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DESCRIPTION JP2007036525

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DESCRIPTION JP2007036525
A condenser microphone unit and a condenser microphone capable of achieving further
miniaturization by devising the structure of a vibrator and its peripheral members, and having
high sensitivity and little noise. A condenser is formed by a vibrating body that vibrates by
receiving voice and a fixed pole disposed opposite to the vibrating body, and a condenser
microphone that converts it into an electric signal by a change in capacitance of the condenser.
unit. The vibrating body 40 is a cylindrical member, and the fixed electrode 36 is a columnar
member disposed inside the vibrating body 40. The vibrating body 40 is disposed via the spacer
42 disposed on the outer circumferential surface of the fixed pole 36, and a cylindrical space 46
sealed by the outer circumferential surface of the fixed pole 36, the spacer 42 and the vibrating
body 40 is formed. [Selected figure] Figure 1
コンデンサーマイクロホンユニットおよびコンデンサーマイクロホン
[0001]
The present invention relates to a condenser microphone unit and a condenser microphone that
can increase the sensitivity even when miniaturized.
[0002]
Condenser microphone units used for small microphones such as tie pin microphones and
headset microphones are required to be as small as possible so as not to be noticeable.
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1
At present, a small-diameter condenser microphone unit with a diameter of about 2.5 mm is
commercialized, and a polarization voltage is applied by an electret.
[0003]
3 and 4 show the structure of a conventional condenser microphone unit. In FIGS. 3 and 4,
reference numeral 12 denotes a case of the condenser microphone unit, that is, a unit case. The
unit case 12 has a cylindrical shape with a bottom, and the top and bottom are inverted in the
figure, and the portion corresponding to the bottom is on the top. The upper flat wall
corresponding to the bottom portion is formed with a plurality of holes 121 for introducing
sound waves into the unit, and these holes 121 are covered with a front mesh (not shown) on the
inner surface side of the unit case 12 . A diaphragm assembly 30 is disposed in the unit case 12
at a position closest to the bottom of the unit case 12. The diaphragm assembly 30 comprises a
ring-shaped diaphragm support 24 and a diaphragm-shaped diaphragm 22 whose outer
peripheral edge is fixed to one end face of the diaphragm support 24 by adhesion or the like.
[0004]
The fixed electrode 16 is disposed to face the diaphragm 22 with the spacer 20 interposed. The
spacer 20 is a ring-shaped member made of a thin resin and is in close contact with the outer
peripheral edge of the rear end surface (lower end surface in FIGS. 3 and 4) of the diaphragm 22.
A gap corresponding to the thickness of the spacer 20 is formed between the diaphragm 22 and
the fixed electrode 16. The fixed electrode 16 uses a metal disc as a base material, and the
electret plate 18 is attached to at least one surface side thereof, for example, the opposite surface
side to the diaphragm 22, to constitute an electret board. The diaphragm 22 and the fixed
electrode 16 constitute a type of capacitor, and as the diaphragm 22 vibrates in accordance with
the sound wave introduced from the front mesh, the capacitance of the capacitor changes and
The change in capacity is output as an audio signal. The diaphragm 22 is formed by the air
pressure of the enclosed space formed by the electret plate 18, the spacer 20 and the inner
surface of the diaphragm 22, and the atmospheric pressure applied to the opposite surface of the
diaphragm 22 by the formation of the holes 121. The position changes depending on the
difference with. When a sound wave is introduced from the hole 121, the pressure applied to the
atmosphere side of the vibrating plate 22 fluctuates according to the sound wave, and the
vibrating plate 22 vibrates.
[0005]
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In the unit case 12, a cylindrical fixed pole support 14 is disposed on the rear side of the fixed
pole 16. The inner periphery of the front end portion of the fixed pole support 14 is expanded
radially outward to form a circular step 141, and the fixed pole 16 is fitted to the step 141. The
disc-shaped printed circuit board 10 is in contact with the rear end face of the fixed pole support
14, and the printed circuit board 10 is fitted to the rear end open portion of the unit case 12. Is
fixed to the unit case 12 by means such as caulking the rear end opening portion of the unit case.
