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DESCRIPTION JP2009065433

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DESCRIPTION JP2009065433
To operate as a secondary sound pressure gradient type giving priority to noise resistance when
there is noise in the surroundings, and to operate as a primary sound pressure gradient type
giving priority to sound quality when there is no noise in the surroundings. SOLUTION: One of
the two primary sound pressure gradient microphones is included, one of which is a film electret
main microphone unit 10 and the other is a back electret sub microphone unit 20. In a
microphone device operating as a secondary sound pressure gradient type in which a signal
output and a negative phase signal output of the sub microphone unit 20 are subtracted and
taken out through the two-wire microphone cable 3, a third method for detecting ambient noise
The microphone unit 30 is provided, and when the ambient noise is large, the secondary
microphone unit 20 is operated with the main microphone unit 10 as a secondary sound
pressure gradient type, and when the ambient noise is small, the secondary microphone With the
unit 20 inoperative, the main microphone unit 0 only by operating as a primary sound pressure
gradient type. [Selected figure] Figure 1
Microphone device
[0001]
The present invention relates to a microphone device, and more particularly to a microphone
device having excellent noise resistance suitable as a close-talking microphone.
[0002]
As described in Patent Document 1, the close-talking microphone utilizes the proximity action of
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a spherical wave and is low in sensitivity to a sound wave coming from a distance, but an
appropriate output to a near sound source. It is designed to get the level.
Directivity is included in the narrow directivity class, and is used, for example, as a headset
microphone for the purpose of clearly picking up the voice of the speaker under an environment
where the ambient noise level is high.
[0003]
Normally, an electret condenser microphone unit is used as a close-talking microphone, but in
this case, power supply and signal are transmitted via a two-wire microphone cable (a cable in
which a core wire is covered with a shield wire) The method of taking out is often used. Some
manufacturers refer to this method as plug-in power.
[0004]
In order to narrow the directivity of close-talking microphones, it is known that the outputs of
two primary sound pressure gradient type (for example, single directivity) microphone units may
be subtracted to make a secondary sound pressure gradient type. ing.
[0005]
However, when two electret condenser microphone units are used as the primary sound pressure
gradient type microphone unit, each microphone unit is equipped with an FET (field effect
transistor) as an impedance converter, so that it can be used as a power source The following
problems will occur.
[0006]
For example, when the externally supplied power supply voltage is as low as 1.5 V, the two FETs
can not be operated in series.
In parallel, it is possible to operate two FETs even at a low voltage of about 1.5 V. In this case,
adding the signals of the respective microphone units by connecting the drains of the respective
FETs in an alternating manner Can.
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[0007]
However, when the two microphone units are either of the membrane electret type or the back
electret type, adding the respective signals as described above results in no directivity and a
secondary sound pressure gradient type. It must not be.
[0008]
Therefore, in the invention described in Patent Document 2, a close-talking microphone that
operates as a secondary sound pressure gradient type by two electret condenser microphone
units while using a two-wire microphone cable to supply power and extract a signal. It is possible
to realize a microphone device suitable for
The configuration of this microphone device will be described with reference to FIG.
[0009]
Since this microphone device is a secondary sound pressure gradient type, it comprises first and
second two primary sound pressure gradient type condenser microphone units 10 and 20, each
of which is an impedance converter. FETs (field effect transistors) 11 and 21 are connected to
each other.
[0010]
Although both electret condenser microphone units are used for the condenser microphone units
10 and 20, for example, one condenser microphone unit 10 is a film electret type, whereas the
other condenser microphone unit 20 is a back electret type. .
[0011]
Each condenser microphone unit 10, 20 is connected to an external DC power supply E via a twowire microphone cable 3 having a core wire 3a and a coated shield wire 3b, and a signal via this
two-wire microphone cable 3 Is taken out outside.
