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JPH0698391

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DESCRIPTION JPH0698391
[0001]
FIELD OF THE INVENTION The present invention relates to microphone devices, and more
particularly to a microphone array using a plurality of microphones.
[0002]
2. Description of the Related Art Conventionally, as shown in FIG. 8, for example, as shown in FIG.
8, a plurality of, for example, three unidirectional microphones 10 are separated by an interval d
so that their reference axes are parallel to each other. And the outputs of the microphones 10 are
added by the adder 12.
[0003]
Assuming that each unidirectional microphone 10 has a directivity of (1 + cos θ) / 2 (θ is the
incident angle of a sound wave (see FIG. 8)), the directivity of this microphone array is as follows.
That is, when a plane wave is incident at an incident angle θ, a phase difference is generated in
the sound pressure at the installation position of each microphone 10 due to a distance that is an
integral multiple of d · sin θ as shown in FIG. Assuming that the sensitivities of the respective
microphones 10 are all equal, the voltage appearing at the output terminal of each of the
microphones 10 is P, and the wavelength constant of the plane wave is k, the total output ((θ)
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generated in the adder 12 is expressed by .
[0005]
If only the series part of Eq. 1 is calculated, Eq.
[0007]
Therefore, the total output Φ (θ) is expressed by Equation 3.
[0009]
The total output Φ (0) when the plane wave is incident from the front (θ = 0) is expressed by Eq.
4, and if it is defined that the directivity characteristic R is expressed with reference to this, R is
expressed.
[0011]
Furthermore, since each microphone 10 is uni-directional, P changes according to (1 + cos θ) / 2
according to the incident angle θ, so the directivity characteristic of the microphone array of
FIG. Be done.
[0013]
As apparent from the equation (6), in this microphone array, the sensitivity does not become
equal to zero for the case of θ = 90 °.
Therefore, there is a problem that noises from the direction of θ = 90 ° are easily collected.
Further, the wavelength constant k in the equation 6 changes depending on the frequency of the
incident sound wave, but the interval d is constant.
Therefore, as shown in FIG. 9, the directivity characteristic changes according to the change of
the frequency of the incident sound wave, and there is a problem that a stable narrow directivity
characteristic can not be obtained over a wide frequency band.
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[0014]
SUMMARY OF THE INVENTION The present invention has been made to solve each of the above
problems, and a plurality of sound pressure secondary gradient microphones are disposed in a
state in which the reference axes are substantially parallel to each other. The output signals of
the respective sound pressure secondary gradient microphones are respectively supplied to a
plurality of equalizer means having frequency characteristics substantially complementary to the
frequency characteristics of the sound pressure secondary gradient microphones, and the output
signals of these equalizer means are added Is added by
[0015]
In the sound pressure secondary gradient microphone used in the present invention, two single
directional microphones are arranged at intervals in the reference axis direction so that these
reference axes substantially coincide with each other. The deviation of the output signal of the
microphone is obtained.
Therefore, sound waves from a direction (incident angle = 90 °) perpendicular to the reference
axis are incident on the respective microphones without phase delay.
Therefore, when the deviations of the output signals of these microphones are determined, sound
waves from an incident angle of 90 ° cancel each other. As a result, the sensitivity to an incident
angle of 90 ° can be made zero.
[0016]
Also, the sound pressure secondary gradient microphone has a specific frequency characteristic
because the microphones are arranged at intervals in the reference axis direction, but an
equalizer means having a frequency characteristic substantially complementary to the frequency
characteristic. By inputting the output signal of the sound pressure secondary gradient
microphone, the frequency characteristic of the sound pressure secondary gradient microphone
is made flat over a wide frequency band. The reason why a plurality of sound pressure secondary
gradient microphones are used is to arrange the array in an array to make the directivity narrow
and to increase the sensitivity in the front direction (incident angle θ = 0 °). It is.
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[0017]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In this embodiment, which is
disposed, for example, at each desk of a conference hall, as shown in FIG. 1, it has three sets of
sound pressure secondary gradient microphones 14, 16, 18. As shown in FIG. Since these sound
pressure secondary gradient microphones 14, 16, 18 have the same configuration, only the
sound pressure secondary gradient microphone 14 will be described in detail with reference to
FIG.
[0018]
As shown in FIG. 2, the sound pressure secondary gradient microphone 14 includes two
unidirectional microphones 20 and 22. Each of these unidirectional microphones 20 and 22 has
directivity of (1 + cos θ) / 2, and the distance D, for example, approximately, in the reference
axis direction is set so that the reference axes 25 and 26 coincide with each other. It is arranged
at a distance of 27 mm. The output signals of the unidirectional microphones 20 and 22 are
supplied to the adder 24 and the difference between the two is output.
