engineering - American Radio History

engineering - American Radio History
ENGINEERING
NO MORE
HOT- WEATHER
PROBLEMS
tion later on. The moisture problem has been solved
at its most vulnerable point -in the lacquer itself!
By the addition of a special moisture resisting
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Audiodisc lacquer has been made permanently
resistant to humidity. Its outstanding "all weather"
performance has been proved by countless tests in
our "weather room ", under the most severe conditions of temperature and humidity. But the most
conclusive proof of all has come from the field. For,
during the summer of 1948, one of the most humid
on record, none of our customers have reported any
difficulties in recording or reproduction due to moisture conditions.
See for yourself what a big difference this improvement can make in your summer recordings. Ask your
dealer for Audiodiscs!
To the recordist, the hot, summer months have generally meant plenty of trouble -not because of the
heat, but due to the accompanying high humidity.
For moisture which is absorbed by the lacquer of a
recording disc has a serious effect on the cutting
characteristics. The noise level increases progressively while recording, and the cut gets greyer and
greyer. This problem has affected the entire lacquer
disc industry. But, with Audiodiscs, it is a problem
no longer. You can now record as well on the hottest
and dampest day as you could on a crisp day in fall
or winter.
-
This freedom from humidity troubles is the result
of an exclusive Audiodisc improvement perfected in
1947. It is an improvement which goes far beyond the
control of atmospheric conditions during manufac-
ture- for that alone doesn't prevent moisture
absorp-
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Parir
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AUDIO ENGINEERING
JULY, 1949
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AUDIO ENGINEERING
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www.americanradiohistory.com
JULY, 1949
4
D. S.
Potts, Publisher
C. G. McProud, Editor
Lawrence LeKashman, Asst. Editor
Louisa
B.
S.
DeSoto, Edit. Prod. Mgr.
David Saltman, Production Manager
DICENGINEERIN
r
Howard A. Chinn
URE AU
RADIO
S.
JULY,
Representatives
105 Bolsover
Harris
Young White
CONTENTS
Devine, Circ. Mgr.
Dale International Publications, Ltd.
St., London W. 1, England
George M. Nixon
Winston Wells
Established 1917
B.
James C. Galloway, Pacific Coast Sales
816 W. 5th St., Los Angeles 13, Calif.
J. P. Maxfield
RCULAII
Adv. Director
Sanford R. Cowan, Mid -West Sales
342 Madison Ave., New York 17, N. Y.
C. J. LeBel
wits
Successor to
L.
Editorial Advisory Board
John D. Colvin
Una
L. Cahn,
H. N. Reines, Adv. Mgr.
&
Floyd, 297 Swanston St.
Melbourne C.
1,
Victoria, Australie
1949
Vol. 33,
No.
Letters
4
Editor's Report
8
New Sortable Audio Amplifier for AM-FM-TV - -W. W. Dean
11
Auditory Component Control for the Legitimate Theatre -John H. Beaumont
15
Importance of Groove Fit in Lateral Recordings-D. R. Andrews
18
Problems in Audio Engineering, Part III -Lewis S. Good /riend
20
Record Revue -Edward Tatnall Canby
22
New Products
21.
The Language of Audio -John D. Goodell
25
Techni- Briefs
38
'
Advertising Index
7
40
COVER
ie
Bell Telephone Laboratories' "disc" lens, by means of which sound waves are
delayed and thereby focused. Consisting of metal discs arranged in an
open structure, the lens was built originally for three- centimeter
microwaves, but can be used for simultaneous focusing
of microwaves and sound waves.
J
AUDIO ENGINEERING (title registered U. S. Pat. Off.) is published monthly at New York. N. Y., by Radio Magazines,
President: Lawrence LeKashman, Vice Pres. Executive and Editorial Offices at 342 Madison Avenue. New York 17. N. Y.
United States, U. S. Possessions and Canada. $3.00 for 1 Year. 95.00 for 2 years: elsewhere 54.00 per year. Single copies 35e.
All rights
d. Entire contents copyright 1949 by Radio Magazines. Inc. Entered as Second Class Matter July 29. 1948
New York, N. L. under the Act of March S. 1879.
AUDIO ENGINEERING
JULY, 1949
-
Inc.. D. S. Potts,
Subscription rates
Printed in U. S. A.
at the Post OI&e,
3
www.americanradiohistory.com
TAPE
DISK
OR
Sir:
YOU CHOOSE FAIRCHILD
FOR TOP PERFORMANCE
Your J unt L,w. gi%e- mr several incentives for letters comment: (I) Charles Irwin Cohn's letter is strongly
remindful of mine (in your July issue of
1947) in which I stressed the psycho- acoustic
conditioning of reproduced music listeners
by their previous musical experiences with
live music, and with reproduced music of
varying degrees of quality.
12) Ted Powell's letter re: (a) Prof.
Richardson's conclusions that the attack and
decay times of sounds. rather than their harmonic overtones, largely determine their tone
quality and Ibl
* The
Fairchild "Synchroll" Drive
advantages of the
transfer of power through soft rubber
idlers with those of direct gear control
of the capstan. This unique development of Fairchild results in a no -slip
synchronous tape drive.
System combines
* High
Frequency
Flutter causes
roughness in a reproduced sine wave
tone. Smooth motion in the Fairchild
Tape Recorder is apparent in the
cleanliness of simple musical tones.
* Hum
problems are generally recognized as inherent in magnetic recorders.
The high efficiency of Fairchild Playback Head design and amplifier construction results in a hum measurement
at least 68 db down. (ref. 2%
distortion).
THE FAIRCHILD PROFESSIONAL TAPE
RECORDER easily outperforms requirements set by NAB Standards. Features
include: "plug -in" type construction,
both mechanical and electrical, for uninterrupted service; interlock system
to prevent accidental erasing; volume
indicator and circuit metering; adjustment of playback head during operation for optimum performance with
all tapes; simultaneous monitoring
from the tape during actual recording.
Major network and recording studios
are using Fairchild Tape Recorders.
Write for complete information.
FAIRCHILD SYNCHRONOUS DISK RECORDERS
PROGRAM TIMING -Synchronous direct to the center gear
drive for shows "on the nose".
ACCURATE
FREEDOM
page.
make
FROM
Wow -No slip-
No musical pitch change to
listeners aware the show is
transcribed.
SOUND ON
FILM DUBBING-Many
of the motion picture sound tracks
you hear and enjoy are first recorded
on Fairchild
Synchronous Disk
Recorders.
Above are some of the features that have gained FAIRCHILD the reputation for
the finest in recording equipment. Fairchild Synchronous Disk Recorders are manufactured in 3 models; Unit 523 for the finest fixed studio installation; Unit 539K
for the small budget studio; Unit 539G (shown above) for console performance
in a portable unit. Maintain your reputation for making the finest transcriptions
and masters with Fairchild equipment. Write for illustrations and complete
specifications.
RECORDING EQUIPMENT
CORPORATION
154TH STREET AND 7TH AVENUE, WHITESTONE,
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transient distortion.
(a) In the Proceedings of the Radio Club
of America, January 1934, the Journal of
the A.S.A., January 1935, and Proceedings
I
I.R.E., November 1936, and elsewhere,
which
have described my electronic piano,
period
time
has controllable attack and decay
for the hammer-excited string vibration, as
translated by capacitance and magnetic
pick-ups, amplifier and speaker. With this
instrument, a normal piano tone may be
just like
made to sound (as reproduced
tone
an organ or other wind instrument
Iof moderate duration) with percussive
transients removed. Also, with normal percussive attack, the damping rate of the reproduced tone may be greatly increased.
Both the attack and decay rates may be
continously varied through wide limits, so
that the reproduced tone, always of the same
harmonic content as determined by mixing
of the out-puts of several pickups along the
I
string) can be made to sound all the way
(tom the highly damped, banjo type, thru
normal piano (attack and decay) to a thoroughly organ.like tone. This I have called
"tone envelope control" and is a very important means of controlling "quality ", if
by that we include more than mere control
of the relative amplitudes among the tone
partials.
I do not agree that such envelope differences are more important than the harmonic
(or enharmonic) content of tones or sounds,
but they are certainly equally important.
(b) I used the term "transient distortion'
in 1921, in my electro- phonographic researches, concerning the effects of more or
less rapidly damped mechanical and electrical resonances in the recording- repro ducing system. In 1931 and later, I tested
electronic piano amplifier- reproducer a.f.
systems for inter -modulation by striking two
piano keys in the 2000-2500 cycle range and
separated by say 200 -300 cycles in frequency,
while listening for the inter -modulation beat
tone. (See my letter J.R.E. 1942. page 429.
re John K. Hilliard paper on "Distortion
Tests by Inter- modulation Method".) This
test indicated that power ratings of such
a.f. systems were overated (by the totalharmonic- content test for pure tones) by
about 400 to 500 per cent.
(3) There is one more matter on which
I have speculated for years and have referred to the Harvard Pyscho- Acoustics
l.ahoratory (without reply) : I listen a lot
to sounds of 120 -cps frequency, sometimes
quite loud, from loud speakers, a.c. motors.
airplane motors, and from an old Model
A Ford truck without muffler, which I have
on my place for odd transport jobs.
After listening to such loud 120 -cps tones
for some time and then going to a quiet
place. I can still hear intermittently, slowly
pulsating, and weakly, this abolutely def.
[Continued on page 391
AUDIO ENGINEERING
4
www.americanradiohistory.com
JULY, 1949
,%/
©
You've seen this. or something else "unfortunate,"
on too many live TV shows. It simply couldn't
happen if the show were on 16 -mm film.
J. A. MAURER, INC.
37-03 31st Street, Long Island City
16 -mm
AUDIO ENGINEERING
1, N. Y.
The Maurer
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Professional Motion Picture Camera.
Professional Production Equipment
JULY, 1949
www.americanradiohistory.com
5
RCA "Plá
am p iii rs
of secant's AS amplifier or power supply
can be connected Jr di,connected. Guide strips on
the new RCA Ahelf (Type BF -2A) and guide pins on
plug at back of amplifi:r a:sure smooth, rapid installation. Levers at front hook into slot in shelf and
pull amplifier into place- Sockets on bracket at rear
of shelf permit self alignment of receptacle with amplifier plug. (Shown it the 3X -1B Power Supply Unit.)
In a matter
Two-stage Preamplifier (Type BA -1A) -ideal for use
as a microphone preamplifier, turntable preamplifier,
booster amplifier, or low -level isolation amplifier. High
gain: 40 db. High output: +10 db. Lou' noise level: -80
db. Low distortion: 0.5% rms, 50 to 7500 cycles. Isolation
factor: approx. 90 db; over 100 db with special Volume
Control Kit. Frequency response: ±1 db, 30 to 15,000
cycles. Small size: six units will fit on a 36 -B or new
BR -2A shelf!
Booster Amplifier (Type BA -2C) -A two -stage unis
having applications similar to those for the BA -1A; also
valuable where a high -gain amplifier between announce
microphone and limiting amplifier is required. High
gain: 50 db. Lou, noise level: -68 db. Low distortion:
0.75% rms, 40 to 15,000 cycles. Frequency response:
t1.5 db, 30 to 15,000 cycles. Compact: two units can be
mounted on one 36 -B or BR -2A shelf. Features plug -in
capacitors and built-in power supply.
www.americanradiohistory.com
for quick interchanges- and
easy maintenance
All units available for immediate delivery
install or remove as an electronic tube! Pull a
lever near the front of the amplifier and the plug on the
rear of the unit is smoothly withdrawn from its socket
automatically disconnected from the supply voltage. No
longer is it necessary to crawl around to the back of hardto-get -at racks and unsolder or unscrew countless connections. System changes can be made quickly; minutes can be
slashed from inspection, servicing, and testing time.
This new RCA line now includes the four amplifiers and
one power-supply unit shown. Others will be added in the
near future. New, carefully selected characteristics make
these units ideal for a large number of studio jobs.
All units use the same standard plug. To assure maximum
convenience, a new shelf (Type BR -2A) has been designed.
With a few easy changes, however, the conventional RCA
Type 36 -B panel and shelf can be used, if desired. The necessary accessories are available for this purpose.
Aeasy to
-
The RCA Type BR-2A Sielf fits any standard rack; takes
83t inches of panel space. If desired, however, RCA Type
36 -B panels and shelves now in use can be easily adapted
for plug -in amplifier service.
Here, we believe, is a real opportunity to modernize your
amplifier system -a quick, convenient way to get better performance at low cost. Descriptive leaflets are yours for the
asking. Write: Dept. 7G, Audio Equipment Section,
Radio Corporation of America, Camden, N. J.
BROADCAST EQUIPMENT
(14
RADIO CORPORATION
In Canada. RCA VICTOR Company
1w Program Amplifier (type BA -13). The most versatile high f'delity amplifier ever designed for broadcasting. Ideal as a
r. gram or li le amplifier, bridging amplifier, isolator amplifier,
cuing or monitoring amplifier. Improved layout for greater
accessibility; "plug -in" electrolytics for ease in servicing. Output,
p
watts (approx.). Higher gain, 65 db for matching input; 28 db
for bridging input. Lower noise level, -82 db (with max. gain).
2
Lower distortion. less than 0.5 to 1% rms, depending on output
level. Frequency response,
1 db, 30 to 15,000 cps.
t
of AMERICA
ENGINEERING PRODUCTS DEPARTMENT, CAMDEN, N.J.
limited, Montreal
Monitoring Amplifier (Type BA -4B)- Designed for operation at microphone levels. High output of 12 watts
is sufficient to drive several speakers or, in some applications, a recording head. Other uses include application as line amplifier for portable and mobile transmitters. High gain: 105 db. Low noise level: -20 db (with
maximum gain); -40 db (with minimum gain). Low
distortion: less than 3% at 12 watts. Frequency
12 db, 30 to i 5,000 cycles.
www.americanradiohistory.com
responses
EDITOR'S REPORT
STANDARDIZATION (Cont'd)
IN
1
fit. SutsJECT of standardization of equipment
«t various types, there is always much to ve said.
0suit
ranstormers have long been in the limelight, and
impedances in a complete system-sucn as a
broadcasting plant -are intimately related to translorntcrs, or vice versa.
Veparting from the discussion of professional equipment, there is much work to be done with components
in the public address and home amplifier held. As an
example of this, it will be noted that amplifiers are
rated in a variety of ways, usually such that the best
possible numerical values are credited to the equipment
being described. Consider the rating for hum and noise
levels -in the professional class, amplifiers are described
as having a noise level of n db below a reference level,
usually I mw. In the p. a. line, most equipment is rated
as having a noise level of n db below maximum power
output. Obviously, then, an amplifier with an output
of twenty watts, corresponding to +43 dbni, will appear
to be better under its rating of "80 db below maximum
output" than a professional amplifier rated at -65 dbm,
although the hum and noise level of the former is
actually only -37 dbm. It is not the number of db
below maximum output that is of interest, for an amplifier having an output of +50 dbm and a noise level 60
noise
db below this value is not very quiet at all
level of -10 dbm is hardly acceptable for a good quality
i
-a
system.
The maximum noise level from a good amplifier designed for use in a home reproduction system should
be no higher than -40 dbm, and preferably as low as
-60 dbm, to ensure the extreme of quiet desired by
critical listeners. In selecting any amplifier, therefore,
it is good policy to translate the published rating to a
level referred to some standard, preferably 1 mw, before
comparing a number of figures, which unless intelligently
considered, mean little.
Going to another question -it is well understood that
the gain of an amplifier is based on the ratio of the
output power to that delivered to the input. Thus, in
a typical amplifier, the input is rated as 5 megohms and
a signal of .001 volts from any source is sufficient to
drive the amplifier to full output. However, if the
same amplifier were rated at an input impedance of
50,000 ohms, the same signal would also drive the
amplifier to full output. But -the calculated gain of
the amplifier differs by a factor of 100, or a difference
of 20 db. Thus, though the actual gain of the amplifier
has not changed, the figures denoting this gain have
changed appreciably.
The object of this discussion is to point out the fallacies in the methods of rating an amplifier. To make
8
valid comparisons, it is necessary that all the ratings be
translated to the same basis, so that the equipment can
be evaluated fairly, and without prejudice to one or the
other on account of the method of presenting the facts.
