 in. /sec. at 70° F. Using this
value, combining constants and solving
for V, the formula becomes :
V=
4.657x10"A
f! ( L + .886 VA )
(2)
The first step is to determine the design frequency, f, which may be done in
the following manner: with the loudspeaker in open air and connected to the
output of an audio oscillator, vary the
frequency slowly from about 30 to 150
cps. Note the frequency at which the
cone amplitude is greatest. The peak
may be rather broad; so run across
it several times, noting the frequencies
above and below the peak at which the
diaphragm motion noticeably decreases,
and average these two readings. Bits of
paper torn up and placed on the cone
may assist in observing the amplitude
of the cone movement.
A better method, particularly with
small speakers, is to isolate the signal
generator and voice coil by means of a
series resistance several times the nominal voice coil impedance, and read the
voltage developed across the voice coil
with a good a.c. rectifier -type voltmeter.
These readings may be plotted against
frequency and the resonant peak may
be read accurately from the graph. This
method is also the best for testing the
completed enclosure.
Now that f is known, there remain an
infinite number of combinations of V, A
and L which would yield the desired result. A value for A may be arbitrarily
chosen; it should be from one half to
16
one times that of the speaker opening.
Past practice seems to indicate this
choice; at least, a number of successful
enclosures have port areas within this
range. The larger area is preferable since
it radiates more sound energy, but, if it
is too large the internal dimensions of
the box may approach quarter wavelength, since the volume increases with
port area. The area of the speaker cone
may be computed from:
A' =rS(D?
d,
(3)
where
A' = speaker cone area, square
inches
S = slant height of cone, inches
D= diameter at outer edge of
cone, inches (do not include
corrugations)
d= voice coil diameter, inches
From here on, the following procedure
is suggested. Choose a value for A, say
A = A' to begin with. Set L equal to the
thickness of the material of the box plus
the absorbent lining, as this will be
easiest to construct, then solve for V.
Compare this computed volume with the
space available, or cabinet size desired;
and if it seems too large, either increase
L or decrease A or both until a satisfactory compromise is obtained.
herently stronger and will require less
material, the closer its shape is to a cube.
To the calculated net volume, V, must
be added the volumes of the speaker itself, of that portion of the port which
projects within the cavity, and of any
other objects to be located within the
box. The dimensions corresponding to
the resulting gross volume will be inside measurements, and the thicknesses
of the enclosure walls and lining must
be added in order to obtain the overall
dimensions. The volume displaced by
the speaker may be estimated by computing the volumes of the cone plus a
cylinder enclosing the magnetic structure. A table of approximate values is
given below for convenience; however,
individual speakers vary greatly, and
actual measurements should be used
whenever possible.
E
z gi.71
6
10- 20
20
8
30- 60
70-140
100 -200
200 -400
38
10
12
15
60
150-200
100-150
70-100
85
115
60- 85
40- 65
Box Shape
Now a word as to the shape of the
box : the only restriction is that the inside lengths should be kept small in order
to discourage air column resonances
which may occur at frequencies where
such dimensions are equal to a quarter
wavelength. With the usual proportions,
these resonant frequencies are high
enough to be readily absorbed by the
lining of the box, but if the enclosure
were unusually long, trouble might be
encountered. Also, the box will be in-
of ported
port of finite length.
Fig. 3. Basic arrangement
cabinet using
a
The actual shape of the enclosure, if
not dictated otherwise, usually develops
in this fashion: the front face area is
made large enough to accommodate the
speaker and port comfortably, and its
area computed. The gross inside volume
divided by the (inside) area of the
front face gives the required depth. The
frontal area, port depth, or port area
may be changed, if necessary, to adjust
the depth to a satisfactory value.
An example may help to clarify the
foregoing. Suppose a reflexed enclosure
is to be designed around a 12 -in. speaker
which shows cone resonance at 70 cps.
The cone area [A' in. Eq. (3)] is computed to be 85 sq. in., and this value will
be used for A in Eq. (2). Now, assuming
4 -in. plywood for the box and 4 -in.
lining, L=1% in. for the first trial. The
net volume as computed from Eq. (2)
is 8355 cu. in. Adding 200 cu. in. for the
speaker gives a gross volume of 8555
cu. in.
The area of the front is estimated as
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DECEMBER, 1950
follows : the long side of the port may
be made approximately equal to the diameter of the speaker cutout; this is
economical in space and balances the appearance. The diameter of the speaker
opening (and one side of the port rectangle) is 10/ in. The other side of
the port opening is then 85/10/ = 8.1
in. (Great acin., or approximately
the resosince
necessary,
is
not
curacy
root
the
square
nant frequency varies as
of the volumes, areas, etc., [See Eq.
(1)]. Allowing 3 in. edge clearance and
2 in. between the speaker and port, the
inside dimensions of the front will be
+2+ 12 +3) = 28Y8 in. long by
(3
(3 + 12 + 3) = 18 in. wide (speaker di-
8/
+8/
ameter is 12 in.). The frontal area is
(18) (28h) = 506 sq. in. and the depth,
then, must be 8555/506 = 16.9 in. inside.
Allowing 1/ in. for the wall thickness
including lining, the outside dimensions
become 313 x 21 x 19.9 inches. Suppose,
now, that the front dimensions are satisfactory but the depth is too great. The
port length L may be arbitrarily increased, say to 4 in. The volume, Eq.
(2), now becomes 6639 cu. in. net; adding 200 cu. in. for the speaker and 289
cu. in. for that portion of the port tube
projecting into the enclosure, measured
as shown in Fig. 4, the gross internal
volume equals 7128 cu. in. The inside
depth, then, is 7128/506 = 14.1 in. or 17.1
in. outside.
Construction Notes
The box should be very rigid in order
to resist vibration. All joints, corners,
etc. should be strong and tight, preferably reinforced with strips, and large
panels should be braced. The back should
be attached with a liberal number of
screws so that it may be removed to
give access to the interior. If a pliable
material such as hair felt is used for
lining the enclosure, it may be attached to
furring strips, thus spacing the lining
away from the wood and increasing the
low- frequency absorbtion. Take precautions against air leakage; the speaker
gasket should seat against the wood,
wiring should be brought out through a
bulkhead type of plug or receptacle
which may be mounted securely with
screws, and the removable back panel
should fit snugly. A good method for
attaching the back is shown in Fig. 5.
Items of equipment may be located
AUDIO ENGINEERING
within the box provided they are not affected by the high pressures developed
insided the resonator. Output transformers and dividing networks may be
mounted in the box, but amplifying
stages, for instance, might be subject to
acoustical feedback if placed inside.
Tweeter mechanisms should be well protected from this pressure.
Adjustment Procedure
Install the speaker in the completed
enclosure and screw the back into place.
Connect an audio oscillator to the loudspeaker input, and adjust the signal to
a comfortable level. Now vary the frequency through the range below 200 cps,
noting the frequencies of any peaks
which may appear in the output. One of
These dtmens,ons
used to compute
vol me displaced
by port
_I
Fort
i
Lmmg
cabinet appearance,
measurements to compute
port displacement.
Fig. 4. Reflexed
showing
three conditions is likely to be encountered, as follows:
1.
2.
3.
Enclosure frequency too high or too
low. Two large peaks appear ; one at
loudspeaker resonance and the other
at enclosure resonance.
Enclosure frequency slightly too high
or too low. Two peaks appear, equally
spaced above and below loudspeaker
resonant frequency, but one noticeably
stronger than the other. The enclosure
frequency should be adjusted toward
the smaller peak.
Correct tuning. Two peaks of equal
amplitude, equally spaced above and
below loudspeaker resonance.
The enclosure resonant frequency can
be increased by decreasing the enclosed
volume, V. A simple method for doing
this is to place wooden blocks, such as
might be cut from 4 x 4 material, inside
the enclosure. These may simply be
tossed in through the port while adjust-
DECEMBER, 1950
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Sude, top or
bof enclosure
--rj:
Bock
2' strip glued to
top, bottom and sides
panel
Fig. 5.
e
bottom
Construction detail for corners
of speaker cabinet.
ments are being made, and fastened
down later. The easiest way to lower
the frequency is to decrease the port
area, A, which may be done with strips
of wood cut to fit along one side of the
port, the width being equal to the port
depth, L. These strips may be fastened
in place with screws.
When the frequency has been correctly adjusted, the damping may be increased by stretching porous cloth material (burlap, etc.) over the port opening. Experiment with various weights
and layers of cloth until the two peaks
just disappear. Too much damping will
cause the single peak at speaker resonant frequency to appear.
As an alternative to merely detecting
the resonant peaks by ear, a voltmeter
may be used as described previously, and
the response curve plotted.
It may be advisable to recheck the frequency adjustment after the system has
been in use for some time. Loudspeakers,
particularly when new or recently reconed, tend to show a lower value of
resonant frequency after a period of time
due to the cone suspension becoming
more pliable with use. The loudspeaker
resonance may always be found by
blocking off the port and exploring with
the audio oscillator. The only peak
which shows up with the port blocked is
that due to the loudspeaker cone resonance.
One more requirement is that the
amplifying equipment used to drive this
speaker system be capable of good frequency response, low distortion, and low
output impedance. Then, a correctly adjusted and well damped reflexed enclosure will add greatly to the "presence"
effect by providing extended bass response that sounds full and true without the usual resonant "boom" or "rain
barrel" effect. Percussion instruments,
plucked strings and other signals with
high transient components come through
clean and sharp because of the excellent
response to such signals. In short, the
improvement in overall performance due
to the enclosure is great enough to more
than justify the labor and expense involved.
A Continuously Variable
Loudness Control
E. E.
JOHNSON
A new approach to the problem of adjusting frequency response simultaneously
with changes in level in order to compensate for varying sensitivity of the ear.
cuits. None of these has given the
performance of a truly continuously variable loudness control. The tapped volume control affords compensation only
when its contactor is at the tap but does
not provide proper compensation when
located away from the tap. To obtain
wider spread of compensation, two or
three taps are used, but such controls
are more difficult to manufacture and,
therefore, are more expensive. The
0
Schematic of new loudness control which may be assembled from
standard parts.
Fig.
1.
IT IS WELL KNOWN in audio circles
that the human ear is very sensitive
to both low and high frequencies at
reduced volume levels. The accepted
standard used in compensating for this
hearing deficiency in audio systems is a
set of curves at different levels known as
the Fletcher -Munson curves. These
curves show the amount of low -frequency and high- frequency boost that is
required above some mid -range level to
make the sound output of an amplifier
appear balanced at all volume control
settings.
Many attempts have been made to obtain the required compensation by use of
single or multiple tapped volume controls, stepped loudness controls, and various types of bass and treble boost cirE ngi
Company.
nc e
r,
International Resistance
! i'
t1
mmnor
CO
o
Fig. 2. Response
curves for control
at various level
settings.
>
.
I=
a
tal
..
-
IIIIImio:I..;:HOIIi
stepped type loudness control does not
provide full flexibility of adjustment and
is relatively expensive. The bass and
treble boost circuits require multiple adjustments with change of volume for
ideal compensation.
The control described in this article
is a continuously variable loudness control that may be assembled easily from
-R
18
-
1,!.Ie,io
laniz..amasio,
FREQUENCY
Fig.
+eo
1
7
a
This new loudness control consists of
three variable resistance units
R2,
and R3- operated from one common
shaft and in combination with the proper
resistors and capacitors, as shown in
Pictorial schematic showing
exact wiring of components.
+90
fil®®
20
Description
3.
tow.
loll .,;11
standard parts available widely from
radio parts distributors. It may be wired
into most audio systems as easily as an
ordinary volume control.
Fig.
networks. The center section R, forms
one variable leg of a potentiometer circuit and the rear section R, forms the
other leg. Fixed resistor R4 acts as a
limiting resistor to keep the input impedance as constant as possible when the
control is set near maximum output.
The center control in combination with
capacitor C, forms the arm of the variable voltage divider network which decreases in impedance as the frequency
1.
The panel section R, functions as a
standard volume control supplying a
variable voltage to the other sections
which form the frequency- compensating
IN
OM
CYCLES PER SECOND
increases, causing the output voltage to
rise at frequencies above 1000 cps. The
response curves for this control at various settings are shown in Fig. 2. The
monitor level figures represent the actual listening level at which the compensation most closely follows the Fletcher Munson curves, one of which is shown
dotted for a level of +60 db. (Normal
listening level in the average living room
will range from +65 to +75 db.)
The rear section R,, fixed resistor R,,
and capacitor C, form the arm of the
variable voltage divider network that
increases in impedance as the frequency
is decreased, causing the output voltage
to rise at frequencies below 1000 cps, as
shown in Fig. 2.
This arrangement offers a truly continuously variable loudness control that
can be used to improve the sound quality
of many radio, FM and TV receivers,
as well as many sound systems. It must
AUDIO ENGINEERING
[Continued on page 40]
DECEMBER, 1950
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NGINEERIN
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Put the "655rrthrough the
See Why
Studio-Test
Audio Engineers Switch to This
SLIM -TRIM
TV DYNAMIC
Test
SECTION OF
,dU D 1 O
ENCINEEPINC
it for lows!
Test it for highs!
CONTENTS
Test it for fidelity!
CBS Television Studio Intercommunication Facilities
Robert B. Monroe
Audio Systems for TV Service
W. L. Lyndon
Remote Television Broadcasting
W. I. McCord
New Products
New Literature
Subject Index for 1950
-
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Test it for music!
Test it for versatility!
Test it for ruggedness!
Test it for "non -pop "!
Test
DECEMBER, 1950
it for convenience!
Test it indoors, outdoors!
It's the only Microphone with
all these Features!
-
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V13
V13
V15
C. G. McProud, Editor
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Calibrated
Power Rating -53 Pop -Proof Head;
built-in Blast Filter stops wind and breath blasts
Exclusive Acoustalloy Diaphragm withstands severest
service Omnidirectional; requires no closely associated auxiliary equipment Changeable Low Impedance
Removable Swivel
1/2" or Vs " -27 thread
mounting Cannon XL-3 Connector All parts precision ground
20 ft. broadcast type cable. Write
today for further facts! Model 655. Price.. . $200
Ladd, Haystead, Publisher
Luci Turner, Production Manager
Lucille Carty, Circulation Manager
S. L. Cahn, Advertising Director
H. N. Reizes, Advertising Manager
Editorial Advisory Board
Howard A. Chinn
Robert M. Morris
Rodney D. Chipp
Chester A. Rackey
Representatives
Sanford R. Cowan, Mid -West Sales
342 Madison Ave., New York 17, N. Y.
James C. Galloway, Pacific Coast Sales
816 W. 5th St., Los Angeles 17, Calif.
Technical Book b Magazine Co.
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MICROPHONES
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INC.
BUCHANAN, MICHIGAN
40th St.
New York 16, N.Y., U.S. A. Cables: Arlob
PHONO PICKUPS
SPEAKERS
TV BOOSTERS
Construction of the new antenna tower
for the top of the Empire State Building
is proceeding rapidly, and the antenna
is expected to be in use early in 1951.
This photograph was taken from the top
of 10 East 40th Street by Omar Marcus.
VIDEO ENGINEERING
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DECEMBER, 1950
CBS Television Studio
Intercommunication Facilities
ROBERT
differences
between an aural and a television
broadcast is the number of technical and production personnel required
in the broadcast studio. In the case of an
aural broadcast, as a rule, three or
four persons are involved. In a television broadcast, on the other hand,
a considerably larger staff is required.
Included are the director, assistant director, studio floor manager, announcer,
video switcher, audio mixer, cameramen,
camera -control operators, sound -effects
operator, microphone boom operators,
studio lighting operator, telecine projectionist, telecine camera -control operator,
and others.
With such a large staff, it might be
expected that considerable confusion
would exist in the television studio.
However, anyone who has observed the
i
veys intelligence serving to aid, direct,
or cue a member of the TV staff or cast
in the performance of their duties. Obviously, this includes the spoken words
of the program director as well as other
key personnel in the control room. Not
as obvious, but quite as important to
many members of the staff, is the audio
portion of the program material from
which many cues are obtained. For example, the orchestra leader usually takes
cues for his music from the dialogue of
the program. The video picture monitor,
although not commonly thought of as a
conveyor of cues, also falls into the classification of an intercom device. In studio operations most of the staff depend
on a picture monitor for information of
one kind or another ; the lighting operator to check the effectiveness of lighting effects, the audio operator to avoid
boon -suspended microphones or microphone shadows in the picture, and the
sound effects operator for synchronizing
sound effects with studio action. Thus it
can be seen that the intelligence transmitted via the studio intercom system
will take the form of spoken words,
audio program material, and picture program material. All three are needed to
convey the intelligence necessary to coordinate the activities of the large group
of technical, production, and performing
personnel.
The staff in the studio control room,
which includes the director, assistant director, camera control operators, video
switcher, and audio mixer, usually carry
on direct conversation without the use of
any special intercom facilities. When the
director speaks, all in the control room
hear him, and if necessary, answer him
directly. The monitoring loudspeaker
permits all to hear the audio portion of
the program. If the basic design principles of control room layout have been
followed, all are seated in a manner providing good visibility not only of the
outgoing line picture monitor but also
the monitor associated with each individual studio camera. Therefore, it can
be seen that the intercom facilities serve
mainly to convey information to the
staff outside the control room, and in
some cases, permit them to talk to the
control room. The staff outside the control room include those in the studio,
those in an associated telecine room, as
well as those at other points remote from
the studio.
The Program Director
Robert
B.
Monroe, Project Engineer
CBS General Engineering Department
Born in Brooklyn, New York on October 17.
1908, Mr. Monroe attended Pratt Institute
from 1937 to 1942 while being employed by
Columbia Broadcasting System. Inc., where
he went in 1934 and where he has since
been continuously employed except for the
war years.
From 1942 to 1945 he was associated with
the Radio Research Laboratory, Harvard Uni-
progresses.
DESIGN CONSIDERATIONS
The term ""ITV intercom," as used in
this paper, includes any facility that con-
VIDEO ENGINEERING
MONROE
A complete description of the facilities required
to make possible the direction and control of
personnel in the production of a TV program.
ONE OF THE OUTSTANDING
production of a program in a well designed and well equipped television studio has noted that the operation is unusually well coordinated with little, if any,
confusion or misunderstanding on the
part of any of the staff. The reason for
this smooth functioning and good coordination lies in the use of an intricate
system of studio intercommunication
whereby each member of the staff is cued
and directed in his activities.
In the past, the design of TV studio
intercom facilities has often been looked
upon as a minor task that could quickly
be dispensed with after all important design details of the audio and video facilities had been completely worked out. It
is now generally recognized that the TV
intercom facilities represent one of the
major elements of the TV studio plant.
Furthermore it is realized that the equipment arrangement and circuitry of these
facilities can become quite complex. The
TV intercom facilities should, therefore,
receive the same careful planning and
attention to design detail as is accorded
to the audio and video facilities of the
plant.
It is the purpose of this paper to discuss the philosophy underlying the design of television intercom systems and
to describe briefly some of the facilities
which have proven satisfactory in CBS
TV studio operations. It must be recognized, however, that television is a
dynamic, fast growing industry, and the
requirements demanded of the intercom
facilities are likely to change as the art
B.
DFc.es'R,
versity (sponsored by the Office of Scientific
Research and Development). He served successively as head of the Planning Department, head of the Standards Laboratory, and
assistant to the Executive Engineer.
Mr. Monroe is a senior member of the Institute of Radio Engineers.
1950
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It is at the program director's desk in
the studio control room, Fig. 1, that
most of the coordination of a television
program takes place. Because of the
many responsibilities of the program director, it is very desirable that he be
provided with the absolute minimum of
equipment that he must operate. Ideally,
all that should confront the director is a
microphone; when he speaks, all concerned should hear him.
A TV intercom system should be designed to conform with this ideal situation as closely as possible, however, it
has proven desirable to make some compromises and provide a few controls at
the director's position for several special,
although infrequent, operations described
below. In addition, it has also proven desirable to provide a telephone jack into
which a telephone headset or handset
V3
I (left). The director's position in a CBS -New York television studio. Four of the key switches on the small control panel connect the
director's interphone instrument to various interphone stations in the studio. Two other key switches connect his desk microphone to the studio
talkback loudspeaker and to the telecine room intercom loudspeaker. The assistant director is equipped with identical facilities. Fig. 3 (right).
The type of telephone headset shown is generally used by CBS cameramen and camera control operators. The microphone boom operator in the
background is wearing a pair of split headphones by means of which he receives instructions and cues.
Fig.
can be plugged to permit the director to
participate in two-way conversations
with the studio cameramen or with other
points equipped with two -way telephone
facilities. It is good practice to provide
the assistant director, who is usually
seated immediately alongside the director, with independent facilities identical
with those provided for the director.
The Interphone System
The only facility usually associated
with the term "TV intercom" is the
private telephone system mentioned
above which provides two -way communication between control room, cameramen, and at times, other points. To differentiate these private telephone facilities from other studio intercom facilities,
the telephone system may be referred to
as the interphone system. The terminal
equipment for these interphone facilities is usually supplied as an integral
part of TV cameras and certain other
video components, such as video switching units. When interphone stations are
required at other points, the components
may be procured and installed as desired.
In the case of TV field pick -ups, this
relatively simple interphone system often
constitutes the entire and only intercom
facilities. While adequate for intercom
purposes on the simpler type of remote
pick -ups, these basic intercom facilities
must be substantially augmented to meet
the additional requirements encountered
in TV studio operations.
Figure 2 shows, in simplified form, a
typical studio interphone system of the
type employed by CBS. It will be noted
that the switching facilities permit either
private camera-to- camera- control conversation, or a conference connection between all desired stations. The private
camera -to-camera -control connection is
useful in the routine alignment and
maintenance of cameras. Should a camera fail during a rehearsal or air program, it is possible for the maintenance
staff to work on it without interfering
V4
with, or being distracted by, other conversations on the interphone system. In
the conference position, where all desired interphone stations are paralleled,
a portion of the audio from the director's
microphone circuit is introduced into the
interphone system permitting all stations
to hear the director even though he is
using a desk microphone rather than an
interphone instrument. It is desirable to
adjust the level from the director's microphone so it reproduces several decibels higher in level than other interphone conversations. By doing this the
director's comments override and take
priority over other conversations.
Should the director desire to engage
in a two -way conversation with one of
the interphone stations in the studio, he
may employ an interphone instrument although this is usually only necessary
when the studio is on the air. During
rehearsals persons in the studio can be
heard in the control room by means of
the studio microphones and control room
monitoring loudspeaker.
It is customary for the cameramen
and camera control operators to employ
telephone headsets of the type shown in
Fig. 3, as this type of headset leaves both
hands free for the many other operations
they must perform. Some interphone
systems employ headsets with two receiver units, one used with the interphone system, the other to reproduce
audio program material. Most cameramen at CBS, however, prefer the single
receiver type of headset as this leaves
one ear free to hear directly what is
happening in the studio. In this way they
hear the aural portion of the program
directly from the performers on the set.
The camera control operators in the
control room are served well by the
single receiver type of instrument as
they hear the audio portion of the program from the control room monitoring
loudspeaker. For these reasons, the
single headphone type of interphone instrument has been standardized at CBS.
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Either the headset or hang -up handset type of instrument may be used by
the director, assistant director, switcher,
and audio operator depending upon the
extent to which the interphone is used.
A jack is provided at each of these positions to permit the use of either type.
Currently the preference seems to be
for the headset type of instrument.
Other Interphone Stations
In addition to the main interphone
system connecting the cameramen, camera control operators, video switcher,
and director, it is often advantageous to
provide several interphone branch circuits permitting personnel in the control room to engage in conversation with
certain members of the studio staff such
as the studio floor manager, sound effects
operator, and lighting operator. Thereby
the director can work out special problems with the floor manager or can discuss lighting effects directly with the
lighting operator. Similarly, the audio
operator can discuss sound- effects levels
or other problems directly with the
sound- effects operator.
As described in the following sections,
the floor manager, sound effects operator, and lighting operator receive their
regular communication from other circuits and this telephone is an auxiliary
facility for use in working out special
problems, usually during studio rehearsals. For this reason, the hang -up handset type of instrument is preferred at the
lighting and -sound effects stations. A
flashing light is used for calling, rather
than a bell, to permit the calling circuit
to be used when the studio is on the
air. The floor manager uses the "pro duction" headset jack, which is available
in many studio cameras, when it is necessary for him to talk to the control
room.
As can be seen in Fig. 2, these branch
circuits are not a part of the main interphone system. When used, the station in the control room usually is disNt11EERING
DECEMBER, 1950
connected from the main interphone
system and engages in a private conversation with the branch station.
Headphone Cueing Circuits
The two -way interphone system, as
noted above, serves mainly to provide
continuous communication with studio
cameramen and occasional two-way communication with other persons in the
studio. It is necessary to provide continuous cueing circuits to other personnel in the studio, such as the microphone
boom operators, orchestra leader, announcer, as well as the sound -effects and
lighting operators. This is accomplished
through the use of headphones which
may be connected into receptacles which
are provided at strategic locations
CONTROL
4. Communication to the studio floor
manager (as well as other studio personnel who
must be free of the encumbrance of a wire
connection) is accomplished by means of a
low- frequency, induction -field radio circuit.
One of the ultra -compact receiver units is
shown in the above photograph.
Fig.
throughout the studio. Unlike the interphone system which employs headsets
with a single receiver unit, these headphones are equipped with two receiver
units which have been wired to permit
the reproduction of different information
in each. These split- headphone cueing
facilities are known as headphone cue.
It is necessary to provide two types
of headphone cue. The first type is for
the general use of technical and production personnel and, at CBS, is known as
regular headphone cue. Regular cue reproduces the voice of the director in one
of the two earphones and audio program
material in the other earphone. The second type of headphone cue is specifically
for the use of the microphone boom operators and, for that reason, is known
as boom headphone cue. Like regular
cue, boom cue reproduces the voice of
the 'director in one earphone and audio
program material in the other; however, the control room audio operator
can break into the audio program side of
the circuit and talk directly to the microphone boom operators at any time.
Radio Link
The interphone system and headphone
cue circuits provide communication and
cueing facilities for most of the studio
VIDEO ENGINEERING
motion picture film and still slides or
opaques. This film and slide material is
integrated into the live portion of the
program in the studio control room. For
practical reasons, all projectors and associated film camera chains are usually
centralized in a special area known as
the telecine room. The telecine room
serves all studio units in the plant.
Because of the physical separation of
the telecine room and the control room,
it is necessary to provide adequate intercom facilities between the two points.
As the motion picture projectionist must
be free to move about in loading, unloading, and rewinding film, it is desirable to provide a loudspeaker reproducer
rather than the telephone headset type
employed in the studio. In CBS studios,
it is standard practice to provide twoway loudspeaker service between control
room and telecine room. The telecine
loudspeaker must be capable of operation at fairly high level, considerably
higher than the conventional office type
intercom systems, because of the high
noise level that exists when several pro-
technical and production staff. Both systems, however, require a direct wire connection and therefore restrict the movement of the persons at each end of the
circuit. This is not a disadvantage in
most cases since most of the studio staff
are closely associated with equipment
requiring other wire connections such as
a camera, microphone boom, lighting
panel, or sound -effects console. Other
persons, however, notably the studio
floor manager, must often be free to
move to any part of the studio without
the encumbrance of a cable yet must remain at all times within the range of the
voice of the director in the control
room. A radio circuit is provided for
these persons. The receiver is an ultracompact battery operated unit which is
carried over the shoulder as shown in
Fig. 4.
The radio link employed in CBS television studios is an amplitude-modulated
induction -field system which operates
with a power of a few watts in the
low- frequency range between 100 and
200 kc. It is necessary to assign different
frequency channels to systems operating
in adjacent studios to prevent interference.
Some television studios have successfully employed radio cueing transmitters
and receivers operating in the VHF portion of the spectrum. Such transmitters
must, of course, be licensed.
In TV studio productions, portions of
tl e program material often originate on
jectors are in operation.
Inasmuch as the telecine room serves
all studios, switching facilities must be
provided at each camera to permit the
projectionist to connect his intercom facilities to the particular studio with
which he is working. He must also be
equipped to select audio program material, video program material, and headphone cue (which may be used in the
STUDIO
ROOM
CAMERA CONTROL
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FACILITIES
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INTERPHONE
TERMINAL FACILITIES
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TELEPHONE HEADSET
IE, MICROPHONE A RECEIVER
LEGEND
Fig. 2. The interphone system, one component of TV studio intercom facilities, provides telephone communication between control room and studio cameras as well as other points in the
studio.
DECEMBER, 1950
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V5
event of an intercom failure) from the
desired studio. Furthermore, he must be
equipped to extend control of starting
and stopping motion picture projectors
to the desired studio. His switching can
be simplified by ganging as many of these
functions as practicable on a single selector. In practice, it has proven desirable to gang the intercom circuits, audio
program circuit, and headphone cue circuit on a single selector, and provide
separate selectors for the video monitor
and for projector extension control circuits. This permits him to control the
projector and monitor the camera locally
during setup yet maintain his intercom
connection with the studio. A separate
loudspeaker cueing circuit, similar to
those employed on transcription turn ables for cueing records, is provided
when it is necessary to cue motion picture film aurally.
(telops), Fig. 5, which are used for
originating opaque as well as transparent
slides. This is explained by the much
closer cooperation required between the
operators of these telop machines and
the control room. In the case of the motion picture projectors, the actual starting and stopping of projectors is done
usually by the video switcher in the control room. On the other hand, the telop
operator must set up, change, fade, and
superimpose slides directly from the
telop and must therefore carefully follow the director's instructions, as well
as the program continuity, at all times.
For this reason, the continuous flow of
cueing information on the regular headphone cue circuit is more desirable, in
this case, than the intermittent instructions intended specifically for operators
of film projectors on the intercom loud-
Duplicate intercom facilities must be
provided at each of the telecine camera control units unless these control units
are located immediately adjacent to their
associated film camera and projectors
and can therefore make use of the same
microphone, loudspeaker, and switch.
These camera- control intercom stations
may be equipped with independent studio
selecting facilities or, if desired, the intercom facilities at both camera and
camera-control may be switched by a
common selector which may be located
at either of the two points. The latter
system is simpler but less flexible than
the former method.
Although loudspeaker intercom reproduction has been found preferable at film
cameras originating motion picture sequences, it has been found that headphone cue is more desirable for the operators of television optical projectors
speaker. At the same time, the head-
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S2 - Emergency Telecine Intercom
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- Bridging
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S3 - Dressing Room Call Control Switch
S4 - Studio Tolkbock Control Switch
S5 -Boom Tolkbock Control Switch
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a
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modern televison studio. These facilities augment the
VIDEO ENGINEERING
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DECEMBER, 1950
1
Fig. 5 left ). Operators of telop equipment in the telecine room receive instructions on cues on split headphones. They can talk to the studio control
room by means of the microphone mounted near the top of the projector. The intercom control panel, lower right, contains a talkback key switch,
Fig. 7 Iright).The CBS studio floor monitor shown above is a mobile unit containing
a studio selector switch, and two headphone receptacles.
a picture monitor, a loudspeaker, and a clock.
I
tors.
marked TELECINE EMERGENCY is operated. After the attention of the telecine
operator has thus been attracted by his
emergency circuit, he can set up the
regular intercom circuit which will provide the desired two -way communication.
Emergency Telecine Intercom Facilities
Loudspeaker Talkback to Studio
As already described, each film camera
in the telecine room is provided with an
intercom system which can be switched
to operate with the intercom facilities in
any desired studio control room. It is
the usual practice for the projectionist
to set this switch to provide communication with the studio with which he is
to work. A problem often arises when
another studio desires to communicate
with telecine (for example during routine maintenance or for a special test)
and the intercom selector switch in telecine is not set to communicate with that
studio. Similarly, the same difficulty
would be encountered had the telecine
operator forgotten to set up this switch
or had inadvertently set it to the wrong
position.
One way of establishing communication under these circumstances would be
for the studio to call telecine on the
regular telephone; however, this is not
desirable as the need for communication
with telecine may well be urgent and
the telecine extension is often busy with
other calls. For this reason, it has
proven desirable to provide an "emergency" telecine intercom system.
