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JP2006340187

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DESCRIPTION JP2006340187
A narrow directional microphone capable of obtaining high directivity and reducing wind noise.
A tubular acoustic tube 10, a microphone unit 14 disposed in the acoustic tube 10, and a front
acoustic chamber 11 and a rear acoustic chamber 13 formed by dividing the acoustic tube 10 by
the microphone unit 14. A front acoustic terminal 22 for communicating the front acoustic
chamber 11 with the external space, a rear acoustic terminal 24 for communicating the rear
acoustic chamber 13 with the external space, and a film 26 covering the front acoustic terminal
22. . The rear acoustic terminal 24 may also be covered with a film 28. The films 26, 28 may be
made of vinyl chloride and formed into a wave shape. [Selected figure] Figure 1
Narrow directional microphone
[0001]
The present invention relates to a narrow directional microphone that can effectively reduce
wind noise.
[0002]
A typical configuration for narrowing the conventional microphone is to use an acoustic tube.
For example, the end of an acoustic tube made of a metal tube is used as an acoustic terminal,
and an opening is provided in the peripheral wall of the acoustic tube, and this is used as
acoustic resistance in many cases. Moreover, what attached the acoustic resistance to the said
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opening is used. FIG. 5 shows an example of a conventional narrow directional microphone.
[0003]
In FIG. 5, the microphone unit 14 is attached to one end (right end in the figure) of the cylindrical
acoustic tube 10, and the other end of the acoustic tube 10 is an acoustic terminal 22. In the
peripheral wall on the front side of the microphone unit 14 of the acoustic tube 10, a slit 18
serving as an acoustic resistance is provided in parallel with the central axis of the acoustic tube
10. The sound waves from other than the direction of the central axis of the sound tube 10
interfere with each other as the sound waves entering the sound tube 10 from the sound
terminal 22 on the front end side of the sound tube 10 and the sound waves entering the sound
tube 10 from the slit 18 on the tube side The principle is that the sound pressure level is reduced
and only the sound wave in the central axial direction is converted into an electrical signal by the
microphone unit 14.
[0004]
FIG. 6 shows the results of measuring the frequency characteristics of the above-described
conventional narrow directional microphone, where the horizontal axis is the frequency (Hz) of
the sound wave, and the vertical axis is the output signal level (dBV). Based on the Japan
Electronic Machinery Manufacturers Association standards (hereinafter referred to as "EIAJ"),
based on the output voltage at a specified sound pressure under a specified condition and at a
specified frequency at a specified incident angle, It is expressed in decibels as a function of.
Hereinafter, the characteristic curves shown in FIG. 2, FIG. 11, and FIG. 13 are also measured
under the same conditions. Curve a represents the position of the sound source at 0 degrees, ie,
directly in front of the central axis of the acoustic tube, curve b represents the position of the
source at 180 degrees, ie directly behind the central axis of the acoustic tube, The case where the
position of the sound source is 90 degrees, that is, right beside, with respect to the central axis is
shown. It can be said that the directivity is higher as the curves b and c are farther from the
curve a. FIG. 7 shows the directivity of the above-described conventional narrow directional
microphone, in which one scale of the concentric circles is 1 dB, and the vertical direction of the
drawing coincides with the longitudinal direction of the acoustic tube. The EIAJ standard is also
applied to the measurement of the characteristics showing directivity as shown in FIG. 7, and
represents the free sound field sensitivity of the microphone for a specified frequency or a
narrow frequency band as a function of the incident angle of the sound wave. The results of
measurement under the same conditions are shown in FIGS. 3, 12, and 14 as well. The frequency
of the sound source is 1000 Hz. Looking at the measurement results in FIG. 7, the directivity was
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relatively good, 133 degrees.
[0005]
FIG. 8 shows the result of measuring the wind noise of the conventional narrow directional
microphone. Wind noise is noise other than the sound to be captured which is generated by air
flow hitting and crossing the acoustic tube, and is noise in a relatively low frequency region. In
accordance with the EIAJ standard, the speed and direction are expressed as the equivalent
sound pressure level by the wind with no sound field for the specified wind. Specifically, the
generated voltage at a wind speed of 2 m / s was measured, and the equivalent sound pressure
level at that time was determined. The characteristics shown in FIG. 4 are also measured under
the same conditions. In FIG. 8, the horizontal axis is the frequency of the sound wave (Hz), and
the vertical axis is the output level of the microphone (dB). As can be seen from FIG. 8, there is a
disadvantage that the level of wind noise is high, and unpleasant low frequency noise tends to be
mixed.
