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DESCRIPTION JP2005323157

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DESCRIPTION JP2005323157
An object is to provide a narrow-angle directional microphone capable of having a narrow angle
directivity in a wide frequency band with a very short, compact and lightweight structure. A short
acoustic pipe having an opening for phase interference is attached to the front of a rectangular
thin first directional microphone capsule on the side of the pipe where narrow angle directivity
can be obtained only at high frequencies, The thin rectangular second and third microphone
capsules are spaced apart from the first microphone capsule by a predetermined distance in the
direction opposite to the first microphone capsule by 180 degrees, and the output signal of the
second microphone capsule and the third microphone capsule are separated. The subtraction
result obtained by subtracting the output signal of the microphone capsule is added to or
subtracted from the output signal of the first microphone capsule to synthesize. [Selected figure]
Figure 2
Small narrow-angle directional microphone
[0001]
The present invention relates to narrow-angle directional microphones, and in particular to
microphones having extremely short dimensions and narrow-angle directivity in a wide
frequency range from low to high frequencies.
[0002]
A narrow-angle directional microphone, which is generally used widely, has an acoustic tube with
an opening for phase interference on the tube side in order to obtain narrow-angle directivity at
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the front of the microphone capsule, which is usually a line It is called a microphone.
In such a configuration, with a microphone (having a microphone capsule housing length of
about 100 mm for a microphone), narrow angle directivity can be obtained at least at a
frequency band of 2 kHz or more, which is lower than that. In the frequency band, narrow angle
directivity is not exhibited.
[0003]
In a microphone using an acoustic tube as described above, the frequency range in which the
narrow angle directivity is achieved by the acoustic tube in principle is limited to a frequency
range higher than the frequency at which the length of the acoustic tube matches the wavelength
in the lateral direction of the microphone. Also, in the back direction of the microphone, the
length of the acoustic tube is limited to a frequency range higher than the frequency at which the
half wavelength matches the half wavelength. Therefore, in order to obtain narrow angle
directivity in a wide frequency band from low frequency to high frequency, a long acoustic tube
is required, and hence the total length of the microphone becomes extremely long, making it
inconvenient to use because of the large size. There is a problem that the operability is bad.
[0004]
In order to solve such a problem, the inventors of the present invention place a secondary sound
pressure gradient microphone in which the line microphone and the directional axis are aligned
with the line microphone, and use the secondary sound pressure gradient microphone for low
frequency use. The sound from the sound collection target side is collected by this, and the sound
from the sound collection target side is collected by the line microphone used for high frequency,
and the output signals of these microphones are divided into bands and synthesized. A method
has been proposed to obtain narrow angle directivity in a wide frequency band from low to high.
However, even with this method, the length of the microphone is at least 100 mm or more at the
shortest, and there is a problem in operability, for example, when attached to a boom hanger. .
[0005]
Furthermore, in the conventional narrow-angle directional microphone, it is impossible to select
the frequency band where the level of the ambient noise component is large and adjust the
directivity of the microphone so as to make the directivity of the band particularly sharp. The
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[0006]
Japanese Patent Application Laid-Open No. 6-233371
[0007]
Therefore, in view of the above problems, the present invention aims to provide a small-sized
narrow-angle directional microphone that can have narrow-angle directivity in a wide frequency
band with a very short, small-sized, lightweight configuration. Do.
[0008]
Another object of the present invention is to provide a small-sized narrow-angle directional
microphone that can also perform directivity adjustment.
[0009]
In order to achieve the above object, according to the present invention, a cover is attached to
the front and back of the diaphragm so that the microphone diaphragm is square and the
pointing axis of the microphone is substantially parallel to the diaphragm, and the diaphragm is
external By using three rectangular thin directional microphone capsules formed by forming
sound wave introduction ports before and after the vibrating film so as to contact with each
other, and adding / subtracting the output signals of these first to third microphone capsules A
small-narrow-angle directional microphone that achieves sharp directivity in a wide frequency
band from low to high frequencies, and in which the narrow-angle directivity can be obtained
only at high frequencies on the front surface of the first microphone capsule A short acoustic
tube with an opening for phase interference on it, and pointing the second and third microphone
capsules respectively to the first microphone capsule along the acoustic tube Are spaced 180
degrees away from each other by a predetermined distance, and the output signals of the second
and third microphone capsules are subtracted by a subtractor, and the subtraction result is
output of the first microphone capsule. It is characterized in that the signal is added to or
subtracted from and synthesized.
[0010]
According to a preferred embodiment of the present invention, the first microphone capsule has
directivity in the mid-bass frequency range to produce a directivity pattern of opposite phase to
the front in the back direction of the directional axis, and the second and third microphones The
capsule is made to have single directivity in the direction opposite to the pointing axis of the first
microphone capsule.
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[0011]
According to another preferred embodiment of the present invention, the output signals of the
second and third microphone capsules are respectively amplified to required values by an
amplifier circuit before subtraction by a subtractor, and subtraction by the subtractor The result
is fed to a low pass filter circuit to obtain narrow angle directivity at a wide frequency.
