JP2001268685

Patent Translate
Powered by EPO and Google
Notice
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
financial decisions, should not be based on machine-translation output.
DESCRIPTION JP2001268685
[0001]
The present invention is directed to obtain directivity in the front-rear direction by arranging two
microphones at predetermined intervals in the front-rear direction and mutually canceling output
signals of the respective microphones. Microphone device.
[0002]
2. Description of the Related Art Conventionally, as a directional microphone device of this type,
one having a configuration as shown in FIG. 3 is known. This directional microphone device
utilizes a so-called secondary sound pressure gradient type microphone method, and has a front
(front) microphone unit 10 and a rear (rear) microphone unit 12 of the same characteristics. The
front stage microphone unit 10 and the rear stage microphone unit 12 are disposed at
predetermined intervals in the front-rear direction. By canceling the outputs of both the
microphone units 10 and 12, the microphone units for the horizontal sound are obtained. The
outputs 10 and 12 are offset, and the sound in the front and back direction is obtained by the
phase difference of the sound input due to the difference in the position of each of the
microphone units 10 and 12. Theoretically, the sound input in the lateral direction becomes a
common signal component in each of the microphone units 10 and 12 and is completely
canceled, and in the sound input in the front-rear direction, the distance between the microphone
units 10 and 12 becomes the wavelength λ of the sound. On the other hand, the maximum
output can be obtained when corresponding to λ / 2.
04-05-2019
1
[0003]
In FIG. 3, the output signal of the front stage microphone unit 10 is input to the mixing circuit
14, and the output signal of the rear stage microphone unit 12 is input to the mixing circuit 14
via the inverting circuit 16. That is, the output signal of the rear stage microphone unit 12 is
phase-inverted by the inverting circuit 16 and mixed (in this example, added) with the output
signal of the front stage microphone unit 10 by the mixing circuit 14 to obtain a cancel signal.
Then, the cancel signal from the mixing circuit 14 is input to the equalizer circuit 18 in the
subsequent stage, and the equalizer circuit 18 mainly flattens the frequency characteristics and
then is output as a microphone output.
[0004]
By the way, when the above-mentioned directional microphone device is used as, for example, a
conference microphone, the high frequency band and the middle frequency band where the
influence of howling due to the speaker sound etc. is large are described above. Although the
cancellation signal is effective, a sufficient output level can not be obtained for the low frequency
band. Therefore, conventionally, the low frequency band is dealt with by reducing the amount of
cancellation by shifting the phase of the inverted signal in the low band portion. However, in the
method of raising the output level of the low frequency band by shifting the phase of the
inverted signal in this way, the frequency characteristic of the low band portion of the equalizer
circuit 18 fluctuates significantly (so-called f characteristic deviation) due to a slight error of the
cancellation amount. There is a problem that it is difficult to obtain an appropriate output.
[0005]
In addition, in terms of sound quality, there is a problem that noise (cancel noise) in the low band
portion becomes large due to the phase shift as described above, and the above-described
deterioration of S / N is further promoted. Also, especially in the case of a conference
microphone, there are many cases where a document etc. is placed between the microphone and
the speaker, the distance between the microphone and the speaker is large, and the speaker
sound is easily input to the microphone. Since it is easy to receive, there is a demand for a
microphone device having stronger directivity.
[0006]
04-05-2019
2
Therefore, it is an object of the present invention to provide a microphone device in which
directivity is obtained using a cancellation signal of a microphone unit disposed in the front and
back direction, a simple configuration and sufficient low frequency without using phase shift of
the cancellation signal. An object of the present invention is to provide a microphone device
which can obtain an output and can further improve the S / N and the directivity.
