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JP2013172391

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DESCRIPTION JP2013172391
Abstract: In a unidirectional microphone, it is possible to share insulators supporting fixed poles
with microphones having different distances between acoustic terminals. SOLUTION: A
predetermined sound hole 32 of a plurality of sound holes 32 is made acoustic by means of a
predetermined sound hole closing means as a rough adjustment process for an insulating seat 31
in which a plurality of sound holes 32 are bored. In the sound wave passage from the rear
acoustic terminal to the back surface of the diaphragm by applying a predetermined compression
force to the acoustic resistance material 40 by the acoustic resistance adjustment means 50
(adjustment nut 51) as a fine adjustment step. Adjust the acoustic resistance. [Selected figure]
Figure 3
Unidirectional condenser microphone and acoustic resistance adjustment method thereof
[0001]
The present invention relates to a unidirectional condenser microphone and a method of
adjusting the acoustic resistance thereof, and more particularly, to share an insulating seat
(insulator) supporting a fixed pole to a unidirectional condenser microphone having a different
distance between acoustic terminals. It relates to the technology that makes it possible.
[0002]
A unidirectional condenser microphone has a front acoustic terminal for capturing sound waves
from a sound source on the front side of the diaphragm, and a rear acoustic terminal for
capturing sound waves on the back side of the diaphragm, and is bidirectional. The components
are adjusted by acoustic resistance.
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[0003]
The acoustic resistance value on the rear acoustic terminal side is a front acoustic terminal in
addition to the directivity required (for example, cardioid, hypercardioid or supercardioid etc.)
and the stiffness of the air chamber present at the rear of the fixed pole. It is designed based on
the distance between the acoustic terminals of and the rear acoustic terminals (see, in particular,
FIG. 1 of Non-Patent Document 1).
[0004]
In a conventional unidirectional condenser microphone, since the distance between acoustic
terminals is as long as 5 cm or less, a relatively low acoustic resistance value is adopted.
[0005]
On the other hand, in the case of a narrow directional microphone in which an acoustic tube is
attached to the microphone unit, the distance between acoustic terminals at low frequencies may
reach 50 cm.
[0006]
For this reason, the acoustic mass in the acoustic pipe is added to the front surface of the
diaphragm of the condenser element, and the acoustic resistance value on the rear acoustic
terminal side is extremely high in order to obtain unidirectivity such as hypercardioid. There is a
need to.
Not only that, but in order to achieve accurate directivity, it is necessary to make fine
adjustments while maintaining high acoustic resistance.
[0007]
By the way, in the condenser microphone, the fixed pole is supported by an insulator (insulator),
and in uni-directionality, the fixed pole is porous in order to make the sound wave from the rear
acoustic terminal act on the back side of the diaphragm. Since the electrode plate is used, a
sound hole as a sound wave passage is drilled in the insulating seat, and an air chamber is
present between the insulating plate and the fixed pole, the insulating seat is important in
designing the acoustic resistance value. Element.
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[0008]
On the other hand, since the fixed pole is connected to the gate of a FET (field effect transistor)
as an impedance converter through an electrode lead rod inserted into the insulating seat, the
insulating seat has a volume resistivity and a surface resistance. Materials having a high rate
(polycarbonate as an example) are used.
[0009]
Even if the material has such a high resistivity, when the insulating sheet is manufactured by
cutting, the surface resistivity may be lowered by the fact that the surface has small cracks and
small cracks on the surface.
[0010]
According to injection molding, such problems due to cutting hardly occur, but it is required for
ordinary unidirectional condenser microphones having a short distance between acoustic
terminals and narrow directivity condenser microphones having an acoustic tube. The diameter
and the number of sound holes formed in the insulating seat differ from each other in relation to
the acoustic resistance value.
[0011]
Moreover, even if the condenser microphones have the same narrow directivity, the diameter and
the number of the sound holes formed in the insulating seat differ depending on the length of the
acoustic pipe to be used from the relationship with the acoustic resistance value. There is a
considerable cost burden to make a mold for each model.
[0012]
Akio Mizoguchi, "Considerations on Miniaturization of Directional Capacitors and Microphones"
Journal of the Acoustical Society of Japan, Vol. 31, No. 5 (1975)
[0013]
Therefore, an object of the present invention is to make it possible to share insulators (insulators)
that support fixed poles, preferably by injection molding, with microphones having different
distances between acoustic terminals in a unidirectional condenser microphone. .