The emergency telecine intercom facilities consist simply of one or more
loudspeakers installed where they are
clearly audible throughout the telecine
area. These loudspeakers are driven by
an amplifier of adequate size to produce
the necessary sound level. Facilities in
each of the studio control rooms, shown
in Fig. 6, connect the director's microphone to the input of this amplifier
whenever a control room key switch
The facilities described thus far pro vide aural communication and cueing
phones tend to close out distracting
sounds and permit the telop operator to
concentrate on his work. The same facilities are used to talk to the studio from
the telop projectors as are used in the
case of the motion picture film projec-
VIDEO ENGINEERING
circuits for all technical and production
staff concerned with a television studio
production. Communication to performers in the studio is accomplished during
radio rehearsals through a talkback
loudspeaker. This talkback circuit, which
is similar to those employed in aural
broadcasting studios, permits the program director or his assistant to direct
the activity of the performers at any
[Continued on page V131
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8. The circuit arrangement employed to transmit transcribed program material simultaneously to both a studio loudspeaker and the audio program line. The resistance isolation
network serves to prevent studio microphone program material in the audio mixing network
from reaching the input to the studio loudspeaker amplifier. Without the isolation network,
acoustic coupling between studio microphones and studio loudspeaker would result in singing.
Fig.
DECEMBER, 1950
www.americanradiohistory.com
AmericanRadioHistory.Com
V7
Audio Systems For TV Service
W.
L.
LYNDON
A discussion of the equipment necessary for use with a single- studio TV installation
capable of presenting live programs in addition to transcribed and network shows.
THE PREVIOUS ARTICLE in this series
was devoted to the description of a
simple audio -video switching unit,
RCA Type TTC -3A1, which would permit a television system capable of handling only film, slides, and network programs to be placed on the air with a
minimum outlay of equipment. Consideration shall now be given to the
audio equipment requirements for a television system having a single studio, an
announce booth, and facilities for handling film and remote or network program service. The lineup of audio equipment required for such an installation
does not vary greatly from that of a
comparably sized AM or FM installation; the main differences are the additional facilities necessary for handling
the audio output of the film projectors
and a communication system to be used
by the program director for coordinating
the program sequences.
This audio system is based on the use
of standard stock speech input units and
consists of three main items:
1.
One 76B5 Consolette
2. One BCS -3A
3.
Control Unit
One rack of Speech Input Equipment
This arrangement is capable of switching, mixing, and monitoring the following program sources:
1.
Studio
2. Announce Booth
3.
Film
* Television
Terminal Engrg., Engineering Products Dept., Radio Corporation of
America, Camden, N. J.
i-
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Transcription
Network and Remotes
Loudspeaker monitoring facilities are
provided in the main control room.
studio, announce booth, and projection
room. The speaker in the studio serves
as both a cue and talkback speaker. The
studio speaker is also tied in on an override circuit which will permit trans scriptions or sound effect records to be
heard in the studio during "on- the -air"
operation.
In order to simplify the description of
this system, reference should be made to
Fig. 1, a single -line block diagram of the
76B5 consolette which is employed as the
system's basic unit.
4.
5.
The Consolette
It will
be noted that the consolette
four pre -amplifiers feeding into a
six -position mixer system. Two of the
mixers are connected through isolation
line coils to six -position mechanically interlocked line switches. The program
level from the remote lines, after equalization, and from the two turntable positions, is controlled by these two mixers.
Each of the six mixers feed into a lever
key which will permit placing the circuit to either a program or an audition
bus. This feature permits circuits to be
monitored before being switched to the
program bus. These lever switches associated with the mixers are tied in
with the studio cue and talkback circuit.
When they are in the PROGRAM position.
the talkback or cue circuit cannot be operated. In the normal OFF position, prohas
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relays.
The input to the monitoring amplifier
is terminated in a row of mechanically
interlocked push -type switches which select the circuit to be fed to the input of
the amplifier. This includes the audition
position, talkback circuit, and five "cue"
line inputs. Two of these "cue" positions
are used in this television audio system
to monitor the output of the two equalized remote line circuits.
The power supply for this consolette
is a self contained unit housed in an
electrically interlocked cabinet with the
rectifier chassis so constructed that it
may be readily hinged out for servicing.
This unit is normally mounted at a point
remote from the consolette and interconnections macle by suitable shielded
leads.
Figure 2 is a single line block diagram
indicating how the consolette and the
external units are combined to make
up this TV audio system. The studio
as having a total of eight
microphone circuits. four of which are
normalled through jacks on the speech
input rack to the consolette preamplifier
inputs. The remaining four positions are
terminated on jacks to be patched into
the circuits as required.
is shown
11'ÌI'I'I'i
Fig. 1. Block Diagram of 76B5 consolette used for small station operation.
V8
gram is automatically fed into the studio.
In the audition position the talkback circuit between the control room and the
studio can be operated. The program
amplifier
bus contains a program
equipped with an interstage master gain
control and has a normal output rating
of + 18 dbm with 0.5 per cent distortion
from 50 to 7500 cps, and a maximum
output level of + 26 dbm with 1 per cent
rms distortion over the same frequency
range. Across the.output of this amplifier
is located a standard VU meter with an
adjustable input control. This meter is
also capable of indicating the plate current of each amplifier tube located in the
program channel.
The monitoring amplifier located in
the audition channel is provided with
considerably higher gain and higher
power output in order that it may be
used in conjunction with a talkback circuit and also to provide sufficient volume
for the speaker system. There are three
speaker control relays located within
the consolette and in this TV system
they are used in conjunction with the
control room speaker, studio speaker, and
headphone monitoring for the microphone boom operator. The additional relays required for the projection room
and announce booth are mounted on the
rack equipment along with the AUDITION
and ON AIR studio signal light control
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DECEMBER, 1950
3 (left). Typical station installation employing the audio system diagrammed in Fig. 2. The audio units are located on a higher level in order
that the audio operator has visible access to the video monitors and to the studio. (Courtesy WENR -TV) Fig. 4 (right). This station also employs
the audio system of Fig. 2, but is arranged differen-ly. Note turntables at left, audio TV control at center, program director's console, and camera
units at right, forming a single operating unit.
Fig.
Microphones
The quantity and types of microphones
to be used is generally determined by
the type of programming that is contemplated. Simple productions usually
involve simpler microphone technique
and many presentations can be handled
very effectively with one microphone
placed on a movable boom stand with
possibly one additional floor -stand or
desk microphone for commentary or announcement purposes. Productions of a
more complex nature -such as dramatic
presentations where more than one set
is involved-present a greater problem
and to do the job effectively and have
the microphone in the right place at the
correct time requires the use of a quiet,
highly flexible boom stand having a
large range of extension with a wide
vertical and lateral swing. There are
two types of microphone boom stands in
general use today for television service.
One of these is a semi -adjustable type
which can have its extension and elevation adjusted beforehand and then
wheeled into position. This type of stand
can be used quite effectively on such production that will permit the microphone
to be placed above the scene being televised and not requiring any extensive
movement of the microphone during the
show.
Shows of a variety or dramatic type
where there is considerable movement
of the artists require a boom stand that
will literally permit the microphone to
follow them around the set. This type of
stand is in general use in the motion
picture industry and one model recommended for TV programming i$ the
MI- 26574. This particular stand provides an operating station for the boom
operator and the whole structure is
mounted on rubber tired wheels which
permit it to be readily moved across
the floor. The length of the boom can be
extended from 7 to 17 feet. and the
microphone can be "gunned" through an
angle of 280 deg. This boom stand, in the
hands of a trained operator. can do
VIDEO ENGINEERING
much :o offset the disadvantages of picking up sound at a greater distance from
the source than is encountered in the
regular AM or FM system of broadcasting. In selecting this latter type of
stand. consideration should be given to
the size of studio in which it is to be
operated. In small stations where staging
space is at a minimum, it would be more
practical and more economical to use
the semi -adjustable stand.
Microphones that are used for broadcast service can also be employed for
television programming. The microphone generally recommended for boom
service is the type 77D. This is basically
a ribbon microphone operating on a
velocity-pressure principle. It has three
directional characteristics, namely: uni-
1
g
Monitor and Signal Circuits
The studio monitor speaker serves
three functions. namely:
1. Talkback
2. Cue or
3. Effects
Monitor
Speaker
The latter circuit permits sound effects
records or transcriptions to be fed into
the studio for special effects purposes
while it is "on- the-air ".
Relays are included in the rack
1
I
OMMI
directional, bi- directional, and non -directional. For boom service it is generally set in the uni -directional position,
which will permit artists to operate at
a greater distance from the microphone
and its directive characteristic will favor
reduction of reverberation and background noTie level.
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DECEMBER, 1950
www.americanradiohistory.com
AmericanRadioHistory.Com
a
small TV station.
V9
Fig. 5. A flexible and
easily operated boom
stand
piece
is an
invaluable
studio
of TV
microphone pickup
equipme nt.
'ourte
ment that will permit the operation of
an ON AIR studio signal and AUDITION
lights.
The equipment required for the announce booth consists of an announce
microphone, a monitor loud speaker, and
ON AIR signal light. Any of the previously mentioned microphones may be
used for this service. When the studio
is "off-the- air ", program is automatically
fed into the announce booth. The operation of the ANNOUNCE key on the con solette places the microphone in the
circuit, opens the monitor speaker circuit, and turns on the ON -AIR signal light.
The output of this announce microphone circuit may be fed directly through
the consolette to the line as, for example,
in supplying commentary for slides or
silent motion pictures, or it may be
mixed with the output of the sound from
the studio, motion picture projectors, the
remote line circuits, or, if necessary, may
be mixed with the output transcriptions.
The audio equipment for the projection room is of minor nature. Stations of
this size would normally use two type
TP-16B 16 -mm projectors whose output level is +4 dbm. This should be attenuated to approximately -20 dbm before being fed into two of the remote
line positions on the consolette. Due to
the fact that considerable variation in
frequency characteristic is likely to be
encountered from the various types of
films that may become available for television use, it is recommended that an
MI -26313 equalizer be employed in the
audio output of each projector. The
equalizer has three bass and three treble
boost positions as well as three bass and
three treble attenuator positions, in addition to a flat response position. This
equalizer is a "T" network and should
be isolated from the input of the consolette by means of a line coil in order
to obtain correct performance from the
equalizer.
The loudspeaker serves as a monitor
speaker and is tied in with the program
director's talkback system.
In order to provide facilities for handling network and remote program circuits, two type BE -1B line equalizers
and two type BA -13A studio amplifiers
are included as part of the rack equipment. The line equalizers are capable of
V10
.
.VOR -TV)
equalizing normal program line circuits
up to and including 15.000 cps. The studio
amplifiers have sufficient gain to bring
the equalized line levels up to such an
output that they may be read on a standard VU meter. This permits the lines to
be equalized and level adjusted before
being placed on the air. The outputs
of the BA -13A amplifiers are fed
through a fixed attenuator pad to two
of the remote line positions on the con solette, as well as to two of the monitor
inputs, thus permitting complete remote line checking before going on the air.
There are a sufficient number of jacks
located on the rack to permit the termination of a maximum of 24 remote line
circuits.
Transcription service does not play as
important a part in television broadcasting as required for AM or FM
broadcasting, yet such facilities must be
provided for producing background
music, fill-in for slides and silent motion
pictures as well as sound effects. This
system employs two type 70D turntables.
The output of each machine feeds into
a type BA -2C preamplifier and then to
the transcription inputs of the consolette.
Across the outputs of the preamplifiers is
located a two -way lever key switch
which will permit the signal to be fed
to the input of a BA -14A monitoring
amplifier. This key switch also operates
a relay which will permit this signal to
be fed to the studio loudspeaker. This
feature makes it possible for records to
be used for dance purposes, accompaniments, and sound effects. The transcription service can also. at the same time,
be fed through the consolette channel to
the line.
The regular line output position of
the consolette is normalled through jacks
and an isolation transformer to the outgoing line. This line is also bridged by
another BA -13A amplifier which normally acts as an isolation amplifier to
feed a house monitoring bus. It may also
be used as a spare amplifier when required. A spare BA -14A amplifier is
provided with its 600-ohm and bridging
input circuits terminated on jacks. Its
output is also normalled through jacks
and a line coil to provide a spare line
output circuit.
A standard consolette alone very sel-
dom satisfies the complete requirements
of a broadcasting installation, and a
television system is no exception to the
rule. In order to increase the flexibility
of the system and provide additional features, a companion unit, BCS.-3A, has
been developed to mount adjacent to the
consolette. It contains a standard VU
meter with a calibrated input control and
a ten -position selector switch. A number
of circuits are normally connected to the
input of this switch, such as the output of the two line amplifiers, the output
of the spare BA -14A amplifier, and the
regular output of the consolette. Across
this switch is located a jack which will
permit the use of a pair of headphones.
On this panel is mounted the key switch
for controlling the output of the two
transcription turntables for the studio
speaker over -ride circuit and a suitable
volume control for the input of its associated amplifier.
A spare 250 -ohm volume control is
mounted on the console and its input and
output circuits are terminated in line
transformers whose 150 /600 -ohm inputs
and outputs are terminated in jacks so
that they may be patched into a circuit
when so required. Located on the right
side of the BCS -3A unit is a six position
ring -down circuit, consisting of six relays, six indicator lights, and six ring talk lever key switches. A jack is provided for inserting a standard telephone
unit. These six input circuits are also
terminated on jacks on the rack which
permits them to be patched into the
incoming lines as required. The power
for operating the calling signal lamps is
obtained from the 12 -volt d.c. relay
power supply. The ringing current is
not supplied as part of this equipment.
This intercom circuit, placed adjacent to
the consolette, permits the operator to
communicate directly with remote points
without having to leave the equipment
during a program.
In order that a program director may
successfully produce a show, a means of
dispatching information to a number of
strategic points must be provided. To accomplish this, a separate talkback circuit
consisting of a microphone, BA -I4A
amplifier, four relays and four control
keys, is included as part of this system.
The four lever key switches are to he
located near the program director's point
of operation. These circuits permit talk back to the following points by interrupting she program monitor circuit:
1. Projection Room
2. Studio
3. Announce Booth
4. Order Wire Circuit.
The order wire circuit is normally connected into a video switching unit such
as a TS10A switching panel, which also
provides a two -way phone circuit between the camera operator and the video
operator.
The various amplifiers, equalizers, relays, isolation transformers, and six
jack strips are assembled and wired in
a standard cabinet rack which may be
mounted as a single unit or in line with
other equipment racks that are required
[Continued on page V14]
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DECEMBER, 1950
V
Remote Television Broadcasting
W.
I. McCORD
Continuing the description of the DuMont Telecruiser to cover the video
phase of remote pickup operation with this versatile "portable studio."
TIME, in television
broadcasting, there are many
schools of thought regarding the
manner in which various types of programs should be handled. After having
carefully studied all of these various
ideas, we have designed the Du Mont
Telecruiser which is engineered for efficiency and versatility. It is a complete
television studio on wheels, transporting
men and equipment to the scene of action. Its arrangement is quite flexible
and allows the use of the Telecruiser
either as a mobile vehicle or as an adjunct to studio operations. Many of the
smaller stations who use the same equipment for remote operations and studio
pickup have made provision for the Telecruiser to be driven into the studio area
or adjacent to it and operate the Telecruiser as a studio control room. This
manner of operation requires only the
removal of the cameras from the Telecruiser and the playing out of the necessary amount of camera cable to connect
with them. Handling of the equipment is
thus minimized, and the Telecruiser is
ready to roll in a few minutes time making possible close scheduling between
studio programs and remote pickups.
Also, this system makes it possible to
use other large auditoriums or buildings,
such as municipal stadiums, armories,
halls, and so on, for studio operations
that cannot be accommodated in the
small area of the station's own studio.
Television broadcasters who plan to use
the Telecruiser for more than one of
their stations dispatch it from station to
station as needed. Also, it is possible to
rent out the facilities to stations in the
near vicinity thereby deriving some
revenue from time when the Telecruiser
would normally be inactive.
Being completely self -sufficient, the
Telecruiser can readily be used advantageously for picking up special events
or to cover emergencies at a moment's
notice, providing a source of "on the
spot news coverage," such as the televising of a fire, train wreck, floods,
flood conditions, or other catastrophies.
These scenes can be transmitted over the
microwave relay back to the station,
where they may either be rebroadcast
to home receivers immediately, or
through the use of the tele- transcription
(recording on film) at a later time so as
not to interfere with a scheduled show.
AT TILE PRESENT
VIDEO ENGINEERING
Willis
I.
McCord, Manager,
Television Specialties Department of the
Research Division, Allen B. Du Mont
Laboratories, Inc.
Complete equipment is transported on
the Telecruiser to cope with any conditions which might be encountered in
this line of work either for daytime or
night operations.
Every effort has been made in designing the unit to minimize the time and
labor required to set up for a television
program and to replace equipment in the
vehicle at the close of operations. The
savings effected by labor- saving devices
result in less overtime hours and require
fewer operators than would otherwise be
necessary. The morale of operators
working in a unit which is so planned
and arranged is a big factor and results
in ...letter employer /employee relationship and improved picture quality. Employees take more pride in the appearance of their equipment and will be
more careful not to damage or abuse it.
As a result, there are fewer instances of
equipment failure and the station owner
has the satisfaction of seeing his investment and capital equipment being protected.
Description
The basic vehicle which is used as our
Telecruiser is a bus-type vehicle having
been selected for its maneuverability,
riding quality, and streamlined appearance. It is a Flexible Coach, 30 ft. long
and 8 ft. wide, and with 9 ft. 3 in. overhead clearance. The wheelbase is 182 in.
with a turning radius of 38 ft. 5 in. It is
powered with a Buick 150 h.p. Fireball
engine mounted in the rear and is
DECEMBER, 1950
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equipped with Bendix Westinghouse air
brakes and all other standing road equipment to meet State and ICC regulations.
All replacement parts are of standard
manufacture available any place in the
country. The vehicle is capable of over the-road speeds up to 70 miles per hour
and can negotiate rough road conditions.
In many cases these units have been
driven over open fields where one would
hesitate to take an automobile. The short
wheelbase makes possible getting the
vehicle into small confined areas and the
exceptionally low overhead clearance has
many times allowed us to use the Telecruiser in places where it would have
been impossible to take a higher unit.
The interior of the Telecruiser has
been arranged to accommodate a triple
image -orthicon chain transported in
operable condition with all cameras, tripods, and cables quickly accessible. Three
main sections divide the interior as follows : (1) Driver's compartment with
provision for transporting personnel in
comfortable seats. (2) A control room
compartment containing the audio console director's desk and video operating
console. (3) Storage compartment containing cable reels, camera tripods,
microwave relay transmitter and parabolic reflector, lighting equipment and a
5 -kw gasoline- driven generator to provide 120 -volt 60 -cps a.c. power.
The control room is the largest area
and arranged so that the video console
runs crosswise of the vehicle. Seated in
comfortable operating chairs in front of
this console are three video control operators. One of these operators is the
switcher or technical director, who is
responsible for the selection of the
proper picture to feed to the phone line
or microwave relay. On the top of the
console, four units are mounted. Three
of these units are identical individual
camera control monitors, each one
coupled directly with its associated camera and displaying the picture coming
from that camera. The fourth unit is
the mixer monitor and amplifier which
contains the switching buttons and can
accommodate up to four cameras.
The special effects are controlled by this
unit and the switcher can lap fade or
superimpose the pictures. The lap and
fading from one camera to another can
VII
Fig.
1.
The KBTV
Telecruiser in use
on location with
the
microwave
relay "dish" in
operation on its
collapsible tower.
be done either manually or automatically
with varying time rate, i.e. instantane-
ous, slow, medium, or fast, set by merely
turning a knob control to either position. Underneath the console are located
five units: one low- voltage supply and
distribution amplifier, three power supplies, and the synchronizing generator.
Each of these power supplies is connected by multi- conductor cable directly
to the monitor unit above it, and to the
low- voltage supply and distribution am-
plifier which distributes composite synch
to each camera unit. The synch generator is coupled directly to the low -voltage supply and distribution amplifier
unit.
Video Circuits
The output of the camera control
monitor is fed directly to a built -in studio
type video patch panel. All the video
signals are controlled through the video
patch panel which in turn feeds the signal to a picture distribution amplifier
capable of providing up to eight video
channels for line feeds. The output of
the picture distribution amplifier is returned to eight points on the video patch
panel and from there is distributed to
microwave relay, line monitors, telephone line, etc. This signal is a standard
2 -volt peak -to-peak. Over the video console is a 12 in. air /line monitor receiver,
used to monitor either outgoing signal
or to check on the signal from the station. A 'scope is also mounted on this
panel and is used to monitor the video
either from the various lines or the output of the picture relay transmitter. The
director is located in this control room
area and from his position can view all
of the picture monitors. He is coupled to
the camera control operators and the
camera men by an intercom system and
can direct camera angles or instruct the
switcher over intercom hookup. Each
position is also provided with a field
telephone unit which in turn is connected to provide phone line to remote
V12
relay transmitter position or to the main
studio or transmitter. The audio man is
also connected into this circuit from his
position as described in the previous
article.
All of the equipment mounted on these
consoles is equipped with shock mounts
and quick-action releases so that they
can easily be pulled out for servicing or
for removal from the vehicle if it is
necessary to operate outside of the Telecruiser. Spacing of the units on the consoles has been done with adequate provision for ventilation and accessibility
for changing tubes without removing the
units. This also provides more working
space for the operators. Two large exhaust fans have been provided behind the
console to exhaust the heat produced by
the power supplies and other equipment.
The shelf over the console acts as a collector hood to conduct this heat into the
exhaust fans. Having operated in this
unit in very hot weather in Texas and
elsewhere, we find that these fans are
essential and that we can maintain comfortable operating conditions even under
extreme sun loading.
In the Telecruiser, the operators follow the modern trend of working blind,
observing all action on the camera control monitors. No provision being made
for viewing live action through large
windows which have proved to be a
hangover from audio operating days. It
is essential for the video operator to concentrate on picture quality and the distraction of live action will take his
attention off the television picture. All
of the a.c. power distribution is controlled from the control room area by a
circuit breaker panel and a Variac compensates for fluctuation in line voltage.
A main a.c. power switch is located in
the rear compartment with provision for
selecting either the self -contained 5 -kw
gasoline driven generator or outside
commercial service. This system can
accommodate either single-phase 120-V,
single -phase 120/240, or three-phase a.c.
power. A 250 -foot reel of four conductor
#8 wire has been provided for connection to commercial power source that
may be distant from the Telecruiser location. In the rear compartment, cable
reels accommodate several assorted
lengths of camera cable, microwave control cable, and a.c. power cable. All of
these large cable reels are motor driven
for ease of rewinding the cable. Other
small cable reels are provided to accommodate microphone cable and video
coaxial cable (RG59U).
The camera tripods are also located in
this rear compartment along with four
250 -watt flood lights for night operation.
Other accessory equipment, adapter connectors, and various spare parts and
tools are also included in this compartment. A removable door in the back of
the video control console gives access
from the storage compartment to the
rear of the camera control units and provides an easy means of connecting and
checking cables on this equipment.
Roof Platform
On the roof of the vehicle is a deck
20 ft. long and 6 ft. wide, covered with
nonskid rubber material to provide safety
for the operators. In addition a removable guard rail is also provided to keep
the operators from accidentally backing
off of the roof. Mountings to accommodate three cameras are attached to the
deck and a clamping arrangement secures the camera tripod in place. With
the cameras thus secured, it is possible
to drive along while picking up a television picture. The microwave relay can
also be secured to the roof and the picture relayed hack from this vantage
point. In order to relay the picture back
to the tower however, it is essential to
have an unobstructed line of sight air
path between the microwave relay transmitter and the microwave relay receiver
position. Sometimes it is necessary to
place the microwave transmitter as far
as 1000 ft. from the Telecruiser. In order
to do this, the control unit is removed
from the vehicle to a point closely associated with the transmitter unit and the
video signal is fed to the control unit
from the telecruiser by RG59U 72 ohm
coaxial cable. This cable can be run as
far as 2000 ft. when necessary.
In the WDTV Telecruiser (Pittsburgh) access to the roof is gained
through a large hatch opening into the
control room area. A ladder is provided
on the control room wall so that the
men can climb up onto the roof deck or
pass equipment through the hatch. In
the KBTV unit, the access to the roof is
by a means of an exterior removable
ladder.
STL Relay Facilities
On the KBTV Telecruiser, using the
[Continued on page V14]
VIDEO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
DECEMBER, 1950
NEW PRODUCTS
Luprured Inputuner. Providing
greater gain than any previous Du Mont
Inputuner, the new series T3A is de-
signed both mechanically and electrically
for replacement of switch -type tunera in
existing TV receivers. Standard mounting holes and identical space requirements make interchange of tuners a matter of minutes. Electrically the new Inputuner is designed to work into the i.t.
illustrated folder describing and illustrating RCA's latest field TV equipment,
including an improved friction head, a
new tripod, new field desk, and a rotatable
mount and remote control for microwave parabola. Requests should be addressed to Department No. 522 at the address above, and should ask for booklet
titled New TV Field Equipment.
Andrew Corporation, 363 E. 75th St.,
Chicago 19, Ill. will mail Bulletin 39, fully
describing the Andrew Type 738 ultralow -loss coaxial transmission cable, free
on request of prospective users. Type 738
is a semi -flexible % -in. line suitable for
connecting antennas to transmitters or
receivers at frequencies from 25 mc to
2500 mc.
necessary, the signal being fed directly
from the antenna into Individual isolation boxes.
TV Deflector Yoke Core. Designed for
deflection of wide -angle picture tubes, the
new Westinghouse deflector yoke core is
made of Hipersil, a cold -rolled grain-
system of TV receivers using a separate
sound Lt. Input impedance is 300 ohms.
As in earlier models, the new T3A provides continuous tuning covering all TV
channels as well as the FM band. It has
low oscillator radiation and low noise
figure. Cost is substantially lower than
any previous Inputuner. Available at
once to both jobbers and manufacturers
from Electronic Parts Division, Allen B.
Du Mont Laboratories, Inc., East Paterson, N. J.
TV Monitor. Developed especially
for TV station use, the new MTV -12 offthe -line monitor recently announced by
Raytheon Manufacturing Company, Waltham, Mass. is ideal for viewing programs
oriented electrical steel. The core is
wound and bonded in circular form from
a continuous strip of 5 -mil material. The
resultant thin laminations plus excellent
magnetic characteristics tend to produce
superior linearity and sharper pictures.
The core is entirely free from magnetic
instabilty due to temperature change.
Complete data will be supplied by Westinghouse Electric Corporation, P.O. Box
2099, Pittsburgh 30, Penn.
in control rooms, film rooms, announcers'
booths and executive offices. Picture tube
size is 12% in. An audio channel and
speaker are included in the unit and may
be used for either cueing or monitoring.
Sturdy construction and light weight
make the MTV -12 well suited for remote
pickup use. Overall dimensions are 16 x
18 x 21
in.
TV Demonstration System. As many
as 100 TV receivers may be fed from a
single antenna through use of the Taco
master antenna distribution system, recently placed in production by Technical
Appliance Corporation, Sherburne, N. Y.
In operation the signal is fed through
a power amplifier into a mixer and then
into isolation boxes feeding one or two receivers each. Where no more than eight
receivers are to be used the amplifier may
be used alone without isolation circuits.
In high -signal areas the amplifier is not
VIDEO ENGINEERING
NEW LITERATURE
Superior Electric Company, Bristol,
16 -page booklet
fully describing the complete line of
Powerstat variable voltage .transformers.
In addition to excellent illustrations, performance curves and wiring diagrams,
the booklet contains a handy rating chart
which provides engineers and purchasing
agents with a quick selector index. When
writing request Bulletin P550.
Conn. is now releasing a
Allen B. Da Mont Laboratories, Television Transmitter Division, 1000 Main
Ave., Clifton, N. J. is now distributing
an 18 -page illustrated booklet on the
Du Mont industrial color television system. Available to executives writing on
business or professional stationery.
RCA Engineering Products, Camden
2, N.
J. has available for broadcasters an
DECEMBER, 1953
www.americanradiohistory.com
AmericanRadioHistory.Com
C B S
TELEVISION
INTERCOM FACILITIES
ß.i,ú,,, page
i
time during rehearsal. Talkback microphones are also available to the video
switcher and audio mixer permitting
them to use this loudspeaker circuit to
communicate with members of the technical staff who may be away from their
stations and therefore not wearing their
regular headsets or headphones. Interlocking relays, which disable this circuit when the audio console line key
switch is thrown to the "air" position,
are incorporated, thereby preventing accidental use of the talkback loudspeaker
when the studio is on the air.
When compared to aural broadcasting
studios, television studios are usually
quite large; as a matter of fact, studios
which a short time ago were considered
large are now regarded as medium in
size. The talkback speaker must be capable of producing quite high levels at
the stage in use, as for example. when being used over the playing of a large
orchestra. Rather than attempt to cover
a large studio with a single high power
talkback loudspeaker and driving amplifier, it has proven more practical to
employ a small mobile loudspeaker unit
which is moved to the area of the studio
in use. This talkback loudspeaker is one
component of the studio floor monitor
described below.
The Studio Floor Monitor
The studio floor monitor, Fig. 7, is an
indispensable unit of studio equipment.
It is customary to provide at least two
of these units in each studio. As can
be seen, this unit combines, in a single
cabinet, a picture monitor, a loudspeaker,
and a clock. As described above, the
loudspeaker is normally connected to
the studio talkback circuit.
It is customary to place one or more
of these floor monitor units at the stage
in use in positions where they are visible
to the greatest number of persons concerned with the production. Thus the
performers, floor manager, and other
studio personnel can see the production
exactly as it is leaving the studio.
Equally important, it is possible for them
to follow the program continuity at
V13
times when the action is originating on
another set, on motion picture film, or
from a remote point.
Smaller monitoring units containing
only the picture monitor are provided
for technical and production personnel
who must closely follow the program
continuity. Such units are installed at
the sound-effects station, lighting panel,
and in the announcer's booth.
For this reason, the design details of
at the window just right of the open
the intercom facilities should be worked door. The exterior of the vehicle is atout with the greatest forethought and
care. For dependability, only the most tractively styled to serve as an adverreliable components should be employed. tising medium for the station.
In addition, the circuits should be arBecause of special operating condiranged to provide all possible emergency
operating facilities including such fea- tions in various parts of the country and
tures as a jackfield providing access to specific desires and needs of individual
all important circuits and components broadcasters there are no two Teleand, as well, emergency sources of a -c,
Material
Transcribed Audio Program
relay, plate, and filament power. If cruisers built alike. Each one is custom
Portions of the audio material used in plug -in amplifiers are used in the audio built to incorporate the features deemed
TV programs often originate on electri- system, the same amplifier types should necessary. These features are established
cal transcriptions or magnetic tape. be employed in the intercom system to by close cooperation
between the engiQuite often it is necessary for the per- permit complete interchangeability of
formers in the studio to hear this re- amplifiers. As a matter of fact, the in- neering staff of the station and the Du
corded program material. One example tercom facilities should be treated as an Mont Television Specialties Department,
where this would be necessary is in the extension of the audio system and em- so that when the Telecruiser
is delivered
case of a program wherein the inner ploy the same components and constructhoughts of a performer are being made tion practices. The essential requirement it is completely equipped and wired for
audible to the audience. This material is is the ability to restore the intercom fa- audio, video, and a.c. having been thorpreviously recorded and is played back cilities to a normal operating condition oughly tested and checked out in all reat the appropriate time. It is essential, in a minimum of time in the event of a
spects so that it will be operable imof course, that the performer in the stu- failure of any portion of the system. If
dio hear this recorded material in order this is not possible, a failure of the in- mediately upon arrival at the station.
to properly coordinate his actions. An- tercom system may easily result in the
With a well trained crew of five men,
other example where recorded program complete disruption of an important proit has been possible in many instances
material must be heard by the performers gram production.
is in the case of music to which people
Intercom facilities of the type de- to leave the studio and proceed to a rein the studio are dancing. If this music
scribed above have been in operation mote location having a picture for air
is recorded, it is necessary that the in the CBS -New York television studios
dancers in the studio hear the music. for several years and have proven ade- broadcast in less than one hour's time
Appropriate circuits must therefore be quate to handle the requirements of the after arrival at the pickup point. After
provided which will transmit recorded most elaborate programs originating the program has been completed, the
program material to a studio loudspeaker from these studios. The basic design of
when desired, as well as to the regular these intercom facilities is not new but Telecruiser can be ready to return to its
outgoing audio program line. A block has evolved as a result of CBS' many base in a matter of approximately 30
diagram of a suitable circuit arrange- years of experience in television studio minutes.
ment intended for use with transcription operations. Ideas and suggestions which
The two units described and shown in
turntables is given in Fig. 8. A similar resulted in the design described have
arrangement will serve for magnetic been contributed by many members of this article are now in active service in
tape reproducers.
the CBS television staff. Many contri- Pittsburgh and Dallas and have been
The loudspeaker unit in one of the butions were also made by Howard A.
studio floor monitors may be employed Chinn, CBS Chief Audio -Video Engi- used to pick up many hours of programto reproduce this recorded material in neer, under whose direction the design ming for their respective stations. They
the studio.
and installation of the facilities were un- have proved through actual operation to
dertaken.
be an indispensable piece of programDressing Room Call System
ming equipment, especially in those
Another branch of the TV studio intercom system which has proven exareas not presently connected with the
tremely valuable in coordinating proREMOTE TELEVISION
various networks. Heretofore, stations in
gram production is a call system between
these areas have been dependent on film
the studio control room and the dressing
BROADCASTING
rooms. This call circuit permits the dior recorded shows for the greater porrector or his assistant to call each per[from page V12]
tion of their program material.
former to the studio well in advance of
his scheduled appearance.
