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JP2001119782

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
complete, reliable or fit for specific purposes. Critical decisions, such as commercially relevant or
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DESCRIPTION JP2001119782
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
sound pickup device, and more particularly to a sound pickup device having two microphones
whose sensitivities are substantially equal even if the distance from the sound pickup object is
different.
[0002]
2. Description of the Related Art A conventional sound pickup apparatus called an array type
microphone having a plurality of microphones generally adopts a construction as shown in FIG. 9
in order to obtain a noise canceling effect for reducing ambient noise. The A plurality of
microphones 201, 202, 203... 20N are arranged at equal intervals and fixed to the support frame
40 to make an array type microphone. Since the phase and the signal strength of voices incident
on a pair of microphones from a long distance are almost equal, canceling the voice signal of the
voice from a distance by reversing the phase of the voice signal of one microphone and
superposing Can.
[0003]
Also, in the case of voice from a short distance, voices are input to the microphone units with
different phases and signal strengths, so it is necessary to extract directional voice signals by
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1
detecting the phases and signal strengths. Can. Therefore, the voice signal with directivity can be
taken out for the voice from the short distance, and the voice signal obtained by canceling the
voice signal from the far distance, that is, the noise and the noise can be taken out.
[0004]
However, in the array type microphone as shown in FIG. 9, the sensitivity of each microphone is
lowered so that only the voice of the speaker from a short distance can be captured with
directivity. There is a problem that sound collection becomes difficult when the distance from the
microphone to the speaker increases. In addition, it is necessary to use a plurality of microphone
elements in order to give a noise cancellation effect or to give directivity. There is a problem that
it is extremely difficult to obtain a noise cancellation effect by obtaining a correlation among a
plurality of elements and to obtain directivity because there is a variation in characteristics
among a plurality of microphone elements. The present invention has been made to solve these
problems, and it is possible to pick up sounds with equal sensitivity without using a large number
of microphone elements and at different distances between the speaker and the microphone. It
aims to provide a possible sound collection device.
[0005]
According to the present invention, there is provided a sound collection apparatus comprising: a
first microphone directed to a first sound collection object at a first distance in a first direction;
and a first microphone making a predetermined angle in the first direction. A second microphone
directed to a second sound pickup object at a second distance in a direction 2 and switching
means for selectively switching between the first microphone and the second microphone; A
vibrating plate, a light source for irradiating the vibrating plate with a light beam, and a
photodetector for receiving the reflected light of the light beam emitted to the vibrating plate and
outputting a signal corresponding to the vibration of the vibrating plate Using an optical
microphone comprising: a light source drive circuit driven to supply a predetermined current to
the light source; and a negative feedback circuit supplying the signal output from the light
detector to the light source drive circuit as a negative feedback signal Is configured to in
conjunction with the switching of the microphone switching the negative feedback amount of the
negative feedback circuit of said switching means.
[0006]
Further, in the sound collection device of the present invention, the negative feedback amount
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can be set so that the audio output signal levels of the first and second microphones become
substantially equal.
Furthermore, in the sound collection device of the present invention, the negative feedback
amount can be set according to the first distance and the second distance.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION In the sound pickup apparatus of the present
invention, two microphone elements placed at the same place are directed to a sound pickup
object at a predetermined angle, and the microphone elements are selectively switched. . Also, an
optical microphone element is used as the microphone element. Therefore, prior to describing
the embodiment of the sound collection device of the present invention, the basic principle of the
optical microphone and the structure thereof will be described.
[0008]
FIG. 3 is a view showing the structure of the head portion of the optical microphone element 50.
As shown in FIG. Inside the microphone head 1, a diaphragm 2 that vibrates when a sound wave
strikes is stretched, and the surface 2a on the side where the sound wave strikes is exposed to
the outside. Accordingly, the sound wave 7 reaches this surface 2 a to vibrate the diaphragm 2. A
light source 3 such as an LED for irradiating a light beam obliquely to the surface 2 b of the
diaphragm 2 and a light beam from the light source 3 inside the head 1 located on the surface 2
b opposite to the surface 2 a of the diaphragm 2 To enlarge the displacement of the optical path
of the reflected light due to the vibration of the diaphragm 2 and the lens 4 for making the light
beam into a predetermined beam shape, the light detector 5 that receives the reflected light that
the beam surface reflects on the surface 2 b A lens 6 is provided. As described above, when the
sound wave 7 strikes the surface 2 a of the diaphragm 2 and the diaphragm 2 vibrates, the light
receiving position on the light receiving surface 5 a of the reflected light incident on the light
detector 5 changes.
[0009]
If the light detector 5 is configured as a position sensor, an electric signal corresponding to the
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vibration of the diaphragm 2 is extracted from the irradiation position of the reflected light. This
is the basic structure of the optical microphone. However, in the optical microphone shown in
FIG. 3, the noise reduction effect can not be expected so much. That is, the diaphragm 2 vibrates
also by the noise reaching the diaphragm 2, and this is superimposed on the vibration of the
normal sound wave 7 as a noise signal.