One other component that comes into this discussion
is the microphone. In the consideration of various
microphones of any type, they too must be compared
on an equal footing. It will be noted that some are
rated at a given output for a sound pressure of 1 bar,
while others are rated for a pressure of 10 bars. This
alone will make a difference of 20 db in the actual output, provided the difference in the reference is not
observed.
The whole point to standardization is to make it
possible to substitute equipment readily without the
necessity of making extensive changes in other circuit
elements in case a single element must be replaced.
There is nothing wrong with the ratings usually published-but to make comparisons that are valid, everybody must be talking about the same thing. It would
be helpful if all conditions were standardized. Until
then, though, remember that old axiom to which every
engineering student has been exposed -read the problem
thoroughly before attempting to solve it.
NEW MICROPHONE DESIGNS
One of the principal tnruhle encountered in TV
sound pickup is the inability of standard microphones
to produce acceptable quality at the distances required
by camera placement. Thus it appears that a new
microphone design may be desirable. With all due
respect to presently used microphones, most of which
produce excellent sound quality when operated under
conditions normal in radio, it is nevertheless a fact that
these microphones -almost without exception -are
merely modifications of early telephone transmitters.
Instead of the microphone being designed to fit the
application, the application has usually been modified
to fit the requirements of the microphone, and so far
it has apparently not been possible to adapt TV techniques to produce consistently good quality with any
existing mike.
Perhaps the next move should be a study of present
designs to determine the possibility of bringing out a
completely new type of microphone which is suited for
TV use. Such a design might well incorporate a pattern
whichkip essentially a cone with an included angle of
30 to 45 deg. and with the response at the back and
sides at an absolute minimum. Considering the per formanCe of present uni- directional microphones, this
should not be too difficult for the design engineers, and
it is well agreed that such a microphone is badly needed.
AUDIO ENGINEERING
www.americanradiohistory.com
JULY, 1949
Magnetic
Maw
The Arnold Engineering Company
offers to the trade a complete line of
Magnetic Materials
PERMANENT MAGNET MATERIALS
Cast Magnets, Alnico
1,
II,
IY, Y, YI, XII, X -900
111,
Sintered Magnets, Alnico II, 1V, Y, VI, X -900, Remalloy*
Vicalloy
Remalloy* (Comol)
*
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Cunife
Cast Cobalt Magnet Steel
HIGH PERMEABILITY MATERIALS
Dcltamax Toroidal Cores
Supermalloy* Toroidal Cores
Powdered Molybdenum Permalloy* Toroidal Cores
Permendur*
*Manufactured under licensing arrangements with WESTERN ELECTRIC COMPANY
inrbimatór7 /e/a;7g
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THE ARNOLD ENGINEERING COMPANY
SUBSIDIARY
ALLEGHENY LUDLUM STEEL CORPORATION
147 EAST ONTARIO STREET, CHICAGO 11, ILLINOIS
AUDIO ENGINEERING
JULY, 1949
9
www.americanradiohistory.com
ban,
,t
//
//
Words Transcríbed by .AM PEX oiter -die great shrfws at, radío
Here's why
300
he new series
AMPEX
MAGNETIC TAPE RECORDER
a
veers industry
need!
Designed by es.gineers
who had your engineering
needs in mind!
Console Model 300 - $1573.75*
Portable Model 300 - $1594.41
$1491.75
Rack Mounted 'Meter panel extra
F. O. B. Factory, San Carlos, Calif.
/-iTGLWGG,)1UAU'i
*
Original program quality preserved
Use of independent reproduction facilities allows instantaneous
SPECIFICATIONS
monitoring and makes possible the most stringent comparisons
between recordings and originals.
*Tap* and playback noise non- existant
Use of special record and bias circuits has eliminated tape noise.*
Extreme care has been exercised to eliminate hum pick-up.
* Editing made easy
N: ith Ampex editing is almost instantaneous. Single letters have
been actually cut off the end of words. Scissors and scotch tape
are all the tools needed.
* You can depend on Ampex
Read what Frank Marx, Vice President in charge of Engineering,
American Broadcasting Company, says: "For the past two years
A.B.C. has successfully used magnetic tape for rebroadcast purposes ... A.B.C. recorded on AMPEX in Chicago ...17 hours per
day. For 2618 hours of playback time, the air time lost was less
than 3 minutes: a truly remarkable record."
FREQUENCY RESPONSE:
At 15 "± 2 db. 50- 15,000 cycles
At7.5 " ±2 db. 50- 7,500 cycles
*SIGNAL-TO -NOISE RATIO: The
overall unweighted system noise
is 70 db. below tape saturation,
and over 60 db. below 3% total
harmonic distortion at 400 cycles.
STARTING TIME: Instantaneous.
(When starting in the Normal
Ploy mode of operation, the tape
is up to full speed in less than
.1 second.)
FLUTTER AND WOW: At 15
inches per second, well under
0.1% r.m. s., measuring all flutter
components from 0 to 300 cycles,
using a tone of 3000 cycles. At
7.5 inches, under .2%.
Manufactured by Ampex Electric Corporation, San Carlos, Calif.
DISTRIBUTED
CROSBY ENTERPRISES
9028
Sunset Blvd.,
Hollywood 46. Calif.
BY
GRAYBAR ELECTRIC CORP.
Graybar Building, New York
17,
AUDIO & VIDEO
N. Y.
Y.
AUDIO ENGINEERING
IO
www.americanradiohistory.com
JULY, 1949
Fig. I. Front panel of portable amplifier. Access plate at left end is removed to permit
connection of microphone cables.
W. W. DEAN*
Practical, standard engineering provides a design which features compactness, reliability, flexibility, and
performance.
nom
Audio Amplifier for
T,IE FUNCTION
of a portable amplifier
to receive the signals from the
microphones at a remote-broadcast
is
location, combine them in the desired
proportions, and amplify the resulting
signal to a level suitable for transmission to the broadcast studio. Since a.c.
power is not available at all locations,
portable amplifiers must operate from
batteries, or from both a.c. and batteries. The electrical performance must
be of broadcast quality, although the
specifications of most earlier amplifiers
are not as rigid as those on studio
equipment. As the unit is frequently
carried from studio to a remote location, and from one remote to another,
it must be light in weight, easy to
carry, and of sturdy construction.
In the design of any piece of portable
audio equipment, eouo compromise
must be made between the features of
the equipment and the size and weight.
One of the main determining factors
in this compromise is the type of mixing system used. In low-level mixing,
the microphone outputs go directly to
the mixer system where they are combined and then amplified. High -level
mixing, on the other hand, uses an amplifier between each microphone and the
mixer system.
Signal -to -noise ratio in a properly
designed amplifier is largely determined
'General Electric
Co., Syracuse, N. Y.
AUDIO ENGINEERING
¿PDJif«6k
AM -FM -TV
by what happens
at the grid of the first
stage. A practical average value of
noise in an input stage using a modern
low -noise tube is in the order of -125
dbm. This noise can be made to consist
essentially of tube and circuit hiss, with
the hum appreciably lower in level.
Since broadcast microphones have
effective output levels in the order of
-50 dbm in moderately loud sound
fields, the signal -to -noise ratio at the
first grid seldom starts out better than
75 db. In weaker sound fields this ratio
is correspondingly degraded.
Now assume that a four-channel,
low -level mixing system is interposed
between the microphone and the first
grid. Such a mixer has an initial loas
of approximately 10 db and usually is
set by the operator to have a loss closer
to 20 db. It is seen that such a mixing
system generally reduces the signal -totoise ratio to 55 db.
These figures are based on the use
of the very best type low- noise, low microphonic input tubes. It can be
demonstrated that the use of receivingtype tubes, especially certain types of
miniature tubes, will raise the noise an
additional 10 to 20 db and change its
character from smooth hiss to very annoying hum or to microphonic ringing
noises.
Therefore, for portable amplifiers using low -level mixing systems and receiving-type input tubes, it is not unusual to measure signal -to -noise ratios
JULY, 1949
of only 40 or 45 db under standard
test conditions approximating a microphone in a moderately loud sound
field. Consider what the ratio becomes
when the microphone is in a weak
sound field. Hardly the background of
"dead silence" required by today's new
transmitting systems.
When high -level mixing is used, the
story is much more attractive since the
signal -to -noise ratio seldom goes below
that established at the first grid. High level mixing plus the use of modern
low -noise tubes insures the lowest possible noise level at all times.
Consider the output of the microphone in our moderately strong sound
field to be -50 dbm. In a high-level
mixing system it is first given a boost
of 40 db in a low -noise pre -amplifier
stage. Then the signal drops, say 20 db,
in the mixer. It is still 20 db above
microphone level when it is applied to
the tube following the mixer. By making the booster stage design the same
as that of a low -noise pre -amplifier, the
mixer settings can be increased to give
a 40 -db loss before the signal -to -noise
ratio has been reduced below that prevailing at the first grid.
High-level mixing gives other ad.
vantages. Since input transformers are
used ahead of each tube, the microphone lines may be operated balanced
to ground. This gives a noise reducing
advantage where the cables are quite
long and must run through interference
II
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a
Fig. 3. Schematic of GE Type BA -6 -A portable amplifier.
AUDIO ENGINEERING
12
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JULY, 1949
fields. Also, the use of input transformers permits tap changing to match
various source impedances.
A.
ION
C. and Battery Power Supply
Portable amplifiers which operate
from both a.c. and batteries may be
divided into two general classifications:
(1) Those which have the batteries in
a separate case, and (2) Those which
have the batteries included in the same
case with the amplifier. The advantages
of a.c. and battery power in the amplifier case, rather than in a second container, are many. It is safe to assume
that most pickup locations have reasonably reliable a.c. power available. However, this power has been known to fail,
and in such cases, the inclusion of batteries in the amplifier case where they
are always available is a great asset.
Because of the additional space and
battery power required by the pre -ampplifiers of a high -level mixing type of
remote amplifier, it is not feasible to
include an extended -life complement of
batteries in the single -case design.
However, lightweight, emergency batteries may be included. In the event of
a.c. power failure these would be expected to operate only until the end
of the program.
To make this single unit design practical, it was necessary to reduce the
power drain to a minimum. In fact,
miniature tubes were used throughout
the entire amplifier during the early
stages of the design because of the reduced heater drain (150 ma for the
miniature 9001 tube as compared to
300 ma for the octal base 1620). Type
9001 tubes were employed in the preamplifiers and also in the booster and
driver stages since this tube makes a
very effective high -gain pentode stage,
and can also be used as a triode where
desired. A ßAK6 tube was used in the
output stage and a 6X4 tube as a rectifier. Unfortunately, the hum and microphonics resulting from the 9001 tubes
in the pre -amplifier and booster stages
were intolerable and these tubes had to
be replaced by 1620's, which are especially designed for low -level audio applications. The 9001 was retained in
the driver stage. as this stage operates
at a level sufficiently high that overall
performance is not degraded by the
tube. The 6AK6 was chosen since it is
the only available tube with a 150 ma.
heater which would deliver the required
+18 dbm output through a pad of
adequate size. The drain on the "B"
supply is small enough so that it presents less of a problem.
In addition to the partial use of low heater -drain miniature tubes, the "A"
battery life was further increased by
opening the heaters of tubes not in use.
Many remote broadcasts use only one
or two microphones; therefore the pow-
AUDIO ENGINEERING
Fig. 2. Portable amplifier with rear cover and
er switch was wired to disconnect the
heaters of the pre- amplifier tubes not
in use. This switch has five operating
positions in addition to the OFF position. The first position permits a.c.
operation with all tubes connected, the
next four positions are for battery operation with either four, three, two or
one pre -amplifier heater connected.
When the amplifier is operating from
its a.c. supply and a power failure occurs, the VIT meter pilot lamps and a
neon a.c. indicator lamp will go out.
The operator then has approximately
two seconds in which he can turn the
power switch to one of the battery positions without noticeable loss of program level or quality. In the event that
a.c. power is restored before the end of
the program, the operator is notified
by the a.c. indicator lamp and he may
then turn the power switch back to the
Ac position after allowing time for the
rectifier cathode to heat. The power
changes are not noticeable on the air.
To eliminate the possibility of the
internal batteries running down due
to the operator forgetting to turn off
the amplifier at the conclusion of a
broadcast, the batteries are interlocked
with the a. e. power cord. This cord
must he plugged into the amplifier for
the internal batteries to he operative
and must he removed to close the case
for transit. The power receptacle is
also arranged so that external batteries may be used when desired.
Test Tone
A unique feature of the amplifier is
the inclusion of a 400-cycle test oscillator for adjusting operating levels. The
oscillator is of the relaxation type and
employs a 1/25 watt neon -lamp which
also serves as a low -drain d.c. pilot lamp
JULY, 1949
battery cover removed.
when it is not used for adjusting levels.
This oscillator provides a direct method
for adjusting the level to the control
room, eliminates the necessity of setting
up a separate microphone near the amplifier, "woofing" the sound peaks and
watching the VIT meter. Test -tone is
also a help where the set up and level
check must be made under conditions
where "woofing" into a microphone is
not desirable. This sometimes happens
during a nightclub floor show where
quiet is demanded, or in a church where
the set-up must he made during part
of n service.
Monitoring Circuits and P. A. Feed
In the use of many portable amplifiers, it has been found that sufficient
volume has not been provided for head rhone monitoring in noisy locations,
so two jacks are provided for the phones.
The low -level jack is connected across
half of an isolated secondary winding
and operates at line level which is
normally satisfactory for headphone
monitoring. The high -level jack is connected across the full winding and allows the operator to monitor at a 6
db higher level, which helps to overcome extremely high background noise.
A third monitoring jack, for two -way
talkback to the control room, is con neeted directly across the line terminals
on the line side of the output pad.
When the headphones are plugged into
this jack, the operator can communicate with and receive program cue from
the control room preparatory to going
on the air.
The monitoring winding is also con neeted to a pad which furnishes microphone -level output to a 50 -ohm balanced
load. The connection is very useful for
feeding public address system inputs
13
www.americanradiohistory.com
or other portable amplifier. In the latter case seven input channels, with
sub -master control over four of the
channels, may be provided by connecting the MIKE LEVEL OUTPUT Of one
G -E portable amplifier to one of the
inputs of a second portable amplifier.
A full -size illuminated VU meter is
provided for convenience of operation.
A dimmer control and switch are used
to dim the pilot lamps or turn them
completely off if it is desired to decrease the drain on the batteries. In
addition to two volume - indicating
range positions on the VU meter selector switch, there are positions for
checking the two "A" batteries and
the `B" batteries. This makes it possible to check the condition of the bat-
teries without the necessity of using
external meters. The normal operating
position of the VU meter selector
switch is the +8 VU position corresponding to normal line level. A +14
VIT position is also included so that
the telephone lines can be fed at a
higher level in case of an emergency
condition where it may be necessary to
override high line noise. Although the
amplifier is rated at +18 dbm ( +8 VU
with a 10 db peak factor), listening
tests have demonstrated that quality
was acceptable at +14 VU even with
reduced battery voltages.
6 -DB Output Pad
The output of any amplifier which is
intended to feed a telephone line should
first go through an isolation pad. Such
a pad performs the following functions:
1.
Provides an essentially resistive source
for the telephone line by minimizing
the effects of varying amplifier internal
impedance.
2.
Provides an essentially resistive load
for the amplifier and VU meter by
minimizing the effects of varying telephone-line impedance.
The reason for the pad, then, is to
minimize the effects of impedance
variations in amplifier and line. It follows that the larger the attenuation of
the pad the less will be the effect of
varying impedances. Use of an adequate
loss pad will permit better line equalization, give more accurate VU meter
readings and permit the amplifier to
function at peak efficiency.
Examination of curves showing the
reduction of impedance variations versus pad loss indicated that at least 6
db must be used for high -quality performance. More than 6 db loss would
require an excessively large output
stage. A loss of 6 db in the isolation
pads was therefore indicated.
Either 600- or 150 -ohm output transformer connections and isolation pads
may be used. Selection is by means of
a screwdriver -operated switch. 600 ohms
is standard for use on 600 -ohm equalized circuits. 150 ohms is used on relatively short, unequalized circuits where
the low sending impedance provides n
degree of equalization which tends to
compensate for the transmission characteristics of the line.
Construction
The Type BA -6 -A Portable Amplifier
is housed in a lightweight aluminum
alloy case 12 inches high by 17is inches
long, and 8íi inches deep. It weighs
approximately 35 pounds, including the
weight of the emergency batteries.
