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Патент USA US2121778

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June 28, 1938.
, 2,121,778
Filed Feb. 12, 1935
2 Sheets-Sheet
June 28, 1938.
Filed Feb- 12, 1955
2 Sheets-Sheet- 2
Patented June 28, 1938Y
I l
‘ Y
Stuart Ballantine, Mountain Lakes, N.Í I. u
Application February 12, 1935, sci-iai Nc. 6,245
14 omme-
(ci. 11s-1)
This invention relates to sound translating ap-
essary for intelligible transmission in a, tele-Ä.
paratus and particularly 'to sound translating ' phone circuit, since these are the principal com.
» apparatusadapted for incorporation in an elec- .-‘stituents Yof the majority of consonants. _ _
trical communication system.
. ' - Iv have discovered that the higher speech fre
The ordinary ktypes of microphones, designed
to be actuated by aerial sound waves, must be
supported in front of, and preferably. close to,
quencies are represented, in appreciable magni- 5_
tudes, in the vibratory energy available at the
larynx, and that the frequency-vibration ampli
" ,the mouth. There are many applications and,
tude characteristic is such that a high degree of
uses for microphones, however, where this is quite
naturalness in the reproduced sound may be ob-»
A 1o 'inconvenient . even in those cases where somel tained by restoring the balance in the frequency 101
means of support, other ythan the hands, are distribution oi energy. Broadly speaking, this is .
provided. Examples of such use areY in gas and
accomplished by designing the pickup device and
oxygen masks. -According to this invention, I `its associated apparatus' to be much more einabandon the method of picking up the sound cient at high frequencies than at low frequen
.lll5 from the air and instead pick up the sound as cles, or in other Words, to have a, rising fre- 15>
it exists in the vibration oí ,the upper parts of quency response characteristic.
the body which are set up by the acoustical and . ‘Objects of the invention are to provide novel
mechanical actions of 'the voice. These vibra- methods and apparatus for converting into elec
tions are particuia'riy >strong ini-,he region of the . trical currents, for transmission over an electri
' 20 larynx and associatedV cartilaginous structures
cal system, the acoustical vibrations of certain 20.
such as the thyroid cartilage. Devices embody- Darts 0f the body. Objects are t0 provide meth
ing the invention include apparatus that is ap- ods of and apparatus for producing electrical
plied to the vibrating parts so as to be directly R currents from mechanical vibrations of the
actuated by the mechanical vibrations thereof
‘£25 and 'acoustical transmission through the air plays
-a minor role. ’
throat, the electrical currents being such that,
when converted back to sound, the sound re- g5
production will closely resemble the original voice
Throat microphones have been proposed but, - of the person as heard in the ordinary way or
so far as I know, none .of the prior devices has as picked up by a microphone of conventional
been successful in yielding an electrical output
3o which was a faithful replica of the'natural sound
„ of the voice. The sound reproduced by the 'prior
devices was composed largely of low frequency
components and was muilled,rdeep and booming,
type designed for aerial sound `waves.'
A further object is to provide apparatus for. 3th
use in an electrical communication system, the.
apparatus being designed for actuation by me
chanical vibrations of the throat and being capa
being so highly unintelligible as to be totally un` 35 ñt for electrical communication purposes. ,
ble of producing electrical currents> which are
comparable with the currents produced by a good 36;
I have made an experimental study. by wave microphone when favorably positioned for actu
analysis, of the mechanical vibration amplitudes ation by the voice or sound waves in air.> More
of the larynx at different .frequencies and have particularly, an object is to provide a mechano-`
found the reason for the failure of the prior electrical transducer adapted to be placed in con-z
. 40.V devices. I,_have found that the vibration am- tact with and actuated by the mechanical vibra.. ‘i0~`
Plítlldes 0f the larynx' diminish Very> rapidly as , tions of the body and a. transmission network co
the frequency ' increases and, COHSeCillently, the
operating with the transducer to deliver electrical- .
priorart devices did not yield intelligible sounds,
Waves ,évmßh’ when impressed u'pon a telephone
- for the devices were designed Simply t0 reproduce
‘45 the vibrations as they exist with total disregard
oi their spectral distribution.`
This frequency distribution of the vibratory.