[0014]
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In order to solve the above problems, the invention according to claim 1 is stretched on a
support ring in a cylindrical unit case having a front acoustic terminal at one end and a rear
acoustic terminal at the other end. A microphone unit in which the diaphragm and the fixed
electrode supported by the insulator are arranged opposite to each other with a predetermined
distance, and the sound from the rear acoustic terminal is placed on the insulator on the back
side of the diaphragm And a sound resistance material formed to cover all of the sound holes,
and a compressive force is applied to the sound resistance material. And the acoustic resistance
adjusting means for making the acoustic resistance variable, wherein the acoustic resistance
material acoustically closes a predetermined sound hole of the sound holes. Sound hole closing
means is provided It is characterized.
[0015]
The invention as set forth in claim 2 is characterized in that, in the above-mentioned claim 1, the
sound hole closing means is made of a non-air-permeable member dottedly provided in a portion
facing the sound hole of the acoustic resistance material. And
[0016]
The invention according to claim 3 is characterized in that, in the above-mentioned claim 2, the
non-air-permeable member is made of a resin material applied or stuck to the acoustic resistance
material.
[0017]
The invention according to claim 4 is characterized in that, in the above-mentioned claim 2, the
non-air-permeable member is made of a heated and melted material of the acoustic resistance
material.
[0018]
The invention according to claim 5 is characterized in that, in any one of the above-mentioned
claims 2 to 4, the non-air-permeable member is formed in the shape of a projection fitted to the
sound hole.
[0019]
In the invention according to claim 6, according to claim 1, the sound hole closing means is made
of a non-air-permeable sheet material disposed between the insulating seat and the acoustic
resistance material, and the non-air-permeable sheet material An opening portion is formed in
the sound resistance member to make sound holes other than the predetermined sound holes
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that are acoustically closed in communication with the sound resistance material.
[0020]
In the invention according to claim 7, according to any one of claims 1 to 6, the acoustic
resistance adjusting means is in contact with the entire back side of the acoustic resistance
material, and the acoustic resistance material between the acoustic seat and the insulating seat. A
disc-shaped adjusting plate for holding the sheet, and pressing means for applying a variable
pressing force to the adjusting plate, wherein the sound wave from the rear acoustic terminal
enters from the peripheral end face of the acoustic resistance material It is characterized.
[0021]
The invention according to claim 8 relates to a method of adjusting acoustic resistance of a
unidirectional condenser microphone, in a cylindrical unit case having a front acoustic terminal
at one end and a rear acoustic terminal at the other end, It has a microphone unit in which a
diaphragm attached to a support ring and a fixed pole supported by an insulating seat are
disposed opposite to each other with a predetermined distance, and the sound from the rear
acoustic terminal is transmitted to the insulating seat. A plurality of sound holes leading to the
back side of the diaphragm, and an acoustic resistance material formed on the back side of the
insulating seat so as to cover all the sound holes, and the acoustic resistance. In the acoustic
resistance adjustment method of a unidirectional directivity condenser microphone provided
with an acoustic resistance adjustment means for applying a compressive force to a material to
make its acoustic resistance variable, as a rough adjustment step, a predetermined one of the
sound holes is provided. Sound hole of After acoustically closing by a predetermined sound hole
closing means, a predetermined compressive force is applied to the acoustic resistance material
by the acoustic resistance adjusting means as a fine adjustment step, so that the rear acoustic
terminal is applied to the back surface of the diaphragm. It is characterized in that the acoustic
resistance present in the sound wave passage is adjusted.
[0022]
The invention according to claim 9 is characterized in that, in the above-mentioned claim 8, as
the sound hole closing means in the rough adjustment step, a curable resin is enclosed in the
sound hole.
[0023]
In the invention according to claim 10, in the above-mentioned claim 8, as the sound hole closing
means in the rough adjustment step, a non-air-permeable member dottedly provided in a portion
facing the sound hole of the acoustic resistance material. It is characterized by using.
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[0024]
The invention according to claim 11 uses the non-air-permeable sheet material disposed between
the insulating seat and the acoustic resistance material as the sound hole closing means in the
rough adjustment step. It is characterized.
