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DESCRIPTION JP2013251746

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DESCRIPTION JP2013251746
PROBLEM TO BE SOLVED: To provide a condenser microphone that suppresses distortion of an
output signal due to excessive input without changing a signal-to-noise ratio. SOLUTION: First
and second condenser microphone units whose output signals are reverse to each other, and two
variable resistors connected to the output side of the first condenser microphone unit and the
second condenser microphone unit, , And the output signal of the first condenser microphone
unit and the output signal of the second condenser microphone unit are combined in the first
variable resistor included in the two variable resistors, and the input of the first condenser
microphone unit is input. , And are combined at a second variable resistor included in the two
series of variable resistors and added to the input of the second capacitor microphone unit.
[Selected figure] Figure 1
コンデンサマイクロホン
[0001]
The present invention relates to a condenser microphone, and more particularly, to a condenser
microphone that prevents distortion of an output signal by adjusting an input level to an
impedance converter without deteriorating a signal-to-noise ratio.
[0002]
The condenser microphone has a high impedance of a condenser microphone unit which is an
electroacoustic transducer, and requires an impedance converter such as a FET (field effect
transistor, hereinafter the same).
18-04-2019
1
The impedance converter requires an operating power supply. Since the maximum output level
of the condenser microphone is limited by the voltage of the operating power supply, the output
signal is distorted if the magnitude of the sound wave input to the condenser microphone unit
exceeds the maximum output level. become.
[0003]
In order to prevent such distortion of the output signal, “PAD” is used to attenuate the input
level to the impedance converter. The PAD is composed of a capacitor connected in parallel to
the condenser microphone unit, and attenuates the input signal level of the impedance converter
in accordance with the ratio of capacitance with the condenser microphone unit. This can
prevent excessive input to the impedance converter.
[0004]
On the other hand, although the impedance converter generates inherent noise, this noise level is
constant regardless of the level of the input signal. That is, if the input level to the impedance
converter is attenuated by using PAD to prevent distortion due to excessive input, the signal-tonoise ratio of the condenser microphone will be lowered.
[0005]
In a conventional condenser microphone, a condenser microphone is known which balances the
output of an impedance converter which is unbalanced and reduces distortion of an audio signal
output from the impedance converter in order to improve a reduction in signal-to-noise ratio.
(See, for example, Patent Document 1).
[0006]
JP, 2006-101302, A
[0007]
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2
The condenser microphone of Patent Document 1 can reduce output distortion by canceling out
second-order distortion of the impedance converter.
However, since PAD is necessary to cope with an excessive input that exceeds the maximum
output level, a decrease in signal-to-noise ratio occurs due to PAD.
[0008]
In addition, among conventional condenser microphones, it is known that the operation of PAD
can be selected according to the magnitude of the input level.
FIG. 9 shows an example of a conventional condenser microphone. The condenser microphone
100 shown in FIG. 9 includes condenser microphone units 21 and 22, impedance converters 31
and 32, and a PAD 40.
[0009]
The fixed pole 212 of the condenser microphone unit 21 is connected to the input terminal of
the impedance converter 31, and the first PAD capacitor 41 is connected in parallel to the
condenser microphone unit 21 via the switch 43. The diaphragm 221 of the condenser
microphone unit 22 is connected to the input terminal of the impedance converter 32, and the
second PAD condenser 42 is connected in parallel to the condenser microphone unit 22 via the
switch 43. The diaphragm 211 of the condenser microphone unit 21 and the fixed pole 222 of
the condenser microphone unit 22 are both grounded.
[0010]
The connection on / off of the first PAD capacitor 41 and the second PAD capacitor 42
constituting the PAD 40 can be switched by the switch 43. When the level of the sound wave
input to the condenser microphone 100 is small, the switch 43 is opened to turn off the
operation of the PAD 40, and when the level of the sound wave input is large, the switch 43 is
closed to turn on the operation of the PAD 40. The on / off of the PAD 40 is appropriately
switched by the user operating the switch 43.
