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DESCRIPTION JP2016086283

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DESCRIPTION JP2016086283
Abstract: A variable directional electret condenser microphone that does not change the
characteristics of the microphone including sensitivity even when directivity is switched. A
unidirectional first microphone unit Uf and a second microphone unit Ub are disposed back to
back. In the first microphone unit, the electret dielectric film 16f is formed on the diaphragm 12f,
and in the second microphone unit, the electret dielectric film 16b is formed on the fixed
electrode 14b, and the first and second microphone units are formed. Each fixed pole 14f, 14b of
the microphone unit is connected to the reference potential point of the circuit by DC. When
nondirectionality is selected, respective signals of the diaphragm electrode of the first
microphone unit Uf and the diaphragm electrode of the second microphone unit Ub are
balancedly output. When unidirectionality is selected, only the signal of the diaphragm electrode
of the first microphone unit Uf is balanced. [Selected figure] Figure 2
Variable directivity electret condenser microphone
[0001]
The present invention relates to a variable directional condenser microphone in which two
unidirectional microphone units are disposed back to back, and more particularly, to a variable
directional electret condenser microphone in which characteristics such as sensitivity and S / N
do not change when directivity is switched. .
[0002]
A microphone in which two condenser microphone units are arranged back to back is known as a
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microphone whose directivity can be varied.
In one example, the two microphone units each have uni-directionality (cardioid characteristics).
The respective diaphragm electrodes of the first microphone unit having a directional axis on the
front side and the second microphone unit having a directional axis on the rear side are
connected in parallel in an alternating manner by a coupling capacitor.
[0003]
The conventional microphone realizes variable directivity by varying the polarity and voltage
value of the polarization voltage applied to the diaphragm or fixed pole of the second
microphone unit. This is disclosed in, for example, FIG. 4 of Patent Document 1. In this case, the
directivity of the microphone can be varied stepwise or continuously from omnidirectional to
bidirectional, and unidirectionality can be obtained between omnidirectional and bidirectional.
[0004]
When the variable directional condenser microphone of this configuration is used as a single
directivity, the audio signal from the diaphragm electrode of the second microphone unit is not
used or output. However, since the diaphragm electrodes of the first and second microphone
units are connected in parallel in an alternating manner, the sound signal generated on the first
microphone unit side is attenuated by the capacitance on the second microphone unit side.
Become. Therefore, when the capacitances of the first and second microphone units are almost
the same, the audio signal level output from the microphone will be attenuated by 6 dB, and the S
/ N will be degraded accordingly. Become.
[0005]
For example, a means for doubling the polarization voltage by a DC / DC converter may be
considered to compensate for the above-mentioned 6 dB attenuation, but when the value of the
polarization voltage is increased, the withstand voltage problem of the element And other
problems such as increased current consumption. In this case, when the electret is used without
using a polarization voltage source, the DC / DC converter can be made unnecessary. However,
the attenuation of the audio signal due to the parallel connection of the front and rear diaphragm
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electrodes in an AC manner is left as a problem as well.
[0006]
On the other hand, Patent Document 2 discloses a variable directional condenser microphone in
which two condenser microphone units are arranged back to back and back-to-back, the output
of each microphone unit is coupled by a variable capacitance condenser (varicon), and directivity
is changed continuously. It is done.
[0007]
According to this variable directional condenser microphone, the fixed pole of the first
microphone unit and the fixed pole of the second microphone unit are disposed in close
proximity to each other.
Moreover, the fixed pole of the first microphone unit is connected to one pole of the varicon, and
the fixed pole of the second microphone unit is connected to the other pole of the varicon. Then,
by sequentially changing the capacitance of the variable capacitor, the output level and the
polarity from the second microphone unit side change, and as a result, the directivity changes
continuously.
[0008]
According to the variable directional condenser microphone disclosed in Patent Document 2
described above, since each fixed pole of the first and second microphone units is connected to
any pole of the varicon, any fixed pole is also included in the circuit. The state of floating from
the reference potential point (ground), in other words, the potentials of the respective fixed poles
are made unstable. For this reason, due to the capacitance between the fixed poles of the first
and second microphone units (the stray capacitance between the fixed poles), a phenomenon
occurs in which the audio signal leaks and is always mixed. Therefore, the variable directional
microphone of Patent Document 2 has a problem that the directivity can not be normally
switched.
