JPH05284590

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DESCRIPTION JPH05284590
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
microphone apparatus having single directivity.
[0002]
2. Description of the Related Art A conventional unidirectional microphone consists of a single
unidirectional microphone unit.
[0003]
When such a conventional unidirectional microphone is attached to a camera integrated VTR, the
microphone unit should be soft in order to make it difficult for the vibration from the camera
integrated VTR to be transmitted to the microphone unit. Since it was made to catch with rubber
etc., the microphone became a complicated structure and had the fault that it became large.
Furthermore, the conventional unidirectional microphone attached to such a camera integrated
VTR also has a disadvantage that its directivity can not be changed.
[0004]
In view of such a point, the present invention is intended to propose a microphone device having
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a simple structure and having a vibration isolation effect, and moreover, having a single
directivity which can change directivity characteristics.
[0005]
SUMMARY OF THE INVENTION The microphone device of the present invention comprises first,
second and third omnidirectional microphone units Ma, Mb and Mc, whose respective sound
receiving surfaces Sa, Sb and Sc are microphones. From the first microphone unit Ma and the
microphone M, which is arranged at a predetermined interval so as to be perpendicular to the
front direction of the microphone and in which only the second nondirectional microphone unit
Mb can not receive sound. First subtracting means 1 for subtracting the audio signal from the
second microphone unit Mb from the audio signal from the second microphone unit Mb, and the
audio signal from the second microphone unit Mb from the audio signal from the third
microphone unit Mc The output of the directivity changing unit 3 is reduced from the output of
the second subtracting unit 2, the directivity changing unit 3 to which the output of the first
subtraction unit 1 is supplied, and the output of the second subtraction unit 2 And third
subtracting means 6 for obtaining a microphone output sound signal, and changing the
directivity changing means 3 to obtain a microphone output sound signal having a desired single
directivity. It is.
Also, the directivity changing means 3 is composed of a cascade circuit of a variable delay 4 and
a variable attenuator 5.
[0006]
According to the present invention, the sound is not received by the second microphone unit Mb,
but the sound signal from the first microphone unit Ma is transmitted from the first microphone
unit Mb by the first subtraction means 1. By subtracting the audio signal, an audio signal in
which vibration sound components of the first and second microphone units are canceled is
output. Further, by subtracting the sound signal from the second microphone unit Mb from the
sound signal from the third microphone unit Mc by the second subtraction means 2, the
vibration sound component of the third and second microphone units is A canceled audio signal
is output.
[0007]
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The voice signal outputted from the first subtracting means 1 is supplied to the directivity
changing means 3 and from the voice signal outputted from the second subtracting means 2 by
the third subtracting means, the directivity changing means The audio signal output from 3 is
subtracted to obtain a microphone output audio signal. Then, by changing the directivity
changing means 3, that is, by changing the delay amount of the variable delay 4 and / or the
attenuation amount of the variable attenuator 5, a desired unidirectional microphone output
sound signal is obtained. be able to.
[0008]
BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will now be described in
detail with reference to the drawings. FIG. 1 shows an embodiment of the present invention, in
which (A) shows its microphone M and (B) shows its audio signal processing circuit. The
nondirectional microphone units (microphone capsules) Ma, Mb, Mc that constitute the
microphone M are spaced at a predetermined distance so that their respective sound receiving
surfaces Ga, Gb, Gc are perpendicular to the front direction of the microphone, From the side
opposite to the front direction of the microphone, the tubes are arranged and fixed in this order
in a cylinder T in a rigid holding body H such as urethane.
[0009]
In this case, the sound receiving surfaces Ga and Gc of the microphone units Ma and Mc are
directed to the front direction of the microphone, but the sound receiving surface Gb of the
microphone Mb is directed to the opposite direction to the front direction of the microphone .
Moreover, among the microphone units Ma, Mb and Mc, only the microphone unit Mb can not
receive sound, that is, a large number of holes in the sound receiving surface are closed so that
sound is not transmitted to the diaphragm.
