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JPS5656289

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DESCRIPTION JPS5656289
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of an example of a
conventional variable directional microphone, and FIGS. 2 and 3 are secondary sound pressure
gradient uni-directional obtained by the circuit shown in FIG. Characteristic diagram and its
frequency characteristic diagram, FIG. 4 is a block system diagram of one embodiment of the
variable directional microphone according to the present invention, FIG. 5 and FIG. 6 are phase
characteristic diagrams of the phase shift circuit shown in FIG. The specific circuit diagram, FIG.
7 and FIG. 8 are respectively the 90 ░ direction and O ░ force direction frequency characteristic
diagrams obtained by the circuit shown in FIG. 4, and FIG. 9 is the directivity obtained by the
circuit shown in FIG. FIG. 10 is a specific circuit diagram of the variable equalizer shown in FIG.
DESCRIPTION OF SYMBOLS 1 ... sound source, 2a, 2b ... microphone, 5 ... output terminal, 6 ...
variable primary phase shift circuit, 7 ... mixer (adder), 8 ... variable equalizer.
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a variable
directional microphone, in which a variable phase shift circuit is connected to the output of the
microphone to mix with the outputs of other microphones. The directional characteristics can be
arbitrarily changed according to the change of the amount, and the loss of the level especially at
the low frequency can be prevented, and the equalizer for performing the frequency correction is
used with a small correction amount. , 7 ') An object of the present invention is to provide a
variable directional microphone adapted to obtain a signal without deterioration of the SN ratio.
Conventionally, as a method of changing the directivity of microphones, as shown in FIG. 1,
microphones 2a and 2b having flat frequency characteristics and primary sound pressure
gradient single directivity (hereinafter referred to as primary unidirectivity) are used. The
microphone 2a is placed forward on the axis l with respect to the sound source 1. The output of
2b is mixed in the reverse phase in mixer 3 and the mixing ratio is changed to change the
primary unidirectionality to the secondary sound pressure gradient unipolarity (hereinafter
referred to as secondary unidirectionality There is an example to obtain). In this case, the
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sensitivity of the microphone 2a is m, the sensitivity of the microphone 2b is B, the angle
between the axes l of the microphones 2a and 2b and the sound source 1 is ?, the distance
between the microphone 2a and the microphone 2b is D, the wavelength constant is X Then, a
directivity pattern P in which the microphone 2aO output and the output of the microphone 2b
are mixed is p-m, j (alt, 1 + cos # j (?t + KDcos #), 1 + cos # 2B @ 2 (1. (Powder + ? и ?), and the
sensitivity of the microphone 2a and the sensitivity B of the microphone 2b are the same, and if
it is AB, the above equation can be expressed as PA и prefecture 91.ej "t41-ej ( KD cos) ... (2). Also,
if the value of M is appropriately selected in the formula (2), it is possible to obtain a pattern of
secondary unidirectivity as shown in FIG. The frequency characteristic as shown in FIG. 3 can be
obtained, which mixes the output of the microphone 2a and the output of the microphone 2b in
reverse phase, so as shown in FIG. The wavelength dips at the frequency 11.3 kHz of the
wavelength with the distance D (?31) between the microphone 2a and the microphone 2b, while
the wavelength of the incoming sound wave is 6 dB, 7c, at a frequency extremely lower than the
distance. The response tends to decrease at the rate of cT. Therefore, since the low frequency
sound can not be picked up with certainty, the output of the mixer 3 is converted to the
frequency (3) by the equalizer 4 having the frequency characteristic opposite to the frequency
characteristic as shown in FIG. By correcting the number, the frequency characteristics near the
low and mid frequencies are made flat and the output terminal 5 is output. Therefore, this
conventional microphone is an equalizer 4 with a frequency of, for example, around 100 Eif. As it
must be corrected about 21 clB, an equalizer with a large amount of correction must be used. As
a result, the 8N ratio is degraded, so-called wind noise is likely to occur, and so-called touch noise
occurs when touched. There was a drawback such as easy.