When operated without internal batteries it weighs approximately 30 lbs.
A neat appearance is presented by the
Fig. 4. Measured performance characteristics of portable amplifier.
grey baked -enamel finish of the case
proper and the contrasting blue vinyl
plastic-coated fabric applied to both
tront and rear covers.
Removal of the front cover gives accesa to the panel, Fig. 1, on which all
of the operating controls are located.
The center section of the panel is finished in blue. The remainder of the
panel is finished in satin aluminum.
Above each mixer control is a write -in
space in which notes may be pencilled
and erased. Provision is made to store
the a.c. power cord within the front
cover.
Removal of the rear cover provides
access to the tubes, transformers, and
the battery compartment, Fig. 2. The
batteries are clamped in place by a
cover which is easily released by means
of four thumb nuts. Spare tubes and
fuses are clamped to the inside of the
rear cover.
Flush-mounted, snap-in access plates
are provided on the sides of the case
for access to the input and output connectors of the amplifier. The four input receptacles are mounted on the left
side, while the power, line output, and
mike level output receptacles, the line
output terminals, monitoring jacks,
and the output - impedance selector
switch are all located on the right side.
The access plates are attached to the
amplifier by small bead chains.
Audio Circuits
The schematic, Fig. 3. shows that
the unit consists of four pre-amplifiers,
a mixer system, and a program amplifier with booster, driver and output
stages. The master gain control precedes the driver stage.
The pre-amplifiers use type 1620 low noise, low- microphonic tubes, pentode-
connected for maximum gain. Inverse
feedback is used in these amplifiers to
reduce distortion at high input levels.
The taps on the input transformers
may be adjusted so that the amplifier
will operate from 30, 150, 250, or 600
ohms depending upon the type of microphone used. To further reduce microphonic and shock disturbances, the preamplifier assembly is cushioned with
soft rubber shock mountings.
The four pre-amplifiers feed directly
into a high -impedance mixing system
which eliminates the need for all transformers between pre-amplifier and program amplifier. The impedance ratio
of the ladder network attenuators is 1 :2
for minmum loss. High -quality, step type attenuators are used throughout
for smooth, noise -free operation and
long life.
Another 1620 is used in the booster
stage, as it may operate at a level only
slightly higher than microphone level
for extreme settings of the gain con [Continued on page 39]
AUDIO ENGINEERING
14
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JULY, 1949
Auditory Component Control
For
The Legitimate Theatre
JOHN H. BEAUMONT*
Sound for the theatre is rapidly coming into prominence, and the author
summarizes
the principal requirements which differ widely from broadcast and recording
practice.
of this article is to outline some of the requirements for
integrated systems for the control
of the auditory component of theatrical
production, and to indicate a line of
approach to their design. Theatrical
controls are a specialized application of
audio equipment; mere grouping of
commercially available units does not
constitute an adequate control system,
nor should control systems designed for
other audio applications be transferred
to a theatrical application without
modification. The problems of the operator in the theatre are to some extent
unique. as will be seen, and the demands
made on his equipment more complex than those encountered elsewhere.
While there seems to have been little
incentive for the development of this
type of control in the past, the initiation
of highly flexible electronic lighting
controls, as well as a growing recognition of the importance of the auditory
component of production, indicate a
need for the design and further development of flexible control facilities for
the legitimate theatre.
There is a general agreement among
those who have worked on auditory component control that the scope of this
control should include the following
elements:
THE PURPOSE
1.
2.
3.
4.
5.
'
6.
Control of the intensity of all sound
sources (loudspeakers).
Control of the apparent movement of
sound sources on the stage and in the
auditorium.
Controlled reinforcement of speech and
and other sounds originating on stage.
Controlled dubbing of voices or other
sounds onto actors, props, or scenery.
Control of the audio spectrum for dra
matic effect.
Control of the apparent reverberation
of the space in which sounds are heard.
In terms of control equipment these
require a system capable of controlling
the gain, frequency response, reverberant quality and distribution of one or
more signals. Control should be in the
hands of a single operator, placed where
he can see the stage and hear the sound
he is controlling exactly as the audience
'Vice President, Audio Facilities Corp.
AUDIO ENGINEERING
is hearing it. This indicates a type of
control which is complete, compact, easy
to operate, and capable of being remoted
from the bulk of its associated amplification units. Development up to this
time has followed broadcast practice in
many respects. Input devices have
usually been associated with an input
amplifier; control has been applied at
line level and the resulting signal given
further amplification before distribution.
Advantage of Remote Control
In theatrical control equipment, it
has generally been the custom to control
the signal directly. When the control
console is remeted from the amplification facility, as is often the case, signals
must be carried through relatively long
mechanical controls on the basis of
simplicity. Non -signal controls, whether
the control intelligence be a.c. or d.c..
releases the remote console from practical considerations of line length, and
renders the control cable installation
non -critical in terms of hum pickup and
frequency losses.
Usually a single input source is associated with a single input amplifier
(no switching being done at this point).
and a single loudspeaker unit with a
single output amplifier. While it is not
generally necessary to shift a speaker
from one amplifier to another during a
show, this control should be available
in case of amplifier failure. Control
systems should he designed to allow
insertion of the number of units which
Fig. I. Vertical type
mixer attenuator
manufactured
by
Tech Laboratories.
Photo by Bullock
lines to and from the control position,
and other elements of control added to
the signal at this point. Neither of these
limitations are particularly satisfactory
and this author prefers, as a design axiom, that the audio signal should not
leave the amplifier facility between the
input amplifier and the speaker distribution point. This requires the use of
non -signal controls. There are several
possible approaches to such control;
electronic means being preferable to
JULY, 1949
will be needed for a given operation so
that the above associations may be used.
Use of frameworks or banks bussed for
the largest expected installation not
only provides this flexibility for portable equipment but allows a fixed installation to be increased in capacity as
needs and budgets dictate.
Flexibility
Flexibility is usually provided by the
use of a number of signal busses between input and output amplifiera. The
15
www.americanradiohistory.com
Fig. 2. High quality tape recorder which may be used on location recording, as
well as for reproducing previously recorded tracks in the theatre.
Courtesy Ampex Electric Corporation
amplifiers are bridged onto these as de-
sired, providing a number of separate
channels which may be controlled independently. Control may be inserted in
these busses or bridged onto them with
the amplifiers, depending upon the control solution. The number of busses is
indeterminate, though three has been
considered an optimum. Further flexibility is generally provided in the form
of speaker distribution switching, for
reasons mentioned previously. When
other distributions or divisions of equipment are desired, such as disposition of
amplifier elements between two or more
control units, they may be accomplished
by the use of patching panels at the
amplifier facility. Patching should be
used only where it will not be changed
during an operating setup.
It has seemed desirable to provide
level control for both input and output
amplifiers, providing, in effect, a dual
control in any complete signal path.
This is necessary because the general
case will be a single input source operating into a number of output amplifiers
whose controls will be needed to provide
control of the sound distribution. Master gain control should be added in the
busses when the total number of input
or output controls is too great to be
handled at the same time by one operator.
Trends in control element design are
indicated by Fig. 1, which shows a
type of vertical acting gain control
which has been used for theatrical purposes. Vertical action finds favor with
operators because of ease of operation,
readability during operation, and the
possibility of operating several adjacent
controls with one hand. Commercially
available units are still too large for
effective spacing, and the best solution
is a fabricated unit not. more than an
inch in width overall. Rotary controls
are definitely unsatisfactory for theatre
systems and should never be specified
where settings must be made from cue
sheets or where more than one control
must be operated at a time.
Input Signai Sources
Operating experience leaves little
doubt that tape reproducers are the
most satisfactory input devices for theatrical use. Units such as the one shown
in Fig. 2 provide a convenient, quickly
cued, high -quality input source. Recording is a relatively simple process, and
tapes may be edited for minimum operating complexity. Most, or all of the re-
Fig
.
3.
Transcription turntable suitable
for theatrical use.
Courtesy Gray Research
&
Development Co.
quired sound for a show may be collected on a single track, edited for sequen
tial playback, and run with a minimum
possibility of error.
Turntables will be needed in a corn prehensive control setup in addition to
tape inputs. These should be 16" transcription type tables with a cuing device
such as that offered on the turntable
of Fig. 3. Special effects may be produced with variable speed turntables,
though such effects should normally be
recorded on tape rather than being produced on the spot.
Other input sources will include special tone generators, effect devices, voice
synthesizers, and so on. They need not
be mentioned here, though Fig. 4 illustrates a device used for the electronic
production of rumbles and thunder. This
device consists of the driving unit from
a Farrand inductor speaker with a taut
square of wire screening attached in
place of the cone. It is essentially a
crude form of contact microphone which
produces excellent rumbles when the
screen is stroked with the fingers.
There are a number of opinions about
the best speaker and baffle for use in
any application. Infinite baffles with
high-quality cone radiators seem currently to be gaining favor over conventional reflex types because of better
damping and absence of peaks in the
response characteristic. In theatrical
applications, where loudspeakers are often driven at extremely high levels, any
housing which allows excessive cone excursions at the low frequencies is inadvisable. For this reason it is felt that
the best enclosure for theatre use is a
heavily constructed infinite baffle using
a good cone radiator. When extended
high-frequency response is desired,
horns and crossover networks should be
added. Enclosures should be constructed
of heavy plywood and fitted with connectors capable of withstanding the
rough handling they will receive. They
should be fitted with flying rings for
theatre use, and may have carrying
handles and casters. These will be sources of rattle unless provision is made
to dampen them.
With the development of high-efficiency radiators the need for high output power is being diminished. The
Western Electric 728B offers an acoustic level of 93.5 db at thirty feet on the
axis for a power input of 30 watts, while
the 754A of the same manufacture offers a level of 94 db at the same distance
for a power input of 15 watts. The frequency range of the two is substantially
the same, and it would seem logical to
use the lesser power in order to reduce
hulk and weight in the equipment.
Equalization
Equalization networks must be cap -
AUDIO ENGINEERING
16
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JULY, 1949
able of relatively complete and flexible
control over the audio spectrum. The
type most used in the theatrical work
is the well known cut and boost control
for the ends of the spectrum, and one
should be available to every input device in a control system. In addition,
a set of band-pass filters offering spectrum control over at least three bands
should be available for control at the
signal busses.
All equalizers should have continuously variable controls. Switching types
may cause noise if used during an effect, and there is a psychological advantage to the operator in having continuous control even though it is not
likely that increments smaller than
those provided by switching systems
will be net.lcd.
control systems it should be optional,
under the control of the operator.
In many cases the controls mentioned
may be used in a recording setup, thus
simplifying the nature of the playback
operation considerably. When tape is
used all possible control should be applied to it during the recording process
for this reason. It is probable that most
theatre installations will make use of
the same equipment for both recording
and playback operations, so the controls
must be considered part of the system.
Control consoles should be operated
from the auditorium to provide the operator with maximum visibility and audibility. In the ideal case the ear should
be situated in the saine location as the
audience ear, surrounded by no enclosure. This is seldom possible, but all
compromise positions should attempt as
far as possible to allow the ear of the
operator to share the auditory experience of the audience. Enclosures should
be no larger than needed for conceal-
Level Indicators
While the VU meter seems to be of
little technical value in theatre control
systems since there is no relation between its indication and the sound level
Dependability and ease of maintenance are universal requirements for
electronic apparatus. Theatrical systems
must be designed according to the best
current practice for easy and rapid
maintenance and replacement of units.
Preset Controls
No attempt, so far as this author
knows. has yet been made to apply preset control to theatrical sound equipment. Preset devices have been used in
stage lighting controls, and the most
recent of these instruments has proved
to be an important advance in the capabilities of that control. The application
to sound control apparatus would be
valuable in that it would further reduce
operational complexity and the possibility of operational error. All functions
of control described can be subjected to
preset operation.
Summarizing the main requirements
for effective auditory component control, we find that the following are desirable:
I. Maximum flexibility. of control; all
elements controlled from a single op2.
3.
Electronic
thunder - screen
Fig. 4.
mechanism.
4.
5.
6.
Photo by Bullock
7.
7.
in the auditorium, it is the standard
and most economical means of indicating the signal level in the system.
Meters are usually bridged onto the
signal busses, where they provide a visual signal reference, and may be used
as a means of monitoring. For cue setting, meter indications are inferior to
an aural monitor, which may include
a hearing aid type earphone.
Systems must be so designed that
they cannot overload on the largest expected input modulation with all controls full open. This should be done
without recourse to level limiting amplifiers or compression circuits. The use
of output amplifiers having an adequate
peak power capacity will aid in this, as
well as providing an adequate dynamic
range without the use of expansion circuits. Such circuits are to be avoided
because of the resulting circuit complexity and possibility of distortion.
Discussions regarding the use of loudness control tend to the conclusion that
if this feature is to be used in theatrical
AUDIO ENGINEERING
inert, and should be located as near as
possible to the optimum acoustic position in the auditorium. Enclosed booths
using a secondary monitor for the sound
are no better than a backstage position
so far as the operator's oar is concerned.
Ag.
5. Example
erating position.
Control console remoted from equipment facility; operator in position of
good visibility and audibility.
Uninterrupted signal path from input
device to output distribution; no
signal leaves epuipment facility for
control purposes.
Ease of operation; preset control.
Dependability and ease of maintenance.
Unitized construction, and standardization of units.
Reduction of bulk and weight to a
practical minimum.
Assured high fidelity.
\o theatrical control system up to
the present time has offered all these
features. While dependable, high control systems are in existence, they are
not yet completely engineered in terms
of the above discussion. The legitimate
theatre needs this extension of its facilities for the control of production
elements.
of inadequate theatre sound system, which is simply
assembled with p -a system techniques.
a
makeshift
Photo by Bullock
JULY, 1949
17
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Importance of Groove Fit in
Lateral Recordings
D. R.
ANDREWS'
Relating frequency response to groove
THE process of reproducing disk re-
cordings is done primarily with a
mechanical system. The power to
actuate the transducer is derived from
the force developed between the stylus
tip and the sidewalls of the record
groove. It is obvious that good contact
must be maintained between stylus and
groove sidewalls for faithful reproduction. With the introduction of permanent styli, soft thermoplastic record materials, and fine-groove recording, this
contact becomes even more important.
Some means of determining the amount and position of contact between
stylus and groove is of fundamental importance to the development or design
engineer, and:
Measurements of frequency response
may furnish clues to groove fit if properly interpreted.
2. Another valuable source of information
is a proper analysis of intermodulation
distortion measurements.1
3. A third method, and one simpler to
interpret, is simply to compare visually
the size and shape of both stylus and
1.
groove.
this subject entitled "Intermodulation Distortion Analysis
as Applied to Disk Recording and Reproduc1
A general discussion of
Sound Engineering Section,
RCA Victor
Division, Camden, N. J.
alms
PLAYBACK STYLUS
AVM'
PLAYBACK STYLUS
TIP
8..0025'
m
TIP R..0025'
GROOVES CUT WITH 70' STYLUS
(TIP RADIUS .0017')
fit
in
practical discussion.
ins Equipment" by H. E. Roys was published
resonant conditions, especially the one
occurring at the high frequency, the
stiffness and yield of the record maResonance and Damping
terial cannot be disregarded. The term
As stated in the introduction, a phono- "yield" is applied to any pliable materigraph reproducer is essentially a me- al which changes position with time.
chanical device. Regardless of the type This is the property of a material which
of electrical or accoustical generator provides good damping qualities. It
employed, its primary system must be does not necessarily imply that the maassociated with all the advantages and terial takes a permanent set in the
disadvantages of a mechanical system. changed position. When the material
It is well to remember that a mechani- takes a permanent set in the changed
cal system usually has a very high "Q ". position, it is known as "cold flow."
The driving force which operates the
Unless proper damping is employed,
resonant conditions may be present. reproducer is transmitted from the recThe mass of the moving system, in ord material to the stylus tip through
conjunction with its centering spring a linkage formed by the contact between
and the compliance of the record ma- the stylus tip and the sidewalls of the
terial, resonates at some high frequency. record groove. It is obvious that any
Since the stiffness of the record materi- variation in the amount of contact area
al is usually many times that of the will change the effective stiffness and
centering spring, this stiffness becomes damping of this linkage, and consean important factor in establishing the quently the stiffness and damping of the
frequency of the resonance point. This entire system. The record material,
frequency is usually kept near or above especially if it is a vinyl compound or
the upper limit of the usable frequency some soft thermoplastic substance, has
range. The mass of the entire repro- considerable compliance. Changes in
ducer and tone arm in conjunction with vertical force on the reproducer will
the compliance of the centering spring therefore change the amount of contact
resonates at some low frequency. This area between the stylus and record mais generally known as "tone arm reso- terial due to compliance and yield. The
nance". In considering either of these contact area will vary even more with
changes in vertical force when using
fine groove records due to the small radius of the stylus tip. With a smaller
tip, the unit pressure between stylus and
record is increased. Differences in size
and shape of the stylus and record
groove can also vary the contact area.
