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Патент USA US2121781

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June 28, 1938.
.,s. BALLANTINE
2,121,781
SOUND TRANSLATING DEVICE`
Filed April 1:5, 19:56 .Y
2 Sheets-Sheet l
»w¿1%.
..
June 28, 1938.
A
2,121,781
s. BALLANTINE
soUND TRANSLATING DEVICE
Filed April l5, 1936
2 Sheets-Sheet 2
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„ÍÍÄÉ‘ÄÍÜZÍÈÈÉÍÈÈÍÜÄM
9
(ci. 11a-114)
This inventionerelates to apparatus for translating mechanical vibrations of the body in the
Fig. 12 is a vlongitudinal section through a
transducer which includes a _diñerent form of vi-v
' region of the throat due to the voice into articu»l y bratory armature; and
late speechy sounds or into electrical currents.
Fig. ,13 is a fragmentary circuit diagram of a
5 which yield articulate speech sounds when reproduced.
>
,
A
-
complete electrical system which embodies the 5
~invention.
,
Apparatus and methods for this general puri ' 'I'he microphone is adapted to be> worn around
' posehavebeen described in my copending appli-~- the neck like a collar, as shown in Fig. 1 of my
cations Ser. Nos. 6,245 and 6,246, filed Feb. 12,
v 10 1935; Ser. No. 8,392. flied Feb. 26, 1935, and Ser.
No. 54,347,1l1ed December 13, 1935.
l
»
i
copending application Ser. No. 6,246, but other
methods of support may be employed. When 10
. worn as a collar, the .microphone M has the gen-
«
i
A l
-An object of the invention is to provide a device eral fOrm 0f a narrow band 0r casing in which
of novel construction for converting acoustical two mediano-electrical transducers are symmet
vibrations of the body due to the voice into elec- rically arranged, and an adjustable elastic band
.
' 15 tric currents for transmission in an electrical B is sewed to the casing toV form a collar that may 1s
' communication'system. An object is to provide'A be placed around theV neck in such a way that
. a microphone, of the character stated, ‘ which
operates on the electromagnetic principleand
_
which therefore does not requirethe battery or-
20 dinarily used with microphones of the carbon
’
granule type,
' -
.
~ -
lFurther objects are to provide a larynx micro-
phone which is characterized by 'a >simple and
rugged mechanical construction and by an elecl
the microphone units are in contact with the neck
in the region of the larynx. `
,
'
The. covering or elongated casing I for the `
transducer unit or units may be of any suitable 20
material, such as-glove leather, with a snap fas
tener 2 and fibre stiffener 3 fastened to one end ' - `
of the casing. The side of the microphone whichcontacts with the neck 'will be designated, for
25 't1-ical oui-,put which compensates, in part atleast, ^ convenience of description., as the “front” of the 25
for the deficiency of the higher frequency constituents in the mechanical vibrations or the larynx.
_
~
These and other objects and advantages of the
invention will be vapparent from the -following
30 specincation whentaken with the accompanying
'
drawings in which: ,
Y”
>
microphone. >The front wall of the casing I is
provided with two holes which are covered by a
thin membranous material l _which may be ce
mented to the front leather wall, and the actu-` 1
ating buttons 5 of the microphone units extend 3o
through these holes. 'Not all materials are suit
Fig. 1 is a sectional view of an embodiment of ' able for the membrane I on account of attenu- f
the invention;
‘
`_
ation of the higher frequency vibrations. Ma
Figs. 2 and 3 are front and rear views, respec- ' terials which have been used successfully are thin
35 tively, with parts broken’away, of one of the
transducer units;
`
Y
'
`
rubber, animal intestinal linings which may be -35
grouped under the name of “colon leather”, and
Y
Fig.` 4 is a schematic view of the wiring con- f- ordinary leather of the >order 'ci .005" to .015"
nections and shielding of the microphone shown thickness. ‘ Thinglove leather has been employed
in Fig. 1; ¿ '
40
«
-
-
f
in most of my constructions becauseof its good
Figs. 5a and 5b are corresponding mechanical
and electrical impedance diagrams;
Fig. 6 is a curve sheet showing typical output
voltage-frequency characteristics which may be
obtainedvwith embodiments of the invention;
_
45 Fig.7 isa front view of another transducer con-
mechanical qualities and because its physical ap-` 40
struction which is particularly- adapted for oil
pearance can be made to match the rest of the
leather covering. This is cemented to the cov
ering I with rubber cement and extends over Vthe
entire area of the side toward the'neck. In order
to reduce the strain on the .covering I and the `4,5 .`
thin protective- covering 4', a thin metal grommet
damping; »
'8 is sewed and/or cemented around the edge of
_
_
f
I‘T'ig. 8.is a longitudinal section on line 8_8 of . the openings in the front wall I. "Fig 7;
A 5o
'
'
l
Fig. 9 is a central transverse sectioni ï
The electromagnetic transducer units may be, .