[0010]
An optical microphone having a structure as shown in FIG. 4 is known as an optical microphone
in which the effect of noise is reduced and a noise reduction effect is further achieved. In the
structure shown in FIG. 4, the diaphragm 2 that vibrates by the sound wave 7 is stretched at a
substantially central portion of the head 1. Then, the first opening 15 and the second opening 16
are provided on both sides of the head 1 so as to be symmetrical with respect to the diaphragm
2. By this configuration, the sound wave penetrates into the head 1 from any opening to vibrate
the diaphragm 2.
[0011]
In the optical microphone element 50 shown in FIG. 4, when the amplitude and the phase of the
sound wave invading from the first opening 15 and the sound wave invading from the second
opening 16 are equal, these two sound waves are both sides of the diaphragm 2. The diaphragm
2 is not vibrated by canceling each other in 2a and 2b. It is known that when two microphone
elements with equal reception sensitivity are arranged close to each other and sound waves
generated at a long distance are received, the two microphone elements detect incoming sound
waves equally.
[0012]
In general, sound waves originate from the mouth of a person at a short distance from the
microphone element, i.e. sound is produced at a short distance from the 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 at a long distance, for example, noise and
sound, have the characteristics of a flat field. The acoustic intensity of a spherical wave is
substantially 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.
08-05-2019
4
[0013]
Therefore, since the optical microphone element as shown in FIG. 4 can be considered as a
combination of two microphone elements, when it is placed in the far-field, the first and second
openings 15 and 16 can be used. Sound waves having substantially the same amplitude and
phase characteristics arrive at the diaphragm 2, 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 15 or the second opening 16, the diaphragm 2 is
vibrated and is extracted from the light detector 5 as a signal. In this way, an optical microphone
element capable of further reducing the influence of noise is obtained by the structure of FIG.
[0014]
FIG. 7 is a diagram showing the directivity pattern of the optical microphone element shown in
FIG. 3 and FIG. (A) shows the directivity pattern of the optical microphone element 50 shown in
FIG. 3, and a substantially circular directivity having the maximum sensitivity in the direction
perpendicular to the diaphragm 2 toward the opening (left direction in the drawing) Have sex
patterns. (B) is a directivity pattern of the optical microphone element 50 shown in FIG. 4 and
has a nearly 8-shaped directivity pattern having maximum sensitivity in both directions of the
openings 15 and 16.
[0015]
Here, as shown in FIG. 2 or 6, the directivity pattern of the optical microphone element 50 shown
in FIG. 3 and FIG. 4 is extended in the axial direction showing the maximum sensitivity or
changed to narrow down in the direction orthogonal to the axis. be able to. In order to change
the directivity pattern in this way, part of the detection output from the light detector 5 is
negatively fed back (negative feedback) to the light source drive circuit that drives the light
source 3 using a negative feedback circuit. Good. FIG. 5 is a view showing a schematic
configuration of an optical microphone device using a feedback circuit 100 for changing a beam
pattern as shown in FIG. 2 or 6.
[0016]
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5
The output from the light detector 5 is taken out through the filter circuit 8 and amplified by the
amplifier 9 to become a microphone output. The filter circuit 8 is used to extract only signal
components in the desired frequency range. Here, in the optical microphone device shown in FIG.
5, a part of the output signal taken out from the light detector 5 is supplied with a predetermined
current to the light source 3 through the negative feedback (negative feedback: NFB) circuit 100.
The light source drive circuit 13 driving the light source 3 is configured to be supplied as a
negative feedback signal.
[0017]
The negative feedback circuit 100 comprises a small signal amplification circuit 10, a filter
circuit 11 for taking out only a signal component in a desired frequency range from the output,
and a comparator 12. The non-inverting input terminal of the comparator 12 is connected to a
reference power supply 14 serving as a reference voltage. The signal extracted via the filter
circuit 11 is supplied to the inverting input terminal of the comparator 12. With such a
configuration, the comparator 12 outputs a smaller output level as the output of the filter circuit
11 is larger, whereby the light source drive circuit 13 operates to reduce the current supplied to
the light source 3.
[0018]
Here, the small signal amplifier circuit 10 amplifies the signal only when the input signal level is
lower than a predetermined level, and does not amplify a signal higher than a certain level.
Therefore, when the input signal level is equal to or higher than a certain level, the output signal
level does not change and the amplification (gain) becomes zero. When the input signal is lower
than a predetermined signal level, amplification is performed so as to increase as the signal level
decreases. Furthermore, the rate of increase of the output signal relative to the input signal is
higher as the input signal level is smaller. Here, since the output from the light detector 5 is in
proportion to the received sound volume, the output of the small signal amplifier circuit 10 is
amplified and output as it is smaller the smaller volume.
[0019]
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Since this output is input to the inverting input terminal of the comparator 12 through the filter
circuit 11, the output of the comparator 12 decreases its output level as the volume decreases.
As a result, the current supplied to the light source 3 operates to lower the light output of the
light source 3 as the volume becomes smaller. That is, the sensitivity of the microphone
decreases as the volume decreases. Also, since the signal above the predetermined level is not
amplified, the light output is not limited at that signal level. Therefore, the sensitivity of the
microphone does not decrease either.