[0009]
Japanese Patent Application Laid-Open No. 54-133320 Patent No. 4828375
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[0010]
The present invention has been made to solve the above-described problems of the conventional
variable directional condenser microphone, and even if the directivity is switched, no change in
sensitivity and S / N occurs, and each fixing of the microphone unit is performed. It is an object
of the present invention to provide a variable directional electret condenser microphone which is
not affected by the capacitance (stray capacitance) between the poles.
[0011]
The variable directivity electret condenser microphone according to the present invention, which
has been made to solve the above-mentioned problems, has a unidirectional directivity first
microphone unit and a second microphone unit in which a diaphragm and a fixed pole are
disposed to face each other. Are arranged back to back so that the respective sound collecting
axes are directed back and forth with each other, wherein the first microphone unit is formed by
depositing an electret dielectric film on a diaphragm. In the second microphone unit, an electret
dielectric film is formed on a fixed pole, and each fixed pole of the first and second microphone
units is DC connected to a reference potential point of the circuit. It is characterized by
[0012]
In this case, a directivity selection switch is preferably provided to select one of the first
directivity mode and the second directivity mode, and when the first directivity mode is selected,
the diaphragm of the first microphone unit The respective signals from the electrode and the
diaphragm electrode of the second microphone unit are balancedly output, and when the second
directivity mode is selected by the directivity selection switch, the signals from the diaphragm
electrode of the first microphone unit are output. A configuration is adopted in which the signal
and the signal at the reference potential point of the circuit are balanced and output.
[0013]
More preferably, the signal from the diaphragm electrode of the first microphone unit is
converted into one balanced output signal via a first impedance converter and a first buffer
circuit connected to the first impedance converter. And a signal from the diaphragm electrode of
the second microphone unit selected by the directivity selection switch, or a signal at a reference
potential point of the circuit via a DC cut capacitor, a second impedance converter, and the
second impedance converter. A configuration is adopted in which the other balanced output
signal is provided via a second buffer circuit connected to the impedance converter.
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[0014]
In addition, a subtraction circuit for subtracting the balanced output signal is provided, and a
configuration for obtaining an audio signal by the subtraction circuit is employed.
[0015]
According to the electret condenser microphone of the above-described configuration according
to the present invention, the first microphone unit adopts the film electret system, and the
second microphone unit adopts the back electret system.
Thereby, the signals obtained from the respective diaphragm electrodes of the first and second
microphone units can be obtained in the relation of mutually opposite phase.
Therefore, by using the signals obtained from the respective diaphragm electrodes of the first
and second microphone units as balanced output signals, it is possible to obtain audio signals
with nondirectionality.
Further, by using the signal obtained from the diaphragm electrode of the first microphone unit
and the non-signal at the reference potential point as the balanced output signal, it is possible to
obtain an audio signal with single directivity.
[0016]
In this case, when directivity is switched, as shown in Patent Document 1, one microphone unit
becomes a load of a signal obtained from the diaphragm electrode of the other microphone unit,
and an element that attenuates an audio signal is It does not occur.
Therefore, it is possible to provide a variable directional condenser microphone that does not
generate changes in sensitivity as well as S / N.
[0017]
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Furthermore, a configuration is adopted in which each fixed pole of the first and second
microphone units is DC connected to the reference potential point of the circuit.
Therefore, as shown in Patent Document 2, it is possible to provide a variable directional
condenser microphone which is not affected by the electrostatic capacitance (stray capacitance)
between the fixed poles.
[0018]
It is a sectional view of a variable directivity electret condenser microphone concerning the
present invention.
It is an example of a circuit connection of the condenser microphone shown in FIG.
[0019]
A variable directivity electret condenser microphone according to the present invention will be
described based on an embodiment shown in the drawings. FIG. 1 is a cross-sectional view
showing an overall configuration in which two electret condenser microphone units are
combined back to back. The entire configuration shown in FIG. 1 is referred to as a composite
unit 1 for the convenience of description. Then, the unidirectional single microphone unit
disposed on the sound collecting axis side indicated by the arrow 0 deg in the composite unit 1 is
referred to as a front unit Uf, and the unidirectional single microphone unit disposed on the
opposite side Is called a rear unit Ub.