.
. Fig. 10 is a longitudinal section -through '
and V,preferably are, _fof substantially identical 50 '
construction.A The motion transmitting button
transducer which includes adjustableY elements
5 is of substantiallyrigid material, such as “bake-
for controlling the air gap;
lite”, balsa wood,vwhite pine, etc., andis fastened _v `
~
i
'
Hg.11isasectionalviewofatransducerwhich. Vtothe middle of the vibratoty element‘l. ,This ,
‘ 55 includes another form'of magnet structure;
_ vibratory element is- a resilient strip ,of` mag-55 ' _
l
2
2,121,7s1
netic material, such as silicon steel, which may
have metallic pieces 8, 8' soldered at the ends
thereof to assist in deñning the eifective length
l
'
c
`
by varying this dimension the impedance of the
transducer can be regulated inrelation to that
of the larynx with which it is in contact. lWith
of the vibratory strip or amature, thus render
ing the resonant frequency substantially inde
a length and thickness as given above', widths of
from 0.2 to 0.7 inch are suitable for the aver
age larynx.
pendent of the vicissitudes of` assembly, screw
pressure, etc. The end pieces are not essential
but, when used, are usually somewhat thicker
than the vibratory strip and partake of its vi
10 brations only to a minor extent. The magnetic
strip'1 bridges across the ends of a ñat E-shaped
magnetic yoke that, as shown in Figs. 1 and 2,
comprises end pole pieces 9, 9' on a backing strip
I0 which carries a central and somewhat shorter
15 pole piece I0'. The pole pieces 9, 9’ are perma
nent magnets of suitable material such as co
balt steel, aluminum-iron steel or the like which
1
`
l
The air gap may be> adjusted by screws I8
which pass through the resilient strip 1 and
into the back piece I0, but such an adjustment »
oi the air gap adects the resonant period of the 10
armature and this effect must be taken into
consideration in the design. Other methods of
adjusting the air gap will be described later.
Flexible conductors Id, , I4' of tinsel or the
like are soldered to the pins I2 and are relieved 15
from strains by fabric tabs Il“ which are woven
-into thecords and tied to eyelets 'II". The cords
are magnetized, as indicated by the polar desig- v pass through shielding springs I5 that are sol
dered to the clamps I8 and thus grounded on
nations, N, S, to present like polesto the vibra
the unit. The springs are of phosphor bronze, 20
tory
armature.
The
back
piece
or
strip
I0
is
of
20
,iron having a lowvariational reluctance, such as Y steel or other material which will stand repeated
bendings. `The unit itself is protected from ex
ternal ñelds by a close ñtting metallic c_asing I1
which has `a `slightly domed bottom wall to pro
vide space for the terminal connections and the 25
ends of springs I5. The connecting cords branch
from the main cable at the middle of the mi
pure annealed or Swedish iron. A small air gap
of the order of from 0.001 to 0.010 inch is pro->
vided between the pole piece I0' and the vibra
25 tory strip 1, and a multi-turn coil of _insulated
wire Il surrounds this pole and has its leads
brought out through terminal pins I2 that pass
through insulating bushings I2' which are held crophone strap, see Fig. 4, the shielding lead or
braided conductor I8 being connected to the neg
in the back piece I0 of `the magnetic yoke
The vibrations. of the throat are picked up by ,ative terminal pin I2 of one unit and to the shield 30
30
the button 5 and communicated to the amature springs I5 of both units by a T-shaped metallic
1 and, due to the mass of the transducer unit « piece I9 that fits around the bifurcation of the
which prevents it from vibrating as a Whole, the cable and prevents relative movement loi the
forces imparted to the armature 1 result in a cable and the branch connections. The central
vibration
of the amature with respectto the conductor 20 of the cable is .connected to the
35
magnetic ñeld system. The air gap is therefore positive terminal of the other unit by one lead Y
I4, and the unlike terminals of the two units t
periodically altered in conformity with the vi
are’ connected by lead I4’. The braided lead IB
brations and the variations influx through the
central pole I0' inducevan electromotive force ' preferably has an outer covering I8' - of soft
in the'coil Ii which may be led to the. external rubber and the entire cable is, of course, quite 40
electrical circuits, ampliiiers, line, etc. Due to _iiexible. -The described connections place the
the polarity of the permanent magnets, their. two units lin series, and this has given good re
flux adds up in the central pole and the two ìs‘ìults erin practice but other connections could
e us
.
l
halves of the symmetrical magnetic circuit may
The transducer units may be protected against v
be regardedas in parallel.
