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JP2010136044

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DESCRIPTION JP2010136044
The present invention provides a condenser microphone unit and a condenser microphone which
are simple in structure, easy to adjust, and can obtain good low frequency response
characteristics. SOLUTION: A unidirectionality comprising a diaphragm 3 which receives and
vibrates a sound wave, a fixed electrode 4 opposed to the diaphragm 3 with a thin air layer, and a
back air chamber 6 formed on the back of the fixed electrode 4 A condenser microphone unit
having an acoustic terminal including a plurality of holes 51 for opening the back air chamber 6
to the outside, and communicating with the back air chamber 6 via at least one of the plurality of
holes 51; There are two air chambers 10. [Selected figure] Figure 1
コンデンサマイクロホンユニットおよびコンデンサマイクロホン
[0001]
The present invention relates to a condenser microphone unit and a condenser microphone, and
in particular to provide a technique for improving low frequency response in a single direction.
[0002]
A general configuration example of the condenser microphone unit is shown in FIGS. 5 to 7.
In FIGS. 5 to 7, internal components such as the diaphragm holding ring 2, the diaphragm 3, the
spacer 9, the fixed electrode 4, the air chamber 6, and the insulating base 5 are incorporated in
the cylindrical unit case 1. . The front end (left end in FIG. 5) of the unit case 1 is an inward
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flange 11, and the diaphragm holding ring 2 is pressed against the inner surface of the inward
flange 11. A diaphragm 3 made of a thin film is attached to the back side of the diaphragm
holding ring 2. A ring-shaped spacer 9 is disposed on the outer peripheral edge portion of the
back surface side of the diaphragm 3, and the fixed electrode 4 is disposed on the back surface
side of the spacer 9.
[0003]
The outer shape of the insulating base 5 is formed in the same manner as the inner surface of the
unit case 1 and, as shown in FIG. A step 54 is formed in a portion corresponding to the bottom of
the recess 53, and another recess 55 is formed on the inner circumferential side following the
step 54. The fixed electrode 4 is dropped into the recess 53 and is in contact with the step 54.
The air chamber 6 is formed by the depression 55 whose front side is divided by the fixed
electrode 4. The air chamber 6 is packed with, for example, a sponge. At the open rear end of
unit case 1, a suitable pressing member is fitted which prevents the falling off of internal
components including insulating base 5 and presses internal components toward the front of
unit case 1. ing.
[0004]
The insulating base 5 is pushed forward by the pressing member, and the step 54 pushes the
fixed electrode 4 forward, and the fixed electrode 4 moves the spacer 9, the diaphragm 3 and the
diaphragm holding ring 2 in this order to the front I'm pushing towards. Since the diaphragm
holding ring 2 contacts the inward flange 11 of the unit case 1, the built-in component is held in
the unit case 1 with an appropriate pressing force. A step between the jetty 52 and the step 54 is
set such that a gap is generated between the jetty 52 of the unit case 1 and the diaphragm 3.
Thus, a minute gap corresponding to the thickness of the spacer 9 is formed between the
diaphragm 3 and the fixed electrode 4.
[0005]
The diaphragm 3 and the fixed electrode 4 constitute a capacitor by the presence of an air layer
therebetween. When the diaphragm 3 receives a sound wave and vibrates, the capacity of the
capacitor changes, and the change in the capacity is converted into a change in voltage, which is
used as the output of the microphone unit. The fixed electrode 4 constitutes one of the electrodes
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of the capacitor, and this electrode is in communication with the diaphragm holding ring 2 and
the unit case 1. The fixed electrode 4 constituting the other electrode of the capacitor is
connected to a cylindrical extraction electrode 7 fixed through the central portion of the
insulating base 5. The lead-out electrode 7 is electrically connected to an FET which is a main
component of an impedance converter mounted on a circuit board (not shown) or the like.