[0006]
The applicant filed a patent application for a narrow directional condenser microphone provided
with an acoustic terminal before and after the microphone unit (see, for example, Patent
Document 1). FIG. 9 schematically shows the invention described in Patent Document 1. As
shown in FIG. In FIG. 9, the inside of the acoustic tube 10 is divided into a front acoustic chamber
11 and a rear acoustic chamber 13 by the microphone unit 14, and the front acoustic chamber
11 and the rear acoustic chamber 13 It is connected acoustically by the gap 15 on the inner
circumferential surface. The front end of the front acoustic chamber 11 is opened to be an
acoustic terminal 22, and a circular hole opened in the side wall of the acoustic tube 10
constituting the rear acoustic chamber 13 is an acoustic terminal 24. Since the gap 15 functions
as an acoustic impedance, and the acoustic terminals 22 and 24 before and after the microphone
unit 14 are short-circuited by the acoustic impedance, a sound wave of very low frequency like
wind noise is reduced. Ru.
[0007]
The longer the acoustic tube, the higher the directivity. On the other hand, the vibration noise of
the narrow directional microphone depends on the air mass in the acoustic tube, and the longer
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the acoustic tube, the larger the air mass in the acoustic tube. Become. However, according to the
invention described in Patent Document 1, since the acoustic terminals at the front and back of
the microphone unit are short-circuited by the acoustic impedance, vibration noise can also be
reduced.
[0008]
However, when wind strikes the acoustic terminal 22 at the front end of the acoustic tube 10,
low frequency wind noise is generated, and the level of the frequency range of the wind noise is
large, so that unpleasant noise such as buzzing There is a drawback to be done. As means for
reducing such wind noise, it is conceivable to electrically reduce the low frequency response of
the microphone by using a low cut circuit. However, when a low cut circuit is used, the
diaphragm of the microphone unit vibrates at a low frequency due to wind, so it is difficult to
avoid the output of voice modulated at a low frequency. Therefore, in an extreme case, the voice
may be intermittent with wind noise such as "bubbling".
[0009]
As described above, it is difficult to reduce wind noise while obtaining narrow directivity, and
various proposals have been made in addition to the invention described in Patent Document 1.
For example, attempts have been made to attach an acoustic resistance to the acoustic terminal
on the front side of the acoustic tube or to close the acoustic terminal on the front side. FIG. 10
shows still another example of a conventional narrow directional microphone. In FIG. 10, the
inside of the acoustic tube 10 is divided into a front acoustic chamber 11 and a rear acoustic
chamber 13 by a unit holder 12 holding a microphone unit 14. The front end of the front
acoustic chamber 11 is opened to be an acoustic terminal 22, and a circular hole opened in the
side wall of the acoustic tube 10 constituting the rear acoustic chamber 13 is an acoustic
terminal 24. In the tube wall of the acoustic tube 10, at least one linear slit 18 is formed in
parallel with the central axis of the acoustic tube 10 on the front acoustic chamber 11 side. The
slit 18 is covered by an acoustic resistance 20 attached to the outer peripheral surface of the
acoustic tube 10. The acoustic resistance 20 is made of cloth, non-woven fabric, film or the like.
Although not shown in FIG. 10, the front acoustic terminal 22 may also be covered with an
acoustic resistance, or the acoustic terminal 22 may be closed.
[0010]
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FIG. 11 shows the result of measuring the output signal level (dBV) with respect to the audio
frequency (Hz) of the configuration as shown in FIG. 10 in which the acoustic resistance is
attached to the acoustic terminal 22 at the front end of the acoustic tube 10. As in the case of
FIG. 6, when the position of the sound source is 0 degree or directly in front of the central axis of
the acoustic tube, the curve b is 180 degrees or directly behind the central axis of the acoustic
pipe. In the case, the curve c shows the case where the position of the sound source is 90
degrees, that is, just beside the central axis of the acoustic tube. As can be seen from this
measurement result, the sensitivity is rather lowered and the high tone range is deteriorated as
compared with FIG. 6 showing the measurement result of the conventional example shown in
FIG. FIG. 12 shows the measurement results of the directivity in the configuration as shown in
FIG. 10 according to FIG. As can be seen from FIG. 12, the directivity is also deteriorated
compared to the conventional example shown in FIG.