[0007]
SUMMARY OF THE INVENTION In order to achieve the above object, the present invention
arranges a pair of microphones at predetermined intervals in the front-rear direction, and cancels
each other's output signals. In a directional microphone device in which directional directivity is
obtained, a cancel unit that cancels each other's output signals of the microphone units and
outputs a cancel signal, and extracts a low frequency band signal from an output signal of the
microphone unit A filter unit, and a first mixing circuit that mixes a cancellation signal from the
cancellation unit with a filter signal from the filter unit.
[0008]
In the directional microphone device of the present invention, in the cancel unit, the output
signals of a pair of microphone units arranged at predetermined intervals in the front-rear
direction are input, and one output signal is phase inverted to be the other output signal. By
mixing, the cancel signal which canceled each output signal mutually is output.
The filter unit extracts a low frequency band signal by, for example, low-passing the output signal
of one of the microphone units.
The first mixing circuit mixes the cancel signal from the cancel unit and the filter signal from the
filter unit. Therefore, in the high frequency band and the middle frequency band where the
influence of the howling is large, by obtaining the effective directivity by the cancellation signal
of each microphone unit, peripheral sound other than the voice of the speaker input to each
microphone unit is excluded. And howling can be suppressed.
[0009]
On the other hand, in the low frequency band where a sufficient output level can not be obtained
04-05-2019
3
by the cancellation signal, a sufficient output level can be obtained by the filter signal by the
filter unit. As a result, the output level of the low frequency band can be increased without
shifting the phase of the cancel signal as in the prior art, noise in the low band portion (cancel
noise) can be suppressed, and the S / N is improved. it can.
[0010]
In addition, in the configuration of such a directional microphone device, by providing the first
stage high gain amplifier in each microphone unit, S / N can be improved, and a plurality of pairs
of microphone units are provided in parallel, and each cancel signal By mixing these, it is
possible to obtain stronger directivity. Thus, it is possible to configure, for example, a
microphone device effective for the conference microphone.
[0011]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred embodiments of the
directional microphone device according to the present invention will be described below. FIG. 1
is a block diagram showing the configuration of the directional microphone device according to
the embodiment of the present invention, FIG. 1 (A) shows the entire configuration, and FIG. 1 (B)
shows the configuration in each microphone capsule. There is. As shown in FIG. 1A, in the
directional microphone device according to the present embodiment, a pair of microphone units
(pre-stage microphone units 110A, 110B, 110C and a rear-stage microphone unit) are arranged
at predetermined intervals in the front-rear direction. Three sets 120A, 120B, 120C) are
provided in parallel. Then, as shown in FIG. 1B, each of the microphones 110A, 110B, 110C,
120A, 120B, and 120C provides the microphone element 102 and the first stage amplifier 104
in the unidirectional microphone capsule 100, and The capsule 100 is directed forward, and the
microphone capsule of the front stage and the microphone capsule of the rear stage are disposed
at a predetermined interval in the front-rear direction.
[0012]
By setting the distance between the front stage microphone unit and the rear stage microphone
unit to λ / 2 with respect to the wavelength λ of the sound, the input of the sound from the
front can be a maximum value, and the input of the sound from the side can be effectively
canceled. For example, when it is desired to obtain an output of 10 kHz as the specification, the
04-05-2019
4
usable frequency is about 1 / λ × 0.8, and assuming that the sound speed is V, the distance L
between the front microphone unit and the rear microphone unit is It can be expressed by a
calculation formula. L = V [m / s] ÷ 10 [kHz] /0.8 [mm] V = 331 + 1, 6 × t Here, 331 is the
speed of sound at 0 ° C., and t is the assumed temperature [° C.]. FIG. 2 is an explanatory view
showing calculated values when the interval L and the microphone output and the usable
frequency are obtained using such conditions, showing a case where the assumed temperature is
set to 20 ° C. to 30 ° C. There is. As can be seen from this figure, an output of 10 kHz can be
obtained at L = 27 mm.
[0013]
Also, the first-stage amplifier 104 performs amplification and impedance conversion of the
output signal from the microphone element 102 to improve the S / N of the microphone output,
and for example, by using a high gain amplifier of 40 dB, S / N A microphone device having a
spec of 50 dB or more is configured.
