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FIELD OF THE INVENTION The present invention relates to microphone devices. Prior Art
Configuration and Its Problem FIG. 1 shows a conventional microphone device. In FIG. 1,
reference numeral 1 denotes an acoustic pipe having a plurality of sound holes 2. A resistive
surface cloth 3 is attached to the acoustic pipe 1 so as to cover the sound holes 2, and nondirectionality is provided at its end. A microphone 4 is attached and these constitute a line
microphone. Next, the operation will be briefly described. In FIG. 1, the line wave enters the
acoustic tube 1 from each sound hole 2 and reaches the nondirectional microphone 4 provided
at the end through the acoustic tube 1, but in this case, the acoustic tube 1 The direction of O0
which is the longitudinal direction of the image is not phase-cancelled, and the other direction is
adjusted by the resistive face cloth 3 so as to cancel the phase. That is, this microphone device
does not utilize the wave effect of the sound wave, and the directivity becomes sharp in
proportion to the frequency above the frequency at which the length of the sound @ tube 1 and
the wavelength of the wave become equal. Therefore, in order to provide directivity to the low
frequency range, the length of the acoustic tube 1 must be increased. FIG. 2 shows a sharp
directivity in the high range as seen from the figure showing the frequency w characteristic when
the sound tube length l is about 2 ocIn, but in the low range, the omnidirectional microphone u7
”4 It is almost the same as the characteristics of the single substance. As described above, in the
conventional microphone device, when a nondirectional microphone is used, it is necessary to
lengthen the length of the acoustic tube to obtain directivity in the low range-the directivity of
the high range Has the disadvantage of becoming too sharp. SUMMARY OF THE INVENTION It is
an object of the present invention to eliminate the above-mentioned conventional drawbacks, and
to provide a microphone device which can have directivity over the entire band and which has a
high housing margin. SUMMARY OF THE INVENTION In order to achieve the above object, the
present invention provides a secondary gradient microphone and a line in which four differential
microphones are disposed near the front end and the rear end of a line microphone and the
output difference is taken out. A microphone device adapted to combine with the output of a
ficrophone, which is designed to obtain narrow directivity over a wide band. Description of the
Embodiments The configuration of the embodiments of the present invention will be described
with reference to the drawings. . FIG. 3 shows an embodiment of the present invention, and the
same -S components as in FIG. 1 are indicated by the same numbers. In FIG. 3, 5.6 are two
differential microphones which are unidirectional and relatively similar in characteristics, and
differential microphones 7 "; 5 are acoustic tubes 1 and # 1 are flat. The output is connected to
one input terminal of the subtraction circuit 7 near the tip on the E j -axis.
Also, the differential microphone 6 is similarly located near the rear end on a substantially
parallel axis, and this output is coupled to the other input terminal of the subtraction circuit 7
through the volume 8 and the output of the differential microphone 5 ° 6 The difference is
taken out from the output terminal, and the output thereof is combined with the output of the
nondirectional microphone 4 by the combining unit 9. The same is true even if the volume 8 is
configured on the differential microphone 5 side. The operation of the soil hC embodiment will
now be described. In FIG. 3, L is an interval of the differential microphones 6.6, and the outputs
of the respective volumes are appropriately adjusted in level by the volume 8, and the output
difference is obtained by the subtraction circuit 7. A differential microphone 5, 6. ! The M3E
circuit 8 constitutes a secondary gradient type microphone, and FIG. 4 shows an example of the
characteristic in the case of L-20 positive. As can be seen from the figure, the acoustic phase
difference between the microphones 5 and 6 is 00. Therefore, the frequency f is proportional to
the frequency in the range of kL ≦ 2, and is maximum at the frequency where the wavelength λ
is 2L (approximately kL−π point), and the frequency f where λ = L. It is the lowest at n times h.
(K = −, ω = 2πf + c: sound velocity, j: frequency. The same applies to n: positive integer) 1800,
but since the differential microphone itself has directivity to 00, directivity equivalent to that of a
single differential microphone can be obtained. On the other hand, in the 90 'direction, since
there is no acoustic phase difference 1 difference, in theory there is no output regardless of the
frequency. As described above, this secondary gradient microphone exhibits narrow directivity.