[0011]
FIG. 13 shows the result of measuring the output signal level (dBV) with respect to the audio
frequency (Hz) in the configuration as shown in FIG. 10 with the acoustic terminal 22 at the front
end of the acoustic tube 10 closed. Show. As can be seen from the measurement results, it can be
seen that the sensitivity and the directional frequency response of the voice band are reduced.
Moreover, FIG. 14 has shown the measurement result of the directivity in the thing of the said
structure according to FIG. As can be seen from FIG. 14, the sound level coming from the rear
side increases and the directivity also deteriorates.
[0012]
JP 2000-83292 A
[0013]
The present invention was made to solve the problems of the conventional narrow directional
microphones described above, and to provide a narrow directional microphone capable of
obtaining high directivity and reducing wind noise. To aim.
[0014]
The present invention relates to a cylindrical acoustic tube, a microphone unit disposed in the
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acoustic tube, a front acoustic chamber and a rear acoustic chamber formed by dividing the
acoustic tube by the microphone unit, and a front acoustic chamber The rear acoustic terminal
has a front acoustic terminal for communicating with the external space, a rear acoustic terminal
for communicating the rear acoustic chamber with the external space, and a film covering the
front acoustic terminal.
The rear acoustic terminal may also be covered by the film.
The film may be made of vinyl chloride and formed into a corrugated shape.
[0015]
The film covering the front acoustic terminal acts as a diaphragm, and it is difficult to pass low
frequency sound waves due to its stiffness and allows high frequency sound waves to pass.
Moreover, the said film can block the flow of the air flow by wind. Therefore, the microphone
unit does not pick up wind noise, so that sound quality deterioration due to wind noise can be
prevented and discomfort caused by wind noise can be prevented. Wind noise can be reduced
more effectively by using a film made of polyvinyl chloride which is formed into a corrugated
shape.
[0016]
Hereinafter, embodiments of the narrow directional microphone according to the present
invention will be described with reference to FIGS. 1 to 4. The same components as those of the
conventional example described above are denoted by the same reference numerals. In FIG. 1,
reference numeral 10 denotes an acoustic tube made of an elongated cylindrical member. The
acoustic tube 10 may be formed of a metal cylinder, or may be formed of a resin cylinder. The
interior of the acoustic tube 10 is divided into a front acoustic chamber 11 and a rear acoustic
chamber 13 by a unit holder 12 holding a microphone unit 14. The microphone unit 14 is
disposed closer to the rear end (right end in FIG. 1) of the acoustic tube 10, and the front
acoustic chamber 11 is considerably longer than the rear acoustic chamber 13. The front end of
the front acoustic chamber 11 is opened to form a front acoustic terminal 22 which allows the
front acoustic chamber 11 to communicate with the external space. A round hole is opened in the
side wall of the acoustic tube 10 constituting the rear acoustic chamber 13, and this circular hole
serves as a rear acoustic terminal 24 which allows the rear acoustic chamber 13 to communicate
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with the external space. In the tube wall of the acoustic tube 10, at least one linear slit 18 is
formed in parallel with the central axis of the acoustic tube 10 on the front acoustic chamber 11
side. The slit 18 is covered by an acoustic resistance 20 attached to the outer peripheral surface
of the acoustic tube 10. The acoustic resistance 20 is made of cloth, non-woven fabric, film or the
like. The acoustic resistance 20 may be attached to the outer peripheral surface side of the
acoustic tube 10 or may be attached to the inner peripheral surface side.
[0017]
The opening of the front end of the acoustic tube 10 is covered with a film 26. Therefore, the
front acoustic terminal 22 is covered with the film 26. A film 28 is wound around the outer
periphery of the acoustic tube 10 at a portion where the rear acoustic terminal 24 is located, and
the film 28 covers the rear acoustic terminal 24. The films 26, 28 are made of plastic. In the
example, a 30 μm thick film made of vinyl chloride was used. And in order to prevent resonance,
it is good to shape in a wave shape. The pitch (interval) of the corrugation may be about 0.2 to 1
mm. In the embodiment shown in FIG. 1, both the front acoustic terminals 22 and the rear
acoustic terminals 24 are covered with the films 26, 28, but only the front acoustic terminals 22
may be covered with the film 26.
[0018]
According to the embodiment shown in FIG. 1, the acoustic terminals 22, 24 at the front and
back of the acoustic tube 10 are covered with the films 26, 28 made of vinyl chloride so that
these films 26, 28 operate as diaphragms, It resonates with the sound, especially with the lower
frequency sound. In addition, since these films 26 and 28 have stiffness, they do not transmit low
frequency sound waves but transmit high frequency sound waves. In addition, air can be
prevented from entering and exiting by the wind. As a result, it is possible to prevent wind noise
from being mixed in the signal converted by the microphone unit, and to prevent the sound from
being interrupted together with an unpleasant sound such as "buzzing".
