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JP2003032797

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DESCRIPTION JP2003032797
[0001]
[0001] This application claims the benefit of US Provisional Patent Application Ser. No. 60 /
301,736, filed Jun. 28, 2001, and US Provisional Patent Application Ser. No. 60 / 284,741 claims
priority.
[0002]
The present invention relates to a miniature microphone having a housing which may be
generally cylindrical in shape and having a back plate integrally provided with a connecting
portion for connection to an internal electronic device.
[0003]
BACKGROUND OF THE INVENTION Conventional hearing aids include a miniature microphone
that receives an acoustic signal wave and converts the acoustic signal wave into an audible
signal.
The audible signal is then processed (eg, amplified) and sent to the receiver of the hearing aid.
The receiver then converts the processed signal into an acoustic signal and sends it towards the
tympanic membrane.
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[0004]
Pushing reduces the volume required for these devices, as it is desirable to make the receiver and
microphone as small as possible so as to fit easily into the patient's ear canal. Many square
shaped electroacoustic transducers are available. However, with square shapes, space is not
optimally used, requiring a large volume of transducer.
[0005]
There are also small microphones of cylindrical shape. These cylindrical microphones can be
reduced in size, but at the expense of performance and manufacturability. For example, if the
diaphragm is too small the sensitivity will be reduced or the backplate can not be scaled up in
proportion to the diaphragm, increasing parasitic capacitance. Furthermore, the positioning and
mounting of the components within the cylindrical housing is extremely difficult.
[0006]
Furthermore, it is often difficult to make an electrical connection between the conversion
assembly and the electronic devices in the microphone. This is typically done by soldering a thin
wire to both the conversion assembly and the electronics.
[0007]
Accordingly, there is a need for a microphone with improved performance that can be more
efficiently manufactured and assembled.
[0008]
SUMMARY OF THE INVENTION The microphone of the present invention includes a separate end
cover with an acoustic port.
The diaphragm, which moves in response to the sound, is attached directly to the end cover. The
back plate is positioned at the ledge of the housing. This ridge is adjacent to the diaphragm. The
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spacer is positioned against the diaphragm. The diaphragm engages the spacer when installing
the end cover with the diaphragm attached thereto in the housing. Preferably, the housing has a
generally cylindrical shape and the end cover has a circular shape to fit into one end of the
housing.
[0009]
In another aspect of the invention, the back plate of the microphone has an integral connecting
wire formed of the same material as the back plate. An integral connecting wire electrically
connects the back plate to the electronic components in the housing and receives a raw audible
signal corresponding to the movement of the diaphragm. The integral connection wire forms an
electrical connection to the electronic component using only contact pressure.
[0010]
In another aspect of the invention, the generally cylindrical housing has a first circumferential
ledge provided at the first end and a second circumferential ledge provided at the second end.
The printed circuit board is attached to the first circumferential edge of the housing. A portion of
the electret assembly, typically the back plate, is attached to the second circumferential ledge of
the housing. The ledge may be formed by a groove extending into the outer surface of the
cylindrical housing. These grooves on the outer surface receive a pair of o-rings to attach the
microphone to the external structure.
[0011]
In another embodiment, the microphone includes a transducer assembly with a flexible back
plate to reduce the sensitivity of the microphone to vibrations. The above description of the
present invention is not intended to represent each embodiment or every feature of the present
invention. This is the purpose of the drawings and the detailed description that follows.
[0012]
The foregoing and other advantages of the present invention will become apparent upon reading
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the following detailed description and upon reference to the accompanying drawings in which:
While the invention is susceptible to various modifications and alternative forms, specific
embodiments are shown by way of example in the accompanying drawings and are described in
detail below. However, it should be understood that the invention is not intended to be limited to
the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and
alternatives falling within the spirit and scope of the invention as defined by the appended
claims.
[0013]
DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1, a microphone 10 according to
the present invention includes a housing 12 having a cover assembly 14 at its upper end and a
printed circuit board (PCB) 16 at its lower end. The housing 12 has a cylindrical shape, but may
have a substantially cylindrical polygonal shape. In one preferred embodiment, the axial length of
the microphone 10 is about 2.5 mm, but the length may vary according to the required output
response from the microphone 10.