[0025]
According to the present invention, the acoustic resistance value on the rear acoustic terminal
side is roughly determined by acoustically closing a predetermined sound hole of the plurality of
sound holes drilled in the insulating seat by the sound hole closing means. The acoustic
resistance value on the rear acoustic terminal side can be finely adjusted by applying a
predetermined compression force to the acoustic resistance material by the acoustic resistance
adjustment means.
Therefore, if the insulating seat is designed based on the specifications for a conventional
unidirectional directivity microphone with a short distance between acoustic terminals, the
insulating seat also applies to a narrow directional unidirectional directivity microphone with a
long distance between acoustic terminals. It is possible to
[0026]
Sectional drawing which shows one Embodiment of the microphone unit with which the
unidirectional directivity condenser microphone of this invention is provided.
The rear view which looked at the above-mentioned microphone unit from the back side of an
insulation seat.
The disassembled perspective view which shows the structure by the side of the rear acoustic
terminal of the said microphone unit.
(A)-(c) The side view which shows three types of unidirectional directivity condenser
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microphones from which the distance between acoustic terminals differs.
The rear view which shows the insulation seat in which the sound hole was closed for the narrow
directivity capacitor microphone of FIG.4 (c).
(A) A rear view showing the insulating seat in which the sound hole is closed by the acoustic
resistance material, (b) a front view showing the sound resistance material having the sound hole
closing means, and (c) a sectional view taken along the line A-A.
(A) Rear view showing the insulating seat in which the sound hole is closed by the non-airpermeable sheet material, (b) front view showing the non-air-permeable sheet material, (c) front
view showing the acoustic resistance material, (d) Sectional drawing which shows the state which
affixes non-air-permeable sheet material to acoustic resistance material.
The graph which shows (a) polar pattern at the time of fine adjustment (at the time of 0 rotation)
by the adjustment nut of an acoustic resistance material, (b) the directivity frequency response.
The graph which shows the (a) polar pattern at the time of fine adjustment (at the time of 0.5
rotation) by the adjustment nut of an acoustic resistance material, (b) that pointing frequency
response.
The graph which shows the (a) polar pattern at the time of fine adjustment (at the time of 1.0
rotation) by the adjustment nut of an acoustic resistance material, (b) the directivity frequency
response.
The graph which shows the (a) polar pattern at the time of fine adjustment (at the time of 1.5
rotations) by the adjustment nut of an acoustic resistance material, (b) the directivity frequency
response.
The graph which shows the (a) polar pattern at the time of fine adjustment (at the time of 2.0
rotations) by the adjustment nut of an acoustic resistance material, (b) the directivity frequency
response.
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[0027]
Next, embodiments of the present invention will be described with reference to FIGS. 1 to 12, but
the present invention is not limited thereto.
[0028]
First, referring to FIG. 4, according to the present invention, as shown in FIG. 4 (a), a
unidirectional condenser microphone 1A of a normal form having a distance between acoustic
terminals of, for example, 7.9 mm, FIG. 4 (b). A middle-sized narrow directional condenser
microphone 1B having an acoustic tube 2B as shown in FIG. 4 and having a distance between
acoustic terminals of, for example, 220.4 mm, an acoustic tube 2C as shown in FIG. A unidirectional condenser microphone such as a long-sized narrow directivity condenser microphone
1C having a distance of, for example, 433.4 mm (hereinafter simply referred to as "microphone").
), But all have the microphone unit 1 shown in FIG.
[0029]
The microphone unit 1 includes a cylindrical unit case 10 made of a metal material such as a
brass alloy.
In FIG. 1, the front opening portion on the left side of the unit case 10 is a front acoustic terminal
10a directed to the sound source side (not shown) at the time of sound collection, and the rear
opening portion on the right side is a rear acoustic terminal 10b.
[0030]
In an actual device, the unit case 10 is housed in a microphone case (not shown), and in most
cases, the microphone case is provided with an opening for receiving a sound wave from the
rear.
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Further, in the narrow directional microphones 1B and 1C shown in FIGS. 4B and 4C, the acoustic
tubes 2B and 2C are directly connected to the front acoustic terminal 10a of the microphone unit
1.
[0031]
In the unit case 10, the diaphragm 20 stretched on the support ring (diaphragm ring) 21 and the
fixed electrode 30 supported on the insulating seat 31 are disposed opposite to each other via a
spacer member (not shown). An electrostatic-type acoustoelectric transducer is housed.