[0012]
One pole of each condenser microphone unit 10, 20 is connected to the gates 11g, 21g of the
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FETs 11, 21 respectively, and the other pole is the shield wire 3b of the two-wire microphone
cable 3 together with the sources 11s, 21s of the FETs 11, 21. Is connected to ground via
[0013]
The drains 11d and 21d of the FETs 11 and 21 are connected in parallel to the core wire 3a of
the two-wire microphone cable 3. In this case, the drains 11d and 21d are alternately connected
via coupling capacitors C1 and C2. Connected
[0014]
Further, current is supplied to the drains 11d and 21d of the FETs 11 and 21 from the external
DC power supply E through the load resistance R and the core wire 3a of the two-wire
microphone cable 3, but often the FETs There is a variation in the IDSS (current when the gate
voltage is 0).
[0015]
Therefore, when the drains 11d and 21d of the FETs 11 and 21 are connected in parallel to the
core wire 3a of the two-wire microphone cable 3, in order to balance the DCs of the FETs 11 and
21, variable resistance (Semi-fixed resistance) R1 is connected.
[0016]
Since one condenser microphone unit 10 is a film electret type, the signal output of its drain 11 d
is positive phase.
On the other hand, since the other condenser microphone unit 20 is a back electret type, the
signal output of its drain 21 d is in reverse phase.
[0017]
According to the conventional example according to the invention described in Patent Document
1, the positive phase signal output of the drain 11 d on one capacitor microphone unit 10 side
and the negative phase signal output of the drain 21 d on the other capacitor microphone unit
20 side are added Since the signal is output from the core wire 3a of the two-wire microphone
cable 3 (that is, subtracted), it operates as a secondary sound pressure gradient type.
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[0018]
JP, 2003-9275, A JP, 2005-277489, A
[0019]
However, as described above, the close-talking microphone (noise-resistant microphone)
operating as a secondary sound pressure gradient type has a low frequency response that is
inferior to that of a normal primary sound pressure gradient type microphone, so the sound
quality is not high. not good.
That is, there is a problem that although it is suitable for transmission when there is noise in the
surroundings, a voice with inferior sound quality is output when there is no noise.
[0020]
Therefore, the subject of the present invention operates as a secondary sound pressure gradient
type by giving priority to noise resistance when there is noise in the surroundings, and operates
as a primary sound pressure gradient type by giving priority to sound quality when there is no
noise in the surroundings. And providing a microphone device.
[0021]
In order to solve the above problems, the present invention, as described in claim 1, includes two
primary sound pressure gradient microphone units each having a FET as an impedance
converter, one of the microphone units being a membrane In the electret main microphone unit,
the other microphone unit is a back electret sub microphone unit, and the drains of the FETs are
connected to the core of the two-wire microphone cable, and the sources of the FETs are
Secondary sound pressure connected to the shield line of a wire microphone cable and
subtracted from the positive phase signal output of the main microphone unit and the negative
phase signal output of the secondary microphone unit and taken out through the two-wire
microphone cable In a microphone device operating as a gradient type, ambient noise can A third
microphone unit for outputting, and an output control means of the sub microphone unit for
controlling the negative phase signal output of the sub microphone unit according to the output
level of the noise signal detected by the third microphone unit; It is characterized by being
equipped.
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[0022]
According to a preferred aspect of the present invention, as described in claim 2, the output
control means comprises a variable resistive element connected to a source of the FET of the sub
microphone unit, and an output level of the noise signal. And variable resistance element drive
means for making the resistance value of the variable resistance element variable in response to
the variable resistance element, wherein the variable resistance element drive means sets the
variable resistance element to a low resistance when the output level of the noise signal is high.
When the output level of the noise signal is low, the variable resistive element has high
resistance.
[0023]
Preferably, a visible light conductive element is used as the variable resistive element, and a light
emitting diode is used as the variable resistive element driving means.
[0024]
Preferably, a nondirectional microphone unit is used for the third microphone unit.
[0025]
According to the present invention, in addition to the membrane electret main microphone unit
outputting a positive phase signal and the back electret secondary microphone unit outputting a
negative phase signal, a third microphone detecting ambient noise Unit, which controls the
negative phase signal output of the secondary microphone unit according to the output level of
the noise signal detected by the third microphone unit, and operates as a secondary sound
pressure gradient type when there is noise in the surroundings, By operating as a primary sound
pressure gradient type when there is no noise in the surroundings, noise resistance is obtained
although the sound quality is degraded when operating as a secondary sound pressure gradient
type noise resistant microphone, and a primary sound pressure gradient type Good sound quality
is obtained by the main microphone unit.