[0012]
Furthermore, according to another preferred embodiment of the present invention, the directivity
is most sharpened by changing the amplification degree of the output signals of the second and
third microphone capsules by the amplification circuit and the cutoff frequency of the low pass
filter circuit. Make it possible to shift the frequency band.
[0013]
Even in the method of obtaining narrow-angle directivity in a wide frequency band from low to
high, using three conventional microphone capsules, the minimum length of the microphone
capsule storage portion needs to be 100 mm or more. According to the invention short
dimensions of 60 mm are possible.
As a result, it is possible to realize a narrow-angle directional microphone with a good television
image.
Further, in recent years, the angle of view of a television has been broadened, and there has been
an increasing demand for smaller and lighter microphones used by attaching them to boom
hangers, and the demand for smaller and lighter microphones mounted on video cameras will be
satisfied.
[0014]
Hereinafter, embodiments of the present invention will be described with reference to the
drawings.
[0015]
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FIG. 1 is a block diagram of an embodiment of a microphone capsule constituting a small-sized
narrow-angle directional microphone according to the present invention.
Each of the three microphone capsules 1, 2 and 3 used in the present embodiment is, for
example, a square thin directional microphone capsule known from Japanese Patent No.
3,325,913.
In such a thin rectangular directional microphone capsule, the diaphragm of the microphone is
rectangular, a cover is attached to the front and back of the diaphragm, and a sound wave inlet is
formed so that the diaphragm is in contact with the outside of the microphone capsule. The
configuration of the microphone capsule is made thin so that the directional axis of the
microphone is substantially parallel to the diaphragm.
[0016]
In the present embodiment, in order to obtain narrow angle directivity only at high frequencies
on the front surface of the first microphone capsule 1, a plurality of phase interference for a
short interval, for example 45 mm, for phase interference at regular intervals on the side surface.
An acoustic tube 5 having an opening 4 is attached, and the acoustic tube 5 and the first
microphone capsule 1 constitute a line microphone, on which the first microphone capsule 1 and
the directivity axis are 180 °. A second microphone capsule 2 of unidirectionality is mounted in
the opposite direction, and a single microphone capsule 2 is mounted in the same direction as
the second microphone capsule 2 also on the acoustic tube 5 in front of the second microphone
capsule 2, for example 45 mm. The third microphone capsule 3 of one directivity is installed, and
the second and third microphone capsules 2 and 3 form a secondary sound pressure gradient
type microphone. So as to be made.
Also, the first microphone capsule 1 is always directed in the mid-bass frequency band to a
directivity between the uni-directionality and the bi-directionality, that is, a directional pattern
that produces a directional pattern opposite in phase to the front in the back direction of the
directional axis. To have sex.
[0017]
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FIG. 2 shows a block diagram of a small-sized narrow-angle directional microphone according to
the present invention, where 10 corresponds to the first microphone capsule 1 constituting the
line microphone to which the acoustic tube 4 shown in FIG. 1 is attached. 20 and 30 are spaced
apart from each other by a predetermined distance, and constitute a second-order sound
pressure gradient type microphone, and microphone capsules corresponding to the second and
third microphone capsules 2 and 3 shown in FIG. 40a to 40c are head amplifiers for impedance
conversion, 50a and 50b are amplification circuits, 60 is a subtractor, 70a and 70b are low pass
filters, and 80 is a circuit for adding or subtracting.
[0018]
The outputs of the microphone capsules 10, 20 and 30 respectively pass through the head
amplifiers 40a, 40b and 40c acting as impedance conversion circuits, and the outputs of the
microphone capsules 20 and 30 are appropriately amplified by the amplification circuits 50a and
50b respectively. After that, they are subtracted by the subtracter 60 and become a secondary
sound pressure gradient type output.
This second-order sound pressure gradient type output signal is a two-stage output signal that
cuts high frequency components higher than a preset cutoff frequency and extracts low
frequency components in order to obtain narrow angle directivity in a wide frequency range. It is
supplied to the low pass filters 70a and 70b.
The amplitude and phase of the signal in the back direction of the microphone capsule 10 and
the secondary sound pressure by the microphone capsules 20 and 30 by the amplification
circuits 50 a and 50 b and the low pass filters 70 a and 70 b and amplification and high-cut
electric circuit. When the magnitude and phase of the gradient type output signal approach each
other, and the secondary sound pressure gradient type output is subtracted from the output of
the microphone capsule 10 by the subtractor 80, the sensitivity of the microphone capsule 10 in
the back direction is As a result, a combined output with narrow angle directivity is obtained as
the output of the subtractor 80.
[0019]
The phase of the secondary sound pressure gradient type output becomes opposite to the phase
of the output of the first microphone capsule 10 depending on how the amplification degree of
each of the amplifier circuits 50a and 50b is set with respect to the outputs of the microphone
capsule 20 and the microphone capsule 30. In some cases, the outputs of each other can be
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summed to obtain a narrow angle directivity output.