The effect of these differences on frequency response may be quite interest.00s\
ing.
PLAYBACK STYLUS TIP 8..0025'
in Proc. I.R.E., October, 1947.
PLAYBACK STYLUS TIP
GROOVES CUT WITH
8..0025'
90'
STYLUS
(TIP RADIUS 0017')
Fig. I. Groove fit for various radii of the reproducing stylus when superimposed
on different groove shapes.
Typical Groove Fit Examples
Figure 1 shows a sketch of the fit
between stylus and groove when using
various sizes of styli. Under ideal conditions the stylus is pinched firmly between the sidewalls of the groove. The
stylus tip should also be well off the
bottom of the groove. If the stylus
touches the bottom of the groove, the
sidewalls do not have complete control
of the stylus, and if the stylus contacts
the groove too near the top, the irregu-
larities of the surface may introduce
AUDIO ENGINEERING
18
www.americanradiohistory.com
JULY, 1949
Fig. 2. Shadowgraph of stylus riding on bottom of groove, resulting in curve (A) of Fig. 3. Fig. 4. More nearly ideal
groove fit, with curve (B) of Fig. 3. Fig. 5. Groove fit resulting from use of stylus too large for the groove being
reproduced. Response curve (C).
noise. Figure
S
r
2 shows a photograph of
shown in Fig. 2. The center curve on
of record grooves have been used. At
an actual stylus and groove illustrating Fig. 3 shows the frequency response ob- the present time, it looks as if this conpoor groove fit with the stylus touching
tained with this test record. The sharp dition will be relieved somewhat. The
the bottom of the groove. This photo- resonant peak of the top curve has now National Association of Broadcasters
graph was made from a frequency test been reduced to a mere hump.
has appointed a committee for the purrecord with the aid of a shadowgraph
A third frequency record is shown in pose of setting up standards for disk
projector. The record was first shattered. Fig. 5. This photograph shows that the recording. This committee has now ofA section was then selected with a bro- stylus will be pinched tightly between fered proposals for establishing groove
ken edge perpendicular to the record the sidewalls of the record groove. This size used on transcriptions. The Radio
grooves. This section was placed on the is not an ideal groove fit because the Manufacturers Association also has a
projector so that the surface of the rec- sidewalls are contacted so near to the committee working on standards for
ord was tilted approximately 20 deg.
record surface that noise may be in- use with home phonograph records. The
from a plane through the center of the
troduced. The bottom curve on Fig. 3 R.M.A. committee has proposed limits
light beam. The film on which the shad- shows the frequency response obtained of 2.5 to 3.2 mils as the radius for
ow was projected was tilted approxifrom this test record. The resonant peak reproducing styli to be used with this
mately 20 deg. from a plane perpendichas now been nearly entirely eliminated type of recordings.
ular to the center of the light beam. with damping.
The new fine -groove records are cut
This was done so as to correct partly
By careful observation of Fig. 3, it with a 0.5-mil or smaller stylus and
for the error in the included angle of may be seen that as the groove fit is im- should be played back with a stylus havthe record groove caused by the angle proved the frequency of the resonant ing a tip radius of 1.0 mil. At present,
of the record material in the light beam. peak is increased. This indicates that the size of this playback tip is generally
This correction method is not mathe- the stiffness of the mechanical system accepted by all those concerned with
matically correct due to the keystoning has also been increased.
fine-groove records. It is hoped and it
effect on the film, but its simplicity Summary
seems entirely possible that eventually
seems to justify its use since the error
The layman will undoubtedly ques- all disk recordings will be cut with fine
is negligible for all practical purposes.
tion the need for such painstaking care. grooves and one standard will be estabThe stylus was also projected onto a
Even many technical people do not lished for all classes of records.
film by means of the shadowgraph prorealize the fact that standardization
In conclusion, if consistency of rejector using the same magnification fac- has not been followed in the choice of sults and high quality is expected,
the
tor. The two films were then superim- stylus size by all concerned. Many dif- factor introduced by the size and
shape
posed making a composite picture such ferent radii have been used for the tips of reproducing stylus and groove canas that of Fig. 2.
of recording styli. Also different depths not be disregarded.
The frequency record used for making the photograph in Fig. 2 was reproduced with a standard model tran45
scription reproducer before shattering.
The upper trace in Fig. 3 shows the
40
frequency response obtained from this
ó
35
test record. There is a noticeable peak
in the curve near 8500 cps. This peak
30
is probably due to the mechanical resoá
nance described above. Since there is
25
o
very poor contact between stylus and
sidewalls, as evidenced by Fig. 2, very
i 20
P
little damping is supplied to the me15
chanical system from the record maá
terial.
10
A second frequency record was shat5
tered and shadowgraphed in the same
manner. Fig. 4 shows a photograph of
020
2o0oo
this record. The stylus does not touch
100
1000
10000
the bottom of the groove but is very
FREQUENCY IN CYCLES PER SECOND
near. The groove fit is not ideal but is Fig. 3. Frequency response curves made from the same record with three different
a considerable improvement over that
stylus radii.
,
AUDIO ENGINEERING
JULY, 1949
I9
www.americanradiohistory.com
A portable audiometer with bone conduction receiver
at center and air conduction receiver at right. The small knob
atleft is for calibration. The large knobs are for frequency and
intensity.
(Courtesy Bell Telephone Laboratories)
Fig. I.
ókahIc'n44
in
Clue/to
EiiRinernincj
LEWIS
GOODFRIEND*
S.
Articulation, its measurement, and its relation to
intelligibility in the determination of the degree of deafness.
Part III.
TILE Sol' \Ili of speech are
joined to form words they are
said, by definition, to be articulated and the process is known as articulation. This word-articulation-has
been borrowed by audio and communications engineers to describe the ability
of a system to transmit articulated
speech sounds without reducing the listener's ability to understand them. In
adapting the word it has been convenient to express the degree of understanding as the percentage of the original speech sounds fed into the system.
This appears to be easy, but after more
than thirty years of use of the method
there is no standard technique available to determine the percentage of
articulation. All of the common systems
are similar, and it will suffice to describe only the fundamentals here.
Basically an articulation test consists
of a reader who actually makes the
speech sounds, the system to be tested,
and a listener to record the sound as
transmitted by the system. In order to
obtain a quantitative result special lists
of speech sounds and words have been
prepared. In general several lists read
by several readers and recorded by
several listeners are used.
The types of sounds that go into a
list such as the Bell Telephone Laboratories' "The Standard Articulation
Testing List" are carefully selected
to include all the sounds used in
speech. These sounds are combined
into vowel -consonant, consouant- vowel,
and consonont-vowel- consonant forms.
WHEN
These tests, however, can be used only
with trained observers. It is therefore necessary to have lists of English
words, of either one or two syllables,
and in groups such that they will include all the basic speech sounds. Using only the combined speech sounds
it is possible to obtain more information in a shorter time than with
word lists, but with the word lists, unskilled observers and callers may be
used with the possible introduction of
memory and association effects that
may cause error.
In the Bell Lab's speech sounds list
we find groups like his, moush, ár
and fin. In the list of monosyllablic
words we find these: tie, thy, by, wing.
high, wick, and so on. It can be seen
that, with either of these or with the
new phonetically-balanced word lists
prepared by the Psycho- Acoustic Lab oratory, if the degree of articulation of
the system is poor, many of the sounds
will be confused with others and hence
the percentage articulation will be low.
S. T.
AUOIOGOAM Or
Intelligibility Test
Another torn' of test that is similar
to the articulation test is the intelligibility test. In this type test the listener is called upon to derive intelligence from a sentence, either interrogative or imperative. In either case a
single word or mark acts as an indication of understanding or intelligibility
However in this type of test the listener
receives cues to hard sounds from context. Nevertheless, it appears to be a
fairer test of the usefulness of a piece
of sound transmission apparatus, since
that apparatus will be used to transmit
intelligence, not disconnected sounds.
It is only natural that the articulation and intelligibility tests are used to
study the characteristics of rooms
which are actually communications systems involving acoustical paths -and in
the study of deafness, which involves
both acoustical and psychological paths.
To see how they are applied in this latter case we must first understand deaf Iles.
c
-
42
Bronson
0,.,
.6/7 42
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4413
Fig.
2.
Audio -
gram of a subject
with nerve deafness. High (95db)
110411/144
ID 0
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ro.
IOU Or *MAW/6 VON AG
w
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10
20
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SWIM/ ).0.:_
In artillery --
hearing loss
above 2 kc is indicated.
É
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sm
100
ao
120
141.1/1110(7
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*Rangertone, Inc., 73 Winthrop St., Newark
4, N. J.
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10248
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AUDIO ENGINEERING
20
www.americanradiohistory.com
JULY, 1949
Deafness is the condition that exists
when a listener does not perceive sounds
of normal character and intensity but
has a threshhold of hearing which is
considerably above the normal, or when
a listener is unable to understand speech
at normal levels. Persons who have dif-
ficulty in the perception of normal
speech and music are assumed to be
deaf, but there are many people who
are partially deaf and, although their
personal efficiency and possibly their
social adequacy has been impaired, they
are not aware of the condition. To determine qualitatively whether one is
deaf it is necessary to measure his
threshhold of hearing, and his scores
for articulation or intelligibility tests.
There are three common types of
deafness: nerve, conduction, and central deafness. In nerve deafness, some
of the sensory cells or nerve fibres of
the inner ear may degenerate, and a
loss of hearing in the frequency region
associated with those nerve or cell tissues will result. In conduction deafness,
however, the nerve cells are intact but
there is some obstruction in the acoustical path which reduces the intensity
of the signal as it passes through the
outer and middle ear. This can result,
tor example, when wax blocks the ear
canal or gets on the ear drum, or in
otosclerosis when a bony material forms
about the ossicles and inhibits their
motion. In central deafness the nerves
and path to the inner ear may function
Fig. 3. Two cases of conduction deafness. Subject of (A) did not require an
aid, while subject of (B) did.
,
MS
.»
.. ..
-10
10
0
0
1a5
10
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É
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3
a
yp
N
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100
110
110
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70
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100
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B
AUDIO ENGINEERING
-r
110
1m
Results
5
of hearing tests
a
conducted at
1939 - 1940
15
Fig.
4.
World's Fair.
Hearing
z..
10.19
TV
o
.
3039
.-
...
40-49
30-39
WOMEN
MI
loss vs
frequency
is
plotted for various age groups.
(After Steinberg, Montgomery and Gardner; courtesy J.
Acons. Soc. Am.
and Bell Telephone Laboratories)
20-29
0
5oy;
10-19
0-29
Sp-39
s
10
15
40-19
MEN
.0
0'5.
I5
4
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0
990
FREQUENCY
normally, but the brain itself does not
take cognizance of the signals from the
auditory nerve. This may be the situation in cases of psychological deafness
such as battle- fatigue, and in cases of
brain diseases or injury.
Threshold Measurement
In order to measure an individual's
ability to hear, early tests used the distance a watch tick or coin click could be
heard as an index. However, tests of
this type include only narrow bands of
frequencies and actually indicate
threshold only for this group of frequencies. In order to compare the
threshold of hearing of a given subject
to the normal threshold, we need an
instrument that will indicate how many
decibels the subject's threshold is above
or below the normal. Such an instrument has been devised and is known as
an audiometer. Figure 1 shows a typical
audiometer of the type used to obtain
the data, known as audiograms, which
will be discussed. To obtain these data
the instrument is calibrated with a self contained calibrating signal, and is
then set to the lowest frequency with
the output control set to minimum. The
level is then raised until the subject
indicates that he just hears the tone. To
aid in determining this point a switch
that cuts the signal on and off is provided. The level at which the subject
first hears the tone is recorded and the
data for all the other test frequencies
are obtained in like manner. In performing the test the subject has the
headphone on one ear for the entire run
of frequencies and then repeats the test
for the other ear. Several factors must
be watched. carefully in performing this
test. Thè most important is the back grouñd nóise, which should be very low.
Another is the understanding on the
JULY, 1949
1760
IN
CYCLES
3520
PER
7040
SECOND
part of the subject as to what he shall
indicate. Several authorities believe in
using cotton in the ear not under test,
but this usually does not increase the
comfort of the subject and, therefore,
may lead to erroneous results. The audiometer may also be provided with a
microphone, bone conduction receiver,
sound level indicator, and a masking
source or provision for masking input.
This last item is used when testing
the poorer ear in which case the sound
travels to the good ear by bone conduction through the skull. It is necessary
to mask this tone in the good ear with
noise from the masking source. In conduction deafness where the sound path
from the air to the inner ear is obstructed, the results of the bone conduction
test using the audiometer should be
about the same as hone conduction results for a person with normal hearing,
and the bone conduction receiver is
used for that test. This is the common
test for determining whether conduction or nerve deafness exists.
In testing for the ability of a person
to meet the problems of daily life (social adequacy) articulation tests prove
very useful. A person with partial hearing loss may not require a hearing aid
at all in order to maintain social adequacy, although he may have a flat
20 -db loss throughout the entire audio
spectrum. Other people with "notches
in their audiogram may find it very
difficult to get intelligence out of normal speech although their audiogram
is almost normal. The microphone can
be used to give audiometer articulation
tests to find the speech threshold.
Determining Hearing Aid Need
It is difficult to judge whether a given
subject requires a hearing aid or not,
[Continued on page 37]
21
www.americanradiohistory.com
HAVM. DISPOSED of Koeschel & Co. last
month, this department moves on to
more of those inexplicable terms that
constantly stare you in the face (or hit your
suavely in the ear as parts of musical titles.
This month's main problem is Italian, allegro
EDWARD TATNALL CANBY*
con variazione.
Two aspects to tackle here -the facts and
the prejudices. Take the latter first. Now as
any Italian knows, the Italian language is
just another language (albeit, to him, God's
Own language, no doubt). It may be highflying and elegant or it may be slang or
worse. Language, any language, is designed
to cover all possible situations. It is a funny
thing, then, that whenever a language is
borrowed by those who speak another
tongue, it turns up high brow. French frieds
are just potatoes, but pommes /rites are
something else again. In French Canada a
chien chaud is exactly what it says, a hot
dawg. But in New York it might turn up
daintily
as a
Saucisson a la Frank/urtois-
and even though that term maybe doesn't
exist, it sounds lots fancier than Frankfurter.
It's hard for us to believe, but when you go
to Paris you'll discover that the French use
English terms when they want to be really
fawncy, just as we use French.
And so the use of Italian terms in music
(to be explained in a moment) is automatically a high brow business, as every
radio announcer knows. The higher the brow
the better. Your announcer doesn't just rattle off the Italian -he puts sauce on it. No
matter that if translated it may mean nothing more than `fairly fast but not too much
so "! The Italian musical menu sounds just
as superduper (to us) as the French one
looks. Therefore, let us first of all realize
that this high brow stuff is neither here nor
there, or it wasn't when Italian first became
common for musical designations. It's neither
the music's fault nor the performer's that
we insist on it.
And why Italian? Consider first, that music is very much an international language
of its own, with national dialects, so to speak,
but using roughly the same musical sounds.
And music is widely exchanged internationally. The musical notes themselves are universal-they have meaning anywhere-even
in Russia. But musical notes (we do not
often enough realize) are only the merest
approximate indication of the actual sound
of music. Composers either (a) expect you
to know what was intended or (b) they
supplement the written notes with instructions. Even so, with the fanciest instructions,
music still isn't written down exactly, or
anywhere near it. And so those instructions
may loom quite important.
But if music is international, language
279
W.