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[0011]
Further, the amount of attenuation of the input signal level to the impedance converter can be
varied in multiple stages by switching the configuration of the PAD 40 by switching a plurality of
capacitors having different capacitances. However, since the attenuation can not be varied
continuously and can not be amplified even if the input level to the impedance converter is small,
the signal-to-noise ratio can not be kept constant.
[0012]
The present invention has been made in view of the above problems, and can continuously
reduce the input level without changing the signal-to-noise ratio, and functions as a PAD against
excessive input, It is an object of the present invention to provide a condenser microphone
capable of continuously increasing an input level when the level is small.
[0013]
The present invention comprises first and second condenser microphone units whose output
signals are in opposite phase to each other, and two variable resistors connected to the output
side of the first condenser microphone unit and the second condenser microphone unit. The
output signal of the first capacitor microphone unit and the output signal of the second capacitor
microphone unit are combined in the first variable resistor included in the two variable resistors
and added to the input of the first capacitor microphone unit, The second embodiment is mainly
characterized in that it is synthesized at a second variable resistor included in the variable
resistor of and is added to the input of the second capacitor microphone unit.
[0014]
According to the present invention, even if the input level to the impedance converter is
attenuated, the amount of attenuation can be adjusted continuously without changing the signalto-noise ratio.
[0015]
It is a circuit diagram showing an example of a condenser microphone concerning the present
invention.
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It is a circuit diagram which shows an example when moving the slider of the variable resistance
with which the capacitor | condenser microphone in an Example is equipped to one terminal side.
It is a circuit diagram which shows another example when moving the slider of the variable
resistance with which the capacitor | condenser microphone in an Example is equipped to one
terminal side.
It is a circuit diagram showing an example when a slider of variable resistance with which a
condenser microphone in an example is equipped is moved to the other terminal side. It is a
circuit diagram showing another example when moving the slider of the variable resistance with
which the condenser microphone in an example is provided to the other terminal side. It is a
frequency response special diagram when the slider of the variable resistance with which the
capacitor | condenser microphone in an Example is equipped is in a middle point. It is a
frequency response special diagram when the slider of the variable resistance with which the
capacitor | condenser microphone in an Example is equipped is on the plus side. It is a frequency
response special diagram when the slider of the variable resistance with which the capacitor |
condenser microphone in an Example is equipped is on the minus side. It is a circuit diagram
showing an example of a conventional condenser microphone.
[0016]
Hereinafter, an embodiment of a condenser microphone according to the present invention will
be described with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment
of a condenser microphone 10 according to the present invention. As shown in FIG. 1, the
condenser microphone 10 includes a first condenser microphone unit 11, a second condenser
microphone unit 12, a first impedance converter 13, a second impedance converter 14, and two
variable resistors 15. And.
[0017]
The first condenser microphone unit 11 has a diaphragm 111 and a fixed electrode 112, and the
diaphragm 111 and the fixed electrode 112 form a predetermined gap via a spacer (not shown).
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It is placed inside. The second condenser microphone unit 12 has a diaphragm 121 and a fixed
electrode 122, and the diaphragm 121 and the fixed electrode 122 form a predetermined gap via
a spacer (not shown). It is placed inside.
[0018]
The first impedance converter 13 and the second impedance converter 14 are both impedance
converter circuits having FETs. The first condenser microphone unit 11 is a fixed pole output,
and a fixed pole 112 which is an output end is connected to an input end (a gate terminal of the
FET) of the first impedance converter 13. The second condenser microphone unit 12 is a
diaphragm output, and a diaphragm 121 which is an output end is connected to an input end (a
gate terminal of the FET) of the second impedance converter 14.
[0019]
The output signal of the first condenser microphone unit 11 is output from the output end (the
drain terminal of the FET) of the first impedance converter 13, and the output signal of the
second condenser microphone unit 12 is the output end of the second impedance converter 14.
It is output from (the drain terminal of the FET). Since the first condenser microphone unit 11 is
a fixed pole output and the second condenser microphone unit 12 is a diaphragm output, the
output signals of the first condenser microphone unit 11 and the second condenser microphone
unit 12 are signals in reverse phase with each other. The output of the condenser microphone 10
is a balanced output. As shown in FIG. 1, the output end of the first impedance converter 13 is
used as a balanced output HOT terminal, and the output end of the second impedance converter
14 is used as a balanced output COLD terminal.