[0032]
For the diaphragm 20, a thin film of synthetic resin having a metal deposition film on one side is
used. For the fixed electrode 30, for example, an electrode plate made of an aluminum material is
used. In the case of back electret type, the fixed electrode 30 is electreted. The dielectric films are
fused together.
In the case of the film electret type, the electret dielectric film is integrally fused to the
diaphragm 20 side.
[0033]
A material (polycarbonate as an example) having high volume resistivity and surface resistivity is
used for the insulating seat 31.
The insulating seat 31 may be manufactured by cutting, but is preferably manufactured by
injection molding in order to maintain a high surface resistivity.
[0034]
A porous plate is used for the fixed electrode 30 and a plurality of sound wave passages are used
for the insulating seat 31 in order to make the sound wave from the rear acoustic terminal 10 b
act on the back side of the diaphragm 20 (the side facing the fixed electrode 30). A sound hole
32 as a hole is bored.
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[0035]
In addition, an electrode lead rod 34 is inserted through the central portion of the insulating seat
31.
The electrode lead rod 34 is electrically connected to the fixed pole 30 via a wiring member (not
shown).
[0036]
A female screw 10c is formed on the inner peripheral surface of the rear opening of the unit case
10, and the acoustoelectric transducer including the diaphragm 20 and the fixed pole is insulated
by the lock ring 35 having an external thread screwed with this. It is pressed from the back side
through the seat 31 and is firmly fixed to the stopper ring 11 provided on the front opening side
of the unit case 10.
[0037]
When the unit case 10 is made of, for example, an aluminum material which is easily plastically
deformed, the rear surface of the insulating seat 31 is formed by curling the end edge of the rear
opening end inward instead of the lock ring 35 and caulking. It may be pressed.
[0038]
With reference to FIG. 2 and FIG. 3 together, on the back surface 31 a side (anti-fixed electrode
support surface side) of the insulating seat 31, a compressive force is applied to the acoustic
resistance material 40 and the acoustic resistance material 40 and the acoustic resistance value
thereof And an acoustic resistance adjusting means 50 for making the variable.
[0039]
In this embodiment, an air chamber 33 having a predetermined volume of a concave portion is
formed on the fixed electrode support surface side of the insulating seat 31, and although not
shown, the air chamber 33 is also made of, for example, a felt material Acoustic resistance
material may be accommodated.
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[0040]
As the sound resistance material 40, a sponge material having air permeability, a resin sheet, a
non-woven fabric, or the like is used, and is formed in a disk shape having a predetermined
thickness so as to cover all the sound holes 32.
The acoustic resistance material 40 is compressed by the acoustic resistance adjusting means 50.
Preferably, the acoustic resistance material 40 is preferably compression-molded in advance at a
predetermined compression rate.
[0041]
In this embodiment, an adjustment nut 51 that covers the entire surface on one side of the
acoustic resistance material 40 is used as the acoustic resistance adjustment means 50.
[0042]
In order to attach the adjustment nut 51, a male screw cylinder 36 which is screwed with the
female screw hole 52 of the adjustment nut 51 is planted at the central portion on the back side
of the insulating seat 31.
Further, a hole 41 through which the male screw cylinder 36 is inserted is also formed in the
acoustic resistance material 40.
The electrode drawing rod 34 is inserted into the male screw cylinder 36.
[0043]
As described above, since the acoustic resistance material 40 is sandwiched between the
insulating seat 31 and the adjustment nut 51, sound waves enter the acoustic resistance material
40 from the peripheral end face 40a, and higher acoustic resistance is obtained. It is preferable
for obtaining.
[0044]
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A plurality of sound holes 32 are provided in the insulating seat 31. However, in order to enable
the insulating seat 31 to be shared with the microphones 1A, 1B, and 1C shown in FIGS. 4A to
4C, for example, The number is set to be applicable also to the unidirectional microphone 1A of
the normal form of FIG. 4 (a) in which the required acoustic resistance on the rear acoustic
terminal 10b side is the lowest.
[0045]
In this embodiment, twelve sound holes 32 having a diameter of 1 mm are formed in the
insulating seat 31 having an outer diameter of 24 mm.
The sound holes 32 preferably have the same diameter to adjust the acoustic resistance, but the
arrangement need not be uniform.
[0046]
In the present invention, when adjusting the acoustic resistance, the predetermined sound hole
32 is closed to perform rough adjustment, and the acoustic resistance material 40 is compressed
to perform fine adjustment.