[0006]
The inner peripheral side of the inward flange 11 is opened at the front end of the unit case 1 to
be an entrance for sound waves from the front side of the diaphragm 3. Although not shown in
the drawings, the fixed electrode 4 is provided with an appropriate through hole. An appropriate
number of through holes 51 are also formed in the insulating base 5, and the through holes 51
constitute a rear acoustic terminal. Therefore, the back surface of the diaphragm 3 is in
communication with the through hole of the fixed electrode 4, the air chamber 6, and the
through hole 51 of the insulating base 5. Some of the plurality of through holes 51 are covered
with the acoustic resistance material 8. In the illustrated conventional example, twelve through
holes 51 are formed, and one of the through holes 51 is covered with the acoustic resistance
material 8.
[0007]
By providing an acoustic terminal on the rear side of the diaphragm 3 as in the conventional
example described above, a unidirectional microphone microphone can be obtained. FIG. 8 shows
the acoustic equivalent circuit. The elements etc. which comprise an equivalent circuit are
defined as follows. P1: Sound pressure of sound wave coming from the front P2: Sound pressure
of sound wave coming from the rear acoustic terminal m0: Mass of the diaphragm 3 s0: Stiffness
of the diaphragm 3 r0: Acoustic resistance of the front of the diaphragm 3 r1: Rear Acoustic
resistance of acoustic terminal s1: Stiffness of air chamber 6 In the above-mentioned
conventional example, the larger the number of acoustic resistive members 8 covering the twelve
through holes 51 formed in the insulating base 5, the acoustic of the rear acoustic terminal The
resistance increases, and the directivity tends to be more omnidirectional.
[0008]
FIG. 9 shows the frequency response characteristic of the above-mentioned conventional
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example, in the case where a sound wave enters from an angle of 0 degree, that is, from the
front, from 90 degrees, that is, from right beside, and from an angle of 180 degrees, that is from
right behind. It shows separately. As apparent from FIG. 9, the characteristics of 90 degrees and
180 degrees in the low region are reversed, and in the low region, the characteristics of 180
degrees approach the characteristics of 0 degree. This is called "proximity effect", and one
problem to improve low frequency response is to eliminate the "proximity effect".
[0009]
By the way, the lower limit of the frequency response from the front in the unidirectional
condenser microphone is higher frequency than the omnidirectional condenser microphone, and
the lower limit does not exist in the omnidirectional. Therefore, in the unidirectional condenser
microphone, if the directivity in the low band is controlled to be non-directional, the pressure
operation can be increased with respect to the low band frequency, and the characteristic in the
low band is deteriorated. It can compensate.
[0010]
Heretofore, various techniques have been proposed for improving the low frequency response in
a unidirectional condenser microphone. In the first technique, diaphragms are provided on the
front side and the back side, and each diaphragm is used as an acoustic terminal. More
specifically, two unidirectional microphone units are back-to-back to construct an acoustically
coupled structure. According to the microphone unit having such a structure, the distance
between the front and rear acoustic terminals is twice that of one microphone unit, and thus the
microphone unit is often used for a relatively large microphone unit. Since the distance between
the front and rear acoustic terminals is long, it is difficult to obtain good directional frequency
characteristics up to high frequencies.
[0011]
The second technique for improving low frequency response in a unidirectional condenser
microphone consists of acoustically connecting an air chamber with an acoustic resistance
attached to the air inlet to the back air chamber of the microphone unit. is there. In the case of
the structure of the conventional example shown in FIGS. 5 to 7, an air chamber is provided on
the back side of the insulating base 5 and this air chamber is in communication with the air
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chamber 6.
[0012]
As a conventional example corresponding to the said 2nd technique, the invention of patent
document 1 can be mentioned, for example. The invention described in Patent Document 1 can
be described according to the conventional example shown in FIGS. 5 to 7. In the insulating base
5, the through holes 51 are formed concentrically at intervals on concentric circles, and An
acoustic resistance material is disposed in the hole 51, and a back air chamber communicating
with the air chamber 6 is provided on the back side of the acoustic resistance material. Also, on
the back side of the acoustic resistance material, a disc capable of changing the degree of
polymerization of the insulating base 5 with the through holes 51 by changing the rotational
position is disposed, and the rotational position of the disc is changed. The acoustic resistance
value of the acoustic resistance material can be changed.
