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JP2009182756

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DESCRIPTION JP2009182756
An object of the present invention is to provide a narrow directional microphone which can
change its directivity continuously by electrical switch operation. SOLUTION: The inside of an
acoustic tube 2 is divided into a front acoustic capacity chamber 21 and a rear acoustic capacity
chamber 22 by a unidirectional microphone unit 3, and the microphone unit 3 is disposed on the
side of the rear acoustic capacity chamber 22 of the acoustic tube 2. In the narrow directional
microphone provided with the rear acoustic inlet 24 for the rear acoustic terminal 32 and the
rear acoustic resistance control means for changing the acoustic resistance of the rear acoustic
inlet 24 portion, as the rear acoustic resistance control means, A piezoelectric valve 40 which is
displaced in accordance with an applied voltage supplied from a DC power supply is used.
[Selected figure] Figure 2
Narrow directional microphone.
[0001]
The present invention relates to a narrow directional microphone, and more particularly, to a
variable directional narrow directional microphone (line microphone) capable of appropriately
switching directivity.
[0002]
A narrow directional microphone is known as a microphone with a small angle that can be picked
up even in outdoor news gathering etc., and its basic configuration is a single directivity (primary
sound pressure gradient having a front acoustic terminal and a rear acoustic terminal) Type)
microphone unit and an acoustic pipe (interference pipe) having a slit-like acoustic resistance
hole in the pipe peripheral wall, the acoustic pipe is connected to the front acoustic terminal side
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of the microphone unit, and the rear acoustic terminal is in free space It is coming.
[0003]
In this line microphone, the sound waves from the side or the back reach the sound pipe from the
acoustic resistance hole of the sound pipe and the front opening of the sound pipe respectively,
but from the phase difference due to the difference in their arrival paths Interference occurs,
which attenuates the sound waves from the side or the back.
On the other hand, sound waves from the front opening reach the diaphragm of the microphone
unit without attenuation.
[0004]
The advantage of this line microphone is that its frequency response characteristic is relatively
flat, and its sensitivity and intrinsic noise are superior to those of the secondary sound pressure
gradient microphone.
Line microphones are often used in professional video cameras and the like where this point is
evaluated and high-quality sound collection is required.
[0005]
By the way, by making the rear acoustic terminal face free space, a fairly narrow directivity can
be obtained, but on the other hand, it picks up external wind noise etc. Also, the proximity effect
that distorts the low range when the sound source is close is high. There was a problem of
becoming This is because the sound wave introduction port of the front acoustic terminal is the
tip of the acoustic tube, and the distance between the front acoustic terminal and the rear
acoustic terminal in the low band becomes long.
[0006]
In order to solve this point, according to the invention described in Patent Document 1, by
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housing the unidirectional microphone unit inside the rear end side of the acoustic tube, the
front acoustic capacity chamber and the rear acoustic capacity chamber are accommodated in
the acoustic pipe. The acoustic wave inlet for the rear acoustic terminal of the microphone unit is
bored on the rear side of the acoustic capacity chamber.
[0007]
In this case, the outer diameter of the microphone unit is smaller than the inner diameter of the
acoustic tube, and a predetermined gap is provided between the outer circumferential surface of
the microphone unit and the inner circumferential surface of the acoustic tube. And the rear
acoustic terminal are connected acoustically.
[0008]
In this way, the rear acoustic terminal of the microphone unit communicates with the free sound
field via the acoustic wave inlet and is also acoustically connected to the front acoustic terminal
through the gap, so that the acoustic in the low frequency range The distance between the
terminals is mainly governed by the distance between the acoustic terminals of the microphone
unit, whereby the influence of wind noise and the proximity effect can be reduced.
[0009]
By the way, in the line microphone described in the above-mentioned Patent Document 1, in
order not to pick up the sound wave from the side, by adjusting the acoustic resistance of the
acoustic tube and the microphone unit, the polar in the middle to low frequency range The
pattern is hypercardioid.
[0010]
However, this would result in sound waves of a particularly low frequency in the direction of 180
degrees being picked up.
On the other hand, if the directivity of the middle to low range is set to the cardioid in order to
reduce the low range sound waves coming from the 180 degree direction, the sound waves
arriving from the side at the mid frequency will be easily collected. It will
[0011]
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For this reason, there is a demand for making the directivity of the middle and low range variable
according to the situation in which the sound is picked up, but this has had the following
problems.
[0012]
In an ordinary line microphone, in order to make directivity in the middle to low range variable,
there is a method of making the leakage resistance (acoustic resistance) of the acoustic tube
variable, and a method of making the acoustic resistance inside the microphone unit variable.
There is.
