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JP2017005654

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DESCRIPTION JP2017005654
Abstract: To achieve high directivity regardless of the frequency of sound waves. SOLUTION: In a
unidirectional condenser microphone having a front opening and a rear opening 17 for
transmitting sound waves to the front surface and the rear surface of a diaphragm 111 of a
microphone unit 11, respectively, on the front side of the front opening. A first air chamber 13
provided between the provided acoustic tube 12 and the rear opening 17 and the back surface of
the diaphragm 111 of the microphone unit 11 and having a predetermined acoustic capacity is
in communication with the first air chamber 13 And the second air chamber 15 having an
acoustic capacity larger than a predetermined acoustic capacity, and the sensitivity to the
direction of the directional axis 0 ° is improved by the first air chamber 13 and the acoustic
tube 12, and the second air chamber 15 It prevents the proximity effect due to sound waves from
the direction of the shaft 180 °. [Selected figure] Figure 2
Unidirectional Condenser Microphone
[0001]
The present invention relates to a unidirectional condenser microphone.
[0002]
Unidirectional microphone sensitivity and low frequency limits vary with diaphragm tension.
In a unidirectional microphone, the higher the diaphragm tension, the higher the sensitivity of
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the microphone. However, since the sound collection limit of the low band shifts to a high
frequency, sound waves of low frequency can not be collected. On the other hand, when the
tension of the diaphragm is low, the sound collection limit of the low band shifts to a low
frequency, and sound waves of low frequency can be collected. However, the sensitivity of the
microphone is reduced. Further, in the unidirectional condenser microphone, when the tension of
the diaphragm is low, the diaphragm is easily attracted to the fixed electrode by the electrostatic
attraction force. Unidirectional condenser microphones can not collect sound when the
diaphragm is attached to a fixed pole.
[0003]
As described above, in the unidirectional condenser microphone, the frequency response and
sensitivity of the diaphragm are in a trade-off relationship.
[0004]
In order to obtain good directional frequency response and high sensitivity, a technique relating
to a unidirectional microphone having a cylindrical acoustic resistance tube in front of the
diaphragm is disclosed (see, for example, Patent Document 1).
[0005]
JP, 2013-46194, A
[0006]
However, when there is a sound source of low frequency at a position close to the microphone in
the direction of 180 ° from the sound collection axis, the conventional unidirectional
microphone disclosed in Patent Document 1 collects the sound wave of the sound source. I had
to sound.
Thus, when there is a sound source at a position close to the microphone, the microphone
emphasizes and picks up the low frequency sound wave.
Such a phenomenon is generally referred to as proximity effect.
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The directivity of the unidirectional microphone is controlled by the sound pressure difference
between the two points. For this reason, a conventional unidirectional microphone has two
openings at the front and the back for receiving sound waves. In the conventional unidirectional
microphone, when there is a sound source near the rear opening, the proximity effect causes a
low frequency sound off the sound collection axis to be emphasized and collected. Therefore, the
emphasized unnecessary bass is affected by the sound to be picked up, and the sound quality is
lowered.
[0007]
An object of the present invention is to provide a unidirectional condenser microphone capable
of realizing high directivity regardless of the frequency of sound waves.
[0008]
The present invention is a unidirectional condenser microphone having a front opening and a
rear opening for transmitting sound waves to the front surface and the rear surface of the
diaphragm of the microphone unit, provided on the front side of the front opening. An acoustic
capacity is provided between the acoustic tube, the rear opening and the rear surface of the
diaphragm of the microphone unit, the first air chamber having a predetermined acoustic
capacity, and the first air chamber being larger than the predetermined acoustic capacity. A
second air chamber having a second air chamber and an acoustic tube to improve sensitivity in
the direction of the 0.degree. Directional axis, and a second air chamber preventing a proximity
effect by a sound wave from the direction of the 180.degree. Directional axis It is characterized
by
[0009]
According to the present invention, high directivity can be realized regardless of the frequency of
the sound wave.
[0010]
FIG. 1 is a side cross-sectional view showing an embodiment of a unidirectional condenser
microphone according to the present invention.
