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DESCRIPTION JP2013085025

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DESCRIPTION JP2013085025
Abstract: A condenser microphone capable of adjusting sensitivity without changing a voltage
between a diaphragm and a fixed electrode, and having no electrostatic adsorption of the
diaphragm due to sensitivity adjustment and no variation in acoustic characteristics. SOLUTION:
The output impedance of the microphone unit 5 is low, which is connected to one of a condenser
microphone unit 5 that performs electroacoustic conversion by a change in capacitance between
a diaphragm 52 and a fixed pole 51, the diaphragm 52 or the fixed pole 51. A non-inverting
amplifier 1 including an impedance converter for converting into an impedance, an output signal
of the non-inverting amplifier 1 is input through an input resistor R10 and an inverting amplifier
2 having a feedback resistor R11, an output of the non-inverting amplifier 1 and an inverting
amplifier 2 The variable resistor VR includes a variable resistor VR connected between the output
and the one connected to the diaphragm 52 or the fixed pole 51 not connected to the noninverting amplifier 1. The sensitivity changes depending on the position of the child. [Selected
figure] Figure 1
コンデンサマイクロホン
[0001]
The present invention relates to a condenser microphone capable of adjusting variation in
sensitivity among individuals without changing the electrostatic attraction between a diaphragm
and a fixed pole.
[0002]
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1
The condenser microphone has a diaphragm and a fixed pole facing each other with a
predetermined gap, and outputs as an audio signal a change in capacitance between the
diaphragm and the fixed pole due to vibration of the diaphragm upon receiving a sound wave. It
is a thing.
As the condenser microphone, there is a DC bias condenser microphone that applies a DC voltage
to a condenser composed of a diaphragm and a fixed pole. The sensitivity of the DC bias
capacitor microphone depends on the bias voltage, and the sensitivity becomes higher as the bias
voltage becomes higher. Therefore, there is a DC bias condenser microphone whose sensitivity
can be adjusted by adjusting the bias voltage. FIG. 6 shows an example thereof.
[0003]
In FIG. 6, reference numeral 15 denotes a condenser microphone unit. Condenser microphone
unit 15 has a diaphragm and a fixed pole opposite to each other with an appropriate gap, and
when the diaphragm receives a sound wave and vibrates, it is electroacoustically converted as
described above and voices from the diaphragm and the fixed pole A signal is output. The fixed
pole is connected to the non-inverted input terminal of the first amplifier 11, and the diaphragm
is connected to the inverted input terminal of the amplifier 11. The amplifier 11 is provided with
an impedance converter composed of a FET, and converts the output signal of the condenser
microphone unit 15 of very high output impedance into a low impedance signal and outputs it to
the next stage.
[0004]
The output terminal of the amplifier 11 is connected via the input resistor R10 to the inverting
input terminal of the inverting amplifier 12 which is the second amplifier. The noninverting input
terminal of the inverting amplifier 12 is connected to ground via a capacitor C12. A feedback
resistor R11 is connected between the inverting input terminal and the output terminal of the
inverting amplifier 12. The resistance value of the input resistor R10 and the resistance value of
the feedback resistor R11 are equal, and the voltage amplification factor of the inverting
amplifier 12 is -1.
[0005]
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The output terminal of the amplifier 11 is also connected to the non-inverting input terminal of
the third amplifier 13 and the output terminal of the inverting amplifier 12 is connected to the
non-inverting input terminal of the fourth amplifier 14. The output terminal of the amplifier 13 is
connected to the second pin 22 of the 3-pin connector and to the inverting input terminal of the
amplifier 13. The output terminal of the amplifier 14 is connected to the third pin 23 of the
connector and to the inverting input terminal of the amplifier 14. The connector is a balanced
output connector, and the second pin 22 connected to the output terminal of the amplifier 13 is
the hot output pin of the balanced output, and the third pin 23 connected to the output terminal
of the amplifier 14 is the cold output of the balanced output The pin and the first pin 21 are
earth pins.
[0006]
The positive power supply terminals of the amplifiers 11, 12, 13, 14 are connected to the
positive power supply output terminal of the DC power supply 16, and the negative power
supply terminals of the amplifiers 11, 12, 13, 14; the ground terminal of the DC power supply
16; The first pins 21 of the connector are connected to one another. The DC voltage output from
the DC power supply 16 is also connected to the diaphragm of the condenser microphone unit
15 as a DC bias voltage. The DC bias voltage can be adjusted by operating a variable resistor
VR11 included in the DC power supply 16, and this adjustment can adjust the sensitivity of the
condenser microphone unit 15.