[0013]
However, when making the leak resistance of the acoustic tube variable as in the former case, the
acoustic resistance hole is provided along the axial direction of the acoustic tube, so that the
acoustic resistance can be varied uniformly and stably. It is extremely difficult to do.
Even if the acoustic resistance can be made ideally variable, the characteristic impedance of the
acoustic tube itself is impaired, and as a result, the narrow directivity of the middle and low
range changes, and depending on the situation, the narrow directivity itself is impaired. There are
times when
[0014]
Further, as in the latter case, making the acoustic resistance inside the microphone unit variable
should be avoided since it directly manipulates the acoustic conditions of the unit, and even if it
is possible, the reproducibility is poor.
[0015]
In addition, as an exceptional existence, a line microphone having variable directivity is known by
connecting in series a plurality of acoustic tubes whose acoustic resistances in the tube side are
adjusted, and changing the number of connected stages. (See, for example, Patent Document 2).
[0016]
However, this microphone is used for business purposes such as coverage, because the
mechanical strength of the connecting part to which the acoustic tube is added can not be
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secured sufficiently and the acoustic tube to be always added must be carried. It was only
commercialized as a consumer microphone for a while.
[0017]
Further, when the acoustic tube is made longer, in addition to the directivity of the low band
becoming more bi-directional, there is a problem that the directivity of the high band becomes
sharper than necessary.
As described above, it is difficult to change the directivity of the low band without changing the
directivity of the high band or the length of the acoustic tube.
[0018]
Therefore, the applicant of Patent Document 3 has a simple configuration and can switch the
directivity to either hypercardioid or cardioid in accordance with the sound collection situation. A
narrow directional microphone that is divided into a front acoustic capacity chamber and a rear
acoustic capacity chamber by a unidirectional microphone unit, and a rear acoustic wave inlet for
the rear acoustic terminal of the microphone unit is provided on the rear acoustic capacity
chamber side In the above, a narrow directional microphone provided with rear acoustic
resistance control means for changing the acoustic resistance of the rear acoustic wave inlet
portion is proposed.
[0019]
According to this configuration, the directivity of the hypercardioid can be obtained by keeping
the acoustic resistance of the rear sound wave introduction port at the initially set acoustic
resistance.
On the other hand, the directivity of the cardioid can be obtained by increasing the acoustic
resistance of the rear acoustic wave inlet.
[0020]
Japanese Patent Laid-Open No. 62-118698 Japanese Utility Model Laid-Open No. 56-19992
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Japanese Patent Laid-Open No. 2000-50385
[0021]
However, in the narrow directional microphone described in Patent Document 3, the acoustic
resistance of the rear acoustic wave inlet can be varied using the switching cover that is movably
fitted to the outer peripheral surface of the acoustic pipe as the rear acoustic resistance control
means. There are the following problems because
[0022]
Since the switching cover is mechanically operated, rattling is likely to occur in the sliding
portion or the like, and the operation is also troublesome.
In the case of a strong wind or the like, the entire screen is covered with a windscreen, but this
makes the operation of the switching cover difficult.
In order to change the directivity continuously, subtle operation of the switching cover is
required.
In addition, the switching cover may be inadvertently moved due to vibration or shock.
[0023]
Therefore, an object of the present invention is to provide a narrow directional microphone
capable of continuously changing the directivity by electrical switch operation.
[0024]
In order to solve the problems described above, the invention according to claim 1 includes a
unidirectional microphone unit having a front acoustic terminal and a rear acoustic terminal, and
an acoustic tube in which the microphone unit is housed, An acoustic pipe is divided into a front
acoustic capacity chamber and a rear acoustic capacity chamber by the microphone unit, and a
rear acoustic wave inlet for the rear acoustic terminal of the microphone unit on the rear
acoustic capacity chamber side of the acoustic pipe, In a narrow directional microphone provided
with rear acoustic resistance control means for changing the acoustic resistance of the rear
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acoustic wave inlet portion, displacement is performed according to an applied voltage supplied
from a DC power source as the rear acoustic resistance control means. It is characterized in that
a piezoelectric valve is used.
[0025]
The invention according to claim 2 is characterized in that, in claim 1, the DC power supply is a
phantom power supply for supplying operating power to the microphone.
[0026]
The invention according to claim 3 is characterized in that, in claim 1 or 2, a feed switch for the
piezoelectric valve is provided in a portion other than the acoustic pipe.
[0027]
The invention according to a fourth aspect is characterized in that in the third aspect, the power
supply switch includes voltage adjusting means capable of adjusting the voltage applied to the
piezoelectric valve substantially continuously.