[0014]
The PCB 16 includes three terminals 17 of ground, a power supply input, and an output for a
processed electrical signal corresponding to the sound converted by the microphone 10 (see FIG.
2). The sound enters the sound port 18 of the cover assembly 14 and encounters an electret
assembly 19 located slightly below the sound port 18. It is this electret assembly 19 that
converts sound into electrical signals.
[0015]
The microphone 10 includes an upper leading edge 20 which extends circumferentially over the
inside of the housing 12. The microphone 10 further includes a lower leading edge 22
circumferentially extending over the inside of the housing 12. These ridges 20, 22 may be
formed by circumferential recesses 24 (i.e., recesses) disposed on the outer surface of the
housing 12. The ridges 20, 22 need not be continuous, but may be intermittently disposed on the
inner surface of the housing 12. As shown, the ledges 20, 22 have a circular cross-sectional
shape.
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[0016]
The upper ledge 20 bears against a portion of the electret assembly 19 to provide a surface for
mounting within the housing 12. As shown, the rear plate 28 of the electret assembly 19 engages
the upper ledge 20. Similarly, the lower ledge provides a surface for mounting and positioning
the PCB 16 within the housing 12. The ridges 20, 22 have a radial length (i.e., a length measured
inward from the inner surface of the housing 12), typically 100 [mu] m to 200 [mu] m, to
support the associated components.
[0017]
In addition, the recesses 24, 26 on the outer surface of the housing 12 hold o-rings 30, 32 which
allow the housing 10 to be mounted within the external structure. These O-rings 30, 32 may be
formed of several materials such as silicone or rubber typical of hearing aid face plates which
allow them to be mechanically loosely coupled to external structures. Thus, the present invention
contemplates a novel microphone comprising a generally cylindrical housing having a first ledge
at a first end and a second ledge at a second end. The printed circuit is a substrate attached to
the first ridge of the housing. The electret assembly is attached to a second ridge in the housing
to convert sound into an electrical signal.
[0018]
The back plate 28 includes integral connecting wires 34 that electrically connect the electret
assembly 19 to the electrical components of the PCB 16. As shown, integral connection wires 34
are connected to integrated circuits 36 disposed on the PCB 16. An electret assembly 19
including a back plate 28 and a diaphragm 33 positioned at a known distance from the back
plate 28 receives sound through the acoustic port 18 and converts the sound into a raw audio
signal. Integrated circuit 36 processes (eg, amplifies) the raw audio signal generated within
electret assembly 19 into an audible signal, which is transmitted from microphone 10 through
output terminal 17. The integral connecting wire 34 further simplifies the assembly process, as
will be described in more detail below. This is because it is only necessary to attach one end of
the integral connection wire 34 to an electrical component disposed on the PCB 16. In other
words, the integral connection wire 34 is already in electrical contact with the back plate 28
because it is “in one” with the back plate 28.
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[0019]
FIG. 2 shows the electret assembly 19 in more detail. In particular, the back plate 28 includes a
base layer 40 and a charge layer 42, typically made of polyimide (eg, Kapton). The charged layer
42 is typically charged Teflon (eg, fluorinated ethylene propylene) and further includes a metal
(eg, gold) coating for transmitting signals from the charged layer 42. The charged layer 42 is
typically exposed directly to the diaphragm 33, and is separated from the diaphragm 33 by the
spacer 44. The thickness of the spacing spacer 44 determines the distance between the charging
layer 42 of the back plate 28 and the diaphragm 33. The diaphragm 33 may be polyethylene
terephthalate (PET), the gold layer of which is directly exposed to the charge layer 42 of the back
plate 28. Alternatively, the diaphragm 33 may be a pure metal foil. The spacer 44 is typically PET
or polyimide. Rear plate 28 is discussed in detail below in conjunction with FIGS. 5A and 5B.
Furthermore, although the electret assembly 19 has been described with respect to the backplate
28 with the charged layer 42 (i.e., the electret material), the present invention is useful in
systems where the diaphragm 33 includes a charged layer and the backplate is metallic.
[0020]
FIG. 3 shows the cover assembly 14 serving as a carrier for the diaphragm 33. As shown in FIG.