4th St., New York 14, N.Y.
isn't. And hasn't been since Latin went out
as an internationally used language. What
to do, if you want your instructions to go
along with your written notes? That problem
came up first when Europe began to get out
of the feudal state and the invention of printing made it possible really to distribute
knowledge in written form from one place to
another in the mass. Music was a bit late in
getting down to the idea of specific written
notation, complete with instructions. (Earlier scores take a large amount for granted,
including even the choice of voices or any
instrument that happened to fit.) By the
time it did, the great center of music happened to be Italy. For some two and a half
centuries Italy was the musical country; almost all musicians were as a matter of
course Italians, and Italian music and musical style were carried everywhere. (Germany became a top musical center only in
the 19th century and lasted in top position
just about a hundred years.) What could
be more natural then, that during this period
musical instructions were written in Italian,
the language that went along with the music and most of the musicians that played
it. Italian was so universally used that Handel in England wrote operas in Italian and,
later on, so did Mozart, in Austria.
And naturally, the Italian instructions
tended to form a kind of slang; they
crystallized into fixed phrases that quite
often were slang -that is, their literal meanings were changed for a special meaning
that everybody knew. Andante is, literally,
a term meaning "to go "; but in music it
has been applied to music of a certain speed
which seems to "go" right along -yet not
fast. Everyone knows, within a rather large
plus-or -minus tolerance, what kind of music
"Andante" indicates. We find, today, the
same kind of thing in our own language,
applied to our own musical specialties where
we Americans are on top. "Hot ", for instance -and that term with its special meaning is already international, as witness the
famous French book, "Le jazz hot".
In the long history of music the top ranking place was Germany's for only a short
while, and today it is anybody's with Russia
and France about equally important and
America clearly on the upswing and likely
to take over. Many composers have patriot-
ically (if somewhat impractically) used their
own language for instructions. Schumann always used German and so did other German
musicians. Numerous Britishers have used
the British tongue, and Debussy-typical
Frenchman -plastered his scores with quite
elaborate French. But so far Italian remains,
out of convenience, the language that one
uses for international purposes; musically it
is every composer's second language. The
tradition continues because it is still useful,
even though Italian music is relatively but
a memory nowadays. (Remember that since
we today spend most of our musical time in
the past, playing older music, the great
period of Italian importance is for all intents and purposes still very much with us,
even though living Italian composers and
performers no longer dominate music.)
I'll save the question of what is meant by
the various and confusing Italian terms for
a later opus, but one more point before
the editor begins to cut this to size. Why do
they use Italian instructions for titles
especially if they are not really highbrow
but merely so much matter -of -fact slang?
Why do we solemnly print on our programs
such jargon as "allegro con moto ma non
troppo" as the "name" of a piece? ( "Fast
-originally it meant happy -with movement, but not too much "). Why, in a symphony of four or even more movements, do
we print, one under the other, a whole set
of these terms?
Logical, if you look at it. In the first
place, music makes its own sense and it
doesn't necessarily have to have an explanatory title in the usual sense. It may be
just music. A piece doesn't have to be
named "Mount Fiddlesticks by Moonlight
in September" to make sense. Most music
is not given any name at all unless merely
to indicate its general type or shape
which case we usually print that as its official title- rondo, for instance-plus an
identification of some sort to distinguish it
from a thousand other rondos. But there may
be lacking even this, and there usually is.
Composers write music, not stories. In fact
the only bit of description in printed words
that is attached at all to many pieces of
music is the simple indication in Italian at
the beginning that gives an idea of the
speed and /or the mood.
So, if you are to print a program which
lists the music to be played and you want a
handle for it, there's nothing to get hold of
except that -unless you give it a real musical title and print actual musical notes!
That being slightly impractical, the printed
instructions at the beginning are taken as
an official title and we speak of "the" andante ma non troppo from so- and -so symphony, which is utter nonsense if taken
literally ( "We will now play the going but
not too much ") but quite reasonable and in
fact inevitable, if you follow my somewhat
-
-in
lengthy logic!
)Continued on page 331
AUDIO ENGINEERING
22
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JULY, 1949
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For Hand or Stand.
List Price
JULY, 1949
-53
Impedance Selector.
$60
23
www.americanradiohistory.com
NEW PRODUCTS
The Omegatron Brush is the newest
contender for the honors .d static elimination, and when first seen appears to be "out
of this world." It consists of a fine three inch camel hair brush on which is mounted
a strip of polonium, a decay product of the
uranium- radium series. With the Omegatron
brush. record collectors can maintain the
fidelity of their discs indefinitely because
they can remove thoroughly the accumulation of dust and lint. Wiping with a conventional brush or with a cloth only causes
a greater static charge, which immediately
reattracts the dust. This is particularly objectionable with vinylite records, and the
Omegatron makes it possible to clean the
disc completely.
Polonium is a pure alpha particle emitter
(no harmuful beta or gamma) and the
velocity of the particles is sufficient to enable
them to traverse about 4 cm of air. Near
alpha particle sources, air loses its insulating properties and dissipates the accumulation of static electricity in nearby
objects. The renewable polonium strip has
a life of one to two years.
The Omegatron brush is manufactured
by Nuclear Products Co., 424 So. Broadway.
Los Angeles 13, California, who will supply
any further information desired.
Omegatron
ii
Sorensen & Co. Inc.
Audio Instrument Co.
The Sorensen B- Nobatron, bearing
a regulated d.c.
power supply which provides easily adjustable output voltages in two ranges -from
0 to 325 volts at a maximum of 125 ma, and
from 0 to 150 volts at a maximum of 5 ma.
Either terminal of the high -current section
may be grounded, but the 150 -volt supply is
connected internally to the negative terminal
of the 325-volt supply. In addition, the unit
provides 6.3 volts a.c. at a maximum current
of 10 amperes. The regulation is within 1
per cent for any voltage setting from 20 to
325 volts over the range from no load to
full load. Regulation also compensates for
line voltage variations between 105 and 125
volts, holding within 1 per cent over this
range at full load current.
The unit, weighing approximately 45
pounds, is available either in a cabinet or
for rack mounting. Complete specifications
may be obtained from Sorensen & Co., Inc.,
Stamford. Conn.
Anti -Static No 79, mentioned in this
column in the May issue, is the product of
Merix Chemical Company, 1021 E. 55th St..
Chicago 15, 111. This material is a liquid
which is simply wiped onto a surface, and
when dry will prevent static formation.
The Model 121 Logger, a product of
the Audio Instrument Co., 1947 Broadway,
New York 23, N. Y. indicates both maximum
and minimum program level on the same
meter range, and measures system noise level
in silent intervals. The output is linear in
db. and is indicated on the scale of a meter
calibrated uniformly over a range of 50 db,
as shown. With the output feeding a direct
writing oscillograph through a suitable amplifier, it will record acoustical reverberation,
the efficiency of studio operators in riding
gain, or numerous other measurements. With
generally available oscilingraphs. the Logger will record level variations as fast as
2500 db per second.
The logarithmic operation is instantaneous, and is achieved by the use of a new
material operating with accurately stabilized
bias. The built-in meter has the same operating speed as a standard VU meter, and for
more rapid action, output may feed a 'scope.
Unit includes preamplifier and necessary
power supplies.
Magnecord, Inc., 360 N. Michigan
Ave., Chicago, announces a new portable
tape recorder mechanical assembly, the
PT6 -MA, for the professional user. This assembly consists of the basic tape drive mechanism and the auxiliary spooling unit in
a portable carrying case, and is designed
to work with any of the amplifiers manufactured by the same company. With the
larger spools, the combination has a capacity
of 64 minutes at a speed of 7%" per second
or 32 minutes at 15" per second. At the
higher speed the instrument has a frequency
response of 50 to 15,000 cps -* 2 db with
less than 2 per cent harmonic distortion at
full modulation. The unit form of construction permits the user to purchase only such
components as are required.
"Sig -Max,' a simple means of matching FM and TV receiver inputs to the antenna, is a device which slips over the transmission line to improve the strength of low level signals. To adjust, it is only necessary
to tune in the weak signal, clip the unit
onto the 300-ohm line. and slide slowly
along the line to the point where the signal
strength is adequate for good reception.
Once the correct position is determined. Signo relation to the above, is
Magnecord, Inc.
"Sig -Ma.
Livingston Electronic Corp.
Triad Transformer Co.
Max may be secured tightly by squeezing,
or it may be held in place by tacks or
screws. The device is a product of Telcite
Television Corp., East Islip, N. Y.
Livingston Electronic Corporation,
Livingston, N. J. has added to its line of
audio products a commercial version of the
Loudness Control. This unit provides twenty three steps of attenuation compensated in
accordance with the Fletcher- Munson curves.
Fabricated in an aluminum shield can with
a three -terminal connection on the rear, it is
designed to be substituted for the usual
audio grid potentiometer. This control employs a single hole mounting, and requires
a rear space of 2r/" in diameter and 2%"
deep. The photo shows the unit with the
shield cover removed.
Miniature transformers for a wide
variety of low- level, low -power applications
are available from Triad Transformer Mfg.
Co.. 423 N. Western Ave., Los Angeles 4,
[Continued on page 321
AUDIO ENGINEERING
24
www.americanradiohistory.com
JULY, 1949
The 2assrtuarte
o 74(1udia
JOHN
D.
GOODELL*
Words are
less precise than the means
usually employed by engineers to convey a thought. The author clarifies
meanings of many common audio }erms.
A\lu \F:
Who has attempted to de-cribe the character of a certain
sound has found himself baffled in
an attempt to find words that will
surely convey his meaning. In a letter
recently received, a correspondent tried
for several paragraphs to describe adequately how piano records sounded
played on a certain commercial phonograph. He finally wound up with the
phrase,
though. someone were
beating on a mattress with a wooden
spoon."
When a group of people are discussing cabinets for radio -phonographs and
someone says, "I don't like a lot of
fancy carving; I'd rather have the
cabinet functional and simple," there
is a good chance that everyone will
know exactly what is meant. I-Iowever,
if the discussion concerns music reproduction and someone says. "The fiddles sounded a little mushy," the concepts of individuals in the group may
vary considerably. Most audio engineers will relate this term to a specific
quality of tone, usually to low frequencies, a quality that is the opposite of
"crisp." Many people associate the term
(as does the dictionary) with excessive
sentimentality. It is equally likely that
someone checking on the dictionary
definition might find under "mush"
'Radio, a noise, like that of frying,
heard when a receiving apparatus is
tuned to waves from an arc transmitting station; it is due to irregularities
in operation of the arc.'
Ìi
Shalicross
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for
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Shallcross Switches offer a broad
assortment of finely made, low con-
AXIAOHM PRECISION
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special designs.
tact resistance rotary selector switch
types for exacting applications. Nu-
Language of Audio
The language of audio, not the tech-
HIGHYOLTAGE TEST EQUIPMENT
1.5 to 200 KV
merous standard types in single and
nical terminology but the language
with which the character of sound is
described, is a bastard sort of language
made up largely of words borrowed
from visual and tactual terminology.
For the novice the terms are often extremely confusing, and even with professionals who have dealt with the problem of such discussions for years, misunderstandings are not uncommon.
Many of the arguments about reproduction quality unquestionably stem
from semantic confusions. Two people
hear the same thing, have the same re-
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The
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SHALLCROSS MANUFACTURING COMPANY
DEPT. A -79, COLLINGDALE,
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JULY, 1949
www.americanradiohistory.com
25
J/oaiinj
action to it but use different words to
describe it, and wind up debating a
non -existent disagreement at endless
ction
length.
for all TV Cameras
"BALANCED"
TV TRIPOD
Pat.
Pending
tripod
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This
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Previous concepts of gyro
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3
lish. It is unfortunate that even such
common terms as frequency and pitch,
intensity and loudness, are used loosely
as being. synonymous. Conveying intelligence by means of words is difficult
at best, and in dealing with a subject
so inherently controversial as music reproduction it is surely important to
make an effort toward rigorous definition and usage.
Among the more serious dangers is
the one illustrated by the two pairs of
words mentioned. In each case one is
a subjective observation, the other a
Below:
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physical measurement.
Bask Measurements
The
measurements
dependent on frequency but can be appreciably affected by intensity. Loudness is a subjective evaluation that is
primarily a function of intensity but
is strongly influenced by frequency. It
is interesting that a few words have
both physical and subjective validity.
Typical of these are the terms `low"
and "high." As a physical measure
they pertain to a rate of occurrence
with respect to time. Subjectively a
low frequency appears to come from a
lower point in space than a high frequency, though both may actually have
the same source.
A considerable portion of the material that follows represents the results
of a series of five listening tests. These
were conducted at different periods us-
@IMERR
ECJUIPIflEI1T
160C Fti:-Fi n(L eCFe (119
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Only a few are available and
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December 1948
December 1947
January 1949
August 1948
[, March 1949
September 1948
November 1948
E May 1949
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1948 issues
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1949 issues
3 5c
Circulation Dept., Audio Engineering, 342 Madison Ave., New York 17, N.
Y.
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26
basic absolute
that can be made of pure tones are
frequency and intensity. Pitch is a subjective observation that is principally
Write for further particulars
o
o
o
o
It is in the hope of providing a basis
for accepted meanings of more descriptive terms that this article is written.
Perhaps it will be only the basis for
arguments, but even this would be desirable if it would lead to a recognition
of the problem and an effort at closer
mutual understanding. Definitions are
a result of accepted usage and they
change with time. In most applications
of words it is possible to refer to a
standard dictionary and find reasonably accurate references for determining
approximate meanings. In discussing
music reproduction there is a great
lack of words that have been sufficiently defined. On the other hand, an unabridged dictionary does contain an
amazing variety of audio terms. The
trouble is that relatively few people use
it to full advantage.
There are certain basic dimensions
for sound that can be tied down tightly; others are more difficult to estab-
Be aware of the Audio Fair!
AUDIO ENGINEERING
www.americanradiohistory.com
JULY, 1949
ing between 25 and 50 observers, not
more than 20% of which could be considered highly trained in listening.
These tests were conducted solely for
the purpose of checking the concept of
terminologies. All conclusions are based
on a minimum of 80% agreement from
at least four out of five groups. Sources
of sound included live music from
acoustic instruments, electronic musical instruments, recorded music and
various laboratory devices for the direct generation of sound. The tests
were conducted in three different locations under considerably varied acoustic
conditions. Subjective suggestion was
employed only to the extent of indicating the quality to be observed. Every
effort was made to avoid psychological influence. Confirming experimental
work previously accomplished by others
is referenced in many instances.
Volume
A term that has led to a great deal
of confusion is volume, particularly in
its common use as a nomenclature for
the gain control. This has probably become so firmly entrenched in the minds
of the public that it must be accepted
but it is a peculiarly unfortunate
choice. To the public at large, and even
to many non -professional audio enthusiasts, the percentage of maximum output power obtained, regardless of signal source, is thought of in quantitative relationship with mechanical rotation of this control. Volume becomes
a loosely used synonym for output
power, intensity and loudness. This
means that it may be almost impossible
to recover it for usage in its valid connotation as an audio dimension. It has
been experimentally determined that
volume may be observed as a quality
of sound that varies inversely with frequency. In this usage it is undoubtedly
related to a physical concept of size.
The lower the frequency, the greater
its apparent size -yet size is inadequate because the concept should be
three dimensional and this implication
is lacking. Volume, however, is almost
perfectly descriptive. Again it is interesting to note that there is a relationship between the volume of the instrument producing the tone and the subjective evaluation of the tone itself.
Density
One other dimension of pure tones
has appeared to have experimental validity. The word is density and it is
shown to be directly proportional to
frequency. There has been an effort to
demonstrate that the derivation of this
concept is associated with the density
of the stimulation in the nerve structures. In view of the fact that untrained observers with no knowledge of
the mechanism of perception are able
to recognize this quality and differenAUDIO ENGINEERING
When you pride yourself on mechanical and electrical equipment that holds noise better
than 50 db below your program
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JULY, 1949
sndR!cording Equipment and Disc,
27
www.americanradiohistory.com
tiate it, this seems an unlikely theory.
.1 urlax
Trade Mark
reproducers
Microgroove
Discs
Standard DISCS
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ertical DISCS
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It is futile to buy the most modern
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the very BEST pick -up to bring
out their built -in excellence!
There is so much in present -day
discs, that even a mediocre pick -up
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them. However, to obtain the fullest
results of which these discs are capable, they must be reproduced with
the finest reproducer for that purpose-the
AUDAX.
Remember, two singers may both
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deliver not merely WIDE- RANGE,
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AUDA6 COMPANY
500 Fifth Avenue
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"Creators of Fine Electronic.
