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JP2004080255

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DESCRIPTION JP2004080255
The present invention provides a directional microphone which is thin and excellent in directivity
as compared to a conventional microphone. A microphone unit having a diaphragm having a
conductor pattern arranged to face a permanent magnet plate, and a back surface opposite to the
surface of the microphone unit facing the sound source have a predetermined gap. It has a sound
insulation board which spreads along the back and shields the sound toward the back. [Selected
figure] Figure 1
Directional microphone
TECHNICAL FIELD The present invention relates to a directional microphone. 2. Description of
the Related Art In an acoustic facility such as a hall, for example, a sound generated from a sound
source such as a musical instrument is collected by a microphone, and an electrically generated
reverberation is added to the sound to obtain a speaker. The sound field support system which
emits sound from is proposed (for example, refer to patent documents 1 and patent documents
2.). Further, as an example of a microphone, a microphone having a vibrating film having a
conductor pattern disposed to face a permanent magnet plate has been proposed (see, for
example, Patent Document 3). [Patent Document 1] Japanese Patent Application Laid-Open No. 6149276 (Paragraph No. 0011-Paragraph No. 0031, FIG. 1) [Patent Document 2] Japanese Patent
Application Laid-Open No. 6-149277 (Paragraph No. 0009-Paragraph No. Patent Document 3:
Japanese Patent Application Laid-Open No. 9-331596 (Paragraph No. 0016-Paragraph No. 0025,
FIG. 1-FIG. 2) [0007] Problems to be Solved by the Invention Here, it is a howling problem that
becomes a problem when deploying a sound field support system to an acoustic facility such as a
hall. Howling is a phenomenon in which a sound wave emitted by a speaker is picked up again by
a microphone and an oscillation sound of a specific frequency is generated, which is extremely
unpleasant for the listener. In order to prevent this howling, it is necessary to use a directional
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microphone, for example, to pick up only the sound emitted from the sound source to be
originally picked up by the microphone such as a performance sound. However, conventional
directional microphones are long rod-like ones, and when this directional microphone is to be
installed toward a player on the stage, for example, it will hang from the ceiling above the stage,
There is also a problem that the hanging directional microphone does not give a very good view.
Therefore, it is conceivable to adopt a flat microphone as disclosed in the above-mentioned
Patent Document 3. In the case of this flat microphone, it can be installed at a considerably high
place above the stage, and it can not be seen from the passenger seat, and the landscape can be
maintained. However, since the microphone disclosed in Patent Document 3 picks up sound on
both the front surface and the back surface of the flat plate shape, the reflected sound on the
ceiling portion is also picked up, which facilitates howling.
The present invention has been made in view of the above circumstances, and an object thereof
is to provide a thin directional microphone. A directional microphone according to the present
invention for achieving the above object comprises a microphone unit having a diaphragm
having a conductor pattern arranged to face a permanent magnet plate, and the microphone unit
A sound shielding plate is provided extending along the back surface with a predetermined gap
between the front surface facing the sound source and the back surface opposite to the sound
source, for blocking the sound traveling toward the back surface. The microphone unit
constituting the directional microphone according to the present invention is sensitive to sound
on both the front and back sides, but is equipped with a sound insulation board on the back side,
so only the sound incident from the front side with the sound source is picked up Be done. Here,
in the case of the directional microphone according to the present invention, the sound insulation
plate is disposed with a gap between it and the microphone unit, so that the sound wave incident
on the microphone unit from the side is the surface of the microphone unit and It is divided into
the back and picked up on both the front and back. In this case, since the sound picked up on the
front side and the sound picked up on the back side are always in phase, the front and back sides
of the microphone unit are pushed simultaneously or attracted simultaneously, eventually
canceling each other out. Sound incident from the side will not have sensitivity. That is, since the
sound insulation boards are disposed apart from each other, not only the sound directed to the
back surface but also the sound from the side surface is canceled, and only the sound wave
directed to the front surface is detected with strong directivity. Here, in the directional
microphone of the present invention, it is preferable that the sound absorbing material be
provided between the microphone unit and the sound insulation plate. In this case, the sound
wave directed to the back surface of the microphone unit can be attenuated more greatly than in
the case of the sound insulation board alone, and the surface can be made to have strong
directivity. DETAILED DESCRIPTION OF THE INVENTION Embodiments of the present invention
will be described below. FIG. 1 is a perspective view and a side view showing a directional
microphone according to an embodiment of the present invention. FIG. 1A is a perspective view
showing a directional microphone 1. The directional microphone 1 shown in FIG. 1A has a sound
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insulation plate 16 disposed at a predetermined distance L between the microphone unit 11
attached to the frame 18 and the back surface 11 b of the microphone unit 11. , A sound
absorbing material 17 disposed between the back surface 11 b of the microphone unit 11 and
the sound insulating plate 16 in contact with the surface 16 a of the sound insulating plate 16,
and a support rod 191 fixing the microphone unit 11 and the sound insulating plate 16 with a
predetermined distance L. And a small screw 192.