The cover assembly provides protection to the diaphragm 33 and receives incoming sound. A
recess 52 is disposed in the central portion of the cover assembly 14. The acoustic port 18 is
located approximately at the midpoint of the recess 52. The acoustic port 18 is shown as a
simple opening, but may include an elongated tube following the diaphragm 33. Additionally, the
cover assembly 14 may include a plurality of acoustic ports. The recess 52 defines an internal
boss 54 disposed along the circular perimeter of the cover assembly 14. The diaphragm 33 is
held in tension at bosses 54 around the cover assembly 14. The diaphragm 33 is typically
attached to the boss 54 using an adhesive. The adhesive is provided in a very thin layer so that
electrical contact is maintained between the cover assembly 14 and the diaphragm 33. In
another aspect, the adhesive may be electrically conductive to maintain an electrical connection
between the diaphragm 33 and the cover assembly 14. Because the cover assembly 14 includes
the diaphragm 33, the diaphragm 33 is easy to transport and easy to incorporate into the
housing 12.
[0021]
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The cover assembly 14 provides protection for the diaphragm 33, while the recess 52 of the
cover assembly 14 defines a front volume for the microphone 10 located above the diaphragm
33. Furthermore, the width of the boss 54 is preferably reduced so that more of the area of the
diaphragm 33 can be moved when sound is applied. A small front volume is preferred for space
efficiency and performance, but at least some of the front volume is required to provide
protection for the moving diaphragm. In one embodiment, the thickness of diaphragm 33 is
about 1.5 μm and the height of the front volume is about 50 μm. The overall diameter of the
diaphragm 33 is 2.3 mm and the active portion of the diaphragm 33 not in contact with the
annular boss 54 is about 1.9 mm.
[0022]
The cover assembly 14 fits within the interior of the housing 12 of the microphone 10, as best
seen in FIG. The cover assembly 14 is held in place on the housing 12 by a weld connection. The
housing 12 and / or the cover assembly 14 can be coated with nickel, gold or silver to enhance
the electrical connection. Thus, electrical connections are formed between the diaphragm 33 and
the cover assembly 14 and between the cover assembly 14 and the housing 12.
[0023]
Thus, FIGS. 1-3 disclose an assembly method for a microphone, including the step of positioning
the back plate within the housing of the microphone such that the back plate rests on the inner
ledge of the housing. The assembly includes positioning the spacer member within the housing
adjacent to the back plate, and installing the diaphragm-mounted end cover assembly in the
housing. The installation step includes the step of sandwiching the spacer member and the back
plate between the inner ledge and the end cover assembly. In other words, the invention shown
in FIGS. 1 to 3 is a microphone that converts sound into an electrical signal. The microphone
includes a housing with an end cover provided with an acoustic port. The end cover is a separate
component from the housing. The housing has an internal ledge near the end cover and the rear
plate is positioned relative to this internal ledge. The diaphragm is attached directly to the end
cover. A spacer is positioned between the back plate and the diaphragm. When installing the end
cover with the diaphragm attached to the housing, the spacer and the back plate are sandwiched
between the inner ledge and the end cover.
[0024]
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FIG. 4 is a cross-sectional view along the lower portion of the microphone 10 showing the
mounting of the PCB 16 on the lower lead 22 of the housing 12. An integral connection wire 34
extends from the back plate 28 (see FIGS. 1 and 2) and is electrically connected to the contact
pads 56 of the PCB 16. Electrical connections can be made at the contact pads 56 by double
sided adhesive tape, droplets of conductive adhesive, heat sealing or soldering.
[0025]
The periphery of the PCB 16 has an exposed ground plane, which is in electrical contact with the
ledge 22 or with the housing 12 immediately adjacent to the ledge 22. Thus, the same ground
plane used for integrated circuit 36 is also in contact with housing 12. As mentioned above with
respect to FIG. 3, the cover assembly 14 is in electrical contact with the housing 12 via a weld
joint and is also in electrical contact with the diaphragm 33. The raw acoustic signal generated
from the back plate 28 and the output acoustic signal at the output terminal 17 since the
diaphragm 33, the cover assembly 14, the housing 12, the PCB 16 and the integrated circuit 36
are all connected to the same ground Is relative to the same ground.
[0026]
PCB 16 is shown with integrated circuit 36 which may be a flip-chip design feature. The
integrated circuit 36 can process the raw acoustic signal from the back plate 28 in various ways.