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On the other hand, high -frequency
wave forms in air are obviously denser
and more compact than low frequencies. At any rate, the word is clear in
its descriptive quality and is readily
demonstrable as a dimension upon
which groups of observers will agree.
In logical sequence, terms should
now be considered that apply to isolated topes of complex wave form. All
the terms used for pure tones are
equally valid with regard to complex
tones, provided that the fundamental
is strong enough so that the observation of pitch may be definitely ascribed.
There are endless adjectives that may
be used to describe the character of
complex tones as differentiated from
pure tones, but only a few of the more
common ones are mentioned here.
Brightness is a characteristic that is
observed in connection with pure tones,
but appears experimentally to be synonymous with density rather than being a separate dimension. In connection with complex tones it is a function of harmonic structures and is particularly influenced by the odd order of
higher harmonics. Experimentally, the
addition of a second harmonic does not
appear to affect appreciably the quality
of brightness, while even a relatively
small amount of third and fifth harmonics has a pronounced effect. This
quality is also affected directly by intensity, is directly proportional to fundamental frequency and is influenced
considerably by the rate of attack. A
bell tone, for example, even though it
may be produced from a pure source,
appears to llave appreciably greater
brightness than a continuous tone or
one with a slow attack. Doubtless this
could be tied down to the presence of
upper partials in transients inevitably
n,<ociated with abrupt attack. An ex(( (lent example of this is observable
with recorded piano tones. If the recording is observed by playing it normally versus playing it in reverse, the
normal rendition of the tones will appear to be very bright by comparison
with the tones played backwards where
the attack is extremely slow and gradual. The frequency content and the average intensity will be essentially the
same, and the only factor that is obviously varied in this experiment is
the rate of attack. The term also bears
some relationship to the rate of decay
for staccato playing appears brighter
than the same music from the same instrument where the notes are largely
sustained.
Brightness
Musicians often refer to one key as
being brighter than another. It is conceivable that some musicians are able
to differentiate this on a basis that is
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not related to any specific piece of music but, if so, the quality appears to
be as rare as perfect pitch. In all experiments with random observers, the
higher keys for a specific piece of music sounded brighter. In the one experiment conducted with musicians this
was equally true. except for a few who
insisted that they could differentiate
the sharp keys from the flat keys on
the basis of brightness. The only physical basis readily conceivable for this
would have to do with fact that the perfect pitch of C sharp, for example, is
not the same as D flat.
Many terms for complex tones stem
directly from concepts of shape.
"Round" is associated in the observer's
mind with a tone that he thinks of,
literally, as being round in shape. Experimentally this seems to be associated with tones that have a predominance of even harmonies (although this
is far from a limiting factor), and
especially with toues that have a fairly
slow attack with a minimum of initial
transients. It has to do with continuous tones rather than abrupt tones. It
is most often applied to horn tones,
vocals (especially sopranos) and to
certain organ tones. On the other hand,
it would rarely be applicable to a violin
tone or an oboe.
"Thin" might be chosen as an antonym although it must not be implied
that this is a matter of black and
white. A violin tone might not be considered round, but still not be thin.
The word "thin" is recognized as being
descriptive of sounds with a relatively
Weak fundamental and strong, very
high harmonic content, particularly
odd order harmonics. It is also used to
describe orchestral arrangements lacking in adequate bass, as well as reproducing systems with poor low frequency response.
In discussing the quality of a reproducing system, it is seldom that its
ability to reproduce a straight melodic
line from a single instrument is considered. It is worthwhile to digress to
the extent of pointing out that this
fact may well be the basis for some of
the confusion experienced in listening
tests. It is not intended here to minimize the importance of having a system capable of responding properly to
the full impact of an entire symphony
orchestra. The point is that listening
tests are terribly confused by psychological factors and also by the extremely complex dynamic wave forms the
ear is required to judge. It is educational and interesting to investigate
the qualities of a system on the basis
of reproduction of individual instruments. For many reasons, a discussion
Be :more of II.c .audio Fair!
AUDIO ENGINEERING
Cardioid pickup pattern.
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The Model 77 Tru -Cardioid is recommended for quality
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JULY, 1949
Y9
www.americanradiohistory.com
of which in detail would be out of
place her it is often easier to select
the better of two high quality reproducing systems on the basis of such an
observation. Many engineers find speech
more revealing than music, perhaps for
this very reason.
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"Fuzzy" is applicable to single tones,
and also may be used to describe the
over -all characteristics of a system.
Usually it has its source in non -linear
distortion where it is applied to reproducers. Deliberately introduced harmonic distortion, however, appears to
bring a response from observers of a
change in character-an increase, for
example, in brightness or even harshness. Fuzziness is more related to intermodulation or to extreme alterations
in quality such as might stem from a
rubbing speaker cone or a stylus striking the pole piece of a magnetic pickup.
The antonym for "fuzzy" is "clean."
This is perhaps the most expressive and
satisfactory word available for describing extremely good reproduction. Still,
it is by no means an all encompassing
term. It means freedom from nonlinear distortion when applied to reproducing systems. It means unwavering
attack of each note (whether it be
abrupt or slow) in describing live music. "Clean" is probably synonymous
with "clear," but in the mind of the
audio engineer is more satisfactory because it expresses freedom from fuzziness and from any non -linear distortion. Again, though, a limited amount
of harmonic distortion does not always
reflect any lack of cleanness to the observer, while intermodulation is instantly detected as affecting the clean
quality of reproduction. There is one
more difference between "clean and
"clear" "Clean" does not contain
any implication of frequency response.
"Clear" may, on the other hand, indicate something about the high -frequency characteristics of a system, particularly with reference to some instruments with very high fundamentals.
Serious music (either classical or
jazz music may under proper circumstances be so classified) is recognized
as a vehicle for conveying an idea or
mood-call it what you like- between
the composer or performer and the listener. It is reasonable then that the
words chosen for describing it should
be words that correspond to a subjective
experience that the music suggests.
"Hard" is a term that is commonly
used for tones that are relatively loud,
that have a fairly abrupt attack and
have harmonic content that may be
small numerically but is strong in relation to the fundamental. It would
seem reasonable that this word would
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DYNAMIC NOISE SUPPRESSOR* PREAMPLIFIER
You haven't heard LIVE high -fidelity reproduction until you have
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SPECIFICATIONS:
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Power supply
Frequency range
Gain
Input
Tube
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115
-
volts, 50 -60 cycles, a.c.
40 to 15,000 c.o.s.
volts input produces .8 volts output
megohm.
fo volume control of .25 to
magnetic or crystal pickups,
sources
and FM or AM detector output.
2- 6SL7GT, I- 6SK7GT,
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I-6SJ7GT, I.5Y3GT,
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Installation and operation require
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A wide- range, high fidelity (30- 15,000 cps) record reproduction system is of little
value if it must be limited by tone or treble controls to 4,000 or 5,000 cps to avoid
excessive surface noise. Such a control cannot eliminate the surface noise without also
cutting off high frequency tones and destroying the quality of the music. The Somerset
Noise Suppressor eliminates excessive surface noise more effectively than any prior device
and does this dynamically without impairing the program quality. The Somerset device
When middle and high- frequency volume level
is neither a filter nor a tone control.
is sufficient to mask the surface noise, the suppressor unit is effectively out of the
decreases, surface noise which would
frequencies
the
higher
intensity
of
circuit. As the
otherwise be heard is eliminated by a dynamic inversion process.
Thus the musk quality is never impaired, but disagreeable high-frequency
surface noise is reduced at all times to the point where it ceases to be
objectionable.
`Patent Pending
SOMERSET LABORATORIES, INC.
1701 Palisade Avenue,
Union City, New Jersey
AUDIO ENGINEERING
30
www.americanradiohistory.com
JULY, 1949
r
be the antonym for "soft," but such is
not the case. A tone may seem hard
and still not be loud, while "soft" is
used to describe relative loudness only
and not to indicate other qualities.
If the reactions to sound were objectively measurable quantities, the
problem of conveying understanding
by means of words would at least be
simplified. Anyone who believes that
the problem is unimportant is invited
to review the literature of semantics.
It isn't too easy to talk about everyday
practical matters and be sure of conveying exact meanings, much less a
subject of such tenuous and complex
ramifications as subjective reactions to
audible energy.
Audio Language Growth
The language of audio grows as a
result of one person's expressing his
reaction to a certain quailty of tone in
terms of his subjective association of
it with something quite different. An
observer feels that the adjective applies
in terms of his own reaction and uses
it again himself. This is the history of
all language except for words that are
deliberately built from other words of
long established meaning. It is a natural but dangerous and difficult way
for a language to grow. Many words
that have purely subjective implications must develop in this manner
through usage and somehow, intuitively, most people who hear the word may
understand its meaning almost exactly
as it is intended by the individual who
uses it. It is important that this be a
hoped for goal, and not one that is
taken for granted. With words that can
be tied down to objective definitions,
it is of utmost importance that they
be used correctly. It is well worthwhile
for everyone periodically to check the
dictionary definitions of the words they
most commonly use, and to make an
effort to conform reasonably with this
reference for established concepts.
In connection with spoken words,
there is the great advantage that the
listener may question the meaning
(though he doesn't do so as often as
he should when he isn't certain of
understanding), and elaborations will
serve to clarify any possible misunderstanding. Inflection and all of the remarkably varied qualities of the voice
may lend intelligence and understandability to words when they are spoken.
The written word is quite another
matter. Requests for definition are not
possible from the reader. Usage is considered to be more authoritative and
may more greatly influence general
concepts. Few people ever reach with
the spoken word the enormous audience
that is possible to the person who
writes. Consequently every word that
is written has much more influence,
AUDIO ENGINEERING
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JULY, 1949
RHEOSTATS
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may lend to greater misunderstanding
and greater confusion, than a thousand
words spoken in general conversation.
It therefore behooves every person who
Las the privilege of conveying his
knowledge, his thoughts and his ideas
by means of words on paper to be extremely careful that he be rigorous and
accurate in his use of the language.
It is more than likely that this article
contains many of the mistakes it condemns. It is not possible in its limited
length to do more than present the
problems involved in very brief outline
and to indicate the derivation and definition of a few of the most commonly
used words. If it serves only to emphasize the importance of the problem,
to aid a few people in examining the
meanings of the words they use, it will
have been well worth writing. Words
are without doubt the most powerful
tools that men possess, and progress of
all kinds depends directly on the development of associated verbal methods
of conveying intelligence. Unquestionably a large portion of the misunderstandings, arguments a n d disagreements in the audio industry are a function of semantic confusion. Progress
has been and will be intimately related
to the accuracy with which knowledge
is disseminated by means of words.
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[Irons page 241
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AUDIO ENGINEERING
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JULY, 1949
RECORD
for tfie f'ü;t time
REVUE
[from page 22)
Naturally if there happens to be a better
used. If your composer calls
Isis piece "The Sunken Cathedral" or "The
Afternoon of a Faun,' so much the better.
But, again, it must be remembered that
such titles are in a way freaks, for music
speaks in terms of music first of all and to
describe music in exact words is like trying
to translate something that can't really be
translated, rather merely suggested. From
title it gets
this point of view, you see, the use of the
Italian terms is an excellent idea for at least
they tell you something specific about the
music itself. What more could you ask?
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Recent Recordings
Controls are marked for simple selection, according to type of records to be played. Records
Walton, "Facade" (to the poems of Edith
Sitweul.
Edith Sitwell, Reader; Chamber Orchestra. F. Prausnitz.
Columbia LP: ML 2047 (MM 829)
Here is an extraordinary LP. (The
standard album is not yet released.) It is
recorded here as performed with great éclat
this spring in New York's Museum of Modern Art, with the great Sitwell herself reading her own poems to the music, as in the
first performance twenty -five years ago. This
will fascinate you or violently repel you
perhaps both! The stuff was put together in
the high 20's, when William Walton the
was 19) and Miss Sitwell were strictly
avante garde young people; it was one of
the typically dizzy, jazzy, experimental efforts of that time, out to shock, funny,
brassy, inelegant (but it seems elegant now,
in spite of the jazz in it). It shocked all
right. Noel Coward walked out before it was
halfway through. But the early recording,
made soon after, has kept turning up here
and there ever since as an increasingly valuable collector's item; now, what with the
enormous publicity the Sitwells, Edith and
brother Osbert, got on their visit here (see
recent Lile magazine) the piece finally comes
into its own, and if you don't enjoy it, or
enjoy being mad at it, your blood pressure
must be low.
The piece is a combination of music and
narrator, but, as you'll very quickly find out,
something utterly different from the now -sosmooth radio technique of music and voice
that we are so accustomed to. Today, it's the
fade technique: music down, voice up, musical bridges, music in and around and behind the voice. And a wonderfully effective
technique it is. But Walton and Sitwell were
strictly pre-radio. Background music didn't
exist, nor did bridge music. Here you have
a squawky, weedling,
jazzy waltzy small
orchestra that never stops a second except
between poems, and you have Miss Sitwell's
jazzy mellifluous, full- bottomed poems, never
stopping for a split second. An extraordinary
effect, for the two occur exactly in time,
simultaneously, and neither gives way a
fraction of a decibel to the other. The battle is humorous but relentless to the very
end; the forces are exactly equal and the
energy produced is fabulous. Only way to
cope with it via the ear is to listen first to
one, consciously, then (on the next playing)
to the other. La Sitwell has Personality -plus
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Strauss, Salomé; final scene.
WRITE FOR DESCRIPTIVE
3
voice and a balloon -full of breath plus a
superb sense of rhythm and timing. Moreover there is a devilish spark of enjoyment
perfectly visible in her eye! No need to
see it; you can hear it.
Recording? Excellent. Of all pieces this
perhaps takes top prize as benefiting the
most from "high fidelity ". I've heard it wide
range, and on a small radio (approx. cutoff 3000 cps) and the difference is incredible
both in the orchestra's tone color and in the
sibilants of the spoken words. Music? Dry,
witty, humorous. good stuff for a 19-year
old (or anybody, for that matter). A fine
tango and a fox trot, some fake hill-billyish
stuff, a wonderful take -off on "William Tell"
(he figures in the accompanying poem)
with odds bits of the familiar music worked
in. Poems? Amusing, surrealistic, semi -intelligible. highly expressive mumbo -jumbo.
You get a bit more on each hearing. Shades
of Gertrude Stein (who also had a sense
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Ljuba Welitch; Metropolitan Opera Orch.
Reiner.
Columbia MX 316 (2)
And here is the extreme opposite and
an excellent contrast to the Walton -Sitwell
madhouse. This, twenty -odd years before.
was one of the two operas-to- end -all -horrorstories perpetrated by Richard Strauss upon
a staggering world.
(The other was the
suave, murder-ridden, lustful "Elektra ", recently recorded in part by Beecham.) Sal.
omé, the gal who asked for John the Baptist's head and then made love to it, does
exactly that in this scene and in the greatest
of detail. She smacks her lips and you shiver
your spine. Nevertheless. it's a scene whose
clinging horror is undoubtedly a masterpiece
of music drama. Welitch is one of the superb
voices of our time, newly discovered in this
country. Absolute control, a fantastically
accurate sense of pitch, a high feeling for
drama, an intuitive sense of style are a few
of her outstanding accomplishments.
The recording made practically yesterday
and rushed through processing, is as fine
as anything Columbia has done. A departure
from earlier Columbia Met. Opera recordings is the placing of the voice at stage
distance (as one hears it) instead of close.
up. It was interesting, for instance, to heat
a voice like Pinza's almost tonsil -close in
his "Mozart Opera Arias" album; but the
present arrangement is musically far better.
Keep an eye and an ear on Welitch.
Berfok, Concerto for Orchestra (1943).
Amsterdam Coneertgebouw Orch. Van
Beinum.
Decca ffrr EDA 105 (5)
If you tried out the recent Columbia
version of this, standard or LP, by Reiner,
you may want to compare. This is a fine
Performance of the modern but very easily
listenable music. though at times it seems
a bit stolid and heavy as compared with
the always dynamic Reiner version. It has
all the beauty of ffrr recording, but once
again the standardized ffrr acoustics (always the same ultra-live effect) are not entirely suitable. The Columbia version comes
out better. Trouble. though slight, comes
from the fact that this is a concerto for
U'atels for The .Audio Fair!