It is an expanded sectional view of the side which shows the unidirectional directivity condenser
microphone of FIG.
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It is a circuit diagram which shows the acoustic equivalent circuit of the unidirectional directivity
condenser microphone of FIG.
It is side sectional drawing which shows the unidirectional directivity condenser microphone of a
reference example. It is a circuit diagram which shows the acoustic equivalent circuit of the
unidirectional directivity condenser microphone of a reference example. It is a characteristic view
which shows the (a) directivity pattern of the unidirectional directivity condenser microphone of
FIG. 1, and a graph which shows (b) directivity frequency characteristics. It is a characteristic
view which shows the (a) directivity pattern of the unidirectional directivity condenser
microphone of a reference example, and a graph which shows the (b) directivity frequency
characteristic. It is a characteristic view which shows the (a) directivity pattern of the
unidirectional directivity condenser microphone of another reference example, and a graph
which shows the (b) directivity frequency characteristic.
[0011]
Hereinafter, embodiments of the unidirectional condenser microphone according to the present
invention will be described with reference to the drawings.
[0012]
Schematic Structure of Unidirectional Condenser Microphone As shown in FIG. 1, the
unidirectional condenser microphone 10 includes a microphone unit 11 and an acoustic tube
provided in front of the microphone unit 11 (on the left side of FIG. 1). And 12.
In addition, the unidirectional condenser microphone 10 is provided at the rear of the
microphone unit 11 from the first air chamber 13 provided behind the microphone unit 11 (right
side in FIG. 1) and the first air chamber 13. And a second air chamber 15.
[0013]
The unidirectional condenser microphone 10 includes a first acoustic resistor 14 serving as an
acoustic resistance of a sound wave reaching the rear of the microphone unit 11 and a
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communication passage 18 communicating the first air chamber 13 with the second air chamber
15. Have. Also, the unidirectional condenser microphone 10 transmits a second acoustic
resistance 16 provided between the first air chamber 13 and the second air chamber 15 and a
sound wave from the outside to the rear of the microphone unit 11 And a rear opening 17 for
[0014]
The unidirectional condenser microphone 10 is electrically connected to a cylindrical metal case
21, a circuit board 22 housed in the case 21, and the circuit board 22 behind the second air
chamber 15. And an output connector 23. On the circuit board 22, for example, an FET (Field
Effect Transistor) as an impedance converter, an amplifier circuit, a low cut circuit, etc. are
mounted.
[0015]
Specific Configuration of Unidirectional Condenser Microphone A specific configuration example
of the unidirectional condenser microphone 10 will be described using the enlarged crosssectional view of the side shown in FIG. The microphone unit 11 includes a diaphragm 111 that
vibrates by an external sound wave, and a fixed electrode 112 that constitutes a capacitor
together with the diaphragm 111. The microphone unit 11 further includes an insulating holder
113 for holding the diaphragm 111 and the fixed electrode 112, and a unit case 115 for holding
the diaphragm 111, the fixed electrode 112 and the like. The insulating holder 115 is provided
with a through passage 114 for transmitting the sound wave taken in from the rear opening 17
to the first air chamber 13.
[0016]
The acoustic tube 12 is a hollow tubular member provided at the front opening of the
microphone unit 11 on the front side of the diaphragm 111. The acoustic tube 12 has a front
opening 121 provided at a position facing the front of the diaphragm 111 and a tube wall
opening 122 provided in the tube wall on the side of the acoustic tube 12. The acoustic tube 12
transmits the sound wave from the front of the unidirectional microphone 10 to the front surface
of the diaphragm 111 through the front opening 121 and the tube wall opening 122.
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[0017]
The first air chamber 13 is formed by the fixed electrode 112 and the unit case 113 on the back
side of the diaphragm 111 as described above. The first air chamber 13 is also referred to as a
predetermined acoustic capacity (hereinafter referred to as a "predetermined acoustic capacity").
Space). The first air chamber 13 is in communication with the rear surface of the diaphragm 111
through an opening provided in the fixed electrode 112.
