JPS6033676Y2 - electret microphone - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an electret microphone.

Some microphones are used built-in to sound collecting devices such as tape recorders, and sound collecting devices such as tape recorders have many built-in mechanical parts such as motors and pulleys that are likely to generate vibrations.

Therefore, in a tape recorder with a built-in microphone, the vibrations generated from the above-mentioned mechanical parts are transmitted to the microphone housing, and are further transmitted into the microphone as sound waves through air propagation. This is undesirable because it mixes with the output signal of the device and interferes with the purpose of collecting sound.

Conventionally, as a countermeasure to this problem, a method was adopted in which the microphone was lifted from the tape recorder housing using an elastic member such as rubber to suppress the vibrations transmitted to the microphone housing, but electret microphones have a small weight. Therefore, sufficient effects are not obtained.

An object of the present invention is to provide an electret microphone that can reliably remove noise based on vibrations transmitted to a microphone housing with a simple configuration.

The electret microphone according to the present invention includes an electret microphone unit for collecting sound and a vibration pickup means for picking up vibrations transmitted to the housing in the same housing, and a piezoelectric element constituting the vibration pickup means. The weight added thereto is housed in a case made of an insulating material and fixed to the case.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a sectional view of an embodiment of an electret microphone according to the present invention.

In the figure, reference numeral 1 denotes an electret microphone unit for collecting sound, which is housed in a housing 2 made of metal such as aluminum.

The housing 2 has a front sound guiding opening 2a and a rear sound guiding opening 2b, and further includes built-in vibration pickup means 3 for picking up vibrations transmitted to the housing 2. There is.

The vibration pickup means 3 is composed of a ceramic piezoelectric element 4 which is polarized in its thickness direction and has one electrode in close contact with the housing 2, and a weight 5 which is in close contact with 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 and fixed to the housing 2 by a set screw 6. It is elastically fixed to the housing 2 within the case 7 which has a smaller depth.

That is, the vibration pickup means 3 is arranged in the main axis direction (where the electret microphone unit 1 is transmitted to the housing 2
In order to exhibit high sensitivity to vibrations in the direction of arrow A in the figure), the direction of sensitivity is also in the direction of the principal axis.

The output signals of the electret microphone unit 1 and the vibration pickup means 3 are supplied via output terminals 1a and 3a, respectively, to a signal processing circuit section 8 for performing impedance conversion and characteristic compensation, and for synthesizing them in opposite phases.

FIG. 2 is a cross-sectional view of another embodiment of the electret microphone according to the present invention, in which parts equivalent to those in FIG. 1 are designated by the same reference numerals.

In this embodiment, only the fixing structure of the case 70 to the housing 20 differs from the embodiments described above.

That is, threaded portions are formed on the inner wall of the housing 20 and the outer wall of the case 70, so that the case 70 is connected to the housing 20.
The ceramic piezoelectric element 4 and the weight 5 are elastically fixed to the housing 2 by screwing them together.

FIG. 3 is a circuit diagram of an example of the signal processing circuit section 8 in FIG. 1.

In the figure, the output signal of the electret microphone unit 1 is supplied to the gate of an impedance conversion FET (field effect transistor) Ql.

The source of the FET Qt is grounded, and the drain thereof is connected to the power supply 1B via a resistor R□ and to the output terminal 9 via a 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 FETQ2.

The source of the FET Q2 is grounded, and the drain thereof is connected to the power supply 1B via a resistor R2 and to the input terminal of the characteristic compensation circuit 10 via a DC cut capacitor C2.

The characteristic compensation circuit 10 includes a transistor Q2 and a capacitor C.
3 and resistors R3 to R5 as shown in the figure, the sensitivity (vibration characteristics) or frequency characteristics of the output signal of the impedance-converted vibration pickup means 3 can be changed to the sensitivity (vibration characteristics) or frequency characteristics of the output signal of the electret microphone unit 1 to vibrations. It corrects the frequency characteristics to be equal to the frequency characteristics and outputs a signal with the opposite phase to the input signal.

The output signal of the characteristic compensation circuit 14 is added to the output signal of the electret microphone unit 1 via a DC cut capacitor C4.

Here, the vibration characteristics of a condenser microphone when vibrated at a constant speed are as follows: In the case of a directional microphone, the low limit frequency 1 in the frequency characteristics with respect to sound pressure is
It is constant up to 1, and at higher frequencies it is 5 dB 1
Attenuates at 0ct.

In the case of omnidirectional microphones, the stiffness of the diaphragm is large due to the difference in the control method of the acoustic circuit, and the mechanical impedance is high, so the vibration sensitivity is lower than that of directional microphones, and the frequency characteristics are constant up to the high limit frequency fh. It is.

On the other hand, the vibration characteristics of the vibration pickup means 3 are constant up to a resonance frequency fo=',7'' determined by the mass m of the weight 5 and the stiffness S of the ceramic piezoelectric element 4.

2π m Therefore, considering the frequency band used by the microphone,
If the microphone is non-directional, the characteristic compensation circuit 10 only needs to correct the sensitivity; if the microphone is directional, it is necessary to correct the sensitivity and frequency characteristics.

FIG. 4 is a diagram showing frequency characteristics when a unidirectional microphone unit is used as the electret microphone unit 1 and is vibrated at a constant acceleration in the main axis direction by a vibrator (not shown).

In the figure, the solid line a shows the output of the electret microphone unit 1 after impedance conversion, the broken line shows the output of the vibration pickup means 3 after characteristic compensation, and the dashed line C shows the microphone output after combining both outputs in opposite phase. ing.

As is clear from the figure, the microphone according to the present invention equipped with the vibration pickup means 3 has a vibration noise level of 20 to 39 dB, especially in the mid-low range, compared to the conventional microphone with only the electret microphone unit 1.
It can be seen that it is decreasing.

As described in detail above, according to the present invention, the vibration pickup means can be constructed without using adhesive or the like, so assembly is easy, the output is reliable, and the device can be miniaturized.

In addition, since noise caused by vibrations transmitted to the microphone housing can be reliably removed, it is possible to improve the S/N of the target sound to be collected. It is most suitable as a built-in microphone in a sound collecting device such as a cine camera or a video camera, and especially as an ultra-small built-in microphone in a pocketable device such as a micro cassette tape recorder.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of one embodiment of the electret microphone according to the present invention, FIG. 2 is a cross-sectional view of another embodiment of the electret microphone according to the present invention, and FIG. 3 is a cross-sectional view of an example of the signal processing circuit section in FIG. The circuit diagram and FIG. 4 are diagrams showing frequency characteristics when vibration is applied at a constant acceleration. Explanation of symbols of main parts, 1... Electret microphone unit, 2, 20... Housing, 3
... Vibration pickup means, 4 ... Ceramic piezoelectric element, 5 ... Weight, 7,70
... Case, 8 ... Signal processing circuit section,
10...Characteristic compensation circuit.

Claims (1)

[Scope of utility model registration request] An electret microphone unit for sound collection,
Vibration pickup means for picking up vibrations transmitted to the housing, which includes a piezoelectric element and a weight added thereto and is housed in the same housing as the electret microphone unit, and the electret microphone unit and the vibration pickup means. and a signal processing circuit that synthesizes each output signal in opposite phases to each other, and the piezoelectric element and the weight are housed in a case made of an insulating material fixed to the casing. Microphone.