Du Mont 2000 -mc relay, a permanently
The loudspeaker arrangement emmast is provided to support the
ployed in the dressing room area will attached
depend on the location and arrangement relay transmitter reflector, as shown in
AUDIO SYSTEMS
of the dressing rooms. Usually one or Fig. 1. This reflector is light weight with
metal
perforated
reflecting
surface,
and
two loudspeakers placed in the dressing
FOR TV SERVICE
room corridor will be adequate. At other the ribs are made of a fiber glass matimes. it may be necessary to install a terial. When not in use, the reflector
[from page 1/10]
small loudspeaker in each of the dressing dish is removed from the mast and
rooms. In either event, the loudspeakers stowed in the rear compartment. The as part of the overall television installashould be clearly audible at all points mast itself can be folded back onto the
tion.
in the dressing room area. The associ- roof. Figure 1 also shows the
exterior
Several of these systems have been
ated circuits in the studio control room
features
of
the
KBTV
Telecruiser.
At
are shown in Fig. 6.
installed and are daily feeding programs
the roof level are waterproof outlets
which provide a.c. to the flood lights or to the local stations and in some inCONCLUSION
stances, to a network. Each has all the esIt can \yell be realized that a failure to service cords. Also provided is an sential facilities required for
a small
outlet
for
announcer's
the
microphone.
of the television studio intercom system
during the production of a program Looking through the open door, an studio installation, and its circuit flexibilwould be just as devastating as a break- operator can be seen seated at the video ity has proven its worth on more than
down of the sound or picture facilities. console and the audio man can be seen one occasion.
V14
VIDEO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
DECEMBER, 1950
Here's why those in the know
Video Engineering
1950
SUBJECT INDEX
-demand
Audio
Audio Systems for TV Sers.
W. L.
Lyndon, I May, V9; II Dec.,
CBS -TV Sound Effects Console; R. B.
Monroe and P. E. Fish, I March, V12;
II May, V 12.
Steps to Improve TV Audio; Arthur
Davis, March, V14.
1
.
CANNON
Patented exclusive latchlock
device
Intercommunication Systems
TV Intercommunication Systems; R. B.
Monroe, Dec., V3.
Lighting
Practical Television Lighting;
Rackey, I July, V3; II Sept., V8.
C.
A.
PLUGS
All contacts, machined from solid bar
Shel design saves space.
stock, electroplated with silver.
Networks
CBS "Loss- Less" Video Isolation Network; D. E. Maxwell, Sept., V4.
Socket contacts are full.floating
Economical 10 "- to -16" Conversion Practices; Vinton K. Ulrich, March, VS.
...
turn through 360..
Receivers
Gros nd contact mates
first;
breaks last.
Recording
Mechanics of TV Recording, The; Skip with W. Athey, May, Vb.
Remotes
Hand tinned solder cups tinned
tisice only.
Insert retaining screw
threads into metal barrel
instead of plastic...inserts
can be quickly removed.
Co- ordination in Remote TV
Broadcasting; W. I. McCord, July, V7.
Remote TV Broadcasting; W. I. McCord,
Audio
Dee., V11.
Sound Effects
CBS -TV Sound Effects Console; R. B.
Monroe and P. E. Fish, I March, 112;
II May, V18.
Studios
a
Television City; E. Chisholm Thomson,
Sept., V3.
Systems
Audio Systems for TV Service; W. L.
Lyndon, I May, V9; II Dec., VS.
Basic Video System Planning; C. A.
Rackey, March, V4.
Compression gland having a soft rubber bushing grips
the cable; fibre washer takes care of bushing thrust.
Cable entry has strain relief spring.
TV Intercommunications Systems; R. B.
Monroe. Dec., V3.
Laboratory TV System, A; Ralph L.
Hucaby, Sept., V9.
AUTHOR INDEX
Athey, Skipwith W.
Mechanics of TV Recording, The; May,
Vb.
Davis, Arthur
Steps to Improve TV Audio; March,
V14.
Fish, P. E. and Monroe, R. B.
CBS -TV Sound Effects Console; I
March, V18; II May V12.
Hucaby, Ralph L.
Laboratory Television System, A; Sept.,
V9.
Lyndon, W. L.
Audio Systems for TV Service; I May,
V9: II Der.. V8.
McCord, W. I.
Audio Co-ordination in Remote
TV
No corners are cut ... nothing is overlooked to assure you
outstanding performance with Cannon Plugs. So long an
engineer's choice, the words "Cannon Plugs" have become
part of our electrical language. Continued excellence of de-
sign ... ability to meet your changing requirements ... are
good reasons why the Cannon line of connectors continues
to excel where specifications must be met. XL Connector
Series is just one of the many Cannon types -world's
most complete line. Request bulletins by required type or
describe your needs.
Broadcasting; July, V7.
Remote TV Broadcasting; Dec., Vii.
Maxwell, D. E.
CAN NON
ELECTRIC
CBS "Loss-Less" Video Isolation Network; Sept., V4.
Monroe, R. B.
TV Intercommunication Systems; Dec..
V3.
and Fish, P. E.
CBS -TV Sound Effects Console;
March, V12; II May, VIP,
Rackey, C. A.
I
Since 1915
LOS ANGELES
Basic Video System Planning; March,
31, CALIFORNIA
July,
REPRESENTATIVES IN
PRINCIPAL CITIES
Thomson, E. Chisholm
Television City; Sept, V3.
Ulrich, Vinton K.
Economical 10 " -to -16 "Conversion Practices; March, VS.
In Canada & British Empire: Cannon
Electric Co., Ltd., Toronto 13, Ontario.
World Export (Excepting British Empire): Frazar & Hansen, 301 Clay St.,
San Francisco.
V4.
Practical Television Lighting;
II Sept, V8.
V3;
VIDEO ENGINEERING
I
DECEMBER, 1950
www.americanradiohistory.com
AmericanRadioHistory.Com
There are 12 items in the XL line. Insert
arrangements available 3 -15 amp. con.
tacts, 4 -10 amp. contacts- working voltage 250 volts. Zinc and steel plugs with
bright nickel finish are standard. Satin
chrome finish also available on steel plugs.
:
-
V15
o
Wonderful way fo feel
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Why not? Your car is paid for and your house is
halfway there. You're making pretty good money
and your
the kids are healthy and happy
wife just bought a new outfit -shoes to chapeau!
You don't owe anybody a red cent. Not only
that- you've got a little money salted away for
the kids' education and your own retirement.
Wonderful way to feel, isn't it?
If this description doesn't fit you -make it!
You can. Here's how:
...
...
!
Start saving right now! Just as much as you
possibly can -and regularly.
One of the best ways ... one of the safest, surest
is to buy U. S. Savings Bonds through
ways
the Automatic Payroll Savings Plan where you
work. Or, arrange to purchase Bonds regularly at
your post office or bank.
U. S. Savings Bonds will bring you, in ten years,
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Start your plan today. It's the very wisest way
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...
Automatic Saving is Sure Saving
U.S. Savings Bonds
Contributed by this magazine in co- operation with the Magazine Publishers of America as a public service.
V16
VIDEO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
DECEMBER, 1950
Rapid Attenuator Calculation
Using the Vector Slide Rule
A.
E.
RICHMOND
A time saving method of arriving at results which often require considerable figure -work.
are used in a
wide variety of audio circuits.
They find application in audio level
adjustment and in impedance matching,
and are very widely used in such systems as recording, public address, and
broadcasting.
Some attenuator design procedures
have been used which are quite time -consuming and tedious. The procedure given
in this article, using the "Vector" slide
rule,' is comparatively rapid. With this
method, attenuating pads having losses
as great as about 26 db can be calculated
quickly.
The very common "T" pad circuit of
Fig. 1 will be used as the basis of this
article. Based upon the method shown,
the reader will doubtless be able to adapt
the equations for other attenuator circuits to slide -rule computation.
RESISTIVE ATTENUATORS
other procedures. However, as will be
shown, only ten easy steps complete the
side-rule solution of the entire attenator,
and knowledge of the theory of the hyperbolic functions is not even necessary.
The hyperbolic functions are obtained
by the use of scales Ski. S42, and Th,
which are illustrated in Fig. 2. This figure shows one side of the slide rule.
These scales indicate the angles in radians whose hyperbolic sines and tangents,
respectively, are given on scale D.
The equations used2 as the foundation
of the procedure are:
R3
\JZLZ2
sink 0
I,
:15
,
B
R,
L(8) -¿V(5)
L
Cm* (4)
110211
639.211
L me
(I)
Line (2)
tree (3)
1.727 neeers
R,
(6) -
Line
do
Line (5)
Line (6)
(5 ) . 5 2 9
.
0
Ji
/59.811
49.612
Line (7)
Lme (8)
Line (9)
R,496R R,529011.
150150J
1
60017
Rs:
021i
(i)
Fig. 3. Example of "paper" calculations. This figure shows the entire
amount of paper work involved in designing attenuator to meet specifications of example in text. The remainder
of the work is done directly on the slide
rule. Bottom: the completed attenuator design required in the example.
Equations (1), (2) and (3) are from
"Reference Data for Radio Engineers,"
Federal Telephone & Radio Corp., New
York, 3d Ed., pp. 158-9, by permission.
The equations forming the basis of the
procedure make use of hyperbolic functions, the hyperbolic sine sink and the
hyperbolic tangent tanh. At first glance,
these formulas may seem to complicate
the work beyond that required for some
R,
R,
Fig.
/5011
600J2
Loss
LossISeE
Equations
*Consulting Engineer, Portland, Oregon.
The article is based on the Log Log Duplex Vector slide rule No. N4083 of
Keuffel & Esser Co. Illustrations used by
permission.
z,
Z=
tank
R9
Z,
= tank
(2)
0
O
(3)
Rs
where Z, and Z, are the input and output impedances between which the attenuator is matched, and either Z, or
Conventional "T" attenuator
circuit, used as example in text.
1.
t
«o
L
e
.
I
l
....
Ì
"t
iI
I
.
.
IIHu
1l
4T'
II
Fig. 2. The N4083 Slide Rule, showing the hyperbolic scales. Illustration shows one side of rule. Hyperbolic tangents are
obtained by use of Th scale, while hyperbolic sines are given by use of scales Sh 1 and Sh2. (Copyright by Keuffel & Esser Co.)
AUDIO ENGINEERING
DECEMBER, 1950
www.americanradiohistory.com
AmericanRadioHistory.Com
19
mozz'
in nepers, by dividing the number of
decibels by 8.686. Use scales C and D in
the usual manner. The loss in nepers is
represented by the symbol O.
Hairline
of runner
VT-4.3001L
o
111111111M1
5112
9.1.727
(In our example, 0=15/8.686 = 1.727.
This is entered as line 4 on the calculating
sheet of Fig. 3. Some of the results, incidentally, will be given herein to a slightly
greater accuracy than that obtainable with
the 10 -inch rule.)
2.
(a)
Fig. 4. Setting of O on scale Sh2 (corresponds to step 4 in text). (Copyright
by Keuffel & Esser Co.)
Procedure
Assume that a pad is required to have
specified loss and is to operate between known input and ouput impedances. The problem is to find the values
of Rs, R, and R1 for the required "T"
pad of Fig. 1.
a
(As an example, let Z, be the input impedance of 150 ohms, Z, the output impedance of 600 ohms, and the required loss
15 db. This information is entered as lines
1, 2, and 3 on a slip of paper, as shown in
Fig. 3. This figure, incidentally, shows the
entire amount of "paper" work required in
the attenuator design, the remainder of the
figuring being done on the slide rule.)
The first calculation is the determination of the value of Rs, which is a somewhat longer procedure than that for Rs
or R1. Proceed as follows:
1. Convert the loss in decibels to loss
Hairline
of runner
600 /L
D
Th
=MEW
21111111111M
C
1.727
Fig. 5. Setting of O on scale Th (corresponds to step 6 in text). (Copyright
by Keuffel & Esser Co.)
20
the pad is to match un-
A A
.
V
R2
Zs may be the source and the other the
load; and
0= the loss introduced by the attenuator
in nepers
= the loss in decibels divided by 8.686
The simple procedure for the design
of the "T" pad will now be given, including a detailed example. In this discussion, it is assumed that the slide-rule
operator is skilled in the common manipulations of the rule, locating decimal
points, etc. Illustrations are included for
those slide -rule operations involving the
hyperbolic scales.
If
z,
z2
3
the example is 529.0 ohms, and is entered
as line 7 on the calculating sheet.)
The procedure for obtaining R, is
similar to that for Rs, and does not require additional diagrams, for its explanation.
8. Set the index to Z1 on scale D.
(For our example, Z, is 150 ohms.)
9. Set the runner to O on scale Th,
just as in step 6. Record the reading of
scale CI at the runner.
(In the example, this is 159.8 ohms, and
is entered as line 8 in Fig. 3.)
10. From the reading found in step
9, subtract Rs as determined in step 4.
The remainder is the value of R1 for the
required pad.
(In the example, R, is 49.6 ohms. The
completed attenuator design is shown at
the bottom of Fig. 3.)
For the convenience of those who
Fig. 6. The basic "T" attenuator circuit. Conversion to minimum -loss Lpad is made by eliminating R2; values
of R1 and R:, are determined in accordance with text.
equal impedances, i.e., is unsymmetrical,
multiply these impedances Z1 and Zs
together on scales A and B, and set the
runner of the slide -rule to the square
root of this product on scale D.
(In the example, 150 X 600=90,000, the
square root of which is 300 on scale D. It is
not necessary to record either the product
or its square root, or even to observe the
values.)
(b) If, on the other hand, the pad is
symmetrical (matches equal impedances), simply set the runner to this
impedance Z on scale D.
3. Set the index (the end of the scale)
of the slide to the runner.
4. Set the runner to O on scale Shl or
Sh2, and read the value of Rs on the
CI scale.
(In the
given example, set 0 =1.727 on
scale Sh2 as shown in Fig. 4. If the rule is
now turned over, R, will be found as 110.2
ohms on scale CI. Enter the value of R,
as line 5 on the calculation sheet.)
Next, we find the value of R,.
5. Set the index of the slide to Zs on
scale D.
(In the example being worked, Z, is 600
ohms.)
6. Set the runner to O on scale Th, and
record the reading at the runner on scale
CI as line 6 on the calculation sheet.
(In
the example, set 0=1.727 on scale Th
as shown in Fig. 5. The rule is now turned
over, and the corresponding reading on
scale CI, 639.2 ohms, is recorded as line 6.)
7. From the reading found in step 6,
subtract Rs as determined in step 4. The
result is the value of Rz for the desired
pad.
(The value of R, for the attenuator in
F'g. 7. Graphical solution for resistors
in parallel; a handy device for attenuator design and general audio work.
(From "Motion Picture Sound Engineering," D. Van Nostrand Co., Inc., New York,
N. Y., by permission)
do not have ready access to tables of hy-
perbolic functions, the decimal points of
the sink and tanh values can be located
as
follows:
The value of sinh 0 is roughly equal to
0 for values of O from 0 to 0.5. Sinh
0 =1 when 0 is roughly 0.89, and sink
C
becomes 10.02 when
0
The value of tank 0 is roughly equal to
for values of 0 from 0 to 0.4. Tante
[Continued on page 46]
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0
= 3.0.
DECEMBER, 1950
Determining Unknown
Impedances in Transformers
LOUIS H. HIPPE
simple method for obtaining information
about the characteristics of unknown transformers.
A
AUDIO INSTALLATIONS the
technician is sometimes faced with
the problem of determining quickly
and with reasonable accuracy the unknown impedances of transformer windings. At other times the technician may
find himself with a transformer that
could be put to good use, but unfortunately he is unable to obtain sufficient
data on the impedance capabilities of the
transformer to make it usable in a practical application. At other times he may
find that he has available several of the
400 -cps power transformers of the type
used in surplus military equipment.
These transformers can often be used in
audio installations where the power requirements are not too great -depending,
of course, upon the internal insulation of
the power transformer but "spec" sheets
on winding impedances for audio service
are not available for this type of transformer.
Once the impedances of primary and
secondary windings of any transformer
are known the transformer then becomes
valuable and usable as a component in
construction of new equipment or replacement in equipment already in use.
However, unless the technician experiments by cut- and -try, he is not apt to
know, even in a general sense, just what
tubes or other components the transformer will allow him to match. Since
cut -and -try requires a lot of time, and
since there is no logical place to start,
the transformer is likely to be relegated
to the junk box where it will kick around
until it eventually finds its way to the
ash can. Good equipment can be saved
from such a fate with a little effort and
a minimum of equipment.
IN MANY
4
ferably of the vacuum tube type) ; a impedance checks on a transformer that
1,000 -cps audio oscillator can be built . will eventually be used in the voice easily. With these two pieces of equip- frequency range. A 60 -cps test voltage
ment, plus a few odds and ends, the un- source is somewhat less accurate especiknown impedances of any transformer ally if the transformer has poor response
winding or choke can be quickly com- at 60 cps.
puted.
With the meter and test oscillator we
Figure 1 is the schematic of a 1,000 - can conduct our impedance determining
cps audio oscillator which will prove a experiment on the assumption that voltvaluable asset to the workshop and lab- age ratio is proportional to the turns
oratory in addition to the specific use ratio and that the impedance of a windabout to be described. It is inexpensive ing varies as the square of the turns.
to build since parts are held to a mini- This is expressed by the formula:
mum and may be selected from spare
v
za
(1)
part components.
Z,
V, )
In making impedance calculations, it
Where Z, is the known primary imis well to remember that one of its conpedance.
stituents is reactance. Reactance of a
Z, is the unknown impedance.
given coil or transformer winding
V, is the known applied voltage.
changes with the frequency applied. Beand
cause reactance changes with frequency,
V, is the voltage measured
impedance
it follows that
also changes.
across the unknown winding.
We are therefore interested in an osNote the statement, "where Zs is the
cillator as a source of voltage at 400 to
1,000 cps because it allows us to obtain known primary impedance." This value
[Continued on page 43]
a greater degree of accuracy in making
Calculation Methods
There are several possible transformer
impedance calculation methods and techniques available which will give results
of reasonable accuracy. Although not of
the caliber of laboratory measurements,
the tolerances are accurate enough for
average service.
Most audio technicians own or can
borrow a volt -ohm-milliammeter (pre* 10636 Victory Blvd.,
North Hollywood, Calif.
AUDIO ENGINEERING
1. Simple 1000 -cps oscillator which can be constructed readily and
which is useful in making measurements of the type described in this article.
CH is small a.c. -d.c. filter choke; SR, and SR., are 60 -ma selenium rectifiers;
T, and T, are 6.3 -volt, 1.5 amp filament transformers "back to back."
Fig.
DECEMBER, 1950
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21
AUDIO DESIGN NOTES
'
Resonant Loudspeaker
Enclosures
'
'
.:: 'r
SMITH'
BOB H.
THIS CHART is based upon the assumptions that the dimensions of the enclosure
are small compared to wavelength, that the
thickness of the port is negligible, and that
the amount of air moving in the port is
equal to the three halves power of the area
of the port. Thus, the inertance of the
port is :
M = -Ç
VA
where A is the area of the port and p is
the density of air. The compliance of the
enclosure is :
Division of Engineering, University of
California.
_
Ca
and represents a very heavy load, no oscillatory transient occurs at this frequency.
However, a new transient of higher frequency appears. It is caused by the mass
of the moving system going into anti -resonance with the compliance of the box. Thus,
the resonant enclosure does not completely
eliminate the production of oscillatory transients but usually the new transient will be
of shorter duration than the one which
would have occurred without a resonant
enclosure.
The radiation resistance is proportional
to the area of the port and is usually too
low for efficient energy transfer. Thus, the
[Continued on page 49]
=p=
where V is the volume and c is the velocity
of sound. The resonant frequency of a
Helmholtz resonator is :
1
_ c Ai
fr
2sV MCa 2n Vi
This expression seems to agree well with
experiment. In a typical case the error is 5
per cent.
It is customary to choose the resonant
frequency of the enclosure equal to the anti resonant frequency of the moving system of
the speaker. Since the impedance of the
resonator is purely resistive at resonance
_
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AUDIO ENGINEERING
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pill
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DECEMBER, 1950
ALIDI() enjineering society
Containing the Activities and Papers of the Society, and published monthly as a part of AUDIO ENGINEERING Magazine
OFFICERS
Bob Hugh Smith Western Vice. -Pres.
President
John D. Colvin
Lawrence Shipley Central Vice. -Pres.
C. G. McProud Executive Vice -Pres.
Treasurer
Ralph A. Schlegel
Secretary
Norman C. Pickering
Audio Engineering Society,
Box F, Oceanside, N.
Y.
Convention Report
THE SECOND ANNUAL CONVENTION Of
the Audio Engineering Society fulfilled the hopes of the Society members and officers and, along with the
Audio Fair, attracted a large number
of visitors from the New York area as
well as many hundreds from out of
town. The five technical sessions were
well attended, and some of the papers
will appear in these pages in future
issues.
At the Business Meeting, held on
Thursday morning as the first session
of the convention, witnessed the installation of the officers for the coming year.
Theodore Lindenberg, retiring president, announced the results of the election, and after a brief farewell message
relinquished the chairmanship of the
meeting to John D. Colvin, newly elected
president. The others taking office at
this time were: C. G. McProud, executive vice president; Bob Hugh
Smith, Western vice president; Lawrence Shipley. central vice president;
Norman C. Pickering, secretary ; and
Ralph A. Schlegel, treasurer. The latter
two were continued in the offices they
hehl for the past year. Howard A. Chinn,
H. E. Roys, and Theodore Lindenberg
were elected to two -year terms as governors.
The annual honors were presented at
the Banquet, held on Thursday evening.
October 26. The Society's own award
was presented to C. A. Rackey in recog-
nition of his continued work in furthering the progress of the Society since it
was founded. Howard A. Chinn received
the John H. Potts Memorial Award "for
outstanding achievement in the field of
audio engineering," a plastic- embedded
silver medal awarded annually to a person chosed by the Society. Presentations
were made by C. J. LeBel, acting on behalf of W. L. Black, chairman of the
Awards Committee, who was unable to
be present.
Following the banquet and the presentation of the honors, the diners were entertained by a musical group composed
of Johnny Johnson and Harry Lennon
with accordion and bass, and by Lee
Irwin and The Mariners, from the
Arthur Godfrey programs.
SAN FRANCISCO SECTION
ELECTS
The San Francisco chapter of the
Audio Engineering Society announces
the results of an election held recently
for officers of the section for the 1950 -51
term. The results were as follows: chairman, Dr. Vincent Salmon, Stanford Research Institute ; vice -chairman, Harold
Lindsay, Antplex Electric Corporation;
secretary, Frank Haylock ; treasurer,
Myron J. Stolaroff, Ampex Electric
Corporation; executive board members,
Walter T. Selsted. Jack Hawkins, and
Ross Snyder.
II
T. M. McCarty
SOUTHERN MICHIGAN
SECTION ELECTS NEW
OFFICERS
The Southern Michigan Section of the
AES announces the following results of the
annual election: Chairman, T. M. McCarty,
president, Gibson, Inc., Kalamazoo, Micb. ;
Vice -chairman, Earl S. Stone, chief engineer WELL, Battle Creek, Mich.; Secretary- Treasurer, Walter Fuller, chief
electronics engineer, Gibson, Inc.; director
(two -year terni), Wade Allen, Allen Electric Co., Kalamazoo, Mich.; director (one
[Continued on page 59]
/
Left, C. A. Rackey (left) receiving Society's Award from C. J. LeBel. Center, John D. Colvin, new president, welcomes
visitors to the Convention and the Audio Fair. Right, Howard A. Chinn receives the John H. Potts Memorial Award from
Mr. LeBel.
AUDIO ENGINEERING
DECEMBER, 1950
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23
The Audio Fair Review
F AIR has come and gone
a.c. power was cut off signifying the end
with appreciably more success than of the exhibit hours. Without this drastic
its forerunner, the First Audio Fair. means of signalling the closing hour, it is
Again, for three days, the halls of the fifth doubtful if the visitors would have left at
and sixth floors of the Hotel New Yorker all -especially on Friday evening, the only
were more than filled with a milling time many were able to attend. The folthrong interested in audio to the extent lowing paragraphs will cover the exthat they were willing to spend long hibits in detail, with each exhibitor's
hours on their aching feet to hear the display being described briefly.
newest in speakers, amplifiers, pickups,
Altee Lansing Corporation exhibited a
and recorders. And the new items were new corner cabinet housing two 15-inch
there en masse, along with the time - driver units and a multicellular horn,
tested- and -tried devices that are always along with the other more familiar meminteresting to the enthusiast when demon- bers of its line -the 800, the 604B, the 603,
strated under what are the best condi- the 600, and the 8 -inch model 800. The new
tions possible, in the opinion of the manuunit, with the advantage of two
facturers, for their particular equipment. frequency drivers, showed excellent low
reActually, from the listeners viewpoint, it sponse characteristics, and an extremely
is doubtful if this is an ideal condition,
large power handling ability. The interest
because of the background of noise from in this entire exhibit was so great that it
the many exhibition rooms. However, was usually difficult to get into the room,
there is no doubt about the over -all value but nearly everybody did at one time or
of this type of exhibit, because-even another, and the demonstration of the
though the conditions are not perfect
strength of the field magnet used in one
the visitors do get an impression of the of the larger speakers was convincing
quality of performance of the many items, even to anyone who did not understand
and the interest awakened by it is suffi- what it all meant to the performance of
cient to warrant further investigation the speaker. The always- present -butunder more intimate conditions.
little -seen condenser microphone was also
For the professional engineer, the ex- on hand for display, while others were
hibits of tape recorders were of great
in continual service for sound reinforceinterest, with many types being displayed ment during the technical sessions and
for the first time. Microphones suitable
the banquet.
for all purposes were seen, speakers of
Ampex Electric Corporation's new
the highest quality for monitoring purModel 400 Tape Recorder -of which much
poses, and all types of recording mahas been heard during the past few
chines, tape, and discs. One complete months- proved th
tt lived up to its
display of a broadcast console attracted specifications as to quality. The demonthe broadcast engineers almost as much stration consisted of playing a tape on the
as the tape recorders-of which there big Ampex, re- recording it on the 400, and
were many more than one.
reproducing the output of the playback
On the whole the Second Audio Fair
head of the smaller machine on an AB
was a much greater success than the first,
test with the signal being recorded. This
with a fifty per cent increase in exhibitors
was a truly convincing method of demonand in registration -the preliminary fig- strating the quality of a new product in
ures for the attendance indicate that comparison to that of the already well
approximately 4700 visitors were present established performance of the leader of
over the three -day exhibit, with many of the line. After hearing this demonstration,
them being on hand two or even three the listener had no doubts of the ability
days.
of the small machine to perform comThe photographs of the various exhibit pletely In accordance with its specificarooms will give to those unable to
tions, which are sufficiently stringent for
attend an idea of the highlights of the practically any professional application.
Fair -every exhibitor has something inAmplifier Corporation of America preteresting to show, and each one of them sented a 29 -hour, 3 % -in. per second respent a long and arduous three days of corder with quality considerably better
explaining and demonstrating, so that all
than most 7% -inch machines of a year
felt a sense of relief each day when the ago. The improvements in slow -speed tape
THE SECOND AUDIO
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From the top, reading counterclockwise: Audio Engineering, Altec Lansing
Corp., Arrow Electronics, Inc., Amplifier Corporation of America, Ampex
Electric Corp., Cinema Engineering Co.
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AUDIO ENGINEERING
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DECEMBER, 1950
recorders has been truly remarkable in
the last twelve months, and for applications requiring a high quality source of
sound for long periods, a machine of the
type exhibited here would certainly serve
the purpose admirably. With such an installation, hotels and restaurants could
be freed from the need for wired services,
and would be able to schedule the kind of
music or entertainment that was most
suitable for the hour or location. In addition to the long -playing machine, a large
number of other types of recorders were
on display, of sufficiently wide variation
of cabinet, styling, and facilities to fill
the needs of most semi -professional users.
Arrow Electronics, Inc., a New York
City jobber, kept its display room full of
visitors during most of the show hours,
and well it might, because of the wide
variety of components for high-quality
music systems that were on display. The
jobbers had somewhat of an advantage
over some manufacturers because they
have available all types of equipment, and
are therefore able to make comparisons
right on the spot. Tuners, turntables,
amplifiers, even television parts, all were
on display here.
Audak Company, preferring to demonstrate for quality of sound rather than
quantity, conducted its displays of performance behind closed doors. To many
visitors, this was a welcome change from
the somewhat overpowering sound which
filled the corridors of the fifth and sixth
floors of the hotel. Using a choice of two
recognized amplifiers and a high- quality
two -way speaker system, the performance
of the Audax Polyphase pickup was
shown at normal living room levels, and
with the finest of taste in selection of
program material. Available now with
special adapters to fit the Webster and
Garrard changers, the Audax Polyphase
-with two styli and therefore capable of
reproducing all types of home records
without changing arms or heads -is
rapidly gaining favor, both for its quality
and for its convenience in use.
Audio Devices, Inc. had only two items
to exhibit -but each of these was available in so many varieties that their display was still quite elaborate. First, the
famcus Audiodiscs were there in full
force, in many diameters and in all grades
from the perfection required for masters
to the smaller and lighter -base types used
by the amateur. Second, the variety of
magnetic tapes on display was so great
as to surprise those who have previously
known only of the standard ':a -In. plastic
or paper tape used on conventional tape
recorders. Types shown included plastic base tape from 1/ to 2 inches wide,
several widths of paper -base tape, 16 -mm
film with single and double perforations,
17.5 -mm film with single perforations,
and 35 -mm film with double perforations.
Ali it takes to bring out a special tape is
to show a need for it, and anything
imaginable can be made.
Audio Instrument Company showed a
new device intended to generate a signal,
composed of both low and high frequencies, which could be used with any
oscilloscope to give a qualitative measurement of intermodulation distortion, as
well as with the Bridger -an instrument
designed to permit the measurement of
small audio voltages without appreciable
loading of the source. This instrument has
fulfilled the need for an a.f. coupling unit
of extremely high impedance, a necessity
in development and laboratory work, and
a useful accessory in the service and experimenter's shop. The Intermodulation
Set offers in compact form a source of
signal for IM measurements which is entirely suitable for most developmental
work.
The Audio 3Iaster Company displayed
a number of portable record and transcription players which fill the need for
a small unit suitable for the salesman
who has a product which is best demonstrated by the use of records, or by a
salesman for the records or transcriptions themselves. These units are also
well adapted for p.a. system use, as well
as for schools and other educational applications.
Bell Sound Systems Inc. displayed for
the first time a new amplifier of exceptional merit, Model 2145. This all- triode
unit with an output in excess of 15 watts
combines a number of useful features,
principal of which is the use of a remote
control unit which is connected to the
main chassis by a single cable. All inputs
are plugged directly into the amplifier
chassis, and by the use of cathode followers the signal can be fed to the control
unit by a cable as long as 25 feet without
frequency discrimination. The high -gain
input employs a two -stage preamplifier
on the main chassis, thus Isolating the
low -level signals from the cable. The
selector switch on the remote control
assembly makes a choice between phono
and radio signals, compensates for record
characteristics, and adjusts high -frequency roll -off. Bass and treble tone
controls and a compensated volume con-
From the top, reading counterclockwise: Burlingame Associates, British Industries Corp., Browning Laboratories, Inc., Bell Sound Systems, Inc., The
Audio Master Co., Audak Company, Inc., Audio Instrument Co., Audio
Devices, Inc.
