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JP2013046194

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DESCRIPTION JP2013046194
Abstract: A unidirectional microphone with high directional frequency response and high
sensitivity. SOLUTION: In a unidirectional microphone including an electrostatic microphone unit
10 having a front acoustic terminal 10a and a rear acoustic terminal 10b, a part or all of a tube
wall is an opening having an open front end. A cylindrical acoustic resistance tube 30 formed of
a predetermined acoustic resistance material 31 is provided, and the microphone unit 10 is
housed inside the acoustic resistance tube 30 with the front acoustic terminal 10a facing the
front end opening 30a, and the rear A sound wave is guided to the acoustic terminal 10b through
the acoustic resistance member 31 provided in the acoustic resistance cylinder 30, and no sound
wave enters the rear acoustic terminal 10b from the rear end opening 30b of the acoustic
resistance cylinder 30 on the rear acoustic terminal 10b side. Thus, the rear end opening 30b of
the acoustic resistance cylinder 30 is closed by a predetermined member, and the inner
circumferential surface of the acoustic resistance cylinder 30 and the outer circumferential
surface of the microphone unit 10 During the, provide a gap G of the low-frequency sound waves
communicating between the front acoustic chamber A1 and rear acoustic chamber A2 of the
possible acoustic resistance cylinder 30 passes. [Selected figure] Figure 1
Unidirectional microphone
[0001]
The present invention relates to unidirectional microphones, and more particularly, to techniques
for improving directional frequency response and enhancing sensitivity.
[0002]
In a unidirectional condenser microphone, a baffle is added around the microphone unit in order
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to increase the distance between the front acoustic terminals and the rear acoustic terminals to
improve the sensitivity. (Refer patent document 1, 2).
[0003]
According to this method, the sensitivity is improved by increasing the diameter of the baffle, but
on the other hand, diffraction effects occur in a low frequency band, which may degrade the
directional frequency response.
[0004]
Apart from this, if an acoustic tube as used in a narrow directional microphone is attached to the
front acoustic terminal side of the microphone unit, the distance between the acoustic terminals
will be equivalently increased, and high sensitivity is obtained. be able to.
[0005]
However, when the acoustic resistance attached to the opening of the tube wall of the acoustic
tube is high like a narrow directional microphone, the directivity becomes narrow directivity in a
high frequency band.
Moreover, since it becomes equivalent to the fact that a short tube is connected to the front
acoustic terminal, resonance occurs in the acoustic capacity by the internal volume of the
acoustic tube and the acoustic mass of the acoustic tube, and the directional frequency response
is degraded due to this. .
[0006]
Japanese Utility Model Application Publication No. 6-58696 Japanese Utility Model Application
Publication No. 6-77 394
[0007]
Therefore, an object of the present invention is to provide a unidirectional microphone having a
high directional frequency response and high sensitivity.
[0008]
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In order to solve the above problems, the present invention is directed to a unidirectional
microphone including an electrostatic microphone unit having a front acoustic terminal and a
rear acoustic terminal, the opening having an open front end, and The microphone unit is housed
with the front acoustic terminal directed to the front end opening, in the inside of the acoustic
resistance cylinder, including a cylindrical acoustic resistance cylinder whose part or all is
formed of a predetermined acoustic resistance material. A sound wave is guided to the rear
acoustic terminal of the microphone unit through the acoustic resistance material provided in the
acoustic resistance cylinder, and a rear end opening of the acoustic resistance cylinder on the
rear acoustic terminal side is connected to the rear acoustic terminal The rear end opening of the
acoustic resistance cylinder is closed by a predetermined member so that sound waves do not
enter, and the inner peripheral surface of the acoustic resistance cylinder and the outside of the
microphone unit Between the surface and the surface, a low-frequency sound wave can pass, and
a gap communicating the front acoustic chamber and the rear acoustic chamber in the acoustic
resistance cylinder partitioned by the microphone unit is provided. And
[0009]
In the present invention, as the acoustic resistance material, an acoustic resistance material
having a low acoustic resistance without the directivity of the microphone unit becoming a
narrow directivity is used.
[0010]
According to the present invention, the front end of the acoustic resistance tube on the front
acoustic terminal side of the microphone unit is opened, and a sound wave is guided to the rear
acoustic terminal of the microphone unit through the acoustic resistance material provided in the
acoustic resistance cylinder. Since the rear end opening of the acoustic resistance cylinder is
closed by a predetermined member so that the sound wave does not enter the rear acoustic
terminal from the rear end opening of the terminal-side acoustic resistance cylinder, substantially
front acoustics The terminal is extended to the front end side of the acoustic resistance tube, and
operates equivalently to the distance between the acoustic terminals being extended, thereby
enhancing the sensitivity of the unidirectional microphone.
[0011]
In addition, a low frequency sound wave can pass between the inner peripheral surface of the
acoustic resistance cylinder and the outer peripheral surface of the microphone unit, and there is
a gap communicating the front acoustic chamber and the rear acoustic chamber in the acoustic
resistance cylinder. By being provided, the resonance which generate | occur | produces with the
acoustic capacity by the internal volume of an acoustic resistance pipe | tube, and the acoustic
mass of an acoustic resistance pipe | tube can be prevented.
