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JP2008103818

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DESCRIPTION JP2008103818
In a condenser microphone in which an opening for switch operation is formed in a microphone
case, a shield of the opening is assured to prevent noise generation due to an external
electromagnetic wave. A microphone unit is mounted on one end, and the other end includes a
cylindrical microphone case made of a metal material having an output connector, and the
microphone case is characterized by switching predetermined characteristics of the microphone
unit. A condenser microphone is housed in which the circuit board 11 on which the changeover
switches 13 and 14 are mounted is accommodated, and openings 15 and 16 for switch operation
are formed in the microphone case 10 corresponding to the switches 13 and 14. The switch
knobs 13a and 14a are provided with an electric shield means preferably made of a conductive
cloth 17 for closing the openings 15 and 16 from the inside of the microphone case 10. [Selected
figure] Figure 1
コンデンサマイクロホン
[0001]
The present invention relates to a condenser microphone having a characteristic changeover
switch for switching the characteristic of a microphone unit, and more particularly to a technique
for preventing electromagnetic wave noise caused by an opening for switch operation.
[0002]
The condenser microphone has an acousto-electric converter in which a diaphragm and a fixed
pole are disposed opposite to each other via a spacer and which constitutes a kind of capacitor.
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1
This kind of acousto-electric converter has a high impedance. Because of this, an audio signal is
obtained via an impedance converter.
In many cases, FETs (field effect transistors) are used as impedance converters.
[0003]
In addition, some models of condenser microphones have the characteristics of microphone units
such as a sound pressure level switching switch for switching the maximum allowable input
sound pressure level, and a low cut switch for reducing noise due to wind or external vibration. A
characteristic changeover switch to switch is provided.
[0004]
An example of a condenser microphone provided with this kind of characteristic changeover
switch will be described with reference to FIGS.
3 (a) is a front view of the condenser microphone, FIG. 3 (b) is a sectional view taken along the
line A-A of FIG. 3 (a), FIG. 4 is an enlarged sectional view taken along the line B-B of FIG. 3 (a),
FIG. It is an equivalent circuit diagram showing a pressure level change switch.
[0005]
As shown in FIGS. 3A and 3B, the condenser microphone basically has a cylindrical microphone
case 10 made of a metal material such as a brass alloy and a microphone mounted on one end
side of the microphone case 10 A unit 20 and an output connector 30 mounted on the other end
side of the microphone case 10 are provided.
[0006]
In the microphone unit 20, an acoustoelectric converter 21 having an extraction electrode 22 for
an audio signal is accommodated.
The acoustoelectric converter 21 is a converter in which a diaphragm 211 and a fixed electrode
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2
213 stretched on a diaphragm ring 212 are disposed opposite to each other via a spacer ring
214 as shown in FIG. Are drawn from the fixed pole 213.
[0007]
For the output connector 30, a connector defined in EIAJ RC-5236 "Latch lock type round
connector for audio equipment" is generally used. This output connector 30 has a ground
terminal pin 31, a hot side terminal pin for signal. 32 and 3 pins of the cold side terminal pin 33
of the signal.
[0008]
In addition, since the hot side terminal pin 32 and the cold side terminal pin 33 overlap for
convenience of drawing, only one of them is shown.
The output connector 30 is connected to a phantom power supply (not shown).
[0009]
A circuit board 11 is accommodated in the microphone case 10, and the microphone unit 20 and
the output connector 30 are connected to the circuit board 11. On the circuit board 11, the FET
12 shown in FIG. 5 as an impedance converter and a power supply circuit for the microphone
unit 20 are mounted. From this, the microphone case 10 may be called a power module unit.
[0010]
In this case, the circuit board 11 serves as a characteristic switching switch for switching the
characteristics of the microphone unit 20, a sound pressure level switching switch 13 for
switching the maximum allowable input sound pressure level, and noise due to wind or external
vibration. Low-cut switch 14 is mounted.
[0011]
Among these, the sound pressure level changeover switch 13 will be described. As shown in FIG.
5, the fixed electrode 213 (extraction electrode 22) of the microphone unit 20 is connected to
the gate G of the FET 12. And the sound pressure level changeover switch 13 is connected in
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parallel with an attenuator 17 made of a capacitor.
[0012]
The attenuator 17 is also referred to as a PAD (pad). For example, when the microphone is
brought close to a musical instrument and collected, the attenuator 17 can be fixed to the
diaphragm 211 and the fixed pole by turning on the sound pressure level switch 13. And 213 are
connected in parallel to the capacitor.
The low cut switch 14 switches a filter circuit (not shown) and the like.
[0013]
As shown in FIG. 4, the microphone case 10 is formed with openings 15 and 16 for operating the
sound pressure level switching switch 13 and the low cut switch 14.
