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JP2000050385

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DESCRIPTION JP2000050385
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
narrow directional microphone, and more particularly to a variable directional narrow directional
microphone (line microphone) which can switch directivity appropriately.
[0002]
2. Description of the Related Art A narrow directional microphone is known as a microphone
having a small angle at which sound can be collected even in outdoor news gathering and the
like. This is roughly divided into a line microphone and a secondary sound pressure gradient type
microphone, but here, only the line microphone related to the present invention will be
described.
[0003]
The line microphone has, as its basic configuration, a unidirectional (primary sound pressure
gradient type) microphone unit having a front acoustic terminal and a rear acoustic terminal, and
a slit-like acoustic resistance hole in the peripheral wall of the tube. And an acoustic pipe is
connected to the front acoustic terminal side of the microphone unit, and the rear acoustic
terminal faces free space.
[0004]
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1
In this line microphone, the sound waves from the side or the rear reach the acoustic tube from
the acoustic resistance hole of the acoustic tube and the front opening of the acoustic tube
respectively, but the position is different due to the difference in the arrival path of them. The
phase difference causes sound wave interference, which attenuates the sound wave 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.
[0005]
An 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.
[0006]
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. and proximity which
distorts the low range when the sound source is close. There was a problem that the effect
became high. 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.
[0007]
In order to solve this point, the present applicant has proposed one in Japanese Patent
Application Laid-Open No. 62-118698. This is taken as a conventional example of the present
invention, and its configuration is shown in a schematic cross sectional view of FIG. A brief
description will be given based on this.
[0008]
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2
That is, in the line microphone 1, 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 made into the front
acoustic capacity chamber 21 by the microphone unit 3. And the rear acoustic capacity chamber
22.
A slit-like acoustic resistance hole 2a is formed on the front side of the acoustic tube 2, and an
acoustic resistance material (not shown) is attached to the acoustic resistance hole 2a.
[0009]
A front acoustic terminal 31 is provided on one side (left side in FIG. 12) of the microphone unit
3, and a rear acoustic terminal 32 is provided on the other side (right side in FIG. 12). A sound
wave introduction port 2 b for the rear acoustic terminal 32 is bored on the rear acoustic
capacity chamber 22 side of the tube 2. Although not shown in detail, an appropriate acoustic
resistance material is attached to the sound wave inlet 2b.
[0010]
In this case, the outer diameter of the microphone unit 3 is smaller than the inner diameter of the
acoustic tube 2. That is, a predetermined gap G is provided between the outer peripheral surface
of the microphone unit 3 and the inner peripheral surface of the acoustic tube 2, and the front
acoustic terminal 31 and the rear acoustic terminal 32 of the microphone unit 3 are acoustically
Connected.
[0011]
As described above, the rear acoustic terminal 32 of the microphone unit 3 communicates with
the free sound field via the acoustic wave inlet 2b, and is acoustically connected to the front
acoustic terminal 31 through the gap G. Therefore, the distance between the acoustic terminals
in the low band is mainly governed by the distance between the acoustic terminals 31 and 32 of
the microphone unit 3, whereby the influence of wind noise and the proximity effect can be
reduced. .
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3
[0012]
By the way, in this type of line microphone, the acoustic resistance of the acoustic tube 2 and the
microphone unit 3 is adjusted in order to prevent the sound wave from being picked up from the
side. The polar pattern is hypercardioid in the low to mid frequency range.
[0013]
However, in this case, particularly low frequency sound waves in the direction of 180 degrees are
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
[0014]
For this reason, there is a demand for making the directivity of the middle and low regions
variable in accordance with the situation in which the sound is picked up, but this has had the
following problems.
[0015]
In the ordinary line microphone, in order to make the directivity in the middle to low range
variable, the method of making the leakage resistance (acoustic resistance) of the acoustic tube
variable and the acoustic resistance inside the microphone unit are variable. There is a way to
[0016]
However, in the case of 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 is uniform and stable. It is extremely difficult to make
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
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times when
[0017]
Also, as in the latter case, making the acoustic resistance inside the microphone unit variable
should be avoided because it directly manipulates the acoustic conditions of the unit, and even if
it is possible, the reproducibility is poor. .