[0018]
The first acoustic resistance 14 is provided in the passage of the sound wave introduced into the
first air chamber 13 through the through passage 114 and becomes the acoustic resistance of
the sound wave introduced into the first air chamber 13 from the rear opening 17 .
[0019]
The second air chamber 15 communicates with the first air chamber 13 through the
communication passage 18.
The second air chamber 15 communicates with the first air chamber 13, thereby communicating
with the back surface of the diaphragm 111 of the microphone unit 11. The second air chamber
15 is a space having an acoustic capacity larger than the predetermined acoustic capacity of the
first air chamber 13.
[0020]
The second acoustic resistance 16 is provided between the first air chamber 13 and the second
air chamber 15, specifically, on the front side of the communication passage 18 when viewed
from the second air chamber 15. The second acoustic resistance 16 is an acoustic resistance of a
sound wave passing between the first air chamber 13 and the second air chamber 15. The
second acoustic resistor 16 passes sound waves of a low frequency region lower than a
predetermined frequency between the first air chamber 13 and the second air chamber 15.
[0021]
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As described above, the unidirectional condenser microphone 10 has the two air chambers of the
first air chamber 13 and the second air chamber 15 behind the diaphragm 111. The functions of
the first air chamber 13 and the second air chamber 15 will be described. The sound wave taken
in from the rear opening 17 where the rear acoustic terminal is located is divided into two paths
according to its frequency and To reach.
[0022]
A sound wave of a frequency in the middle and high range higher than a predetermined
frequency is divided by the first acoustic resistor 14 and the first air chamber 13 and pressure is
applied to the back surface of the diaphragm 111 to realize unidirectivity. That is, the sound
wave of the frequency of the middle and high range reaches the back surface of the diaphragm
111 only via the first air chamber 13.
[0023]
On the other hand, sound waves of low frequencies lower than a predetermined frequency are
divided by the first acoustic resistance 14 and the second acoustic resistance 16 and reach the
back surface of the diaphragm 111. That is, the effect of the second air chamber 15 larger than
the first air chamber 13 is dominant in the sound wave of low frequency. As a result, by the
second air chamber 15, the nondirectional component of the components constituting the
unidirectionality is enhanced, and even when there is a sound source near the rear opening, the
increase of the bass range due to the proximity effect can be prevented. .
[0024]
Acoustic Equivalent Circuit FIG. 3 shows an acoustic equivalent circuit of the unidirectional
condenser microphone 10. In FIG. 3, a sound wave taken in from the front of the acoustic tube
12 is P 1, the acoustic mass of the diaphragm 111 is m 0, the stiffness of the diaphragm 111 is s
0, the damping resistance of the diaphragm 111 is r 0, and the rear opening 17 Let P 2 be the
sound wave taken in from the front of. Further, in FIG. 3, the acoustic resistance of the first
acoustic resistor 14 is r 1, and the acoustic resistance of the second acoustic resistor 16 is r 2.
Further, in FIG. 3, the acoustic capacity of the first air chamber 13 is s 1, and the acoustic
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capacity of the second air chamber 15 is s 2.
[0025]
In the unidirectional condenser microphone 10, the sound wave P 1 reaches the front surface of
the diaphragm 111 to obtain an omnidirectional component, and the sound wave P 2 reaches the
rear surface of the diaphragm 111 to obtain a bidirectional component. By achieving it, unidirectionality is realized. Specifically, in the unidirectional condenser microphone 10, the
acoustic capacitance s 1 of the first air chamber 13 and the second air chamber 15 are
connected by the acoustic resistance r 2. Therefore, the sound wave of low frequency is divided
by the acoustic resistance r 1 and the acoustic resistance r 2 and reaches the back surface of the
diaphragm 111. Therefore, the acoustic capacity s 2 is equivalent to operating in a larger air
chamber, and the driving power of the nondirectional component is increased.
[0026]
As described above, since the acoustic capacity s 2 of the second air chamber 15 is larger than
the acoustic capacity s 1 of the first air chamber 13, the acoustic capacity s 2 of the second air
chamber 15 is dominant at low frequencies. Works. Moreover, in the unidirectional directivity
condenser microphone 10, since the sound wave of the frequency of middle to high frequency
operates with the acoustic capacity S 1 of only the first air chamber 13, it operates in the same
manner as a general unidirectional microphone.