[0014]
Next, in FIG. 1A, the output of the first stage microphone unit 110A of the first set (microphone
block A) is a second mixing circuit (in this example, an adder) 140A and a fourth mixing circuit
(in this example, an adder) ) Is connected to 160).
The output of the rear stage microphone unit 120A is connected to the inverting circuit 130A,
and the output of the inverting circuit 130A is connected to the second mixing circuit 140A. The
phase of the output signal of the rear stage microphone unit 120A is inverted by the inverting
circuit 130A, and the output signal of the opposite phase is output to the second mixing circuit
140A. Therefore, in the second mixing circuit 140A, the positive phase output signal of the front
stage microphone unit 110A and the reverse phase output signal of the rear stage microphone
unit 120A are added to generate cancel signals of the respective microphone units 110A and
120A. The output of the second mixing circuit 140A is connected to the third mixing circuit (in
this example, the adder) 150, and the first set of cancellation signals is output to the third mixing
circuit 150.
[0015]
Next, the output of the preceding stage microphone unit 110B of the second set (microphone
04-05-2019
5
block B) is connected to the second mixing circuit 140B and the fourth mixing circuit 160. The
output of the rear stage microphone unit 120B is connected to the inverting circuit 130B, and
the output of the inverting circuit 130B is connected to the second mixing circuit 140B. The
phase of the output signal of the rear stage microphone unit 120B is inverted by the inverting
circuit 130B, and the output signal of the opposite phase is output to the second mixing circuit
140B. Therefore, in the second mixing circuit 140B, the positive phase output signal of the front
stage microphone unit 110B and the reverse phase output signal of the rear stage microphone
unit 120B are added to generate cancel signals of the respective microphone units 110B and
120B. The output of the second mixing circuit 140B is connected to the third mixing circuit 150,
and a second set of cancel signals are output to the third mixing circuit 150.
[0016]
Next, the output of the preceding stage microphone unit 110C of the third set (microphone block
C) is connected to the second mixing circuit 140C and the fourth mixing circuit 160. The output
of the rear stage microphone unit 120C is connected to the inverting circuit 130C, and the
output of the inverting circuit 130C is connected to the second mixing circuit 140C. The phase of
the output signal of the rear stage microphone unit 120C is inverted by the inverting circuit
130C, and the output signal of the opposite phase is output to the second mixing circuit 140C.
Therefore, in the second mixing circuit 140C, the positive phase output signal of the front stage
microphone unit 110C and the reverse phase output signal of the rear stage microphone unit
120C are added to generate cancel signals of the respective microphone units 110C and 120C.
The output of the second mixing circuit 140C is connected to the third mixing circuit 150, and
the third set of cancellation signals is output to the third mixing circuit 150.
[0017]
The third mixing circuit 150 mixes cancellation signals from the three second mixing circuits
140A, 140B, and 140C, and the output of the third mixing circuit 150 is connected to the
equalizer circuit (EQ) 170. The equalizer circuit 170 corrects the attenuation, the characteristics
and the like of the output signal from the third mixing circuit 150 according to the frequency to
flatten the frequency characteristics. Then, an output signal from the equalizer circuit 170 is
output to a first mixing circuit (in the present example, an adder) 190. The above inverting
circuits 130A, 130B and 130C, the second mixing circuits 140A, 140B and 140C, the third
mixing circuit 150, and the equalizer circuit 170 constitute a cancel unit.
04-05-2019
6
[0018]
Further, the fourth mixing circuit 160 mixes output signals from the three front stage
microphone units 110A, 110B, and 110C, and the output of the fourth mixing circuit 160 is
connected to the filter circuit 180. The filter circuit 180 is a low pass filter (LPF), passes only the
low frequency band signal component included in the output signal of the fourth mixing circuit
160, and outputs the low frequency signal component to the first mixing circuit 190.