AUDIO ENGINEERING
DECEMBER, 1950
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25
trol complete the remote unit complement,
with the slanal being fed back through
the cable from the output of another
cathode follower in the remote box. In
all, this unit appears to have had much
thoughtin its design, and was apparently
planned with the needs of the user well in
mind.
British Industries Corporation had a
number of imported Items on display,
including the Garrard RC80 record
changer, the Leak "Point One" amplifier,
and the complete line of Wharfedale
speakers. Both the changer and the
amplifier are well known in this country
by this itme, but the Wharfedale Hne
is relatively new. This group of speakers,
ranging from an 8 -inch model up to a
15 -inch heavy -duty job, provide a full
range of types for all applications where
quality Is a requisite. Most of the models
are built with cloth surrounds, resulting
in lowered resonant frequencies, and
giving an extremely flexible cone mounting. The Point One amplifier, of a type
similar to the "Williamson" now so famous in this country, derives its name from
the distortion at rated output, 0.1 per
cent.
Browning Laboratories had on display
its entire line of tuners, just recently improved with the addition of automatic
frequency control. Two models of the
AM -FM receivers were shown, one with
a power supply on the same chassis and
with complete tone control facilities, and
another consisting solely of a tuner for
both bands and designed for systems
where the control of tone and volume is
incorporated in a separate amplifier
unit. The smaller FM -only chassis is
primarily intended for use where a suitable AM chassis is already available, or
for those critical listeners who do not
want anything but FM. This unit has its
own power supply, but does not have the
tone controls. All models have exceptional
sensitivity on the FM band, and the quality is above normal on either type of receiver.
Burlingame Associates and Brujac
Electronic Corporation exhibited a number of unusual items, among them being
a Danish importation in the form of an
elaborate oscilloscope. The entire standard line of Hewlett- Packard products
was shown, with prominence being given
to the newer types of combined gain
sets and oscillators. Laboratory power
supplies, high -gain a.f. voltmeters, and
the versatile Tektronix oscilloscope filled
out the line of equipment shown.
Cinema Engineering Company had a
number of useful and practical items of
particular interest to the professional, although the advanced experimenter is
also likely to find many uses for the convenient chassis available from this company. In addition to these shock mounted, quick change chassis, a wide
line of attenuators, filters and equalizers
was shown, all designed with the needs
of the particular application uppermost
in the requirements for the product.
The Daven Company, long established
as one of the "standard" manufacturers,
exhibited its newer line of instruments.
topped oft by the distortion and noise
measuring set described in these pages
last month. The Daven line of laboratory
instruments is expanding gradually, and
each new addition lives up to the reputation of the builder and further enhances it. The 11 -A Gain Set, announced
last year, is now a familiar item, and
many of them are in continuous service.
It is expected that the new distortion
measuring instrument will soon achieve
wide use among those who require high
precision in measurements.
Electronic Workshop exhibited a variety of equipment ranging from a cleverly
designed miniature audio oscillator to
complete custom equipment for the home.
Their own design of amplifier was presented in a highly polished chrome plated
model for the Fair or for those who enjoy having equipment which may be
shown off as a prized possession. With
a preamplifier having the same knob
spacing as the Browning tuners usually
employed by EW in their custom work.
the resulting appearance of the installation is well above average.
Electronics of Staten Island, a newcomer to the audio field this year, had
two new corner speaker cabinets on display, one containing the speaker alone
and another with a built -in tuner, amplifier, and record changer. The perform nace from these cabinets was above
average, indicating the advantage of
using the room corner as an element of
the speaker housing by reducing the
solid angle into which the speaker must
radiate. Cabinetry and finish on both
models displayed were of excellent appearance, and because of their relatively
small size these units would make welcome additions to most living rooms.
Electro -Voice, Inc. displayed its entire
line of microphones, pickup cartridges,
and speakers, the latter including mechanisms only as well as a number of
furniture cabinets. Outstanding among
the line is the Patrician, a massive corner
cabinet constructed under license from
Klipsch, and incorporating a low -fre-
From the top, reading clockwise: Electronic Workshop, Electronics of Staten
Island, Electro- Voice, Inc., The Daven Company, Fairchild Recording Equipment
Corp., Fisher Radio Sales Co., Inc.
26
AUDIO ENGINEERING
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DECEMBER
1950
From the top, reading clockwise: Gates Radio Company, Gawlor -Knoop Co.,
Hudson Radio & Television Corp., General Electric Co., Harvey Radio Co., Inc.,
Harrison Radio Corp.
quency horn folded into the corner, two
direct- radiating cones, and two multi cellular horns, the smaller covering the
range from around 3500 cps as far as
the signal source required.
Fairchild Recording Equipment Corporation exhibited a complete line of
high -quality disc recording apparatus,
together with a rack of equipment designed for the better quality transcription studio where off- the -air recordings
are made as a regular business. Outstanding interest was shown in an equalizer which featured continuously variable
peak frequencies at both low and high
ends of the spectrum, and with continuously variable amounts of equalization
at the frequencies selected.
Fisher Radio Corporation showed their
line of high -quality radio receivers and
amplifiers along with the new Concertone tape recorder, which is the most
compact model yet shown which will
handle the standard 10 -inch reels on
NAB hubs. Incorporating a three-motor
chassis of cast aluminum, with the amplifiers mounted directly on the unit, the
entire recorder can readily be carried
in a single case. This model is made with
two speeds -7jß and 15 inches per sec ond-and with either single or double
track heads, either type of which is
readily changed for the other in a matter of minutes.
Gates Radio Company had on display
a complete console for broadcast station use, along with several types of
amplifiers and remote input equipments.
One model of remote amplifier, designed
for use with either a.c. or batteries, is
equipped with an automatic changeover
feature which connects the battery supply immediately in case of failure of the
power source. The station console, with
two turntables, is so arranged as to provide for comfortable operation and has
facilities for two separate programs, or
for one program and one audition channel. Neatness of design and construction
features the entire Gates line, and accessibility for maintenance is one of the
strong features of the equipment.
Lawlor -Knoop Company, manufacturers' representatives, showed the lines of
Allen B. DuMont Laboratories, Ballentine Laboratories, and Clough Brengle
Co., with cathode ray oscilloscopes with
attached Polaroid Land camera for per-
manently recording the traces under observation, a product of the DuMont
organization. From Ballentine, the new
models of electronic voltmeters -always
so popular in the field-were shown, together with a number of accessories
which extend their usefulness. The
Clough Brengle Audiomatic sweep genAUDIO ENGINEERING
erator, which provides a frequency swept
signal over the entire audio range or over
any selected part of it, was also a hit
with the visitors who are engaged in
any sort of development work.
General Electric Company exhibited
two of its major products in the audio
line-pickups and loudspeakers. A mammoth phonograph cartridge efnploying
the quick- change stylus assembly was
an attractive feature, since It showed
the method by which the styli were
changed for standard or LP records, and
in a form large enough for everyone to
see the actual working of the device. The
display of a S -1201 speaker actuated by
a 60-cps a.c. source and illuminated by
means of a Strobotac gave convincing
demonstration of the operation of the
speaker cone under high -level excitation.
A moving cutaway of one of the same
speakers served to show the features of
the internal construction, with the magnet, polepieces, voice coil and support
being plainly visible when the unit split
apart.
Harrison Radio Corporation featured
the Electronic Workshop A -18 amplifier,
shown for the first time at the Fair. In
addition, the current most popular lines
of equipment
including turntables,
phonograph pickups, speakers, and radio
tuners, were all there in abundance.
Harrison also had a novelty item as a
giveaway which was the source of fun
for the visitors all through the Fair days.
Harvey Radio Company, Inc., featured
the Magnecorder in its various forms,
together with the Lansing corner
speaker, Rek-O -Kut turntables, and the
Audak Polyphase pick -up, and with this
assembly of components which are now
familiar to the music lover and audio
hobbyist alike produced a quality of
-
sound which was only to be expected
from such distinguished equipment.
Hudson Radio & Television Corporation, another New York City jobber, exhibited a wide variety of components for
sound systems, ranging from the Audio
Pacific, Bell, Electronic Workshop, and
H. H. Scott amplifiers through Radio
Craftsmen AM /FM tuners, a selection
of speakers, and the Masco tape recorder.
The Audio-Pacific amplifier, exclusive at
Hudson, was shown to have exceptionally
flat frequency response and low distortion throughout the entire range.
HAS THE
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Langevin Manufacturing Corporation,
showed a full line of quality transformers along with a number of professional
type plug -in amplifiers and two power
amplifiers designed for home or professional use. One of these latter units,
encased in a convenient wall mounting
cabinet, and of excellent quality, is
DECEMBER, 1950
www.americanradiohistory.com
AmericanRadioHistory.Com
27
first
reels
of a
wind
LEONARD RADIO
Proudly presents
Markham .Williamson
Ampli
15 WATTS
Incorporathig a Ranote Catrd Unit
adhil
kr
standard model to handle 10 -inch
on NAB hubs without the addition
special panel for the feed and rereels.
McIntosh Engineering Laboratory exhibited its two amplifier models, the
50 -W -2 and the 20 -W-2, along with the
new preamplifier AE -2 which incorpor-
ated the input stages and controls
necessary for a complete reproducing
system. The McIntosh amplifier circuit
has been proven more efficient than most
others, and it is of unquestionable
quality. The smaller model, using two
6V6's in the output stage, has an output
of 20 watts, which is remarkable for
6V6's. The unit is compact, being housed
in a single chassis unit of unconventional
design. The 50 -W -2 model, using 6L6's,
consists of two similar chassis, the power
supply being separate from the amplifier. These models are extremely flexible,
-
Panoramic Radio Products, Inc. put a
new note-or rather lots of new notes
into the Fair by showing the frequency
structure of various signals, such as a
number of musical instruments and a
number of human voices. The Panoramic
sound analyzer continually sweeps over
the audio spectrum and indicates the
amplitude of all frequencies present on
the screen of a c -r tube, thus permitting
the user to observe the characteristics
of the signal present or in the case of
amplifier testing, to observe the amount
and character of distortion present in
the output signal. A number of similar
instruments for a wide variety of different purposes were also on display, but
the analyzer attracted the most attention.
Peerless Electrical Products Division of
Altec Lansing Corporation had a large
number of interesting items on display.
The now -famous Musicians amplifier,
described in lE in November 1949, leads
10W
Upper left, Leonard Radio, Inc. Center, left to right, Magnecord, Inc., Langevin
ratory, Measurements Corp.
especially suitable for use in wired music and are readily adaptable to a wide varisystems or for p.a. use in such places as ety of requirements.
restaurants, dance halls, skating rinks,
Measurements Corporation displayed
and other such locations where the highits line of precise laboratory instruments,
est quality and reliability are requisite. with the intermodulation meters-two of
James B. Lansing Sound, Inc. had on them and both new -taking the spotdisplay one of their largest speaker sys- light. These instruments, which were
tems for home use, although from its described in last month's issue, incorquality and output power it would porate several new and useful features,
definitely be suitable for monitoring in and serve to round out the line of measprofessional applications. This model, the uring instruments designed for the laboratory or for the advanced experimenter
D-1005, incorporates two woofers and an
his needs warrant the most accurate
eight -cell horn with a crossover in the
vicinity of 1000 cps. It was finished in instrumentation.
a light blond hardwood, and presented a
Midway Radio and Television Corporavery attractive appearance. The entire tion, another New York jobber recently
line of speaker mechanisms was also to enter the field, displayed the Radio
shown, ranging from the 8 -inch model Craftsmen tuner, and offered to visitors
up to the heavy -duty 15 -inch woofers. a stroboscope disc useful in checking
Leonard Radio, Inc., with a complete accuracy and constancy of turntable
line of radio tuners, amplifiers, speakers, speed. Midway also featured the Rauland
turntables, and even a TV console suit- 1825 amplifier with its unique preampliable as an entertainment center for the
fier which can be mounted in a number
home, featured the Markham -Williamson of methods so that the user can select
amplifier, a new 15 -watt unit with a rethe mounting which best fits his requiremote control unit permitting adjustment
ments. When a relatively small space
of tones and volume to the user's satisis available for the controls of the amplifaction without the need for him to leave fier, the Rauland is especially attractive.
his favorite easy chair. This amplifier is
Milo Radio & Electronics Corporation
built along the lines of the entire Wil- offered as its most interesting exhibit a
liamson circuit-from low -level input to display of the new ModulaR amplifiers
output stages -and is sure to be another and components which incorporate a new
contender for amplifier honors.
style of construction which permits the
Magnecord, Inc. had several models of joining of several units or component
its recorders available and all on demon- assemblies together to make a single,
stration, ranging from the portable solid chassis. Thus a power supply can
PT63J through its various forms up to
be placed on a chassis along side the
the new console PT7 -AX in a cabinet power amplifier, and other parts or secwhich contains all the amplifiers neces- tions of amplifier can be added as resary with the machine. This model has quired or as the need for them develops.
attracted considerable attention, largely The Garrard changer was also featured
because of its mechanical features and by Milo, along with the new Audax head
the convenience of operation. It is the mounting for this changer.
-if
28
Mfg. Corp., McIntosh Engineering Labothe line for popularity, and it is now followed by the Musicians Amplifier, Senior,
which 1s a theatre -type 50 -watt unit employing 845's. This unit is intended to be
driven by the original Musicians unit.
Also shown was a new amplifier using
the space-charge -grid tubes which have
finally reached the market. This model
will be described shortly in these pages.
and will undoubtedly follow the Musicians amplifier into the Hall of Fame
for good audio equipment.
The Permofiux Corporation proved how
good their Royal Eight speaker could be,
with performance essentially comparable
to that from earlier 12 -inch speakers. In
a small cabinet with a single speaker,
the performance was better than would
be expected from standard console radio
receivers, and when four units were
mounted in a single housing, the output
at the lower frequencies was remarkable
considering the size of the basic cone
speaker. Also on display were the high fidelity headphones, which consist essentially of a pair of minute cone
speakers mounted in receiver cases and
equipped with sound-proof pads to ensure good coupling between the units
and the eardrums.
Pickering & Company, Inc. presented
a modern display showing drawings of
their units in normal position, and augmented with the actual components
alongside. A number of the model 180L
column loudspeakers adorned the room,
and the choice of music showed off the
performance of the speakers to advantage. Most striking of the demonstrations
was the performance of the model 190
arm playing on a turntable an angle of
45 deg. from the horizontal, showing the
remarkable balance of the arm, with its
AUDIO ENGINEERING
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AmericanRadioHistory.Com
DECEMBER, 1950
cartridge, during the playing of records
on normal turntables.
Presto Recording Corporation displayed
a full line of recording equipment for
both tape and disc. A new professional
model of tape recorder, designed to mount
either on a rack or on a conventional recorder console, was shown for the first
time, and its many features pointed out
in detail. The smaller Model PT900 was
also on display, as were a number of
different models of disc recording machines of varying capabilities. The large
tape machine is designed to operate either
directly or remotely, and it provides for
the 10 -inch reels on NAB hubs. Both of
the basic Presto chassis are three -head
models, and permit simultaneous monitoring of the recorded signal during recording.
Radio Corporation of America exhibited
two physical arrangements of its tape
recorder, one being rack mounted so that
I
formance better than would normally be
expected from a study of the cabinet
dimensions.
Rangertone, Inc. exhibited their lip sync system which permits the use of
1/2-in. magnetic tape with sprocket hole
driven motion picture film at a considerable saving in cost over the use of optical film for the sound recording. By recording a 60 -cps signal from the camera
motor supply at the same time as the
sound is recorded, it is possible on playback to compare the 60 -cps recorded signal with the frequency of the power
supply driving the projector and to vary
the speed of the tape recorder so as to
keep the sound track in exact synchronism with the picture. This is an important improvement in tape recorders,
and is resulting in their widespread use
in motion picture production.
Reeves Sonndcraft Corporation presented a modern display of magnetic tape
LP's and other plastic records. The basic
210 -B amplifier is a complete unit with
provision for phonograph equalization
and has. in addition. tone controls giving
a wide range of variation of both bass
and treble response
Scully Machine Company displayed one
of their famous recording machines. complete on its own console table. and with
microscope, elapsed-time meter, and control switches This machine, well known
for its reliability and ease of operation,
still remains one of the finest instruments of its type. It will cut either inside -out or outside-in, with both standard
and microgrooves, and has an automatic
spiralling feature which contributes to
its adaptability in recording studios of
the highest quality.
Nark Simpson Mfg. Co. Inc. featured
their new Masco Sound -Reel magnetic
recorder, with a number of interesting
features for a small and inexpenshe ma-
t
Midway Radio
Reading clockwise; Midway Radio Cr Television Corp., Milo Radio Cr Electronics
Corp., Peerless Electrical Products Div. of Altec Lansing Corp., Panoramic Radio
Products, Inc., The Permoflux Corp., James B. Lansing Sound, Inc.
the functioning of the mechanism could
be studied readily without the necessity
of crawling into a console. Mounted in
a console cabinet, the same chassis becomes a more -familiar design of recorder,
and can be controlled remotely if desired by a similar set of operating controls. Also shown in the room occupied by
the Engineering Products Department
was the new Starmaker microphone, a
miniature ribbon microphone designed
for use on audience participation shows
or on television where the performer
should not be hidden by the microphone.
Two cabinet mountings for the LC1A
speaker were also shown and, with a
signal of undoubted quality from the tape
recorders, showed excellent characteristics.
In another of RCA's rooms the new
model of the duo -cone speaker-the 515S2
-was on display, both visual and aural.
This unit is lower priced than the LC1A,
but gives the listener who wants good
quality a high degree of performance
with a two -way unit combined in a single
housing.
Radio Music Corporation displayed a
number of professional -type transcription pickups, using a single arm and
three interchangeable heads. One head
is designed solely for lateral transcriptions, another solely for vertical, and a
third serves to play both about equally
well. Alai) on display were a number of
amplifiers for wired music systems,
restaurants, and other such applicaitons
where continuous reliable operation is
required. A new line of speakers and
speaker housings were shown, with per-
AUDIO ENGINEERING
in several dimensions and spoolings along
with a variety of recording discs ranging
from 6 inches up to 171 inches in
diameter. Newest products of this company include a line of TV picture tubes,
principally of the dark face rectangular
types which are being used almost exclusively in current production sets.
With this diversification, the Reeves line
is now usable in practically all branches
of the electronic entertainment field.
Rek -O -Hut Company, Inc. displayed a
variety of turntables and disc recording
mechanisms, together with amplifiers for
use in recording and playback. Outstanding among the turntables is the heavy duty type with hysteresis motor drive,
having the smoothest of drives and a
minimum of external hum fields. The use
of a 6 -inch speaker in an especially designed cabinet was noted as an eye opener as to the quality of tone obtainable. For applications where an inexpensive monitor speaker is desired-as
in schools or other places where the budget does not permit the use of more
elaborate systems-this model would he
ideally suited. The Rek -O -Kut line also
includes a variable speed turntable, adjustable over a wide range, and several
transcription players designed for portable use.
Hermon Roemer Scott, Inc. exhibited
the model 210 -B Dynaural Amplifier,
along with several smaller items of
equipment intended for use with phonograph reproduction systems to reduce
the needle scratch usually heard from
shellac records. The new units also operate to reduce pops and crackles from
DECEMBER, 1950
www.americanradiohistory.com
AmericanRadioHistory.Com
29
nnww
Left, from top to bottom: Pickering & Cc., Inc., RCA, (Harrison, N. J.), Rangertone,
Inc., RCA (Camden). Above: upper left, Presto Recording Corp.; upper right, Radio Music Corp.; lower left, Scully Machine Co.; lower right, Reeves Soundcraft Corp.
chine. Extremely compact, the Sound
Reel will record at 3% or 71/2 inches per
second, and is reversible so as to record
on two tracks. Also shown was the small
tweeter designed to mount in front of a
12- or 15 -inch cone and to be connected
across the voice coil of the large cone
without any crossover network.
Somerset Laboratories, Inc. displayed
their new noise suppressing amplifier
with a remote control unit designed to
permit the user to adjust volume, tone,
and suppression from his easy chair. Also
shown were several models of the noise
suppressor unit separate from the main
amplifier and for use with existing equipment. In one form of the complete equipment a separate control panel is supplied
which can be mounted in a cabinet at
some suitable spot, permitting the placement of the amplifier at some more con -
venient location than is usually available
at the desired control panel.
Sonar Radio Corporation demonstrated
a new tape recorder equipped to handle
10 -inch reels and of quality superior to
the usual home -type machine. This model
is equipped with three heads, permitting
simultaneous monitoring of the recorded
tape during the actual recording process.
Complete in four panels for rack mounting, the unit is approximately 24 inches
high, providing for the recorder chassis,
record and playback amplifiers, and the
loudspeaker and power supply panels. In
another model, the recorder chassis is
separate, and the amplifiers and speaker
are rack mounted units which may be
Below: upper left, Rek -O -Kut Co., Inc.; upper right, Hermon Hosmer Scott, Inc.;
lower left, Mark Simpson Mfg. Cc., Inc.; lower right, Somerset Laboratories, Inc.
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AmericanRadioHistory.Com
31
I
.
Top row, left to right: Sonocraft Corp.;
Stephens Mfg. Co. Inc.; Sonar Radio Corp.;
at right, Tech Laboratories, Inc. At left, upper,
Sun Radio & Electronics Co. Inc.; lower, University Loudspeakers, Inc. Below, upper row,
left to right: Terminal Radio Corp.; The
Tetrad Corp.; Transit Sound Systems, Inc.;
lower row, Triad Transformer Mfg. Co.;
United Transformer Co.; U. S. Recording Co.
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32
located remote from the recorder unit.
Sonocraft Corporation featured the entire line of Magnecorder equipment, for
which they are one of the Jobbers in the
New York area. On display were both the
PT6 and PT63 recorder units, the auxiliary chassis for large reels with the NAB
hubs, and several models of amplifier speaker -power supply units, along with
the multichannel mixer for up to four
microphones.
Stephens Manufacturing Corporation
exhibited its complete line of speakers
and cabinet models, with the two -way
systems taking the lead in favor among
the visitors. The Hy-Son super tweeter,
first shown at the 1949 Fair, is now In
complete production, and the addition of
this unit to a regular two -way system
improves the performance in the upper highs to a remarkable degree. Stephens
models include crossovers at both 600 and
800 cps, and multicellular horns are available in a wide variety of sizes and shapes
to fit every requirement.
Sun Radio & Electronics Co. Inc., one
of the most aggressive Jobbers in the New
York area, exhibited a new min known
as the Realist
corner cabinet incorporating a high- frequency speaker directed upwards at an angle from the rear
of the unit. In usual hard -walled living
rooms, this model gives a remarkable distribution of sound, and by the very realism of the sound source makes the unit
live up to its name. Another feature of
this display was the presence of a
shadowgraph unit on which visitors
could compare their own styli with the
standard shape for a given type in order
to determine if wear had progressed to a
degree which would make replacement
advisable.
Tech Laboratories, Inc. displayed the
artificial reverberation generator developed by Audio Facilities Corporation
and marketed solely by Tech. This unit
is capable of introducing a controllable
amount of reverberation to any signal,
and eliminates the need for costly echo chamber equipment setups for radio sta-
-a
AUDIO ENGINEERING
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AmericanRadioHistory.Com
[Continued on page 53]
DECEMBER, 1950
if it's TAPE...ìt!s
PRESTO
if it's PRESTO...it's the BEST
Combining the features of machines costing hundreds of dollars more,
the PT -900 answers the need for a recorder of ultra-high fidelity in a
completely portable, compactly designed unit. Equipped with separate
amplifiers for recording and monitoring; individual heads for erase,
record, playback; three microphone input; dual speed (15" and
7%/sec.). Frequency response from 50 to 15,000 cps.
PRESTO PORTABLE RECORDER RC -10/14
This machine is identical to the RC- 10/24, except for panel size and
selector control. With a panel 19"x14", the RC-10/14 is shown mounted
in a durable, leatherette carrying case. Weighing just 68 pounds, this
tape transport mechanism has all the audio quality, speed regulation
and reliability of a fine console type unit, at a cost far below a studio
recorder. PRESTO amplifier (model 900 -A2), as shown with model
PT -900, is recommended.
The number one choice of engineers seeking the finest tape machine
for relay rack mounting. Rugged construction and precision engineering combine to bring almost faultless operation. Push- button control,
three magnetic heads, speeds of 15" and 7t/Z" /sec.; fast -forward and rewind speed of 250 " /sec.; frequency response to 15,000 cps. Accommodates reels up to 101/s" in diameter. Panel size: 19 "x24'/2". Constant
tape tension assured by torque motors. Illustrated with the PRESTO
900-A2 amplifier, recommended for use with this recorder.
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www.americanradiohistory.com
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LEWIS
S.
GOODFRIEND
High Fidelity
IN THE PREVIOUS ARTICLE, the conclu- ripple out of the high -voltage supply, we
sion was reached that high fidelity have already used some of their power
defined as the acoustic facsimile
capabilities. The unbalance between
can never be attained using single -chan- tubes in a push -pull stage, unless carenel systems. However, it must be ad- fully compensated, will permit an exmitted that there are many excellent cessive hum level. The distortion caused
sound reproducing systems installed in by unbalance may be less than the
rooms and studios. To reconcile these fatigue level.
two facts an examination of the good
A survey of a number of amplifiers in
single -channel systems shows that all of the medium price range shows that 31
the system components are of the highest
out of 55 have no filter choke ahead of
quality, and that no compromises have the output -stage high -voltage supply.
been made in order to save either space These figures include an FM receiver
or money. In other words, a single - specifically designed for quality listenchannel system can be made to approach
ing. Without a detailed study of tone
the acoustic facsimile and thus provide controls and variable equalizers, it is
pleasing reproduction. After the multi- still safe to say that equalization is gentude of listener tests that have been con- erally achieved without regard to the
ducted to date, there is little doubt left phase delays introduced by most trick
that the nearer the approach to the equalizers. And as hard as many have
facsimile goal the more pleasing is the tried to prove otherwise phase distorresult.
tion changes timbre, the quality or body
No manufacturer or designer can say of sound. These seemingly innocent
that any sacrifice of quality is justified moneysavers are obviously large factors
by the existing inherent spatial distorin the lowering of the quality level from
tion introduced by a single -channel sys- a near -facsimile to a merely pleasing
tem. Such compromises with cost and system. If there is any question of the
quality all tend to decrease the accepta- reduction of power capabilities by the
bility of the unit. Nonetheless, many filtering action in the push -pull output
manufacturers and designers continue to stages, a quick check of the equations in
produce units with inadequate frequency any vacuum tube or electronics text
compensation for phonographs, insuffi- will give the answer.
cient power before acceptable distortion
Power vs. Distortion Curves
is exceeded, and insufficient power -supply filtering. In listing these three, it is
The matter of poster level and distorassumed that there is sufficient copper tion have been detailed before, but the
and iron in the transformers to prevent fact remains that many units have a
overheating of the power transformer single- frequency distortion rating that
and to prevent saturation in the output is exceeded at many other frequencies.
transformer.
One way to avoid this is to check the
According to several tests, the per- maximum output level for the rated disceptible harmonic distortion for both tortion level. If the power available at
speech and music is one per cent. This all frequencies is not greater than half
is the point at which the distortion is
the rated power the unit does not meet
perceived during a listener test. A dis- the power rating and obviously cannot
tortion as low as 0.2 per cent may be fulfill the requirements of an amplifier
sufficient to cause auditory fatigue over of that rated power. This is the major
long periods of listening. Improperly
stumbling block for most amplifiers in
equalized phonograph (and radio) chan- the high -quality performance group.
nels and FM de-emphasis circuits cause They are good at low levels, but at
a response that sounds different. This high level they just do not seem to fill
means that the listener cannot associate the room. When a power rating and
what he hears with fact. Thus the lack distortion level are given they should
of proper equalization leads to outright indicate that at the rated power level
annoyance. Finally, if we force our push - the rated distortion will not bé exceeded
pull output tubes to filter the 120-cps at any frequency. In any case, if the dis-
-
34
tortion at normal output levels is greater
than 1 per cent the builder or purchaser
should reject it as not suited to his need.
The comments made here are not
really a criticism of the manufacturers.
They are intended only to point out the
need for job- rating amplifiers and designing them with the acoustic facsimile
as a goal.
Other components of the single -channel system from microphone or recording through to the loudspeaker are
equally important to the quality. However, an excellent group of transducers
is available having far lower harmonic
distortion from non -linear elements than
the acceptable minimum. Few individuals
are in a position to design and build
their own transducers but here, at least,
manufacturers agree on most basic design requirements. A real problem in the
use of transducers is to make them cosmetically attractive. But this is no topic
for discussion here.
One problem in high -fidelity, always
present, is noise, and most frequently,
record surface noise. Unfortunately, it
is present in most shellac records, even
though they are of the highest quality.
A good audio system reproduces the
noise. It is up to the listener to decide
whether to sacrifice musical fidelity to
achieve noise -free reproduction, and
most good audio systems include cut -off
filters or noise suppressors. But this
noise is part of the signal and the
equipment is not to blame if it reproduces the surface noise along with the
desired music. Many of the modern record pressing techniques have helped reduce surface noise and bring our recorded channel nearer to our goal.
Finally, no delicate set of electronic
instruments can remain trouble -free indefinitely. To maintain the quality of
transducers and amplifiers they should
be properly enclosed, ventilated as required, and subjected to preventive maintenance.
If the acoustic facsimile is considered
the goal in audio reproducing equipment
design, it becomes easy to provide pleasing quality and results in a satisfied
listener. Compromise with quality compromises our objective -high fidelity.
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DECEMBER, 1950
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AmericanRadioHistory.Com
MICHIGAN
35
EDWARD TATNALL CANBY
Towards Audio Fair III
Pops
THE MANIFOLD BENEFITS
accruing from is that these people were also present at the
Audio Fair II, held this October, will Audio Fair, by the thousands. Some were
without the slightest doubt continue to engineers too, professional or amateur;
make themselves felt right up until Audio many had dabbled in technicalia enough to
Fair III bursts upon us next fall, a bigger feel some confidence at the sight of a batand better show as the result of our experitering ram woofer, about to give with the
ence this year. So, though this'll appear a
bass. Most, on the other hand, were sudbit en retard, constructive remarks seem denly launched into an unfamiliar and dedefinitely in order.
cidedly strange environment, to put it
Let me at once praise the management of mildly.
the Fair as fulsomely as I can, including
Think this way : our industry has exseveral officers of this sheet who had, so panded enormously in the last couple of
to speak, an enormous hand in the vast years -that, after all, is the very reason
quantity of dirty work that had to be done for the Audio Fair itself. But that expanin preparation. The whole thing was a sion has been largely via conversion of
model of smoothness and efficiency and I
many music lovers to "hi-fi," about which
can't remember a single flaw of any sort in you can be dead sure, almost all of the
that smoothness -all was trouble -free and converts knew nothing whatsoever, previeasy, even to the pre- fabricated badges for ously. That means that most of them (the
the entire exhibiting personnel
ones who are out buying up expensive audio
However, I have a few small bones to equipment) still know very little about the
pick with that personnel, and indeed I sort technical aspects and-here's the point
of feel, to use the old phrase, that it's my are decidedly awed by the professionals and
duty to do so, on behalf of my clients, the the heady shop talk, as any green -horn is,
musicians and the music -lovers, since I who suddenly finds himself in the Holy of
represent a passle of 'em in this magazine. Holies, the very temple of Audio! Most of
Let's waste no more words. The Fair our converts, then, are given to extreme
was beautifully managed but there wasn't timidity. Which doesn't indicate any lack
a thing the management could do (other of interest ; merely a lack of aggressiveness
than providing virtually sound proof in the presence of audio people.
rooms) to reduce what became by the final
Now, as I saw it, things went something
day a most frightening bedlam.
like this. Most exhibit rooms were crowded
Look, gentlemen of the Audio profession with on-listeners. (Like onlookers -get
-this is from the horse's mouth. I know it
Up front and aggressive were the
you had a lot of powerful equipment to engineers, the sales people, the manufacdemonstrate and the neighbors made so turers, the professionals, the habitués, the
much noise that you had to whomp up your
advanced and long-time amateurs. These
50- watters to drown 'em out. I also know
people, very much at home and thoroughly
that there were thousands of engineers, aggressive did all the talking, asked the
radio servicemen, and others whose interest
questions, put out with opinions, looked big
was not so much musical as technical. and important.