[0019]
FIG. 2 shows the results of measuring the frequency characteristics of the embodiment shown in
FIG. 1. The horizontal axis is the frequency (Hz) of the sound wave, and the vertical axis is the
output signal level (dBV). Curve a represents the position of the sound source at 0 degrees, ie,
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directly in front of the central axis of the acoustic tube, curve b represents the position of the
source at 180 degrees, ie directly behind the central axis of the acoustic tube, The case where the
position of the sound source is 90 degrees, that is, right beside, with respect to the central axis is
shown. The level is lowered by about 3 to 10 dB at a frequency of 100 Hz or less where wind
noise is particularly large, as compared with FIGS. 6, 11 and 13 showing the frequency
characteristics of the respective conventional examples. It can be seen that the wind noise is
reduced. Since wind noise is uncorrelated noise, wind noise can be reduced to 1/2 to 1/10.
Further, in the region where the frequency of the sound wave exceeds 500 Hz, the curves b and c
are far apart from the curve a, and according to this embodiment, it can be said that the
directivity becomes high.
[0020]
FIG. 3 shows the directivity of the narrow directional microphone according to the above
embodiment in the same manner as FIG. 7 and the like. The scale of one concentric circle is 1 dB,
and the vertical direction of the drawing coincides with the longitudinal direction of the acoustic
tube. There is. The frequency of the sound source is 1000 Hz. As can be seen from FIG. 3, the
power levels for the sound waves from the back and side directions are well suppressed and
show good directivity. By the way, the pointing angle was 133 degrees.
[0021]
FIG. 4 shows the result of measuring the wind noise of the narrow directional microphone
according to the above-mentioned embodiment in accordance with the measurement result
shown in FIG. In FIG. 4, the horizontal axis is the frequency of the sound wave (Hz), and the
vertical axis is the output level of the microphone (dB). As can be seen by comparing FIG. 4 with
FIG. 8, the level of wind noise is low and the level of unpleasant low frequency noise is low.
[0022]
According to the embodiment of the narrow directional microphone according to the present
invention, in addition to the above effects, since the acoustic terminal is covered with a film,
droplets such as rain are shielded by the film and intrusion of water droplets into the inside of
the microphone There is also an effect that it can be prevented.
[0023]
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According to the present invention, wind noise can be reduced more effectively by covering both
the front acoustic terminal and the rear acoustic terminal with a film, but at least the front
acoustic terminal is covered with a film. Well, even without covering the rear acoustic terminals
with film, wind noise can be reduced more effectively than conventional narrow directional
microphones.
[0024]
The Example of the narrow directivity microphone concerning this invention is shown, (a) is a
front view, (b) is a longitudinal cross-sectional view.
It is a characteristic line which shows the frequency characteristic of the narrow directivity
microphone concerning the said Example.
It is a characteristic diagram which shows the directivity of the narrow directivity microphone
concerning the said Example. It is a characteristic line which shows the measurement result of
the wind noise of the narrow directivity microphone concerning the said Example. It is a
longitudinal cross-sectional view which shows an example of the conventional narrow directivity
microphone. It is a characteristic diagram which shows the frequency characteristic of the said
conventional narrow directivity microphone. It is a characteristic diagram which shows the
directivity of the said conventional narrow directivity microphone. It is a characteristic line which
shows the measurement result of the wind noise of the said conventional narrow directivity
microphone. It is a longitudinal cross-sectional view which shows another example of the
conventional narrow directivity microphone. It shows another example of the conventional
narrow directional microphone, wherein (a) is a front view and (b) is a longitudinal sectional
view. It is a characteristic diagram which shows the frequency characteristic of the said
conventional narrow directivity microphone. It is a characteristic diagram which shows the
directivity of the said conventional narrow directivity microphone. It is a characteristic diagram
which shows the frequency characteristic of the said conventional narrow directivity microphone.
It is a characteristic diagram which shows the directivity of the said conventional narrow
directivity microphone.
Explanation of sign
[0025]
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Reference Signs List 10 acoustic tube 11 front acoustic quality 13 rear acoustic chamber 14
microphone unit 18 slit 20 acoustic resistance 22 front acoustic terminal 24 rear acoustic
terminal 26 film 28 film
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