[0007]
Thus, in the DC bias condenser microphone, the sensitivity can be adjusted by adjusting the DC
bias voltage. However, when the bias voltage is increased, the electrostatic attraction force
generated between the diaphragm and the fixed electrode is increased, the diaphragm is
attracted to the fixed electrode, the diaphragm can not vibrate, and the microphone functions as
a microphone. It may disappear.
[0008]
Further, even if the diaphragm is not electrostatically attracted to the fixed electrode by the bias
voltage, when the strong air flow hits the diaphragm, the diaphragm is easily electrostatically
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attracted to the fixed electrode. Therefore, in consideration of the stability of operation, the bias
voltage is set to such a bias voltage that electrostatic adsorption does not occur even when
strong air flow hits the diaphragm. If the DC bias voltage can be varied continuously, the
sensitivity of the condenser microphone can be varied continuously, and even if a strong air
stream strikes the diaphragm, it can operate stably without causing electrostatic adsorption. The
bias voltage can be set to
[0009]
For example, in an electret condenser microphone in which an electret layer is formed on the
surface of a fixed pole, it is not necessary to add a DC bias, and a DC bias generation circuit is
unnecessary. However, in order to make the sensitivity of the electret condenser microphone
variable, it is necessary to expose the electret layer on the surface of the fixed electrode and
adjust the surface voltage of the electret layer.
[0010]
The applicant has proposed an electret condenser microphone capable of adjusting the
sensitivity by varying a DC voltage to be applied (see Patent Document 1). According to the
electret condenser microphone described in Patent Document 1, it has become possible to adjust
the sensitivity, but if the DC voltage to be applied is too high, the diaphragm is electrostatically
attracted to the fixed electrode as described above. There is a limit to increasing sensitivity
because it Therefore, it is desirable to realize a condenser microphone that enables sensitivity
adjustment without changing the voltage between the diaphragm and the fixed pole.
[0011]
By the way, since the condenser microphones have individual sensitivity variations, the quality
adjustment process is performed during the manufacturing process to achieve uniform quality.
The DC bias condenser microphone can eliminate variations in sensitivity by adjusting the DC
bias voltage. However, adjusting the DC bias voltage has the above-described disadvantages, and
there is also a disadvantage that the frequency response characteristic fluctuates. Therefore, it is
desirable to realize a condenser microphone capable of sensitivity adjustment without changing
the voltage between the diaphragm and the fixed pole even in adjustment for eliminating
variations in sensitivity among individuals.
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[0012]
Unexamined-Japanese-Patent No. 2006-295357
[0013]
The present invention makes it possible to adjust sensitivity without changing the voltage applied
between the diaphragm and the fixed electrode, and thus, problems such as electrostatic
adsorption of the diaphragm and fluctuation of acoustic characteristics by enhancing the
sensitivity. An object of the present invention is to provide a condenser microphone that can be
avoided.
[0014]
A condenser microphone according to the present invention comprises: a condenser microphone
unit having a diaphragm and a fixed pole disposed opposite to each other and performing
electroacoustic conversion by a change in electrostatic capacity between the diaphragm and the
fixed pole; Or a non-inverting amplifier including an impedance converter connected to one of
the fixed poles and converting the output impedance of the condenser microphone unit to a low
impedance, and the output signal of the non-inverting amplifier is input through the input
resistance and An inverting amplifier connected between the output of the non-inverting
amplifier and the output of the inverting amplifier, wherein a slider is connected to one of the
diaphragm and the fixed pole which is not connected to the non-inverting amplifier A variable
resistor, and the most important thing is that the sensitivity changes depending on the position of
the slider of the variable resistor. And butterflies.
[0015]
The diaphragm or fixed pole which is not connected to the inverting amplifier is driven by the
voltage of the slider of the variable resistor, and the output level of the condenser microphone
unit with respect to the ground corresponds to the position of the slider of the variable resistor.
Will be adjusted.
Since the voltage between the diaphragm and the fixed pole of the condenser microphone unit
does not fluctuate, it is possible to avoid problems such as electrostatic adsorption of the
diaphragm and fluctuation of acoustic characteristics due to sensitivity adjustment.
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[0016]
It is a circuit diagram showing an example of a condenser microphone concerning the present
invention.
It is a circuit diagram showing another example of a condenser microphone concerning the
present invention.
It is a frequency response characteristic diagram at the time of setting a sensitivity adjustment
position to the center in the said Example. It is a frequency response-characteristic diagram at
the time of setting a sensitivity adjustment position to the high sensitivity side in the said
Example. It is a frequency response characteristic diagram at the time of setting a sensitivity
adjustment position to low sensitivity in the said Example. It is a circuit diagram showing an
example of a conventional condenser microphone.