In order to prevent this kind of characteristic changeover switch 13 and 14 from being used
frequently and to prevent an erroneous operation while using a microphone, the switch knobs 13
a and 14 a are retracted from the openings 15 and 16. , And is operated with the tip of a ball pen
or the like (not shown) only when it is necessary to switch the characteristics.
[0014]
In addition, although a slide switch or a toggle switch is usually used for the said characteristic
change switches 13 and 14, in the case of a directivity change switch, a rotary switch may be
used rare.
[0015]
However, since the shields of the switch openings 15 and 16 are incomplete, a high frequency
current due to an external electromagnetic wave or the like may easily enter the microphone
case 10, and the high frequency current may be detected by the FET 12 to generate noise.
[0016]
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4
Since the switch knob of the slide switch is usually made of synthetic resin, the electromagnetic
waves entering from the openings 15 and 16 of the switch are easily taken into the audio output
circuit through the switch.
[0017]
In addition, with the toggle switch, there are also switch knobs that are made of metal and can be
connected to the shield of the circuit board 11, etc. However, if wiring is made to have
impedance at high frequency for that connection, high frequency current will be taken into the
microphone. Will be
[0018]
In recent years, mobile phones have become widespread rapidly, but from electromagnetic
phones (for example, within a range of several centimeters to several tens of centimeters, tens of
thousands times the electric field intensity generated in the market by commercial radio waves)
The generation of noise when the portable telephone is used near the microphone is a serious
problem because the electric field strength to reach is generated.
[0019]
In particular, since the sound pressure level switching switch 13 is connected to the gate G of the
FET 12 as shown in FIG. 5, it is larger when the high frequency current by the electromagnetic
wave entering from the opening 15 of the switch flows to the gate G of the FET 12 Generate
noise.
[0020]
As another problem, when there is a rattling between the switch knob and the switch body due to
an assembly error of the switch, mechanical noise of "Katakata" may be generated when the
microphone is vibrated.
[0021]
Therefore, an object of the present invention is to provide a capacitor microphone in which an
opening for switch operation is formed in the microphone case, and the shield of the opening is
assured to prevent noise generation due to external electromagnetic waves, and a switch The
purpose is to prevent the generation of mechanical noise due to rattling of the knob.
[0022]
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5
In order to solve the above problems, the invention according to claim 1 includes a cylindrical
microphone case made of a metal material having a microphone unit mounted on one end side
and an output connector on the other end side, the above microphone case A circuit board on
which a characteristic changeover switch which is electrically connected to the microphone unit
and the output connector and which switches a predetermined characteristic of the microphone
unit is mounted is housed therein, and the characteristic of the microphone case is
accommodated. In a condenser microphone in which an opening for switch operation is bored in
a part facing the changeover switch, and the switch knob of the characteristic changeover switch
is operated through the opening, the switch knob has the above-mentioned from the inside of the
microphone case Electrical shielding means are provided to close the opening. It is characterized
in that there.
[0023]
According to a second aspect of the present invention, in the condenser microphone of the first
aspect, a conductive cloth having both elasticity and conductivity is used as the shielding means,
and an end of the conductive cloth contacts the inner surface of the microphone case. It is
characterized by
[0024]
The invention as set forth in claim 3 is characterized in that, in the condenser microphone
according to claim 1 or 2, the characteristic changeover switch is a sound pressure level
changeover switch for switching the maximum allowable input sound pressure level to the
microphone unit.
[0025]
According to the first aspect of the present invention, the switch knob is provided with the
electric shield means for closing the opening of the switch from the inside of the microphone
case, whereby the extraneous electromagnetic waves enter the microphone case through the
switch opening. Is prevented, noise generation due to extraneous electromagnetic waves is
prevented.
[0026]
According to the second aspect of the present invention, the conductive cloth having both
elasticity and conductivity is used as the shield means, and the end of the conductive cloth is
brought into contact with the inner surface of the microphone case. In addition, the generation of
mechanical noise due to rattling of the switch knob can also be prevented.
01-05-2019
6
[0027]
According to the third aspect of the invention, the electric shield means of the first aspect or the
conductive cloth of the second aspect is applied to a sound pressure level switching switch for
switching the maximum allowable input sound pressure level to the microphone unit. Directly
prevents high frequency current from flowing into the gate of the FET as an impedance converter
due to extraneous electromagnetic waves, so that even if the portable telephone is used in the
vicinity, noise generation due to it is effectively suppressed. Can.
[0028]
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 an enlarged cross-sectional view similar to FIG. 4 showing the main part of the present
invention, and FIG. 2 is a schematic plan view showing the opening of the switch.
For the entire configuration of the condenser microphone, refer to FIGS. 3A and 3B of the prior
art described above, and for the sound pressure level switching switch, refer to FIG. 5 of the prior
art described above. .