[0018]
As an exceptional case, a line microphone having variable directivity is known by connecting in
series a plurality of sound tubes whose sound resistances on the tube side are adjusted, and
changing the number of connected stages. It is done.
[0019]
However, due to the fact that this microphone can not ensure sufficient mechanical strength of
the connecting portion to which the acoustic tube is to be added, and because it is necessary to
carry the acoustic tube to be constantly added, etc. It was not commercialized for a while and was
only commercialized for a while as a consumer microphone.
[0020]
In addition to the fact that the directivity in the low band becomes more bi-directional when the
acoustic tube is made longer, there is a problem that the directivity in 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.
[0021]
The present invention has been made to solve the above-mentioned problems, and its object is to
make the directivity either hypercardioid or cardioid depending on the sound collecting situation
while having a simple configuration. It is an object of the present invention to provide a narrow
directional microphone which can be switched to
03-05-2019
5
[0022]
SUMMARY OF THE INVENTION In order to achieve the above object, the present invention
provides a unidirectional microphone unit having a front acoustic terminal and a rear acoustic
terminal, and an acoustic system in which the same microphone unit is housed. The acoustic pipe
is divided into a front acoustic capacity chamber and a rear acoustic capacity chamber by the
microphone unit, and the rear acoustic capacity chamber side of the acoustic pipe is divided into
the rear acoustic capacity chamber of the microphone unit. A narrow directional microphone
provided with a rear acoustic wave inlet to a terminal is characterized in that it comprises rear
acoustic resistance control means for changing the acoustic resistance of the rear acoustic wave
inlet portion.
[0023]
According to this configuration, the directivity of the hypercardioid can be obtained by keeping
the acoustic resistance of the rear acoustic wave inlet at the initially set acoustic resistance.
On the other hand, the directivity of the cardioid can be obtained by increasing the acoustic
resistance.
[0024]
In order to make the acoustic resistance variable, in the present invention, the rear acoustic
resistance control means is made of an acoustic resistance material having a predetermined
acoustic resistance value which is detachably put on the rear acoustic wave inlet. Is preferred.
[0025]
In this case, it is preferable that the above-mentioned acoustic resistance material is attached to
the switching cover which is movably fitted to the outer peripheral surface of the abovementioned acoustic tube, and according to this, the rear sound wave introduction with simple
operation. The acoustic resistance of the mouth can be made variable.
[0026]
The switching cover may be slidable along the axial direction of the acoustic tube, or may be
rotatable along the circumferential direction with respect to the acoustic tube, any of which is
included in the present invention. Be
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[0027]
A plurality of acoustic resistance materials having different acoustic resistance values can be
provided along the movable direction of the switching cover, whereby the acoustic resistance of
the rear acoustic wave inlet can be switched stepwise. Is possible.
[0028]
In addition, the switching cover may be provided with at least one opening having an opening
area smaller than the rear sound wave introduction opening along the movable direction.
That is, the acoustic resistance of the rear sound wave introduction port can also be made
variable by narrowing the opening surface of the rear sound wave introduction port.
In addition, the aspect which provides the acoustic resistance material which has a
predetermined | prescribed acoustic resistance value in the opening is also contained in this
invention.
[0029]
In the present invention, the front acoustic capacity chamber and the rear acoustic capacity
chamber are acoustically connected by the gap between the outer peripheral surface of the
microphone unit and the inner peripheral surface of the acoustic tube. Preferably, a
predetermined acoustic resistance is connected in series to the acoustic mass present in the gap.
[0030]
According to this, there is provided a short narrow directional microphone of an acoustic tube
which can reliably suppress the resonance by a simple means without losing the resistance to
wind noise and the like.