[0020]
In the composite unit 1, an insulating seat 2 formed in an annular shape is disposed at the
central portion thereof. Retaining rings 3 f and 3 b are fitted to and attached to the front and rear
of the insulating seat 2. The front unit Uf is mounted between the insulating seat 2 and the front
pressing ring 3f, and the rear unit Ub is mounted between the insulating seat 2 and the rear
pressing ring 3b. The composite unit 1 is configured to be mounted.
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[0021]
A diaphragm 12f held by a diaphragm holding ring 11f is disposed in the front unit Uf. The fixed
pole 14f is disposed on the back of the diaphragm 12f via a ring-shaped spacer 13f. At this time,
the peripheral edge of the fixed pole 14 f is in contact with the insulating seat 2. A diaphragm
electrode (not shown) is formed on the front surface of the diaphragm 12f. A part of the
diaphragm electrode is electrically connected to the diaphragm electrode terminal 15f
superimposed on the diaphragm holding ring 11f via the conductive diaphragm holding ring 11f.
[0022]
An electret dielectric film 16f is attached to the surface of the diaphragm 12f of the front unit Uf
that faces the fixed electrode 14f. That is, the front unit Uf in this embodiment constitutes a film
electret uni-directional condenser microphone unit.
[0023]
The rear unit Ub is substantially the same as the configuration of the front unit Uf described
above. The diaphragm 12b held by the diaphragm holding ring 11b is disposed in the rear unit
Ub. A fixed pole 14b is disposed on the back of the diaphragm 12b via a ring-shaped spacer 13b.
At this time, the peripheral edge of the fixed pole 14 b is in contact with the insulating seat 2. A
diaphragm electrode (not shown) is formed on the front surface of the diaphragm 12b. A part of
the diaphragm electrode is electrically connected to the diaphragm electrode terminal 15b
superimposed on the diaphragm holding ring 11b via the conductive diaphragm holding ring
11b.
[0024]
An electret dielectric film 16b is attached to the surface of the fixed electrode 14b of the rear
unit Ub facing the diaphragm 12b. That is, the rear unit Ub in this embodiment constitutes a back
electret uni-directional condenser microphone unit.
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[0025]
In the vicinity of the central portion of the insulating seat 2 described above, the damper 4
functioning as an acoustic resistance is attached to the insulating seat 2 and disposed. Back air
chambers 5f and 5b are respectively formed between the fixed pole 14f of the front unit Uf and
the fixed pole 14b of the rear unit Ub by the damper 4.
[0026]
FIG. 2 shows an example of circuit connection that constitutes a variable directivity electret
condenser microphone using the composite unit 1 shown in FIG. 1 described above. In FIG. 2, the
main members of the composite unit 1 shown in FIG. 1 are denoted by the same reference
numerals, and thus the detailed description thereof is omitted.
[0027]
M1 in FIG. 2 shows a circuit configuration on the electret condenser microphone side including
the composite unit 1 described above. A mixer M2 is connected to the electret condenser
microphone M1 via a balanced shield cable Ca. The circuit is configured to obtain an audio signal
from the electret condenser microphone M1 on the mixer M2 side.
[0028]
As shown in FIG. 2, the fixed poles 14f and 14b of the composite unit 1 described above are
connected in common, and are DC connected to the reference potential point (ground) of the
circuit. The diaphragm electrode terminal 15f of the front unit Uf in the composite unit 1
described above is connected to the impedance converter F1. The first impedance converter F1 is
mounted with an FET (field effect transistor), and is configured of, for example, a source follower
circuit.
[0029]
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An output signal from the first impedance converter F1 is supplied to a first buffer circuit E1. The
first buffer circuit E1 is configured by an emitter follower circuit using, for example, a bipolar
transistor, and an output signal from the first buffer circuit E1 is output as a hot-side output
signal to the terminal pin P2 of the electret condenser microphone M1. Be done.