[0026]
Next, an embodiment of the present invention will be described with reference to FIGS. 1 and 2,
but the present invention is not limited thereto.
FIG. 1 is a schematic view showing a microphone device according to the present invention, and
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FIG. 2 is an exploded sectional view showing two condenser microphone units included in the
present invention.
In the description of this embodiment, the same reference numerals are used for constituent
elements that are considered identical or identical to the above-described conventional example
described with reference to FIG.
[0027]
As shown in FIG. 1, since this microphone device is basically a secondary sound pressure
gradient type microphone, it comprises two primary sound pressure gradient type condenser
microphone units 10 and 20, each of which has FETs (field effect transistors) 11 and 21 as
impedance converters are connected to one another.
[0028]
Each of the condenser microphone units 10 and 20 is connected to an external DC power supply
E via the two-wire microphone cable 3 described above with reference to FIG. 3, and a signal is
externally output via the two-wire microphone cable 3 Taken out.
In the practice of the present invention, the two-wire microphone cable 3, the external DC power
supply E and its load resistance R can be used as they are without any change.
[0029]
In this embodiment, one condenser microphone unit 10 outputs a film electret type positive
phase signal, and the other condenser microphone unit 20 outputs a back electret type opposite
phase signal. In some cases, one condenser microphone unit 10 may be referred to as a "main
microphone unit", and the other condenser microphone unit 20 may be referred to as a "sub
microphone unit".
[0030]
As shown in FIG. 2A, in the main microphone unit 10, the diaphragm 110 stretched on the
support ring 111 and the fixed electrode 120 are disposed to face each other via the spacer ring
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130.
As shown in FIG. 2B, the sub microphone unit 20 also has the diaphragm 210 tensioned to the
support ring 211 and the fixed pole 220 opposed to each other via the spacer ring 230.
[0031]
As a preferred embodiment, the diaphragms 110 and 210 are made of the same electret material.
As an example of this type of diaphragm, one obtained by vapor-depositing gold on one side of a
film of fluoroethylene polymer (FEP) of 12 μm thickness can be mentioned.
[0032]
Moreover, as a preferred embodiment, electret boards 121 and 221 are provided on the fixed
poles 120 and 220, respectively.
Although the same electret material is used for the electret boards 121 and 221, it is preferable
that all of the diaphragms 110 and 210 and the electret boards 121 and 221 are the same
electret material (for example, FEP).
The fixed electrodes 120 and 220 themselves may be aluminum, copper alloy or the like.
[0033]
Since the main microphone unit 10 is a film electret type, negative charges are charged (charged)
only in the diaphragm 110, and no charge is given to the electret board 121 on the fixed
electrode 120 side.
[0034]
On the other hand, since the sub microphone unit 20 is a back electret type, no charge is given to
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the diaphragm 210, and only the electret board 221 on the fixed pole 220 side is charged with
minus charge.
[0035]
The FET 11 on the main microphone unit 10 side and the FET 21 on the secondary microphone
unit 20 side are connected in parallel to the two-wire microphone cable 3.
That is, the drains 11 d and 21 d of the FETs 11 and 21 are connected in parallel to the core wire
3 a of the two-wire microphone cable 3.
[0036]
Further, one pole (for example, the diaphragm side) of each of the microphone units 10 and 20 is
connected to the gates 11 g and 21 g of the FETs 11 and 21, and the other pole (for example,
fixed electrode side) is the source of the FETs 11 and 21 11s and 21s are connected to the
ground via the shield wire 3b of the two-wire microphone cable 3.
[0037]
When the drains 11d and 21d of the FETs 11 and 21 are connected in parallel to the core wire
3a of the two-wire microphone cable 3, the drains 11d and 21d are AC-connected via coupling
capacitors C1 and C2.
[0038]
Further, current is supplied to the drains 11d and 21d of the FETs 11 and 21 from the external
DC power supply E through the load resistance R and the core wire 3a of the two-wire
microphone cable 3, but often the FETs There is a variation in the IDSS (current when the gate
voltage is 0).