[0028]
The acoustic tube is divided into a front acoustic capacity chamber and a rear acoustic capacity
chamber by a unidirectional microphone unit, and a rear acoustic inlet for the rear acoustic
terminal of the microphone unit on the rear acoustic capacity chamber side of the acoustic tube,
In a narrow directional microphone provided with a rear acoustic resistance control means for
changing the acoustic resistance of the rear acoustic wave inlet portion, as a rear acoustic
resistance control means, a piezoelectric which is displaced according to an applied voltage
supplied from a DC power supply According to the first aspect of the present invention in which
the valve is used, the directivity can be varied by the electrical switch operation and the
operation can be easily performed, and there is no mechanical sliding portion as in the switching
cover. It is also advantageous in terms of durability.
[0029]
According to the invention described in claim 2 wherein a phantom for supplying operating
power to the microphone is used as a DC power source for driving the piezoelectric valve, it is
not necessary to prepare a separate power source in adopting the piezoelectric valve. .
[0030]
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According to the invention of the third aspect in which the power supply switch for the
piezoelectric valve is provided in a portion other than the acoustic tube, the directivity can be
easily switched even in a state where the windscreen is covered on the acoustic tube.
[0031]
According to the fourth aspect of the present invention, the directivity can be continuously
changed according to the fourth aspect of the present invention, in which the power supply
switch includes the voltage adjusting means capable of adjusting the voltage applied to the
piezoelectric valve substantially continuously.
[0032]
Next, an embodiment of the present invention will be described with reference to FIGS. 1 to 5.
1 is a plan view showing a narrow directional microphone according to an embodiment of the
present invention, FIG. 2 is a sectional view taken along the line AA of FIG. 1, FIG. 3 is a
schematic view showing a piezoelectric valve, and FIG. (A) is a polar pattern diagram of a
hypercardioid, (b) is a polar pattern diagram of a cardioid, and FIG. 5 is an acousto-mechanical
equivalent circuit diagram of the narrow directional microphone. It is.
[0033]
With reference to FIGS. 1 and 2, in the narrow directional microphone 1 as well, the
unidirectional microphone unit 3 is housed inside the rear end side of the acoustic tube 2, and
the inside of the acoustic tube 2 is formed by the microphone unit 3. It is divided into a front
acoustic capacity chamber 21 and a rear acoustic capacity chamber 22.
The rear end side of the rear acoustic capacity chamber 22 is closed by an end plate 23 having a
cord insertion hole 23a.
[0034]
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A series of acoustic resistance holes 2a in a slit shape are formed on the front side of the acoustic
tube 2, and an acoustic resistance material 2b (for example, nylon mesh # 508 manufactured by
NBC) is attached to the acoustic resistance holes 2a. It is attached.
The acoustic resistance holes 2a may be formed by axially arranging slit holes formed partially
along the circumferential direction of the acoustic tube 2 at predetermined intervals.
[0035]
The front acoustic terminal 31 is provided on one side (left side in FIG. 2) of the microphone unit
3, and the rear acoustic terminal 32 is provided on the other side (right side in FIG. 2). A rear
acoustic wave inlet 24 for the rear acoustic terminal 32 is bored on the rear acoustic capacity
chamber 22 side.
[0036]
The microphone unit 3 is mounted in the acoustic tube 2 through the rubber elastic ring 3 a
having air permeability, but the outer diameter of the microphone unit 3 is smaller than the inner
diameter of the acoustic tube 2. A gap G as an air passage is provided between the acoustic tube
2 and the acoustic tube 2.
[0037]
The front acoustic terminal 31 and the rear acoustic terminal 32 of the microphone unit 3 are
acoustically connected via the gap G, thereby reducing the influence of wind noise and the
proximity effect.
[0038]
According to this embodiment, as shown in FIG. 2, the rear sound wave introduction ports 24 are
respectively bored in the tube wall portions facing each other at 180 degrees, and each rear
sound wave introduction port 24 is made of, for example, NBC nylon mesh. An acoustic
resistance material (not shown) made of # 200 is provided.
[0039]
The narrow directional microphone 1 includes rear acoustic resistance control means for varying
the acoustic resistance of the rear acoustic wave inlet 24. In the present invention, the
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piezoelectric valve 40 is used as the rear acoustic resistance control means.
Piezoelectric valves 40 are provided in each of the rear sound inlets 24 in the acoustic tube 2.
[0040]
As schematically shown in FIG. 3, the piezoelectric valve 40 is a bimorph piezoelectric actuator
formed by laminating two piezoelectric ceramics 40a and 40b opposite in polarization direction
with a central electrode plate 40c, and applies an electric field. It is displaced by doing.