[0013]
Japanese Utility Model Application Publication No. 6-46158
[0014]
According to the invention described in Patent Document 1, uni-directionality is achieved by
varying the acoustic resistance between the air chamber behind the fixed electrode and the back
air chamber formed on the back side of the acoustic resistance material. The low frequency
response of the condenser microphone can be adjusted to the optimum position.
Further, as in the first technique for improving the frequency response in the low frequency
range, it is possible to avoid an increase in the distance between the front and rear acoustic
terminals, so that the unidirectional frequency response characteristic is excellent in the high
frequency region. Can be obtained. The aforementioned "proximity effect" can also be improved.
[0015]
However, according to the invention described in Patent Document 1, it is necessary to adjust the
acoustic resistance of the acoustic resistance material by providing a compression degree
adjustment mechanism of the acoustic resistance material in addition to the rotational position
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adjustment mechanism of the rotary plate. Is complicated and the adjustment is also
troublesome.
[0016]
The present invention further improves the invention described in Patent Document 1, that is, to
obtain a condenser microphone unit and a condenser microphone that can be easily configured,
easily adjusted, and can obtain good low frequency response characteristics. With the goal.
[0017]
The present invention is a unidirectional microphone with a diaphragm that receives and vibrates
a sound wave, a fixed electrode facing a diaphragm and a thin air layer, and a back air chamber
formed at the back of the fixed electrode. A second air chamber in communication with the back
air chamber through at least one of the plurality of holes. The most important feature is what you
are doing.
[0018]
With a relatively simple structure in which an acoustic terminal for opening the back air chamber
to the outside is constituted by a plurality of holes, and a second air chamber communicating
with the back air chamber through at least one of the holes is provided. It is possible to improve
the front frequency response characteristics of the low frequency without impairing the
directional frequency response characteristics of the low frequency region.
The frequency response in the 180 degree direction was also improved.
That is, the proximity effect can be reduced, and good characteristics can be obtained as a
unidirectional microphone array.
[0019]
Hereinafter, embodiments of a condenser microphone unit and a condenser microphone
according to the present invention will be described with reference to the drawings.
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The same components as those of the conventional example described above are denoted by the
same reference numerals.
[0020]
In FIG. 1, internal components such as a diaphragm holding ring 2, a diaphragm 3, a spacer 9, a
fixed electrode 4, an air chamber 6, and an insulating base 5 are incorporated in a tubular unit
case 1. The front end (left end in FIG. 1) of the unit case 1 is an inward flange 11, and the
diaphragm holding ring 2 is pressed against the inner surface of the inward flange 11. A
diaphragm-like diaphragm 3 made of a thin film is attached to the back side of the diaphragm
holding ring 2 with an appropriate tension applied. A spacer 9 made of a ring-shaped thin plate
is disposed on the outer peripheral edge portion of the back surface side of the diaphragm 3, and
the fixed electrode 4 is disposed on the back surface side of the spacer 9.
[0021]
The outer shape of the insulating base 5 is formed in the same manner as the inner surface of the
unit case 1 and, similarly to the insulating base in the conventional example shown in FIG. It is
done. A step 54 is formed in a portion corresponding to the bottom of the recess 53, and another
recess 55 is formed on the inner circumferential side following the step 54. The fixed electrode 4
is dropped into the recess 53 and is in contact with the step 54. The air chamber 6 is formed by
the recess 55 whose front side is divided by the fixed electrode 4 and has a predetermined
volume. The air chamber 6 is packed with, for example, a sponge. At the open rear end of the unit
case 1, an appropriate pressing member for preventing the falling off of the internal components
including the insulating base 5 and pressing the internal components toward the front side of the
unit case 1 is provided. It is fitted.
[0022]
The insulating base 5 is pushed forward by the pressing member, and the step 54 pushes the
fixed electrode 4 forward, and the fixed electrode 4 moves the spacer 9, the diaphragm 3 and the
diaphragm holding ring 2 in this order to the front I'm pushing towards. Since the diaphragm
holding ring 2 contacts the inward flange 11 of the unit case 1, the built-in component is held in
the unit case 1 with an appropriate pressing force. A step between the jetty 52 and the step 54 is
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set such that a gap is generated between the jetty 52 of the unit case 1 and the diaphragm 3.