[0019]
In this sound pressure secondary gradient microphone 14, when a sound wave of a plane wave is
incident on the microphones 20, 22 from the direction just beside (incident angle θ = 90 °)
with respect to the reference axes 25, 26, the reference axis 25, Since the H.26 matches, there is
no phase difference in the sound pressure at the position of each microphone 20,22. Therefore,
when the difference between the two outputs is determined by the adder 24, the sensitivity
becomes zero with respect to the incident angle of 90 °. FIG. 3 shows the directional
characteristics of the sound pressure secondary gradient microphone 14 at a frequency of 1 KHz,
and the sensitivity is zero from the incident angle of 90 °, and the directivity pattern is sharper
than that of the conventional microphone array. It is clear that
[0020]
Such sound pressure secondary gradient microphones 14, 16, 18 are arranged at an interval d,
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for example 300 mm, such that the reference axes of the unidirectional microphones 20, 22
constituting them are substantially parallel. Yes. Therefore, the composite of the output signals of
the sound pressure secondary gradient microphones 14, 16, 18 has a sensitivity of zero at an
incident angle of 90 ° at each frequency, as shown in FIG. 4, for example. In order to obtain a
sharper directivity pattern in the low region, as shown in FIG. 1, the high-pass filter 38 is applied
to the output of the sound pressure secondary gradient microphone 16 in the central portion.
Only the outputs of the sound pressure secondary gradient microphones 14 and 18 are
synthesized. Also, in order to prevent the occurrence of extreme side lobes on the directivity
pattern in the high region, as shown in FIG. 1, low-pass filters 36, 40 are provided on the outputs
of the sound pressure secondary gradient microphones 14, 18 at both ends. In operation, the
outputs of the sound pressure secondary gradient microphones 14 and 18 at both ends are not
combined in the high frequency band. By using the low pass filters 36 and 40 and the high pass
filter 38 as described above, it is possible to obtain a substantially uniform directivity pattern
from the low band to the high band as shown in FIG.
[0021]
However, the unidirectional microphones 20, 22 constituting the sound pressure secondary
gradient microphones 14, 16, 18 are disposed at a distance D in the direction of the reference
axes 25, 26, so that the front direction is obtained. The sound pressure at the position of the
microphones 20 and 22 has a phase difference with respect to the sound wave incident from the
point. Accordingly, as shown in FIG. 5, the front sensitivity of the sound pressure secondary
gradient microphones 14, 16, 18 differs depending on the frequency of the incident sound wave.
For example, in this example, since D is selected to be 27 mm, a dip occurs at 12.6 kHz, and the
sensitivity is greatly reduced. The reason why D is 27 mm is as follows. As D increases, directivity
can be provided even at a low frequency, but as D increases, the frequency at which dips occur
decreases. In general, the audio band contains components of about 10 kHz at the maximum, and
in order to pick up frequency components up to this level sufficiently, the dip is made to occur at
12.6 kHz with a distance of 27 mm.
[0022]
The outputs of such sound pressure secondary gradient microphones 14, 16, 18 are equalizers
28, 30 having frequency characteristics substantially complementary to the front sensitivity
frequency characteristics of the sound pressure secondary gradient microphone 14 as shown in
FIG. 6, for example. , 32, the front sensitivity frequency characteristics of the sound pressure
secondary gradient microphones 14, 16, 18 respectively become substantially flat frequency
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characteristics over a wide frequency band as shown in FIG. It is possible to obtain an
omnidirectional microphone device stable in a wide frequency band by adding together the
output signals of the sound pressure secondary gradient microphones and the equalizer having
such flat frequency characteristics by the adder 34. it can.
[0023]
The reason why the distance d between the sound pressure secondary gradient microphones 14,
16, 18 is 300 mm is as follows. As the distance d is increased, directivity can be provided even at
a low frequency. However, since this microphone device is installed on a desk in a conference
hall or the like, each sound pressure secondary gradient microphone 14, In order to arrange 16
and 18 on a desk and fit within the width of the desk, it is necessary to set the distance between
the microphones 14 and 18 at both ends to approximately 600 mm. Therefore, d is selected to be
300 mm.
[0024]
Further, in the above embodiment, three sets of sound pressure secondary gradient microphones
are provided, but the number of sets can be arbitrarily increased.
[0025]
As described above, according to the present invention, a microphone array is configured using a
sound pressure secondary gradient microphone.
Therefore, since the sensitivity can be made zero in the lateral direction, that is, in the direction
of 90 ° with respect to the front, ambient noise is not picked up. Moreover, since the front
sensitivity frequency characteristic of this sound pressure secondary gradient microphone is
made flat using the equalizer, stable narrow directivity can be obtained over a wide frequency
band. Since the microphone array is configured using a plurality of sets of sound pressure
secondary gradient microphones whose sensitivity is zero and whose frequency characteristics
are flattened in this way, the sound pressure secondary gradient microphones It is possible to
have a directivity pattern sharper than that when used alone, and it is possible to obtain, for
example, a microphone device suitable as a microphone device provided on each desk of a
conference hall. In addition, since the output of the center one of the sound pressure secondary
gradient microphones is input to the high pass filter, only the output of the sound pressure
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secondary gradient microphones at both ends is synthesized in the low frequency range, so sharp
in the low frequency range A directional pattern is obtained. Also, since the outputs of both ends
of each sound pressure secondary gradient microphone are input to the low pass filter, only the
output of the central sound pressure secondary gradient microphone is output in the high region,
and the directivity in the high region is output. Extreme side lobes on the pattern do not occur.
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