Additionally, the PCB 16 may include an integrated A / D converter to provide a digital signal
output from the output terminal 17.
[0027]
FIGS. 5A and 5B show the rear plate 28 in plan and side views, respectively, prior to assembly
into the housing 12. FIG. The base layer 40 is the thickest layer, typically made of a polymeric
material such as polyimide. The charged layer 42, which may be a charged Teflon layer, is
separated from the base layer 40 by a thin gold coating 60 provided on one surface. The gold
coating 60 provided on the base layer 40 is laminated with the charge layer 42 to form the back
plate 28. This charged layer is "uncharged" at this point. After lamination, the process of
"charging" the charged layer 42 is added. In one embodiment, the charging layer 42 is made of
about 25 μm Teflon, the gold layer is about 0.09 μm, and the base layer 40 is made of about
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125 μm Kapton.
[0028]
The thin gold coating 60 has an extension 62 which provides a signal path for the integral
connection wire 34 which extends from the back plate 28 to the PCB 16. A gold extension 62 is
supported by the base layer 40. The integral connection wire 34 has a generally rectangular
cross section. Although the integral connecting wire 34 is shown as being flat, it can be easily
bent to a predetermined shape that facilitates its installation in the housing 12 and its
attachment to the PCB 16.
[0029]
In another embodiment, the charge layer 42 may comprise a gold coating. In this variation, the
base layer 40 terminates before extending into the integral connecting wire 34, and the charging
layer 42, along with the gold coating 60, serves as the main structure to provide strength to the
extension of the gold coating 60. Extend.
[0030]
To properly position the backplate 28 within the housing 12, the base layer 40 includes a
plurality of support members 66 extending radially from a central portion of the base layer 40.
These support members 66 engage with the upper edge 20 of the housing 12. As a result, the
back plate 28 is mounted in the housing 12 at three points.
[0031]
The microphone 10 according to the invention has fewer parts than current microphones and is
easy to assemble. After the rear plate 28 and the spacer 44 are positioned on the upper ledge 20,
the cover assembly 14 is fitted into the housing 12 to "squeeze" the electret assembly 19 into
place. The cover assembly 14 can then be welded to the housing 12. Then, the free end 46 (see
FIG. 2) of the integral connection wire 34 is electrically connected to the PCB 16, and then the
PCB 16 is pressed against the lower lead 22 and fitted in place. The length of the integral
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connecting wire 34 can preferably extend through the housing 12 through the integral
connecting wire 34 and can be attached to the PCB 16 when the PCB 16 is outside the housing
12, preferably the housing Longer than 12 lengths. The PCB 16 is held on the lower edge by
placing a silver adhesive dot on the lower edge 22. A sealing adhesive, such as Epotek adhesive,
is added to the PCB 16 to seal tightly and hold the PCB 16 in place.
[0032]
FIG. 6 illustrates another embodiment of the present invention in which the microphone 80
includes an electret assembly 81 which makes pressure contact electrical connection to the
printed circuit board 82. Although specific materials can be varied, electret assembly 81 is
preferably between Kapton layer 84, Teflon layer 86, and Kapton layer 84 and Teflon layer 86 as
disclosed in the above-described embodiments. A rear plate including a thin metal (eg, gold) layer
(not shown). The flex region 88 causes the integral connecting wire 90 to extend downwardly
from the main flat region of the back plate opposite the diaphragm of the electret assembly 81.
Because the Kapton layer 84 and the Teflon layer 86 are stacked in a substantially flat
configuration, the flex region 88 causes the integral connection wire 90 to tend to be urged
upwardly toward a horizontal position by resilient spring action. . Thus, the distal end 92 of the
integral connecting wire 90 is in contact pressure engagement with the contact pad 94 provided
on the printed circuit board 82.
[0033]
The spring force provided by flex region 88 can be varied by changing the dimensions of Kapton
layer 84 and Teflon layer 86. For example, to reduce the spring force on the integral connection
wire 90 and thus reduce the force acting between the distal end 92 of the integral connection
wire 90 and the contact pad 94, the Kapton layer 84 in the bending region 88 It can be thin.
Because the Kapton layer 84 is thicker than the Teflon layer 86, it is the Kapton layer 84 that
provides most of the spring force.