Thus, a thin air layer having a minute gap corresponding to the thickness of the spacer 9 is
formed between the diaphragm 3 and the fixed electrode 4.
[0023]
The diaphragm 3 and the fixed electrode 4 constitute a capacitor by the presence of a thin air
layer therebetween. When the diaphragm 3 receives a sound wave and vibrates, the capacity of
the capacitor changes, and the change in the capacity is converted into a change in voltage,
which is used as the output of the microphone unit. The fixed electrode 4 constitutes one of the
electrodes of the capacitor, and this electrode is in communication with the diaphragm holding
ring 2 and the unit case 1. The fixed electrode 4 constituting the other electrode of the capacitor
is connected to a cylindrical extraction electrode 7 fixed through the central portion of the
insulating base 5. The lead-out electrode 7 is electrically connected to an FET which is a main
component of an impedance converter mounted on a circuit board (not shown) or the like.
[0024]
The inner peripheral side of the inward flange 11 is opened at the front end of the unit case 1 to
be an entrance for sound waves from the front side of the diaphragm 3. Although not shown in
the drawings, the fixed electrode 4 is provided with an appropriate through hole. An appropriate
number of through holes 51 are also formed in the insulating base 5, and the through holes 51
constitute a rear acoustic terminal. Therefore, the back surface of the diaphragm 3 is in
communication with the through hole of the fixed electrode 4, the air chamber 6, and the
through hole 51 of the insulating base 5. The configuration described so far is almost the same
as the configuration of the conventional example shown in FIG. The characteristic configuration
of the present invention will be described below.
[0025]
In FIG. 1, the plurality of through holes 51 constituting the acoustic terminal open the back air
chamber 6 to the outside, and one through hole of the plurality of through holes 51 is a second
air chamber 10. It is in communication with In other words, the back air chamber 6 and the
second air chamber 10 communicate with each other through one of the through holes 51. The
second air chamber 10 communicates with the back air chamber 6 and also communicates with
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the thin air layer between the diaphragm 3 and the fixed electrode 4 through the through hole of
the fixed electrode 4. The second air chamber 10 is a bottle-like member sealed except for the
insertion portion 12 at the tip end, and the insertion portion 12 is inserted into one through hole
51. Therefore, the volume of the back air chamber 6 is expanded by the volume of the second air
chamber 10 through the one through hole 51 and the insertion portion 12, and the other
through holes 51 excluding the one through hole 51 are opened. It is done.
[0026]
The volume of the second air chamber 10 is appropriately set according to the design
specification of the basic configuration of the condenser microphone unit including the
diaphragm 3, the fixed electrode 4, the insulating base 5, the back air chamber 6 and the like. In
order to set the volume of the second air chamber 10, for example, the tip of the cylinder of the
syringe is inserted into the through hole 51 in the trial production stage, and the insertion
amount of the plunger to the cylinder is changed to change the volume of the cylinder. The
frequency response was measured while varying the volume of the second air chamber 10
substantially. In the example, a good frequency response characteristic could be obtained by
setting it to about 2 cc.
[0027]
In the embodiment shown in FIG. 1, the through holes 51 constituting the rear acoustic terminals
are formed at 12 places, and the second air chamber 10 is connected to one of them. The
chambers 10 may be connected. Alternatively, the second air chambers 10 may be individually
connected to the plurality of through holes 51, respectively. The through hole 51 to which the
second air chamber 10 is not connected may be opened as it is or may be covered with an
acoustic resistance material as appropriate.