A force is applied to the circuit board 10 to press the fixed pole support 14, the fixed pole 16, the
spacer 20, and the diaphragm assembly 30 in this order toward the inner bottom surface of the
unit case 12, and these members are in predetermined positions. It is fixed.
[0006]
A field effect transistor (hereinafter referred to as “FET”) 9 constituting an impedance
converter is disposed at the center of the upper surface of the printed circuit board 10. Since the
output impedance of the condenser microphone unit is extremely high, an impedance converter
mainly composed of the FET 9 is incorporated. A part of the terminals of the FET 9 is connected
to a predetermined circuit pattern of the printed circuit board 8 by soldering or the like, and one
of the other terminals is in pressure contact with one end of a contact 28 made of a curved
elastic conductor. . The other end of the contact 28 is in pressure contact with the fixed pole 16,
and the contact 28 electrically connects one of the terminals of the FET 9 to the fixed pole 16.
[0007]
The condenser microphone unit used for the tie pin type or the headset type condenser
microphone has a very small diameter of 2.5 mm and a length (height) of 2.0 mm, and the
configuration is as shown in FIGS. There is basically no change. The tie-pin type or headset type
microphone unit is often nondirectional. As the diaphragm 22, for example, a plastic film as a
base material on which gold or the like is vacuum-deposited is used. The diaphragm assembly 30
is configured by sticking the diaphragm 22 to the ring-shaped diaphragm support 24.
[0008]
In order to enhance the sensitivity of the condenser microphone unit, reduce noise, and improve
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various characteristics, it is preferable to increase the effective capacity. The capacity that
contributes to producing an electrical signal by the vibration of the diaphragm 22 is referred to
as an effective capacity, but in the condenser microphone unit, there is a stray capacity that
lowers the sensitivity in addition to the effective capacity. The effective capacity depends on the
area of the vibrating portion of the diaphragm 22 and the distance to the fixed pole 16 (more
specifically, to the electret plate 18). The stray capacitance is a value obtained by subtracting the
effective capacitance from the capacitance between the diaphragm 22 and the fixed electrode 16.
The stray capacitance also includes the input capacitance of the FET 26 that constitutes the
impedance converter. Assuming that the effective capacity and the stray capacity are equal, the
sensitivity at the signal input to the FET 26 is reduced to half. Therefore, the sensitivity of the
condenser microphone unit can be increased by increasing the effective capacity and reducing
the stray capacity.
[0009]
When the effective capacity is small, the sensitivity is lowered as described above, and
additionally, the intrinsic noise due to the gate portion of the FET 26 is increased. This inherent
noise is called 1 / f noise. For example, although the equivalent sound pressure level of the
natural noise of a large condenser microphone unit having a diameter of 21 mm of diaphragm
22 is about several dBSPL, the characteristic sound pressure is specific to a small condenser
microphone unit having an outer diameter of about 2.5 mm. The equivalent sound pressure level
of noise is about 30 dBSPL. In microphones for broadcasting services, the equivalent sound
pressure level of intrinsic noise is required to be 30 dBSPL or less. Therefore, the miniaturization
of the condenser microphone unit can be said to have an outer diameter of 2.5 mm at present.
[0010]
There is also a manufacturing problem with the miniaturization of the condenser microphone
unit. As described above, in order to increase the sensitivity, the effective capacity may be
increased. To increase the effective capacity, the inner diameter of the diaphragm holder 24 is
increased to effectively function the diaphragm 22 as a diaphragm. The area should be increased.
However, in the tie-pin type or headset type microphone unit, it is desirable to minimize the
components including the diaphragm 22 and the diaphragm holding member 24, and conditions
that are contrary to increasing the effective area of the diaphragm 22. It will have to be satisfied.
In order to satisfy the contradictory conditions, it is conceivable to reduce the bonding margin of
the diaphragm 22 to the diaphragm holder 24 as much as possible.
