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Dec. 3, 1946.'
c. M. sl‘NNET-r
2,412,015 _ .
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Dec. 3, 1946.v
c. M. slNNETT
Filed March 20. 1944
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Dec. 3, 1946.
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Patented Dec. 3, 1946
v 2,412,015
Chester M. Sinnett, Westmont, N. J., assignor to
Radio Corporation of America, a corporation
of Delaware
Application March 20, 1944, SerialNo.. 527,264
19 Claims. (Cl. 179-1004)
My present invention relates generally to a
whose condenser element acts as an electrostatic
novel method of, and systems for, reproduction
of audible frequencies existing in the form of
stated to reside in the provision of a frequency
A further object of the invention may be `
angle modulation on a superaudible wave.
responsive network, adapted to have angle modu
In the past it has been proposed to reproduce
sound records by translating the recorded varia
tions into reactance variations, angle modulating
a superaudible oscillator in accordance with the
reactance variations, converting the angle modu
lated oscillations into corresponding amplitude
modulated oscillations, and ñnally rectifying the
lated waves applied thereto, which consists of a
coil and a condenser providing together a
resonant circuit tuned off-resonance relative to
the mean frequency of the applied waves, and
either the coil or condenser acting as a repro
ducer element whereby the angle modulation on
the applied waves is directly converted into sound.
latter and reproducing the audio frequency cur
rents resulting from rectification. The generic
term “angle modulated” is intended to include
A still further specific object of this invention
is to provide a phonograph, or other sound re
frequency modulation (FM) and phase modula 15 producer device, operating onl the frequency
modulation principle and employing a super
tion. The aforesaid converting and rectifying
audible frequency modulated carrier, wherein the
steps have been common to other sound repro
modulated carrier is amplified and fed into a
ducing methods and systems, whether the source
tuned discriminator circuit, one reactive element4
of input energy was a record bearing impressions
representative of audio signals or angle modu 20 of which functions as an electrostatic loud
lated superaudible oscillations. In the case of
A further object of my present invention is to`
frequency modulation radio reception, as well,
provide a. novel method of operating a condenser
discrimination and rectifying steps are employed
type of sound reproducer, wherein the polariz
to provide modulation signals for ñnal reproduc
ing voltage of the reproducer is provided by
A general object of my present invention is to
provide a system for reproducing frequency
modulated superaudible waves, wherein the. dis
criminator of the system has a reactive element
thereof which functions as a modulation repro
superaudible wave energy applied to the repro
30 whether condensive or magnetic, wherein angle
ducer thereby eliminating the need for the con
ventional form of discriminator-rectifier network
commonly employed in frequency modulation
Still other objects of my invention are to pro.
vide novel sound reproducer . arrangements,
According to another important object of my
present invention, I utilize an electrostatic type
of reproducer as an essential reactive element of
a simple tuned circuit acting to convert angle
modulated superaudible waves into correspond
ing amplitude modulated waves with concurrent
acoustic reproduction of the modulation on the
amplitude modulated waves.
Still another important object of my present
invention is to provide a novel method 4of re
producing sound, wherein angle modulation of a 45
superaudible wave is employed to represent the
currents corresponding to the sounds to be re
produced by a transducer, and the transducer
modulated superaudible carrier waves are directly
applied to the reproducer for acoustic reproduc
tion of the modulation.
Still other features of my invention will best
be understood by reference to the following de
scription, taken in connection with the drawings,
in which 1 `have indicated diagrammatically
several circuit organizations whereby my inven
tion may be carried into effect.
Fig. l schematically shows one embodiment of
the invention,
Fig. 2 is a graphic representation of an ideal
resonance curve of the discriminator network of
Fig. 1,
Fig. 3 is a modification of the system of Fig. 1
wherein further circuit details are shown,
Fig. 4 presents an idealized graphical analysis
of the functioning of the present> system,
Fig. 5 shows a further embodiment of the in
itself acts as an essential reactive component of
a discriminator network for the >angle modulated 50 vention applied to reproduction of frequency
A more specific object of my invention is vto
provide a system of reproducing sound records,
modulation-recorded impressions,
Fig. 6 schematically shows the invention ap
plied to a modification of the system of Fig. 1,
wherein a pickup is employed to convert the
Fig. 7 'illustrates an embodiment of the in
record impressions into capacity variations of a 55 vention showing both condenser and magnetic
superaudible oscillator circuit thereby to provide
frequency modulated superaudible oscillations;
the essential improvement in the system includ
ing the replacement cf the usual discriminator
rectiñer network by a discriminator network 60
reproducer elements,
Fig. 8 shows a modification ofv the circuit of
Fig. '7,
Fig. 9 illustrates schematically the manner of
embodying the invention in a frequency modu
lated carrier wave receiving system.