[0020]
FIG. 3 shows the directivity pattern of each microphone capsule at 250 Hz as an example, where
a is the directivity pattern of the microphone capsule 10 and b is the directivity of the secondary
sound pressure gradient type microphone by the microphone capsules 20 and 30. The pattern c
is the directivity pattern of the microphone after the output signals from the microphone capsule
10 and the microphone capsules 20 and 30 are synthesized.
[0021]
As apparent from FIG. 3, the directivity pattern of the microphone after synthesis is reduced in
that the directivity pattern of the back surface is reduced by subtracting the directivity pattern b
of the secondary sound pressure gradient type from the directivity pattern a of the microphone
capsule 10. c is obtained.
[0022]
FIG. 4 shows frequency characteristics of 0 °, 90 ° and 180 ° with respect to the front of the
sound wave incoming direction of the line microphone alone (see FIG. 1) in which the 45 mm
acoustic tube 5 is attached to the first microphone capsule 1.
[0023]
FIG. 5 shows the 0 °, 90 ° and 180 ° frequency characteristics of the microphone according
to the present invention at the setting where the directivity on the back is sharpest at 100 Hz,
and FIG. 6 shows the back of the microphone according to the present invention at 250 Hz.
Shows the frequency characteristics of 0 °, 90 ° and 180 ° in the setting in which the
directivity of the microphone becomes the sharpest, and FIG. 7 shows 0 in the setting of the
directivity of the back of the microphone according to the present invention being the sharpest at
500 Hz. Figure 8 shows the 0 °, 90 ° and 180 ° frequency characteristics of the microphone
according to the present invention in the setting where the back directivity is most sharp at 800
Hz. It is shown.
[0024]
As is clear from FIGS. 5 to 8, according to the microphone of the present invention, sharp
directivity is shown in a wider frequency band from low to high frequencies than that of a line
microphone of the same length alone, and further amplification circuit 50a And 50b change the
setting of the degree of amplification of the secondary sound pressure gradient type output by
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the microphone capsule 20 and the microphone capsule 30, and change the cutoff frequency
value of the low pass filter 70 to obtain the frequency with the most sharp directivity. It can be
electrically shifted.
[0025]
Further, according to the microphone of the present invention, the frequency characteristic in the
0 ° direction of the microphone capsule 10 for the purpose of picking up the target sound is not
affected at all by the combination of the signals, so Since the frequency in the 0 ° direction does
not change even when shifted, the directivity can be adjusted without changing the sound
quality.
[0026]
FIG. 9 is a perspective view showing an example of a small-sized narrow-angle directional
microphone according to the present invention, wherein 100 is a microphone capsule and a head
amplifier storage unit, 101 is a post, 102 is an amplifier circuit, a subtractor and a low pass filter.
A stand base incorporating an electric circuit, and 103 is a cable.
[0027]
It is a perspective view which shows the arrangement configuration of the microphone capsule of
embodiment of this invention.
FIG. 1 is a block diagram showing an embodiment of a narrow angle directional microphone
according to the present invention.
It is a figure which shows the directional polar pattern of the microphone capsule which
comprises a line microphone, the microphone capsule which comprises a secondary sound
pressure gradient type | mold microphone, and each output signal in 250 Hz after a synthesis |
combination.
It is a frequency characteristic figure of the output signal level in 0 degree, 90 degrees, and 180
degrees of the line microphone single-piece | unit used for this invention.
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It is a frequency characteristic figure of the output signal level in 0 degree, 90 degrees, and 180
degrees at the time of setting the frequency which sharpens directivity to 100 Hz of the
microphone of the present invention to 100 Hz.
It is a frequency characteristic figure of the output signal level in 0 degree, 90 degrees, and 180
degrees at the time of setting the frequency which sharpens directivity to 250 Hz of the
microphone of the present invention to 250 Hz.
It is a frequency characteristic figure of the output signal level in 0 degree, 90 degrees, and 180
degrees at the time of setting the frequency which sharpens directivity to 500 Hz of the
microphone of the present invention to 500 Hz.
It is a frequency characteristic figure of the output signal level in 0 degree, 90 degrees, and 180
degrees at the time of setting the frequency which sharpens directivity to 800 Hz of the
microphone of the present invention to 800 Hz.
FIG. 1 is a perspective view of an example of a small narrow angle directional microphone
according to the present invention made using a microphone capsule.
Explanation of sign
[0028]
1 first microphone capsule 2 second microphone capsule 3 third microphone capsule 4 aperture
5 acoustic tube 10 to 30 microphone capsule 40a to 40c head amplifier 50a to 50b amplification
circuit 60 subtractor 70a, 70b low pass filter 80 subtractor 100 microphone capsule and Head
amplifier storage section 101 Support 102 Stand base with built-in electric circuit 103 Cable
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