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JP2001189987

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DESCRIPTION JP2001189987
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
narrow directional microphone particularly suitable for use in an on-vehicle hands-free speech
system and a speech recognition system.
[0002]
2. Description of the Related Art The basic configuration of a conventional narrow directional
microphone is shown in FIGS. 3 and 4. FIG. As shown in FIG. 3, does the conventional narrow
directional microphone consist of two unidirectional microphone units 31 and 32 whose frontal
direction is oriented in the main axis direction, a delay network 33 and a subtractor 34
Alternatively, as shown in FIG. 4, it comprises two single directional microphone units 41, 42
whose frontal direction is oriented in the main axis direction, a high pass filter 43, and a
subtractor 44.
[0003]
A narrow directional microphone is a secondary sound pressure gradient type (when directivity
of one nondirectional microphone unit is f (θ) = 1, directivity f when two unidirectional
microphone units are used f Although (θ) = (1 + cos θ) 2) is generally used, two microphone
units 31 (41) and 32 (42) are used as shown in FIGS. 3 and 4 in order to improve the uniformity
of the frontal characteristics. Among them, the output of one of the microphone units is delayed
by the delay network 33 or after high frequency components are removed through the high pass
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filter 43, it is subtracted by the subtractor 34 (43).
[0004]
SUMMARY OF THE INVENTION According to the above-described prior art, narrow directivity in
the entire voice band, particularly in the low band, can not be obtained, so it is easy to pick up
running noise and vibration noise, and voice clarity Is low.
Therefore, it can not withstand practical use in vehicles such as hands-free call systems.
[0005]
The present invention has been made in view of the above circumstances, and two uni-directional
microphone units are arranged on the same axis at intervals corresponding to half wavelengths
of the telephone voice band, and the outputs of the two microphone units are An object of the
present invention is to provide a narrow directional microphone particularly suitable for use in a
car, which can obtain narrow directivity in the entire audio band from low to high frequencies by
subtracting high frequency components by subtraction. I assume.
[0006]
SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, a narrow
directional microphone according to claim 1 comprises two unidirectional microphone units
arranged on the same axis at predetermined intervals. And a computing unit that computes the
difference between one output signal of the unidirectional microphone unit and the other output
signal, and a low pass filter that removes high frequency components of the computing unit
output.
[0007]
As a result, by setting the installation interval of the microphone unit to, for example, 50 mm
(corresponding to the upper half wave length of the telephone voice band), the phase difference
generated in the microphone unit from 3.4 kHz which is the upper limit of the telephone voice
band 6 dB / oct characteristic is realized, for example, by incorporating a low-pass filter with a
cutoff frequency of 500 Hz and 6 dB / oct, the microphone output becomes a characteristic that
passes through a band pass filter from 500 Hz to 3.4 kHz, and the entire audio band It is difficult
to pick up road noise due to the low directivity of human voice and the low sensitivity of low
frequency components, so it can be used in hands free calls in cars. Can.
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2
[0008]
DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 is a view showing an embodiment of a
narrow directional microphone of the present invention.
FIG. 2 is a diagram referred to in order to explain the operation of the embodiment of the present
invention, and is a diagram showing the frequency characteristics of the signal at each point a, b
and c in FIG.
[0009]
In FIG. 1, reference numerals 11 and 12 denote unidirectional microphone units, which are
spaced apart by 5 cm and installed on the same axis.
Here, the front microphone unit 11 and the rear microphone unit 12 will be referred to as being
near the front in terms of the installation position.
The interval of 5 cm corresponds to the upper half frequency of 3.4 kHz of the telephone voice
band. 13 is a computing unit. The computing unit 13 subtracts the output of the rear microphone
unit 12 from the output of the front microphone unit 11 to generate an output signal having the
frequency characteristic shown in FIG. That is, by subtracting the outputs of the two microphone
units 11 and 12, the front characteristic is 6 dB / up to the frequency at which the phase is
inverted due to the phase difference (3.4 MHz when the installation interval D of the microphone
units 11 and 12 is 5 cm). It rises by oct. Note that since the sound picked up from the side
becomes an in-phase input at all frequencies, it is subtracted and the output becomes zero.
[0010]
14はローパスフィルタである。 As the low pass filter 14, one having the frequency
characteristic shown in FIG. 2 (b) is used. That is, a high frequency component of the calculator
13 output is removed using a low pass filter with a cutoff frequency of 500 Hz and 6 dB / oct.
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This produces an output having the characteristics shown in FIG. 2 (c). Therefore, the output of
the microphone has a characteristic of passing through a band pass filter from 500 Hz to 3.4
kHz, and it is possible to enhance the intelligibility of human voice and to suppress low frequency
components such as traveling noise.
[0011]
As described above, by passing the low-pass filter 14 having the characteristic shown in FIG. 2
(b) to the microphone output (subtractor 13 output) having the characteristic shown in FIG. It is
possible to obtain the characteristics passed through the filter, that is, shown in FIG.
[0012]
The microphone for obtaining the characteristics of FIG. 2A is obtained by arranging two single
directional microphone units on the same axis and subtracting the output of the rear microphone
unit 12 from the front microphone unit 11 by the computing unit 13 Can.
In these microphone units 11 and 12, by setting the installation interval to 50 mm, the front
characteristic of the microphone is 6 dB / oct as the phase difference generated in the
microphone unit 11 (12) from 3.4 MHz which is the upper limit of the voice band of the
telephone. Realizing the characteristics, this lowers the low frequency sensitivity and thus makes
it difficult to pick up road noise. Also, since the sound picked up from the side of the microphone
units 11 and 12 is input to the two microphone units 11 and 12 in the same phase, it is canceled
by subtraction, and as a result, the sound of only the front is output Narrow directivity is realized.
[0013]
As described above, according to the present invention, two unidirectional microphone units are
arranged on the same axis at a predetermined interval, and the outputs of the two microphone
units are subtracted and output by a computing unit to obtain high frequency signals. The
component is removed. Thus, by setting the microphone installation interval to, for example, 50
mm (corresponding to the upper half wave length of the telephone voice band), the frontal
characteristic is a phase difference generated in the microphone unit from 3.4 kHz which is the
upper limit of the telephone voice band. A characteristic of 6 dB / oct is realized, and for
example, by incorporating a low pass filter with a cutoff frequency of 500 Hz and 6 dB / oct, the
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microphone output becomes a characteristic that passes through a band pass filter from 500 Hz
to 3.4 kHz. Therefore, narrow directivity can be realized over the entire voice band, human voices
become more intelligible, and low-frequency components become less sensitive, making it
difficult to pick up road noises, and hence, in hands-free communication in a car Can withstand
the practical use of
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