While the present invention is of wide utility,
as will be clear after a reading of lthe followingdescription of .the various aspects and features of
the invention, the embodiment of .the invention
shown in Fig. 1 will be presented with a View to
explaining the functioning of my novel discrimi
lated wave energy. The term “discriminator”
used in the description and claims denotes a cir
cuit which functions to produce an amplitude
variation in the frequency modulated wave
energy, which amplitude variation is representa
tive of the frequency deviations of the wave
energy. The latter wave energy is then capable
of being rectified in order to provide the modula
nator-reproducer network. f AAs stated above., it
tion signals for reproduction. This is true
has been proposed in the past -to reproduce sound 10 whether the sourceof the frequency modulated
records by employing a superaudible carrier
energy is directly responsive to a record, or
which is frequency modulated by reactance' vari
whether a frequency modulation radio receiver is
ations derived from the record impressions.' Ac
being employed.
cordingly, in’Fig. 1 I have schematically repre
According to my present invention, acoustic
sented by the numeral I a superaudible oscillator 15 reproduction of the modulation signals occurs si
network which is provided with the usual resonant
multaneously with discrimination of the angle
tank circuit 2. The latter consists of a coil 3 and
modulated wave energy. Stated differently, I
shunt condenser 4, and is tuned .to a predeter
have provided a discrimin-ator circuit which
mined normal oscillation frequency Fc. The pre
. automatically and concurrently acoustically re
determined frequency of the superaudible oscil 20 produces without the usual rectification .the am
lator may be chosen from a wide range of fre
plitude modulated wave energy produced by dis
quency values depending upon the design of the
crimination. Reference to Fig. 1 will show that
other networks of the system. The oscillation fre
the FM wave energy, subsequent -to amplification
quency may be in the megacycle (mc.) range, or
- v- at 9, is applied to a condenser C and coil L pro
it may be in the lower kilocycle (kc.) values. By 25 viding a parallel resonant circuit. The condenser
way of specific example, let fthe-assumed that
C is actually an electrostatic .type of acoustic re
the oscillator I has its tank circuit 2 tuned to a
producer. Those skilled _in the lart of sound
frequency of 20 kc. The frequency of ythe tank
reproduction are acquainted with the manner of
circuit 2 is modulated or deviated by virtue of
Y designing an electrostatic type of reproducer, such
reactance variations caused by the tracings of 30 as a condenser loud-speaker.
the needle or stylus through the record grooves.
A .condenser loud-speaker is .a loud-speaker in
By way of specific illustration, the numeral 5
which the mechanical forces result from electro
denotes a record on a turntable 6. An electro~
static reactions. The -plates of a condenser loud
static pickup device is schematically shown, and
speaker are relatively charged .due to polarizing
comprises a small condenser one of whose plates 35 voltage. The polarizing voltage may be as high
‘I is relatively fixed. The plate 'I is connected to
as +200 volts or more. The mobile electrode of
the high alternating potential side oi’ tank cirn
a condenser loud-speaker radiates the sound di
cuit 2. The mobile electrode 8 is indicated as
rectly into the air. Provision must be made to
grounded, and, therefore, is effectively connected
keep the electrodes of the .condenser separated
to the grounded side of lthe oscillator tank circuit.
without at the same time incurring much me
The mobile electrode has operatively associated
chanical stiffness. 'I‘o obtain an efficient system
therewith a stylus which runs through .the record
the mass of the mobile electrode is best kept low.
grooves. Hence, the capacitance of condenser
The impedance of the amplifier .tube driving the
'I-8 will vary in accordance with the physical
condenser speaker is preferably made approxi
displacements of the stylus. These capacitance
mately equal to the capacitative impedance at the
variations are translated into' frequency devia»
highest audio frequency to be reproduced so .that
tions of tank circuit 2. The electrostatic pickup
the capacity current drawn by the speaker will
device may be constructed in accordance with the -
not cause excessive falling-off of voltage at the
teachings of my application Serial No. 414,305,
higher audio frequencies. It is an impor-tant and
ñled October 9, 1941, now Patent No. 2,376,456 50 novel feature of my invention .that the modulated
issued May 22, 1945. However, the invention is
superaudible voltage applied to the condenser
not limited to this type of Idevice .as any other
form of pickup maybe used, as long as it'l is
capable of transforming the physical displace
ments of the stylus into reactance variations of
the oscillator tank circuit.
The extent or range of frequency deviation
with respect to Fc, the predetermined normal
oscillator frequency, will be representative of the
speaker C serves to provide polarizing voltage as
required by the electrostatic speaker. A special
or auxiliary polarizing voltage source is thereby
The showing of the reproducer .construction in
Fig. 1 is highly illustrative and schematic, since
the particular type of reproducer is well known,
and my invention is not dependent upon any par- .
amplitude of the sounds which are recorded on 60 ticular reproducer construction. In general, it
record 5. while the rate of frequency deviation will
be representative of the audio frequencies per se.
’I'he maximum frequency swing on either side of
the mean frequency will depend also upon the
design of the oscillator circuit. For example, the
overall frequency swing or range may be some 10
kilocycles (kc). The frequency modulated oscil
lations may then be amplified as at 9. Accord
ing. to my invention, Ithe amplified frequency
comprises a metal backing plate I0 of wavy con
figuration so as to provide spaced peaks. The lead
II connects the plate I0 to the lower end of .coil
L. The condenser I2 establishes both the lower
end of coil L and the plate'I 0 at ground potential
for alternating current. The upper end of coil L
is connected to the output electrode (not shown)
ofthe amplifier 9. The +B terminal of the direct
current supply source (not shown) is connected
modulated wave energy is subsequently treated in 70 to the lower end of coil L. The second electrode
an entirely unconventional and novel manner.