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[0011]
On the other hand, in the nondirectional condenser microphone unit, it is necessary to increase
the tension of the diaphragm 22. The reason is that it is necessary to increase the polarization
voltage to increase the sensitivity, and to prevent the diaphragm 22 from being attracted to the
fixed electrode 16 by the high polarization voltage. . However, when a plastic film is used as the
material of the diaphragm 22, creep occurs in the plastic material when tension is high, and the
characteristics deteriorate, so the limit of tension must be such that the plastic material does not
creep. . On the other hand, when the bonding margin is reduced as described above, the bonding
portion can not resist the tension, and the diaphragm 22 is easily detached from the diaphragm
holder 24. Therefore, in the configuration of the conventional condenser microphone unit, it is
difficult to reduce its diameter, and at present, the diameter of about 2.5 mm is limited as
described above.
[0012]
Next, consider vibration noise. When vibration is applied to the microphone unit, the fixed pole
vibrates together with the microphone unit, while the diaphragm tries to stay at the original
position, and the capacitance between the diaphragm and the fixed pole changes. Emits a sound
signal. This sound signal is not due to the conversion of the sound wave into an electric signal,
but is vibration noise based on the vibration added to the microphone unit. According to the
structure of the conventional condenser microphone unit, the diaphragm is flat, and the abovementioned vibration noise is easily generated.
[0013]
The diaphragm of the condenser microphone unit conventionally known including the example
shown in FIGS. 3 and 4 is a flat diaphragm (for example, Patent Document 1, Patent Document 2,
Patent Document 3, Patent Document 4, Patent Document 4, Patent Reference 5, Patent
Document 6, Patent Document 7, Patent Document 8). Therefore, there is a limit to the
miniaturization as described above, and there is a disadvantage that vibration noise is easily
generated.
[0014]
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JP 2005-199896 JP 2005-150991 JP 2004-343377 JP 2004-343368 JP 2004-72235 JP
2003-163997 JP JP 2004-516725 JP Patent Japanese Patent Publication 2004-40584
[0015]
The present invention has been made to solve the problems of the prior art as described above,
and further relates to the shape or structure of the vibrating body and its peripheral members,
and further incorporating the concept which is not limited to the prior art. An object of the
present invention is to provide a condenser microphone unit and a condenser microphone that
can be miniaturized and have high sensitivity and low noise.
[0016]
The present invention is a condenser microphone unit that forms a capacitor with a vibrating
body that vibrates by receiving voice and a fixed pole disposed opposite to the vibrating body,
and converts it into an electric signal by changing the capacity of the capacitor. The vibrator is a
cylindrical member, and the fixed pole is a columnar member disposed inward of the vibrator.
The vibrator may be disposed via a spacer disposed on the outer peripheral surface of the fixed
pole, and a cylindrical space sealed by the outer peripheral surface of the fixed pole, the spacer,
and the vibrator may be formed.
[0017]
The vibrator surrounds the periphery of the columnar fixed electrode, and the fixed electrode
and the vibrator constitute a capacitor.
Since the vibrator and the fixed electrode do not spread in a plane as in the prior art, but spread
in three dimensions, it is easy to widen the effective area of the vibrator even if the diameter of
the unit is limited. It is easy to increase the ratio of the effective capacitance. In order to increase
the capacitance, it is sufficient to lengthen the vibrator and the fixed pole in the central axis
direction, and it is also possible to increase the sensitivity while maintaining the small diameter.
When a physical force such as vibration is applied from outside, the tubular vibrator moves
closer to the fixed pole on one side and moves parallel to move away from the fixed pole on the
other side, so the capacitance increases on one side and decreases on the other side Therefore,
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there is also an advantage that the change in capacitance is totally canceled and noise is less
likely to occur.
[0018]
Hereinafter, embodiments of a condenser microphone unit and a condenser microphone
according to the present invention will be described with reference to FIGS. 1 and 2. FIG. Parts
substantially the same as the parts used in the conventional example shown in FIGS. 3 and 4 are
denoted by the same reference numerals. In FIGS. 1 and 2, reference numeral 12 indicates a case
of the condenser microphone unit, that is, a unit case. The unit case 12 has a cylindrical shape
with a bottom, and the top and bottom are inverted in the figure, and the portion corresponding
to the bottom is on the top. The upper flat wall corresponding to the bottom portion is formed
with a plurality of holes 121 for introducing sound waves into the unit, and these holes 121 are
covered with a front mesh (not shown) on the inner surface side of the unit case 12 .