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[0012]
Fig. 2 shows a cross-sectional view of an embodiment of a unidirectional microphone according
to the invention.
The disassembled sectional view of the unidirectional microphone concerning the said
embodiment.
The equivalent circuit schematic of the unidirectional microphone which concerns on the said
embodiment.
(A) Polar pattern figure measured in the state which covered the acoustic resistance pipe | tube
on the microphone unit, (b) The graph which shows the directional frequency response.
As a comparative example, the (a) polar pattern figure measured with the microphone unit singlepiece | unit, the graph which shows the directional frequency response as (b).
[0013]
Next, an embodiment of the present invention will be described with reference to FIGS. 1 to 5,
but the present invention is not limited to this.
[0014]
With reference to FIGS. 1 and 2, the unidirectional microphone 1 according to this embodiment
includes a microphone unit 10, an audio signal output unit 20, and an acoustic resistance tube
30 which is put on the microphone unit 10.
[0015]
The microphone unit 10 is a unidirectional directivity condenser microphone unit having a front
acoustic terminal 10a and a rear acoustic terminal 10b, and has a diaphragm 11 and a fixed
electrode 13 as a counter electrode thereof. It is disposed in a cylindrical, metallic unit case 15 in
a state of being stretched on a support ring (diaphragm ring) 12.
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[0016]
The fixed electrode 13 is disposed on the back side of the diaphragm 11 via a spacer ring (not
shown) in the unit case 15 in a state of being supported by the insulating seat 14 made of
synthetic resin or the like.
An electrode pin 16 is implanted at a substantially central portion of the insulating seat 14.
The electrode pin 16 is electrically connected to the fixed pole 13.
[0017]
In the unidirectional microphone unit 10, the front side of the diaphragm 11 is the front acoustic
terminal 10a, and the rear side of the insulating seat 14 is the rear acoustic terminal 10b.
A sound hole 14a is bored in the insulating seat 14, and although not shown, a similar sound
hole is bored in the fixed pole 13, and sound waves from the rear acoustic terminal 10b are
transmitted through these sound holes. Acts on the back side of the diaphragm 11.
[0018]
The audio signal output unit 20 is also referred to as an output module unit or a power module
unit, and in this embodiment, the circuit board 22, the output transformer 23, the output
connector 24 and the like are accommodated in a cylindrical grip case 21 made of metal. ing.
Although not shown, an FET (field effect transistor) as an impedance converter, an amplifier
circuit, a low cut circuit, and the like are mounted on the circuit board 22.
[0019]
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An insulating cap 26 is disposed on the tip end side of the grip case 21 via a spacer 25 made of a
metal material, and a female connector terminal 27 which is a counterpart of the electrode pin
16 on the microphone unit 10 side in the insulating cap 26. Is provided.
[0020]
Thereby, the fixed pole 13 is connected to the gate electrode of the FET through the electrode
pin 16, the female connector terminal 27 and a wiring member (not shown).
As the output connector 24, a three-pole (3-pin type) connector connected to a phantom power
supply (not shown) is used.
[0021]
The acoustic resistance cylinder 30 is provided with an acoustic resistance material 31 with low
acoustic resistance such that the unidirectional microphone 1 does not have narrow directivity as
its component.
[0022]
As the acoustic resistance material 31 of this type, for example, non-woven fabric JH-1007
(polyester fiber, 70 g / m <2> basis weight, 0.13 mm thickness) made by Japan Byureen Co., Ltd.
is preferably adopted, but in some cases A perforated plate with low acoustic resistance may be
used as in the above-mentioned non-woven fabric in which a large number of fine holes are
formed in a metal plate or the like.
[0023]
The acoustic resistance cylinder 30 may be constituted by the acoustic resistance material 31
alone, but in the case of non-woven fabric, since the strength is insufficient to maintain the
cylindrical form, a support cylinder for a skeleton made of metal or synthetic resin It is
preferable to hold the acoustic resistance material 31 on the support cylindrical body 32 using
the body 32.
[0024]
In this embodiment, as shown in FIGS. 1 and 2, for example, a slit-like side opening 321 is formed
in a part of the tube wall of the support cylindrical body 32 along the axial direction, and this
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side opening 321 is formed. The acoustic resistance material 31 made of non-woven fabric is
attached to the inner surface side of the support cylindrical body 32 so as to cover the above.
[0025]
Although only one side opening 321 is shown in FIGS. 1 and 2, the side openings 321 may be,
for example, 180 ° apart, 120 ° apart or 90 ° apart along the circumferential direction of the
support cylinder 32. It may be provided in a plurality of places at predetermined intervals of.
In this embodiment, the side openings 321 are formed like a grill, and the reference numeral 322
indicates a crosspiece circumferentially extending around the side openings 322.
[0026]
In addition, for example, a plate having side openings on the entire surface, such as a so-called
punching plate or a grid-like plate, in which a large number of circular openings are formed over
the entire surface may be used for the supporting cylindrical body 32. The non-woven acoustic
resistance material 31 is attached to the entire inner surface of the body 32.