[0020]
If the sound coming from an axial direction perpendicular to the diaphragm does not cause a
drop in sensitivity of the microphone, the sensitivity will be along the original directivity pattern
curve if the sound is shifted from the axial direction It will gradually decline. When the level
becomes lower than a certain level, the small signal amplifier circuit 10 comes to have an
amplification degree, the supply current control of the light source drive circuit 13 works, and
the sensitivity of the microphone further decreases. As a result, in the optical microphone device
having the negative feedback circuit 100, as shown in FIG. 2 or FIG. 6, the width of the
directional beam is narrowed more than the directional pattern of sensitivity.
[0021]
FIGS. 2 and 6 show pattern changes of directivity due to changes in the amount of negative
feedback. (A) shows the directivity pattern when negative feedback is not applied, and in this
case, it becomes a substantially circular directivity pattern. Next, directivity patterns when
negative feedback is applied are shown in (B) and (C). In the case of (B), the amount of negative
feedback is small, and in the case of (C), the amount of negative feedback is large. The amount of
negative feedback is changed by varying the amplification degree of the small signal
amplification circuit 10 in this manner, and the directivity pattern of sensitivity is expanded in
the axial direction of the maximum sensitivity or changed to narrow down in the direction
orthogonal to the axis. be able to. Thus, the directivity characteristic of the sensitivity of the
optical microphone can be changed.
[0022]
In the sound pickup apparatus according to the present invention, the directivity characteristic of
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the selected microphone is changed by using an optical microphone capable of changing such a
directional beam pattern. FIG. 1 is a view showing the main configuration of a sound collection
device according to an embodiment of the present invention. In the present invention, the abovementioned optical microphone is used. The sound collection device of the present invention is
configured, for example, as a hands-free sound collection device attached to a dashboard of a car.
The two optical microphone elements 50a and 50b are attached at a predetermined angle θ in
the direction toward the driver's seat 60 and the passenger's seat 65, respectively.
[0023]
In this case, since the optical microphone elements 50a and 50b are located at substantially the
same position, the distance l1 between the optical microphone element and the driver's seat 60 is
different from the distance l2 between the front passenger's seat and There is. Therefore, the
diaphragms 2 of the optical microphone elements 50a and 50b are attached at an angle θ so as
to be parallel to the driver seat 60 and the passenger seat 65, respectively. Thereby, the
sensitivity directivity of each microphone element with respect to the driver's seat 60 or the
passenger's seat 65 is maximized.
[0024]
The detection output from each microphone element is input to the contact of the changeover
switch 55. By switching the changeover switch 55, the sound detected from any of the optical
microphone elements is taken out as an output signal through the amplifier 9. A part of the
output signal from the optical microphone element 50a is negatively fed back to the light source
drive circuit 13 via the negative feedback circuit 100a, and the detection signal from the optical
microphone element 50b is sent to the light source drive circuit 13 via the negative feedback
circuit 100b. Negative feedback. In this case, the negative feedback amounts of the negative
feedback circuits 100a and 100b are set to be different according to the distance l1 and the
distance l2.
[0025]
The setting of the negative feedback amount can be set to different values by changing the
amplification degree of the small signal amplification circuit 10 in the negative feedback circuit
as described above. By changing the setting of the amount of negative feedback according to the
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distances l1 and l2 as described above, the output signal level of the voice becomes almost equal
even when the voice from either side is taken out by the changeover switch 55. Can be That is,
when the distance l1 to the driver's seat 60 is smaller than the distance l2 to the passenger's seat
65, the amount of negative feedback of the negative feedback circuit 100a is smaller than the
negative feedback circuit of the negative feedback circuit 100b. Increase the beam width. As a
result, it is possible to eliminate the difference in sound collection sensitivity due to the
difference in the distance from the driver's seat and the passenger's seat to the microphone unit.
[0026]
FIG. 8 shows a microphone unit 300, in which optical microphone elements 50a and 50b
arranged at an angle θ with each other, a power supply drive circuit 13 for driving the optical
microphone elements, and different negative values for the respective optical microphone
elements Negative feedback circuits 100a and 100b for setting a feedback amount are
incorporated. In the embodiment shown in FIG. 1, the switch 55 is manually switched to pick up
the sound from the driver's seat 60 and the sound from the assistant's seat 65. The present
invention is not necessarily limited to this, and the voice of the driver's seat 60 or the passenger's
seat 65 may be automatically detected, and the contact of the changeover switch 55 may be
automatically switched based on the detection result. The optical microphone elements 50a and
50b may be either as shown in FIG. 3 or as shown in FIG. However, as described above, the effect
of noise can be further prevented when the configuration of FIG. 4 is used.
[0027]
As described above in detail based on the embodiment, in the present invention, an optical
microphone is used to collect sound with respect to sound collection objects at different
distances in two directions, and switching of the microphone is performed. Since the amount of
negative feedback of the optical microphone is switched in conjunction with this, it is possible to
eliminate the sensitivity difference due to the difference in the distance of the sound collection
target.
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