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Патент USA US2405858

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Aug. 13, 1946.
2,405,858
H. c. SILENT
ACOUSTIC COUPLER FOR CONDENSER MICROPHONES
Filed Nov. 29, 1944
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2,405,858
Patented Aug.,13, 1946
UNITED STATES PATENT OFFICE
2,405,858
ACOUSTIC COUPLER FOB, CONDENSER
MCROPHONES
Harold 0. Silent, Los Angeles, Calif., assignor to
the Government of the United States of
America, as represented by the Secretary of the
Navy
Application November 29, 1944, Serial No. 565,757
6 Claims. (Cl. 181-05)
1
This invention relates to an acoustic coupler
for transmitting sound waves to a condenser
microphone while excluding moisture and dust
2
serves to clamp the ring ‘I and thin rubber dia
phragm 8 against the ?ange 3. The diaphragm
8 is of such thickness and elasticity as to trans
particles from the microphone assembly.
mit sound without substantial attenuation of
It is an object of this invention to provide
means for efficiently transmitting sound waves to
the sound energy.
Fixed on one end of member 2 is the element 9
which has a. cylindrical portion I0 that ?ts snugly
upon the shoulder 4 and is also provided with a
microphones and which will prevent impairment
of the functioning of the microphone due to ac~
cess of dust or moisture when used under ?eld
shoulder H to bind the gasket l2 tightly against
10 ?ange 6. Cooperating with the member 0 to form
conditions.
an enclosed annular chamber is the sleeve !0 that
A further object is to provide such a device
with means to control, to a limited extent, the
frequency response of the device.
The single ?gure of the drawing shows in en
larged longitudinal section a satisfactory embodi
ment of my invention.
It is well known that microphones are used in
military operations to pick up the sounds of gun
?re and thereby to determine the distance and
covers the joint between members 2 and 5. The
chamber so formed is ?lled with a hygroscopic,
or desiccant granular material I 3 which is re~
tained by ?brous or ?lamentary material [4 and
a ?ne Wire screen It? from passing into the breath
or ducts l6 and [1. An opening 26, stopped by
a closure 21, is provided for observing when the
desiccant l3 should be replenished or renewed.
Secured to the member 9 at one end and to the
location of such guns and, to a certain extent, 20
end element l8 at the other, surrounding mem
the caliber of the guns.
ber 2 and spaced therefrom, is a highly ?exible
The most frequent equipment failure encoun
rubber bellows I9. This bellows is held in air
tered with such instruments when the micro
tight relation to the members 9 and I8 by tightly
phone is of the condenser type is in the con
denser element, wherein the small space between 25 drawn threads 20 disposed over the bellows I!) in
grooves. Bellows I9 is protected externally by a
the stator plate and the diaphragm is exposed
sleeve 2| which may be of any suitable material'
to an outer chamber through a ?lter plug pierced
such as one of the well known synthetic plastics
with several small holes, and the outer chamber
provided with an opening through which atmos
is in turn open to the atmosphere through a
pheric pressure may act upon bellows l3. The
similar plug. These passages offer no barrier to
construction just described con?nes a body of
the entrance of dust particles and moisture laden
air within the tubular assembly back of the dia
air into the condenser element as a result of tem
phragm B and inside the bellows IS. The pres,
perature and barometric pressure changes.
sure on the opposite sides of diaphragm 8 is thus
The entrance of moisture not only reduces the
equalized by movement of air between the space
necessarily high resistance of the condenser, re
enclosed by bellows l9 and member 2, and the
sulting in loss of sensitivity, but causes the ele
space in the member 2 by way of the ducts l5
ment to become erratic or noisy. The presence
and I‘! and through the desiccant material I3
of even exceedingly small quantities of dust in
and thus any moisture in the air so con?ned is
the condenser chamber which usually is a space
of only 0.006 inch will cause noisy and erratic 40 removed as it passes through the desiccant ma
terial l3 in response to variations of atmospheric
operation of the instrument. The reconditioning
pressure.
of a microphone under ?eld conditions is ex
The end element I8 is provided with external
tremely di?ioult to accomplish. Accordingly, the
threads 22 for connecting the coupler to the
coupler constituting the present invention has
been devised to protect the microphone against 45 microphone housing in place of the ?lter plugs
above mentioned. The passages 23 through the
the entry of dust and moisture.
end element 18 permit transmission of sound
Referring now to the drawing, it will be noted
waves to the microphone mechanism. A removthat the coupler comprises in general a tubular
able screw 24 is disposed in the end element l8
assembly constituted by the major portions I and
2. Fixed to one end of the member I, as by 60 and may be taken out when it is desired that the
upper limit of the frequency response of the de
sweating or brazing, is a ?ange 3 having formed
vice should be raised. For example, with the
thereon a shoulder 4. Secured to the flange 3 is
screw 24 in place the upper limit of response may
an element having a tubular portion 5 of the
be 60 cycles per second but when it is removed
same radial dimensions as members I and 2 and
also having a radially extending ?ange 6 that 55 that upper limit will be 100 cycles per second.
I
2,405,858
3
The end of the assembly remote from the mi
crophone is preferably provided with a wire screen
25 to prevent entry of any large particles of dirt
or other matter that might damage, or interfere
with the sound response of, diaphragm ii.
