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DESCRIPTION JPS5723091

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DESCRIPTION JPS5723091
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of a microphone
according to the present invention, FIG. 2 is a schematic perspective view of one embodiment
mounted on a tape recorder, and FIG. 3 another embodiment mounted on a tape recorder. Fig. 4
is a schematic perspective view of an example, Fig. 4 is a circuit diagram of an example of the
circuit section in Fig. 1, Fig. 5 is a diagram showing frequency characteristics when vibrating at
constant acceleration, and Fig. 6 is stored in a tape recorder FIG. 7 is a view showing a noise
spectrum in the case where the support arm is extended and contracted. Explanation of symbols
of the main part, 1 ... electret microphone unit, 2 ... housing, 3 ... vibration pickup means, 4 ...
ceramic piezoelectric element, 5 ... weights, 8 ... circuit part , 10 ... tape recorder, 11 ° 12 ... arm.
7 乙 3 j 56 σ
The present invention relates to a microphone in a sound collecting device, and more particularly
to a microphone attached to a sound collecting device such as a tape recorder. For example, in a
tape recorder as a sound collecting device, many mechanical components such as a motor or a
pulley that easily generate vibration are incorporated. C. In a tape recorder incorporating a
microphone, the vibration generated from the above-described mechanical component is
transmitted to the housing of the microphone, and further, it is incident on the microphone as a
sound wave by air propagation, so noise based on this vibration Is undesirable because it
interferes with the target sound to be collected mixed with the output signal of the microphone.
As a countermeasure for this, conventionally, the microphone is floated from the tube recorder
case by an elastic member such as rubber, but in the electret microphone, the force effect is not
obtained because the weight is small. 2- The purpose of the present invention is to provide a
microphone in a sound collection device that can reliably remove noise based on vibrations
generated inside the sound collection device. The microphone in the sound pickup apparatus
according to the present invention comprises an electret microphone unit for sound pickup, and
a piezoelectric pickup means housed in the same housing as the electret microphone unit and
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picking up the vibration transmitted to the housing. , And is supported by an arm which is
attached to a sound collecting device and which can be protruded from a housing of the sound
collecting device. Hereinafter, embodiments of the present invention will be described in detail
with reference to the attached drawings. FIG. 1 is a cross-sectional view of a microphone
according to the present invention, and FIG. 2 is a schematic perspective view of an embodiment
mounted on a sound collection device. In FIG. 1, reference numeral 1 denotes an electret
microphone unit for sound collection, which is housed in a housing 2. The housing 2 further
incorporates a piezoelectric vibration pickup means 3 for picking up the vibration transmitted to
the housing 2. The vibration pickup means 3 is composed of a ceramic piezoelectric element 4
whose one surface is in close contact with the housing 2 and a weight 5 which is in close contact
with the other surface of the piezoelectric element 4. Is housed in a cup-shaped case 7 fixed to
the housing 2 by a set screw 6. The vibration pickup means 3 has high sensitivity to the vibration
in the main axis direction (direction of arrow A in the figure) in which the electret microphone
unit 1 is transmitted to the housing 2 and the sensitivity direction is also the main axis direction.
The output signals of the electret microphone unit 1 and the vibration pickup means 3 are
supplied to the circuit unit 8 for performing impedance conversion and characteristic
compensation via the output terminals 1α and 3α, respectively. As shown in FIG. 2, the
microphone 9 having such a configuration is attached to, for example, a tape recorder 10 as a
sound collecting device, and is supported by an arm 11 which can freely project from a casing of
the tape recorder IO of the bracket. The arm 11 is configured to be extendable as shown in the
figure, and at the time of extension, the microphone 94-is pulled away from the case of the tape
recorder 0 and at the time of shortening, the microphone 9 is stored in the case of the tape
recorder 0. Therefore, at the time of sound collection, by extending the arm 11, it is possible to
reduce the acoustic energy of the sound wave incident on the microphone 9 by air propagation
based on the vibration generated from the tape recorder casing. FIG. 3 is a schematic perspective
view of another embodiment mounted on a sound collecting device, and in the drawing, the same
parts as FIG. 2 are indicated by the same reference numerals. In the present embodiment, the
arm 12 supporting the microphone 9 is rotatably supported by the support member 13 in a
plane parallel to the main body of the tape recorder 00, and the support portion = material t3 is
the tape recorder 10 It is attached to the tape recorder O so as to be rotatable in a plane
perpendicular to the main body, within 1 °. A recess 14 for housing the microphone 9 is formed
in the housing of the tape recorder O, and the microphone 9 is stored in the recess 14 by
rotating the arm 12 in the direction of the arrow A in the figure. Become. On the other hand, at
the time of sound collection 5-, since the microphone 9 is separated from the housing of the tape
recorder 10 by rotating the arm 11 in the direction of arrow B in the figure, air is transmitted
based on the vibration generated from the tape recorder housing. The acoustic energy can be
reduced for sound waves incident on the microphone and the “□ rophone 9”. Further, in the
case of a directional microphone, the microphone 9 can be oriented in any direction by the
rotation of the arm 12. FIG. 4 is a circuit diagram of an example of the circuit unit 8 in FIG. In the
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figure, the output signal 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 train is
connected to the power source B via the resistor R1 and to the output terminal 15 via the DC cut
capacitor C1.