[0020]
A variable resistor 15 is connected between the output end of the first impedance converter 13
and the output end of the second impedance converter 14. The variable resistor 15 is a double
variable resistor having a first variable resistor 151 and a second variable resistor 152, and the
first slider 153 of the first variable resistor 151 and the second variable resistor 152 The second
slider 154 interlocks.
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[0021]
The first variable resistor 151 has an output terminal of the first impedance converter 13 which
is an output terminal of the first capacitor microphone unit 11 and an output terminal of the
second impedance converter 14 which is an output terminal of the second capacitor microphone
unit 12. It is arranged to connect. The second variable resistor 152 has an output terminal of the
second impedance converter 14 which is an output terminal of the second capacitor microphone
unit 12 and an output terminal of the first impedance converter 13 which is an output terminal
of the first capacitor microphone unit 11. It is arranged to connect.
[0022]
In the following description, the terminal on the first impedance converter 13 side of the first
variable resistor 151 is “first terminal 21”, and the terminal on the second impedance
converter 14 side of the first variable resistor 151 is “second terminal 22”. A terminal on the
second impedance converter 14 side of the second variable resistor 152 is referred to as a "third
terminal 23", and a terminal on the first impedance converter 13 side of the second variable
resistor 152 is referred to as a "fourth terminal 24". In the following description, the first
terminal 21 and the third terminal 23 are referred to as "plus side", and the second terminal 22
and the fourth terminal 24 are referred to as "minus side".
[0023]
The first terminal 21 of the first variable resistor 151 and the fourth terminal 24 of the second
variable resistor 152 are connected, and the second terminal 22 of the first variable resistor 151
and the third terminal 23 of the second variable resistor 152 are connected. There is.
[0024]
Here, “interlocking” of the first slider 153 and the second slider 154 will be described.
When the first slider 153 is moved to the first terminal 21 side, the second slider 154 moves to
the third terminal 23 side, and when the first slider 153 is moved to the second terminal 22 side,
the second The slider 154 moves to the fourth terminal 24 side. Naturally, when the second
slider 154 is moved to the third terminal 23 side, the first slider 153 is moved to the first
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terminal 21 side, and the second slider 154 is moved to the fourth terminal 24 side. The first
slider 153 moves to the second terminal 22 side. As described above, by moving one of the first
slider 153 and the second slider 154, the other slider moves in a predetermined direction.
[0025]
The first slider 153 is connected to the diaphragm 111 of the first condenser microphone unit
11. The second slider 154 is connected to the fixed pole 122 of the second condenser
microphone unit 12.
[0026]
A composite signal of the output signal of the first condenser microphone unit 11 and the output
signal of the second condenser microphone unit 12 is applied to the diaphragm 111 of the first
condenser microphone unit 11 via the first slider 153. . Here, the output signal of the first
condenser microphone unit 11 and the output signal of the second condenser microphone unit
12 are in reverse phase. Further, the resistance value of the first variable resistor 151 with
respect to each output signal is determined according to the position of the first slider 153. The
ratio of the resistance value of the first variable resistor 151 to each output signal combines the
output signals in reverse phase with each other.
[0027]
Similarly, a composite signal of the output signal of the second condenser microphone unit 12
and the output signal of the first condenser microphone unit 11 via the second slider 154 at the
fixed pole 122 of the second condenser microphone unit 12 Is added. As described above, the
output signal of the second condenser microphone unit 12 and the output signal of the first
condenser microphone unit 11 are in opposite phase. Further, the resistance value of the second
variable resistor 152 for each output signal is determined according to the position of the second
slider 154. The ratio of the resistance value of the second variable resistor 152 to each output
signal combines the output signals in reverse phase with each other.
[0028]
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As shown in FIG. 1, when the first slider 153 and the second slider 154 are at the midpoint
between the first variable resistor 151 and the second variable resistor 152, respectively, the
signal from the first condenser microphone unit 11 is obtained. Since the resistance value of the
first variable resistor 151 for the output signal and the output signal from the second condenser
microphone unit 12 is the same, the output signal from the first condenser microphone unit 11
and the output signal from the second condenser microphone unit 12 are Offset each other.