of condenser C is provided by a thin metal sheet
In the prior art, it is usual to subject frequency
I3, as for example, tin or aluminum foil. It is
modulated carrier wave energy to discrimination
obvious Ithat this metallic surface could be com
in order to translate the frequency modulated
posed of sputtered or deposited gold or silver lof
wave energy into corresponding amplitude modu 75 essentially molecular thickness as long as .con
tinuous contact were maintained. This sheet I3
is. stretched across an insulation sheet, such as a
sheet of rubber I4., The latter -functions as an
elastic dielectric for the condenser C.
ter voltage is applied, tothe input grid of the am
The input grid of ampliflertube 2| is connected
by the direct current blocking condenser 20 to the
I8., The remainder'of the ,
plate of oscillator tube;
The vlead >I5 connects the electrode I3, the mo
circuit elements electrically connected to tube 2I
bile or diaphragm electrode, to the high potential
are conventional in nature, and need not. be de
end of coil L. Hence, the spaced metal electrodes
scribed in detail. The plate circuit of tube 2| in
I0 and I3 are effectively connected in shunt with
cludes a tuned circuit 22- which is resonated to. '
coil L. Since the elastic dielectricy sheet I4 is
10 the mean frequency Fc. Hence, across tuned cir
stretched over the outer face of the ñxed elec
cuit 22 there will be developed amplified fre
trode I0, there is mechanical contact'between the.
sheet vHI and ,electrode Iû only atgthe -peaks of the _
latter. The metallic or metallized sheet I3~is in
contact With the dielectric sheet I4 at all points. '
Hence, the metallic surface is rendered effectively
elastic clue to the subjacent dielectric. As stated
previously; the specific structure of the condenser
speaker C is not part of my present invention;
See, for example, U. S. Patent No. 1,644,387 to
Kyle for a reproducer construction which is sim
ilar to that shown herein.
quency modulated superaudible oscillation volt
age, >This voltage may be further amplified in
the output tube 2'5. The input grid of the latter
is coupled by direct current blocking condenser
23 to the plate side of the resonant circuit 22. A
suitable choke coil 24 connects the input grid of
'tube 25 to ground. The plate of tube I1 is con
nected to the +B terminal of the direct current
20T supply source through the ¿coil L which was de
scribed in connection with Fig. i. The condenser
speaker C, schematically represented, is shown
The' ideal discriminator characteristic of the
connected in parallel with coil L.
As stated previously, it is desirable to have the
output impedance of tube 25 match the capacita
tive impedance of the condenser speaker C at the
highest audio frequency to be reproduced. The
circuit L~-C acts as a high impedance in the plate
circuit offtube 25. The tube 25 may be operated
circuit L--C is shown in Fig. 2. It is to be under- ‘
stood that the graphicrepresentation of Fig. 2
is purely illustrative. . The curve in Fig. 2 is a
single peak resonance curve Whose peak fre
quency is the resonant frequency of the circuitl
which includes the coil L in shunt with the con
denser C. The predetermined mean or center
as a class A, class B or class C ampliiier. There
frequency Fe of the tank rcircuit 2 of the super 30 are advantages in class C operation; for example,
audible oscillator is off-tune with respect to the
peak frequency of circuit L-C. The extent of
off-tuning will be determined by the shape of the
considerable power output could be secured even
though tubes of relatively reduced dimensions
were used. If desired, the power output stage
may use a pair of-,tubes in push-pull relation.
The bypass condenser I2 is connected from the
lower end of coil L to ground, as in Fig. 1. Since
the particular construction of the condenser re
producer C is no part of my invention, the repro
The peak frequency of the electrostatic repro
ducer circuit L--C is preferably so chosen that
the mean frequency of the modulated Waves ap
plied to the reproducer circuit will fall on a point
on either flank of the resonance curve which has 40 ducer is schematically represented in Fig. 3. 'I'he
a substantial slope. Hence. it will be seen that
mobile electrode, or diaphragm, is denoted by
the applied frequency modulated superaudible
oscillations will be translated into correspondingv
amplitude modulated oscillations. Such ampli-l
tude modulated wave energy will be reproduced
by the electrostatic reproducer C. Accordingly;
my method generically contemplates the trans
lation of angle modulated superaudible oscilla
tions into corresponding amplitude modulated
oscillations and concurrent reproduction of the
audio modulation which exists on the translated
wave energy,
In Fig. 3 I have shown ’specific circuit elements
which may be employed in the schematic net
works of Fig. 1. A morev detailed explanation of
the operation of the condenser reproducer will
be given in connection with Fig. 3. The electro
static pickup device 8-,-1, which constitutes a
condenser, is shown. as having its fixed electrode
l connected to the junction of the coil I6 and
blocking condenser I1. The coil I6 and condenser
8--1' provide a resonant grid circuit for the oscil
lator'tube I3. The resonant grid circuit will nor- l
mally be tuned to the predetermined mean fre
quency Fc. The plate circuit of tube I8 includes
a resonant circuit I9 which is also tuned to the
mean frequency Fc. It will, therefore, be recog
nized that Athe superaudible oscillator shown in
Fig. 3, is of the well known tuned grid-tuned plate
type. The variations in capacitance of the pick
up device 1_8 in response to stylus motion cause
_ frequency modulation of the oscillations produced
in the oscillator circuit. Hence, there will be de
veloped across the plate circuit I9 frequency mod--y
ulated super'audible oscillation voltage. -Thelat
numeral I3', While the numeral I0’ designates
the fixed electrode corresponding to electrode III
of Fig. 1. Circuit L--C is tuned to the peak fre
quency of the curve shown inFig. 2. The fre
quency Fc Will fall on either flank of the curve;
at about 70% of resonance.