The sound insulation plate 16 is disposed at a position facing the back surface 11 b of the
microphone unit 11 with the support rod 191 interposed between the sound insulation plate 16
and the frame 18. Here, the microphone unit 11 and the sound insulation plate 16 are inserted
through the small screws 192 inserted through the through holes 18 b provided at the four
corners of the frame 18 and the through holes 16 b provided at the four corners of the sound
insulation plate 16. Machine screws 192 are screwed into both ends of the support rod 191 and
fixed with a predetermined distance L. As described above, since the directional microphone 1 is
configured by attaching the sound insulation plate 16 which is a thin flat plate to the thin flat
microphone unit 11, the directional microphone 1 is slightly thicker than the microphone unit 11
alone. However, it has a thin flat plate shape. FIG. 1 (b) is a side view of the directional
microphone 1 shown in the perspective view of FIG. 1 (a). The microphone unit 11 constituting
the directional microphone 1 has directivity such that it has strong sensitivity only to sound from
a direction perpendicular to the front surface 11a or the back surface 11b. The directivity of the
microphone unit 11 will be described later using another drawing. Since the directional
microphone 1 is provided with the sound insulation plate 16 and the sound absorbing material
17 on the back surface 11 b side of the microphone unit 11 as described above, the sound wave
incident from the back surface 1 b of the directional microphone 1 is canceled It will be done.
When the sound wave W incident to the directional microphone 1 from the side reaches the edge
18 a of the frame 18, it divides into the sound wave Wa directed to the surface 11 a side of the
microphone unit 11 and the sound wave Wb directed to the back surface 11 b. The sound wave
Wa directed to the surface 11 a side is picked up on the surface 11 a of the microphone unit 11
which constitutes the surface 1 a of the directional microphone 1. Since the sound insulation
plate 16 is disposed apart from the microphone unit 11, the sound wave Wb directed to the back
surface 11b is transmitted along the back surface 11b of the microphone unit 11 and picked up
on the back surface 11b. Since the sound wave Wa picked up on the surface 11 a of the
microphone unit 11 and the sound wave Wb picked up on the back surface 11 b are always in
phase, they simultaneously push or attract the surface 11 a and the back surface 11 b of the
microphone unit 11 simultaneously. And cancel each other. Therefore, the directional
microphone 1 cancels not only the sound wave incident from the back surface 1 b but also the
sound wave incident from the side, and has strong sensitivity only to the sound wave incident
from the direction perpendicular to the surface 1 a It will have directivity.
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FIG. 2 is a schematic view showing the directivity of the directional microphone 1. As described
above, the directional microphone 1 has strong directivity only on the surface 1 a side. For this
reason, this directional microphone 1 has high sensitivity to the front surface 1a, and the
sensitivity on the back surface 11b side is suppressed. FIG. 3 is an exploded perspective view
showing the permanent magnet plate 110 and the vibrating membrane 120 which are main
components of the microphone unit 11. The microphone unit 11 includes two permanent magnet
plates 110 and a vibrating membrane 120 disposed between the two permanent magnet plates
110 so as to face the permanent magnet plate 110. The permanent magnet plate 110 is a
rectangular flat plate and has through holes 111 at the four corners. Further, the permanent
magnet plate 110 has a strip-like magnetized N-pole area 112 and an S-pole area 113. The N
pole region 112 and the S pole region 113 are alternately arranged in parallel stripes. The
permanent magnet plate 110 is provided with a large number of vent holes 114 for passing
sound waves along the boundary Z between the N pole region 112 and the S pole region 113.