AUDIO ENGINEERING
34
www.americanradiohistory.com
JULY, 1949
{
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whole-orchestra and numerous soloists within the orchestra -there is wonderful music
for solo clarinets, trumpets, oboes, etc. Columbia, with considerable close -to accentuation, brings out these solo passages beautifully; ffrr, smoother and finer in over -all
sound, keeps the soloists in the background
via (evidently) a distant, one-mike pickup.
In either version, in any case, this is a fine
piece for test purposes, what with the combination of a big, romantic orchestra, lots
of brass, and the profuse solo work for all
sorts of instruments.
Liszt, Orpheus (tone poem).
Debussy, Printemps (symphonic suite).
Sir 'Thomas Beecham, Royal Philharmonic
orchestra.
RCA Victor DM 1295 (2)
DM 1293 (2)
Two more in the current series of odd
Beecham items being reissued here by Victor. Both are well recorded with appropriate
acoustics, both a somewhat less than brilliant in the highs, posing the usual question
-what
did the British originals they're
suppose to reach 20,000 cps) sound like?
"Orpheus" is one of the quiet, introspective
pieces; its moods, today, seem corny -all
sweetness and light, with a harp (lyre) for
Orpheus. But L. was no piker; the stuff
grows on you and may well become your
favorite bit of romantic music, for a while.
"Printemps" is early and seldom heard Debussy, written before he had worked into
his later and famous Impressionist style.
This one impresses all right but it's about
one half sweetened Tchaikowsky. Fine if
the style pleases you. Though it's hardly important music this is a great deal better
than a lot of the pretentious music in similar
style we hear today at the movies. It makes
a fine background.
Liszt, Les Préludes
(
(symphonic poem).
Leopold Stokowsky and His Symphony
Orchestra.
RCA Victor DM, WDM 1277 (2)
This stands next to "Orpheus" in a
Liszt group of symphonic poems and it
couldn't be more opposite in effect. "Les
Préludes" is the brash, noisy, brilliant kind
of Liszt. It has every stock movies mood
you've ever heard but the dominant one is
the heroic. This is Lizt as the P. T. Barnum of music and it is hardly surprising
that as a show piece it's heard in a thousand performances to one of the more quiet
"Orpheus ", as well as in dozens of earlier
recordings. The Stokowski performance here,
plus the best of RCA's recent recording,
makes it sound good; this is one of "Stoky's"
more careful and (relatively) restrained efforts. When he's in that mood. Stokowski is
absolutely tops.
Strauss, "Rosenkavalier" waltzes.
Boston "Pops" Orchestra, Fiedler.
RCA Victor 12-0762 (1); 49 -0307 (I Vg)
One of the first offerings on both standard and 45. (Why must RCA assign different numbers-when the albums in standard and Victorgroove have the same number?) Musically a rather heavy -handed job
for the usually sprightly Fiedler gang (better known as the Boston Symphony)'. The
phrasing here is oily, greasy (the phrases
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JULY, 1949
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dency to wide -range but overly close
and
dead recordings of Romantic works -that
by rights should have a big, spacious, live
sound.
Note that Decca ffrr is often exactly the opposite, with big, live recordings
of music that should be sharp and dry.)
This is probably not too recent, but that is
of little matter. The string tone has technically- a wonderful edge and clarity here,
brasses too are sharp and piercing but clean
-and for those who are not too bothered
by the wrong-style acoustics it makes a good
demonstration record. Musically, this is another of those post- Franck works that, if
sou like the Cesar Franck symphony will
run together without the clean, crisp articulation one might expect from Boston( and
the whole adds saccharine to maple syrup.
Acoustics good, recording variable: side 1,
shellac, seems distorted, as though playing
stylus were worn, but side 2 is markedly
clearer. The saine is apparent on the Victor groove versions. indicating perhaps a common faulty original at some stage. Possibly
this applies only to a few copies.)
Chausson. Symphony in B flat, opus 20.
Minneapoli- Symphony Orch. Mitropoulos.
Columbia MM 825 (4)
LP: ML 4141 (I)
Another example of the Columbia ten-
(
CARTRIDGE
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Here's another similar to the above
not
quite such dead
playing,
but with better
acoustics. Szell's Cleveland Orchestra tends
to play a bit on the rough side in its recent
new Columbias, making his Mendelssohn
for instance, something less than suave and
perfect for Schumann it is good and the
Szell intensity makes it exciting. Compared
to older European recordings this one is,
again, too close, too dead for the romantic
music; clean, sharp qualities do much to
make up for it. Here I have tried both LP
and standard and (allowing as always for
the numerous inevitable differences in playing conditions, curves, equipment etc.) my
impression is that the LP version in this
case is considerably superior. Shellac sounds
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Mendelssohn, Symphony #4 ( "Italian ").
Cleveland Orchestra, Szell.
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please you for similar reason. Ihausson was
one of Franck's most devoted imitators and
with considerable success. The performance
here is full of life and full of rather careless playing, notably in the strings. Sounds
like inspired sight reading in some spots.
Schumann, Symphony #4 in D minor.
Cleveland Orchestra, Szell.
FOR BULLETIN
i11;\
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New York
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LP: ML 4127 (Y2)
Here is the same outfit, in the Mendelssolin style of music -more precise, less romantic, requiring more accurate, exact and
skillful playing. Szell makes this familiar
symphony more exciting and more intense
than you've ever heard it before, notably
in the last movement; but in the long run
the RCA Victor recording (DM 12591 of
Koussevitsky is much nearer the music's intentions. Acoustics in the Koussevitsky are
broad, spacious, gracious, like the music;
Szell's are again rather hard and dry (accentuating the somewhat harsh, driving performance). Koussevitsky's famous strings
heat the Cleveland's by far. The LP reverse
has a Capriccio for piano and orchestra of
Mendelssohn, recorded back before the war.
Symphony #6 ( "Pathetique ").
NBC Symphony Orchestra, Toscanini.
RCA Victor DV 27 (5 pl.)
This luxury item on plastic is, I suggest, nothing you'll want to have; the Sixth
is best heard on several European recordings of earlier days, occasionally to be found
in this country at specializing stores. The
Toscanini performance is, true to form. extremely intense to the point of nerve- frazzling, but to my ear it is cold as a stone and
quite lacking in the measured expansiveness
that is the only justification for Tchaikowsky's music, the broad, weeping emotion that
some conductors, oppositely to Toscanini.
overdo until it fairly drips. Not so here. And
the recording, like most of the Toscanini
jobs, is narrow. very dry and altogether unsuited to the music. (It is clearly noticeable, during the past few years. that the
NBC as recorded with other conductors
comes out with a better recorded sound than
with Toscanini. No doubt a matter of conductorial cooperation in the always -touchy
job of placing microphones, arranging personnel.)
Tchaikowsky,
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www.americanradiohistory.com
JULY, 1949
PROFESSIONAL
DIRECTORY
PROBLEMS IN AUDIO
Worn page 21]
and illustrative audiograms are shown
for typical cases. However, these should
not be used as indices by the hard of
hearing. Each person is subject to a
set of circumstances
n
and
Instrumentation Irartietdar
Sound Recording
-hould emisun his own physician.
Figure 2 shows the audiogratu of a
man with high loss above 21100 cps, but
370 RIVERSIDE DRIVE
NEW YORK 25. N. Y.
echo had no difficulty in cnvcrs;rtiuu
or work. This is a ease of nerve deaf .n - -. Examples of conduction deafness
are shown in Fig. 3. Although the per -on with the audiogram of (A) has a
:;0 db loss, he dill not require a hearing
aid; the subject of the :LUdiogram of
Designer and Consultant
LB) did.
Acoustical, Electronic and Nuclear
It is of interest to note the results of
Research
the tests conducted by Steinberg, MontMU 4-3487
307 East 44th St.
gomery, and Gardner at the New York
New York 17, N. Y.
World's Fair its 1939 and 1940. They
are shown in part in Fig. 4. These
curves show the average hearing characteristics in the age groups indicated.
The increasing loss at Iti_ll frequencies
Custom -Built Equipment
with increasing age i, attributed to degeneration of the sensory cells. In the
U. S. Recording Co.
higher age groups particular cases may
require hearing aids; this is not to be
121 Vermont Ave., Washington 5, D. C
considered a strange malady, but a
normal occurrence with increasing age.
STerlinq 3 62 6
Two additional effects which accompany deafness are tinnitus and recruitment. Tinnitus is the naine given to
the "ringing" sound heard whets people
are fatigued or have been subject to
Consukation Design Fabrication
Lntd sound for long periods. It also ocits- as a result of non- acoustic stimulation of the nerves in the inner ear,
Audio Facilities Corporaion
:itch non -acoustic stimuli can be pres-ore on the eardrum or actual degenera Fifth
Avenue
608
ion of the cell tissue or nerves. Recruitment is the name given to the phenomNew York 20, N. Y.
enon occurring with people who have
hearing loss for low intensities, and
normal sensitivity for high intensities.
Often the sensitivity for high tones
HERMAN LEWIS GORDON
may be increased. The person suffering
lir,rolrrrd Patera .11lwnc)
from this condition becomes annoyed
when people raise their voices. The subject first complains that he cannot hear
Patent Investigations and Opinions
and then complains that the speaker is
shouting.
Warner Building
100 Normandy Drive
This article has sketched die uses of
Washington 4. D. C. Silver Spring, Md.
NAtional 2497
Shepherd 2433
articulation and intelligibility tests and
has presented a brief outline of certain
,,Iuditions arising in deafness. The references already listed in the previous
RATES FOR
articles have valuable material for those
PROFESSIONAL CARDS
who wish to make a complete study of
IN THIS DIRECTORY
the subject. In particular. 1)r. Hallowell
Davis's "Hearing and Deafness" gives
a good non- technical treatment of these
$10 Per Month.
three topics. The next article of the
Orders Are Accepted
series will begin the study of sound
for 12 Insertions Only
enerators.
J. LEBEL
C.
AUDIO CONSULTANT
Winston Wells
1
1
I
AUDIO ENGINEERING
JULY, 1949
www.americanradiohistory.com
TYPE "O"
Type "0" Series -shown
at right is the 03 -11 Plug,
with three 30 -amp. contacts, fits certain quality
types, notably Western
Electric.
TYPE
P
"P"
Type
Series- P3- CG-125
Plug shown at right, is
standard with most
broadcast stations
and used with RCA
and other equip-
ment...
7
inter -
changeable inserts.
TYPE
"XI."
Type "XL" Series-XL-1.I
Plug shown at right, is
I
standard on certain
RCA, ElectroVoice and
Turner microphones.
Two inserts:
XL-3, XL-4.
Used on many types of sound and
communication equipment in addition to microphone, Cannon Plugs are
recognized by engineers, sound men
and hams as the quality fittings in the
field. Over a period of years various
improvements have been made in
insulating materials, shell design, material and clamp construction.
Available through many parts jobbers in the
U.S.A... In Louisville: Peerless Electronic
Equipment Co. In Flint: Shand Radio Special.
ties. In Syracuse: Morris Dist. Co. In Toledo:
Warren Radio. In Nor folk: Radio Supply Co.
Bulletin P0-248 covers all the engineering
data on the above 3 series; RJC -2 the prices;
CED-8 Sheet lists jobbers. For copies address
Department G-109.
SINCE 1915
I
Cwq'1C)l1
ILICTRIC
,44/9C,;avy
3209 HUMBOLDT ST., LOS ANGELES 31, CALIF.
IN
CANADA- CANNON
ELECTRIC CO.. LTD.
37
Techrú o Briefs
Ready July 5th
ULTRASONIC
FURTHER NOTES ON A 6AS7 -G AMPLIFIER
FUNDAMENTALS
By S.
7N7
Young White
6AS7G
50p
o
36
8'';
pp
,
34
11
S1.76
illus. Paper
Postpaid.
03<<
óo
CO.e.r,
compilation of articles appearing in
Audio Engineering over the past two years
on this fascinating new branch of the audio
field.
A
o
03
O
Óo
a,
Covers: Elements, generation, coupling to load, testing, and applications in biology; effects in liquids
and solids, economic considerations,
and opportunities.
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5R4GY
Irr
Book Division, Dept. A
New York
r
nö
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An important subject which is rapidly
coming into prominence in
myriad of
industries, and one in which big opportunities are open to anyone familiar with
the methods used in working with "silent
sound."
342 Madison Ave
150V.
n
115 V. A.C.
N.Y
THE October 1948 issue, the writer
published some notes on a 6AS7G
amplifier. Since then, the driving
stage has been modified; it is still push pull throughout, but it now uses resistance- capacitance coupling instead of
transformer coupling. In view of the
large voltage needed for driving the
6AS7G, the voltage drop across the
plate resistor is compensated by a rathr large power supply voltage: with
each half of a 7N7 taking 9 ma at 250
volts on the plate, the voltage drop
across a 50,000-ohm plate resistor is
450 volts, and a supply voltage of 250
-t- 450 = 700 volts can be used without
going beyond the tube ratings. The
supply voltage employed is of the order
of 530 volts, which is obtained by using
the same power supply transformer
with two different rectifiers. A 5V4G
with a choke-input filter gives exactly
:300 volts needed for the 6AS7G, and a
5R4GY with a capacitor -input filter
gives 530 volts for the 7N7. An Amp erite 15- second time relay delays this
voltage until the cathode of the 7N7
IN
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Each month
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1
is hot.
A 7N7 is used instead of a 6SN7GT,
because of the symmetry of the socket
connections : this allows symmetrical
wiring, with extremely short connections. The circuit is shown above.
The two cathodes of the 7N7 have a
common resistor. Two different resistors ran be used, and a certain amount
AUDIO ENGINEERING
www.americanradiohistory.com
JULY, 1949
vi feedback introduced there. There is
room for experimentation at this point.
If the amplifier is to be used with a
single -ended tuner with a pre -amplifier,
any conventional system of phase inver-
:T1
sion can be used.
Using the same parts as for the amplifier previously described, it may be said
that, there is a slight, but definite, improvement in quality. The volume is about the same.
John van Heijenoort
27 Coolidge Ave.
Amityville, V.S.
AUDIO
[
A 425
/rom page 14]
trots. A partially by- passed screen circuit is used to provide current feedback, which reduces distortion and
raises the input impedance of the
booster tube at high frequencies. This
effect makes the frequency response essentially independent of mixer adjustments.
The driver and output stage use tube
types 9001 and 6AK6 respectively. Inverse voltage feedback is taken from
a tertiary winding on the output transformer to the driver stage to minimize
the overall distortion and noise. The
output impedance is changed from 150
to 600 ohms by changing the two load
windings from the parallel to the series
connection. The 6-db isolation pads are
inserted between the transformer and
the output receptacle for both 150- and
600 -ohm connections.
Typical performance characteristics
are shown in Fig. 4. The frequency response is within 1 db from 50 to 15,000
cycles. The distortion is less than one
per cent from 50 to 15,000 cycles. Noise
is 70 db below the standard output of
+18 dhm with the controls in typical
operating positions. The maximum gain
The new Altec Lansing line of input
amplifiers meets a demand for units of
small size with excellent characteristics.
Dimensions of the A -425B Pre- Amplifier with mixer control, the A -426B Line
Amplifier and the P -505B Power Supply
are 2% inches wide by 10 inches long.
The 10675 Mounting Base permits
mounting G units of any type in a standard rack or in a mixer console. Thus,
complete facilities for 4 microphone inputs with line amplifier and power sup-
a
91Rw
505
P
B
ply will occupy the space 19 inches wide
by 10ír_ inches high.
All amplifiers have a flat frequency
response from 20 to 20,000 cycles.
* * * ?'
Full technical description upon request.
1161
North Vine St.
Hollywood
161
Cs1if.
Sixth Avenue
New York
13.
N.Y.
ALTEC
audio 9
e
THE BRIDGER
MODEL
100
BRIDGER- Connecta
a vacuum -tube voltmeter, distortion meter. and /or
oscilloscope to a high-impedance circuit, such as an amplifier
or counter. without loading
it and changing the operating characteristics. A shielded cable may be used for eliminating
hum without loading the circuit under test with the cable capacitance.
Using an improved
cathode follower and a specially designed double-shielded cable,
the Bridger offers an
input impedance of 100 megohms in parallel with 6 mmf at the end of
a three -font shielded
cable, and an output impedance of 200 ohms.
MODEL 104 VOLTAGE DIVIDER-Extends input -voltage range to 250 volta when
slipped
on tip of the cable -probe of Bridger. Input impedance 100
megohms in parallel with 5 most:
vulture rat is 100:1.