Before explaining the functioning of circuit
L-C, let it be understood that the following
analysis is equallyapplicable to an‘ electromag
netically-operated device of the diaphragm type.
The only requirement is that the original dis
placement of the diaphragm be secured in re
sponse to carrier Voltage. In any event the car
the system should be of
superaudible frequency, and is required'to be'of
an intensity capable of providing initial displace
ment of the diaphragm. Under these conditions,
assumethe sound reproducing element is either
- riez` wave employed in
the coil or condenser of the resonant discrimina
tor circuit, and that Fe of the applied frequency
variable waves falls on either flank of the dis
criminator resonance curve, The variations in
frequency of the modulated Wave energy Will
cause a change in polarizing voltage, and conse
quently the diaphragm displacement will change.
If the variations in frequency of the FM energy
applied to circuit I_r-C occur at an audio fre
quency rate, sound will be emitted by the re
producer reactance element.
Another Way of looking at the action of vthe
discriminator circuit L-C is as follows: Regard
less of the polarity of the super-audible fre
quency current, the diaphragm elect-rode will be
displaced in the same direction thereby-produc-4
ing second'harmonic output of the applied super
audible carrier frequency. This can bethought
(3+ and -~)_` thereto. 'In circuit L-C there will
appear across coil L, and'consequently across C,
an alternating voltage having the frequencyFc.
Since the opposite ends of coil L must 'havefop
of 4as a form of rectification. Once the diaphragm
electrode has been :displaced by the carrier cui'
ren‘t„ variations in carrier amplitude produced
posite‘polarit’y potentials, the opposite electrodes
of C must be of opposite'polarityl thereby caust->
by, thedetunin’g-'of?the L-C circuit (which is
madeup impart by the reproducer element per
ing attraction between them.
se) v_willV result in _acoustic output from the re- `
producer element in step with carrier frequenc
~- `In order more clearly to depict the functioning
This gives therequired initial displacement of
the speaker` diaphragm electrode I3. The amount'
1,0 ofdisplacement increases as the voltage across-`
coil L increases. 1‘The carrier voltage of _mean
frequency Fc will produce a displacement of-.the
the-curves A, B, C and D of Fig. 4. These curves
diaphragm for each half cycle, since the only. re
are ideal representations, and are purely illus
quirement for the attractionv between the »di
trative.- K'Cu'rve A shows a modulating audio Wave 15 aphragm I3 and fixed electrode I0 is that oppo
assumed »to represent the recorded sound wave.
site polarity potentials be applied. Thus, as far.
This curve can represent the change of capacity
as the diaphragm is concerned the pull on it will
of-»the -FM pickup 1-8 which produces changes'
occur at double the carrier frequency Fc. Since
in oscillator frequency as I*shown by curve B. The
Fc is fundamentally above audibility the> vari
curve A' could also 'represent the voltage output 20 ation in pull on thediaphragm at 2Fc cannot be
of piezo-electric `crystal 4I) of Fig.'6. The curve
heard. Therefore, the same effect is produced,
pictorially shows the relative values of the mod
asfar asv the electrostatic speaker is concerned,
ulating and modulated frequencies. Curve B
a's though direct current voltage were applied to»
represents the frequency modulated wave re
the electrodes in the well known manner.
of the present system, attention is directed to»
sulting fromY variation of the pickup device 1_8
Having initially displaced the diaphragm I3
in response to the variations of curve A. vThe
against the resilient -sheet or darn I 4, there is
created a restoring-force due to the stressed dam.
This force tends to return -the diaphragm I3 to
its original. normal position'. If we now change
oscillator voltageduring modulation would gen
erally follov’i7 the wave form of curve B. The am
plitude is constant, while the frequency is vari
able. vThe effect 'of' circuit L-C on the 'wave
the magnitude of the polarizing voltage, the
sound output must result. >This acoustic output
form of curve Bl is depicted'in curve C. It will
be> observed that the frequency-variable wave
now has variable amplitude as well. It will fur
ther be seen that the variable amplitude of curve
occurs as the attraction between the electrodes
I0 and I3 varies with the applied voltage, and the
variation Will occur'at an audio frequency rate
C follows the variation of the modulating audio
correspondingv to the modulating frequency yap
wave of curve A. Finally, curve D illustrates the
plied to the carrier wave.