The vent holes 114 are opened at a constant pitch along the boundary Z. Furthermore, by
shifting the arrangement of the vent holes 114 on the adjacent boundary lines Z by half pitch,
the multiple vent holes 114 of the permanent magnet plate 110 are arranged in a staggered
pattern. The vibrating membrane 120 is a rectangular thin film of substantially the same size as
the permanent magnet plate 110 in which a meandering conductive wire 122 is printed on the
flexible resin film 121. Through holes 123 are formed at the four corners of the vibrating
membrane 120 at positions corresponding to the through holes 111 provided at the four corners
of the opposing permanent magnet plate 110. The meander-shaped conducting wire 122 is wired
such that the linear portion 122 a of the conducting wire 122 is located along the boundary Z
between the N pole region 112 and the S pole region 113 of the opposing permanent magnet
plate 110. FIG. 4 is a side view and a cross-sectional view of the microphone unit 11. FIG. 4A is a
side view of the microphone unit 11. The microphone unit 11 shown in FIG. 4A is disposed
opposite to the permanent magnet plate 110 between the two permanent magnet plates 110
which are overlapped with a predetermined gap. And a buffer member 130 interposed between
the permanent magnet plate 110 and the diaphragm 120, and a support rod 140 for regulating
the relative position of the diaphragm 120 to the permanent magnet plate 110. .
A high magnetic permeability magnetic plate 150 is in close contact with the surface 110 b of
the permanent magnet plate 110 opposite to the vibrating film facing surface 110 a for
preventing the leakage of the magnetic flux. Furthermore, similar through holes 151 are formed
at the four corners of the high magnetic permeability magnetic plate 150 at positions
corresponding to the through holes 111 provided at the four corners of the permanent magnet
plate 110. The buffer member 130 is flexible and air-permeable, and is configured by stacking a
plurality of sheets 131 having substantially the same size as the vibrating membrane 120. At this
time, the sheets 131 are overlapped in a sparse state with a slight gap between each other, and
have freedom in the thickness direction. Similarly to the vibrating membrane 120, the through
holes 132 are formed at the four corners of the sheet 131 that constitutes the buffer member
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130. The support rod 140 is inserted through the through holes 111 and 151 provided in
communication with the four corners, and the two permanent magnet plates 110 and the high
magnetic permeability magnetic plate 150 are provided with nuts at both ends of the support rod
140. The screw 141 is firmly fixed by screwing. Furthermore, the support film 140 is also
inserted through the through holes 123 and 132 provided at the four corners of the vibrating
membrane 120 and the buffer member 130, but in a state where they are not fixed and
supported at the four corners. Since the vibrating membrane 120 and the buffer member 130
are restricted in the in-plane direction because of their existence, they can be freely displaced in
the thickness direction. Thus, since the microphone unit 11 has a structure in which thin flat
plates are stacked, it has a thin flat plate shape. FIG. 4 (b) is a cross-sectional view showing the
main part of the microphone unit 11 shown in FIG. 4 (a). The permanent magnet plate 110 has
the N pole region 112 and the S pole region 113 which are alternately arranged in parallel
stripes, as described above. Furthermore, the permanent magnet plate 110 is provided with a
large number of vent holes 114 for passing sound waves along the boundary Z between the N
pole region 112 and the S pole region 113. In the high magnetic permeability magnetic plate
150 in close contact with the permanent magnet plate 110, the same air holes 152 are formed at
the positions corresponding to the air holes 114 provided in the permanent magnet plate 110.
The vibrating membrane 120 has the meander-shaped conducting wire 122 as described above.
The straight portion 122 a of the conducting wire 122 is wired along the boundary Z between
the N pole region 112 and the S pole region 113 of the permanent magnet plate 110.
In a space sandwiched by the two permanent magnet plates 110, lines of magnetic force H which
pass from the N pole region 112 of the permanent magnet plate 110 toward the adjacent S pole
region 113 pass. The magnetic lines of force H pass substantially horizontally in the vicinity of
the boundary Z between the N pole region 112 and the S pole region 113. Since the linear
portion 122a of the conducting wire 122 included in the vibrating membrane 120 is wired along
the boundary Z between the N pole region 112 and the S pole region 113 of the permanent
magnet plate 110, the linear portion 122a is crossed The magnetic field lines H pass in such a
direction. A sound wave emitted from the sound source and directed to the front surface 11 a or
the back surface 11 b of the microphone unit 11 passes through the air vent 152 provided in the
high magnetic permeability magnetic plate 150 and the air vent 114 provided in the permanent
magnet plate 110. , Is transmitted to the vibrating membrane 120. The vibrating membrane 120
to which the sound wave is transmitted vibrates in the thickness direction according to the
magnitude of the transmitted sound wave. Due to this vibration, the linear portion 122a of the
conducting wire 122 included in the vibrating membrane 120 moves up and down in the
magnetic force lines H passing in the direction crossing the linear portion 122a. Due to the
vertical movement, a voltage is generated in the linear portion 122 a of the conducting wire 122.