[0030]
On the other hand, the diaphragm electrode terminal 15b of the rear unit Ub in the composite
unit 1 is connected to one of the selected terminals of the directivity selection switch SW.
Further, the other selected terminal of the directivity selection switch SW is connected to the
reference potential point (ground) of the circuit through the DC cut capacitor C1. The state of the
directivity selection switch SW shown in FIG. 2 shows a state (first directivity mode) in which the
diaphragm electrode of the rear unit Ub is selected. The selection terminal (common terminal) of
the directivity selection switch SW is connected to the second impedance converter F2.
[0031]
The second impedance converter F2 has the same circuit configuration as the first impedance
converter F1 described above. An output signal from the second impedance converter F2 is
supplied to a second buffer circuit E2. The second buffer circuit E2 also has the same circuit
configuration as the first buffer circuit E1 described above. The output signal of the second
buffer circuit E2 is output as a cold-side output signal to the terminal pin P3 of the electret
condenser microphone M1.
[0032]
Each of the output signals provided to the terminal pins P2 and P3 is a balanced output to the
mixer M2 described above via the balanced shield cable Ca with the terminal pin P1 as a ground
line as an audio signal from the composite unit 1 Be done.
[0033]
A mixer M2 receiving a balanced output signal via a balanced shield cable Ca is mounted with a
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subtraction circuit OP1 by an operational amplifier.
The hot side signal passing through the terminal pin P2 is supplied to the non-inverting input
terminal of the subtracting circuit OP1, and the cold side signal passing through the terminal pin
P3 is supplied to the inverting input terminal of the subtracting circuit OP1. Then, the
subtraction output by the subtraction circuit OP1 is provided to the output terminal Out as an
audio signal by the electret condenser microphone M1.
[0034]
In the composite unit 1 shown in FIG. 1, the front unit Uf adopts a film electret system, and the
rear unit Ub adopts a back electret system. Therefore, when the directivity selection switch SW is
in the first directivity mode shown in FIG. 2, signals of opposite phase are provided to the
terminal pins P2 and P3. Therefore, the output terminal Out of the mixer M2 is provided with a
nondirectional audio signal as its subtraction output.
[0035]
When the directivity selection switch SW is switched from the state shown in FIG. 2 to select the
second directivity mode, the reference potential point (ground) of the circuit via the DC cut
capacitor C1 shown in FIG. 2 is selected. It will be done. In this embodiment, the terminal pin P3
is in a non-signal state. Then, an audio signal from the diaphragm electrode of the front unit Uf is
supplied to the terminal pin P2. Therefore, the audio signal from the front unit Uf is provided as
it is to the output terminal Out of the mixer M2 as its subtraction output. As a result, the
directivity in the second directivity mode exhibits single directivity.
[0036]
As described above, the variable directivity electret condenser microphone according to the
above-described embodiment is switched to nondirectionality and unidirectionality by the
directivity selection switch SW. And when directivity is switched, elements, such as a capacitor |
condenser, which become a load of the audio | voice output from the front side unit Uf or the
back side unit Ub do not arise. Therefore, it is possible to provide a variable directional
condenser microphone in which the sensitivity and the S / N do not change with the switching of
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the directivity.
[0037]
Furthermore, a configuration is adopted in which each fixed pole of the front unit Uf and the rear
unit Ub is DC-connected to the reference potential point of the circuit. Therefore, it is possible to
provide a variable directional condenser microphone which is not affected by the electrostatic
capacitance (stray capacitance) between the fixed poles, and to obtain the operation and effect as
described in the above-mentioned column of the effects of the invention. Can.
[0038]
1 composite unit 2 insulating seat 3f, 3b holding ring 12f, 12b diaphragm 14f, 14b fixed pole
15f, 15b diaphragm electrode terminal 16f, 16b electret dielectric film C1 DC cut capacitor Ca
balanced shield cable E1, E2 buffer circuit F1, F2 impedance converter M1 electret condenser
microphone M2 mixer OP1 subtraction circuit P1 terminal pin (ground line) P2 terminal pin (hot
side output) P3 terminal pin (cold side output) SW directivity selection switch Uf first
microphone unit (front side unit) Ub 2nd microphone unit (rear unit)
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