[0031]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be
described in more detail based on the embodiments shown in the drawings.
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[0032]
FIG. 1 shows a cross-sectional view of a line microphone 1A according to this embodiment. Also
in this line microphone 1A, the unidirectional microphone unit 3 is provided inside the rear end
side of the acoustic tube 2. The inside of the acoustic tube 2 is divided into a front acoustic
capacity chamber 21 and a rear acoustic capacity chamber 22 by the microphone unit 3.
[0033]
A series of slit-like acoustic resistance holes 2a are formed on the front side of the acoustic tube
2. An acoustic resistance material (not shown) (for example, nylon mesh # made by NBC) is
formed in the acoustic resistance holes 2a. 508) is pasted.
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.
[0034]
A front acoustic terminal 31 is provided on one side (left side in FIG. 1) of the microphone unit 3
and a rear acoustic terminal 32 is provided on the other side (right side in FIG. 1). A rear acoustic
wave inlet 2 b for the rear acoustic terminal 32 is bored on the rear acoustic capacity chamber
22 side of the tube 2.
[0035]
Although only one rear sound wave introduction port 2b is shown in FIG. 1, in this embodiment,
the rear sound wave introduction port 2b is bored in the tube wall portions facing each other at
180 degrees. For example, nylon mesh # 200 manufactured by NBC is attached as an acoustic
resistance material also to the rear sound wave introduction port 2b.
[0036]
The line microphone 1A is provided with rear acoustic resistance control means 4 which makes
the acoustic resistance of the sound wave inlet 2b variable.
FIG. 4 (a) shows a side view of the rear acoustic resistance control means 4, and FIG. 4 (b) shows
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8
a cross-sectional view taken along the line A-A.
[0037]
In this embodiment, the rear acoustic resistance control means 4 is provided with a switching
cover 41 slidably fitted in the axial direction with respect to the acoustic tube 2.
The switching cover 41 is formed of a sheet metal member formed substantially in a C-shape,
and a knob 42 for switching operation is continuously provided at one end thereof.
The switching cover 41 may be made of synthetic resin.
[0038]
The switching cover 41 is slid to a position covering the rear sound wave introduction port 2b
and a position away from the rear sound wave introduction port 2b. The switching cover 41
corresponds to each rear sound wave introduction port 2b. A pair of openings 43 formed to have
substantially the same size as that of the leech are provided, and a nylon mesh # 150
manufactured by NBC in this example is affixed to each of them as the acoustic resistance
material 44.
[0039]
On the other hand, the outer diameter of the microphone unit 3 is smaller than the inner
diameter of the acoustic tube 2.
That is, a predetermined gap G is provided between the microphone unit 3 and the acoustic tube
2, and the front acoustic terminal 31 and the rear acoustic terminal 32 of the microphone unit 3
are acoustically connected by the gap G.
This reduces the influence of wind noise and the proximity effect.
03-05-2019
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[0040]
An acoustic resistance member 51 is disposed in the rear acoustic capacity chamber 22 so as to
cover the gap G.
Also, an acoustic resistance material 52 is provided on the front acoustic capacity chamber 21
side so as to cover the gap G.
[0041]
In this embodiment, each of the acoustic resistance members 51 and 52 is formed in a donut
shape from a sponge material (for example, HR 50 manufactured by Bridgestone Corp.,
compression ratio 1/5) appropriately compressed. It also doubles as a shock mount.
[0042]
As shown in FIG. 3, this line microphone 1A is designed so that its directivity becomes a
hypercardioid when the switching cover 41 is at a position deviated from the rear sound wave
inlet 2b. There is.
The directivity characteristic graph in each direction of 0 degree, 90 degrees, and 180 degrees
measured in this state is shown in FIG.
Also, the polar pattern is shown in FIG.