The total voltage generated on the conductor 122 is the sum of the voltages generated on the
individual straight portions 122 a of the conductor 122. This total voltage is detected as an
output signal of the microphone unit 11. FIG. 5 is a schematic view showing the appearance of
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the microphone unit 11 and the directivity of the microphone unit 11. FIG. 5A is a perspective
view showing the appearance of the microphone unit 11. As described above, since the
microphone unit 11 has a structure in which thin flat plates are stacked, it has a thin flat plate
shape. Further, the microphone unit 11 picks up a sound wave by a plurality of sound sensing
units 11 c provided on the front surface 11 a or the back surface 11 b. The sound sensing unit
11 c corresponds to the vent holes 114 and 152 provided in communication with the permanent
magnet plate 110 and the high magnetic permeability magnetic plate 150 shown in FIG. 4. Then,
an output signal of the microphone unit 11 is obtained by adding the output signals generated by
the individual sound sensing units 11 c in accordance with the sound wave picked up. FIG. 5 (b)
is a schematic view showing the directivity of the microphone unit 11. Since the microphone unit
11 has the same structure on the front surface 11 a side and the rear surface 11 b side, the
microphone unit 11 has sensitivity of the same strength on the front surface 11 a side and the
rear surface 11 b side.
FIG. 6 is a diagram for explaining the directivity of the microphone unit 11. FIG. 6A shows that
the microphone unit 11 picks up the sound wave S from the direction perpendicular to the
surface 11 a by the sound sensing unit 11 c on the surface 11 a. At this time, an output signal is
generated in the plurality of sound sensing units 11 c provided on the surface 11 a according to
the sound wave S picked up. FIG. 6A shows the waveforms of the output signals I1, I2, and I3
generated in any three of the plurality of sound sensing units 11c. Since the plurality of sound
sensing units 11c simultaneously pick up the sound waves S, the output signals I1, I2, and I3 are
in phase. Similarly, the output signals generated in the other sound sensing units 11c are all in
phase. Since the sum of the output signals generated by the individual sound sensing units 11 c
is the output signal of the microphone unit 11, the microphone unit 11 is in the same phase if all
the output signals generated by the individual sound sensing units 11 c are in phase. The output
signal of 11 has a large value. FIG. 6B is a view showing how the microphone unit 11 picks up
the sound wave S obliquely incident on the surface 11 a by the sound sensing unit 11 c on the
surface 11 a. Since the sound waves S are obliquely incident on the surface 11 a, the plurality of
sound sensing units 11 c on the surface 11 a pick up the sound waves S with a time difference T
for each adjacent sound sensing unit 11 c. Therefore, the output signal generated in the sound
sensing unit 11c according to the sound wave S picked up is out of phase by this time difference
T for each adjacent sound sensing unit 11c. In FIG. 6 (b), there is a state that a phase shift is
generated in the waveforms of the output signals I1, I2, I3, I4 generated in the four adjacent
sound sensing units 11c among the plurality of sound sensing units 11c. It is shown. Similarly, a
phase shift also occurs in the output signal generated in the other sound sensing unit 11c. Since
a phase shift occurs in the output signal of each sound sensing unit 11c, when these signals are
added, they cancel each other, and the output signal of the microphone unit 11 becomes a small
value. In particular, when the time difference T is equal to the half cycle of the sound wave S, the
phase of the output signal is shifted by a half cycle for each of the sound sensing units 11c, so
the output signal of the microphone unit 11 becomes zero. This means that the microphone unit
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11 has high sensitivity to the sound wave from the direction perpendicular to the surface 11 a
and the sensitivity to the sound wave incident obliquely is suppressed.