However, in the case of this one microphone, the low frequency range becomes about +66 B 10
ct to the frequency, so if it is attempted to widen the necessary reproduction band, L is shortened
by all means and the correction amount of the low frequency range is increased. However, in the
case of the present invention, L is increased, and the frequency that becomes kL-1 is configured
to be in the low frequency range, so it is sufficiently practical even without the low frequency
range correction, and small correction even if corrected. S / N degradation does not occur with it
because it is quantity intensive. On the other hand, the output of the line microphone is as shown
in FIG. 2 and has directivity at a frequency of ke ≧ 1 or more and shows narrow directivity at kd
≧ π. Therefore, the configuration of this embodiment is low. The sound range can be divided
into the output of a secondary gradient microphone and the high band with the output of a line
microphone. If this part 414 is, for example, acoustically filtered, a microphone with narrow
directivity over a wide band can be obtained. Can provide a microphone having a high housing
In addition, since the secondary gradient microphone has less if S / N degradation and the sword
of the line microphone uses a non-directional unit, the S / N is very good, so the S / N should be
generally good. There is an advantage that can be done. In practice, the output of each of the line
microphone and the secondary gradient microphone may give j and m in a frequency range that
is not required. Therefore, the embodiment of FIG. 5 can be considered to further improve the
synthesis characteristics. In FIG. 6, reference numeral 10 denotes a low cut filter circuit, which
cuts the low range of the output of the line microphone 4. A high cut filter circuit 11 cuts the
high range of the output of the secondary gradient microphone. That is, each filter circuit 10.11
can not cut off the unnecessary band and give an adverse effect. A low-frequency correction
circuit 12 corrects the low-frequency band in order to widen the reproduction band as necessary
after the synthesis. Note that this correction is the same as the main point of the present
invention even if it is performed before the output of the secondary gradient microphone, that is,
before the synthesis, other than this embodiment. Since low-frequency correction leads to S / N
degradation, it is desirable to minimize it. Also, if L (l is set well, a sufficiently practical
reproduction band can be obtained without correction. Further, it is preferable to make the cutoff
frequency (crossover) of the filter circuits 10 and 11 substantially equal to around kl = 4 in
consideration of combining the frequency characteristics and directivity characteristics. In the
case of the example, L! Although the case where -il is set has been described, it is not 1 which is
the same as the gist of the present invention even in the case of L> β, or e. It is an example of
the characteristic in the case where it comprised like the Example of FIG. However, in the case of
l = 20 cm, l =, L 2, the crossover frequency is 4 = 4 伺, and the low frequency correction is not
performed. As shown in FIG. 6, it is possible to obtain narrow directivity characteristics in a wide
frequency range, and to provide a microphone device with a high howling margin. However,
when used in close proximity, the tip of the line microphone and It is most desirable to configure
the differential microphone 6 to the same blood in consideration of sound quality deterioration
and the like. As described above, according to the present invention, the high frequency range is
configured to be + J by the line microphone and the low frequency range is generated by the
secondary gradient type microphone, and the noise is set to L- [nearly]. It has a wide playback
range, little S / N degradation, and it falls over the entire range from low to high.] B I: JJ 4 '!
Can have the advantage of being able to provide a microphone device with a high housing
margin as a whole.
Brief description of the drawings
FIG. 1 is a block diagram showing a conventional microphone device, FIG. 2 is a characteristic
diagram in FIG. 1, FIG. 3 is a block diagram of a microphone device in one embodiment of the
present invention, and FIG. FIG. 5 is a block diagram showing another embodiment of the present
invention, and FIG. 6 is a characteristic diagram of the embodiment shown in FIG. 6.
1 ...... acoustic tube, 2 .... omnidirectional micro Bonn, 6.6 ...... differential microphone, 7 ...... MW
circuit, 9 ... · · Synthesis part. Agent's name Mr. Toshio Nakao and one other person Fig. 1 p Fig.
2! □ Perfusate (state, (th) 壜 bL 41- Figure 4 Figure 4
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