[0043]
On the other hand, as shown in FIG. 4, the switching cover 41 is moved to a position covering the
rear sound wave inlet 2b, and the opening 43 with the acoustic resistance material 44 is made to
the rear sound wave inlet 2b. By facing each other, the acoustic resistance value of the rear
acoustic wave inlet 2b is made variable, and the directivity becomes a cardioid.
03-05-2019
10
The directivity characteristic graph in each direction of 0 degree, 90 degrees, and 180 degrees
measured in this state is shown in FIG.
The polar pattern is shown in FIG.
[0044]
Here, based on the mechanical equivalent circuit shown in FIG. 9, the operation principle of this
line microphone 1A will be described.
In the figure, (a) represents the acoustic resistance rb of the rear sound wave inlet 2b by a
variable resistance, and (b) represents the same acoustic resistance by two switchable acoustic
resistances rb1, rb. is there.
[0045]
In this 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 is
the distance between the front opening of the acoustic tube 2 and the rear sound inlet 2b.
[0046]
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 unit diaphragm The stiffness of the unit, r0 is the braking resistance
of the unit diaphragm, s1 is the air stiffness of the unit back air chamber, r1 is the acoustic
resistance in the unit giving directivity to the rear acoustic terminal 31, and rb is the acoustic
inlet 2b at the rear The acoustic resistance of the acoustic resistance material, mb is the mass of
the acoustic resistance 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.
03-05-2019
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[0047]
According to the present invention, by making the acoustic resistance rb of the rear acoustic
wave inlet 2b variable by the rear acoustic resistance control means 4, 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.
[0048]
Also, in this mechanical equivalent circuit, sf (air stiffness in front acoustic capacity chamber 21),
m (acoustic mass in gap G) and sb (air stiffness in rear acoustic capacity chamber 22) resonate. It
is an impedance element which generate | occur | produces and a resonance system is comprised
by these.
[0049]
The overall impedance Z of the acoustic tube 2 increases in proportion to the axial length if the
inner diameter is the same.
Therefore, when the acoustic tube 2 is long, the impedance of the resonance system due to the
above sf, m and sb can be ignored, and the influence of the resonance on the frequency response
and directivity is extremely small.
[0050]
On the other hand, when the acoustic tube 2 is shortened, the total impedance Z approaches the
impedance of the resonance system due to the above sf, m and sb, so the influence of resonance
becomes remarkable, and the frequency response Irregularities in directivity tend to occur, but
assuming that the acoustic resistance of the acoustic resistance members 51 and 52 is r, in the
present invention, the acoustic resistance r is connected in series to the acoustic mass m of the
gap G It is equivalent to
03-05-2019
12
[0051]
Thereby, it is possible to effectively damp the resonance due to the above sf, m and sb.
Therefore, according to the present invention, the directivity in the middle to low range can be
made variable, and the acoustic tube 2 can be made shorter.
[0052]
Next, a modification of the rear acoustic resistance control means 4 will be described with
reference to FIGS. 10 and 11. FIG.
The switching cover 41A in the first modification of FIG. 10 is slidably fitted along the axial
direction to the acoustic pipe 2 in the same manner as the switching cover 41 of the above
embodiment. A plurality of openings of different sizes, in this example, three openings 431, 432,
433 are bored along the axial direction of the acoustic tube 2.
[0053]
In this case, the opening 431 is equal to or larger than the rear sound wave inlet 2b, and the
entire surface of the rear sound wave inlet 2b is opened.
That is, as shown in FIG. 3, the state is equivalent to when the switching cover 41 is moved to a
position away from the rear sound wave inlet 2b, and is used when the directivity is made
hypercardioid.
[0054]
The adjacent opening 432 is smaller than the rear sound wave inlet 2b by a predetermined
03-05-2019
13
diameter, and the opening area of the rear sound wave inlet 2b is reduced accordingly to
increase the acoustic resistance of the rear sound wave inlet 2b. The polar pattern at this time
indicates an intermediate pattern between the hypercardioid and the cardioid. The opening 433
located on the left side is the smallest, and is used when the opening area of the rear sound wave
inlet 2b is narrowed to further increase the acoustic resistance and the directivity is made to be a
cardioid.
