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JP2001119796

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DESCRIPTION JP2001119796
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
optical microphone device and an optical microphone device using the same, and more
particularly to an optical microphone device and an optical microphone device having excellent
noise reduction characteristics.
[0002]
2. Description of the Related Art When a commonly used microphone is mounted on a
motorcycle or used outdoors in a windy area, there is a drawback that the wind pressure causes
noise to cause noise and to significantly disturb speech. A noise preventing microphone device as
disclosed in Japanese Patent Publication No. 58-36879 is known as such a noise reduction
microphone.
[0003]
The microphone device disclosed herein is a through hole in which a microphone element is
housed in a frame, a foam of open cells compressed inside the frame at the periphery and the
rear of the element is filled, and the tension is provided in front of the microphone element. A
foam of open cells is filled between the inner protective plate having the above and the outer
protective film adjusted on the front surface of the frame to form a tapered portion extending
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forward around the frame. Thus, the side and back portions of the microphone element are
covered with foam so that the sensitivity is unidirectional.
[0004]
In addition, electret microphones for noise reduction as shown in FIG. 7 and dynamic
microphones as shown in FIG. 8 are known. 7A and 7B show the structure of an electret
microphone, in which FIG. 7A shows a front view, FIG. 7B shows a front sectional view, and FIG.
7C shows a rear view. A diaphragm 3 vibrating with sound pressure and an electrostatic element
4 for converting the vibration of the diaphragm 3 into an electric signal are housed in a housing
10, and sound is input from an opening 1 provided on the front surface 10a of the housing. A
small opening 2 is also provided on the back surface 10b of the housing 10 at the periphery
thereof.
[0005]
FIG. 8 is a view showing the structure of the dynamic type microphone, and (A) shows a front
sectional view and (B) shows a rear view. A magnet 21 having an opening is accommodated in
the housing 20, and a coil 22 is wound around the magnet 21. A diaphragm 23 is provided on
the front side facing the magnet 21 and a small opening 23 is provided at the periphery of the
rear surface 22b of the housing 20 so that a slightly larger opening 24 is communicated with the
opening inside the magnet 21 at the center. It is done. A change in sound pressure due to the
vibration of the diaphragm 23 is detected as a change in magnetic flux density by the magnet 21
wound with the coil 22, and this is converted into an electrical signal. In the conventional
microphone device as shown in FIG. 7 and FIG. 8, if the sound incident from the front part and
the sound incident through the opening of the back part are uniformly incident on the
diaphragm, those two sounds are They will each cancel out, disappear and not be affected.
[0006]
SUMMARY OF THE INVENTION The microphone device as disclosed in Japanese Patent
Publication No. 58-36879 and the microphone device as shown in FIGS. 7 and 8 have limited
noise reduction capabilities. That is, since the sound from the front direction and the sound from
the back direction do not structurally reach the diaphragm at the contrast, the reduction effect
on the noise is at most 5 to 7 dB, which is more than S / A microphone device with an N ratio
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could not be realized. On the other hand, in recent years, an optical microphone device has
attracted attention as a high-sensitivity and wide-band microphone device which can follow weak
sound wave fluctuations and is not influenced by the use environment.
[0007]
FIG. 6 is a view showing the structure of the head portion of the conventional optical microphone
device. Inside the microphone head 30, a diaphragm 31 which vibrates when a sound wave
strikes is stretched, and a surface 31a on the side where the sound wave strikes is exposed to the
outside. Accordingly, the sound wave 37 reaches the surface 31 a to vibrate the diaphragm 31. A
light source 32 such as an LED or the like for irradiating a light beam obliquely to the surface 31
b of the diaphragm 31 and a light beam from the light source 32 inside the head 30 located on
the surface 31 b opposite to the surface 31 a of the diaphragm 31 Lens 33 for setting the beam
diameter to a predetermined beam diameter, a light detector 35 for receiving the light reflected
by the light beam reflected by the surface 31 b, and the displacement of the light path of the
light reflected by the vibration of the diaphragm 31 The lens 34 is provided.
[0008]
Thus, when the sound wave strikes the surface 31 a of the diaphragm 31 and the diaphragm 31
vibrates, the light receiving position on the light receiving surface 35 a of the reflected light
incident on the light detector 35 changes. If the light detector 35 is configured as a position
sensor, an electrical signal corresponding to the vibration of the diaphragm 31 is extracted from
the irradiation position of the reflected light. This is the basic structure of the optical microphone
device. Even when such an optical microphone device is used, the noise reduction effect can not
be expected so much. This is because the vibration plate 31 vibrates due to the noise reaching
the vibration plate 31, and this is superimposed on the vibration of the normal sound wave 37 as
a noise signal. Therefore, an object of the present invention is to provide an optical microphone
element having a high noise reduction effect and an optical microphone device using the same
while utilizing the characteristics of the optical microphone device.
[0009]
According to the present invention, there is provided an optical microphone element comprising:
a diaphragm which vibrates by sound pressure; a first opening which accommodates the
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diaphragm and which faces the diaphragm and opens at a control position. A storage container
having a second opening, a light source for irradiating the vibrating plate with a light beam, and
light reflected from the light beam emitted to the vibrating plate is received, and a signal
corresponding to the vibration of the vibrating plate is output And an optical detector.