Furthermore, since the microphone unit 11 has the same structure on the front surface 11a side
and the rear surface 11b side, it has strong sensitivity also to sound waves from the direction
perpendicular to the rear surface 11b. Therefore, the microphone unit 11 has directivity such
that it has strong sensitivity only to sound waves from the direction perpendicular to the front
surface 11a or the back surface 11b. FIG. 7 is a plan view and a side view showing a microphone
group 3 in which a plurality of directional microphones 1 are arranged on the same plane 20 as
an example of use of the directional microphone 1. FIG. 7A is a plan view of the microphone
group 3. In the microphone group 3 shown in FIG. 7A, twenty-four directional microphones 1 are
arranged on the same plane 20, four columns vertically and six rows horizontally. Since the
microphone group 3 can pick up the sound wave with the wide surface 3a, it can have strong
directivity even to sound waves with a lower frequency than when the directional microphone 1
is used alone. FIG. 7B is a side view showing the microphone group 3 shown in FIG. 7A picking
up the sound wave S on the surface 3 a. FIG. 8 is a block diagram showing the overall
configuration of a sound field support system 8 using the directional microphone 1. The sound
emitted from the sound source is picked up by a plurality of directional microphones 1, and the
output of the directional microphone 1 is input to the reflected sound generator 5 through the
amplifier 4. At this time, the plurality of directional microphones 1 may be arranged on the same
plane and used in order to give strong directivity even to sound waves of low frequency. The
reflected sound generator 5 is controlled by the controller 6 and, as an acoustic characteristic of
a sound field such as a hall, for example, a signal that electrically simulates a reverberation sound
suitable for playing a musical instrument Add to output signal. The output signal of the reflected
sound generator 5 is emitted to the sound field by the speakers 7 arranged at various places in
the sound field. As described above, since the directional microphone 1 has high sensitivity only
on the surface, for example, when the speaker 7 is arranged on the same plane as the surface of
the directional microphone 1, it is emitted from the speaker 7 Since the directional microphone 1
does not pick up the muffled sound, the occurrence of the howling phenomenon can be
prevented. Further, since the directional microphone 1 has a thin shape, it can be installed
without impairing the view in the sound field.
As described above, according to the directional microphone 1 of the present invention, the
howling phenomenon occurs, for example, by arranging the directional microphone 1 and the
speaker 7 on the same plane. Can be prevented. Furthermore, since the directional microphone 1
of the present invention has a thin shape, it can be installed without impairing the view in the
sound field. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view and a side view
showing a directional microphone according to an embodiment of the present invention. FIG. 2 is
a schematic view showing the directivity of a directional microphone. FIG. 3 is an exploded
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perspective view showing a permanent magnet plate and a diaphragm, which are main
components of the microphone unit, taken out; FIG. 4 is a side view and a cross-sectional view
showing the structure of a microphone unit. FIG. 5 is an external view of a microphone unit and a
schematic view showing directivity of the microphone unit. FIG. 6 is a diagram for explaining the
directivity of the microphone unit. FIG. 7 is a plan view and a side view showing a microphone
group in which a plurality of directional microphones are arranged on the same plane as an
example of use of the directional microphone. FIG. 8 is a block diagram showing an overall
configuration of a sound field support system using directional microphones. Description of the
code 1 directional microphone 1a front surface of directional microphone 1b back surface of
directional microphone 11 microphone unit 11a front surface of microphone unit 11b back
surface of microphone unit 11c sound sensing unit of microphone unit 110 permanent magnet
plate 110a diaphragm facing surface 110b A surface opposite to the diaphragm facing surface
111 A through hole 112 of permanent magnet plate 112 N pole region 113 S pole region 114 A
vent 120 of permanent magnet plate 120 diaphragm 121 film 12 resin film 122 conductor 122
a straight portion of conductor 123 through hole 130 Buffer member 131 sheet 132 through
hole 140 support bar 141 nut 150 high permeability magnetic plate 151 through hole 152 high
permeability Permeable plate air vent 16 Sound insulation plate 16a Surface of sound insulation
plate 16b Through hole of sound insulation plate 17 Sound absorbing material 18 Frame 18a
Frame edge 18b Frame through hole 191 Support rod 192 Machine screw 20 Coplanar 3
Microphone unit group 3a Microphone unit Group surface 4 amplifier 5 Reflected sound
generator 6 Controller 7 Speaker 8 Sound field support system H Magnetic field line I1, I2, I3, I4
Signal L interval S sound wave T delay time W from the side direction toward the sound unit
toward the microphone unit Boundary line between sound wave Z N pole region and S pole
region going to the back side of sound wave Wb
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