[0019]
In the unit case 12, a disk-shaped circuit board 10 is fitted and fixed inside the lower end open
end of the unit case 12. As a fixing means of the circuit board 10, any means may be selected
from press fitting to the unit case 12, adhesion, caulking of the lower end edge of the unit case
12, and the like. In the unit case 12, a cylindrical fixed electrode 36, an electret layer 38, a spacer
42, a vibrating body 40, and an FET 26 which is a main component of an impedance converter
are disposed.
[0020]
The fixed pole 36 is fixed on the circuit board 10 by forming a space 44 between the inner
peripheral surface of the unit case 12 and the ceiling surface corresponding to the bottom of the
unit case 12. A recessed portion is formed on the bottom surface side of the fixed pole 36, and a
circular space 361 sealed by the recessed portion and the circuit board 10 is formed. The FET 26
is disposed on the circuit board 10, and the FET 26 is located in the space 361. The fixed
electrode 36 is made of a conductive material, such as metal.
[0021]
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An electret layer 38 is formed on the outer peripheral surface of the fixed pole 36, and a
polarization voltage is applied to the electret layer 38. For the electret layer 38, a heat-shrinkable
tube made of, for example, FEP (fluororesin: abbreviation of tetrafluoroethylenehexafluoropropylene copolymer (4.6 fluoride)) is placed on the cylindrical fixed electrode 36 and
heated. It can be shrunk and fixed to the outer peripheral surface of the fixed pole 36 and formed
by electretizing it.
[0022]
A cylindrical vibrating body 40 is disposed on the outer periphery of the fixed pole 36, more
specifically, on the outer periphery of the electret layer 38, with the spacer 42 interposed. The
radius of the cylindrical vibrating body 40 is larger than the radius of the fixed pole 36 (more
precisely, the radius of the electret layer 38) by the thickness of the spacer 42, and the vibrating
body 40 and the fixed pole 36 (more accurate A space 46 corresponding to the thickness of the
spacer 42 is created between this and the outer peripheral surface of the electret layer 38). The
length in the central axis direction of the vibrating body 40 is substantially the same as the
length of the fixed pole 36, and the spacers 42 are fixed to the inner peripheral surfaces of both
ends in the longitudinal direction of the vibrating body 40, respectively. It is fitted on the outer
peripheral surface of the layer 38 and fixed by an appropriate means. Therefore, the space 46
sealed by the outer peripheral surface of the fixed pole 36, the upper and lower spacers 42 and
the vibrating body 40 is formed. The vibrating body 40 is formed of a membrane-like member so
as to be able to vibrate in the radial direction by receiving an acoustic wave. For example, a metal
film such as nickel can be formed by an electric casting method which is a type of plating
method, and this can be used as a vibrator. The thickness of this metal film is 5 to 10 μm.
[0023]
As shown in FIG. 1, a capacitor having the electret layer 38 and the vibrating body 40 as
electrodes is configured by facing the fixed electrode 36 (more precisely, the electret layer 38)
and the vibrating body 40 in the space 46. Ru. A space 44 is formed between the outer
peripheral surface of the vibrating body 40 and the inner peripheral surface of the unit case 12
and a ceiling surface corresponding to the bottom of the unit case 12. This space 44 is a hole
formed in the unit case 12 It is open to the atmosphere from 121. Therefore, when a sound wave
enters the space 44 from the hole 121, a difference occurs between the pressure applied to the
space 44 and the pressure of the sealed space 46, and the pressure difference according to the
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sound wave causes the vibrating body 40 to move in the radial direction. Vibrate. The pressure
due to the sound wave is generated in the direction in which the vibrating body 40 is contracted
and expanded around the entire circumference of the vibrating body 40, so the electrostatic
capacitance in the entire circumference of the vibrating body 40 changes in response to the
sound wave. The change in capacitance is output as an audio signal.