line or other electrical communication system, ,
result .in a reproduction of sound that has the.
quality of the voice.
energy is reconcuable with the fact that many invenîzsiîirîlnwdïilcl'tllxi‘îer ggîîaîrïânîngrîïlîhïgfîhgîwîä;
the sounds
of speech,involving
50 of
are formed
in the
the lips
tongue and
by probably
a back-
ward acoustical' transmission which may be more
aerial than mechanica. It is wcii established
specification when taken with the accompanying litiÉ
drawings, in which:
F15 11S a curve sheet ShÜW-lng 9' frequency-Ye'
spons@ 'Óhm'actel'istïc Which Will Yield highly ar“,
ticulated Speech from the mechanical ’fibratìßnß
55 that these higher frequency components are nec-A ot the larynx;
‘. .
Fig. 2 is a circuit diagram of a sound reproduc
' ing system which embodies the invention;
Fig. 3 is a curve sheet showing the frequency
response characteristicspf the Fig. 2 apparatus;
Fig. 4 is a fragmentary circuit diagram of an
other embodiment of the invention;
' Fig. 5 is a curve sheet showing the frequency
response characteristics of the microphone and
of the complete system of Fig. 4; and _ _
detail in my copending United States application
Ser. No. 6,246, filed concurrently herewith.
From a broad point of view, the desired fre
quency characteristic shown in Fig. 1 applies to
the entire system, including the device used to
translate the electrical current back` to sound.
This frequency characteristic may be divided be
tween several elements of the system as may be
v„found economical or expedient. It may be, for
Fig. 6 is a fragmentary circuit diagram illus
trating a modification of the Fig. 4 circuit.
example, incorporated solely in the microphone, 10
or partly in other apparatus. It will usually be
I have determined, from my studies of the re
advantageous to obtain the frequency character
lation between frequency and the vibration ampli
istic as near to the microphone as possible, in
tudes of the larynx, that there is a general pro
15 gressive decrease in amplitude towards the higher
end of the useful voice frequencies of from- 200
to about 4,000 cycles and have determined em
pirically a. frequency response characteristic
which may be employed with satisfactory results
20 to correct for the non-uniform energy input at
different frequencies. The frequency response
order to avoid the necessity of altering existing
circuits into which the apparatus is to work.
A representative embodiment of this invention
is shown in Fig. 2. -This represents a complete
telephone system of a simple type. Here the
microphone I comprises a carbon-granule cell of
conventional type which is provided with a button 20
2 which is driven by the vibration of the larynx.
characteristic of the apparatus can be described, _ The microphone output is fedinto the network
for explanation of this invention and for engi
neer-ing purposes, by means of a curve showing
25 the output voltage of the system when the micro-`
phone is vibrated mechanically by a piston which
is driven sinusoidally at constant velocity at all
frequencies. The
means that the maximum value of the velocity
30 (which varies sinusoidally) is maintained con
stant. This method of defining the frequency
characteristic has been adopted in view of the
difñculty of actuating the microphone over the
entire frequency range for measurement pur
35 poses when it is worn on Vthe throat. -The me
then through transformer T1, the line, and trans
former T2 to the telephone receiver 3. 'I'he con 25
denser Ca serves to confine the direct current
from battery 4 to the microphone circuit. The
desired frequency characteristic, shown in Fig.
1, is obtained by means of the network in combi
nation with the mechano-electrical character 30
istic of the microphone. If the microphone is
so designed as to have a constant output for a
given displacement at all frequencies, its output
voltage, for constant velocity excitation, will vary
inversely as the first power of the frequency as 35
shown by curve B, Fig. 3. The network provides
chanically driven piston is used merely as a con
venient way of imparting a definite and repro
ducible actuation to the microphone.
Lilla, RiRz, C1C2 of the constant resistance type,
The frequency response or transmission char
40 acteristic shown by curve A of Fig. 1 has been
the rising transmission characteristic, curve C,
and these transmission characteristics combine
to provide the required characteristic, curve D.