Furthermore, in the optical microphone element of the present invention, the diaphragm so that
the directivity pattern on the first opening side and the directivity pattern on the second opening
side are in contrast with each other and substantially the same pattern. , The light source and the
light detector are arranged. The optical microphone element, a substrate on which the optical
microphone element is mounted, and at least the first opening and the second opening of the
optical microphone element can be made to come into contact with the substrate with respect to
the sound wave An optical microphone device is configured by making a sound wave uniformly
incident on the first opening and the second opening through the cover.
[0010]
DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a structural view showing the main
configuration of an optical microphone element 100 according to an embodiment of the present
invention. The same parts as those of the conventional element shown in FIG.
[0011]
In the optical microphone element in the present invention, the diaphragm 31 vibrated by the
sound wave 37 is stretched at substantially the central portion of the storage container 40. Then,
the first opening 38 and the second opening 39 are provided on both sides of the storage
container so as to be at mutually opposite positions with respect to the diaphragm 31. With this
configuration, the sound wave enters the storage container 40 from any opening and vibrates the
diaphragm 31.
[0012]
Thus, in the optical microphone element shown in FIG. 1, when the sound pressure of the sound
wave entering from the first opening 38 and the sound pressure of the sound entering from the
second opening 39 are equal, these two sound waves The diaphragm 31 is not vibrated because
the two surfaces 31a and 31b cancel each other out. It is known that when two microphone
elements with equal reception sensitivity are arranged close to each other and sound waves
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generated at a long distance are received, the two microphone elements detect incoming sound
waves equally.
[0013]
FIG. 5 is a diagram showing a characteristic curve of distance from sound source versus acoustic
intensity. As shown in the figure, sound waves are generated from the mouth of a person at a
short distance from the microphone element. That is, sound waves are generated at a short
distance from this microphone element. The voice of this short-distance person has a spherical
field characteristic as shown by a circular curve. On the other hand, sound waves generated by
noise, for example, at long distances have the characteristics of a flat field. Thus the acoustic
intensity of a spherical wave is approximately identical along its sphere or envelope and varies
along the radius of the sphere, but in the case of a plane wave the acoustic intensity is nearly
identical at all points in the plane.
[0014]
Therefore, the optical microphone element as shown in FIG. 1 can be considered to be a
combination of two microphone elements, so when it is placed in the far-field, it is approximately
from the first opening 38 and the second opening 39 Sound waves having the same intensity and
phase characteristics arrive at the diaphragm 31, and as described above, they cancel each other
and their influence is reduced. On the other hand, since the sound wave from the near field is
unevenly incident from the first opening 38 or the second opening 39, the diaphragm 31 is
vibrated and is extracted from the light detector 35 as a signal.
[0015]
FIG. 4 shows the directivity pattern of the sensitivity of the optical microphone element shown in
FIG. 1. The directivity pattern of the front direction toward the first opening 38 and the
directivity pattern of the back direction toward the second opening 39 are eight-shaped It has a
control pattern. As described above, when the optical microphone element of the present
invention is used, noise such as ambient noise is regarded as acoustic from far-field as shown in
FIG. 5, and is equally from the first opening 38 and the second opening, respectively. The
diaphragm 31 is not vibrated because it is incident and mutually cancels out in the diaphragm
31.
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[0016]
On the other hand, since the voice generated from the speaker is regarded as the sound from the
near field, as shown in FIG. 5, the receiving sensitivities of the two microphone elements M1 and
M2 are different. That is, the sound incident from the first opening 38 and the sound incident
from the second opening 39 are different in intensity, and the diaphragm 31 is vibrated. Thus, an
optical microphone element in which the influence of noise is reduced can be realized.
[0017]
FIG. 2 is an external view showing an essential configuration of an optical microphone device
mounted with the optical microphone element 100 shown in FIG. (A) shows its surface view, (B)
shows a side view, and (C) shows a rear view. FIG. 3 is an exploded view showing the internal
structure. Next, the configuration of an optical microphone device using the optical microphone
element of the present invention will be described with reference to FIGS. 2 and 3. FIG.
[0018]
The optical microphone element 100 according to the present invention as shown in FIG. In this
case, the first opening 38 is mounted on the printed circuit board 50 so that the second opening
39 is directed downward, thereby obtaining directivity patterns of equal sensitivity in the upper
and lower directions as shown in FIG. 4. Become. The peripheral circuits 51 for driving the
optical microphone element 100 are disposed and mounted on the upper and lower surfaces of
the printed circuit board 50 so as to surround the optical microphone element 100. A cable 52
for microphone output or power supply is connected to the substrate 50.
[0019]
As described above, while mounted on the printed circuit board 50, the net-like covers 54a and
54b are covered on the top and bottom with the sponges 53a and 53b, and the optical
microphone device is obtained by fixing the covers 54a and 54b. When the optical microphone
device thus configured is placed in the far field, the sound waves reach the diaphragm evenly
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through the net covers 54a and 54b. Further, in the case of being placed in the near field, since
the light is incident unevenly, the diaphragm vibrates to obtain an amplified output.
[0020]
As described above, the optical microphone element of the present invention and the optical
microphone device using the same have a structure in which sound waves come from the
openings provided at the left and right or front and rear control positions with respect to the
diaphragm. Therefore, sound waves such as noise from far-fields cancel each other and
disappear, and only voice input from near-fields is amplified and output. Therefore, it is possible
to realize an acoustic device in which the influence of noise is significantly reduced.
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