[0027]
In the unidirectional directivity condenser microphone 100 of the reference example shown in
FIG. 4, the diaphragm 111, the fixed electrode 112, the insulating holder 113, and the through
passage 116 are provided, and the microphone unit 11 of the unidirectional directivity
condenser microphone 10 is the same. Configuration. In the unidirectional condenser
microphone 100, the second air chamber 15 is not provided behind the air chamber 130 formed
by the fixed electrode 112 and the insulating holder 113, and the insulating cap 110 is provided.
[0028]
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As shown in the acoustic equivalent circuit of FIG. 5, in the unidirectional microphone 100, since
the acoustic capacitance s 2 of the second air chamber 15 and the acoustic resistance r 2 of the
second acoustic resistor 16 are not provided, the low frequency range Non-directional
component by the sound wave of That is, the unidirectional microphone 100 of the reference
example is susceptible to the proximity effect.
[0029]
Directional Pattern and Directional Frequency Characteristic FIG. 6 is a graph showing (a)
directional pattern of the unidirectional microphone 10 according to the present embodiment
and (b) directional frequency characteristic. According to FIG. 6A, in the unidirectional
microphone 10, excellent unidirectionality is obtained. Further, according to FIG. 6B, in the
unidirectional microphone 10, the sound collection of the low frequency band is suppressed also
in the direction of 180 ° from the sound collection axis. Furthermore, the frequency response in
the 90 ° direction is also flat, and the frequency directivity of the unidirectional microphone 10
is stable from low to high.
[0030]
7A and 7B are a characteristic diagram showing (a) directivity patterns of the unidirectional
microphone 100 of the reference example and a graph showing (b) directivity frequency
characteristics. As shown in FIG. 7A, in the unidirectional microphone 100, the direction of 180
° from the sound collection axis is compared with the unidirectional microphone 10 according
to the present embodiment shown in FIG. 6A. But I understand that it is being picked up. Further,
as shown in FIG. 7B, it can be seen that in the unidirectional microphone 100, the low frequency
band is picked up in the direction of 180 ° from the sound pickup axis.
[0031]
That is, compared with the unidirectional microphone 100 of the reference example, the
unidirectional effect microphone 10 according to the present embodiment has the proximity
effect reduced and achieves high directivity regardless of the frequency.
[0032]
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FIG. 8 is (a) a characteristic diagram showing a directivity pattern and (b) a graph showing a
directional frequency characteristic of a unidirectional microphone according to another
reference example.
The unidirectional microphone of the reference example has an acoustic tube attached to the
front of the diaphragm 111 of the unidirectional microphone 100 of the reference.
[0033]
As shown in FIG. 8, even in the unidirectional microphone of another reference example, the low
frequency band in the direction of 180 ° from the sound collection axis is compared with the
unidirectional microphone 10 according to the present embodiment. It can be seen that sound is
picked up for the frequency of.
[0034]
That is, compared with the unidirectional microphone 100 of the reference example, the
unidirectional effect microphone 10 according to the present embodiment has the proximity
effect reduced and achieves high directivity regardless of the frequency.
[0035]
Effect of the Embodiment As described above, according to the unidirectional microphone 10
according to the present embodiment, the first air chamber 13 and the second air chamber 15
allow the sound wave frequency to be determined. It is possible to realize high directivity.
[0036]
In particular, according to the unidirectional microphone 10, the proximity effect of sound waves
of low frequencies in the direction of 180 ° from the sound collection axis can be reduced to
obtain excellent directivity characteristics.
[0037]
Reference Signs List 10 unidirectional microphone 11 microphone unit 12 acoustic tube 13 first
air chamber 14 first acoustic resistor 15 second air chamber 16 second acoustic resistor 17 rear
opening 18 communication passage 21 grip case 22 circuit board 23 output connector 111
vibration Plate 112 Fixed pole 113 Unit case 114 Through passage 121 Front opening 122 Tube
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wall opening
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