'I‘he apparatus shown to the left of line ab of
found, experimentally, to -yield highly articulated
speech from the mechanical vibration of the Fig. 2 may‘be replaced by the equipment illus
larynx. The ordinates represent the Velectrical _ trated in Fig. 4. The device I’ which converts
voltage output while the abscissae indicate the the vibrations of the larynx into electrical
voltages includes two imite 4 that are applied
45 corresponding frequencies at which the micro
symmetrically to the larynx and which, as shown, 45
phone was vibrated, as explained above, by a con
stant velocity piston. To obtain this constant are of the piezoelectric type .such as described in
my copending application. The units are wired
velocity, the amplitude of vibration varied in
versely as the frequency. As shown by the dotted >in parallelso that their effects are additive elec
50 line A', the output of the pickup system varies as trically, and are shielded electrically by the
the 1.3 power of the frequency over the greater metallic housing 5 and shielded cord 6, one ter 50
Dari. of the curve A. It willv be seen from this minal of `each piezoelectric unit being grounded
curve that a considerable readjustment of the '
to the shield.
. »
The output terminals of the microphone are
relation between high and low frequencies is re
connected to the input terminals of the iirst tube
55 quired to compensate for the frequency distribu
Ation in the larynx. It must be understood, of ‘i of a two-stage amplifier. These input terminals 55
course, that the shape and slope of the curve is are shunted by a resistance R1 which serves as a
not critical, but may be varied somewhat from grid leak to fix the direct current bias on thethat shown in Fig. 1. The diagram is intended _ grid G1 of tube 1 and which has the further
00 to show the order of the effect and to indicate function of establishing a definite relation be
_why a device of conventional design (for uniform tween the alternating current voltage applied to 60
response at all frequencies) is doomed to failure. the grid and the voltage generated by the micro
It must also be pointed out that the anatomical phone, the relation being such that the input
and other variations between individuals and of . voltage rises with frequency. A part of the de
the position of the microphone _on the throat sired frequency characteristic of the whole system
would make a closer specification of a desirable may thus be obtained at this portion of the cir 65
cuit. This eiïect is obtained by selecting a value
characteristic of doubtful practical value.
The microphone should respond over as great for resistance R1 which is lower than the capaci
a frequency range as possible, but it has been tive reactance of the piezoelectric crystals in the
microphone at the higher frequencies. A rela70 found in practice _that good telephone communi
tively low value of resistance R1 has other ad 70
cation can be obtained by the inclusion ci' fre
quencies up to from 3000 to 5000 cycles. 'I'he vantages in that it tends to minimize any varia
curve in Fig. 1 represents the performance of an . tion in output due to leakage in the microphone
actual apparatus including a microphone of the- crystals or the connecting cord.
The relation between the voltage across re
piezoelectric type as described below and in more
sistance R1 and the voltage generated by the 75
microphone in a typical
dotted line curve E of Fig. 5.
It will be understood that there is considerable
case is shown by the l latitude in the choice or design of the different_
The various fre
elements of the sound translating apparatus, and
`quency components of the electrical currents
in the frequency response characteristics of the
were generated from the mechanical- vibrations
of the body at- conversion ratios that increased
several elements. The desired frequency response
characteristic of the complete system may be ob
with frequency in the useful voice frequency
range. The conditions under which this curve
tained in a variety of ways other than those here
was obtained were as follows: the two crystals
the resistor R1 could be made larger and the re
sulting reduction in the power of the response 10
versus frequency relation can be compensated in
connected in parallel each had a capacity of I.001
v microfarad atV 20° C., and resistance R1 was
50,000 ohms.
in described. In the Fig. 4 circuit, for example,
the design of the microphone or the amplifier.