[0041]
A DC power supply 41 is used as a drive power supply, and as shown in the drawing, by applying
a voltage, one piezoelectric ceramic is elongated in the longitudinal direction, and the other
piezoelectric ceramic is displaced to be displaced. Act as an on-off valve for 24.
[0042]
In the condenser microphone, since a phantom power source is usually used, if the DC power
source 41 is obtained from the phantom power source, it is not necessary to prepare a drive
power source for the piezoelectric valve 40 in particular.
[0043]
A feed switch (on / off switch) 42 is provided in the feed system of the piezoelectric valve 40.
However, in order to make the valve opening degree of the piezoelectric valve 40 continuously
variable, the variable resistance element 43 is provided to the feed switch 42. It is preferable to
connect in series as a voltage adjustment means.
[0044]
The feed line of the piezoelectric valve 40 is drawn from the acoustic tube 2 through the cord
insertion hole 23a of the end plate 23 together with the microphone cord 33 of the microphone
unit 3 shown in FIG.
[0045]
Therefore, by providing the feed switch 42 and the variable resistance element 43 on the feed
line drawn from the acoustic tube 2, the directivity can be easily varied even when the acoustic
tube 2 is covered with a windscreen.
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[0046]
The narrow directional microphone 1 in this embodiment is designed such that its directivity
becomes a hypercardioid shown in the polar pattern of FIG. 4 (a) when the rear sound wave inlet
24 is open.
[0047]
On the other hand, when the rear sound wave introduction port 24 is closed by the piezoelectric
valve 40, the directivity becomes a cardioid shown in the polar pattern of FIG. 4 (b).
[0048]
By continuously varying the voltage applied to the piezoelectric valve 40 with the variable
resistance element 43, the acoustic resistance due to the thin air layer between the rear sound
wave inlet 24 and the piezoelectric valve 40 can be continuously varied. Switching from cardioid
to cardioid, switching from cardioid to hypercardioid can be made linear, and polar patterns in
between can also be selected.
[0049]
Here, based on the acousto-mechanical equivalent circuit shown in FIG. 5, the operation principle
of this narrow directional microphone 1 will be described.
In FIG. 5, the acoustic resistance rb of the rear acoustic wave inlet 24 is represented by a variable
resistance.
[0050]
In this acousto-mechanical equivalent circuit, PS is a sound source for the front acoustic terminal
31 and is represented by the product PS of the sound pressure P and the effective area S of the
unit diaphragm.
Further, PSe <−jkl cos θ> is a sound source for the rear acoustic terminal 31, and in this case, l
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is the distance between the front opening of the acoustic tube 2 and the rear sound inlet 24.
[0051]
Z is the total impedance of the acoustic tube 2, sf is the air stiffness in the front acoustic capacity
chamber 21, sb is the air stiffness in the rear acoustic capacity chamber 22, m0 is the mass of
the unit diaphragm, s0 is the stiffness of the unit diaphragm, r0 is the braking resistance of the
unit diaphragm, s1 is the air stiffness of the back air chamber of the unit, r1 is the acoustic
resistance in the unit giving directivity to the rear acoustic terminal 31, and rb is the acoustic
placed on the rear sound inlet 24 The acoustic resistance of the resistive material, mb is the mass
of the same acoustic resistive material, and m is the acoustic mass in the gap G between the outer
peripheral surface of the microphone unit 3 and the inner peripheral surface of the acoustic tube.
[0052]
According to the present invention, by making the acoustic resistance rb of the rear sound wave
inlet 24 variable by the piezoelectric valve 40, the directivity in the middle to low range is
controlled.
For example, if the acoustic resistance rb is selectable in the range of rb1 to rb2 (rb1 <rb2), the
directivity becomes a hypercardioid by setting the acoustic resistance rb to rb1, and the acoustic
resistance rb is rb2 The directivity becomes a cardioid by doing so.
[0053]
FIG. 1 is a plan view showing a narrow directional microphone according to an embodiment of
the present invention.
1. AA sectional view taken on the line of FIG.
The schematic diagram which shows a piezoelectric valve.
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The figure which shows two examples of the polar pattern of the said narrow directivity
microphone, (a) polar pattern figure of a hypercardioid, (b) polar pattern figure of a cardioid.
The acousto-mechanical equivalent circuit schematic of the narrow directional microphone.
Explanation of sign
[0054]
DESCRIPTION OF SYMBOLS 1 narrow directivity microphone 2 acoustic pipe 21 front acoustic
capacity room 22 rear acoustic capacity room 24 rear acoustic wave introduction port 3
unidirectional microphone unit 31 front acoustic terminal 32 rear acoustic terminal 40
piezoelectric valve 41 DC power supply 42 feeding switch 43 variable Resistance element
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