[0055]
Next, in the second modification of FIG. 11, the switching cover 41B is rotatably fitted to the
acoustic tube 2 in the circumferential direction. Then, according to this second modification,
three openings 431, 432, 433 having different sizes are also spaced along the circumferential
direction of the switching cover 41B as in the first modification. It is formed with
[0056]
Thus, the acoustic resistance can be made variable by adjusting the opening area of the rear
sound wave inlet 2b by selectively using the openings having different sizes. Note that an
acoustic resistance material such as nylon mesh may be put on the openings having different
sizes.
[0057]
Although not shown, a plurality of openings each having the same diameter as or larger than the
rear sound wave inlet 2b are formed in the switching cover 41, 41A, 41B described above, and
the acoustic resistances are respectively formed in the respective openings. An acoustic
resistance material having a different value may be provided to make the acoustic resistance
value of the rear acoustic wave inlet 2b variable.
[0058]
As described above, according to the present invention, the unidirectional microphone unit is
accommodated in the rear end side of the acoustic pipe, and the microphone unit is disposed in
the same acoustic pipe at the front end. In the line microphone which is divided into the acoustic
capacity room and the rear acoustic capacity room and the rear acoustic wave inlet for the rear
acoustic terminal of the microphone unit is provided on the rear acoustic capacity room side, the
acoustic resistance of the rear acoustic wave inlet part is variable By doing this, it is possible to
03-05-2019
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obtain a variable directivity line microphone capable of switching the directivity in the middle
and low bands to, for example, hypercardioid and cardioid.
[0059]
Furthermore, according to the present invention, it is possible to reliably switch the directivity of
the middle and low frequencies without impairing the directivity of the high region.
Further, in this line microphone, since the acoustic impedance of the rear sound wave inlet
portion is low, even if the acoustic resistance of the same portion is variable, the acoustic
influence on each component is small and the reproducibility is extremely high. .
[0060]
Furthermore, since the microphone unit itself is not operated (altered), it can be implemented
simply by adding a switching cover or the like to the conventional configuration.
Therefore, the cost can be reduced.
[0061]
Brief description of the drawings
[0062]
1 is a schematic cross-sectional view showing an embodiment of the narrow directional
microphone according to the present invention.
[0063]
2 is a side view showing the switching cover incorporated in the above embodiment in an
enlarged manner, and a sectional view taken along the line A-A.
[0064]
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15
3 is a side view of a state in which the switching cover has been switched to the hypercardioid
side in the above embodiment.
[0065]
4 is a side view of the above embodiment with the switching cover switched to the cardioid side.
[0066]
5 is a directivity characteristic graph measured in the state where the directivity of the above
embodiment is hypercardioid.
[0067]
FIG. 6 is a polar pattern diagram measured with the directivity of the above embodiment set as
hypercardioid.
[0068]
[FIG. 7] The directivity characteristic graph actually measured in the state which made directivity
the directivity of the said Example.
[0069]
Fig. 8 is a polar pattern diagram measured with the directivity of the above embodiment set as a
cardioid.
[0070]
9 is a machine equivalent circuit of the above embodiment.
[0071]
10 is a side view showing a first modified example of the switching cover in the above
embodiment.
[0072]
11 is a side view showing a second modification of the switching cover in the above embodiment.
03-05-2019
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[0073]
12 is a schematic sectional view showing a line microphone as a conventional example.
[0074]
Explanation of sign
[0075]
1A line microphone (narrow directional microphone) 2 acoustic tube 21 front acoustic capacity
room 22 rear acoustic capacity room 2a front acoustic resistance hole 2b rear acoustic wave
inlet 3 microphone unit 31 front acoustic terminal 32 rear acoustic terminal 4 rear acoustic
resistance control Means 41, switching cover 42, knobs 43, 431-433, openings 51, 52, acoustic
resistance material
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