[0034]
In order to ensure proper electrical contact between the distal end 92 of the integral connecting
wire 90 and the contact pad 94, at least a portion of the end face of the distal end 92 is in
electrical contact with the contact pad 94 so that metal It must have an exposed portion of As
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shown in FIG. 6, the exposed metallized layer is formed by removing the lower region of the
teflon layer 86 such that the end 92 includes the metallized portion 96 of the Kapton layer 84.
The teflon layer 86 can terminate at an intermediate point along the length of the integral
connecting wire 90 but preferably extends beyond the inflection area 88 to protect the
metallization layer. Additionally, the teflon layer 86 may extend along most of the length of the
integral connecting wire 90 to protect against shorts.
[0035]
FIG. 7 illustrates in detail the interaction between the metallized portion 96 of the Kapton layer
84 and the contact pad 94 of the PCB 82. As shown in FIG. Unlike FIG. 6, in FIG. 7 a metallization
layer 98 is shown on the Kapton layer 84. Because the back plate is formed by the embossing
process from the Kapton side, the metallized layer 98 wraps around the end face 100 of the
Kapton layer 84 and has rounded corners. This increases the contact area of the metallization
layer 98 and helps to ensure proper electrical contact at the contact pad 94.
[0036]
FIG. 8 shows an exploded view of the microphone 80 of FIGS. 6 and 7 and includes details of the
various components. The microphone 80 has the same type of components as the previous
embodiment. At one end of the housing 112, a PCB 82 having three terminals 117 is provided.
The PCB 82 rests on the lower edge 122 of the housing 112. The other end of the housing 112
receives the electret assembly 81. The electret assembly 81 includes a back plate, a diaphragm
133 and a spacer 144 with an integral connecting wire 90. An end cover 114 provided with a
plurality of openings 118 for receiving sound sandwiches the electret assembly 81 between the
upper pressing edge 120 of the housing 112.
[0037]
In the preferred method of assembly, the electret assembly 81 is placed in place on the housing
112. At this time, in the lower position, the integral connection wire 90 is bent such that an angle
formed by the integral connection wire 90 and the rear plate is 90 ° or less as illustrated.
Thereafter, the printed circuit board 82 is moved inward and placed on the lower pressing edge
122. During this process, the printed circuit board 82 is placed in a position where the end 92 of
the integral connecting wire 90 is aligned with the contact pad 94. The distal end 92 is brought
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into contact pressure engagement with the contact pad 94 by moving the printed circuit board
82 inward. In addition, droplets of conductive epoxy are applied to the contact pads 94 of the
printed circuit board 82 to form the more reliable and durable joints required for some operating
environments. The spacer 144 and the cover 114, to which the diaphragm 133 is attached, press
the back plate against the upper leading edge 120.
[0038]
The arrangements of FIGS. 6-8 reduce the number of steps required for the assembly process.
Furthermore, the number of components required for assembly is minimal. This is because it is
not necessary to use a conductive tape or a joint. Thus, the invention illustrated in FIGS. 6-8
includes a method of assembling a microphone, the steps of providing an electret assembly,
providing a printed circuit board, and contact pressure engaging the electret assembly with the
printed circuit board. Electrically connecting without soldering or adhesive engagement.
[0039]
The method of microphone assembly comprises the steps of providing a back plate including an
integral connecting wire, thereafter attaching the plate within the microphone housing, and
integrating the integral connecting wire to the electrical contact pad, of the integral connecting
wire. It can also be expressed as the step of electrically connecting by elastic spring force.
[0040]
The back plate for the embodiment of FIGS. 1-8 may be rigid, but may be relatively flexible in
order to be insensitive to vibrations.
If the back plate is rigid, the diaphragm moves relative to the back plate when exposed to
external vibrations. This movement of the diaphragm induced by the vibration produces a signal
equivalent to a sound pressure of about 50 to 70 dB SPL per 9.8 m / s 2 (1 g). Vibration
sensitivity to acoustic sensitivity is a function of the effective mass of the diaphragm divided by
the area of the diaphragm. This effective mass is the portion of the physical mass that is actually
moved by vibration and / or sound. This portion is determined only by the shape of the
diaphragm. For a particular shape, the vibration sensitivity of the diaphragm is determined by the
thickness of the diaphragm and the mass density of the diaphragm material. Thus, vibration
sensitivity is usually reduced by choosing a diaphragm of small thickness or low mass. For a
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commercially used Mylar diaphragm of 1.5 μm thickness, the vibration sensitivity associated
with the input is approximately 63 dB SPL for a circular diaphragm.