[0010]
The audio signals Sa and Sb from the microphone units Ma and Mb are supplied to the adder 1
and added. In this case, the sound signal from the microphone unit Mb does not include the
sound receiving component, and the vibration sound component based on the vibration from the
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outside is converted to the sound signal from the first microphone unit Ma by the surface facing
effect. Since the absolute value of the vibration sound component based on the contained
external vibration is opposite to that of the vibration sound component and its absolute value is
substantially equal, the sound signal from the adder 1 is only the approximately sound reception
component in the sound signal from the microphone unit Ma. .
[0011]
The audio signals Sc and Sb from the microphone units Mc and Mb are supplied to the adder 2
and added. Also in this case, the sound signal from the microphone unit Mb does not include the
sound receiving component, and the vibration sound component based on the vibration from the
outside is included in the sound signal from the microphone unit Mc by the surface facing effect.
Since the absolute value of the vibration sound component is opposite to that of the vibration
sound component based on the external vibration and the absolute value is substantially equal,
the sound signal from the adder 2 is only the sound reception component substantially in the
sound signal from the microphone unit Mc.
[0012]
The audio signal from the adder 1 is supplied to a directivity variable circuit 3 consisting of a
cascade circuit of a variable delay 4 and a variable attenuator 5. Then, the audio signal from the
adder 2 and the audio signal from the directivity variable circuit 3 are supplied to the subtractor
6, and the latter is subtracted from the former. The audio signal from the subtracter 6 is supplied
to the equalizer 7 and equalized, and the output terminal 8 has directivity characteristics
determined by the adjustment state of the directivity variable circuit 3 and vibration sound
components based on external vibration are removed And an audio signal consisting of a single
directional sound receiving component is output.
[0013]
Now, the delay time τ of the delay unit 4 can be varied as described above, but has the following
limitations. That is, when the distance between the sound receiving surfaces of the microphone
units Ma and Mc is L and the sound velocity is about 340 m / sec, τ is as follows. The amount of
attenuation in the attenuator 5 is about 2 to 3 dB.
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[0014]
Referring to FIG. 2, since the frequency characteristic of the audio signal from the subtracter 6
has a high-frequency rising characteristic of about 6 dB / oct as shown by a straight line, the
correction characteristic of the equalizer 7 is shown by a straight line as -6 dB / oct. By setting
the low frequency rise characteristic to a certain degree, the audio signal from the equalizer 7
becomes flat as shown by a straight line.
[0015]
Next, the directivity characteristic of the speech signal {sin (ωt)} based on the speech from the
sound source will be described.
The directional characteristic S is expressed by the following equation. S = sin (ωt-φ) 〔[{1-α ·
cos (x · cos θ + D)} 2 + {α · sin (x · cos θ-D)} 2] where D = ωτα: attenuation amount of
attenuator 5 x = Ω L / 34 0000 φ = tan-1 [α · sin (x · cos θ) / {1-α · cos (x · cos θ)}] θ: as
shown in FIG. The expression of the directional characteristic S is a function of .theta. It is
understood that this directivity characteristic S can vary the directivity characteristic of the
microphone output sound signal outputted from the output terminal 8 by varying the delay
amount τ of the delay unit 4 and / or the attenuation amount α of the attenuator 5.
[0016]
The example of the polar pattern of this directivity characteristic is shown to FIG. 4 (A)-(C).
Although FIG. 4 (A) shows pure uni-directional characteristics, FIGS. 4 (B) and 4 (C) have some
directivity also behind the microphone.
[0017]
According to the above-described cell of the present invention, it is possible to obtain a
microphone device having a simple structure and having a vibration isolation effect, and
moreover, having a single directivity which can change the directivity characteristic. Therefore,
when such a microphone device is attached to, for example, a camera integrated VTR, it has a
compact and simple structure.
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