[0017]
Hereinafter, embodiments of a condenser microphone according to the present invention will be
described with reference to the drawings.
[0018]
In FIG. 1, reference numeral 5 denotes a condenser microphone unit.
The condenser microphone unit 5 is provided with a diaphragm 52 and a fixed pole 51 opposed
to each other with an appropriate gap. The diaphragm 52 constitutes an electrode of a capacitor
together with the fixed electrode 51. When the diaphragm 52 receives a sound wave and
vibrates, the capacitance of the capacitor changes, and the sound signal corresponding to the
sound wave is fixed to the diaphragm It is output from the pole. The fixed pole 51 is connected to
the non-inverting input terminal of the first amplifier 1. A direct current voltage is applied to the
diaphragm 52 from the direct current power source 6 through the resistor R1.
[0019]
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The DC power supply 6 includes a DC-DC converter that boosts the voltage of a power supply
battery built in the microphone to, for example, about 100 V at maximum. However, the large
power supply of the DC power supply 6 is not limited to the built-in battery, and a phantom
power supply may be used when a phantom power supply is introduced. In addition, it is optional
whether or not to use a DC-DC converter, and it is not necessary to necessarily use a DC-DC
converter as long as a necessary voltage can be secured. The voltage applied from the DC power
supply 6 to the diaphragm 52 of the condenser microphone unit 5 is constant.
[0020]
The first amplifier 1 is provided with an impedance converter mainly composed of a FET, and
converts the signal of very high output impedance outputted from the capacitor microphone unit
5 into a signal of low impedance and outputs it to the next stage . The output terminal of the
amplifier 1 is connected via the input resistor R10 to the inverting input terminal of the inverting
amplifier 2 which is the second amplifier. The noninverting input terminal of the inverting
amplifier 2 is connected to ground via a capacitor C2. A feedback resistor R11 is connected
between the inverting input terminal and the output terminal of the inverting amplifier 2. The
resistance value of the input resistor R10 and the resistance value of the feedback resistor R11
are equal, and the voltage amplification factor of the inverting amplifier 2 is set to -1.
[0021]
The output terminal of the amplifier 1 is also connected to the non-inverting input terminal of
the third amplifier 3 and the output terminal of the inverting amplifier 2 is connected to the noninverting input terminal of the fourth amplifier 4. The output terminal of the amplifier 3 is
connected to the second pin 22 of the 3-pin connector and to the inverting input terminal of the
amplifier 3. The output terminal of the amplifier 4 is connected to the third pin 23 of the
connector and to the inverting input terminal of the amplifier 4. The connector is a connector for
balanced output, and the second pin 22 connected to the output terminal of the amplifier 3 is a
hot output pin of the balanced output, and the third pin 23 connected to the output terminal of
the amplifier 4 is a cold output of the balanced output The pin and the first pin 21 are earth pins.
[0022]
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A variable resistor VR is connected between the output of the non-inverting amplifier 1 as the
first amplifier and the output of the inverting amplifier 2 as the second amplifier. More
specifically, one of the two terminals of the variable resistor VR is connected to the output
terminal of the non-inverting amplifier 1 and the other of the two terminals of the variable
resistor VR is connected to the output terminal of the inverting amplifier 2. Therefore, the
variable resistor VR is connected in parallel to the series connection of the input resistor R10 and
the feedback resistor R11. The slider included in the variable resistor VR is one of the diaphragm
52 or the fixed pole 51 of the condenser microphone unit 5 which is not connected to the noninverting amplifier 1, and thus, in the illustrated example, the diaphragm 52 Connected through.
[0023]
The positive power supply terminal of each amplifier 1, 2, 3, 4 is connected to the positive power
supply output terminal of DC power supply 6, and the negative power supply terminal of each
amplifier 1, 2, 3, 4 and the ground terminal of DC power supply 6 and the above connector The
first pins 21 of are connected to each other, and power for operating the respective amplifiers 1,
2, 3 and 4 is supplied from the DC power supply 6.
[0024]
According to the embodiment of the condenser microphone shown in FIG. 1, the voltage for
driving the diaphragm 52 of the condenser microphone unit 5 changes according to the position
of the slider of the variable resistor VR, and the sensitivity of the microphone changes.
In other words, according to the position of the slider of the variable resistor VR, the voltage
added to the acoustic signal electroacoustically converted by the capacitor microphone unit 5
and output is adjusted to plus or minus, and the sensitivity of the microphone changes Do. Thus,
even if the sensitivity of the microphone is adjusted, the voltage applied between the fixed pole
51 of the microphone unit 5 and the diaphragm 52 is constant without fluctuation. There is no
problem that the diaphragm is likely to be electrostatically attracted or the acoustic
characteristics fluctuate.