[0047]
As an example, among the 12 sound holes 32, in the coarse adjustment step, in the case of the
microphone 1A of the normal form in FIG. 4A, 1 to 3 sound holes are closed, and the narrow
pointing in FIG. In the case of the middle microphone 1B of the sex, the nine sound holes are
closed, and in the case of the narrow directivity long microphone 1C of FIG. 4C, the ten sound
holes are closed.
FIG. 5 shows a state in which ten sound holes are closed and two sound holes are left as effective
(sound holes closed by black circles).
[0048]
The sound holes 32 may be closed by, for example, injection of epoxy resin or the like, by tape
attachment or the like, but a first sound hole closing means preferably adopted in the present
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invention will be described with reference to FIG.
[0049]
As shown in FIG. 6 (b), the first sound hole closing means is composed of non-air-permeable
members 42 provided in a dotted manner in a portion facing the sound holes 32 of the acoustic
resistance material 40.
For example, as shown in FIG. 5, if ten sound holes are closed and two sound holes are left as
effective, the non-air-permeable member 42 corresponds to each part of the sound holes shown
by black circles in FIG. Provided at 10 locations.
[0050]
Thus, by arranging the acoustic resistance material 40 having the non-air-permeable member 42
on the back surface 31 a side of the insulating seat 31, as shown in FIG. 32 is closed by the nonair-permeable member 42, and the two sound holes 32 indicated by solid-line circles are in
communication with the acoustic resistance material 40.
[0051]
The non-air-permeable member 42 may be formed of a resin material applied or stuck to the
acoustic resistance material 40, and when the acoustic resistance material 40 is made of a
sponge material or a resin sheet having air permeability, A portion may be heated and melted to
be in a non-vented closed state.
[0052]
Further, as shown in FIG. 6C, it is preferable that the non-air-permeable member 42 is formed in
the shape of a protrusion fitted to the sound hole 32.
According to this, when the adjustment nut 51 is rotated to compress the acoustic resistance
material 40, it is possible to prevent positional deviation due to the rotation of the acoustic
resistance material 40.
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[0053]
Next, with reference to FIG. 7, the second sound hole closing means preferably adopted in the
present invention will be described.
[0054]
The second sound hole closing means is made of the non-air-permeable sheet material 60 shown
in FIG. 7 (b).
The non-air-permeable sheet material 60 has substantially the same diameter as the acoustic
resistance material 40 shown in FIG. 7C, and as shown in FIG. 7D, one side of the acoustic
resistance material 40 (the opposite surface to the insulating seat 31) And the acoustic resistance
material 40 is disposed on the back surface 31 a side of the insulating seat 31.
The state is shown in the rear view of FIG. 7 (a).
[0055]
Although the non-air-permeable sheet material 60 covers the sound hole 32 to be closed, the
non-air-permeable sheet material 60 includes an opening 61 that brings the other sound holes
32 into communication with the acoustic resistance material 40.
[0056]
For example, as shown in FIG. 5, if ten sound holes shown by black circles are closed and two
sound holes shown by white circles are left as effective, the central portion of non-air-permeable
sheet material 60 is An elliptical opening 61 is provided so as to internally include the two
illustrated white circle sound holes.
[0057]
In the example of FIG. 7, the two sound holes 32 communicating with the acoustic resistance
material 40 are included in the elliptical opening 61, but the opening 61 is formed of, for
example, the acoustic resistance material 40. It may be individually provided in units of one of
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the communicating sound holes.
Alternatively, the non-air-permeable sheet material 60 may be a heat-sealable film material and
heat-sealed in advance to one side of the acoustic resistance material 40.
[0058]
In any case, according to the first and second sound hole closing means, each time the insulating
seat 31 is shared with, for example, the unidirectional condenser microphones shown in FIGS. 4
(a) to 4 (c), Compared to the case where the predetermined sound hole 32 is sealed with a resin
material or the like, the productivity can be enhanced, which is preferable.
[0059]
Next, a narrow directivity long microphone 1C shown in FIG. 4C (as a rough adjustment, as
shown in FIG. 5, a configuration in which ten sound holes are closed in advance and two sound
holes are left as effective) 12 to 12 show polar patterns when the acoustic resistance value of the
acoustic resistance material 40 is finely adjusted by the adjustment nut 51 as the acoustic
resistance adjustment means 50 and directional frequency response characteristics (each figure
Polar pattern at 100 Hz)).