I claim:
1. An acoustic coupler for a condenser micro
phone having a single restricted opening for ac
cess of sound Waves thereto, comprising a ?rst
tub lar part having an internal shoulder adja 10
cen, one end, a second tubular part having one
of its ends secured in the said one end of the
?rst part, a thin rubber diaphragm clamped in
position between said shoulder and the said one
end of the second part to close the opening
through the parts against moisture and dirt,
means de?ning a closed annular chamber around
a portion of said ?rst part, a body of granular
disiccant in said chamber, a flexible member
surrounding the major portion of said ?rst part
secured at its ends to said ?rst part in air-tight
relation and spaced therefrom between its ends,
there being ducts connecting said annular cham
ber to the space within said member and other
ducts connecting said chamber to the space
within said ?rst part, matter ?lamentary mate-
of its ends secured in the said one end of the
?rst part, a thin rubber diaphragm clamped in
position between said shoulder and the said one
end of the second part to close the opening
through the parts against moisture and dirt,
breather means including a ?exible member re
sponsive to changes in air pressure disposed in
air-tight relation around the ?rst part and
spaced therefrom to enclose a body of air, a con
?ned body of desiccant material, and ducts to
permit passage of air between said body of air
and the interior of the ?rst part through the
desiccant material.
4. An acoustic coupler for a condenser micro
phone having a single restricted opening for ac
cess of sound. waves thereto, comprising a ?rst
tubular part having an internal shoulder adja
cent one end, a second tubular part having one
of its ends secured in the said one end of the
?rst part, a thin rubber diaphragm clamped in
position between said shoulder and the said one
end of the second part to close the opening
through the parts against moisture and dirt,
means to equalize air pressure on opposite sides
of the diaphragm including a member cooper
ating with the ?rst part to de?ne an enclosed
space having a volume that is variable with
changes in air pressure, passages to permit
movement of air between said space and the in
30 terior of the ?rst part, and an enclosed body of
rial disposed to exclude the disiccant from said
ducts, and an end member ?xed to and substan
tially closing the other end of the ?rst part, said
member being provided with elements to secure
the coupler to the microphone to conduct sound
hygroscopic material disposed in the path of air
to said opening in the microphone and with pas
moving between the interior of the ?rst part and
sages for the transmission of the sound, and a
said space.
removable closure in one of said passages which,
5. An acoustic coupler for a condenser micro
when the closure is removed, renders the device 35 phone having a single restricted opening for ac
effectively responsive to higher sound frequen
cess of sound waves thereto, comprising a tubu
cies than when the closure is in the passage.
lar assembly, a thin rubber diaphragm across the
2. An acoustic coupler for a condenser micro
interior thereof intermediate its ends, a member
phone having a single restricted opening for ac
?xed to one end of the‘ assembly to attach the
cess of sound waves thereto, comprising a, ?rst 40 assembly to the microphone in operative relation
tubular part having
internal shoulder adja
to said opening, said member having passages for
cent one end, a second tubular part having one
transmission of sound waves to the microphone,
of its ends secured in the said one end of the ?rst
means associated with a said passage to vary the
part, a thin rubber diaphragm clamped in posi
sound frequency response, means to enclose a
tion. between said shoulder and the said one end
volume of air Variable in response to changes in '
of the second part to close the opening through
the ambient air pressure connected to the space
the parts against moisture and dirt, means de
between the diaphragm and the said member,
?ning
closed annular chamber around a por
and material to remove moisture from air pass
tion of said ?rst part, a body of granular desic
ing between said space and said volume of air.
ant in said chamber, a ?exible member sur
6. An acoustic coupler for a condenser micro
rounding the major portion of said ?rst part se
phone having a single restricted opening for ac
ured at its ends to said ?rst part in air-tight re
cess of sound waves thereto, comprising a tubu
ation and spaced therefrom between its ends,
lar assembly, a moisture and dust excluding di
there being ducts connecting said annular cham
aphragm across the interior thereof intermedi
ber to the space within said member and other
ate its ends, said diaphragm transmitting sound
ducts connecting said chamber to the space with
waves without substantial attenuation of‘ the
in said ?rst part, matter ?lamentary material
sound, a member ?xed to one end of the assem
disposed to exclude the desiccant from said ducts,
bly to attach the assembly to the microphone in
and an end member ?xed to and substantially
operative relation to said opening, said member
closing the other end of the ?rst part, said mem 60 having passages for the transmission of sound
her being provided with elements to secure the
waves to the microphone, means associated with
coupler to the microphone to conduct sound to
a said passage to vary the sound frequency re
said opening in the microphone and with pas
sponse, means to enclose a volume of air in re
sages for the transmission of the sound.
sponse to changes in the ambient air pressure
3. An acoustic coupler for a condenser micro
connected to the space between the diaphragm
phone having a single restricted opening for ac
and the said member, and material to remove
cess of sound waves thereto, comprising a ?rst
moisture from air passing between said space
tubular part having an internal shoulder adja
and the said volume of air.
cent one end, a second tubular part having one
HAROLD C. SILENT.
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