The rising frequency characteristic of the
It will therefore be apparent that the invention
is not restricted to the particular methods and
amplifier, principally the first stage, to have a. embodiments herein described and that various
rising frequency characteristic, i. e. a gain _that changes which will occur to those familiar with
rises with frequency. `The plate circuit of the >this art fall within ,the scope of my invention'
pentode tube 1 of this stage includes the primary as set forth in the following claims. '
microphone is supplemented by designing the
' winding of the coupling transformer T1 in paral
lel with a resistance Rs, the reactance of the
transformer being low compared with the resist
ance R3 and plate resistance in parallel, thus
providing a gain characteristic which rises with
frequency. The transformer T1 is in fact made
I claim:
1. Sound translatingapparatus comprising a 20
mechano-electric transducer substantially non
responsive to sound waves in air and actuated by
the vibrations of the body due to the voice, and
an electrical network for transmitting the elec
resonant at a frequency near the upper limit of f trical output of said transducer, said transducer 25
the desired frequency range. The frequency and network having an overall frequency re
characteristic of the second stage, tube 8; is sub
sponse characteristic which rises progressively
stantially flat.' By shunting the output trans
with frequency from 200 to about 4000 cycles
former T2
th a resistance R5, the output im
when the transducer is vibrated at constant veloc
pedance, viewed from the output terminals, may ity, whereby the electrical current output of said
be made a substantially pure resistance at all network may be converted into sound waves hav«
frequencies. In this way, the microphone and ing an acoustical quality comparable to that of
associated amplifier may be adapted to replace
the -conventional carbon¿microphone of about the2. voice..
Sound translating apparatus as claimed in
100 to 200 ohms resistance without aifecting the claim 1, wherein said transducer has a frequency 35
frequency characteristics of other parts of the responseLcharacteristic which falls off with in
creasing frequency, and said network has a char
- circuit.
To limit regeneration, the terminals of trans
acteristic which rises with frequency at a rate
former T1, as shown, are >reversed from their
normal polarity. Grid biases for vthe two amplifier
which ‘ overcompensates the falling vcharacter
of said transducer.
tubes are obtained from the voltage drop through istic
3. Sound translating apparatus as claimed in
and R4, respectively. v
the cathode resistances R2,
claim l, wherein both said transducer and said
The condensers C1, C2, C3 are the usual by-pass network have frequency response characteristics
condensers to limit intercircuit coupling, resist
which rise with frequency.
y ‘ ances ReRi are decoupling resistances in the plate
4. Sound translating apparatus comprising a 4.5v
circuits, and resistance Ra is a so-called bleeder. mechano-electric transducer susbtantially non
The overall >frequency characteristic of the responsive to sound waves in air and actuated'by
amplifleris‘shown by the curve F of Fig. 5 in the vibrations of the body due to the voice, and
which the ordinates represent the output voltage an electrical network for transmitting the elec- ~
plotted against frequency for a fixed voltage trical output of said transducer, said transducer 50
applied across the resistance R1. The relation and network having an overall frequency response
between the voltage output terminals of the characteristic which rises as a predetermined
amplifier andfrequency, for a constant velocity power of the frequency over the voice frequency
excitation of the microphone, is shown by curve rangev of from 200 to about 4000 cycles when the
transducer is vibrated at constant velocity, 55
A of Fig. 1.
It is not always convenient mechanically to whereby the electrical current output of said net-and in such work may be converted into sound waves having
completely shield~ the-'microphone
of the micrephone is in an acoustical quality comparable to that of the
cases, when the wearer
a radio frequency radiation iield, some radio fre
quency energy may leak to the amplifier. Ex
m5,.,-Sound translating apparatus comprising a 60
60 amples of such situations are found in open cock A_a'rfi'echano-electric transducer substantially non
pit airplanes where the microphone may be used responsive to sound waves in air and actuated by
to modulate a radio transmitter. Such stratl " the vibrations of the body due to the voice, and
radio frequency voltages may be prevented from an electrical network for transmitting the elec.
reaching the grid of the amplifier tube by a filter
65 network. such as shown in Fig. 6. The general
form of the ampliñer circuit may be substantially
identical with that shown in Fig. 4, and certain
elements of the Fig. 6 circuit are therefore identi
trical output of said transducer; said transducer
and network having an overall frequency response
characteristic which rises ças'V a power of the fre»
quency which is not lessithan unity over the use-»
ful voice frequency ,range of from 200 to about
4000 cycles when-the transducer is vibrated at 70
The filter circuit for blocking the ‘ _constant velocity, whereby the electrical current
transmission of radio frequency voltages com
output of said network may be converted into
prises the choke coil L and the shunt condenser sound waves having an acoustical quality ,com
C which are connected between the microphone parable to that of the voice.
system com 75.
terminals and the input terminals of the ampli
fled by the corresponding‘reference characters
70 of Fig. 4.