On the other hand, the output signal of the oscillation pink-up means 3 is supplied to the gate of
the impedance conversion FET Q2. The source of the FET Q2 is grounded, and the drain is
connected to the power source B via the resistor R2 and to the input of the characteristic
compensation circuit 160 via the DC cut capacitor C2 via 6-mer. The characteristic compensation
circuit 16 is configured as shown by the transistor Q 2 + capacitor C 3 and the resistors 煽 to R 5,
and the sensitivity (vibration characteristic) or frequency characteristic of the output signal of the
vibration pickup means 3 subjected to impedance conversion is selected as the electret
microphone unit 1 Correction so as to be equal to the sensitivity or frequency characteristics to
the vibration of the output signal of, and output a signal in reverse 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 the DC cut capacitor C4. Here, in the case of a directional
microphone, the vibration characteristic of the capacitor type microphone in the case of
excitation at a constant acceleration is constant up to the lower limit frequency ft in the
frequency characteristic with respect to the sound pressure, and 6 dBloct at frequencies higher
than that. Attenuate. In the case of a non-directional single microphone, the difference between
the control methods of the acoustic circuit makes the stay of the diaphragm large and the
mechanical impedance is high, so that the vibration sensitivity is low compared to directional
microphones. It is constant up to the frequency fh. On the other hand, the vibration characteristic
of the vibration pickup means 3 is a resonant frequency f determined by the mass m of the
weight 5 and the stiffness S of the ceramic piezoelectric element 4. -It is constant up to moths.
Therefore, in consideration of the operating frequency band of the microphone, the characteristic
compensation circuit 16 only needs to correct the sensitivity when the microphone 9 is
nondirectional, and in the case of the directivity, it is necessary to correct the sensitivity and
frequency characteristics. FIG. 5 is a diagram showing frequency characteristics when a single
acceleration microphone is used as the U electret microphone unit 1 and vibration is performed
at a constant acceleration in the main axis direction by a vibrator (not shown). In the figure, the
solid line (α) is the output of the electret microphone unit 1 after impedance conversion, the
output of the vibration pick-up means 3 after m (b) polarity compensation, and the alternate long
and short dash line (C) is the opposite phase adding both outputs. The outputs of the
microphones 9 are shown respectively. FIG. 6 is a diagram showing the noise spectrum of the
male crophone output when stored in the tape recorder. In the figure, the broken line (,) shows
the case of a unidirectional elect 8-let microphone, and the solid line <b) shows the case of a
unidirectional microphone according to the present invention provided with the vibration pickup
means 3 .
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As apparent from this figure, it can be understood that noise based on vibration generated inside
the tape recorder can be removed by adding the output of the vibration pickup means 3 to the
output of the electret microphone unit 1 in reverse phase. FIG. 7 is a diagram showing the noise
spectrum of the microphone output when the arm 11 supporting the microphone is extended
and contracted. In the figure, the broken line (,) shows the case where the unidirectional
microphone according to the present invention is stored in the tape recorder casing by
shortening the arm 11, and the solid line (b) shows the microphone from the tape recorder
casing by the extension of the arm 11. It shows the case of separation. As is clear from this
figure, by separating the microphone from the tape recorder housing, the acoustic energy can be
reduced with respect to the sound wave incident on the microphone by air propagation based on
the vibration generated from the tape recorder housing. It can be seen that the noise due to the
vibration generated inside the tape recorder included in the above can be reduced. As described
above in detail, according to the present invention, noise based on the vibration transmitted to
the microphone case can be reliably removed, and sound waves incident on the microphone by
air propagation based on the vibration etc. generated from the inside of the sound collecting
device can be eliminated. On the other hand, since the acoustic energy can be reduced, it is
possible to improve the S / N of the target sound to be collected. The above-mentioned vibrations
include not only internal vibrations generated from a motor or the like inside the sound
collecting device, but also external vibrations transmitted through a desk or the like on which the
sound collecting device is placed. Also, non-directional microphones with low sensitivity to
vibration are generally used as microphones attached to sound collection equipment, but
directional microphones are preferable in consideration of external factors (noise etc.) during
sound collection It is clear that the present invention is particularly effective when using a
directional microphone with high vibration sensitivity. Furthermore, in the case of a directional
microphone, the support arm can be extended and retracted (turned) so that the microphone can
be directed in any direction for sound collection purposes, and the sound collection device is
placed on a desk etc. By separating only the microphone from the desk, the influence of a
reflective object such as a desk can be reduced. In the above embodiment, although the
microphones mounted on the tape recorder have been described, the present invention is also
applicable to the microphones mounted on a sound collecting device such as a 8 mm cine camera
or a video camera. .
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