[0028]
FIG. 2 shows the acoustic equivalent circuit of the above embodiment. The elements etc. which
comprise an equivalent circuit are defined as follows. P1: Sound pressure of sound wave coming
from the front P2: Sound pressure of sound wave coming from the rear acoustic terminal m0:
Mass of the diaphragm 3 s0: Stiffness of the diaphragm 3 r0: Acoustic resistance of the front of
the diaphragm 3 r1: Rear Acoustic resistance of acoustic terminal s1: Stiffness of air chamber 6
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r2: Acoustic resistance of communication part between air chamber 6 and second air chamber 10
s2: Stiffness of second air chamber 10
[0029]
Comparing the equivalent circuit shown in FIG. 2 with the equivalent circuit of the prior art
shown in FIG. 8, the stiffness s1 of the air chamber 6 corresponds to the acoustic resistance r2 of
the communication portion between the air chamber 6 and the second air chamber 10, The
difference is that the series connection of the stiffnesses s2 of the two air chambers 10 is added
in parallel. The frequency response characteristic of the unidirectional directivity condenser
microphone unit according to the present embodiment to which the acoustic resistance r2 and
the stiffness s2 are added is shown in FIG. The sound waves are shown separately when entering
at an angle of 0 °, ie from the front, at an angle of 90 °, ie at a side, and at an angle of 180 °,
ie from behind.
[0030]
As apparent from the comparison between the characteristics shown in FIG. 4 and the
characteristics shown in FIG. 9, the frequency response from the front is improved in the low
frequency range, and the frequency response from the 180 degree direction is reduced. As the
characteristics have been improved. This also eliminates the "proximity effect" described above.
The middle and high frequencies are almost the same as in the conventional example. Therefore,
the low frequency response can be improved without impairing the mid to high frequency
response characteristics. A condenser microphone unit having such excellent characteristics can
be obtained with a relatively simple configuration in which the second air chamber is provided,
and adjustment is easy.
[0031]
Next, a second embodiment of the present invention will be described. FIG. 3 shows the main part
of the second embodiment. In this embodiment, the second air chamber 10 has a plurality of
communication passages 14, and at least one of the plurality of communication passages 14 is
connected to one of the through holes 51 of the insulating base 5 via the pipe 15. It is configured
to be able to The pipe 15 is flexible and has a length sufficient to connect to the through hole 51,
and one of a plurality of through holes 51 is selected and inserted into the through hole 51. It is
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configured to be able to. The other communication passage 14 of the second air chamber 10 may
be connected to the other through hole 51 as well. The communication passage 14 not
connected to the through hole 51 is configured to close its tip end with an appropriate closing
member 16.
[0032]
According to the embodiment shown in FIG. 3, the same effect as that of the first embodiment
can be obtained, and any communication passage is selected from the plurality of communication
passages 14 possessed by the second air chamber 10 Since it can be connected to any one of the
plurality of through holes 51 that the insulating base 5 has, it is possible to most effectively
improve the low side frequency response without impairing the middle to high frequency
response characteristics. It can be adjusted as you can.
[0033]
By incorporating the condenser microphone unit according to the present invention into the
microphone case and attaching a cable connector etc. to the microphone case as appropriate, it is
possible to construct a unidirectional microphone having the effects as described above. .
[0034]
It is a longitudinal cross-sectional view which shows 1st Example of the unidirectional directivity
condenser microphone unit which concerns on this invention.
It is an acoustic equivalent circuit schematic of the said Example.
It is a longitudinal cross-sectional view which shows the principal part of 2nd Example of the
unidirectional directivity condenser microphone unit which concerns on this invention. It is a
graph which shows the frequency response characteristic of the microphone unit of the said 1st
Example. It is a longitudinal cross-sectional view which shows the example of the conventional
unidirectional condenser microphone unit. It is a longitudinal cross-sectional view which shows
the insulation base in the said prior art example. It is a bottom view of the above-mentioned
insulating base. It is an acoustic equivalent circuit schematic of the said conventional condenser
microphone unit. It is a graph which shows the frequency response characteristic of the said
conventional microphone unit.
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Explanation of sign
[0035]
1 unit case 2 diaphragm holding ring 3 diaphragm 4 fixed electrode 5 insulation base 6 back air
chamber 9 spacer 10 second air chamber 12 insertion portion 51 through hole
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