[0027]
With the opening on the front end side of the sound resistance cylinder 30 as 30a and the
opening on the rear end side as 30b, the sound resistance cylinder 30 is, as shown in FIG. The
microphone unit 10 is covered in such a manner as to be closed by the spacer 25 and the
insulating cap 26 provided on the front end side of the microphone.
[0028]
Thereby, a front acoustic chamber A1 of a predetermined volume is provided in front of the front
acoustic terminal 10a of the microphone unit 10, and a rear acoustic chamber A2 is provided on
the rear acoustic terminal 10b side. The opening 30a on the front end side of the acoustic
resistance cylinder 30 facing the terminal 10a is an opening whose entire surface is open, and
the opening 30b on the rear end side of the acoustic resistance cylinder 30 is closed as described
above. A sound wave does not enter the rear acoustic terminal 10b from the end opening 30b.
[0029]
As described above, the rear end side opening 30b of the acoustic resistance cylinder 30 is
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closed so that the sound wave does not enter the rear acoustic terminal 10b from the rear end
side opening 30b. Since the section opening 321 is formed over substantially the entire length of
the support cylindrical body 32 and the portion 321a on the rear end side of the side opening
321 is disposed to cover the rear acoustic chamber A2, the rear acoustic terminal 10b is The
sound wave is guided through the acoustic resistance material 31 present in the end portion
321a.
[0030]
Thus, since the front end opening 30a on the front acoustic terminal 10a side of the acoustic
resistance cylinder 30 is opened and the rear end opening 30b on the rear acoustic terminal 10b
is closed, substantially the front acoustic terminal Is extended to the front end side of the
acoustic resistance tube, and operates equivalent to the fact that the distance between the
acoustic terminals is extended, whereby the sensitivity of the unidirectional microphone 1 is
enhanced.
[0031]
Furthermore, in the present invention, a gap that allows low frequency sound waves to pass
between the inner circumferential surface of the acoustic resistance cylinder 30 and the outer
circumferential surface of the microphone unit 10, and communicates the front acoustic chamber
A1 and the rear acoustic chamber A2. G is provided.
The distance between the gaps G may be about 0.2 to 0.3 mm, depending on the diameter of the
microphone unit 10 to be used.
[0032]
The presence of such a gap G makes it possible to prevent the resonance generated by the
acoustic capacity due to the internal volume of the acoustic resistance cylinder 30 and the
acoustic mass of the acoustic resistance cylinder 30, and the directional frequency response is
improved.
[0033]
FIG. 3 shows an equivalent circuit of the unidirectional microphone 1 according to this
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embodiment.
P1 is a front sound source, P2 is a rear sound source, mF and sf are the acoustic mass and air
stiffness of the front acoustic chamber A1, m0, s0 and r0 are the mass of the diaphragm 11,
stiffness and damping resistance, r1 and s1 are rear acoustic terminals Acoustic resistance and
air stiffness to give directivity to 10b, rB, sB are acoustic resistance of the sound wave
introduction port (321a) of the rear acoustic room A2, and air stiffness of the rear acoustic room
A2, rS, mS are acoustics present in the gap G Resistance and air stiffness.
The AC signal source shown in the front acoustic chamber A1 is a sound wave taken in via the
acoustic resistance material 31.
[0034]
4 (a) and 4 (b) show graphs of polar patterns and directional frequency responses measured by
the unidirectional microphone 1 covered with the acoustic resistance tube 30 according to this
embodiment. a) and (b) show graphs of polar patterns and directional frequency responses of the
unidirectional microphones measured with the acoustic resistance tube 30 removed as a
comparative example.
The axial length of the acoustic resistance cylinder 30 provided for this measurement is about 40
mm and the inner diameter is about 26 mm, and the acoustic resistance material 31 used is a
non-woven fabric JH-1007 manufactured by Nippon Byuren.
[0035]
As can be seen from FIGS. 5 (a) and 5 (b), in the case of the comparative example in which the
acoustic resistance tube 30 is removed, it is a response as a normal unidirectional microphone.
[0036]
On the other hand, since the distance between the acoustic terminals is extended by covering the
acoustic resistance cylinder 30, as shown in the directional frequency response of FIG. 4 (b), the
sensitivity is approximately compared to the comparative example. It is improved by 2 dB, and
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the frequency response is also improved especially on the low frequency side.
Also, as shown in the polar pattern of FIG. 4 (a), the directivity is slightly closer to the
hypercardioid.
[0037]
DESCRIPTION OF SYMBOLS 1 Unidirectional microphone 10 Microphone unit 10a Front acoustic
terminal 10b Rear acoustic terminal 11 Diaphragm 13 Fixed pole 20 Audio signal output part 21
Grip case 22 Circuit board 23 Transformer 24 Output connector 30 Acoustic resistance cylinder
30a Acoustic resistance cylinder front end 31 acoustic resistance material 32 support cylinder
321 side opening A1 front acoustic room A2 rear acoustic room G clearance
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