There may be some improvement in acoustic
output by operating at point Fc on the curve of
Fig. 2 rrather than at point Fc’ on the high fre
quency ilank ofthe curve. It has previouslybeen
pullïonthediaphragm electrode (I3 in Fig. 1 or
I3' in Fig;v 3) of' condenserreproducer C. Note
that the pull is always in one direction, at double
the carrierffr'equency and of a variable ampli
tude `determined by the voltage across L-C as
shown byl curve C. Due to the audible variations
`explained .that as the voltage applied to speaker
electrodes increases, the pull on the diaphragm
increases. As the diaphragm is displaced in this
fashion by a change in the instantaneous value
of the applied modulated energy, the capacity of
condenser-C .increases thereby to lower the fre.
quency ofL-C.. y.This causesa.further'increase
in pullon the diaphragm> the sound emitted by
the'diaphragm 'will be a' reproduction of the re
corded sound.v Curve D is more closely spaced
than the prior curve C, because it represents the
pull on the diaphragm, and this occurs at double
theA carrier frequency shown in curves B and C.
in voltage and further displacement of electrode
' The frequency'range of the superaudible oscil
lator is preferably Vbetween 15 and 30 kc., al
though notnecessarily limited thereto. Gener
I3. Obviously this cannot'go on very long, since
50 there is not necessarily a linear relation between
capacity change, displacement of the diaphragm
ally, the’ oscillator frequency should be several
times 'higher than the highest audio frequency
and the polarizing voltage. `Some of the eiîect
is present, however. Similarly as the instan
which it v'is desired to reproduce. 'For an oscil
lator having a frequency of 15 kc., it is most likely
that -frequency deviations up to a maximum of
plus orminusA 2 'to 3 kc. should be suilicient. At
an oscillator frequency of 30 kc. it might be de
sirable'to employ frequency deviations up to al
maximum of» plus or minus 10 kc. These -fre 60
quency values are not intended to be limiting in
nature, but are merely illustrative.
YIt has been previously stated that one of the
main features of my invention is to utilize the
appliedicarrier‘voltage as the polarizing voltage
taneous frequency is Lshifted downward by modu
lation, the Voltagenacross condenser C decreases.
This causes decrease in displacement of >electrode
I3, with concurrent upward increase of> the
resonant frequency of L-C thereby causing a
further decrease in voltage across condenser C.
Thus, tuning the circuit L-C sc_.that Fc falls on
the low frequency flank of the resonance curve
of circuit L--C, should result in some increase in
' Assume, now, that the operating point is at
Fa'.y This means that Vthe normal Vfrequency of
oscillator' is 'Fc'. If the instantaneous frequency
of the FM voltage applied' to 'L-C is above ‘Fe’
then a'decrease ofv outputvolta’ge occurs. The'
iliary'direc't current `polarizing voltage is need
displacement of lthe `diaphragm will decrease
ed in my condenser reproducer. If like voltages 70 thereby causinga- decrease in effective capacity
for the condenser. The following explanation is
not necessarily exclusive of other theoretical ex
planations of the demonstrated fact that no aux
(+ and -l-‘) are applied to electrodes I0 and I3,
there will, >of course, be set up a mechanical force
tending to push or repel the electrodes from each
of condenser C.: This will, in turn, cause circuit
L--C- to tune to a higher frequency resulting in'
other. ' 4The electrodes »are attracted to each
condition occurs when. the modulated Lenergy lhas
stillîless voltage and displacement.
A similar
other uponk the application- of unlike 'voltages 75 an -instantaneous:frequency less than Fe'.; There
The resulting FM currents may be amplified.
as atamplifier 42 tuned to the mean frequency
Fc, and then applied to the output amplifier £3.
Fc on the resonance curve of circuit L-fC».
The latter has the circuit L-C in its plate circuit
My invention has many possibilities. The pick
exactly as described in Fig. 3. The action of cir
up device need not be electrostatic, but may be
cuit L-C is the same as previously explained,
of the variable inductance type. The records used
and the audio frequency current repro-duced by
may be of the conventional laterally cut type; the
condenser reproducer C-is emitted as sound.
“hill and dale” type; or nlm recordings of either
As stated previcusiy,. the present invention is
amplitude-variable or frequency-variable types.
to a resilient diaphragm type of
Moreover, the records may be of the frequency
is thus obtained less acoustic output'from-an
overall viewpoint when operating at Fc’ than at
modulation type, wherein frequency modulation
electromagneticaliy-operated device. The dia
signals are directly recorded. In general, any
transducer device can be employed in conjunction
phragm may have sufficient inherent resiliency
to spring back, or restore, into normalA horizontal
with a superaudible oscillator to vary the fre
quency of oscillations thereof, and the resulting
chanical restoring device may be used. The
frequency modulated oscillations after amplifica.
position, orA any well known and suitable me
only requirement is that the original displace
ment of the diaphragm from normal position be
obtained by means of carrier-derived voltage.
The ampliiied voltage at carrier frequency Fc
(applied to the driving coil) should be sufiiciently
pickup device whether of the electrostatic, mag 20 high to provide the necessary polarization and
netic or piezo-electric crystal types or any other
initial', minimum or threshold displacement of
mechanism capable of translating acoustic or re
the diaphragm. In Fig. 7 I have shown the
corded waves into electric currents of audio fre
output ampliñer 5o of a system fed with FM
tion can be reproduced in a discriminator-repro
ducer circuit L-C as described herein. By the
term “transducer” I include a microphone, a
In Fig. 5 I have shown a modincation of the
system or”
3 to the extent that the amplifier
25 is supplied with ampliñed frequency modulated
signals from a piezo-electric crystal pickup de
vice. The record in this form of the invention is
generally of the type disclosed by W. van B.