Miniature Preamplifiers For Use With 640ÁA Condon
Model
No.
12
14
16
LETTERS
Output for
I dyne,cm2
Output Z.
I.. ngth
inches
ohms
-40
-55
dbm
250, bal.
dbm
250, bal.
1.5 mv.open cct 500, unbal.
Diameter, all models
from pnge -il
lnite 120 -cps tone, even if I stopper my ears.
I have observed it for many years and there
is no mistake about my actually hearing it
(no "bats in the belfry"). Is this a form of
Auditory Persistence similar to the persistence of Vision? Comments through your
Letters Column by others with similar ex.
perience may lead to important new
knowledge in this field.
May I tell you again how much I enjoy
AUDIO ENGINEERING
B
-.
IN THE PROFESSION, AN HONORED NAME
The proportions of the amplifier case
make it very easy to carry. It is narrow
enough so that it will hang freely without humping into the operator's legs.
The amplifier is light enough to be
truly portable. The design objective of
a single unit amplifier with high level mixing and emergency battery operation has been accomplished.
- lr;,
I
_________
Power Requirements
Plate E
10
135
6%
4%
136
300
r
.
Plate I
Fil.
E
2.2 ma
2.2 ma
3.0 ma
1.25
r
70 ma
1.25
6.3
.
60 ms
.
200 ma
Fil. I
inche
MODEL 121 LOGGER
Logarithmic voltmeter with 50 db linear
meter scale; output may be used to feed
direct writing recorder (via a suitable
amplifier) for acoustical reverberation tests.
Input impedance- 50.000 ohms; output impedance -1000 ohms.
MODEL 140 DISC -NOISE METER
Overload -proof amplifier voltmeter for
quality control of lacquers. phonograph records, transcriptions. New stable logariithm,.
element. 20 -db linear meter scale. Minimum
reading 75 db below 7 cm /sec. velocity with
pickup cartridge supplied.
Our wide acquaintance with new methods and unusual techniques is used to give improved performance at reduced
cost.
AUDIO INSTRUMENT COMPANY
-
F.
A 426
B
r
PUBLIC ADDRESS & RADIO BROADCAST SYSTEMS
is 93 db.
Benjamin F. Meissner
Van Beuren Road, R.
Morristown, N. J.
,,..
ANNOUNCING A NEW LINE OF PRE -AMPLIFIERS
TO MEET THE NEED FOR GREATER FLEXIBILITY IN
AMPLIFIER
AUDIO ENGINEERING?
4tH
.,,,..,1
,
1947 Broadway
D. 2
JULY, 1949
www.americanradiohistory.com
New York 23, N.
Y.
39
AMPERITE
o. \tO
BROADCASTING
RECORDING
PUBLIC
ADDRESS
wal +TANDARDIZED
INDEX
Studio Microphones
at P.A. Prices
Ideal for
READY TO -USE
ark
Altee Lansing Corp.
Amperite Co., Inc.
Ampex Electric Corp.
Arnold Engineering Co
Audak Company
10
new Amperite Microphone-or stand 2 Not
37
32
Camera Equipment Co.
Cannon Electric Dev. Co.
Cinema Engineering Co.
is
Not affected by
Models
any climatic conditions.
Guaranteed to with.
stand severe "knocking
around."
-200 ohms
RBHG -Hi -imp.
RBLG
List
$42.00
"Kontak" Mikes
Model SKY', list $12.00
Model KKH, list $18.00
ecial IntrodudorY
Writs for Special
folder.
S
I Offffer:
000r,
and 4po9
AMPER/TE Cmpany
561 BROADWAY
Inc.
NEW YORK 12. N. Y.
Conodo'Allos Rodio Corp., Ltd., 560 King
St.
W., Toronto
"THIS AMAZING
HARTLEY- TURNER SPEAKER"
\ \, last had In un n,mmtnts frum Ansel ìu users on the 215 Speaker. Astonishment
is expressed not only at the performance,
hut at the performance which comes from
such an insignificant looking unit at such an
insignificant price. We a. the designers have
no comment to make on this beyond the fact
that the speaker was designed right through
with the sole idea of producing music with
as little distortion as possible. It didn't happen to he our idea of good art for efficiency)
to use a sledge- hammer to crack a nut even
if the nut was a hard one.
In all seriousness we put the performance
of the 215 up against that of any other
speaker you like to think of, but the price
is so right in these hard times that you will
think it the best buy you ever made.
On this matter of price we fear we may
have to increase it slightly in the near future, as costs over here are still taking an
upward trend. Satisfied users have told us
it would still he cheap at double the price.
but we don't m ^tan to double the price or
anything like it. Meanwhile why not buy one
now at 93950? By the time you pay the postman the import duty, it will have coat you
945.00 and you will have got something you
won't get elsewhere at any price. More important, you will have taken the first real
step forward to get really truthful musical
reproduction.
First distribution of data sheets is
now being made to those who ordered
New Notes in Radio." the complete
pocket guide to high fidelity. Send your
91 bill now for your copy and that will
ensure you a regular supply of information on all aspects of realistic sound
reproduction. We have no end of good
ideas we want you to know about.
H.
A. HARTLEY Co., Ltd.
152, HAMMERSMITH ROAD,
LONDON, W. 6, ENGLAND
40
Electro Motive
Mfg. Co., Inc.
Electro- Voice, Inc.
CHASSIS
9
28
Audio Devices, Inc.
Cover 2
Audio Instrument Company
39
Audio Facilities Corp.
37
always perfect.
CABINETS
39
40
"The ultimate in microphone quality," says
Evan Rushing, sound
engineer of the Hotel
New Yorker.
Shout right into the
away -reproduction
BETTER ELECTRONIC EQUIPMENT
ADVERTISING
ALL
NEEDS
Par -Metal
26
Cover
RACKS
Equipment
is
preferred by
Service Men,
Amateurs, and
Manufacturers
because they're
adaptable, easy-
3
23
Fairchild
Recording Equip. Cor P.
Freed Transformer Co.
PANELS
P. A.
to-assemble, eco
t.
nomical. Beautifully
designed, ruggedly
constructed by specialists. Famous for
quality and economy.
4
2
\
Gordon, Herman Lewis
Gray Research & Dev. Co.
37
32
Hartley, H. A. Co., Ltd.
Hollywood Sound Institute
40
40
LeBel, C. J.
37
PRODUCTS CORPORATION
5
LONG ISLAND CITY 3. N.Y.
Export Dept.: Rocke International Corp.
13 East 40 Street, New York 16
Maurer, J. A. Inc.
National Company, Inc.
28
Par -Metal Products Corp.
Pickering & Co., Inc.
Presto Recording Corp.
40
30
Proctor Soundex Corp.
Professional Directory
27
36
37
Racon Electric Co., Inc.
35
Radio Corp. of America
(Broadcast Equip. Div.)
Rek -O -Kul Company, Inc.
Write for Catalog.
PAR-META
32 -62 -49th ST.,
AUDIO ENGINEERING SCHOOL
A
i
No.
Kenmore
LATERAL
REPRODUCERS RECONDITIONED
9 -A, 9-B, D 93906, M1.4856, M1-4876 -O
Complete Stock of New Replacement Parts
for All Types
Types
This service is being used by leading radio
stations and wired music companies from
Factory price. prevail.
meat to coast.
VIBRATION SYSTEMS, INC.
1040
W.
Fort St.
Detroit
26,
Michigan
ADDRESS CHANGES...
37
37
In Sound
T)ISC Re-
VERTICAL
Cover 4
Wells, Winston
and
Annrnred for Veteran and Foreign Viols
1040 -A
34
33
29
40
ooto.e
INSTITUTE Inc
HOLLYWOOD SOUNDHollywood
27, Calif.
I
Vibration Systems, Inc.
Ward Leonard Electric Co.
r
MAGNETIC
Pees -Dlr.
25
Shallcross Manufacturing Co.
Somerset Laboratories, Inc. _ 30
Sun Radio &
36
Electronics Co., Inc.
Sylvania Electric Products, Inc.
United
Transformer Corp.
U. S. Recording Co.
1.11,4111,
1,11.31.
cording: Tran smission Measnrementsl Monitoring and
Mixing. Laboratories contain, Transmission Sets,
Oscillators. Distortion Sets: Harmonic Analyzer: Intermndulatinn Analyzer and other rapt. Recording
Studio assimilating Broadcast, Motion Picture and
Commercial Sound Recording. lt. M. TREMAINE,
34
_
ln. L..
pra,ii..11
Fundanenlal.:
6, 7
Tech Laboratories, Inc.
Terminal Radio Corp.
Turner Company, The
L
Subscribers to AUDIO ENGINEERING should notify our Circulation
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We can not duplicate copies sent to
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31
THE AUDIO FAIR
AUDIO ENGINEERING
your affair
RADIO
342
Details in .%ugust issue!
MAGAZINES, Inc.
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JULY, 1949
1
EL- MENCO'S PLACE
PRODUCT
Wherever fixed mica dielectric capacitors are used,
the first choice with men of experience is always El -Menco
Precision -made under rigid conditions, tested seven ways to meet strict
Army -Navy standards, thoroughly impregnated and provided in water-sealed
low -loss bakelite; these tiny capacitors
protect and maintain your reputation for
quality equipment. To insure performance- excellence, place El- Alenco capacitors in your product. Results will prove
El -Menco to be a wise choice.
THE ELECTRO MOTIVE MFG. CO., Inc.
WILLIMANTIC
CONNECTICUT
CM 15 MINIATURE CAPACITOR
Actual Size
Write
MOLDED MICA
312-"
x
x ;K"
For Radio, Television and Other
Electronic Applications
2 to 420 mmf. capacity at 500v DCw
2 to 525 mmf. capacity at 300v DCw
Temp. Co-efficient ± 50 parts per
million per degree C for most
capacity values
6 -dot standard color coded
firm letterhead for
Catalog and Samples
on your
enc
CAPACITORS
MICA TRIMMER
FOREIGN RADIO AND ELECTRONIC MANUFACTURERS COMMUNICATE DIRECT WITH OUR EXPORT DEPT. AT WILLIMANTIC, CONN.
ARCO ELECTRONICS,
INC.
135 Liberty St., New York, N. Y. -Sole Agent for Jobbers and Distributors in U.S. and Conodo
www.americanradiohistory.com
QUALITY..
THE ULTIMATE IN
e
Audio Transformers represent the closest approach
to the ideal component from the standpoint of uniform frequency response, low wave form distortion, high efficiency, thorough shielding
and utmost dependability.
UTC Linear Standard
feature
UTC Linear Standard Transformers
True Hum Balancing Coil Structure .
mum neutralisation of stray fields.
Balanced Variable Impedance line
Semi -Toroidal
maxi-
distributed
. peron every tap of a universal
line reflections or transverse coupling.
Reversible Mounting
permits above chassis
...
no
or sub -chassis wiring.
Allay Shields
ductive
pickup.
Hiperm-Alloy
shielding from
high
capacity
.
.
.
leakage re-
and
...
Precision Winding
accuracy of winding
.1 % , perfect balance of inductance and capacity;
exact impedance reflection.
...
... maximum
... o stable,
.
actance.
nits highest fidelity
unit
. ,
Multiple Coil Structure
in
High Fidelity
UTC linear Standard Trans formers are the only studio units with a guaranteed uniform response of '- I OB from 20. 20.000
permeability
nickel.iron core material.
.
cycles.
TYPICAL LS LOW LEVEL TRANSFORMERS
Primary
Type Ng.
LS10
LS10X
LS12
Application
Impedance mike.
Pickup. or multiple line
to grid
Low
As Above
Low impedance mike,
pickup. or multiple line
to
L912X
LS26
LS 19
push pull
As above
Rids
Impedance
51).
1.25.
200,
±1
Secondary
Impedance
from
60,000 ohms in
two sections
250. 333. 500/
600 ohms
As above
50,000 ohms
120.000 ohms
:10. 125. 200.
250. 333. 500/ overall. in two
600 ohms
As above
db
sections
60.000 ohms
calll, in two
sections
60.000 ohms In
two sections
't7;000 ohms;
1.25:1 each side
+15 DB
-74
20-20,1100
+14 DB
20- 20.000
+15 DB
-92 DB
-74 DB
20-20,000
+11 DB
1530
LS30X
LS27
L8.50
LS51
LS. 141
MA
25.00
MA
24.00
20.20.000
+11 DB
-74
DB
0
MA
21.00
220. 20.000
+26 DB
-50
DB
.25 MA
31.00
20. 20.000
+17 DB
-71
DB
5
SIA
25.00
As above
29- 20.000
50, 12.5. 200. 250.
30- 12.000
333. 500/600 ohms cycles
50. 125. 200. 250.
15,0110 ohms
20. 20.000
333. 500/600 ohms
30.000 ohms
50. 125. 200. 250.
20- 20.090
plate to plate 3:13. 500/600 ohms
500/600 ohms 500/600 ohms
30- 12.000
+15 DB
+20 DB
-92
-74
DB
DB
3
MA
8 MA
32.00
24.00
+17 DB
-74
DB
0
SIA
24.00
+20 DB
-74
DR
1
11A
24.00
+10 DR
-71
toit
e
S1.t
28.00
turn ratio
turn satin
1.6:1 overall
50. 125. 200.
50, 125. 200. 250.
250. 3:13, 500/ 333. 500 /600 ohms
600 ohms
As above
15.000 ohms
Three - sets of balanced
windings for hybrid service. centertapped
35.00
0
15.000 ohms
plate to plate
Single plate m multiple
line
Single plate to multiple
line
Puah pull low level plates
to multiple line
SIA
0
30.000 ohms
or multi-
5
DB
Lush pull plates to push
pull grids. Split primary
Impedance
-92 DB
-Ti DB
3:1 overall
60.000 ohms;
multiple line
32.00
28.00
-50
135.000 ohms;
pickup.
MA
MA
+17 DB
15.000 ohms
pie line to
As above
5
5
+20 DB
Single plate to push pull
grids. Split primary and
mike.
List
in prim'1 Price
5 MA
525.00
15- 20.000
5.000 ohms
and secondary
SDxing. low
DB
20.20.000
Bridging line to single or
hurls pull grids
Single plate to push pull
grids like 2A3. 6L6. 300A.
secondary
LS-22
Unbalanced OC
20. 20.000
Split secondary
18.21
Max.
Relative
humpickup
reduction
Nun.
Level
LS-t2
rREOUENCr
NEE
LS-50
om
rREOUEtCv
TYPICAL LS OUTPUT TRANSFORMERS
Type
Ne.
LS52
Primary will match
following typical tubes
lush pull
21.5, 250.
Primary
Secondary
Impedance
Impedance
6Ve. 42 or
500. 333. 250.
6.000 ohms
2A5 A prime
±I
List
23- 20.000
Max.
Level
15 watts
Price
528.00
db
from
oe
123, 50. 30.
20. 15. 10. 7.5,
2110.
L8S5
Push pull 2A3's. 0A50's. 300A's,
LS -57
Santee as
275A's, 6A3's, 6Le's
above
5.000 ohms plate
to plate and
3.000 ohms plate
to plate
5.000 ohms plate
to plate and
3,000 ohms plate
500. 333. 250.
200. 125, 511, 30,
20, 15, 10. 7.5,
.. -.o. 1.2
23-20.000
20
watts
28.00
30. 20. 15. 10.
7.5. 5, 2.5. 1.2
25- 20.000
20
watts
20.00
2.500 ohms plate
to plate and
1.500 ohms plate
to plate
9.000 ohms plate
to plate
500. 333. 250.
200. 125. 50. 30.
25- 20.000
40 watts
50.00
_5. 20.000
3e watts
12.00
ü,
_
-
_
=-ascastala=
to plate
LS58
Puai. pull parallel 2Á3's. 6.4513
300A's, 6A3's
LIS-0L1 .Push pull 01Á's self bins
s,
20. 15, 10. 7.5.
.,
2.5. 1.2
500. 333. 250,
200. 125, 50, 30.
20. 15. 10. 7.5.
150 VARICK STREET
Write lot 7v Catalog
NEW YORK 13, N.
EXPORT DIVISION: 13 EAST 40th STREET, NEW YORK 16. N. Y.,
www.americanradiohistory.com
Y.
CABLES: "ARLAE"
PS -439
-
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