.
Y
45
The thickness of the- resilient strip 1, and its the weather and sea spray when used in open
length between the edges of the end pieces 8, 8', cockpit airplanes and seaplanes by placing the _
~ are so chosen that the armature is mechanically ' units in closely ñtting bags of thin rubber hav
resonant> at the upper end of the range of speech Y in_g a thickness of the order of 0.002 to 0.005 inch. `
v
frequencies
to be reproduced.V Good results have
u The open ends of the bags are cemented together 50
beenv obtained by making the _ armature reso
vnant at frequencies above'1000 cycles and, in
most’of my constructions, they have been reso
nant between 2500 and l4000 cycles. The natural
frequency of vibration of an elastic slab clamped
Y at its ends varies as t/l2, where t is the .thickness
and Zvthe'length, and is' independent of the width
and to the rubber covering I8' of the cable by
rubber cement. The transducer _units are then
sewed into the leather covering of the microphone
strap.
The microphone and its associated electrical 55,
circuits are designed and/or adjusted to have
overall frequency characteristics such as de
to the first order. However, no rigorous rule can scribed in my copending applications Ser. Nos. ,i
be given for _the calculation of the resonant fre v 6,246 and 54,347. >A mechanical impedance dla'
60 quency on account ofA thepresence of the buttonv
,5 which‘tends to lower the frequency by adding
mass and to increase it by virtue of the added
resistance `to bending caused by the' cementing
vof the lower planar surface of the button to the ~
05 armature. ' The above rule does furnisha _good
practical guide, however, andthe exact‘diinen-`
sions can be determined experimentally.- Typical
dimensions which I‘have employed with lsilicon
1 steel for a resonant_'frequency in the neighbor
hood of 3500 cycles are l==0.8 inch, t=0.014 inch, ,
I andwidth varying from 0.25 to 0.6 inch. Al
though the resonant frequency is not greatly
affected by variations in the width of the arma.
»ture, theV width does „affect the mechanical im
pedance as Vviewed from the'button 5 «so that
gram of the microphone is shown in Fig. 5a, and l60
an approximate electrical circuit lequivalent of
the mechanical system is shown in Fig. 5b. -In
these diagrams, vo represents the impressed veloc
ity due to the vibrations of the larynx, Zu repre
sents the mechanical impedance of the throat 65
structure (cartilage, muscle, etc.), and m1 repre
sents the mass of the button 5 and the eiiective
mass of the armature 1. C1 represents the com
pliance of the armature, that is the reciprocal of
the deflection per unit force applied between the 70
button and the transducer unit, C: represents the
compliance due tothe elastic band which sup
ports the unit at the neck, and ma represents the
mass of the unit, the housing and the covering.
AThe resistors r1, rn, ra represent the eiiects of dis 75
t
annif/s1
sipation in the several associated elements. The
compliance C: is probably so high as to be
material
even when
of used
protectingv
without
the oil
armature
or other
and
damping
acting
negligible, that is Ca can probably be short-cir
as an acoustical shield to prevent vrind and ex
cuited (omitted) from consideration for -all prac
tical purposes.
'
'
ternal acoustical 4disturbances from reaching the
-
armature.
The voltage generated by the microphone is '
proportional to the velocity- of the armature with
respect to the other elements of the unit, and is
A
.
I
y5
In the embodiment shown in Fig. 10, van an
nular piece 24 of rubber or other resilient` material
is placed between the armature ‘land the cover
piece 2|, `and the central pole piece I0’ is drilledshv
represented in Fig.'5b as v1, the current flowing in
the C1 branch. _'I‘he _form of the vfrequency re _and threaded to receive a cylindrical plug 25 of 10 '
sponse characteristic with _constant impressed resilient material, such as rubber or -“glyptal”,
velocity depends upon the driving impedance of and an adjusting screw 26. .Pressure applied
' the neck, Zo. Ifa piston vvibrating at> constant
through the plug 26 tends to bend the armature
velocity be used for driving purposes, a curve of upward, and this is resisted by the ring 24. >By 15. the type shown in Fig. 6 is obtained for the de
altering the dimensions of the ring 24 and the 15
scribed unit, or pair of units. This curve is chiefly position of the screw 26, some control of the
characterized by a resonant rise in output near -length of the air gap is obtained. The upper ringV '
300 cycles and another near 3500 cycles. The 24 may be omitted if the armature 1 is given an
first is due ~principally to resonance between the initial adjustment to lie against the pole piece
20 armature compliance Ci and the mass- ma of the
l0', the stiifness of the armature itself being then` 20
unit. The upper ~resonance point at 3500 cycles relied upon to oppose the thrust of the plug 25 as
arises principally from resonance between the the screw 26 is adjusted to obtain the desired
mass of the armature m1 and the compliance C1. air gap. Damping may be obtained, as previ
The exact -shape of the characteristic curve may ously described, by materials placed in the space
be controlled by adjustment" of the mechanical. between armature '| and cover piece 2|, or by the 25
10
,
3*
> impedances. The low frequency response, for ex
viscosity of the resilient materials 24. 25.