[0019]
The first mixing circuit 190 mixes the cancel signal from the equalizer circuit 170 with the filter
signal from the filter circuit 180 and outputs the mixed signal as a microphone output. The
microphone output obtained in this manner can obtain high directivity and howling prevention
function by using a cancellation signal for middle and high band signals. The filter circuit 180
can improve the output level of the low band signal whose output level is small in the cancel
signal. In the above configuration, the signal supplied to the filter circuit 180 is obtained from
the three front stage microphones 110A, 110B and 110C, but it is not necessary to obtain signals
from all the front stage microphones 110A, 110B and 110C. It may be obtained from one or one
preceding microphone section. In addition, it is also possible to obtain from the rear stage
microphone unit. However, by mixing and using the output signals of the three microphone units
110A, 110B, and 110C as in this example, it is advantageous in improving the S / N.
[0020]
Next, the operation and effect of the directional microphone device having the above
configuration will be described. First, the S / N can be improved by providing the high-gain firststage amplifier 104 in the microphone capsule 100 of each of the microphone units 110A, 110B,
110C, 120A, 120B, and 120C. The first stage amplifier may be provided outside the microphone
capsule 100. Also, for low-band output, since the outputs of the front stage microphones 110A,
110B, and 110C are used, and these are added to the cancel signal through the low pass filter
unit 180, the necessary output level is obtained. It is not necessary to perform such phase shift,
and fluctuation of frequency characteristics (so-called f characteristic) does not occur.
[0021]
04-05-2019
7
In addition, low-pass noise can also be improved by not performing the phase shift as in the prior
art, and also from this point, the S / N can be improved. Further, in this example, three sets of
front stage microphones 110A, 110B and 110C, rear stage microphones 120A, 120B and 120C,
inverting circuits 130A, 130B and 130C, and second mixing circuits 140A, 140B and 140C are
provided in parallel, Since these signals are mixed using the first, third, and fourth mixing circuits
190, 150, and 160, the directivity characteristic value in the middle and high regions becomes a
value close to 20 dB. You can get a value that you can feel the reduction of
[0022]
As described above, in the directional microphone device according to the present invention, the
cancel unit cancels each other the output signals of the microphone units arranged at
predetermined intervals in the front-rear direction, and outputs the cancel signal. A filter unit for
extracting a low frequency band signal from an output signal of the microphone unit is provided,
and a microphone output is obtained by mixing a cancellation signal by the cancellation unit and
a filter signal by the filter unit.
[0023]
For this reason, in the high frequency band and the middle frequency band where the influence
of howling is large, by obtaining the effective directivity by the cancellation signal of each
microphone section, the peripheral sound other than the voice of the speaker input to each
microphone section is excluded. In the low frequency band in which howling can be suppressed,
but a sufficient output level can not be obtained by the cancel signal, a sufficient output level can
be obtained by the filter signal by the filter unit.
As a result, the output level of the low frequency band can be increased without shifting the
phase of the cancel signal as in the prior art, noise in the low band portion (cancel noise) can be
suppressed, and the S / N is improved. it can.
[0024]
In addition, in the configuration of such a directional microphone device, by providing the first
stage high gain amplifier in each microphone unit, S / N can be improved, and a plurality of pairs
of microphone units are provided in parallel, and each cancel signal By mixing these, it is
04-05-2019
8
possible to obtain stronger directivity. Thus, it is possible to configure, for example, a
microphone device effective for the conference microphone. That is, in the case of a conference
microphone, there are many cases where a document etc. is placed between the microphone and
the speaker, and while the distance between the microphone and the speaker is large, the
speaker sound is easily input to the microphone and is affected by circumferential noise. Since it
is easy to obtain strong directivity by the directional microphone device according to the present
invention, it is possible to realize a good audio conference system.
04-05-2019
9