Those numerous individuals had to be
However, perhaps half of the people in
catered to. The dealers who sell audio parts each exhibit were acting mousy. They
were there, as well as the makers who
snooped around quietly, saying nary a word
needed to find out what was what outside (for fear of making a boner), listening reof their own bailiwicks. All of which is spectfully over peoples' shoulders, hastily
conducive to noise.
backing out of any argument. These were
But as this column has said again and the neophytes, the unsure, audio -wise. They
again (and no further back than the Oc- were, in large measure, the converted music
tober issue), the business of Audio is music. lovers. And though they didn't say much,
The purpose of almost all Audio in the though they acted mouse-like, they were
quality field is music. What, then, of the having thoughts, you may be sure. And
people who acquire Audio in order to hear they were looking for music. Looking for
music? What some of you may not realize audio equipment that could give them the
!
-
*279 W. 4th St., New York 14, N. Y.
36
music they wanted.
[Continued on page 55]
RUDO
GLOBUS*
I received a letter
boldly typewritten on bold paper by
a bold soul who has made his name in
this world by writing record reviews for
whatever bold publications would pay him.
Now retired and content without the mantle
of glory weighing on his shoulders, he indicated that he has been out of the business
for a long time, liked some of the conclusions
that I have drawn, and requested that I
get together with some of the big people
in the business and find out how they feel
about things.
Ever willing to comply with all legitimate
requests, I arranged for an interview with
one of the really great men in the business
and we talked for well over an hour about
all things pertaining. The interview was
arranged with the background of a long
evening spent at Eddie Condon's and the
genius of Edmund Hall echoing in my ears.
In the history of Condon's, I can't remember any group which can top the one that
is now holding forth. Made up of Cutty
Cutshall on trombone, "Wild Bill" Davidson
on trumpet, Gene Schroeder on piano, and
Edmund Hall on clarinet, the group is
valiantly putting Humpty Dumpty back together again. One of the big reasons is the
still enlightened and smoldering blowing of
Mr. Hall, who boasts that he never took
a legitimate lesson in his life and won't be
bothered with all the technical exercises and
practicing that characterizes lesser men.
So
to get to the point
we asked
Edmund Hall the leading question
"How do you feel about recording jazz
...
...
:
under studio conditions,"
The answer is scribbled down on over
twenty pages of yellow stock, but it adds up
to just one thing
he doesn't like it.
The reasons are good and are pretty much
in line with the stuff I've been writing for
months. Ed says that he and practically
every other jazz man freezes in a studio.
You can't loosen, you can't relax. What
¡Continued on page 38]
*960 Park Ave., New York 28, N. Y.
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S.
SEVERAL WEEKS AGO,
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DECEMBER, 1950
BEATEN PATH
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37
IOU
[from page 36]
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with green, red, yellow, orange, purple and
blue signal lights flashing at you, with a
time limit to meet, with a pre- arranged idea
of what you're going to do, it just doesn't
work out
and why?
Hall is very sensitive about recording
technique. When I asked him the usual
question about the best recordings, his
initial answer referred to recordings that
were "cleanest." His first list included those
that had the least surface noise and the
best balance, and sounded remotely like the
original. When we complained bitterly
about such criteria, we got an answer which
was more to the point. The best ones were
impromptu sessions . . , walking into the
studio cold with no idea of what was going
to happen and then letting loose. And here
Hall gave us the big idea of the moment.
You have to have an audience in order to
play jazz. It just doesn't feel right to sit in
an empty studio and play into a mike. There
isn't a mike made than can respond in the
way a live audience does. No matter how
good some recordings are, they're nothing
compared to the kind of stuff that could
and would have resulted from genuine jazz
conditions.
Ed's been in the business for a long time.
He made his first recording in 1926 for
Victor with the "Ross DeLuxe Syncopators" from Jacksonville, Fla. The recording was made in a tobacco warehouse with
one mike and some impromptu drapes hung
indiscriminately around the barn. He has
no illusions about the "Great Old Days."
He prefers modern studio conditions, but
puts the finger right down the line and
points squarely at the people who haven't
learned the big lesson about jazz recording
yet. It goes something like this:
"It's O.K. to call up any bunch of guys
to do a legit date. Any guy who plays good
and can read music will do fine for a regular recording session. But for this kind of
stuff (dixieland and the rest) you gotta
have the right men. If you don't have the
right men, it's no good."
These are the words of a jazz man who's
known all the greats in the business, played
with all of them, and is not prone to telling
stories out of school. The right men don't
grow on every tree. There are only a few
clarinet players, trumpet and trombone men,
pianists, drummers, etc., who can play jazz.
As Ed puts it .
"Any good man can sit in on a session
cold, and as long as the piano man knows
the chords and the trumpet can blow the
melody, we can handle it."
But in this day of the all -wise musical
director, it would not be too far -fetched to
expect to find Jascha Heifetz playing lead
fiddle in a recording session doing a combo
of Muskrat Ramble and Jazz Me Blues.
This is not professional snobbery, nor is it
resentment, because all the big men are
making a lot of money. It is simply a statement of fact which is emphasized by the
naming of those (which we can't do here)
who have become the leading lights in
modern jazz recording. Hall comes out
openly and says they don't know what it's
all about. They may sell a few records, but
in the long run it doesn't pay off because
the stuff is second rate. Hall agrees completely with the thesis that the way to
record the stuff is to find the perfect combo
and catch them at the job. Tape record all
night and edit the next day. The men are
really loose during the session and even if
three quarters of the stuff is worthless,
CHICAGO 18, ILLINOIS
AUDIO ENGINEERING
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AmericanRadioHistory.Com
DECEMBER, 1950
there'll be enough to fill both sides of an
LP. But, with reference to the way things
are now, Ed puts it on the line.
it's who
"It's not what you can do
you know."
That is the trite but true comment on
...
the record business set up now. In the old
days, with after -hour sessions when musicians got together, the big men stood out.
There was never any question about it.
These were the sessions that used to produce the big moments and were the heart
of good jazz. These were the conditions for
perfect jazz recording. Today, with the
domination of music directors, the powers
that be don't know how to pick the right
men, depend upon pull and reputation, and
what remains is a pretty tired speciman
of a good thing. There is further the problem of good days and bad days, and the
final decision as to what should be pressed
and what shouldn't.
Hall used to be the standout at Cafe
Society Downtown during the rough and
ready days, and there is no wonder that
his list of "best" recordings dates back to
those days. Heading the list are two discs
that Hall picked out primarily because
everybody was relaxed on the date. The
first was a complete impromptu. Hall and
the men showed up at the session with no
idea of what they were going to do. It was
the first date for Commodore and they decided to do two blues sides. What resulted
was the memorable Uptown and Downtown
Cafe Society Boogie. One side is fast blues,
the other slow. The other select record was
the great Commodore 10 -inch of The Man
I Love, featuring Emmet Berry on trumpet,
Eddie Haywood on Piano, Sid (Big Sid)
Catlett on drums, and of course the great
E. Hall on clarinet.
In the classical group there are the great
12-inch discs that Hall did for Blue Note
of High Society and Royal Garden Blues,
all done with the original Cafe Society
crew. If you listen to these, what strikes
you immediately is the obvious superiority
of the 12 -inch over the 10 -inch size. The
list is incomplete without the five great
sides on Commodore that Ed did with
Teddy Wilson. Jazz Quartet, on 10-inch,
produced the superlative recordings of
"Night and Day," "Out of Nowhere,"
"Caravan," "Showpiece," and "Sleepy Time
Gal." All the recordings are rare and marvelous manifestations of really great jazz
clarinet playing and pretty much highlight
the inimitable Hall style. Ed, of course,
disclaims style and points to the fact that
there were things he did fifteen years ago
that he wouldn't do the sanie way today. But
there is still something consistent throughout.
Coming out shortly on the Victor label
are a series of things that Hall points to
with pride. Recently recorded, there is a
job on "Walking the Blues" that Ed did
with Gene Krupa, Joe Bushkin, Cutty Cut shall, Wild Bill Davidson and Ernie
Cassires (whom Hall considers the great
baritone sax in the business). The same
date features a job on "I'm Forever Blowing Bubbles" and "The Kiss my Sweetie
Gave to Me." The group sounds magnificent
and it should be a good chance to see what
progress the big companies are making on
the jazz front. Hall says to watch out for
them
we will.
b
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DECEMBER, 1950
www.americanradiohistory.com
AmericanRadioHistory.Com
Zone
State
39
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of the old school and according to the blurbs
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It was therefore with trepidation that I
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With trembling fingers I examined the
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read the blurb which featured such hot bits
of prose as "child of the Andes peaks,"
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LOUDNESS CONTROL
[from page 18]
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to be a specialist in this sort of thing and
is assisted by one Leslie Baxter who is responsible for conducting and arranging the
background. If my memory serves me right,
Baxter is responsible for some other rare
gems, such as "Music out of the Moon."
featuring The Theremin and various other
oddities.
I have listened to all eight sides of this
album and wish to make the following pro nunciamento. I am full of admiration for
Capitol Records and their audacious enterprise in revealing to the world of ears these
wondrous things. But again, they have
taken something which is essentially good
and crummed it up with some of the most
vulgar arranging and trite special effect
recording to be heard in a long time. Sumac
is indeed marvelous. She does have an extraordinary range and can project dramatic
quality beautifully. She has not been helped
by ridiculous overorchestration of primitive
music and simply bad orchestral effects.
The striking quality of the music is lost
under the heavy sway of the lushest of impressionistic
orchestration
techniques.
Those who know authentic South American
Indian music realize that it isn't helped by
sophistication. The same recording date
with a small native group behind the marvelous Yma would have been notable.
Therefore
cheers to Capitol records
for the enterprise, bravos to Miss Sumac
for the voice and "allure," curses to Mr.
Baxter for poor taste. In any case, you
really have to buy the thing. In its present
state, it is a novelty which had marveolus
potentialities (Miss Sumac is a significant
combination of Erna Sach and Sophie
Tucker), which can be listened to with open
mouth and dilated nostrils.
22, N Y.
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
DECEMBER, 1950
assembly instructions are included with
each Multisection. A pictorial schematic
of the assembled unit is shown in Fig. 3,
while its over -all appearance is shown
in Fig. 4.
SUPERIOR
REPRODUCTION
WITH
Demonstration Unit
Those who wish to demonstrate the
remarkable difference this new control
can make in producing a pleasing, well balanced sound output at low volume
levels over the results of an ordinary,
TRANSCRIPTION ARMS
N E rr
DAMPED
108-6 ARM
Fig. 4. External appearance of com-
pleted control.
uncompensated volume control may as-
semble a very effective demonstrator unit
with the use of the new IRC Concentrikit, an arrangement which permits the
quick assembly of a wide variety of concentric controls. When used in conjunction with Multisections will provide a
triple -single concentric control, shown
in schematic form in Fig. 5.
The outer shaft of this demonstrator
unit varies the panel section Rr which is
For all records -33 1 !3, 45
and 78 r.p.m. Radically new
suspension development on the viscous damping principle for perfect
tracking of records and elimination of tone arm resonances. Instant
cartridge change with automatic correct stylus pressure. Solves all
transcription problems. Ideal for LP records. For Pickering, new CE
(short), old CE (long) cartridges. Write for bulletin. Price, less cartridges, $56.00 (effective Sept. 1st). Cartridge slides for both CE and
Pickering are furnished.
MODEL
106-SP ARM
Designed to meet strictest
requirements of modern highly compliant pick -up cartridges. 3 cartridge slides
furnished enable GE -mil, 21/2-mil or 3 -mil cartridges or Pickering cartridge to
be slipped into position in a jiffy. No tools or solder! Superb reproduction of
331/3, 45 or 78 r.p.m. records. Low vertical inertia, precisely adjustable stylus
pressure. Write for bulletin. Price, less cartridges, $45.15
1
Input
L=1
DPDT
rum
Output
EQUALIZERS
OIMeg
R5
82
m
PPt
MODEL
0.3
603
EQUALIZER
Latest of the universally adopted Gray
Equalizers used, with Gray Tone Arms, as
standard professional equipment by broadcast stations. High- frequency characflat, high roll -off, NAB, good records,
teristics obtainable comprise 5 steps
poor records. For both GE and Pickering cartridges. Price, $60.70
-
Fig. 5. Schematic of demonstrator unit
used to show advantages of the new
loudness control.
an ordinary uncompensated volume con-
trol. The inner shaft varies the three
which
rear sections, R,, R,, and
comprise the continuously variable loudness control. By means of a d.p.d.t. slide
switch the output is adjusted for the
same volume level through each control
at 1000 cps and direct comparison may
be quickly made at low level. Appearance
MODEL 602
R
AUDIO ENGINEERING
EQUALIZER
Has 4 control positions, highly accurate response curves. Price, $49.50
Write for bulletins on Gray Equalizers.
GRAY RESEARCHand
18
Development Co., Inc.
Arbor St., Hartford 1, Conn.
Division of The GRAY MANUFACTURING COMPANY
Originators of the Gray Telephone Pay Station and the Gray Audograph
DECEMBER, 1950
www.americanradiohistory.com
AmericanRadioHistory.Com
41
of the completed demonstrator unit is
shown in Fig. 6.
Following are simple assembly instructions for both the continuously variable loudness control and the unique
demonstrator unit.
Assemble to the "Q" control the two
specified Multisections, in the order
shown in Fig. 3, using instructions included with each. Assemble the additional parts and make all required connections as shown, solder, and cut shaft
to required length. Install and wire into
any high -gain audio amplifier.
To construct the demonstrator unit,
assemble Concentrikit by following instructions included using B13 -133 (R1)
as panel unit and B11 -133 (Re) as rear
THE LARGEST INDEPENDENT RECORDING STUDIO IN
THE EAST SAYS: "We've been using Fairchild Disc Recorders
exclusively for many successful years. They stand the test of
continuous operation with high quality output. That's the inter.
national reputation of the work we turn out -high quality!"
Mr. C. L. Stewart, Business Manager,
R
Sound Studios
-Fairchild Thermo -DynoMERCURY RECORDS SAYS: "R
ble combination ...
mic Margin Control repres
progressive
recording techputs Mercury Records at the top in
niques".
Mr. David Hall, Musical Director of Mercury Classics
With Fairchild's exclusive features, you too can
be successful in the new markets for low noise
LP, TV and Theatre film sound track recording.
The FAIRCHILD STUDIO RECORDER with
pitch -variable -while-recording is shown on the
right. No lead screws or gears to change. Continuous pitch change from 80 to over 500 lines
per inch simply by rotating the convenient knob.
This is the famous MARGIN CONTROL which
puts up to 25% more recording time in the same
space -without reducing top recording levels.
OP
Fig. 6. External appearance of demon-
strator unit.
70 db dynamic range on disc is now made possible with the Fairchild THERMO- STYLUS and
MARGIN CONTROL -"an unbeatable combination".
Fairchild Synchronous Disc Recorders
Accurate Program Timing -Synchronous
direct to the center gear drive for "shows
on the nose".
Freedom From Wow -No slippage. No
musical pitch change to make listeners
aware the show is transcribed -extremely
important at 331/3 rpm.
Sound on Film Dubbing -Many of the
motion picture sound tracks you hear
and enjoy are first recorded on Fairchild
Synchronous Disc Recorders.
Microgroove and Standard Pitch recording can be done with any of the
3 Fairchild Disc Recorders: Unit 523 for the finest fixed installation,
Unit 539 -K for the small budget studio, Unit 539-G (shown above) for
console performance in a portable case. Fairchild "sync- disc" recorders
for standard and microgroove recording are made in 3 models, from $715
(less cutter head and pickup).
FR-119
Write for
Series DRS
Literature
Today
It's Free
42
R
and make necessary connections as
shown by schematic, Fig. 5. It is advisable to ground the metal case of
switch, if that type is used, to reduce
possibility of hum pickup during opera-
tion of switch.
-
154th ST. AND 7th AVE.
unit. Omit cover on rear. Assemble M13137 (R,) and M13 -128 (R4) per instructions included with each Multisection. Attach this assembly in place of
rear cover on the above Concentrikit being sure inner shaft rotates both sections
R, and Re. Assemble the additional parts
and make all required connections to the
and R4 in
last three controls R,,
exactly the same manner as described
previously for the loudness control. An
additional connection is required between the most counter -clockwise terminal of the panel section and that of
the second section to form a common
ground.
Assemble d.p.d.t. switch as shown by
photograph of completed control, Fig. 6,
WHITESTONE, L. I., N. Y
(All wiring to and from control
should be as short as possible and should
be shielded to reduce hum pickup. Use
low- capacitance wire to avoid loss of
highs due to shielding. The complete assembly can be mounted in a small steel
box to form a well shielded unit.)
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
DECEMBER, 1950
UNKNOWN IMPEDANCES
IN TRANSFORMER
[from page 21]
must, of course, be found first in order
to make the formula operative.
Impedance, being made up of resistance, can be determined by Ohm's Law
applied to those circuits having impedance. The formula for Ohm's Law in a.c.
circuits is:
Z =
E
MAGNECORD PT6 -1A
RECORDER &
AMPLIFIER
Portable rig for superb professional sound reproduction. Easy
operating, exceptional high fidelity, the finest in Magnetic recording. 10 watts output.
(2)
Where E = e.m.f., in volts
I = current, in amperes
Z = impedance, in ohms.
Procedure
Adjust the output of the audio oscillator to about 25 volts on the meter. Apply this voltage to one winding of the
transformer under test and at the same
time measure the current drawn. (See
Fig. 2.) Since reflected impedance from
Complete Systems from $548
MCINTOSH AMPLIFIERS
Highest quality, efficiency. Full dynamic
range. Frequency range -20 to 20,000
plus or minus 0.2 db; 10 to 200.000 plus
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50W -2 for less than 10/a distortion
Continuous single freq. rating
50 watts RMS -Peak 100
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20W -2 for less than I% distortion
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ELECTRO -VOICE SPEAKER #SP 15
Frequency response 70 -13000 c.p.s. '_ 5db.
Maximum instantaneous power input: 30
watts. Field excitation: 51/4 lb. Alnico V
Orange Streak Magnet. Radax crossover frequency: 3000 c.p.s. Base cone resonance:
38 c.p.s. High Frequency cone resonance:
250 c.p.s.
Fig. 2. Schematic of
arrangement used
for measuring voltage ratio between
transformer windings preliminary to
calculating impedance ratios.
secondary to primary under load will
have an important bearing on the final
result, the secondary of the transformer
under test should carry a load. This can
be a resistor, a speaker or a pair of headphones as an example. If a resistor is
used it should be of the non -inductive
carbon type to avoid reflected reactance.
Once two known values are found, the
impedance may be calculated from the
above formula.
A more accurate method of making
the measurements is to treat the primary
of the transformer as a choke, leaving
the secondary unloaded for the moment,
and determine the inductance of the
winding and find its reactance. This can
be done by substitution as shown in
Fig. 4.
Adjust R so that the voltage drop
across R balances and equals the voltage
drop across the primary. The voltage
drop across the transformer primary is,
of course, not due to inductance alone,
but is caused by its impedance. Measure
the d.c. resistance of that section of R in
which the voltage drop occurs, then
solve for the inductance of the primary
with the formula
:
L =
f
AUDIO ENGINEERING
.
$57.00 net
ELECTRO -VOICE MICROPHONE #650
Response ± 2.5 db. 40- 15,000 cps. Extremely
high output level -46 db. Impedance selector.
External shock mount. Non -metallic Acoustalloy
diaphragm. Individually laboratory calibrated.
Electro-Voice Microphone,
Robin Hood Dell concerts.
.111111.11111111111111111h4 1\'
$90 net
used
exclusively at
BROWNING FM -AM TUNERS
Designed for high fidelity receiving applications in the broadcast band as well
as the 88 -108 MC. FM band. Incorporating Automatic Frequency control for
simplified FM tuning.
From $87.75
PERMANENT DISPLAY
Equipment Shown at Audio Fair
#11170444
Literature Available
-
SOUND & RECORDING COMPANY
1527 CHESTNUT ST., PHILA. 2, PA.
Once the inDECEMBER, 1950
www.americanradiohistory.com
AmericanRadioHistory.Com
RI. 6 -8388
43
SW
exdIu5ivewi
rhTECH LABS
'
ARTIFICIAL REVERBERATION GENERATOR
ductance is known, the inductive reactance (in ohms) of the primary may be
found by the formula : XL = 21IL. Then
the impedance may be found by measuring the d.c. resistance of the winding
with an ohmmeter and solving for the
impedance with the formula:
Where
Z= \Rs +X s
Z= impedance
(3)
R= d.c. resistance
X= Net reactance.
Since we are substituting XL (inductive reactance) for X in the above formula, it is assumed that the net reactance
is equal to the inductive reactance. This
Test
ose
GIVES HIGH QUALITY REVERBERATION EFFECTS WITHOUT
EXPENSIVE EQUIPMENT
SOUND
IS NOT DELAYED AND PLAYED BACK,
AWAY NATURALLY!
BUT DIES
THE RATE OF DELAY IS ELECTRONICALLY CONTROLLED
14" OF PANEL SPACE
PRODUCES AN INFINITE VARIETY OF EFFECTS
ENTIRE UNIT OCCUPIES ONLY
Fig. 3. (A) Method of measuring voltage ratio of simple transformer. (B)
Tapped transformer measurements give
sufficient information for complete
calculations. (C) Example of tapped
transformer.
is not
The basic assembly requires only 14"
of panel space (contrasted
with the thousands of cubic feet in an echo chamber). It's inexpensive, for costly rewind and take -up motors with switching accessories and expensive floor and studio space are not required. Yet,
in terms of program use it will provide exactly the effects clients
specify with excellent reverberant qualities in an infinite variety
of
uses.
completely accurate, but the result
is sufficiently close to make the transformer usable in many audio applica-
tions.
With the proper load on the secondary the impedance reflected back to the
primary would be such as to lower the
primary impedance considerably. For
general application this can be assumed
*DEVELOPED BY AUDIO FACILITIES CORP., N. Y.
Manufactured and sold exclusively by Tech Labs.
Patents applied for.
TECHNICAL SPECIFICATIONS
Input impedance
Bridging for 600 -ohm line
Input & output level
O vu
Output impedance
600 ohms /250 .n.
Controls
Single control operation
Reverberation time
0 to 10 sec., continuously variable
Finish
Grey wrinkle. Others to order
Power requirements
117 volts 60 cps single phase
120 watts
Fig. 4. Method of making measurement by substitution. Signal Generator
voltage is kept constant while adjustments are made. The technique is described and formula given in the text.
to lower the primary impedance to one
For Literature & Demonstration Records Write To:
Manufacturers of Precision Electrical Resistance Instruments
PALISADES
44
PARK,
NEW
JERSEY
fourth. This gives the primary impedance at the lowest frequency responses
of the transformer.
With the impedance of the primary
winding known and with the output of
the audio oscillator still applied to the
AUDIO ENGINEERING
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AmericanRadioHistory.Com
DECEMBER, 1950
primary, but with R removed, voltage
ratio measurements can be made on the
secondary winding, as at A in Fig. 3,
and its impedance determined by the
formula (1). Succeeding measurements
and calculations can be made on any
number of multiple secondary windings.
HARVEY
Presents the
Newest Development In Tape Recording!
Tapped Winding Calculations
Now suppose we have a transformer
with a tapped winding in which the impedance of two sections is known, but
the third unknown, as at B in Fig. 3.
The impedance of the unknown section
can be calculated from the formula:
Z, = Za11IZa -1)
PT63-AH
NEW
(4)
Where Z,= unknown impedance;
Za = impedance of known section
and
Zt = total impedance of sections
and Za.
4
3 HEADS:
In order to make our impedance calculations complete for a given transformer, it is not only necessary to know
the impedance of individual windings
and tapped sections, but also those tapped windings on the same core in combination. The commercially made variable
impedance transformers have this information in chart form for easy reference. Such ready information makes the
transformer more versatile for any given
application and saves the builder much
time and many a headache. We can index the impedance for our transformer
in the same manner. The third and last
formula makes this completeness pos-
Developed from the famous PT6, the new MAGNECORDER PT63
Erase, Record, Playback for MONIoffers 3 separate heads
TORING FROM THE TAPE while recording. The addition of this
feature assures finer results by eliminating most recording errors.
All heads, contained in a single housing, are individually alignable
and replaceable, and each one is triple shielded to eliminate crosstalk and hum. 71/2 -inch and 15 -inch tape speeds, easily interchangeable. (3 speeds ... 3 3/4 ", 7 1/2" and 15 "... are also available at slight additional cost). Attractive black grain leatherette
over wood construction. $350.00 Net, with Case.
,
pg -1 J
PT63 -J
AMPLIFIER
A new single channel portable amplifier which contains a separate record and
playback amplifier so that
you can monitor from the tape while recording. In addition, 10 watts of audio is provided to drive both the
5 -inch monitor speaker or an external loudspeaker.
Response flat from 50 -15kc at 15 ", sec. The 19" x 7"
control panel provides a switch to change equalization
for either 71/2" or 15" tape speeds. Switching is also
provided for record, playback or bias readings on the
3" VU meter. May be directly rack mounted when removed from case. $387.00 Net, with Case
= 368 ohms.
The impedance of any other tapped
winding, combinations can be calculated
in the same manner.
Note also that in this formula it is not
necessary to know the primary impedance. The calculations deal with only the
knowns and unknowns of the secondary
windings. The resultant values apply to
tapped windings on the same core; this
fact should be kept in mind when making
calculations employing the last formula.
AUDIO ENGINEERING
-
-
Suppose we have a transformer in
which we have a two -section tapped
winding having impedances of 500 ohms
and 10 ohms respectively, as shown at
C in Fig. 3.
Substituting in the formula :
10I
... Record ... Playback
Designed To Monitor Directly From The Tape
While You Are Recording!
sible.
Z.
Erase
V SIT THE
Telephone:
LUxemburg 2-1500
AUDIO TORIUM
and
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...all
NOTE: In view
;Z
01 (c)Ì I2:
A
subject te change
\,IY(
IiI)
without notice and
are Net, F.O.B.,
N.Y.C.
103 West 43rd St., New York 18, N. Y.
'
.
..:.ti`..
DECEMBER, 1950
www.americanradiohistory.com
AmericanRadioHistory.Com
45
VECTOR SLIDE RULE
[from page 20]
= 0.9 when 0= 1.47 approximately, and
tanh O becomes about 0.9951 when O = 3.0.
0
Minimum -Loss Networks
MICROPHONES PROVED* TO BE THE
FINE-QUALITY-ECONOMICAL
An impedance- matching device is occasionally required which may nevertheless introduce a certain amount of loss
into a system. In order to keep this loss
at an absolute minimum, a transformer
is often indicated to accomplish the impedance match.
Where some additional loss is permissible, a "minimum-loss" resistive attenuator can often be used. When its loss
can be tolerated, the attenuator is often
much less expensive than the transformer, and is smaller and lighter.
The minimum amount of loss which a
"T" attenuator must be designed to introduce is determined by the ratio of the
impedances which it is intended to match.
The resulting actual design is an "L"
ANSWER TO
MANY MICROPHONE PROBLEMS
revolutionary new
microphone unit that provides the ruggedness,
the clear reproduction, and the high output long
needed for Public Address, Communications, Recording at an amazingly low price!
List Price $14.50
The "HERCULES"- Here is a
MODEL 510
The "GREEN BULLET"- Specially designed to provide quality music and speech reproduction at
moderate cost. A streamlined unit that lends itself
to fine-quality, low -cost installations where durability is an important factor. Features high output, good response, high impedance without the
need of a transformer.
List Price $17.50
pad, based upon the
MODEL 520
"RANGER"- Recommended for those applications where long lines are used and a rugged
hand -held microphone is needed. Ideal for outdoor
public address, mobile communications, hams,
audience participation shows, etc. Designed for
clear, crisp natural -voice response of high intelligibility. Has heavy -duty switch for push-to -talk
operation.
List Price $27.50
The
signed to handle the most
severe field requirements
of paging and dispatching
systems. Ideal for police,
MODEL 520SL
List Price 535.00
MODEL R5
railroad, taxicab, airport, bus, truck and all
emergency communica-
tions work.
CONTROLLED RELUCTANCE
CARTRIDGE
= cosh -' \/Z,Zs
O is the loss of the
attenuator in nepers (= loss in db divided
by 8.686). Z, /Z° is the ratio of the impedances to be matched, so chosen that
the ratio obtained is greater than unity.
The procedure is as follows :
1. Obtain the ratio Z, /Zs on scales A
and B of the "vector" slide rule.
2. Record the reading on scale A of
this impedance ratio, and subtract the
number 1 from this result. Set the runner
to this new value on scale A.
3. The runner now indicates on scale
Sá1 or Sh2 the minimum loss O in nepers
of the desired attenuator. If the ratio
of the impedances is less than 2, then O
will be less than about 0.882 and scale
Sh1 is used ; for greater impedance ratios, refer to scale Sh2.
4. To determine this minimum loss in
decibels, divide O by 8.686. Use scales
C and D.
5. Calculate R° and R,. These resistances are found with the "vector" slide
rule, as explained before. Steps 5, 6
and 7 are omitted, since Rs is not used
in the special case of the minimum -loss
O
" -Complete
unit, includes Model 520 Micro phone, A88A Grip -To -Talk
Slide -To -Lock Switch, and
S36A Desk Stand. De-
pad circuit
In this formula,
MODEL 505C
The "DISPATCHER
"T"
previously discussed. However, when the
pad is designed for the minimum possible
amount of loss for a given impedance
ratio, R, vanishes and only R, and Rs
remain to be calculated (see Fig. 6).
A procedure for the design of minimum -loss pads is based on the equation° :
-
Available for service installation. Ideal for
replacement of crystal cartridges in Shure
cases of Models 707A and 708 Series. Can
also be used in most semi- directional microphones where space permits. Supplied with
rubber mounting ring.
List Price $9.00
*Specific information provided
on reque..t.
pad.
Note that R, is always located on the
high -impedance side of the attenuator.
Patented by Shure Brothers, Inc.
SHURE BROTHERS, Inc.
°
Microphones and Acoustic Devices
225 West Huron Street, Chicago 10,111.
46
Cable Address: SHUREMICRO
From "Reference Data for Radio Engineers," Federal Telephone & Radio Corp.,
New York, 3d Edition, pp. 158-9, by per mission.
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
DECEMBER, 1950
The pad may match a high impedance to
a lower impedance, or vice versa.
The range of the "vector" slide rule
allows minimum -loss pads to be designed
to match impedances having ratios as
great as 100 to 1 (this ratio causing the
minimum loss to be 26 db).
It is often difficult to find the correct
values of resistances from stock for any
certain attenuator. Resistance values can
then be selected which can be connected
in series or in parallel to give the required resistance values. It is found that
the graphical solution illustrated in Fig.
7 speeds up the work considerably when
parallel resistance combinations are
needed.
The following rule applies to the use
of Fig. 7:
If a straight -edge be kid
connect-
ing points corresponding to two resistance values upon alternate scales,
the intersection of the straightedge with the intermediate scale indicates the equivalent resistance of
a parallel combination of the first
two resistances.
Example: If resistors of 100 ohms and 90
ohms be connected in parallel, what is the
resistance of the parallel combination?
Solution: The dotted line (A) in Fig. 7
connects 100 ohms and 90 ohms on alternate
scales (1) and (3). The equivalent parallel
resistance is read as 47.4 ohms on the intermediate scale (2). This process can be
continued for more than two resistors in
parallel. Suppose that a third resistor of
80 ohms be connected in parallel with those
of the example. Dotted line (B) connects
the resistance already in the circuit (47.4
ohms) with the added value of 80 ohms on
scale (4), and the new equivalent resistance is found on scale (3) to be 30 ohms.
This chart, while simple, is found to be
a great time-saver for general use in connection with audio systems.
_Newell
Al
HIGH FIDELITY
MAGNETIC TAPE
RECORDER
Model 400
TERMINAL brings you
this new incomparable
15,000 cycle performance at 71/2 inches per
second that equals the
performance of 15 IPS
full -track recorders
and gives 4 to 1 savings in tape cost.
2 FULL HOURS OF PROGRAM
MATERIAL CAN BE COMBINED ON ONE 10"
-
8
OUTPUT SWITCH
Position "B"
(Level), connects meter "Line Output" plug,
anc "Phones" monitor plug to the output of
METER
the playback for monitoring of playback,
while recording or playing back tapes. Position "A" connects "Une Output" plug, and
"Phones" monitor plug to the record amplifier for direct monitor of the incoming program. Under position "A" there are three
switch positions designated: LEVEL
which
connects the meter to measure record volume
level.
SIAS -which connects the meter to indicate
proper record bias.
ERASE-which connects the meter to indicate
proper erase current.