`
ample below 1000 cycles, may be controlled by the
Another method o_f damping is >to construct the
lower resonance. ; This, in turn, can be controlled armature '| in laminar form, using a strip of
by the mass me of the u_nit and the armature com
damping material _between two resilient strips of
30 pliance C1. The latter can be modified without
4metal. The strips may be pressed or cemented'30
varying the upper resonance byvarying the-Width into an integral whole which may be mounted in
of the armature. The lower resonance peak can the same way as a solid iron armature.
thus be moved up and down in frequency to secure
The magnetic systems so „far described have>
an augmented response at any desired frequency, comprised" a pair of short bar magnets 8, 9’
35 with a sharp decrease in response below that
mounted on the ends of a back piece having an 35 ' '
-frequency, as shown by the solid line curve A integral central pole piece Ill'. As shown in Fig.
of Fig. 6. This particular curve represents the 11, the back piece Ill‘ may be a single- permanent
performance of a microphone having the follow
magnet having an inserted pole piece I0", with
ing characteristics;- armature 'i of silicon steel, short bars of soft iron'9“ at the ends of the bar
Y40 0.8 x- 0.5 x 0.014 inch; button, white pine, mass=
magnet. The magnet. lilEl is magnetized in, a Jig 40 _ »
0.15 gram; mass of unit=15 grams.
or fixtureA so that like .poles (north poles N as
'I'he upper resonance can be controlled, as de
indicated in the drawings) are at opposite ends
a scribed above, by varying the length and thick
of the bar and the opposite poles S are in contact
ness of the armatupé '|. It is not always desirable adjacent the pole piece Inh. This construction
to have a high sharpV peak, such as is present in` has the advantage thatV a longer magnet, and 45
curve A at about 3500 cycles, >and this can bev correspondingly higher coercive forces, are ob
avoided by providing damping in addition to that tained. Due to the extra length of the magnet, '
> arising from the internal viscosity of the metal itis sometimes possible to obtain the required
and the cement used to fasten the button to the Acoercive force with tungsten steel in place of
50 amature. One of the simplest and most eil'ec
cobalt and like steels.y The separate soft iron end 50
tive methods of damping is to -insert a drop or pieces 9* can bejreplaced by integral extensions
two oi’ oil in the air gap between the Apole piece of the bar magnet HP.
.
lli' and the armature 1. Dotted line curve A' of
Fig. 12 illustrates another structure which `of
Fig. 6 illustrates the >effect of a drop of oil, of fers certain advantages. In_ this construction,
55 viscosity 30 in the standard commercial scale for the button and armature are formed in one piece, 55
automotive lubricating oils, inserted in the air
the button being pressed out as a boss on the y
gap. The oil is permanently held in‘place in the
armature strip 1’.
air gap by capillary attraction. ’
the button becoming loosened. Also by utilizing
-
This avoids the possibility of -
Another transducerconstruction which is par. ' the space below the .button section, a greater’
ticularly adapted for oil damping is shown in Figs. number of turns can be .accommodated on the oo
7 to 9.~ The general construction isas previously coil Il', thus increasing the voltage output. A
described and parts which are, or may be, sub
method of adjusting the air-gap is also shown
.stantiaily identical with the elements of Figs. 1,v which may be applied to the other constructions
2 and 3 are identified by corresponding vreference .as well. This is accomplished by sliding the cen,
numerals. A cover plate 2| is arranged parallel _tral pole vpiece |0° through the back plate IIId 65
to the armature 'l and spaced therefrom by a few and fastening the pole. piece by means of a set
. thousandths of aninch by shims 22, 22', the plate screw 26'. _The other parts of this construction
having a central hole through Awhich the button 5 are designated by the reference numerals of the
projects. Damping material 23 is placed in the previous »iigurea
v
space between the plate 2| and armature '|, and
A complete electrical system incorporating the 70’V ì `
this is preferably oil ybut may -be cotton, cloth ‘microphone is shown schematically in Fig. 13.
soaked inV oil, rubber, felt, “glyptal’”, etc. When
oil is used, it is held in `place by capillary attrac
tion. The cover plate 2| _isxpreferably metallic,
75
about if inch'thick, and it presents> the advantage
Only one unit is shown as the microphone M, and
this works into an am'pliiier 21 of the >type which is
described in detail lin copending application Ser.