[0041]
If a flexible back plate is used instead of a rigid back plate, the flexible back plate also moves due
to external vibrations. At low frequencies (i.e. the resonant frequency of the back plate), this
movement of the flexible back plate is designed to be synchronized with the movement of the
diaphragm. By choosing the correct stiffness and mass of the backplate, the amplitude of the
backplate's vibration can be matched to the amplitude of the diaphragm's vibration and the
output signal generated by the vibration can be offset. Furthermore, the acoustic compliance of
the backplate is much higher than the acoustic compliance of the diaphragm, since the backplate
is made much thicker and heavier than the diaphragm. Thus, the influence of the flexible
backplate on the acoustic sensitivity of the microphone is relatively small.
[0042]
As an example, the stiffness of a polyimide back plate having a thickness of about 125 μm with
the shape shown in FIGS. 1-8 is typically about two orders of magnitude greater than the
stiffness of the diaphragm. Due to this high stiffness, the rear plate does not move acoustically.
The effective mass of the rear plate in this example is about 50 times larger than the effective
diaphragm mass, and thus the vibration sensitivity is reduced by 6 dB. By adding some extra
mass to the back plate, for example by bonding a small weight to the back side of the back plate,
the product of the back plate's mass and compliance can be matched with the diaphragm's mass
and compliance. Vibration sensitivity can be further reduced. Extra weight can also be added by
forming the backplate to use an additional amount of material in place for the backplate.
[0043]
Thus, the present invention contemplates a method of reducing the vibrational sensitivity of a
microphone. The microphone has an electret assembly that includes a diaphragm that can move
in response to an input acoustic signal and a back plate opposite the diaphragm. The method
includes the steps of adding a selected amount of material to the backplate to allow the backplate
to move under the effect of vibration without substantially altering the acoustic sensitivity of the
electret assembly. In another aspect, the novel method can be expressed as selecting the
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configuration of the backplate such that the product of the backplate effective mass and the
compliance substantially match the product of the diaphragm effective mass and the compliance.
The novel microphone thus having reduced vibration sensitivity includes an electret assembly
having a diaphragm that can move in response to an input acoustic signal and a back plate
opposite the diaphragm. The backplate has a selected amount of material in place to allow the
backplate to move under the action of an actuation signal applied to the microphone.
[0044]
Although the present invention has been described with reference to one or more specific
embodiments, it will be understood by those skilled in the art that numerous changes can be
made without departing from the spirit and scope of the present invention. Will be understood.
For example, the PCB 16 or 82 may be provided with a small hole to operate the microphone 10
as a directional microphone. Each of these embodiments and obvious variations thereof are
considered to be within the spirit and scope of the present invention as set forth in the claims.
[0045]
Brief description of the drawings
[0046]
1 is a cross-sectional perspective view of a cylindrical microphone according to the present
invention.
[0047]
2 is an exploded perspective view of the microphone of FIG.
[0048]
3 is a cross-sectional view of the cover assembly of the microphone of FIG.
[0049]
4 is a cross-sectional view of the printed circuit board mounted in the housing of the microphone
of FIG.
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[0050]
FIG. 5A is a plan view of the back plate before being incorporated into the cylindrical microphone
of FIG. 1, and B is a side view of the back plate.
[0051]
6 is a cross-sectional perspective view showing a variant in which the integral connecting wire of
the back plate is in contact pressure engagement with the printed circuit board.
[0052]
7 is a side view of the printed circuit board electrical connection for the embodiment of FIG.
[0053]
8 is an exploded perspective view of the microphone of FIG. 6 and FIG.
[0054]
Explanation of sign
[0055]
DESCRIPTION OF REFERENCE NUMERALS 10 microphone 12 housing 14 cover assembly 16
printed circuit board 17 terminal 18 acoustic port 19 electret assembly 20 22 edge 24 24
circumferential recess 28 back plate 30 O-ring
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