[0039]
Therefore, when the drains 11d and 21d of the FETs 11 and 21 are connected in parallel to the
core wire 3a of the two-wire microphone cable 3, variable resistance ( It is preferable to put in
semi-fixed resistance R1.
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[0040]
In this microphone device, the positive phase signal output from the drain 11 d of the FET 11 on
the main microphone unit 10 side and the negative phase signal output from the drain 21 d of
the FET 21 on the secondary microphone unit 20 side are added (or subtracted). It is output from
the core 3a of the two-wire microphone cable 3 and basically operates as a secondary sound
pressure gradient type, but in order to operate as a primary sound pressure gradient type when
there is no or small ambient noise, It further comprises the configuration described below.
[0041]
That is, in addition to the main microphone unit 10 and the sub microphone unit 20, the third
microphone unit 30 for detecting ambient noise is provided, and a variable resistance is provided
between the source 21s of the FET 21 of the sub microphone unit 20 and the ground line 24.
The element 22 is connected.
[0042]
The sub microphone unit 20 is further provided with a variable resistance element drive unit 23
that changes the resistance value of the variable resistance element 22 according to the output of
the third microphone unit 30.
[0043]
The third microphone unit 30 is preferably an electret microphone unit, and a microphone unit
with nondirectional directivity is preferably used.
[0044]
The output of the third microphone unit 30 is converted to a current by the operational amplifier
31 and amplified to a predetermined level, and then detected and rectified by the detection
circuit 32 consisting of a diode, and a smoothing circuit including a resistor 33 and a capacitor
34 Through the variable resistance element driving means 23 via the
[0045]
Thereby, the resistance value of the variable resistive element 22 is made variable by the variable
resistive element driving means 23 according to the output of the third microphone unit 30. In
this example, the photoelectric effect is used as the variable resistive element 22. The visible light
conductive element 22a whose resistance value is reduced by the incidence of visible light is
used as the semiconductor sensor utilizing the light emitting diode 23a.
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[0046]
The light emitting diode 23a is disposed to be optically coupled to the visible light conductive
element 22a, and a capacitor 34 is connected in series between the ground line 24 of the sub
microphone unit 20 and the ground line 35 of the third microphone unit 30. It is connected
together.
The ground lines 24 and 35 are connected to the shield wire 3 b of the two-wire microphone
cable 3.
[0047]
When the ambient noise is large, a large current proportional to that is supplied to the light
emitting diode 23a from the third microphone unit 30, and the amount of light emission
increases, so that the resistance value of the visible light conductive element 22a decreases.
[0048]
As a result, since the sub microphone unit 20 operates, this microphone device becomes a
secondary sound pressure gradient type noise resistant microphone by the main microphone unit
10 and the sub microphone unit 20.
[0049]
On the other hand, when there is no or small ambient noise, the current supplied to the light
emitting diode 23a from the third microphone unit 30 is small, and the light emitting diode 23a
is substantially turned off.
[0050]
As a result, the visible light conductive element 22a becomes high resistance and the sub
microphone unit 20 does not operate, so this microphone device is a primary sound pressure
gradient type (for example, unidirectional) microphone only with the main microphone unit 10.
Act as.
[0051]
In the above embodiment, by using the same material for the diaphragms 110 and 210 and the
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electrets of the electret boards 121 and 221, the two main microphone units 10 and 20 have the
same directivity but opposite polarity. Although the unit has a frequency response, in the present
invention, the main microphone unit 10 may be a film electret type, and the sub microphone unit
20 may be a back electret type.
[0052]
FIG. 1 is a schematic view of a microphone device according to the invention;
Sectional drawing which decomposes | disassembles and shows two main and sub microphone
units included in this invention.
The schematic diagram which shows the conventional secondary sound pressure gradient type |
mold microphone apparatus.
Explanation of sign
[0053]
10 main microphone unit (membrane electret type) 11 FET 20 sub microphone unit (back
electret type) 21 FET 22 variable resistance element 22a visible light conductive element 23
variable resistance element driving means 23a light emitting diode 30 noise detection
microphone unit 3 two-wire type Microphone cable 3a core wire 3b shield wire E DC current R
load resistance R1 variable resistance C1, C2 coupling capacitor
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