No. 54.347; the circuit diagramfappearlng as Fig. _75 I"
2,121,781
4
4 of that application and its frequency response
characteristic as Fig. 5. The overall frequency
response of the microphone and ampliñer, when
the microphone unit is clamped and driven ‘by> a
constant velocity piston, is shown in Fig'. 9 of
V5. A throat microphone of the electromagnetic
type comprising a permanent magnet, a yoke and
pole piece, a coil surrounding Asaid pole piece, a
resilient magnetic strip positioned to complete
the magnetic circuit except for a. small air-gap
between said strip Aand said pole piece, said re«
the earlier application. The amplifier 28 Vmay
siiient magnetic strip being mechanically reso
nant between >2500 and 4000 cycles, and means for
transmitting vibrations of the throat to said re
work into a radio transmitter or, as shown. into
a transformer 28 and headphones 20.
-
I am- aware that microphones operating on >the
10 electromagnetic principle were proposed as early
as 1884, but the constructions herein described
silient strip.-
I claim:
’
resilient magnetic strip .positioned to complete
the magnetic circuit except for a small air-gap
between said strip and said polelpiece, said re
_ siiient magnetic strip being mechanically reso
'
1. An electromagnetic transducer comprising
an E-shaped ileld magnet structure magnetized
to have end poles of one polarity and an inter#
25 mediate pole of the opposite polarity; an armature
consisting of a resilient strip of magnetic material
extending between said like end poles and over but
spaced from the intermediate pole, a coil on the
intermediate pole, and means consisting of a
30 fluid medium between said resilient strip and a
rigid member for damping the vibrations of said
resilient strip.
'
2. An electromagnetic transducer as claimed
"as
v
type comprising a permanent magnet, a yoke and
pole piece, a coil surrounding said pole piece, a
have novel mechanical and'electrical character
istics which particularly adapt this type of mi
crophone for use as a throat microphone. It is
to be understood that the invention is not lim
ited to the exact constructions herein illustrated
and described as many variations which will oc- 1
cur to those familiar with this art fall within
the spirit of the invention as set forth in the fol
20 lowing claims.
»
6. A throat microphone of the electromagnetic
in claim 1, wherein said fluid medium of the
damping means is in the, gap between said re
silient strip and the intermediate pole.
3. An electromagnetic transducer as claimed
nant above 1500 cycles, means for critically damp
ing the vibrations of said _resilient strip, and means 20
for transmitting vibrations of the throat to said
resilient strip.
l 7. In a contact microphone adapted to trans
late vibrations of the throat due- to the voice and
of the ,type comprising a vibration element having
compliance and mass. and Vsupporting means. 2,5
having mass; the method of reducing frequency
" distortion due to the mechanical vibratory char-r '
acteristics of the throat which comprises tuning
the natural vibration frequency due to the co
operation of the mass of said supporting means
and the compliance of said vibrating element to
a frequency between 100 and 1000 cycles, and
30
simultaneously tuning the- natural frequency due
to the cooperation of the mass of said vibrating 35
element and its compliance to a frequency above
1500 cycles.
'
»
8. A throat microphone comprising a resilient
vibration member to which the vibrations of the
throat are transmitted, and means for supporting
said vibration member on the throat, the com 40
in claim 1, wherein the rigid member of said
damping means comprises a relatively rigid cover
40 plate extending in spaced relation over said re rpliance of said resilient vibration member being
siiient strip.
‘
,
4. A throat microphone of the electromagnetic resonant with the mass of said supporting means
at a frequency ofthe order of between 100 and
type adapted to be actuated by mechanical vibra
, tions of the body due to the voice, said microphone 1000 cycles, and said resilient vibration member
K 45 comprising a permanent magnet, a yoke and pole> being resonant at a frequency above 1500 cycles.
9. A throat microphone as claimed in claim 8
piece, a coil surrounding said pole piece, a re
silient magnetic strip positionedto complete the in combination with means damping said vibra
tion member at said resonant frequency above
magnetic circuit except for asmall air-gap be
tween said -strip and said pole piece, said re
1500 cycles.>
50
STUART BALLANT'INE.
silient magnetic strip being mechanically reso
,- 50
' nant above 1500 cycles. and means for transmit
ting vibrations of the throat to said resilient strip.
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