Roberts in his application Serial No. 369,829, ñled
December 12, 1940. The record 5 has cut or en
graved in its face impressions corresponding _to
FM signals whose mean carrier frequency is
superaudible. Here, again, the recorded FM sig- ‘
nals may have a mean frequency chosen from a
waves produced in any of the ways shown in
Figs. 1, 3, 5 or 6. The amplifier tube 50 has
the circuit L--C arranged in its plate circuit asv
previously explained. The condenser C is a re
producer which has a high audio frequency re
spons@ characteristic. In other words it is of
the so-called “tweeter” type. The coil L is the
primary winding of a transformer 5l Whose sec
ondary winding 52 is arranged in a closed circuit
with a low impedance coil 53. The coil 53 isA
provided with a diaphragm 5s which is initially
displaced or polarized by virtue of the carrier
derived voltage developed across coil 53. Coil
range of 15 to 30 kc., with a maximum deviation
range from 2 to l0 kc. The recorded FM signals
are converted into FM currents by the crystal
material readily adapted to providea magnetic
standard amplitude vrecord of the laterally-cut ‘ ‘
53 may be provided with a core 53’ of magnetic
pickup 3B. The latter is schematically repre 40 pull on diaphragm 5s against the illustrative leaf
spring restoring device 55. The magnetic repro
sented, since it is very Well known to those skilled ` ducer 53-54 is of the low audio frequency re
in the art of reproducing recordedrsound.. The
sponse, or so-called “woofen” type.
FM currents produced at the output terminals of
This form of dual reproducer system operates
pickup 3l) are amplified in one or more stages of
in a manner similar to the prior circuits L--C.
amplifica-tion 3l and 3i'. The ampliners 3| and f4.5 In the present case the primary circuit of trans
3l’v are each tuned to a predetermined normal
former 5l is tuned t0 the peak frequency of the
frequency Fc. 'I‘he aforesaid mean carrier fre
curve shown in
2. The mean -frequency of
quency is Fc. The ampliñed FM signals applied
the applied FM signals falls on either flank of
to amplifier 25 are reproduced by the conjoint
the curve as previously explained. The-repro
discrimination and reproduction action of L--C
ducer C functions in response to the envelo-pe of
as previously described.
the rectified amplitude-variable wave, as depicted
In Fig. 6` I have shown a dirferent method of
in Fig. 4 by curve D. The variable amplitude
producing the FM signal energy for application to
carrier currents flowing through primary wind
the circuit L-C. In this system the record 5 is a
ing L will induce similar currents in secondary
type or of the “hill and dale” type. The pickup de
vice 43 is a suitable form of piezo-electric crystal
pickup, as in the case of Fig. 5, and feeds its audio
frequency output current to the input terminals
of a superaudible frequency oscillator ci. ri‘he
latter is normally tuned to produce oscillations ci
a frequency Fc. The enîect of the audio input
current is to vary the frequency of oscillation of
the oscillator di. Any formof relaxation oscilla
tor. such as the well known resistance-capacity -'
oscillator or thel multi-vibrator oscillator, may be
These variable amplitude currents
will vary the position of the initially-displaced
Dotted line A' showsl the dis
placed positionl of the diaphragm at the peaks of
the curve D in Fig. e, while dotted line B’ shows
the minimum signal, or threshold, displaced posi
tion at the valleys of curve D of Fig. 4.
It will
be seen that the diaphragm is pulled towards
the-„magnetic core in response to the minimum
signals flowing-through coil 53. As the signal
current modulatesv therestoring element will be
caused to vary-the diaphragm position.
» i
used at
I prefer tc employ the R'-C type of
In Fig. 8 there is shown a modiñcation of the
oscillator disclosed and claimed for the same
dual reproducer system of Fig. '7. Here the FM
function in my application Serial No. 463,349,
signal current output of tube Bil-flows through
nled Cctcber 26, 1942. The last-named applica
the-»discriminator circuit C'---,-L’. Condenser- Cf
tion explains the manner in which the audio fre
isl a reproducerA whose mobile or diaphragm
quency- currents,_ derived from a sound record,
electrode-is designated by numeral I3', and the
may be used to frequency modulate the oscillatory
static electrode is l0’. Coil L’ is a high imped
output current of-an R-C oscillator of the-¿form
ance coil _and- maybevprovided with core¿i3?4 ,_
and initially displaces diaphrag-m 54’ due to the
carrier-derived polarizing voltage. Circuit C’---
for circuit; L--C to handle. Hence, I utilize cas
caded frequency dividers 6| and 62 to reduce
L’ is tuned to the peak frequency of a resonance
concurrently the mean frequency and frequency
curve (Fig. 2) upon either of whose flanks may
swing to more practicable values of 172 kc. and
fall Fc, the mean frequency of FM signals ap 5 i3 kc. respectively. This method is generally
plied to amplifier 50. Of course, the reproducers
may have different, such as opposite or com
in accordance with the teachings of M. G. Crosby
in his U. S. Patents 2,230,231 and 2,230,232
plementary, frequency response characteristics.
granted February 4, 1931. The frequency di
The plate of tube 50 is connected to the +B
vider 6I reduces the I. F. energy by a factor of
terminal through isolation coil 6I, and direct cur 10 5, and divider 62 reduces the FM energy output
rent blocking condenser 60 connects the plate
of divider 6I by a factor of 5.