The present invention eliminates the above-mentioned drawbacks and will be described with
reference to FIG. FIG. 4 shows a block diagram of an embodiment of the variable directional
microphone according to the present invention, in which the same parts as in FIG. 1 (the same
numerals are assigned). In the figure, the output of the microphone 2a has the phase shown in
FIG. 5, and is phase shifted with a predetermined phase shift amount by the variable primary
phase shift circuit 6 having the circuit configuration shown in FIG. , And are mixed in phase with
the outputs of the microphones 2b and 7fC. Note that the mixing (4) combiner T is not
configured to change the mixing ratio of the outputs of the microphones 2a and 2b. It is apparent
from FIG. 5 that the phase characteristic of the phase shift circuit 6 shows that the ratio of the
angular frequency .omega. To the angular frequency .omega.1 of 10 phase lags is phase-shifted
in the direction of 180.degree. The output of the phase shift circuit 6 is, for example, for the
input signal in a frequency band extremely larger than that of the town 4-1 since the phase shift
is made in the 00 direction on the frequency axis where-is less than 1 inch. Phase is rotated by
180 ░. In the frequency band extremely smaller than -1, the phase does not rotate with respect
to the input signal. Therefore, at high frequencies, the output of the microphone 2a is phaserotated by 180 ░ and mixed with the output of the microphone 2b (the output of the
microphone 2b is subtracted from the output of the microphone 2b). Similar to the output of the
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mixer 3 of the prior art shown in FIG. 3, the same inertia as that of the conventional one shown
in FIG. 3 can be obtained. On the other hand, at low frequencies, the output of the microphone 2a
is mixed (the output of the microphone 2a and the output of the microphone 2b are added) to the
output (S) Q of the microphone 2b without phase rotation. Even if the output of the microphone
2a and the output of the microphone 2b are added at a low frequency where the wavelength of
the signal can ignore the distance between the microphone 2a and the microphone 2b, the
output substantially doubles the output of the microphone 2a or It can be considered that an
output twice as high as the output of the microphone 2b is taken out. Therefore, at this low
frequency, the frequency characteristic is flat and substantially the same characteristic as the
first-order unidirectional microphone is obtained, and it does not attenuate like the characteristic
of the conventional one shown in FIG. Circuit 60 Assuming that the phase characteristic is 9-),
the directivity pattern P in which the output of the microphone 2a and the output of the
microphone 2b are mixed is P-A (Hy 1). j (?t?? (?)) ?B и (k ? и ?j ((at?KDeos 19) иии (3), and
the sensitivity A of the microphone 2a and the microphone (и), -5 2n 2b If the sensitivity B is the
same as A and B, then the above equation is A, <1 ? ? cos 1 ?>,, 1?t, (, j? (cJ, -jxD cos ?). It
becomes (4).
Here, ? (?) is expressed as ? (?) -2tan-?a. Further, in the equation (4), (1 + eos #) ии ja + t is a
constant, (e?j? + e?jKDaos #) is variable L, the variable resistor VR1 of the variable first-order
phase shift circuit 6 is Fig. 7 (a) shows the frequency characteristics when the angular frequency
? of the so ░ phase delay is changed from 10 Hia to 400 Hz and the distances Dm3csm, ?-0
░, so0 are substituted into the above variables. 90 ░) and FIG. 8 (??0 ░) K, and the directivity
pattern is shown in FIG. 9 (when ?amsOHi). As is apparent from FIGS. 7 to 9, in the high
frequency band, the second-order uni-directivity characteristic substantially the same as the
directivity characteristic of the conventional one in FIG. In particular, the response does not
decrease as in the conventional bass shown in FIG. 3 in the low band and (in the mid band, the
difference between the maximum value and the minimum value is .omega.am 50 Hm at most
about 136 B It is smaller than the conventional one shown in FIG. As described above, the
frequency characteristic of the output of the mixer T only decreases by 13 fLB at .omega. & -50
Hz at the mid frequency, so that the variable equalizer 8 for flattening the frequency can correct
about 13 dB as shown in FIG. It may be the one having the opposite characteristic to the
characteristic, and it may be smaller than the correction amount of the conventional equalizer
shown in FIG. 1, thereby there is no deterioration of the 8N ratio as in the prior art, and wind
noise is less likely to occur. , It is hard to produce so-called touch noise. In this case, the variable
equalizer 8 is configured as shown in FIG. 10 such that the variable resistor VP2 is interlocked
with the variable resistor VR of the variable first-order phase shift circuit 6, and the phase shift
amount of the first-order phase shift circuit 6 is changed. At the same time, the characteristics of
the variable equalizer 8 can be varied. The capacitance value of the capacitor C2 is set to be 10
times or more that of the capacitor C1, and the maximum correction amount is obtained at the
maximum value of the resistance value of the variable resistor VR1 ░ vR2 (a)): , And a2 and the
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resistance value of the resistor R are respectively selected. Further, the resistance value of the
resistor R1 is a resistance R1 variable resistor 1. We will also select a larger one than that of
VB2. In the case of general recording, a low frequency signal of 200 Hg or less is recorded as
either one of second-order unidirectivity and first-order unidirectivity, and this effect hardly
changes, so the microphone of the invention Although only a single-order single directivity can
be obtained at low frequencies below IIC 20 OHg, there is virtually no problem, while as apparent
from FIG. 8, the larger the ? 6, the flatter the frequency characteristics and the closer the gap.