Toggle switch permits
SPEED CHANGE
quick choice of 71/2 or 15 i.p.s. tape drive
-
-
speeds.
RECORD BIAS ADJUSTMENT
Biased for
maximum output of 1000 cycle tone (factory
-
adjusted).
Ifrom page
/I
the pentode section is the mixer. The variable oscillator uses a separate triode.
Each of the oscillators is coupled to a grid
of the mixer pentode by adding a pickup coil
to the tuning inductor and connecting this
to the pentode. Assuming that both oscillators are well shielded and the leads
dressed, the main danger of pulling comes
from capacitance between the triode and
pentode plates within the combination tube;
this is indicated by a dotted capacitor in the
drawing, and is by no means negligible.
The output of the pentode plate contains
components of both oscillator frequencies,
so that the variable oscillator frequency
may be coupled to the fixed oscillator
through the dotted capacitor, the lower part
of L, and the bypass capacitor C, to ground.
This creates a potential difference between
the triode anode and grid.
To prevent pulling, Cr is connected between the pentode plate and the upper end
of L. which is connected to the grid through
Cs. This forms a bridge, the arms of which
are the two sections of the coil, the ca-
AUDIO ENGINEERING
-
Adjusts elec
71/2 or 15 i.p.s.
Properly conINPUT TRANSFER SWITCH
nects input plug for: I) 200 ohm microphones
such as R.C.A. 448X, KB -2C, etc. II) Balanced
bridge for bridging telephone lines or balanced studio lines. III) Unbalanced bridge
100,000 ohm input for radio tuner, phono
pre -amp, bridging public address equipment
or unbalanced studio lines.
Volume level
FOUR -INCH "VU" METER
meter used to indicate proper record volume
level. This instrument can be switched for
I functions as listed under "Meter B
Output Switch."
OUTPUT LINE TERMINATION SWITCH
Places 600 ohm terminator across amplifier
when same is not externally loaded (This is
necessary for proper meter calibration).
Switch provides
OPERATION SELECTOR
for normal forward or fast forward or fast
rewind.
CUSTOM SET -BUILDERS
AUDIO PATENTS
REEL
71/2" -15" EQUALIZATION
Ironies for proper operation at
-
-
-
-
AUDIO ENGINEERS
Terminal Radio can furnish promptly all components required
for FAS amplifiers and speaker systems, in addition to turntables,
pickups, and FM -AM chassis necessary to assure the superlative
performance of which FAS installations are capable. If you haven't
a copy of the Terminal Radio catalog on hand, write for one today!
FREE
WRITE FOR YOUR PORTFOLIO OF 15 IDEAS
FOR CUSTOM RADIO -PHONOGRAPH INSTALLATIONS.
This profusely illustrated booklet gives you actual photos of installations in typical room
settings.
New 1951 Terminal Sound Catalog now available
Write for your free copy!
Distributors of Radio & Electronic Equipment
85 CORTLANDT ST., NEW YORK 7, N. Y.
DECEMBER, 1950
www.americanradiohistory.com
AmericanRadioHistory.Com
WOrth 4 -3311
Cable: TERMRACIO
4'e
PRECISION
Setulstjti
E
the GROMME
lof OA
PUY
d
ifj-t v3-
No
Postage Stamp
Necessary
If Mailed in the
Out -performs larger
Response ± DB 20 t
Total distortion 1.57
Peak power 20 watt
United States
1
10 DB
BUSINESS REPLY ENVELOPE
feedback.
50 PG List
Both models
$
First Clem Permit No.
73.5
-43 MILWAUKEE
342
A
NEW YORK
ALLI C V
for your high- fidelity
custom sound components
WORLD'S LARGEST STOCKS
OF ALL FAMOUS MAKES
ON HAND
FOR IMMEDIATE
DELIVERY
Brook
Bell
Browning
Collins
components -ALLIED will deliver immediately from the country's largest in -stock
supplies. Make your selections of tuners,
amplifiers, speakers, baffles, cabinets,
record changers, transcription and phono
equipment, wire and tape recorders, pre amps -all the equipment you want, with
the exact specifications required -at the
price you want to pay. For everything in
hi-fidelity sound, depend on ALLIED.
Livingston
Jensen
Knight
Jim Lansing
Markel
Audio
Bogen
Just name your need in high- fidelity audio
Electro-Ysice
Clarkston
General Electric
Magnecord
Masco
Messner
Mclnlosh
National
Pickering
RCA
Presto
Rek-O -Kul
Radio Craftsmen
Scott
Stephens
Thoidarson
University
Y-M Corp.
Webster -Chicago
Western Electric
FREE
1951 CATALOG
Write today for our omplete Buying
Guide. (Custom Installers ... ask to be
put on our special mailing list.) WE
STOCK
EVERYTHING-FOR IMMEDIATE
SHIPMENT
-
ANYTIME
-
833 W. Jackson Blvd., Dept.
17,
N. Y.
British Hearing Aid
The design of hearing aids in Great
Britain is as controversial as elsewhere, and
in Wireless World for August 1950 A.
Poliakoff describes some of the factors affecting one particular British model.
Listed as the attributes of a good aid in
order of importance are optimum volume,
avoidance of pronounced peaks, low case
noise, and a "nice looking response curve."
The optimum volume is a point which the
author has studied over a period of years
and concludes is within the range 75 to 98
db above reference. In addition, compression
is added so that no bad transients will affect patients with recruitment, and also that
the optimum level may not be exceeded. For
low level signals, a.v.c. action is used. The
use of baked lacquer on the smooth metal
case minimizes case noise. Hinges are eliminated by a sliding case lock on the inside.
The frequency response is varied by use of
different earpieces, and not by changing
amplifier response. Finally, the cost of aids
is discussed in relation to radio receiver
prices.
Transistor Noise
ANYWHERE.
The application of transistors to the solution of various audio problems has been
limited, to date, by their high noise level.
H. C. Montgomery discusses this problem
in the September 1950 Bell Laboratories
Record. Transistor noise level is a function
ALLIED RADIO
17 -M-O
CHICAGO 7, ILLINOIS
48
New York, N. Y.
MADISON AVENUE
IOOK TO
Allec-Lansing
L.
AUDIO ENGINEERING
PRECISIO
Development
P. L. &
feature the
cuits known to electronic
bass and treble controls,
641
41987, See. 84.9',
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
DECEMBER, 1950
A
of the biases on the emitter and the collector electrodes, but its spectrum shape is
constant. The octave noise level is constant
throughout the spectrum which means that
the noise power in the 50-100 cps octave is
the same as that in the 20 to 40 kc octave.
The noise therefore has a predominantly
large low -frequency character. For an average Type A (Bell Telephone Laboratories)
Transistor in a single -stage amplifier, the
noise is 80 db below undistorted output in
the 100-3,000 cps band and 75 db down for
the 10-cps to I -mc band.
Conference Telephone
a
An advanced design conference telephone
system is described in the Ericsson Review,
No. 1, 1950 by G. Thames. The new system known as the Ericsson DYA permits
conference calls to be carried by microphones and loud speakers in addition to the
telephone handset. The entire system is
compatible with PBX or public telephone
exchange systems and may be used without disrupting regular telephone service. In
the DYA system any extension telephone
may be designated as master station for
the conference system. At a master station,
it is always possible to maintain secrecy,
since the main station has control over who
is connected to the conference. The lines
connected to the conference are always indicated by lighted bulbs with numbered
lenses. Also PBX (local internal) calls
may be interrupted and the conference line
used with the PBX line held until the end
of the conference call, at which time the
PBX call may be picked up from the held
position.
The remainder of the article discusses
the detailed operation and installation of
such a system and describes the components.
THE FIRST CHOICE OF
MAGNECORDER
For every purpose
AUDIO DESIGN NOTES
WIevery
More radio engineers use Magnecorders
than all other professional tape recorders combined. Here's why
-
...
purse!
AUDIO ENGINEERING
HIGH FIDELITY, LOW COST
Stations are enthusiastic about the lifelike tone quality and low distortion of
Magnecordings. Magnecorder frequency
response: 50
Skc ± 2 db. Signal noise ratio: 50 db. Harmonic distortion
less than 2 'A. Meets N.A.B. standards.
No other recorder offers such fidelity at
such a moderate price.
-
[from page 22]
amount of power radiated by the port is
approximately proportional to the area. In
practice, this means that for a given resonant frequency the larger the enclosure the
larger will be the port and the more effective the resonator. Usually, one does not
use a port area less than half, nor more
than twice the cone area.
The importance of sturdy construction of
the cabinet can not be overemphasized. Motion of the walls absorb energy which would
otherwise have been radiated from the port.
It is good practice to stiffen the back and
front of the cabinet with 2 x 4's. The force
produced by the voice coil might be as high
as 5 lbs. at the resonant frequency and the
enclosure must be able to stand this force
without rattling.
In order to eliminate radiation from the
port at higher frequencies the interior of
the enclosure is usually lined with some
absorbing material such as Celotex. The material used should have high absorption at
the higher frequencies (500 cps up for
example) but negligible absorption at the
resonant frequency. The objection to simultaneous radiation from the port and cone is
that destructive interference occurs at certain frequencies causing large dips in the
response curve. This difficulty does not occur at the resonant frequency because here
the radiation from the cone is negligible
compared to the radiation from the port.
RADIO ENGINEERS
PT6 SERIES
Most widely used professional tope recorder in
the world.
1
GREATEST FLEXIBILITY
Mount a Magnecorder in a rack or console cabinet for delayed studio and network shows. Slip it into its really portable
cases for remotes. Add to your Magnecord equipment as you need
combine
Magnecorders to suit every purpose.
it-
P563 SERIES
Three
heeds to erase,
MORE FEATURES
record, ood monitor from
the tepe.
Your Magnecorder, new or old, can now
have 3 heads (separate erase, record,
and playback) to permit monitoring from
tape. Three speeds (15
71/2 " -33/,"
-up to an hour on a 7" reell available
on both PT6 and PT63 equipment. Dual
track heads also available if desired.
"-
P17 SERIES
A complete console
for only $930.00.
Outstanding lea lores and flexibil-
ity. Models for portable or rack mount
also available.
Write for NEW CATALOG
MAGNECORD, INC., Dept. A -12
360 North Michigan Avenue, Chicago 1, Ill.
Send me latest catalog of Magnecord Equipment
Name
Company
Address
City
DECEMBER, 1950
www.americanradiohistory.com
AmericanRadioHistory.Com
zone
Stet.
49
NEW PRODUCTS
Audio Generator. Designed essentially for supplying the two -tone test
signals necessary for intermodulation
measurement, General Radio's new Type
1303 -A audio generator is equally well
suited for use as a general purpose beat frequency oscillator. It may be used to
generate a single low- distortion signal
adjustable in frequency from 20 cps to
40 kc; two signals, each separately adjustable, one to 20 kc and the other to 10
single unit in the crossover-frequency
range. Thus is avoided the distortion
which frequently is present when woofer
and tweeter are operated in different
planes. Technical description may be obtained from Tube Department, Radio
Corporation of America, Harrison, N. J.
Cable Tacker. Of particular interest
to installers of sound equipment and juke
boxes is the Phillips cable tacker, a onehand- operated tool which handles all
sizes of cable up to lh in. OD. Concave
center guides instantly center both large
volts into 10,000 ohms with distortion less
than 0.3 per cent from 100 cps to 15,000
cps, and rising no more than 0.5 per cent
at 30 cps. Total frequency error due to
drift and calibration is less than two per
cent. Output control is logarithmic and
is calbrated in output voltage. Dimensions are 4 x 516 x 4 in. Full technical description may be obtained from the manufacturer, The Electronic Workshop,
351 Bleecker St., New York 14, N Y.
kc; or two signals with a fixed difference
in frequency maintained between the
two as the frequency of one signal is
varied. The fixed difference frequency is
adjustable up to 10 kc, and the lower of
the two frequencies is adjustable up to
20 kc. Output of the generator is continuously adjustable up to 10 milliwatts
into 600 ohms with less than 0.25 per
cent distortion. Calibration is in both
volts and db. Descriptive material may
be obtained by writing General Radio
Company, 275 Massachusetts Ave., Cambridge 39, Mass.
High -Quality Speaker. Both high quality reproduction and moderate purchase price are features of the Model
515S2 speaker recently introduced by
RCA. Useful response range is 40 to
12,000 cps and power handling capacity
is 25 watts. The vibrating system of the
51552 consists of two voice coils and
cones excited by a single 2 -1b. Alnico
Dy na in le 31 lerophone. Full vision for
both performer and audience is afforded
by the new : \merican type D -33 micro-
and small cables which are anchored
without damage to insulation. Full description may be obtained from Phillips
Manufacturing Company, Minneapolis,
Minn.
Miniature Attenuator. Following today's trend toward miniaturization of
electronic components, the new Daven
Series 730 T- network attenuator offers
30 steps of attenuation in a unit only
214 in. in diameter. Available in steps of
or 2.0 db, the unit has a fiat
frequency characteristic to 30 kc. Resistance accuracy is ± 5 per cent. Zero
insertion loss and constant input and
output impedance are also characteristic
of the new attenuator. Further information may be obtained by writing The
Daven Company, 191 Central Ave., Newark 4, N J.
0.5, 1.0, 1.5
V magnet. The woofer and tweeter are
so mounted that the larger cone is effectively a continuation of the smaller, and
as a result the two cones vibrate as a
50
Audio Oscillator. Exceptionally compact in size, the new Model 510 -A oscillator has a frequency range of 18 cps
to 210 kc in four decades, and has output
constant within 0.5 db over the entire
frequency range. Power output is 10
phone. Weighing only seven ounces, the
D -33 does not require a pre-amplifier, and
is distinctively finished in gold and black.
Pickup pattern is omnidirectional. Available in all popular impedances. Descriptive material is available from American
Microphone Company, 370 S. Fair Oaks
Ave., Pasadena 1, Calif.
VTVM Kit. The new Knight VTVM
kit brings precision measurements within
the reach of even the most modest purse.
An excellent all- around test instrument
for servicemen, amateurs, experimenters
and laboratories, the instrument offers
four milliampere ranges and six capacitance ranges in addition to the standard
twenty VTVM ranges. Matched -pair resistors are used for accuracy of measure-
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
DECEMBER, 1950
a
PRECISION ELECTRONICS PRESENTS
the GROMMES- CUSTOM AMPLIFIERS
Designed by Sound Engineers
pacitor C,, and the dotted capacitance.
When the bridge is balanced by correct adjustment of C,, feedback from pentode plate
to triode plate in balanced out, and the obtainable audio frequency is much lower than
before. As an illustration, if L happens to
be centertapped, C, and the dotted capacitance should be equal.
for CRITICAL MUSIC LOVERS
For those who want the best
Response 10 to 100,000 CPS
(30.1 DB 10 to 50,000 CPS).
Passes square waves 20to1O,000CPS
...tal distortion 0.27. or less at
20 watts.
Peak power 50 watts.
25 DB feedback; Damping factor -11.
200 PG List $225.00
Out -performs larger amplifiers.
Response
DB 20 to 20,000 CPS.
Total distorsion 1.57 or less at 10 watts
Peak power 20 watts.
t
10 DB
1
feedback.
Fig. 2
50 PG List 573.50
feature the
Both models
m
cuits known to electronics; 4 inputs, feedback pickup pre -amp, calibrated
bass and treble controls, hum inaudible.
Free technical bulletin.
PRECISION ELECTRONICS, INC.
641-43 MILWAUKEE
AVENUE
CHICAGO 22,
ILLIN)IS
look to ALLIED
for your high- fidelity
custom sound components
WORLD'S LARGEST STOCKS
OF ALL FAMOUS MAKES
ON HAND
FOR IMMEDIATE
DELIVERY
AlieLansing
Development
Audio
Bell
Bogen
Browning
Brook
Clarkston
Collins
Jensen
Jim Lansing
Livingston
Knight
Magnecord
Masco
Meissner
Mclnlost
National
Pickering
RCA
Stephens
University
Presto
Rek -O -Kul
Radio Craftsmen
Scott
Thordarson
VM
Corp.
Webster -Chicago
Western Electric
..
ALL /ED HAS IT!
IF IT'S HI -FI
components -ALLIED will deliver immediately from the country's largest in -stock
supplies. Make your selections of tuners,
amplifiers, speakers, baffles, cabinets,
record changers, transcription and phono
equipment, wire and tape recorders, preamps -all the equipment you want, with
the exact specifications required -at the
price you want to pay. For everything in
hi- fidelity sound, depend on ALLIED.
Eleclro-Voice
General Electric
Markel
Just name your need in high- fidelity audio
,
FREE
1951 CATALOG
Write today for our complete Buying
Guide. (Custom Installers... ask to be
put on our special moiling list.) WE
-
ALLIED RADIO
833 W. Jackson Blvd., Dept. 17-M -o
CHICAGO 7, ILLINOIS
I
r,
/a!ir
;N
all the requirements of that country's broadcasting service.
Some of the ideas presented here offer a
fresh approach to the problem for U. S. and
European readers, and although frequent
reference to American sources is made, their
use is not without understanding.
British Hearing Aid
The design of hearing aids in Great
Britain is as controversial as elsewhere, and
in Wireless World for August 1950 A.
Poliakoff describes some of the factors affecting one particular British model.
Listed as the attributes of a good aid in
order of importance are optimum volume,
avoidance of pronounced peaks, low case
noise, and a "nice looking response curve."
The optimum volume is a point which the
author has studied over a period of years
and concludes is within the range 75 to 98
db above reference. In addition, compression
is added so that no bad transients will affect patients with recruitment, and also that
the optimum level may not be exceeded. For
low level signals, a.v.c. action is used. The
use of baked lacquer on the smooth metal
case minimizes case noise. Hinges are eliminated by a sliding case lock on the inside.
The frequency response is varied by use of
different earpieces, and not by changing
amplifier response. Finally, the cost of aids
is discussed in relation to radio receiver
prices.
Transistor Noise
FOR IMMEDIATE
SHIPMENT -ANYTIME -ANYWHERE.
STOCK EVERYTHING
TECHNICANA
Alliea R,dts
-
:
.
.®
The application of transistors to the solution of various audio problems has been
limited, to date, by their high noise level.
H. C. Montgomery discusses this problem
in the September 1950 Bell Laboratories
Record. Transistor noise level is a function
-.
1
48
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
DECEMBER, 1950
The pad may match a high impedance to
a lower impedance, or vice versa.
The range of the "vector" slide rule
allows minimum -loss pads to be designed
to match impedances having ratios as
great as 100 to 1 (this ratio causing the
minimum loss to be 26 db).
It is often difficult to find the correct
values of resistances from stock for any
certain attenuator. Resistance values can
then be selected which can be connected
in series or in parallel to give the required resistance values. It is found that
the graphical solution illustrated in Fig.
7 speeds up the work considerably when
parallel resistance combinations are
needed.
The following rule applies to the use
of Fig. 7:
If a straight -edge be laid connecting points corresponding to two resistance values upon alternate scales.
the intersection of the straightedge with the intermediate scale indicates the equivalent resistance of
a parallel combination of the first
two resistances.
Example: If resistors of 100 ohms and 90
ohms be connected in parallel, what is the
resistance of the parallel combination?
Solution: The dotted line (A) in Fig. 7
connects 100 ohms and 90 ohms on alternate
scales (1) and (3). The equivalent parallel
resistance is read as 47.4 ohms on the intermediate scale (2). This process can be
continued for more than two resistors in
parallel. Suppose that a third resistor of
80 ohms be connected in parallel with those
of the example. Dotted line (B) connects
the resistance already in the circuit (47.4
ohms) with the added value of 80 ohms on
scale (4), and the new equivalent resistance is found on scale (3) to be 30 ohms.
This chart, while simple, is found to be
a great time -saver for general use in connection with audio systems.
_Newell
i1\'11
HIGH FIDELITY
MAGNETIC TAPE
RECORDER
(7I
Model 400
TERMINAL brings you
this new incomparable
15,000 cycle performance at 71/ inches per
second that equals the
performance of 15 IPS
full -track recorders
1
and gives 4 to 1 savings in tape cost.
2 FULL HOURS OF PROGRAM
MATERIAL CAN BE COMBINED ON ONE 10"
-
Position "B"
METER a. OUTPUT SWITCH
(level), connects meter "Line Output" plug,
and "Phones" monitor plug to the output of
the playback for monitoring of playback,
while recording or playing back topes. Position "A" connects "Line Output" plug, and
"Phones" monitor plug to the record amplifier for direct monitor of the incoming program. Under position "A" there are three
which
switch positions designated: LEVEL
connects the meter to measure record volume
level.
BIAS-which connects the meter to indicate
proper record bias.
ERASE -which connects the meter to indicate
proper erase current.
Toggle switch permits
SPEED CHANGE
quick choice of 71/2 or 15 i.p.s. tape drive
-
-
speeds.
Biased for
RECORD BIAS ADJUSTMENT
maximum output of 1000 cycle tone (factory
-
adjusted).
from page
21
the pentode section is the mixer. The variable oscillator uses a separate triode.
Each of the oscillators is coupled to a grid
of the mixer pentode by adding a pickup coil
to the tuning inductor and connecting this
to the pentode. Assuming that both oscillators are well shielded and the leads
dressed, the main danger of pulling comes
from capacitance between the triode and
pentode plates within the combination tube;
this is indicated by a dotted capacitor in the
drawing, and is by no means negligible.
The output of the pentode plate contains
components of both oscillator frequencies,
so that the variable oscillator frequency
may be coupled to the fixed oscillator
through the dotted capacitor, the lower part
of L, and the bypass capacitor C, to ground.
This creates a potential difference between
the triode anode and grid.
To prevent pulline, Cr is connected between the pentode plate and the upper end
of L. which is connected to the grid through
C,. This forms a bridge, the arms of which
are the two sections of the coil, the ca-
AUDIO ENGINEERING
REEL
-
Adjusts elec71/2" -15" EQUALIZATION
tronics for proper operation at Ph or 15 i.p.s.
Properly conINPUT TRANSFER SWITCH
nects input plug tor: I) 200 ohm microphones
such as R.C.A. 445X, KB -2C, etc.
II) Balanced
bridge for bridging telephone lines or balanced studio lines. Ill) Unbalanced bridge
100,000 ohm input for radio tuner, phono
pre -amp, bridging public address equipment
or unbalanced studio lines.
Volume level
FOUR-INCH "VU" METER
meter used to indicate proper record volume
level. This instrument can be switched for
several functions as listed under "Meter 8.
Output Switch."
OUTPUT LINE TERMINATION SWITCH
Places 600 ohm terminator across amplifier
when some is not externally loaded (This is
necessary for proper meter calibration).
Switch provides
OPERATION SELECTOR
for normal forward or fast forward or fast
rewind.
CUSTOM SET -BUILDERS
AUDIO PATENTS
'
.14,;11111.11t
-
-
-
-
AUDIO ENGINEERS
Terminal Radio can furnish promptly all components required
for FAS amplifiers and speaker systems, in addition to turntables,
pickups, and FM -AM chassis necessary to assure the superlative
performance of which FAS installations are capable. If you haven't
a copy of the Terminal Radio catalog on hand, write for one today
F REE. .. WRITE FOR
YOUR PORTFOLIO OF 15 IDEAS
FOR CUSTOM RADIO -PHONOGRAPH INSTALLATIONS.
This profusely illustrated booklet gives you actual photos of installations
settings.
in
typical room
New 1951 Terminal Sound Catalog now available
Write for your free copy
Distributors of Radio & Electronic Equipment
85 CORTLANDT ST., NEW YORK 7, N. Y.
DECEMBER, 1950
www.americanradiohistory.com
AmericanRadioHistory.Com
WOrth 4 -3311
Cable: TERMRADIO
47
ment. Zero- center d.c. dial is included for
FM discriminator alignment. Uses 41 -in.
meter. Complete information may be obtained from Allied Radio Corporation, 833
W. Jackson Blvd., Chicago 7, III.
Record Player -P.A. System. Portable
and self-contained within a single carrying case, the Rauland -Borg Model 1254
record player -p.a. system features a 15-
for location work, or as rackmounted equipment for studio installation. Frequency range of the system is
30-10,000 cps ± one db, flutter is only .04
per cent rms total, and signal -to -noise
cases
ratio is
57 db.
watt amplifier with mixing controls to
permit use of phono background with
live program material. Three -speed
changer is equipped with a dual -type
crystal cartridge and is designed to play
all types of commercial recordings up to
12 in. Heavy -duty 12 -in. speaker is supplied with 35-ft. cable and plug. Weighing only 40 pounds, the entire system is
Intermodulation Meter. Compact and
completely self-contained, the new Model
31 intermodulatjon meter recently introduced by Measurements Corporation.
Boonton. N. J., may be used as a labora-
tory standard in evaluating the performance of audio systems. The meter is
direct- reading in percentage of inter modulation and input volts. Among the
uses for which it is well suited are the
correct adjustment and maintenance of
broadcast transmitters, checking linearity
of film and disc recordings, adjustment of
bias in tape recording, and for quality
control of audio components and equipment. Model 31 is 8 in. high x 19 in. wide
9
in. deep.
housed in a dark green leatherette carrying case. Full description may be obtained by writing Rauland -Borg Corporation, 3523 Addison St., Chicago 18, III.
Tiny Precision Potentiometer. No
larger in diameter than a copper cent is
the new Model AJ Helipot potentiometer,
well suited for both commercial and military applications where space and weight
must be considered. Model AJ is a tenturn unit with an 18 -in. resistance ele-
Some
I
Perha
Brings You Record Fidelity
You Never Believed Possible!
ment, and is available from stock in eight
resistance values ranging from 100 to
50,000 ohms. Power rating is two watts
and weight is less than one ounce.
Further details may be obtained by writing for Bulletin 108 to Helipot Corporation, South Pasadena, Calif.
36-MM Magnetic Recorder- ReproPerformance standards of the
Motion Picture Research Council are surpassed in the new RCA magnetic recording system designed for high -quality professional magnetic recording in film
production. The new system is aimed at
reducing film and processing costs, and
providing greater flexibility in meeting
acoustical conditions. In addition to the
magnetic record -reproduce unit, the system includes a mixer amplifier, recording
amplifier, a bias oscillator for recording,
and an oscillator -preamplifier and equalizer for playback. Also included is a self contained high- and -low voltage power
supply. Both 16 -mm and 35 -mm systems
are available, either in portable carrying
ducer.
AUDIO ENGINEERING
"An exciting discovery," writes Edward Tatnall
Canby, noted authority on sound reproduction, in
The Saturday Review of Literature...
Like a baton in the hands of a symphony conductor, this remárkable new General Electric
stylus brings you the full tonal quality of recorded
music as you've never heard it before! Its feather light tip tracks the record groove with a compliance delicate enough to pick up frequencies
through 10,000 cycles per second!
Ask your dealer for a demonstration today!
H
and L ows
Ps the
this
eqery
inluctance
c/a
otexciting disfamiliar
iár
ade
G É reits long
playing cartridge
seems,
version.
has
already
forts t
problems, e vttal tracttng
meh
of
shingy
Ìbetter...typ,
If you have
the
needle h
dMult area.
--Enit;lRt,
.
eer
nyoptridge
ty7
acquire
progress
aa
T:lr1yALL
CANBY
HOW COMPLIANT CAN A NEEDLE
BE?
SEND FOR
BATON STYLUS
FOLDER -IT'S FREEI
SINGLE -TWIST
BATON
STYLUS
STYLUS
The single-Twist arm and single
damping block of this stylus were
designed for a tracking pressure
Reproduces each tone value with
amazing clarity. Tracks at 6
grams -thus providing the maxi-
of
21 grams. It was recognized,
however, that lighter pressure
would lengthen both record life
and stylus life.
mum degree of compliance that
may be used successfully with
commercially available tone arms.
-GENERAL
oa canrhai
wt
ro/aára!
Write: General
Electric Company,
Section 44120,
Electronics Park,
S y rature, New York
,
DECEMBER, 1950
www.americanradiohistory.com
AmericanRadioHistory.Com
ELECTRIC
51
Reluctance Cartridge Adapter. For
many users of Western Electric 9A Reproducing Equipment, an adapter head
which accommodates a standard variable
reluctance cartridge will be of interest because it permits the playing of microgroove records through the regular switch
and filter with a minimum of expense for
conversion. When the adapter is in use,
the impedance of the filter is matched to
the reluctance cartridge, and the usual
high - fidelity response is assured, together
with high output signal. For vertical and
lateral transcriptions the regular 9A arm
is plugged back into the arm, giving complete flexibility of playing equipment.
Further information is available from the
manufacturer, Broadcast Service Co., Arcade Bldg., St. Louis
1,
Tape Recorder. Although moderately
priced, the new Sonar Model T -10 tape
recorder is claimed by the manufacturer
to meet performance standards fitting it
for many types of professional application.
Amplifier response is 20 to 20,000 cps ± 1
db, and tape response is 35 to 12,000 cps at
7.5 In. per second, according to the manufacturer. Double -track automatic -reverse
recording mechanism permits one hour of
uninterrupted recording or playback. Literature may be obtained free of charge
from Sonar Radio Corporation,
Avenue, Brooklyn 1, N. Y.
59
Myrtle
Motors for Radio Use. For many applications in radio, small motors with a
wide range of speeds are occasionally required. The new Barcol YAZ motor is
reversible, and is equipped with a geared
head; it has high starting torque, and
electrodynamic braking for rapid stopping. The motor itself is the shaded -pole
type, producing no interference in radio
Mo.
leading audio engineers choose
BROWNING FM -AM TUNERS
for discriminating listeners
For custom installations, audio engineers know they must please the most
the serious
severe judge of high-fidelity
music listener. These engineers know, too,
resources
the
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that only
can produce such gratifying performance.
-
..
And that is why leading audio engineers choose from these BROWNING
models for their exacting custom installations.
MODEL RJ -20A FM -AM TUNER
.
Armstrong FM circuit; 20 db quieting
Separate r.f. and
with 61/2 microvolts
AFC on FM with
i.f. on both bands
AM bandwidth selecON /OFF switch
Driftcompensated
tion, 9 kc. and 4 kc.
FM audio 15- 15.000 cycles =11/2 db.
self 20 db treble and bass boost
contained power supply.
receivers, and a balanced rotor minimizes
vibration. In the open type, as shown,
these units are available with speed reductions from 20:1 to 360:1. Closed types
can be supplied with speed reductions
ranging from 7.2:1 to 1,333,800:1. For full
information on this line of motors, write
Barber- Colman Co., Rockford, Ill.
Gronuues Custom .tmpiitiers. A new
line of amplifiers designed for incorporation into home music systems as well as
for high -quality public address installations has just been announced by Precision Electronics, Inc., 641 Milwaukee Ave.,
Chicago 22, I11. Available in two chassis
types for three models, these amplifiers
MODEL RJ -12B FM -AM TUNER
are equipped with four input channels and
Armstrong FM circuit; 20 db quieting
Separate
with less than 10 microvolts
ri. and i.f. on both bands AFC on FM
Drift-compensated
switch
with ON /OFF
FM audio 15- 15,000 cycles =11/2 db
AM audio 20-6600 cycles ±3 db
Triple-tuned i.f.
MODEL RV -10A FM TUNER
Armstrong FM circuit; less than 10
AFC
microvolts for complete limiting
2 -stage
with ON /OFF switch
Dril tcascade limiter Tuned ri. stage
compensated High impedance output.
MODEL
RV -10A
-
Learn the full specifications for Browning
write for complete perhigh- fidelity
formance curves and data on these
models.
In Canada, address:
Measurements Engineering Ltd.
Arnprior, Ontario.
B R
O W N
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Laboratories, Inc.
Winchester.
52
means for convenient switching from
magnetic pickup, crystal pickup, microphone, or radio tuner. Model 200 PG has a
separate control unit which may be operated remote from the main amplifier chassis, which has a power output of 20 watts
with less than 0.5 per cent distortion or
10 watts at 0.1 per cent distortion. Models
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DECEMBER, 1950
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60
10
Magnetic Reproducer. Availability of
the Type L -6 Polyphase pickup with
special connector for plugging into the
Webster changer tone arm is a recent
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Lions and recording studios. The machine
employs a continuous loop of magnetic
tape with suitable amplifiers and control circuits so as to add any desired
amount of reverberation with a controllable decay time. Also shown was a
complete line of attenuators, both of the
conventional type and the newer lever
type, believed by many engineers to be
more convenient in use.
Terminal Radio Corporation exhibited
only a small number of the many lines
they represent in New York, but featured
in their display was the Ampex line of
magnetic recorders. Both the 300 in
portable cases and the newer model 400
were shown, with performance of the
high quality to be expected from the
Ampex machines.