[0060]
In this example, as the acoustic resistance material 40, a material obtained by compressing a
sponge material (product number HR-50) manufactured by Bridgestone Corp. in advance to 1/5
(compression ratio: 1/5) is used.
Further, the acoustic resistance member 40 is axially compressed by 0.2 mm (about 4%
equivalent) every 0.5 rotation (180 ° rotation) of the adjustment nut 51.
[0061]
First, FIGS. 8A and 8B show that the compression force of the adjustment nut 51 on the acoustic
resistance material 40 is substantially "0" (0.0 rotation, compression ratio remains at 1/5). The
polar pattern of and the directional frequency response characteristic are shown.
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[0062]
Next, in FIGS. 9A and 9B, the adjustment nut 51 is rotated by 0.5 rotation (180 ° rotation), and
the compression ratio of the acoustic resistance material 40 is 1⁄5 to 1⁄6 at 0.0 rotation. 25
shows polar patterns and directional frequency response characteristics when .25.
[0063]
Next, in FIGS. 10 (a) and 10 (b), the adjustment nut 51 is rotated once (360 ° rotation), and the
compression ratio of the acoustic resistance material 40 is 1 / 6.25 to 1/8 at 0.5 rotation. The
polar pattern when making it into .33 and the directional frequency response characteristic are
shown.
[0064]
Next, in FIGS. 11A and 11B, the adjustment nut 51 is rotated 1.5 turns (540 ° rotation), and the
compression ratio of the acoustic resistance material 40 is 1 / 8.33 to 1 at 1.0 rotation. The polar
pattern when it is referred to as /12.5 and the directional frequency response characteristic are
shown.
[0065]
Next, in FIGS. 12A and 12B, the adjustment nut 51 is rotated 2.0 rotations (720 ° rotation), and
the compression ratio of the acoustic resistance material 40 is 1 / 12.5 to 1 at 1.5 rotations. The
polar pattern when it is set to /25.0 and the directional frequency response characteristic are
shown.
[0066]
As can be seen from the polar patterns of FIGS. 8A to 12A, as the compressive force of the
acoustic resistance material 40 is increased, patterns close to bi-directionality (FIG. 8A) are
unidirectional. Since the pattern (FIGS. 9A to 10A) changes continuously to a pattern close to no
directivity, stopping rotation of the adjust nut 51 at the desired pattern will match the pattern.
The acoustic resistance value can be obtained.
[0067]
In the narrow directivity long microphone 1C having a distance of 433.4 mm between the
acoustic terminals shown in FIG. 4C, when the optimum acoustic resistance value is verified, the
figure shows the case where the adjust nut 51 is rotated by 0.5. In the directional frequency
response of 9 (b), since the amplitude at 100 Hz is almost the same at 90 ° and 180 °, the
acoustic resistance value when the adjust nut 51 is rotated 0.5 is a standard As the adjustment
03-05-2019
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nut 51 is tightened or loosened around 0.5 rotation, work is performed to find the optimum
value.
[0068]
As described above, according to the present invention, the acoustic seat 31 is provided with the
required number of sound holes 32 having the lowest acoustic resistance on the side of the rear
acoustic terminal 10b. The acoustic resistance value on the side of the rear acoustic terminal 10b
is roughly adjusted by acoustically closing the predetermined sound hole 32 by the sound hole
closing means (preferably the first and second sound hole closing means 42, 60) Then, a
predetermined compressive force is applied to the acoustic resistance material 40 by the acoustic
resistance adjustment means 50 (the adjustment nut 51 as an example) to finely adjust the
acoustic resistance value on the rear acoustic terminal side. If the insulating seat 31 is designed
based on the specifications of the ordinary unidirectional capacitor microphone 1A of FIG. 4 (a)
having a short distance between acoustic terminals, for example, the distance between the
acoustic terminals 31 is long. b), It becomes possible to apply to the narrow directivity
unidirectional condenser microphone c).
[0069]
1A to 1C Unidirectional microphone 1 Microphone unit 10 Unit case 11 Stopper ring 20
Diaphragm 21 Support ring (diaphragm ring) 30 Fixed pole 31 Insulating seat (insulator) 32
Sound hole 40 Sound resistance material 40a Peripheral end surface of sound resistance material
42 Sound hole closing means 50 Sound resistance adjusting means 51 Adjustment nut 60 Nonair-permeable sheet material 61 Opening
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