(Ie closer to the characteristics of a primary uni-directional microphone with flat frequency
characteristics), the smaller the ? 1, the less flat the frequency characteristics (ie, shown in FIG.
3 within the general use band of the microphone) It comes close to the characteristics of the
second-order unidirectional microphones).
Therefore, the desired directional characteristics can be obtained by varying the phase shift
amount in the variable first-order phase shift circuit 11, and this phase shift amount can be
varied continuously from ?a-10Hg to ?a-400Hm. )) (the de "Melle, may continuously variable
allowed range from the primary unidirectional to the secondary unidirectional. Also, the phase
shift circuit can use the variable first-order phase shift circuit as shown in FIG. 6 or the variable
first-order phase shift circuit to obtain the same effect. Furthermore, the number of microphones
used is not limited to two, and in FIG. 4, one microphone is provided in the opposite direction to
the microphone 2b and the diaphragms are flush with each other, for a total of three
microphones. The mixing ratio of the output of each may be varied to obtain nondirectionality,
first order unidirectionality, and second order unidirectionality. Further, in FIG. 4, variable
primary or variable secondary phase shift circuits may be appropriately combined and connected
to the output sides of the microphones 2a and 2b to obtain the frequency characteristics shown
in FIGS. 1 and 6. Good. As mentioned above, the variable directional microphone according to the
present invention is a mixer which connects a variable phase shift circuit to at least one
microphone and mixes the output of this circuit to the output from another microphone to the
variable phase shift circuit. (10)-Since the coupling circuit is connected, the directivity can be
arbitrarily changed according to the change of the phase shift amount of the variable phase shift
circuit, whereby, for example, the directivity can be linked to the zoom mechanism of the video
camera. If it is made variable, it is possible to emphasize the sense of unity between the screen
and the sound, and since the amount of phase shift is made variable in order to make directional
characteristics variable, the mixing ratio of the output of each microphone is made variable. It is
not necessary to provide a buffer circuit like a microphone of, and a circuit can be simply
configured, + Saki 1 steering! Also, since the output of the microphone is phase-shifted and
mixed with the output of another microphone, the high frequency frequency d is substantially
from the microphone. It is similar to subtractive mixing of the outputs, which results in a secondorder unidirectional pattern as in the prior art, while at lower frequencies it is virtually additive
mixing of the outputs from the microphones. In the same way, the directivity after the mixing can
be regarded as the output from one microphone with substantially flat frequency characteristics
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and one primary uni-directional microphone and its directivity is a single-order single Since the
response of the finger (11) pattern does not decrease as in the conventional 40, the frequency
characteristic is the frequency of the conventional one which is only by subtractive mixing of the
output of the primary uni-directional microphone Especially low frequencies compared to
goodness It is possible to prevent the level loss in the number, and therefore, it is possible to set
the correction amount of the equalizer for correcting the frequency to be flat so as to flatten the
frequency characteristic of the mixed signal, thereby improving the 8N ratio. Also, they have
equal lengths such that so-called wind noise and so-called touch noise do not occur.
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