6. 'An electrical communication
>prising a mechano-electrical transducer substan
tially non-responsive to sound waves in air and
actuated_ by the mechanical vibrations of the
body due to voice, a transmission circuit, and a
sound reproducer, said system having an overall
transmission eiiiciency which produces an output
generated by the microphone which rises with
.10. In sound translating apparatus, the com~bination with a throat microphone including a.
transducer unit, and a. vacuum tube amplifier
stage having output terminals; of means for
that rises progressively with frequency in the developing across the output terminals of said
useful voice frequency range of from 200 to amplifier stage an output voltage which rises
about 4000 cycles when the transducer is vibrated , with frequency when said microphone is vi
10 at constant velocity, whereby the reproduced
brated at constant velocity, said means including
sound has an vacoustical value simulating that of an. additional amplifier stage between said mi
the voice.
crophone and said first-mentioned amplifier
7. An electrical communication system of the stage, the additional amplifier stage having a
type including'a mechano-electrical transducer
15 substantially non-responsive to sound waves in
air and actuated by mechanical vibration of the
body due to the voice, a transmission circuit, and
a sound reproducer, characterized by the fact
rising frequency characteristic.
11. 'I‘he invention, as claimed 'in claim 10,
wherein the additional amplifier stage includes
a transformer resonating at a frequency near
the upper limit of the range of frequencies vto
that the system has an output which rises as a be transmitted thereby.
20 power of the frequency over a substantial part of `
12. The invention as claimed in claim 10, in
the useful voice frequency range of the system- combination with a ñlter network between said
of from 200 to about 4000 cycles when the trans
ducer is vibrated at constant velocity, whereby
the reproduced sound has the acoustical quality
25 of the voice.
8. In sound translating apparatus,
nation with a throat microphone of the piezo
electric type, said microphone having a capacitive
reactance over its frequency range of response, of
30 a resistor shunted across the output terminals
of said microphone, the resistorhaving a resistance
less than the capacitive reactance offs'aid micro
phone over the greater part of the said frequency
range of response, whereby the relation between
the output voltage across the microphone termi
microphone and the additional'amplifier stage
to prevent the application of radio frequency
voltages to the additional amplifier stage.
13. 'I‘he process of reproducing speech which
comprises the steps of translating mechanical
vibrations of the body due to the voice into elec- c
trical currents, selectively amplifying the several
frequency components of the vibration-produc d
currents at gains which increase with the frê
quency of such components in the useful voi `e
frequency range of.i’rom 200 to about 4000 cycles,
transmitting the amplified electrical currents tò
a. desired reproduction point, and converting the
transmitted and amplified currents into sound 35
nals and voltage generated by the microphone Waves.
rises with frequency.
14. 'I'he process of reproducing speech which
9. In sound translating apparatus, the combi f includes the steps of selectively generating elec
nation with a throat microphone of the piezo
trical currents from mechanical vibrations of the
40 electric type, said microphone having a capaci--. body due to the Voice at conversion ratios that
tive reactance over its frequency range of re
increase progressively with frequency in the use
spouse, a resistance shunted across the output
terminals of the microphone, a vacuum tube and
connections between the input terminals thereof
and the microphone terminals, and an impedance
network cooperating with said tube to effect oper
ation thereof as an amplifier, `the overall trans
mission emciency of said microphone and ampli
ñer varying with frequency to produce a relation
between 4amplifier output voltage and -the voltage
ful voice range ‘of from about 200 to about 4000
cycles, amplifying the resulting electrical currents
at gains which increase progressively with fre
quency within the said useful voice range, trans
mitting the amplified electrical currents, and
converting the transmitted and amplified cur
rents into sound waves.
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