[0029]
As shown in FIG. 1, the condenser microphone of the present invention also includes a cylindrical
microphone case 10 made of a metal material such as brass alloy, and a circuit board 11 is
accommodated in the microphone case 10.
[0030]
The microphone unit 20 is mounted on one end side (tip end side) of the microphone case 10
and the other end side (rear end side) of the microphone case 10 as in FIGS. 3 (a) and 3 (b) of the
conventional example described above. , And the circuit board 11 is connected to the lead
electrode 22 of the microphone unit 20 and the output connector 30.
[0031]
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The circuit board 11 is provided with an audio output circuit including an FET 12 (see FIG. 5) as
an impedance converter and a power supply circuit for the microphone unit 20. Also in this
example, the circuit board 11 also includes a microphone A sound pressure level switching
switch 13 for switching the maximum allowable input sound pressure level and a low cut switch
14 for reducing noise due to wind or external vibration are mounted as characteristic switching
switches for switching the characteristics of the unit 20. .
See FIG. 5 for the sound pressure level changeover switch 13.
[0032]
In the microphone case 10, openings 15 and 16 for operating the sound pressure level switching
switch 13 and the low cut switch 14 are formed.
As in the prior art described above, the switch knobs 13a and 14a have openings that are not
frequently used in this kind of characteristic changeover switches 13 and 14 and to prevent an
erroneous operation while using a microphone. It is disposed at a position retracted from the
parts 15 and 16 and operated with the tip of a ball pen or the like (not shown) only when the
characteristic switching is required.
[0033]
In this example, since both the sound pressure level changeover switch 13 and the low cut switch
14 are slide switches, their openings 15, 16 are long holes having a length commensurate with
the movement strokes of the switch knobs 13a, 14a. Is formed.
[0034]
In the present invention, an electrical shield means is provided for closing the openings 15 and
16 of the switch from the inside of the microphone case 10.
[0035]
The shield means may be a metal plate attached to the switch knobs 13a and 14a and connected
to the ground of the circuit board 11 or the microphone case 10 via a predetermined wiring, but
a conductive cloth having both elasticity and conductivity. Is preferred.
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[0036]
A conductive sponge of this type can be exemplified by a trade name "Soft Shield 4000 Series"
manufactured by Solar Wire Mesh Co., Ltd., in which a soft sponge is used as a base material and
a reinforced aluminum foil is coated on the surface thereof.
[0037]
1 shows a state in which the conductive cloth 17 is attached to each of the switch knobs 13a and
14a, but in this example, since the switches 13 and 14 are slide switches, as shown by the chain
line in FIG. The conductive cloth 17 is cut into a strip which can close the switch openings 15
and 16 regardless of whether the switch knobs 13a and 14a are in the on position and the off
position, and a hole is opened in the substantially central portion thereof. Preferably, the switch
knobs 13a and 14a are attached.
[0038]
Further, as shown in FIG. 1, the width of the conductive cloth 17 is such that one end thereof can
elastically contact the inner surface of the microphone case 10 which also functions as a shield
case.
[0039]
As described above, even if a mobile phone that generates strong electromagnetic waves in the
vicinity of a microphone is used by closing the switch openings 15 and 16 with the conductive
cloth 17 attached to the switch knobs 13a and 14a The electromagnetic wave flows from the
conductive cloth 17 on the surface of the microphone case 10 and is dropped to a grounding
wire such as a microphone cord (not shown) connected to the output connector 30 and does not
enter the microphone case 10, so noise generation by the electromagnetic wave is effective. Can
be prevented.
[0040]
Since the sound pressure level switching switch 13 is connected to the gate G of the FET 12 as
shown in FIG. 5 above, attaching the conductive cloth 17 to the sound pressure level switching
switch 13 provides a greater effect. .
[0041]
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Further, since the conductive cloth 17 is resiliently arranged between the switch knobs 13a and
14a and the inner surface of the microphone case 10, rattling of the switch knobs 13a and 14a
can be prevented.
When each of the switches 13 and 14 is a toggle switch, the conductive cloth 17 may be a strip
slightly larger than the switch opening.
[0042]
The expanded sectional view similar to FIG. 4 which shows the principal part of this invention.
The typical top view which shows the opening part of a switch by embodiment of this invention.
(A) Front view showing a conventional condenser microphone, (b) A sectional view taken along
the line A-A.
BB line expanded sectional view of Fig.3 (a).
Equivalent circuit diagram showing a sound pressure level changeover switch
Explanation of sign
[0043]
DESCRIPTION OF SYMBOLS 10 Microphone case 11 Circuit board 12 FET (impedance converter)
13 Sound pressure level switching switch 14 Low cut switch 13a, 14a Switch knob 15, 16
Opening 17 Conductive cloth 20 Microphone unit 21 A / S converter 30 Output connector
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