Therefore, the composite signal does not flow to the first slider 153, and neither a signal having
the same phase as the output signal of the first condenser microphone unit 11 nor a signal
having the reverse phase is applied to the diaphragm 111.
[0029]
Similarly, since the resistance value of the second variable resistor 152 for the output signal from
the second capacitor microphone unit 12 and the output signal from the first capacitor
microphone unit 11 is the same, the output signal from the second capacitor microphone unit 12
The output signals from the first condenser microphone unit 11 cancel each other. Therefore, the
composite signal does not flow to the second slider 154, and neither a signal in phase with the
output signal of the second condenser microphone unit 12 nor a signal in reverse phase is
applied to the fixed pole 122.
[0030]
Thus, when the first slider 153 and the second slider 154 are at the midpoint between the first
variable resistor 151 and the second variable resistor 152, respectively, the first capacitor
microphone unit 11 and the second capacitor microphone unit The output signal from 12 is
input to the first impedance converter 13 and the second impedance converter 14 without being
increased or decreased, and balanced output from the HOT terminal and the COLD terminal.
[0031]
FIG. 6 shows an example of the frequency response characteristic of the condenser microphone
10 when the first slider 153 and the second slider 154 are at the midpoint between the first
variable resistor 151 and the second variable resistor 152, respectively. There is.
[0032]
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9
Next, an output signal of the condenser microphone 10 when the first slider 153 and the second
slider 154 are moved from the middle point will be described.
FIGS. 2 and 3 show examples of the condenser microphone 10 when the first slider 153 and the
second slider 154 are respectively moved to the positive side.
[0033]
The combined signal 161 applied to the diaphragm 111 via the first slider 153 is the output
signal 16 of the first condenser microphone unit 11 and the second condenser microphone unit
12 which are lowered according to the resistance value of the first variable resistor 151. Output
signal 17 is a synthesized signal.
As shown in FIG. 2, when the first slider 153 is moved to the positive side, the resistance value of
the first variable resistor 151 with respect to the output signal 16 is the smallest, and the first
variable resistor 151 with respect to the output signal 17. The resistance value of is the largest.
Therefore, the combined signal 161 applied from the first slider 153 to the diaphragm 111 is a
signal having the largest proportion of signal components in phase with the output signal 16 of
the first condenser microphone unit 11. As a result, the output level from the fixed pole 112 of
the first condenser microphone unit 11 is increased.
[0034]
The combined signal 171 applied to the fixed pole 122 via the second slider 154 is the output
signal 17 of the second condenser microphone unit 12 and the first condenser microphone unit
11 which are lowered according to the resistance value of the second variable resistor 152.
Output signal 16 is a synthesized signal. As shown in FIG. 3, when the second slider 154 is
moved to the positive side, the resistance value of the second variable resistor 152 with respect
to the output signal 16 is at a maximum, and the second variable resistor 152 with respect to the
output signal 17. The resistance value of is minimal. Therefore, the combined signal 171 applied
from the second slider 154 to the fixed pole 122 is a signal having the largest proportion of
signal components in phase with the output signal 17 of the second condenser microphone unit
12. As a result, the output level from the diaphragm 121 of the second condenser microphone
unit 12 is increased.
18-04-2019
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[0035]
As described above, when the first slider 153 is moved to the positive side so that the resistance
value of the first variable resistor 151 with respect to the output signal of the first capacitor
microphone unit 11 decreases, the second slider 154 is also positive. Move to the side. As a
result, the resistance value of the first variable resistor 151 with respect to the output signal of
the second capacitor microphone unit 12 is increased, and the resistance value of the second
variable resistor 152 with respect to the output signal of the first capacitor microphone unit 11
is increased. The resistance value of the second variable resistor 152 with respect to the output
signal of the microphone unit 12 decreases. That is, by changing the resistance value of the two
variable resistors 15, the levels of the input signal to the first impedance converter 13 and the
input signal to the second impedance converter 14 can be continuously increased. .