to electrode I3'. Additionally, the condenser C'
Each of dividers 6l and 62 may, if desired, be
may be a normal condenser and non-reproducing,
constructed in accordance with the teachings of
the coil L’ and its diaphragm acting then as the
G. L. Beers in application Serial No. 430,588,
15 filed February 12, 1942, patented Aug. 22, 1944,
To recapitulate the operation of the systems
as U. S. Patent No. 2,356,201. Beers shows a
of Figs. 7 and 8, the circuit L-C performs the
locked-in oscillator whose input terminals has
same as previously described. In Fig. 7 the coil
FM signal energy applied thereto (I. F. stage),
L forms the primary of an output transformer
and in the output circuit there is produced FM
5| which matches the speaker coil 53 to the 20 signal energy Whose mean frequency and fre
output of tube 50. Thus, as the voltage across
quency swing have been reduced by a like factor.
coil L varies with modulation there will be a
Of course, any other form of frequency divider
variation in voltage across coil 53. Consequently
may be used at 6l and 62. It is to be clearly
there will occur a change in displacement of dia
understood, however, that additional frequency
phragm 54. The particular advantage of the
25 division may be employed to reduce the 172 kc.
system of Fig. 7 resides in the fact that dia
mean frequency, or heterodyning action may be
phragm 54 can reproduce low frequencies, where
used for the same purpose if the deviation is not
as it is diiiicult to obtain satisfactory reproduc
to be affected. Further, the receiving system
tion of low audio frequencies from an electro
may operate in any FM transmission band.
static speaker. Coil 53 could be the voice coil 30 Again, either of the reproducer systems of Figs.
of a loudspeaker, and serves to displace the dia
7 and 8 may be employed in place of that shown
phragm 54 initially under influence of the car
Fig. 9. The functioning of the circuit L-C
rier voltage.
in Fig. 9 will be similar to that described in
In Fig. 8 the set-up is somewhat different. In
1 and 3. Circuit L-C is tuned to a fre
this instance L’-C' performs normally. Coil 35 Figs.
quency above or below 172 kc., and as depicted
Lf is, however, magnetically coupled to dia
in Fig. 2. The carrier-derived voltage functions
phragm 54' so that displacement of the latter
as polarizing voltage in this case as well.
varies with changes in voltage across coil L’.
While I have indicated and described several
v'I'his has been explained in connection with Fig.
systems for carrying my invention into effect,
7. Again, the purpose of diaphragm 54’ is to 40 it will be apparent to one skilled in the art that
reproduce the lower audio frequencies while con
my invention is by no means limited to the par
denser C’ reproduces the higher audio frequen
ticular organizations shown and described, but
cies. It is to be clearly understood that the in
that many modifications may be made without
herent restoring characteristic of a springy dia
departing from the scopel of my invention.
phragm may be used in either Figs. 7 and 8. 45 WhatIclaimis:
Hence, in Fig. 8 I omit the leaf spring restoring
1. In a system for reproducing frequency
device of Fig. 7.
modulated carrier waves, a resonant descrimi
My invention is applicable to the reception of
nator circuit including as the capacitative ele- ,
FM broadcast waves in the presently-assigned
ment thereof an electrostatic reproducer, and
42-50 megacycle (mc.) band. Such waves have 50said discriminator circuit being tuned to a fre
a considerable deviation range. For example. at
quency which is substantially off-resonance with
present an FM transmitter in the 42`-50 mc. band
respect to the mean frequency of frequency
is permitted a maximum frequency deviation up
modulated waves applied to the discriminator
to '.75 kilocycles (kc.) on either side of the trans
mitter normal or carrier frequency. Assuming 55 2. In a method of reproducing sound records
superbeterodyne reception of such FM waves at
wherein angle modulation of a superaudible
the receiver system shown in Fig. 9. those skilled
wave is employed to represent currents corre
in the art are fully aware of the fact that the
sponding to sounds to be reproduced by a loud
mean frequency of the received signals is re
speaker; the improved step comprising the simul
duced to a lower frequency value, say of the 60 taneous translation of angle modulated super
order of 4.3 me., without changing the range in
audible Wave energy into corresponding ampli
absolute figures of the frequency swing of the
tude modulated wave energy and reproduction
intermediate frequency (I. F.) energy. Hence,
of the modulation existing on the latter Wave
I. F. amplifier El) is to b-e understood as having
energy in a single discriminator circuit.
its inout terminals coupled to the I. F. output 05 3. A frequency responsive network, adapted
circuit ci’ a prior converter. The I. F. amplifier
to have angle modulated superaudible waves ap
passes FM energy whose mean frequency is 4.3
plied thereto, comprising a coil and a condenser
mc.. and whose frequency swing may cover a
loudspeaker, said condenser loudspeaker being
rance of plus or minus 75 kc.
adapted directly to convert the modulation on
The discriminator-reproducer circuit L-C is 70 the aplied waves into sound, and said coil and
arranged in the output circuit of the last tube
condenser being tuned substantially olf-reso
of the system. It is not practicable to apply
nance relative to the mean frequency of applied
the FM current output of I. F. amplifier 60 to
modulated Waves.
circuit L-C. The mean frequency of 4.3 mc.
