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JPS5726184

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DESCRIPTION JPS5726184
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of an embodiment of an
electret microphone according to the present invention, FIG. 2 is a cross-sectional view of
another embodiment of an electret microphone according to the present invention, and FIG. FIG.
4 is a circuit diagram of an example of the signal processing circuit unit, and FIG. 4 is a diagram
showing frequency characteristics in the case of vibration at a constant acceleration. Explanation
of symbols of main parts, 1 иии и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и vibration pick-up means, 4 и
и и и и и и ceramic piezoelectric Element 5 Weight 7 70 Case 8 Signal processing circuit 10
Characteristic compensation circuit
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electret
microphone. Some microphones, for example, are built-in to be used in a sound recording device
such as a tape recorder etc. =-1 // 7 ░, but sound collecting equipment such as a tape recorder
tends to generate vibrations of a motor or a pulley. Many mechanical parts are built in.
Therefore, in a tape recorder incorporating a microphone, the vibration generated from the
above-described mechanical component is transmitted to the microphone case V and further
incident on the microphone as a masterpiece by air propagation, so noise based on this vibration
is This is undesirable because it interferes with the target sound to be collected together with the
output signal of the microphone. As a countermeasure for this, conventionally, a method has
been adopted in which the microphone is lifted from the tape recorder case by an elastic member
such as rubber to push up the vibration transmitted to the microphone case 11, but in the case of
an electret microphone The effect is not obtained enough because An object of the present
invention is to provide a Li'5M electret microphone that reliably removes noise based on
vibration transmitted to the microphone base with a simple configuration. 2-The electret
microphone according to the present invention incorporates the electret microphone unit for
sound collection and the vibration pickup means for picking up the vibration transmitted to the
housing in the same housing, and constitutes this vibration pickup means It is characterized in
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that the piezoelectric element and the weight attached thereto are accommodated in a case made
of an insulating material fixed to the case (the case is made of an insulating material. Hereinafter,
embodiments of the present invention will be described in detail with reference to the attached
drawings. FIG. 1 is a sectional view of an embodiment of an electret microphone according to the
present invention. In the figure, ? indicates an electret microphone unit for sound collection,
which is housed in a housing 2 made of metal such as aluminum. A front sound conduction
opening 2a and a rear sound conduction opening 2b are formed in the housing 2, and further,
the vibration pickup means 3 for picking up the vibration transmitted by the housing 2V is built
in. There is. The vibration pick-up means 3 is composed of a ceramic 3-tuck piezoelectric element
4 polarized in the thickness direction and one electrode closely contacting the housing 2 and a
wight 5 closely contacting the other electrode of the ceramic piezoelectric element 4. . The
ceramic piezoelectric element 4 and the weight 5 are housed in a cup-shaped case 7 made of an
insulating material such as resin fixed to the housing 2 by a set screw 6, and the thickness of the
piezoelectric element 4 and the weight 5 The housing 2 is lighted and elastically fixed by the case
7 having a smaller depth.
That is, the vibration pickup means 3 has high sensitivity due to vibration V in the direction of
the main axis (direction of arrow A in the figure) to which the electret microphone unit 1 is
transmitted. There is. The respective output signals of the electret microphone unit 1 and the
vibration pickup means 3 are supplied to the signal processing circuit unit 8 which performs
impedance conversion and characteristic compensation via the output terminals la and -Ia
respectively and combines them in reverse phase with each other. . FIG. 2 is a cross-sectional
view of another embodiment of the processing tread microphone according to the present
invention, in which the same parts as in FIG. 1 are indicated by the same reference numerals. In
the fourth embodiment, only the fixing and crushing of the case 70 with respect to the housing
20 is different from the embodiment described above. That is, screw portions are respectively
formed on the inner wall of case 20 and the outer wall of case 70, and ceramic piezoelectric
element 4 and weight 5 are made to case 2 by screwing case 70 into case 20. It is configured to
be elastically fixed. FIG. 3 is a circuit diagram of an example of the signal processing circuit unit
8 in FIG. In the figure, the output signal moon of the electret microphone unit 1 is supplied to the
gate of an impedance converting FET (field effect transistor) Q1. The source of the FET Q + is
grounded, and its dimension is connected to the power source B through the resistor R1 and to
the output terminal 9 through the DC cut capacitor C1. On the other hand, the output signal of
the vibration pickup means 3 is supplied to the gate of the impedance conversion element Q2.
The source of the FET Q2 is grounded, and its train is connected to the power source B through
the resistor rAR2 and to the input end of the characteristic compensation circuit 100 through the
DC cut capacitor C2. The characteristic compensation circuit 10 is constituted by a transistor
Q21 capacitor C8 and resistors R3 to R5 as shown in the figure (constituted by the sensitivity
(vibration characteristic) or frequency characteristic of the output signal of the vibration pickup
means 3 subjected to impedance conversion. The signal to the output signal of the electret
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microphone unit 1 is equal to the sensitivity or frequency custom-order of the output signal of
the electret microphone unit l, and a signal of an opposite phase to the human power signal is
output. The output signal of the custom compensation circuit 14 is added to the output signal of
the electret microphone unit 1 via the DC cut capacitor C4. Here, the vibration custom-order of
the condenser type microphone in the case of constant force l] speed vibration is such that, in the
case of directional microphone, V is constant in the frequency domain% to sound pressure. It
attenuates at 6 dB / 10 ct at frequencies higher than that.
In the case of an omnidirectional microphone, the stiffness of the diaphragm is large due to the
difference in control system of the acoustic circuit, and the mechanical impedance is low, so that
the vibration sensitivity is lower than that of the directional group microphone. It is constant in a
bowl. On the other hand, the vibration characteristic of the vibration pickup 6-means 3 is a coimaging frequency f determined by the mass m of the weight 5 and the stiffness S of the ceramic
piezoelectric element 4. -Constant until LV work. Therefore, in consideration of the use frequency
band of the 2?m microphone, the custom-made compensation circuit 10 only needs to
compensate for the variation in the sense that the microphone is nondirectional, and in the case
of directivity, it is necessary to correct the sensitivity and frequency characteristics. ! FIG. 4 is a
diagram showing the frequency characteristics when a constant acceleration is applied in the
main axis direction by an exciter (not shown) using a single-directional wedge microphone unit
as an electret microphone unit l. In the figure, the solid line (a) is the output of the electret
microphone unit 1 after impedance conversion, the break 14iI (b) is the output of the vibration
pickup means 3 after the characteristic compensation, and the alternate long and short dash line
tc + is after combining both outputs in reverse phase. The respective microphone outputs are
shown. As is clear from this figure, the microphone according to the present invention provided
with the vibration pickup means 3 has a 20 to 30 dB reduction in the vibration noise level 7particularly in the mid-low range compared to the conventional microphone with only the
electret microphone unit 1 It can be understood that As described above in detail, according to
the present invention, since the vibration pickup means is configured and 118 without using an
adhesive or the like, the assembly is easy and the extraction of the output is reliable. is there. In
addition, since noise based on the vibration transmitted to the microphone housing can be
reliably removed, it is possible to improve the S / N of the target sound to be collected, and thus
the electret microphone according to the present invention has a tape recorder of 8 mm. It is
most suitable as a built-in microphone of a sound collecting device such as an overhead camera
or a video camera, etc., particularly as a micro built-in microphone of a pocketable device such as
a microcassette tape recorder.
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