[0025]
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FIGS. 3 to 5 show frequency response characteristics when sensitivity adjustment is performed in
the above embodiment. 3 shows the case where the slider of variable resistor VR is at the center
position, FIG. 4 shows that the slider of variable resistor VR is at the left end in FIG. The case
where the resistance value on the output side of 2 is maximum is shown. The sensitivity of the
microphone at this time is about twice that of the case where the slider is at the center. 5 shows
the case where the resistance of the variable resistor VR at the right end, that is, the output side
of the non-inverting amplifier 1 is maximum and the resistance of the output side of the inverting
amplifier 2 is zero in FIG. The sensitivity of the microphone at this time is about one half that of
the case where the slider is at the center. In both cases, the sound source is measured at the
front, ie at 0 degree, at the 90 degree position, at the back side, ie at the 180 degree position.
The thin line shows the case of 180 degrees.
[0026]
The sensitivity when the slider of variable resistor VR is at the center position is -26.4 dBV, and
the maximum sensitivity is obtained when the slider is at the left end in FIG. 1, and the slider is at
the center position. It was -19.3 dBV of +7.1 dBV than a certain case. Further, the sensitivity was
lowest when the slider was at the right end in FIG. 1 and was -33.1 dBV of -6.7 dBV as compared
to the case where the slider was at the center position.
[0027]
Note that the characteristic diagrams shown in FIG. 3 to FIG. 5 are shown as normalized
(normalized) at the output level at a specific frequency. The characteristic diagrams shown in
FIGS. 3 to 5 substantially overlap. The reason is that, as described above, the voltage between the
fixed electrode 51 and the diaphragm 52 does not change even if the sensitivity adjustment is
performed, and the acoustic characteristics do not change.
[0028]
The present invention can be applied even when the microphone unit 5 is an electret condenser
microphone unit. FIG. 2 shows the embodiment. In the electret condenser microphone unit 5, the
diaphragm or the fixed pole has the electret layer, the surface potential of the electret is kept
constant, and a constant polarization voltage is generated between the diaphragm 52 and the
fixed pole 51. ing. Therefore, in the embodiment shown in FIG. 2, it is not necessary to apply a
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DC voltage to the microphone unit 5, so the DC voltage source 6 used in the first embodiment
shown in FIG. 1 is unnecessary.
[0029]
The second embodiment shown in FIG. 2 is the same as the first embodiment shown in FIG. 1
except that the DC voltage source 6 is not provided as described above. That is, between the
output terminal of the non-inverting amplifier 1 as the first amplifier and the inverting input
terminal of the inverting amplifier 2 as the second amplifier, the first to fourth amplifiers 1, 2, 3
and 4 are provided. An input resistor R10 is connected, and a feedback resistor R11 is connected
between the output terminal of the inverting amplifier 2 and the inverting input terminal. The
value of the input resistor R10 is the same as the value of the feedback resistor R11.
Furthermore, as in the first embodiment, a variable for adjusting the sensitivity of the
microphone between the output of the noninverting amplifier 1 as the first amplifier and the
output of the inverting amplifier 2 as the second amplifier The resistor VR is connected. The
slider of the variable resistor VR is connected to the diaphragm 52 of the condenser microphone
unit 5 via the capacitor C 1, that is, the diaphragm 52 or the fixed pole 51 which is not connected
to the non-inverting amplifier 1. It is connected to the.
[0030]
Power for operating these amplifiers is supplied to each of the amplifiers 1, 2, 3, 4 from a
suitable DC power supply (not shown).
[0031]
The configuration for sensitivity adjustment in the second embodiment shown in FIG. 2 is the
same as the configuration for sensitivity adjustment in the first embodiment, and the principle of
sensitivity adjustment is also the same. The same effect as obtained by
[0032]
In the embodiment shown in FIGS. 1 and 2, the fixed pole 51 of the condenser microphone unit 5
is connected to the non-inverted amplifier 1 which is the first amplifier, and the diaphragm 52 is
connected to the slider of the variable resistor VR. However, the fixed electrode 51 and the
diaphragm 52 may be connected in reverse.
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In this case, since the phase of the output signal of the condenser microphone unit 5 is reversed,
the circuit from the output of the condenser microphone unit 5 to the output of the microphone
is corrected so that the phase of the output signal of the microphone becomes a predetermined
phase. Do.
[0033]
DESCRIPTION OF SYMBOLS 1 non-inversion amplifier 2 inversion amplifier 5 capacitor
microphone unit 6 DC voltage source 51 fixed pole 52 diaphragm VR variable resistor R10 input
resistance R11 feedback resistance
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