4. In combination with a source of frequency
is too high, and the i-75 kc. swing is too great 75 modulated oscillations, a. condenser reproducer,
and a circuit connecting the reproducer to said
source for reproduction of the modulated oscil
lations; the improvement comprising said cir
cuit including a coil which 4forms a tuned fre
quency discriminatcr circuit with the condenser
reproducer, said coil and condenser being tuned
to a frequency sufficiently different .from the
mean frequency of the modulated oscillations to
secure frequency discrimination.
the angle modulated wave energy to a resonant
circuit tuned substantially off-resonance relative
to said Wave frequency, and providing in said reso
nant circuit the simultaneous translation of the
angle modulated superaudible wave energy into
corresponding amplitude modulated Wave energy
and reproduction of the modulation existing on
5. In a system for receiving frequency modu
lated carrier waves, a resonant discriminatcr
circuit including as the active capacitative re
actance element thereof an electrostatic repro
ducer, and said discriminator circuit being tuned
to a frequency which is substantially off-reso
nance with respect to the mean frequency of
frequency modulated carrier voltages applied to
the discriminatcr circuit.
6. In a method of reproducing sound wherein
angle modulation of a superaudible Wave is em
to the mean frequency of frequency modulated
carrier waves applied thereto.
12. A method of reproducing sound records
whose impressions are provided by angle modula
tion o-f a superaudible wave, comprising applying
the latter wave energy.
13. A frequency responsive network, adapted to
15 have angle modulated superaudible waves applied
ployed to represent modulation voltages corre
sponding to sounds to be reproduced; the irn
provement consisting of the concurrent transla
thereto, comprising a coil and a condenser, one
of said latter reactive elements being Ia transducer,
and said coil and condenser being tuned substan
tially off-resonance relative to the mean fre
quency of applied waves.
14. In combination with a source of angle mod
ulated oscillations, a condenser reproducer, an
amplifier Ycircuit connecting the reproducer to
said source for reproduction of the modulated os
tion of angle modulated superaudible wave en
cillations, a tuned discriminator circuit consisting
ergy into corresponding amplitude modulated 25 of a coil in shunt with the condenser reproducer,
Wave energy and reproduction of the modula
said coil and condenser being tuned to a fre
quency sufficiently different from the mean fre
quency of the modulated oscillations to secure dis
tion existing on the latter wave energy in a simple
tuned circuit off-resonance with
said wave
7. A frequency responsive network comprising
15. In combination with a reactive transducer,
a. superaudible oscillator, means for varying the
frequency of the oscillator in accordance with the
transducer output energy, a discriminatcr circuit
substantially off-tune with the mean frequency of
a coil and a condenser, at least one of the two
reactances being adapted to convert modulation
voltages into sound, and said coil and condenser
being substantially off-resonance relative to a
desired mean frequency of frequency modulated
the oscillations, and the capacitative component
carrier waves adapted to be applied to said
8. In combination with a source of angle modu
lated oscillations, a condenser reproducer, a
circuit coupled to said source and including a
coil which forms a tuned discriminatcr circuit
with the condenser reproducer, said coil and con
denser being tuned to a frequency substantially
diñ'erent from the mean frequency of the modu
of the discríminator circuit being an electrostatic
16. A frequency discriminatcr circuit consisting
of two reactive components of opposite reactive
sign related in magnitude to tune to a predeter
mined peak frequency, and at least one of the
reactive components being a transducer.
17. A discriminatcr circuit including as an ele
' ment thereof an electrostatic reproducer, and
lated oscillations to secure discrimination.
9. In combination with a reactive transducer,
a superaudible oscillator, means for varying the
frequency of the oscillator in accordance with
the transducer output energy, means for repro
ducing the frequency modulated oscillations
without rectification, said means comprising a
said discriminatcr circuit being tuned to a fre
quency which is adapted to be substantially cif
resonance with respect to the mean frequency of
modulated carrier waves applied to the circuit.
18. In combination with a source of angle mod
ulated oscillations, a condenser reproducer, a cir
cuit connecting the reproducer to said source for
discriminatcr circuit substantially off-tune with
reproduction of the modulated oscillations, said
the mean frequency of the oscillations, and the
circuit including a coilV which forms a tuned dis
capacitative component of the discriminatcr cir
criminator circuit with the condenser reproducer,
means for polarizing said condenser with voltage
derived from the oscillations, said coil and con
denser being tuned to a frequency substantially
cuit being an electrostatic reproducer,
10. In combination in a receiver of frequency
modulated carrier waves having a. high mean fre
quency and a relatively high frequency deviation
different from the mean frequency of the modu
ratio, and at least one frequency divider for re
ducing the said mean frequency and deviation
ratio by a like factor; the improvement which in
cludes means for reproducing the divided Wave
energy without rectification, said last means com
prising a tuned discriminatcr circuit composed of
at least two reactive elements of opposite sign, at
least one of said reactive elements being a modu
lation reproducer.
11. In a system for reproducing frequency mod
ulated carrier Waves derived from sound records,
lated oscillations to secure discrimination.
19. In combination with a reactive transducer,
a superaudible oscillatc-r, means for varying the
frequency of the oscillator` in accordance with
the transducer output energy, means for repro
ducing the frequency modulated oscillations with
out rectification, said means comprising a dis
criminatcr circuit substantially off -tune with the
mean frequency of the oscillations, ther capacita
tive component of the discriminatcr circuit being
an electrostatic reproducer, and means ïresponsive
a discriminatcr circuit including as a resonating 70 to voltage derived from said frequency modulated
reactive element thereof a transducer, and said
discriminatcr circuit being tuned to a. frequency
which is substantially off-resonance with respect
oscillations for polarizing said electrostatic re
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