The Tetrad Corporation brought a
valuable collection of diamonds to the
Fair and displayed them in a glass case
under the protection of a uniformed
patrolman from the city police force.
These diamonds were industrials which
will be processed into styli for use in
pickups, and the total value of the collection was claimed to be $102,000. Also on
display were a number of charts showing
the faulty tracking resulting from worn
styli, together with a number of photos
showing the stylus wear resulting from
the use on a relatively small number of
plays, using both diamonds and sapphires.
Transit Sound Systems Co. Inc. exhibited a new machine which uses a
1% -in. tape which plays back and forth
on twelve parallel tracks, permitting the
playing of a continuous program from
10 to 20 hours long. The machine uses
multiple heads, making it possible to play
any of six different tracks as selected,
on a single channel, or to have six differ-
ent programs playing on a number of
channels, thus giving the listeners a
choice of programs. Operation is as simple
as a home radio, with a single switch to
turn the machine on or off; after running
the tape through in one direction, it re-
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DECEMBER, 1950
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53
verses automatically, and continues. Production of this machine is to be started
immediately, with completed models expected in from 90 to 120 days.
Triad Tnutsfornur Mtg. Co. exhibited
a full line of transformers for high quality audio use as well as for a number of geophysical applications. The popularity of the line of audio and power
transformer is attested by the list of
users, which includes such names as
Gates, Concertone, McIntosh, Magnecord,
Presto, Newcomb, Lear, Audio Pacific,
Westrex, and others of equal importance
in the field. The Triad line, although relatively new to audio, is well established on
the Pacific coast, largely because of the
ability and reputation of the designer
and chief engineer, Lou Howard, who has
been responsible for the design and production of quality transformers for many
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54
1'. S. Recording Continuo introduced a
portable transcription and record
player employing an all -play stylus and
reproducing through a small speaker
mounted in the cover of the case. The
quality of reproduction would serve admirably in applications where a portable
equipment would be used, and was considerably above the average for similar
equipment. An item of great interest to
most visitors was the spring- driven
magnetic recorder designed for portable
use, and shown as a sample of the work
being done in Germany at the present
time. It is said that negotiations are
being carried on for the manufacture of
this device in the United States, and it
is thought that such a device would be
well received.
I.1i11e1 'l'rtutsformer Company exhibited
a complete line of audio and power components ranging from the smallest
models used in hearing aids up to the
largest used in amplifier service. Also
shown were a number of completed
amplifiers, following the circuits published in UTC literature. From the performance obtained. it is obvious that the
equipment will satisfy the needs of most
users, and the wide variety of transformers in the line ensures full coverage of
all requirements.
University Loudspeakers, Inc. displayed a number of speakers for p.a.
systems of various power requirements,
as well as the line of cone speakers.
coaxial units, tweeters and horns. One
feature of the exhibit was the display of
a cabinet containing a three -way speaker
system with separate controls on the
three ranges. The "highs" channel covered the range from 3000 to 15,000 cps,
the "middles" channel covered the range
from 300 to 3000 cps, while the "lows"
channel covered from 45 to 300 cps.
Separate control of these channels made
it possible for the listener to determine
for himself the effect of varying the response of the sections, and pointed out
the need for good balance throughout
the entire audio spectrum.
With the closing of the exhibits on
Saturday afternoon, both exhibitors and
visitors alike began to plan for the third
Audio Fair, which will be held in the
same place on Nov. 1, 2, and 3, 1951.
Many exhibitors have already expressed
their desires for the same or for more
space, and will of course have first choice
of the rooms they occupied this year.
Several other organizations not yet represented at the Fairs have already indicated their intention of being in next
year, so it is certain to be bigger and
better as time goes on.
new
Zone
Stag
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
DECEMBER, 1950
SUPERIOR RECORD
RECORD REVUE
with SMOOTH RUNNING, NOISELESS
Ii r 0111 ri !/,' 30I
is not audio but music.
In an exhibit with which I was connected
we insisted on keeping the door closed, with
a sign, "OPEN -COME IN" on it, because the instant the door opened the music
we were trying to sell was utterly destroyed.
No music lover worth his salt will listen
to more than one source of music at a time.
I think we garnered a fine harvest of
good will among the mousy music lovers
in that exhibit and I see no reason why
others should not, in Audio Fair III, share
the happy results with us.
Therefore I respectfully-and I. hope,
constructively- suggest that in future exhibits of audio equipment the exhibitors
ponder these principles.
1. Keep your door closed, so that one
source of music, no more, is audible at a
time. Elementary musical principle.
2. Study your room acoustics and deaden
one or two walls with cloth, for good sound
quality. Adds to the visual effectiveness of
your exhibit, as well.
3. Place speakers carefully -in a corner
when possible, and at a distance from the
spot where visitors congregate. There was
enormous variation between good and bad
in this respect at this year's show.
4. Remember the timid music lover and
respect his intentions keep the average
loudness level down low ; save your full
volume for short tests. A good 30- second
burst at full volume will do far more to
impress your audience than a steady pounding can ever do. With average volume low,
you will not drive away customers, as too
many exhibitors did this year.
5. Use good records, new ones, and make
a point of handling them carefully in front
of your visitors. Record collectors are
highly sensitive about this. A pile of dusty,
scratched -up unprotected records is the
worst possible kind of publicity for an audio
exhibit! Make a point, too, of the music
itself, as far as you are able; be aware of
what is playing, keep the record album in
plain sight. A wise exhibitor will have at
least one knowledgeable person on his staff
who can show an intelligent interest in
music -enough to gain the visitor's confidence. (He doesn't know too much himself, after all.)
6. EQUALIZE! Yes, there are plenty of
audio equipment purchasers who want highs,
highs, highs. But there are plenty more who
want faithful reproduction and are out to
buy it. That means correct equalization for
the high pre- emphasis in most commercial
discs. Your machine will never sound the
worse for proper equalization. Again, if
you want to demonstrate highs -do it in
short bursts. But return to the proper setting in between.
7. An after-thought : Many audio exhibitors arrived at the Fair with much audio
equipment and not a thing to play on it.
Both tape and disc machines were shipped
mute, so to speak, until some frantic staff
member could dash over to Macÿ s and buy
the first record that he could get hold of, or
until some other exhibitor would kinrll;
lend a tape. The business of audio is music.
Bring along a good selection of records.
chosen carefully, and have them in plain
sight, where music lovers can see them
and approve. It will do you no harm (and
may bring you new followers) to display
.1
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For every type of recording, a continuously
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Using 33 1 /3 RPM on a 15 minute run,
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the variation was only 2 RPM in 500. On constant voltage, the speed variation was only
/4 RPM or 0.05 per cent.
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ale
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55
a bit of Mozart and Bach and Beethoven.
Even if it never gets played.
So here's to a musical Audio Fair III.
4
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The long awaited compilation of reprints from early issues of
AUDIO ENGINEERING, most of which are unobtainable.
Contains 37 articles on the following subjects:
Amplifiers
Phonograph Equipment
Speakers
Tone and Loudness Controls
Noise Suppressors
Dividing Networks
These articles have been of great interest to readers of AUDIO ENGINEERING over the past three years. Assembled in one volume, they comprise
the most authoritative reference work for the audio hobbyist.
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56
Zone
REB LP
REB 3
#3 (1901 04) ; Music of
It was surely a milestone of some sort or
other in American musical history when,
'tother week, no less than three copies (it
sounded like more) of the Varèse recording
listed above were used at the Audio Fair
to demonstrate hi -fi audio equipment!
Varèse, no less than Ives (of an earlier
generation) has been one of the lost pioneers of ultra -modern music, than which
nothing could be further removed from
electronic engineering -or at least until
now. Varèse is a Frenchman to the core,
in spite of his long residence in the U. S..
and an artist of the longest- haired sort you
can imagine ; but he was one of the first
to discover that things like sirens and bottles and assorted bits of heavy machinery
could be used to make music of a new sort.
His music, in the 1920's, was violently, incredibly radical. Few ever heard it. Now,
in the 50's, it sounds just as radical as ever
-but it makes the most superb hi -fi material for wide range recording. And so
Edgar Varese comes into his own ! The
Varèse record consists of one work for
massed percussion (including sirens), another that surely holds all "records" for
sheer potency of brassed dissonance, and
several more works that fall between these.
You will either howl with pain or giggle
with amusement -but remember that
Varèse is held in very great respect by
musicians, that his noisy experiments led
to much that is already a solid part of
today's music and quite taken for granted
by you yourself.
Points of interest above: Note the listing
of four tiny companies (two record shops,
a lone engineer and a cooperative radio station) which can between them stand up to
the very best on LP from any of the large
companies. Such is LP recording these
amazing days. The smaller companies, dozens of them, are beating the biggies at their
own game.
Ives as a lone wolf experimenter in the
1900 period, also contributed much that is
now taken for granted in music. His 3rd
symphony is a mild work, based on old
fashioned hymn tunes, mostly scored for
strings, and you will find it quite agreeable
though in 1904 it was highly ccentric.
Very nice, quiet string recording, with
what seems to be flat high end. Good.
Schutz and Gabrieli, from the 17th century, were two earlier experimenters. The
Gabrieli brass music makes a superb record,
as done in the live studio at Reeves in New
York. (Note that clean, simple brass har-
'
Board cover
Name (print carefully)
City
by Arthur Mendel.
the Am. Revolution.
National Gallery Orchestra, Bales.
WCFM LP
Now Available!
.
Wm. Hess, Paul Matthen, conducted
LP -1
Agents' inquiries invited
98 Jay Street,
Paper cover
The Cantata Singers; Charlotte Bloecher,
Ives, Symphony
Orders accompanied by check or money order mailed prepaid
You pay postage if we ship C.O.D.
4CONe
ES 503
(The Christ-
mas Story).
di poisi1 /e /or your recorcinf/ enI{tudiall frienJi
SOLD ONLY BY
Brass Ensemble, S. Baron.
Esoteric LP
(3 reel lots)
"Reel Your Own " -3900 -ft. roll
Intégrales; Density 21.5; Ionization; Octandre.
Rene Le Roy, flute; N. Y. Wind
Ensemble, 'Willard Percussion Orch.,
Waldman.
EMS LP
Varèse,
State
AUDIO ENGINEERING
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DECEMBER, 1950
monies allow for very high levels with relatively little tracking trouble.) Gabrieli practieally isweaoted-., iustrumentai `orchestral"
music right here, applying the earlier choral
techniques to massed groups of brasses.
Schütz, writing in the dreary days of the
30 Years' War in Germany, developed much
of the mixed voice -and -instrument style
that Bach and Handel later used. Engineer
Robert Blake (REB) obviously has a fine
ear for miking this difficult variety of music
and his record is worth an engineering
study quite aside from the music itself.
Trumpets, recorders, organ, solo voices,
orchestra, chorus et al. Blake also recorded
the Varèse LP.
Bizet, Carmen Suite: Smetana, Die Moldau
Orch. of the Viennese Symph. Soc.,
Singer.
Remington LP
RLP 149 10
110 ")
Schubert, Symphony #1; Mozart, Fantasia
in F minor, K. 608.
Orch. of Viennese Symph. Soc.; Vienna
Symphony, Fekete.
Remington LP
RLP 199 -2
MODEL 71
112 ")
Here are two of the best from the first
batch of the new bottom priced Remington
LP's, sold through department stores. The
new material and /or processing method
gives a surface that hisses quietly, like fine
British shellac -hardly objectionable. As to
durability, I couldn't say. Also, there is little in the way of quality that will interest
a hi -fi man, some of the recording being
thin and (on a good outfit) considerably
distorted. But the Carmen- Moldau recording above, is really excellent -no complaint
at all and the Mozart is good, too, though
the Schubert on the other side is of the distorted type.
Important point for music -lovers is that
there are a number of quite unusual musical
items already in the list, a development that
was hardly to be expected; the Mozart
Fantasia, originally for mechanical organ,
is one-though the arrangement and playing are both poorish -and another is the
superb voice of Elizabeth Wysor in a potpourri of operatic arias. Keep an eye on
these.
OF
MANUFACTURERS
Generators
Standard Signal
Pulse Generators
Generatms
FM Signal
Generators
Square were
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SPECIFICATIONS
5 to 100,000 cycles.
WAVE SHAPE: Rise time less than 0.2 microseconds
with negligible overshoot.
OUTPUT VOLTAGE: Step attenuator giving 75, 50,
25, 15, 10, 5 peak volts fixed and 0 to 2.5 volts
contiruously variable.
SYNCHRONIZING OUTPUT: 25 volts peak.
R. F. MODULATOR: 5 volts maximum carrier input.
rans ation gain is approximately unity -Output im-
FREVENCY RANGE:
pedance is 600 ohms.
I7 volts, 50 -60 cycles.
POWER SUPPLY:
1
DIMENSIONS: 7" high x
1
5
" wide
x 7I..2 "deep. overall.
Indicators
FM
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MEASUREMENTS
BOONTON
;
©
CORPORATION
NEW JERSEY
The HIT of the AUDIO FAIR
Plays 101/2" Reels!
Brahms, Symphony #4 in E minor.
Boston Symphony, Munch
RCA Victor LP
LM 1086
Rachmaninoff, Piano Concerto
1.
Wm. Kapell; Robin Hood Dell Orch.,
Steinberg.
RCA Victor LP
;
LM 1097
Here are two standard works re -done
under new RCA auspices and on LP, and
the slight perplexity noted last month re
RCA's LPs continues -even though both
of these and plenty more like 'em are excellent recordings.
The new Boston under Munch is a
lighter, more streamlined orchestra in the
sound than recently under Kousevitsky.
The Brahms is given a nicely tailored.
rather French performance that suddenly
turns positively furious in the coda to the
third movement and in the last movement.
Interesting. The Rachmaninoff meanders
its involvedly Romantic way, about as it
always does (to my somewhat jaundiced
ear) and my best comment is technical, that
the piano is nicely balanced, a bit dead
sounding, the orchestra well adjusted in
volume but too much in the background as
to liveness perspective.
As to recording characteristics -doubt.
The Boston recording is on the beam, i.e.
AUDIO ENGINEERING
Complete, for
console installation with
single or dual track heads:
CONCERTONE
"rho profession. quality tape recorder you have been waiting for!
AB standards; tr.odes throughout; 40-15000 cycles at 15 ", 40 -8000
cycles at 71/2". Three motors; flutter less than 0.1 %; signal -to-noise
better than 50 db. Three heads for simultaneous erase, record, playhack. Quick change fron single to dual track. Write for booklet.
C
N
FISHER RADIO CORPORATION Distributors 45 E. 47th St., N. Y.
Los Angeles: Magnetic Re:* dcrs Co., 7120 Melrose Ave., Los Angeles 46, Calif.
In
DECEMBER, 1950
www.americanradiohistory.com
AmericanRadioHistory.Com
57
AMPERITE
Studio Microphones
at P.A. Prices
Ideal for
BROADCASTING
RECORDING
PUBLIC ADDRESS
"The ultimate in microphone quality." says
Evan Rushing, sound
engineer of the Hotel
New Yorker.
Shout right into the
new Amperite Microphone -or stand 2 feel
away-reproduction is
always perfect.
rities-Rachmaninoff's
Not affected by
Models
any climatic conditions.
Guaranteed to with.
stand severe "knocking
around."
RBLG -200 ohms
RBHG -Hi -imp.
List
$42.00
"Kontok" Mikes
Model SKH, list $12.00
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Introductory
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Especially designed by CONCORD engineers to
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bass and treble controls with flat position-- bass gives 10db boost, treble gives 12db boost
and 14db attenuation. Freq. resp. at rated output 40 -15,000 cps tldb. Tubes: (2)6V6, 6SL7,
6SC7, and 6X5 rect. For 117 V, 60 cycle AC.
Brown hammerloid finish. Size: 10 -1/2 z 6 z
5 -1/4 ". With tubes.
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ATTENTION
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-F'I CUSTOM INSTALLERS
Write on business letterhead for information on
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Service designed especially for custom installation men. Write now for FREE information.
CONCORD RADIO CORP.
r
901
Mail Order Center and Showroom
West Jackson Blvd. Chicago 7, Ill.
CONCORD RADIO CORP.
Dept AM -50
901 W. Jackson Blvd. , Chicago 7, Ill.
O Enclosed $
(include shipping charge.
Any excess will be refunded.)
Music Lovers Amplifiers @ $29
O Send FREE latest Bargain Bulletin
Name
Rush
Address
L
58
City
of the sort one now expects from that section of RCA : a clearly distant -mike technique that seemingly dulls the highs on first
hearing (no sharp edge to the strings, etc.).
Yet a perfectly legitimate musical sound
from the concert hall viewpoint-probably
more "natural" than the forced brilliance
of the famous ffrr technique with its steely
sharp tone qualities. The Robin Hood Dell
is a Philadelphia offshoot, recorded in the
Academy of Music, reportedly a very fine
hall for music. This recording is deader,
decidedly, than the Boston recording, the
orchestra similarly distant -miked, by the
sound. Strange-but this one will play very
nicely with only slight roll -off. If it was
not recorded "flatter" than others of the
RCA line, then we have here one of those
combinations of mike technique (softening
of the highs via distance), actual acoustics
and, most important, the composer's sono-
Zone
-
State
50
tend towards the
dark and fusty. Try this one yourself and
be convinced. Not a good recording, however you play it (compare, if you wish,
with the first mvt. of the same music on
the "Twilight Concert" disc reviewed below) ; the piano is tinny, hard, there is no
real bass nor much in the highs of interest.
(In any case, the more I listen the more
am I convinced that mike technique greatly
affects the apparent "curve" of a finished
recording and so, in practice, the equalization that must be used for a balanced sound
in the reproduction.)
"Twilight Concert."
The Columbia Symphony Orchestra,
Bodzinski.
Columbia LP
MI 4311
Sir Thomas Beecham conducting the
Royal Philharmonic and the Columbia
Symphony Orchestras.
Columbia LP
MI 2134
Here are two useful and pleasant potpourris of assorted stuff (too much to list,
but the titles are mostly very familiar)
that most engineers will want to have
around for general test and background
purposes. The Twilight Concert, with eight
numbers including the first movement of
the Rachmaninoff Concerto above, is a
model of excellent recording with fine
acoustics, low distortion, smooth, deep per-
THIS
GET
IN
BUILT
-
TWIN DRIVE
with
CROSS
OVER
4-
and
FEED - BACK
FOR
XMAS
The idea of crossovers and twin units seems to have
gut such
grip that some U. S. friends ask us why
we don't make such things. Well, of course we do,
oily we do it better and build the whole lot into one.
dose of self adjusting feed back which no other
plus
waken. single. twin or triplet. possesses. Our drive
Is patented in U. S. A. as elsewhere and only genuine
Barker speakers have Its resultant quality of full audio
requency range plus freedom from significant resonances plus dead beat motion which pin -points transients and detail, plus an overall smoothness making
highs, middles and lows equally clear -cut and true.
You may ask: Ah! but what aiwut that large cone?
If our cone was normal that might hit home. but again
It is
patented special with perfectly graded compliance from apes to rim, making it comparable with
a whole series of matched cones covering the needs of
efficient radiation from below 40 to over 15,000 rim.
Back to the drive: It Is a very thin, light metal tube
fixed to the cone apex. On It is a coil of fine wire over
skin of long life stabilised latex. Up to the middles
the latex won't lies so the coil drives. but as the
frequency rises the latex gives and the metal tube
takes over by induced currents, giving efficient drive
to beyond audio limits. A simple but true dual action
with in- built, truly matched cross -over. And how the
feed -back? Send for details of the Barker Model 150.
12 ins. unit with 17.500 gun' magnet. ¶60 post
,and I burxure paid to your home ACT NOW!
+
NATURAL SOUND REPRODUCERS
BCM,'AADU, LONDON, W.C.1, ENGLAND.
BARKER
"HAU HEARD
QUALITY?"
THE SOUND
OF
-))))
spective, excellent low bass as well as fine
highs, sharp but not too sharp. Sir Thomas
(who offers the least interesting music)
gets similar sounds from the same Columbia
Orchestra on his ten -inch disc, one side
of which he made here; but the Royal
Philharmonic sound is noticeably duller,
less live, not as satisfactory, by any means.
Who said we couldn't match the British?
Incidentally-here's the same old story:
your tendency will be to boost the highs
a bit for the Royal, to compensate for duller
acoustics; and yet (with tape) the chances
are good that the actual recording curve
is the same for both sides of this record.
e s s s
Obvious conclusion to this month's technical look -see at new recordings: Can't
somebody get after the haughty big companies and badger them into at 'least nominal conformity to one LP curve or perhaps
better, an area of tolerance in respect to
recording curve? By which I mean an accepted set of outside limits, as to : urnover,
pre- emphasis, within which 211 companies
agree to operate. The tolerance should be,
art course, small ideally but it will have to
be quite large practically. Still-even such
wide tolerance as, say, between 400 an+i 600
cps turnover and between 8 and 12 db preemphasis at 10,000 would be immeasurably
better than the constant doubt, to w'hieh
we are now subjected.
Jr
NEWCOMB SOUND
BETTER
Manufacturers of public address, mobile,
phonograph, musical instrument and wired
music amplifiers
Portable systems
Port
able phonographs and radios Transcription
players
Rack and panel equipment.
Write today! Circle items of interest and
indicate whether you ore a Dealer, Parts
Jobber or Sound Specialist.
NEWCOMB AUDIO PRODUCTS CO.
DEPT. T, 6824 LEXINGTON AVE.
HOLLYWOOD 38, CALIFORNIA
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
'
DECEMBER, 1950
(
udio
AES NEWS
A
[from pay,
-I
TIME -TESTED
year term), Arris Geranis, chick engineer,
WECK, Battle Creek, Mich.
Larry Wells, chief engineer for the Allen
Electric Company, has been appointed Program Chairman for the coming year. Section meetings are held the third Tuesday of
each month with the exception of June,
July, August, and December. Members of
other sections who may be traveling through
the area are invited to attend meetings of
the Southern Michigan Section, and may
obtain information about the time and meeting place from any of the officers.
DEPENDABLE
SOURCE
t.
FOR
HIGH -PRECISION FRACTION.
H.P. INSTRUMENTTYPE
AL
MOTORS
O D U
P R
&
C E
GENERATORS
D
T
O
O
E
O
R
GOVERNOR.COHTIOLLED
NEW Intermodulation Meters
r
These are self- contained, precision instruments for the accurate direct -reading of
per cent intermodulation. Compact, both
have integral, high quality signal generators to provide the mixed two-frequency
tone for test input. The output from apparatus under test passes through the
analyzer section for conversion and meas.
urement on the built -in meter.
EEO SYNCHRONOUS
Cu.
DRAG
I ACCELERATION
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flill.
HYSTERESIS
o
meet
a THREE PHASE
U«
a
T
0
r.9u
niqu.
Wenn
m. of wit.
SERVO
.
. .as«
TOTALLY ENCLOSED
EMPLOYMENT OPPORTUNITIES 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 Secretary,
Audio Engineering Society, Box F,
Oceanside, N. Y. before the first of the
month preceding the date of issue. Replies to box numbers should be addressed to AUDIO ENGINEERING, 342
Madison Ave., New York 17, N. Y.
PLy.
DYNMICLLY PARED
.icvlly.
REILMOTOIS
Tern
TwO
Specially designed for factory production
testing and laboratory work, this versatile
meter makes both low and high frequency
tests -since it includes adjustable voltage
ratio and frequency. Low test frequency:
60 cps from internal oscillator, or 40 -150
fps from your own oscillator. High test
frequency: 2, 7, 12 kc from internal oscillator, or 2 -20 kc from your own oscillator.
Signal generator output: + 8 dim. 600
ohms. Analyzer input: 1 volt min., 500 k
ohms. LF /HF voltage ratios: 4:1, 1:1.
Voltage ranges: 3, 10, 30 v. Intermodulalion : full -scale ranges of 3. 10. 30 %. Panel
r, 7
19-. Power o apply: 117 v., 60 cps.
%le9i,d14n
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RELUCTANCE
OC
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cling
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engineers of
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factored .n.s .,ond
PERMANENT MAGNET
AC
«tiry
FA
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COMPOUND
ONE
nm
'
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SERIES
a.
Wet WOO
ELECTRIC INDICATOR
1
Highest Professional
Flexibility at Low Cost!
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PARKER AVENUE
STAMFORD, CONNECTICUT
L
* Positions Open
.
Of n .maim tl a- .Ilility, this precision lab.
ratory instrument covers an exceptionally
wide LF range. Ideal for disc reproducer
testing at 400 and 4000 cps as recommended
by H. E. Rays -and for system testing with
all usual frequencies. 41"I measure- noise
i
levels.
Positions Wanted
MODEL 170 GALVO -PROTECTOR
Connected between the V hcatsionc Bridge
and your galvanometer, it prevents meter
damage and speeds Bridge balancing. Its
non -linear element is an automatically
changing shunt for the meter. keeps
from far-off- balance
the pointer on-scale
through perfect-balance adjustments.
* Very-
('onlldential. Three of the nationally known television manufacturing
companies have come to us for:
1.
2.
3.
ing all component parts for television manufacturing.
Dear Sirs: tun
short
ag
ta friend
-
puT-
cnased one o
ran
transform.
your
ors.
His enthuknew
WRITE
NOW FOR CATALOGA
These positions will pay $10,000 up and
require the highest grade ability. Send
full details of your experience, age, salary
of
Massa
mbusetts
-
Quality Control Engineer
Receiving Tube Engineer
Purchasing Director who has experienced buy-
requirements privately to
Interna-
for
you
1
date
I might
Money
ss with You
ers
business
tional
reLoam
doing
rans
transformers.
d
that
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looking
Tecomta
recommendation
after
Sincerely Yours.
ceived.
am
a*0'
New Model Type 2830B. PH. 10,000 ohm est.,
Incremental Ind. over 100 H. Sec. Z 1.25 ohm,
2.8 ohm, 5 ohm, 7.8 0100. 11.3 ohm, 15.3 ohm
and 20 ohm. Leakage reartanee under 15 mh.
40.0- x 31/4'.
x 4- x 80. F.C.
Size: 5'/e
Weight: 12 IbS. Today's Price: $13.00 post
free, duty extra.
SAVAGE TRANSFORMERS LTD.,
Davie., Wilts. England
`',y,SFOahe4
DEVIZES
(SAVAGE
MIr
AUDIO ENGINEERING
INSTRUMENT COMPANY
Thorndike Deland
1440 Broadway.
New York 19, N. Y.
l
bounds w
Dept.
7C
133 W. 14th
ST.
NEW YORK
II,
N. Y.
We are retained by our clients and do not
charge the individual. All negotiations
handled confidentially.
4( Motion Picture Technicians. The Signal
Corps Photographic Center is interested
in receiving applications from experienced motion picture technicians for
openings as: film editors, recordists,
mixers, cameramen, laboratory technicians, scenic artists, scenario writers,
directors, animators, animation photographers, studio carpenters, grips, property men, studio electricians. and film
librarians. Salaries range from $3450 to
$6400. Those interested should write to the
Signal Corps Photographic Center, 35 -11
35th Ave., Long Island City 1, N. Y.
DECEMBER, 1950
www.americanradiohistory.com
AmericanRadioHistory.Com
'
Available to you direct ham the factory al savings
that make TWIN -TRAX the only professional -type recorder in the popular -price field. More than a dozen
model variations for portability, long -play, continuous operation, ele. For a better lope retarder that
combines professional quality with operating ease
and trouble -bee construction, it's TWIN -TRAX. Write
today for complete literature.
AMPLIFIER CORP. OF AMERICA
New York 13, N.
398 -4 Broadway
Y.
59
CLASSIFIED
Rates: 10e per word per Insertion for noneommerelal
advertisements; 2Se per word for commercial odor.
tlsements. Rates are net, and no discounts will be
allowed. Copy must be accompanied by remittance ln
fall, and must reach the New York once by the first
of the month
ing the date of Issue.
Equipment
WE PURCHASED a Brush Wire Recorder
($800 with extras) to fulfill two -year contract
with national detective bureau for secret recordings. Contract has expired. For three hours
of amazing wire recording quality (50 -8000)
without wows or extraneous noises, this recorder
is peerless. In pinches, we have recorded music
from which masters were dubbed. Price $175.00.
Reco -Art Co., 1305 Market Street, Philadelphia
7, Penna.
FOR SALE: Two UTC LS -50 transformers,
one each LS -12X, HA -101X, LVM -1 (500 -ohm
line to v.c.). Entire lot, $25.00. Box CD -1,
AUDIO ENGINEERING.
FOR SALE: Custom radio -phono assembly in
one -piece solid walnut cabinet, with Hallicrafter
AM -FM chassis, JAP -60 spkr, Webster 100-27
with GE dual pickup, 7 cu. ft. infinite baffle
chamber, Kimsul lined. $410. New York area only.
Box CD -2, AUDIO ENGINEERING.
PRESTO 90-A amplifier for portable or studio
recording. 30-15,000 cps, three microphone inputs,
Weston VU meter. equalization selector, line recording, public address. Excellent condition.
$225.00. Reco -Art Company, 1305 Market Street,
Philadelphia 7, Penna.
ELECTRONICS
TECHNICIANS
WANTED
The RCA Service Company, Inc., a Radio
Corporation of America subsidiary, needs
qualified electronics technicians for U. S.
and overseas assignments. Candidates
must be of good character and qualified
in the installation or maintenance of
RADAR or COMMUNICATIONS equipment or TELEVISION receivers. No age
limits, but must have at least three
years of practical experience.
RCA Service Company offers comprehensive Company -paid hospitalization,
accident and life insurance programs;
paid vacations and holidays; periodic
review for salary increases; and opportunity to obtain permanent position In
our national and international service
*Electronic Sales Engineer. To sell top
quality line of broadcasting, recording and
motion picture studio sound equipment
and components in New York Metropolitan area. Must have five years experience
in sales of this type of equipment. Salary,
commission, and expenses. Box 1201.
*WANTED: Signal Corps Center, Fort
Monmouth, N. J. has openings in the following Civil Service positions:
Military Instructors-Microwave relay,
radar, radio electronics, fixed station
radio, central office techniques, teletype
installation and maintenance, repeater
and carrier, dial central office maintenance, theory of electricity. $3100 -4600.
Electronic
60
AUDIO CONSULTANT
J
Sound Recording. Instrumentation
370 RIVERSIDE DRIVE
NEW YORK 25, N. Y.
In
$3100 -6400.
Custom -Built Equipment
Recording Co.
U. S.
Technical Writers -Write, edit, prepare
technical publications, handbooks, circulars, instruction books, etc. Edit and revise scientific manuscripts on radio, radar,
electronics, communications, and photography. Write instruction manuals on theory, operation, and maintenance of Signal Corps equipment; determine media
and method of presentation of material;
prepare charts, graphs, schematic diagrams etc. $3100 -5400.
Applicants for any of these positions
should write Chief, Civilian Personnel
Branch, Signal Corps Center, Fort Monmouth, N. J., submitting a completed
Standard Form 57, "Application for Federal Employment" (obtainable at any first
or second class post office) for review before going to Fort Monmouth for a personal interview.
Vermont Ave., Washington 5, D. C.
1121
STerling 3626
Consultation
Design
MARCH OF DIMES
Fabrication
Audio Facilities Corporation
133
West 14th Street,
New York 11, N. Y.
HERMAN
LEWIS
GORDON
Registered Patent Attorney
Patent Investigations and Opinions
Warner
Building
Washington 4, D.
100 Normandy Delve
Silver Spring, Md.
C.
Shepherd 243E
NAtional 2497
FIGHT
N FAN TI LE
PARALYSIS
1
RICHARD H. DORF
AUDIO CONSULTANT
Sound Systems
Product Design
Recording Installations
Technical Literature
255 W. 84th Street
New York 24, N. Y.
supervisory ability.
Qualified technicians seeking an advantageous connection with a well- established company, having a broad- based,
permanent peacetime and wartime service program, write to
Mr. C. H. Metz,
Personnel Manager,
RCA Service Company, Inc.,
Camden 2, New Jersey
C. J. LEBEL
design. development, modification, construction, and testing of electronic equipment- radio, radar, wire communications,
instrumentation, sonar, etc. Responsibility deepnding upon experience and ability.
organization, engaged in the installation
and maintenance of AM, FM and TV
transmitters, electronic Inspection devices, electron microscopes, theatre and
home television, r -f heating equipment,
mobile and microwave communications
systems, and similar electronic equip-
ment.