[0024]
Thus, according to the embodiment shown in FIG. 1 and FIG. 2, the capacitance increases in
proportion to the area of the vibrating body 40 facing the space 46 expanding in the
circumferential direction, so the vibrating body 40 and the fixed pole 36 If the dimensions in the
central axis direction of the electret layer 38 are secured to some extent, it is easy to increase the
effective capacity as compared with the case of the flat-shaped diaphragm in the conventional
condenser microphone unit. Even if the diameter of the unit is reduced, the effective capacitance
can be increased by increasing the dimension in the central axis direction, and a condenser
microphone unit having a small diameter, high sensitivity and little noise can be obtained.
[0025]
According to the above embodiment, a condenser microphone unit with small vibration noise can
be obtained. That is, when an impact force or vibration is applied to the unit, the fixed pole 36
and the electret 38 integrated therewith vibrate integrally with the circuit board 10 and the unit
case 12 while the vibrating body 40 remains in place. It moves relative to the fixed pole 36 as a
solder. The relative movement of the vibrating body 40 at this time is a movement close to
parallel movement unlike the case of receiving a sound wave, while the distance between the
fixed pole 36 and the vibrating body 40 is close on one side in the diameter direction. On the
other side in the diameter direction, the distance between the fixed pole 36 and the vibrating
body 40 is long. Therefore, the capacitance increases on one side, decreases on the other side,
and cancels each other out, so that the output signal, that is, the level of noise is small, so that
vibration noise is less likely to occur.
[0026]
In the description so far, the shape of the vibrating body 40 is assumed to be a cylindrical shape,
that is, a cylindrical shape in which both longitudinal end portions are open, but the vibrating
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body 40 has a bag having a bottom portion as shown by imaginary line 401 in FIG. It may be
made of metal film of the shape of a circle. Spacers 42 are fixed to the inner side upper and lower
end portions of the bag-like vibrating body 40, and the vibrating body 40 is covered on the fixed
pole 36 from above with the spacer 42, and the vibrating body 40 is fixed to the fixed pole 36.
The portion corresponding to the bottom portion of the bag-like vibrator 40 is in close contact
with the upper surface of the fixed electrode 36. Alternatively, a space is provided between the
portion corresponding to the bottom of the bag-like vibrator 40 and the upper surface of the
fixed pole 36, and a capacitor is formed by the portion corresponding to the bottom of the baglike vibrator 40 and the upper surface of the fixed pole 36. It may be configured to further
increase the effective capacitance.
[0027]
Although the illustrated embodiment is an example of the electret condenser microphone unit in
which the electret layer 38 is formed on the outer periphery of the fixed pole 36, it may be a
condenser microphone unit in which the electret layer 38 is omitted.
[0028]
The condenser microphone unit shown in FIGS. 1 and 2 can be made into a condenser
microphone by incorporating it into a microphone case and further incorporating necessary
circuits into the microphone case.
In the case of a wireless pin microphone or headset microphone, a transmitter is incorporated,
and in the case of a cable connection microphone, a connector for connecting a cable is
incorporated.
[0029]
In the present invention, the diaphragm and the fixed electrode are devised based on an idea
completely different from that of the conventional condenser microphone or condenser
microphone unit, and the effective capacitance is increased even for a unit of small diameter, and
the sensitivity is high. The condenser microphone unit and the condenser microphone can be
obtained. Therefore, it is likely to be widely used especially for those requiring small size such as
pin microphones or headset microphones.
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[0030]
It is a longitudinal cross-sectional view which shows the Example of the condenser microphone
unit concerning this invention. It is a disassembled longitudinal cross-sectional view of the said
Example. It is a longitudinal cross-sectional view which shows the example of the conventional
condenser microphone unit. It is a disassembled longitudinal cross-sectional view of the said
prior art example.
Explanation of sign
[0031]
10 circuit board 12 unit case 26 FET 36 fixed pole 38 electret 40 vibrator 42 spacer
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