[0036]
FIG. 7 shows an example of the frequency response characteristic of the condenser microphone
10 when the output signals of the first condenser microphone unit 11 and the second condenser
microphone unit 12 are increased. The figure shows that the output level is increased by about 6
dB as compared to the frequency response characteristic (FIG. 6) when the first slider 153 and
the second slider 154 are at the intermediate position.
[0037]
FIGS. 4 and 5 show examples of the condenser microphone 10 when the first slider 153 and the
second slider 154 are respectively moved to the negative side. As shown in FIG. 4, when the first
slider 153 is moved to the negative side, the resistance value of the first variable resistor 151
with respect to the output signal 16 is the largest, and the first variable resistor 151 with respect
to the output signal 17. The resistance value of is minimal. Therefore, the combined signal 162
applied from the first slider 153 to the diaphragm 111 is a signal in which a signal in reverse
phase to the output signal 16 of the first condenser microphone unit 11 is combined at the
maximum ratio. As a result, the output level from the fixed pole 112 of the first condenser
microphone unit 11 decreases.
[0038]
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11
Further, as shown in FIG. 5, when the second slider 154 is moved to the minus side, the
resistance value of the second variable resistor 152 with respect to the output signal 16 is
minimum, and the second variable with respect to the output signal 17 is The resistance value of
the resistor 152 is maximum. Therefore, the combined signal 172 applied from the second slider
154 to the fixed pole 122 is a signal in which the signal in reverse phase to the output signal 17
of the second condenser microphone unit 12 is combined at the maximum ratio. As a result, the
output level from the diaphragm 121 of the second condenser microphone unit 12 decreases.
[0039]
As described above, when the first slider 153 is moved to the minus side so that the resistance
value of the first variable resistor 151 with respect to the output signal of the first capacitor
microphone unit 11 is increased, the second slider 154 is also minus. Move to the side. As a
result, the resistance value of the first variable resistor 151 with respect to the output signal of
the second capacitor microphone unit 12 decreases, and the resistance value of the second
variable resistor 152 with respect to the output signal of the first capacitor microphone unit 11
is small. The resistance value of the second variable resistor 152 with respect to the output
signal of the unit 12 is increased. That is, by changing the resistance values of the two variable
resistors 15, the levels of the input signal to the first impedance converter 13 and the input
signal to the second impedance converter 14 can be continuously reduced. .
[0040]
FIG. 8 shows an example of the frequency response characteristic of the condenser microphone
10 when the output signals of the first condenser microphone unit 11 and the second condenser
microphone unit 12 are reduced. The figure shows that the output level is reduced by about 6 dB
as compared to the frequency response characteristic (FIG. 6) when the first slider 153 and the
second slider 154 are at the intermediate position.
[0041]
As described above, when the level of the sound wave input to the condenser microphone 10 is
small, the impedance can be obtained by moving both the first slider 153 and the second slider
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12
154 of the variable resistor 15 to the positive side. The level of the input signal to the converter
increases. As a result, the level of the balanced output signal output from the HOT terminal and
the COLD terminal increases, and the noise level inherent to the impedance converter does not
change even if the input signal level to the impedance converter increases. Suitable output levels
can be obtained without degrading the noise ratio.
[0042]
Further, the variable resistor 15 can provide the same effect as that of the conventional PAD. The
input level to the first impedance converter 13 and the second impedance converter 14 is
reduced by the variable resistor 15 to prevent distortion of the balanced output signal output
from the HOT terminal and the COLD terminal, and to obtain a suitable output signal. Can.
[0043]
According to the condenser microphone 10 according to the present embodiment, the input level
of the signal to the first impedance converter 13 and the second impedance converter 14 is
continuously changed between -6 dB and +6 dB by the variable resistor 15 be able to. As a result,
it is possible to obtain a condenser microphone that can attenuate the signal level for excessive
input and amplify the signal level for under-input and that does not change the signal-to-noise
ratio.
[0044]
10 capacitor microphone 11 first capacitor microphone unit 12 second capacitor microphone
unit 13 first impedance converter 14 second impedance converter 15 variable resistor 151 first
variable resistor 152 second variable resistor 153 first slider 154 second Slider
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