Rase pay, overseas bonus, payments
for actual living and other expenses,
and benefits mentioned above add up to
$7,000 per year to start for overseas assignments, with periodic review of base
salary thereafter. Openings also available at proportionately higher salaries
for specially qualified technicians with
Engineers-Participate
PROFESSIONAL
DIRECTORY
Phone
Schuyler 4 -1928
AUDIO ENGINEERING SCHOOL
Practical engineering training In Audio fundamentals,
Disc. Film. Magnetic Recording. aril Audio frequency
measurements.
Studio training simulates Broadcast. Motion Pictures,
Telerialon, and Commercial Recording work.
JANUARY 15-31
Approved for V
Hollywood Sound Institute, Inc.
1040 -A North Kenmore. Hollywood 21, Calif.
Spicily if Vetaran or Non -Veteran
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
DECEMBER, 1950
i
SENSATIONAL NEW BOOK
NEW LITERATURE
DIAMOND
Phonograph Needles
It is becoming more and more widely
known that a perfect diamond playback
stylus possesses many advantages over any
other type of needle. Some of these advantages are 111 preservation of records
especially LPs -from wear, and (2) savings
on needle replacements. One Televex diamond stylus will outlast 50 to 100 sapphires,
vet costs only about as much as 10 sap-
-
t
phires.
The Televex diamond styli are the finest
that can be made, are unconditionally
guaranteed, and have been recommended
by leading record critics. They should not
be confused with cheaper diamond needles.
To obtain the full benefit of a diamond
stylus, it is necessary to get the best diamond stylus. It may cost a few dollars more.
but in the long run it is by far the cheapest.
To order, send a sample of the needles)
used in your playback equipment, or if more
convenient send the entire cartridge (except
Pickering). Price for replacement of sapphire tips is $15.00, metal tips $16.00. If
both LP and standard replacements are
ordered at same time, deduct 10%. (Record
changers, etc. with diamond styli available.
Specify make, model and cartridgels) de,,red. Prices quoted without obligation.)
I
LLEVLA
NEW YfORK 63.íN. Y.
Cinema Engineering Co, 1510 W. Ver dugo Ave., Burbank, Calif. is now issuing
Catalog 14 -R titled "Non- Inductive Wire Wound Precision Resistors". The catalog
describes a line of resistors ranging in
accuracy from one per cent to 1/20 of one
per cent, and in wattage capacities from
one -quarter to 10 watts. Charts and illustrations are included.
DIAMOND $9.75
T Y L
EACH
POSTPAID
I
Made from WHOLE
natural DIAMONDS
unconditionally
GUARANTEED!
At the ir.
,.paid, our
., ",.w.o we are
diamond ,i
the only manufacturer offering diamond
styli direct to the consumer. Without
diamond stylus, your valuable records run
the risk of damage unless You change
needles at least every 20 hours of playing time. A DIAMOND tipped needle
will last
minimum of 1000 playing
boon without causing any damage to
your records, while giving you highest
fidelity reproduction and NO distortion.
Using ordinary eedles for the same
1000 hours could cost you as much as
890.00 in needle replacements.
i
Newcomb Audio Products Co., 6824
xington Ave., Hollywood 38, Calif. has
just published a complete new catalog
featuring Newcomb portable sound equipment for schools, churches, clubs, etc. All
items are illustrated and thoroughly described with detailed specifications. Catalog will be mailed free on request.
Tube Department, Radio Corporation
of America, Harrison, N. J. is now supplying to those with technical interest in
receiving tubes a revised edition of the
popular booklet "RCA Receiving Tubes
for AM, FM and Television Broadcast".
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DECEMBER, 1950
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61
Audio Engineering -1950
INDEX
SUBJECT
Acoustics
of London's New Concert Hall;
Nov., 26.
Impact of
on Music, The; Robert
H. Tanner; Nov., 21.
Reverberation -Time Calculation, Simplified; (Chart) Lewis S. Goodfriend;
May, 20.
Audio Engineering Society Papers
Automatic Audio Gain Controls; J. L.
Hathaway: I Sept., 16; II Oct., 27.
Convention Program; Oct., 30.
Diamond as a Phonograph Stylus Material, The; E. J. and M. V. Marcus; July,
25.
Longitudinal Noise in Audio Circuits;
H. W. Augustadt and W. F. Kannenberg: I Jan., 22; II Feb., 18.
Sound Reinforcing Systems; Arthur W.
Schneider; Nov., 27.
Amplifiers
Automatic Audio Gain Controls: (AES)
J. L. Hathaway: I Sept, 16; II Oct., 27.
Cathode Follower Output Stage, The;
Robert M. Mitchell; Feb., 12.
Equipment Report: Rauland 1825 High Fidelity Phono Amplifier: April, 25.
Feedback
Considerations in the
'
Design of; Herbert I. Keroes; I May,
,
14; H June, 17.
For Golden Ears Only: Joseph Marshall;
Mar.,
-
13.
- -, Performance and OperaLimiting
tion of a New; G. A. Singer; Nov., 18.
Loudspeaker Damping as Function of
Plate Resistance of Output Tube; Donovan V. Geppert: Nov., 30.
Reduction in Output Impedance Obtained
with Negative Feedback, (Chart); Willard F. Meeker; Feb., 23.
"Williamson" Type
Using 6A5's;
J. H. Beaumont; Oct., 24.
Amplifiers, Pre Audio Input System for the Discriminating Listener, An: Wayne B. Denny;
Jan.,
9.
Equalized
using Single -Stage
Feedback: Lawrence Fleming; March,
24.
Phonograph Reproductions; (Audiana)
C. G. McProud; I Feb., 24; II March,
20.
Analogies, Dynamical: (Audiana) Lewis
S. Goodfriend; I Sept., 20; II Oct., 36.
Attenuator Calculator using Vector Slide
Rule. Rapid; A. E. Richmond; Dec., 19.
Audiana
Construction Practice; C. G. McProud;
friend: I Sept, 20; II Oct., 36.
Dynamical Analogies: Lewis S. Good-
friend: I Sept, 20; II Oct., 26.
Equivalent Circuits; Lewis S. Goodfriend; Aug., 20.
High Fidelity: Lewis S. Goodfriend; I
Nov., 32; I1 Dec., 34.
Miller Effects, The; Lewis S. Goodfriend;
July, 28.
Phonograph Reproduction; C. G. McProud; I Feb., 24; II March, 20.
Recording Characteristics; C. G. McProud; II, Jan, 20.
Audio in England; H. A. Hartley; I Jan.,
42; II Nov., 36.
Audio Fair, The
Directory of Exhibitors; Oct., 32.
Review: Dec, 24.
Broadcasting
Frequency -Controlled Rotary Converters;
Robert W. Carter; June, 18.
Remote Installations; Elliott D. Full;
Oct., 18.
Cabinets for Home Use, Readers' Sug62
gesti,o
March, 19.
Cathode follower Output Stage, The;
Robert Al. Mitchell; Feb., 13.
Charts
Hygrometric Chart, A New; "Stylus";
April, 24.
Reduction in Output Impedance Obtained
with Negative Feedback; Willard F.
Meeker; Feb, 23.
Resonant Loudspeaker Enclosures: Bob
Hugh Smith: Dec., 22.
Reverberation -Time Calculation, Simplified; Lewis S. Goodfriend: May, 20.
Wavelength for Air; Lewis S. Goodfriend;
Oct., 34.
Components
Frequency Controlled Rotary Converters;
Robert W. Carter; June, 18.
Optimum Use of Nickel Alloy Steels in
Low -level Transformers; L. W. Howard; Oct, 20.
Construction Practice: C. G. McProud;
I April, 2(3; II May, 19; III June, 26.
Controls
Overcoming Fletcher -Munson Effects;
Nathan Grossman and Meyer Leifer;
April, 22.
Continuously Variable Loudness
Johnson: Dee 18.
Equipment Report: Rauland 1825 High Fidelity Phono Amplifier, April, 25.
Filter Characteristics, Measurement of
High -Pass; Werner E. Neuman, Feb.,
E. E.
14.
Flewelling Audio System, The; E. T.
Flewelling; Nov., 15.
Hearing Aid Trends; F. Hardwick; June,
23.
High Fidelity (Audiana); Lewis S. Goodfriend I Nov., 32; II Dec., 34.
Imagery- for Describing Reproduced
Sound: Vincent Salmon; I Aug., 14; II
:
Sept, 14.
Intermodulation Measurements, Simplified; John M. van Beuren; Nov., 24.
Loudness Controls
E. E. JohnContinuously Variable
son: Dee., IS.
FletcherMunson
Effects;
Overcoming
Nathan Grossman and Meyer Leifer:
April, 22.
,
Loudspeakers
Adventure in Loudspeaker Design, An;
Howard T. Souther; June, 14.
Crossover Network for Unequal Voice Coil Impedances; Watson F. Walker:
July,
14.
Design, Construction, and Adjustment of
Reflexed Cabinets; David W. Worden;
Dee., 15.
for the Range from 5 to 20 kc, A:
B. H. Smith and W. T. Selsted; Jan., 16.
New
of Advanced Design, A:
Daniel J. Plach and Philip B. Williams;
Oct., 22.
Resonant
Enclosures, (Chart); Bob
Hugh Smith: Dec., 22.
Sensitivity, Directivity, and Linearity of
Direct Radiator
Harry F. Olson;
Oct., 15.
A; W. E. GilSymmetrical Corner
son and J. J. Andrea; Mar., 16.
;
,
Transient Testing of
Corrington: Aug., 9.
:
Murlan
S.
1listor Lion and Noise Meter, Fixed - Filter
Type: J. P. Smith; Nov., 22.
Filter Characteristics,
of High Pass; Werner E. Neuman, Feb., 14.
Impedance "Jig", An; Allen W. Smith;
March, 18.
Intermodulation
, Simplified; John
M. van Beuren; Nov., 24.
Intermodulation Analyzer for Audio Systems, An; Roy S. Fine: July, 11.
Phase -Shift Method of Measuring Flutter; Charles A. Hisserich and Arthur
Davis; July, 15.
Simple Stroboscopes; L. B. Hedge; Aug.,
22.
Transient Testing of Loudspeakers; Murlan S. Corrington, Aug., 9.
White Noise Generator for Audio Frequencies; J. M. Gottschalk, May, 16.
White -Noise Testing Methods; Emory
Cook; March, 13.
Microphones
Bantam Velocity
The; L. J. Anderson and L. M. Wigington; Jan., 13.
KB -3A High -Fidelity Noise -Cancelling
-, The; L. J. Anderson and L. M.
Wigington; April, 16.
Unobtrusive Pressure
Harry F.
Olson and John Preston; July, 18.
Miller Effect, The, (Audiana); Lewis S.
Goodfriend: July, 28.
Motion Pictures, Magnetic Recording in;
M. Rettinger: I March, 9; II April, 18.
,
;
Negative Feedback
Considerations in the Design of
Amplifiers; Herbert I. Keroes: I May,
14; II June, 17.
Reduction in Output Impedance Obtained
with, (Chart); Willard F. Meeker; Feb.,
8.
Networks, Crossover, for Unequal Voice Coil Impedances; Watson F. Walker;
July, 14.
Noise
Longitudinal
in Audio Circuits
(AES Paper); H. W. Augustadt and
W. F. Kannenberg; I Jan., 22; II Feb.,
18.
White -Noise Generator for Audio Frequencies: J. M. Gottschalk, May, 16.
White -Noise Testing Methods; Emory
Cook: March, 1:3.
P. A. Systems, Aircraft; George H. Warfel; Jan., 19.
Patent Infringement and the Home Experimenter; Albert E. Hayes, Jr., June,
28.
Phnsemeter, An Improved Audio -Frequency; O. E. Kruse and 11. B. Watson;
Feb., 9.
Phonograph Records, The Best British of
1949 H. A. Hartley Nov., 38.
;
;
Phonograph Reproduction
Determining the Tracking Capabilities of
a Pickup: H. E. Roys; May, 11.
(Audiana): C. G. McI'roud; I Feb.,
24; II March, 20.
Diamond As a Phonograph Stylus Material; (AES Paper) E. J. and M. V.
Marcus: July, 25.
Psycho Acoustics
Controversial Idea from England; P. G. A.
H. Voigt; Oct., 40.
Recording, Disc
Measurements
Audio Frequency Phasemeter, An Improved: O. E. Kruse and R. B. Watson;
Feb., 9.
Determining the Tracking Capabilities of
A Pickup; H. E. 'toys; May, 11.
Determining Unknown Impedances in
Transformers; L. H. Hippe; Dec., 21.
Columbia Hot -Stylus Recording Technique, The; William S. Bachman; June,
11.
Heated Stylus Recording Technique
(AES); Leon A. Wortman; July, 24.
New Technique for Reducing Distortion
in Sound Recording; Caldwell P. Smith;
1
Aril, 28.
AUDIO ENGINEERING
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AmericanRadioHistory.Com
DECEMBER, 1950
Recording Characteristics (Audiana); C.
G. McProud; II Jan., 20.
Recording and Fine-Groove Technique;
H. E. Roys; Sept., II.
Recording, Magnetic
Art of Tape Recording, The; Joel Tall; I
May, 13; II June, 20; III July, 22; IV
Aug., 16; V Sept., 15.
of Meter Data; R. E. Zenner; Feb.,
--
Anderson, L. J. and Wigington, L. M.
Bantam Velocity Microphone, The;
12.
KB -3A High- Fidelity Noise- Cancelling
Microphone, The; Apr11, 18.
Andrea, J. J. and Gilson, W. E.
Symmetrical Corner Speaker, A; March,
16.
Augustadt, H. W. and KBnnenberg, W. F.
Longitudinal Noise in Audio Circuits
(AES); I Jan., 22; 1I Feb., 18.
Bachman, William S.
Columbia Hot -Stylus Recording Technique, The; June, 11.
Beaumont, J. H.
"Williamson" Type Amplifier Using
6A5's: Oct., 24.
Beranek, Leo L.
Speech Communication Conference at
M. I. T.
(Report); July,
21.
Illakesley, Jay
Performance Plus Economy Tape Recorder; Nov., 20.
Carter, Robert W.
Frequency- Controlled Rotary Converters; June, 18.
Cook, Emory
White -Noise Testing Methods; March,
1:3.
Corrhfgton, Merlan S.
Transient Testing of Loudspeakers;
Aug., 9.
Davis, Arthur and Hisserich, Charles A.
Phase -Shift Method of Measuring Flut-
ter; July,
15.
Denny, Wayne B.
An Audio Input System for the Dis-
criminating Listener; Jan., 9.
Fine, Boy S.
Intermodulation Analyzer for Audio
Systems, An:. July, 11.
Fleming, Lawrence
Equalized Pre-Amplifier Using Single Stage Feedback: March, 24.
Flewelling, Edmund T.
Flewelling Audio System, The: Nov.,
Full, Elliott D.
Remote Installations; Oct., 18.
Geppert, Donovan V.
Loudspeaker Damping as a Function of
the Plate Resistance of the Power Output Tube: Nov., 30.
Gilson, W. E. and Andrea. .1. J.
Symmetrical Corner Speaker, A; March,
16.
Goodfriend, Lewis S.
Dynamical Analogies ( Audiana); I
Sept., 20; II Oct., 36.
Equivalent Circuits (Audiana); Aug.,
20.
High Fidelity
11
April, 28.
Performance plus Economy Tape Recorder; Jay Blakesley; Nov., 20.
Reverberation -Time Calculation, Simplified (Chart); Lewis S. Goodfriend; May,
20.
16.
Jan.,
in Motion Pictures; M. Rettinger;
I March, 9; II April, 18.
New Technique for Reducing Distortion
in Sound Recording; Caldwell P. Smith;
(
Audiana):
I Nov., 32;
Dec.. 34.
Miller Effect, The ( Audiana): July, 28.
Reverberation -Time Calculation, Simplified (Chart); May, 20.
Wavelength for Air (Chart); Oct., 24.
Gottschalk, J. M.
White -Noise Generator for Audio Frequencies; May, 16.
Grossman, Nathan and Leifer, Meyer
Overcoming Fletcher -Munson Effects;
April, 22.
Hardwick, F.
Hearing Aid Trends; June, 23.
Hartley, H. A.
AUDIO ENGINEERING
Stereophonic Reproduction; Tenny Lode;
Jan., 15.
Transformers
Determining Unknown Impedances in
L. H. Hippe: Dee., 21.
Optimum Use of Nickel Alloy Steels in
Low -Level
L. W. Howard; Oct.,
:
;
20.
AUTHOR
INDEX
Audio In England; I Jan., 42; 11 Nov., 36.
Best British Records of 1949; Nov., 38.
Hathaway, J. L.
Automatic Audio Gain Controls (AES);
I Sept., 16; II Oct., 27.
Hayes, Albert E., Jr.
Patent Infringement and the Home
Experimenter; June, 28.
Hedge, L. B.
Simple Stroboscopes; A ug., 22.
Rippe, L. H.
Determining Unknown Impedances in
Transformers:
11ec., 21.
Hisserich, Charles A. and Davis. Arthur
Phase -Shift Method of Measuring Flut-
ter; July,
Speech Communication Conference at M.
I. T.; Leo L. Beranek: July, 21.
15.
Howard, L. W.
Optimum Use of Nickel Alloy Steels
In
Low -Level Transformers; Oct., 20.
Johnson. E. E.
Continuously Variable Loudness Con-
trol: Dec., IS.
Kannenberg, W. F. and Augustadt. H. W.
Longitudinal Noise and Audio Circuits
(AES): f Jan., 22; II Feb., 18.
Heroes, Herbert I.
Considerations in the Design of Feed back Amplifiers: I May, 14; II June, IL
Kruse, O. E. and Watson. R. B.
Audio Frequency I'hasemeter, An Improved: Feb., 9.
Leiter, Meyer and Grossman, Nathan
Overcoming Fletcher -Munson Effects:
April, 22.
Lode, Tenn)
Stereophonic Reproduction; Jan., 15.
Mcl'roud, C. G.
Construction Practice ( Audiana); I
April, 26; II May, 19; III Jnne, 26.
Phonograph Reproduction (Audiana); I
Feb., 24; II March, 20.
Recording Characteristics ( Audiana):
II Jan., 20.
Marcus, E..1. and M. V.
Diamond as a Phonograph Stylus Material. The: July, 25.
Marshall. Joseph
For Golden Ears Only; March, 13.
Meeker, Willard F.
Reduction in Output Impedance Obwith
Negative
Feedback
tained
(Chart): Feb., 23.
Mitchell, Robert M.
Cathode Follower Output Stage. The;
Feb., 12.
Neuman, Werner E.
Measurement of High-Pass Filter
Characteristics, The; Feb., 14.
Olson, Harry F.
Sensitivity, Directivity, and Linearity
of Direct Radiator Loudspeakers; Oct.,
15.
Olson, Harry F. and Preston, John
Unobtrusive Pressure Microphone;
July, 18.
finch, Daniel J. and Williams, Philip B.
New Loudspeaker of Advanced Design,
A: Oct., 22.
Preston, John and Olson, Harry F.
Unobtrusive Pressure Microphone;
July, 18.
Hettinger M.
Magnetic Recording in Motion Pictures;
I March, 9; H April, 18.
Richmond, A. E.
Rapid Attenuator Calculator using Vec-
DECEMBER, 1950
tor Slide Rule;
Itoys, H. E.
Dec., 20.
I
Determining the Tracking Capabilities
of a Pickup; May, II.
Recording and Fine- Groove Technique;
Sept., 11.
Salmon, Vincent
Imagery for Describing Reproduced
Sound; I Aug., 14; II Sept., 14.
Schneider, Arthur W.
Sound Reinforcing Systems (ABS);
Nov., 27.
Selsted, W. T. and Smith, B. H.
Loudspeaker for the Range from
20 ke. A;
Jan.,
to
5
16.
Singer, G. A.
New Limiting Amplifier, Performance
and Operation of a; Nov.,
I.
Smmth, Allen W.
An Impedance "Jig "; March, 18.
Smith, Bob Hugh
Resonant
Loudspeaker
Enclosures
ICha t): Dec., 22.
Smith, Bob Hugh and Selsted. W. T.
Loudspeaker for the Range from 5 to
20 kc, A;
Jan.,
16.
Smith, Caldwell P.
New Technique for Reducing Distortion in Sound Recording; April, 28.
Smith, J. P.
Fixed- Filter Type Distortion and Noise
Meter, Nov., 22.
Souther, Howard T.
Adventure in Loudspeaker Design, An;
,lune,
14.
"Stylus"
Hygrometric Chart, New; April,
24.
Tall, Joel
Art of Tape Recording, The; I May, 13;
11 .lune, 20; III July, 22; 1V Aug., 16;
V Sept., 15.
Tanner, Robert H.
Impact of Acoustics on Music, The;
Nov., 21.
van Retiree, John M.
Simplified Intermodulation
ments: Nov., 24.
Volgt, P. G. A. H.
Measure-
Controversial Idea from England, A;
Oct., 40.
Walker, Watson F.
Crossover Network for Unequal Voice Coil Impedance; July, 14;
Warfel, George H.
Aircraft P. A. System; ,Ian., 19.
Watson, It. B. and Kruse, O. E.
Audio Frequency I'hasemeter, An Improved; Feb., 9.
Wigington, L. M. and Anderson, L. J.
Bantam Velocity Microphone, The;
.Ian., 12.
KB -3A High -Fidelity Noise -Cancelling
Microphone. The; April, 16.
Williams, Philip B. and Plach, Daniel J.
New Loudspeaker of Advanced Design,
A: Oct., 22.
Worden, David W.
Design, Construction, and Adjustment
of Refiexed Cabinets; Dec., 15.
Wort.man, Leon A.
Heated Styuls Recording Technique
(AES): July, 24.
Zenner, R. E.
Magnetic Recording of Meter Data,;
Feb., 16.
163
}
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INDEX
Ng°.
56
43
48
Acme
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THE POWER OF THE PRESS
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This ad marks the end of the second year of
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Two reasons contribute to this success.
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Secondly, the ability of this company to make
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The 215 has that performance. In the words of
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speakers priced up to $90.00.
and think know good tone Quality. do not like
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We have nothing more to say just now except
that we should like to send a Christmas card to
the thousands of new friends we have made since
we first told you about ourselves. Alas, we
haven't the clerical staff to get them over to you
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you all a very merry Christmas and the best of
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H. A. HARTLEY CO. LTD.,
152, Hammersmith Road,
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64
to the `V 11.LIAMSON'
Specification
37
Cover 2
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12
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14
31
52
V15
38
53
60
61
58
Cover
3
Dorf, Richard H.
Duotone Co.
64
54
Electric Indicator Co.
Electro- Voice, Inc.
59
V2
Fairchild Recording Equipment Corp
Fisher Radio Corp.
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General Electric Co.
General Radio Co.
Gordon, Herman Lewis
Gray Research and Dev. Co., Inc.
51
Hartley, H. A., Co., Ltd.
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35
60
This range of 20 watt push -pull
output transformers is Intended for use In
equipment reproducing the full audio frequency
range with the lowest distortion. The design
and measured performance is exactly as specified by Williamson In the "Wireless World"
August 1949 (see also Audio Engineering
Novemoer 1949). The transformer is available
varied range (separate models suitable
in
for KT86, 807 tubes, etc.) Performance sssured by comprehensive testing procedure *pulled to each unit. Close limits set on shunt
reactance at 50 cps., aeries reactance at
Kc /sec., d.c. resistances and interwtnding
sulation resistances at 2 K.V.
This it the beet possible transformer of its type (weight 14
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Postage, packing and Insurance
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Browning Laboratories, Inc.
Daven Co., The
$249.50
Llfl%Cid[laIlY tested
13
59, 61
Cannon Electric Dev. Co.
Chicago Transformer Div.
Cinema Engineering Co.
Classified Ads
I. Colbert
Concord Radio
50 W -2 Amplifier
Pflrtrí6ge
'Pews
Harvey Radio Co., Inc.
Heath Co.
Hollywood Sound Institute, Inc.
Hudson Radio & Television Corp.
Interstate Supply Co.
LeBel, C.
Magnecord- Inc.
McIntosh Engineering Laboratory,
Inc.
Measurements Corp.
Milo Radio Cr Electronics Corp. ..
Roebuck
Road,
9
BOUND VOLUMES
53
1950
64
Enter your order now for your
39, 49
AUDIO ENGINEERING. For permanent
64
57
61
Partridge Transformers, Ltd.
Permoflux Corp.
Pickering Cr Co., Inc.
Precision Electronics, Inc.
Presto Recording Corp.
Proctor Soundex Corp.
Professional Directory
64
....
Surrey, England
41
58
Radio Corp. of America
Radio Shack Corp.
Reeves Soundcraft Corp.
Rek -O -Kut Co., Inc.
Tolworth,
64
Newcomb Audio Products Co.
4
11
48
33
55
60
60
6, 7
55
40
2
Savage
Transformers Ltd.
Shure Brothers, Inc.
59
46
Tech Laboratories, Inc.
Televex
Terminal Radio Corp.
44
Transcriber Co.
Triad Transformer Mfg. Co.
61
Recording Co.
United Transformer Co.
64
U. S.
TRANSFORMERS LTD
61
J.
RCA Service Co., Inc.
PARTRIDGE
61
47
copy of the
reference, the bound volume is easier
to store, easier to find things in, and
it keeps your copies in mint condition
throughout the years. The ideal way
to keep these valuable issues.
1950 Bound Volumes .. $8.95
FOR 1951
A new offer, made now for the first time
entitles you to subscribe or to renew your
present subscription for one year at the
cost of $10.00, which includes a bound
volume delivered to you around January 1,
1952. Each month you will receive AUDIO
ENGINEERING -read it, cut out coupons
to your heart's content, mark on the pages
as much as you want. At the end of the
year, you receive a fresh, new bound
volume of 1951 issues which you can keep
as a permanent record. Stop trying to
keep each issue neat and clean-use it.
Then, at the end of the year, you'll receive
a completely new set -no creases, no dog eared pages.
Dept. SV
1
Cover 4
AUDIO ENGINEERING
342 Madison Ave., New York 17, N.Y.
AUDIO ENGINEERING
www.americanradiohistory.com
AmericanRadioHistory.Com
1950 bound volume of
DECEMBER, 1950
VEW
TYPE OP
-182
an9e'
meadesigned to
Meters are an audio signal
Power M
by
of the charsue D
power delivered
surf
suited to
the actual P load. However, because
sure me
are admirably
they
system to a given
the circuit,
acteristics of
namely:
of on A.C.
applications.
Impedance
ln+P
other
Characteristic
.. .5
Re-
love ac 2en3 1\Y dr9e,v°t
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dec.:170`.
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2.
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of .1 Ca1ipower
watts'n teps1Aeter:
Me
of
System.
on a Signal
Measurements.
M
a Multi-channel Mixer
of Load Variation
Equalization
Insertion
Line
Transmission of
4 Trensuremen
4. Measurement
come lex circuits.
to:
.
Determination
1.
1
and other
Filter and
Radio Receiver
M
shown
The equipment
standards
stada
well lmo
Measurements.
asur mentsDAVENor
built to
e
write
on this page
Please
recision.
of precision.
engineering department
data
more detailedspecific problems.
help you on
1
20-
0
TYPE OP -962
At
similar can
Characterisë cPst that
s ex to 100 watts.
up
measure
Impedance
impedances
da 000 ohms.
tween 2 and
P
over
Range:
ohms do
jto
20,000 ohms. 2.5
mains essentially
Reover frequency resistive
range of
30 to 10,000
cps, Accuracy
Power Rar
-ge:
0.1
of 0.1 milliwwatts in
arts,
30
db
watts n
to
0.1 rnw st
extenäed
use of
amplifier.
below
Meter:
externa
.01 watt to
1
brateatin9
to +10
fro
100
Range
Flange
milli_
steps
1 raw by
óm -10
Iro
watt
level:
dbttZero meer
Multiplier:
horn
Meter
reading.
scale
times
to 10
SO milli
watts and 0 to
17 decibels.Zero level:
i:nw.
Meter Multiplier
atwer readingExtends
itndi
of the
to i,000x4 meter born 0-Ix
the db. reacale value, or
db
1000
mw
cycles
Indicating Meter:
brated from
CaliI to
to
2
30 to
Accuracy
from __10
Co-
steps of
THE
i85 CENTRAL
www.americanradiohistory.com
AmericanRadioHistory.Com
AVENUE
NEW ARK
NEW ]ERSE?
The UTC type HQ permalloy dust toroids are ideal for all audio, carrier and supersonic
applications. HQA coils have Q over 100 at 5,000 cycles... HQB coils, Q over 200 at 4,000
cycles... HQC coils, Q over 200 at 30 KC... HQD coils, Q over 200 at 60 KC... HQE (miniature) coils, Q over 120 at 10 KC. The toroid dust core provides very low hum pickup...
excellent stability with voltage change...negligible inductance change with temperature,
etc. Precision adjusted to 1% tolerance. Hermetically sealed.
HOA, HOC, HOD CASE
1
13
/16"Dia.
e
3/16"High
1
Inductance
1
5/8'x
HOB CASE
2 5/8 "e 2 1/2"High
Type No.
HQA1
5
mhy.
HQA-2
HQA-4
12.5
20
30
HQA-5
50
mhy.
mhy.
mhy.
mhy.
HQA-6
80
HOA-3
HQA7
125
HQA-8
200
300
HOA-9
HOA-10
H
HOA-12
u
HOE CASE
1
/2'x
1
5/16'x
1
QA-11
3/16 High
Net
Price
Value
.5
mhy.
mhy.
mhy.
mhy.
hy.
.75 hy.
1.25 hy.
HQA-13
HQA-14
2.
hy.
3.
HQA-15
5.
hy.
hy.
Inductance
Type No.
Value
$7.00
7.00
7.50
7.50
8.00
HQA -16
8.00
9.00
9.00
10.00
10.00
10.00
11.00
11.00
13.00
HQB-3
70
HOB-4
120
7.5
10.
hy.
HQA-18
15.
hy.
mhy.
mhy.
mhy.
mhy.
hy.
hy.
hy.
hy.
HOB -1
10
HQB -2
30
HOB -5
HOB-6
NOB-7
.5
1.
2.
3.5
7.5
HOB -8
HQB -9
14.00
hy.
HQA -17
hy.
HOB -10
12.
hy.
HOB-11
18.
HOB-12
25.
hy.
hy.
1
ITC INTERS AGE AND
FILTER CASE
1
1
3/16"x
5/8 "-
2
1
1
M
11/16°
/ fHigh
These U.T.C. stock units take care of most
common filter applications. The interstage
filters, BMI (band pass), HMI (high
pass), and LMI (low pass), have a
nominal impedance at 10,000 ohms.
The line filters, BML (band pass), HML
(high pass), and LML (low pass),
are intended for use in 500/600 ohm circuits.
All units are shielded for low pickup
(150 my /gauss) and are hermetically sealed.
1S0 VARICK STREET
EXPORT DIVISION: 13 EAST
V
Net
Price
Inductance
Type No.
$15.00
16.00
17.00
16.00
16.00
16.00
17.00
17.00
18.00
19.00
HQC -1
2.5
HOC -3
5
HOC -4
10
HOC-5
20
HOD -1
1
2.5
HOD -4
5
HOD -5
15
HOE-1
5
HQE -2
10
131E-3
50
HOE -4
100
HQE -5
200
LI;I
.
mhy.
mhy
mhy.
mhy.
mhy.
mhy.
mhy.
mhy.
mhy.
mhy.
mhy
mhy.
mhy.
mhy.
.
.
$13.00
13.00
13.00
13.00
13.00
15.00
15.00
15.00
15.00
15.00
6.00
6.00
7.00
7.50
8.00
111'iII.A
STOCK FREQUENCIES
(Number after le fers is frequency)
Net Price $25.00
BMI-60
BM1.100
BMI-120
BM1-400
BM 1500
BM1.750
BM1-1000
BMI.1S00
LM1-200
BM -3000
1141-500
BMI-10000
LM1-1000
1M1-2000
LM1-3000
EMI-5000
EMI-10000
1
HM1-200
HM1-500
HMI-1000
HM1.3000
NEW YORK 13, N. Y.
40th STREET. NEW YORK 16. N. Y..
CABLES ARLAB
www.americanradiohistory.com
AmericanRadioHistory.Com
.4
00.2
HOD -3
20.00
21.00
22.00
23.00
24.00
mhy
1
HQC.2
H
Net
Price
Value
8M L-400
BML-1000
HML-200
HML-500
LML-1000
LML-2500
IME-4000
LML-12000
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