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BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional view showing an
embodiment of an unconventional microphone, FIG. 2 is an equivalent circuit diagram thereof,
and FIG. 3 is a diagram showing an outline of a characteristic curve. 1: diaphragm, 2: back
electrode, 3: main body, 4: front chamber lid, 5: front chamber, 6: sound introduction hole, 7:
back chamber case, 8: back chamber, 9: through hole, 10: Field effect transistor, 11: output
DETAILED DESCRIPTION OF THE INVENTION This invention relates to the improvement of
microphones primarily intended for the transmission of sound, such as loudspeakers, hearing
aids, telephone microphones, interphones and the like. The microphones are of the gods type,
and in particular, the condenser microphones can be easily configured to have a frequency range
which can be used by the movement principle person, or a wide range of usually 20 to 20000
Hz. On the contrary, in the case of a microphone for sound transmission as described above, the
frequency range is wider than necessary. (1) 79 λ ¥ // Rash rather makes the target sound
signal unclear. That is, even respiratory sounds that do not need to be transmitted and ambient
noises are sent together with the sound, so these become noises and become unclear. In order to
transmit voice clearly, it is sufficient to transmit a signal in the frequency band that covers most
of the frequencies contained in male and female voices, and transmitting unnecessary frequency
bands is not a meaningless balance. , Produces a disadvantage such as forward convex self. In
particular, extending the low frequency range is as follows. Besides increasing the noise, the
speaker becomes large and the space between the speakers becomes large, which increases the
cost of the entire transmission system and is uneconomical. Also, conventionally, as a condenser
microphone to lower the sensitivity of the low frequency range, it is possible to perforate the
back room to the outside air by drilling it in the back room case surrounding the back of the load
electrode. (2) If you increase perforations in this case to increase directivity, there is a limit to the
cutoff of the bass range, and it is limited to 100 Hz or less. It was being done. The present
proposal is a microphone, in particular a capacitor, capable of clearly transmitting sound by
performing band adjustment that lowers the sensitivity of unnecessary high frequency bands and
low frequency bands from the structure, function and effect different from such conventional
microphones. The microphone is obtained. FIG. 1 for explaining the present invention from the
drawings showing the embodiment below shows a longitudinal sectional view of the embodiment
of the band adjustment type capacitor microphone of the present invention, wherein 1 is a
vibrating film, 2 is a back of the vibrating film 1 Back electrode with impedance converter by
means of small holes, 3 is an insulating body to support and fix these, 4 is a front chamber, 5 is a
front chamber, 6 is a sound introduction hole, 7 is a back chamber case, 8 is a back A chamber 9
is a through hole communicating the front chamber with the back chamber, 10 is a field effect
transistor, and 11 is an output node "1 ', 11". The field effect transistor 0 has a gate connected to
the load electrode 2 by spring contact, a drain and a source are connected to the output terminal
11 to form an impedance conversion circuit, and an output voltage is output from the output
terminal 11 It is.
FIG. 2 shows an equivalent circuit diagram corresponding to the configuration of the condenser
microphone of $ 1. The reference numerals attached to the dotted lines correspond to the
reference numerals attached to the components shown in FIG. Further, P is a vibrating membrane
U of the effective value area S. U, [2 are these acoustics due to the sound pressure P, the
molecular velocity of air flowing into and out of the vibrating element (or the vibration velocity of
the mechanical element), Uo is the molecular velocity when passing through the introducing hole
6 U is the molecular velocity when it hits the vibrating membrane l, IJ 2 is the molecular velocity
when it flows into the through hole 9. Next, the operation of this microphone will be described
with reference to FIGS. 1 and 2. A sound wave of sound pressure P comes to the front of the front
cover 4 and a plurality of small introduction holes 6 (equal mass m1, acoustic Through the
resistance molecule, introduce the front chamber 5 (compliance C, K) 4), and the vibration
membrane 1 (equivalent mass m compliance C8, resistance molecule) as the molecular velocity
U1 of the air from the point a in FIG. Excite). The back electrode 2 is located on the 1ν plane of
the diaphragm 1 via a gap, and a static capacitance CM of about 20 to 50 pF is formed between
the diaphragm 1 and the diaphragm 1. The molecular velocity of the o vibrating membrane,
which causes a small change of CM ± ΔC, flows into the back chamber 8 (compliance C2)
through the multiple apertures of the 1,1′T′Q5 pole 2, and the air in the back chamber 8 The
molecule is crushed and expanded again. Meanwhile, the molecular velocity U of air passing
through the introduction hole 6. Bypasses the circuit of mo, Co, ro through the through hole 9
(shield value m2, acoustic resistance molecule 2) provided in the main body 3 from the point a
and hits the vibrating membrane 1 at the point b as the molecular velocity U2 of air It joins the
molecular velocity UI of air and flows into the back chamber 8 (compliance C2). Now, considering
the frequency of the incoming sound wave, the acoustic impedance Z of the through hole 9 in the
low frequency range (here, 500 lz or less). (2 m, + r2) The mechanical impedance Z of the
vibrating membrane. (5) Renal-[-(-ω1] 1 o c c, + ro) lower than z, << z. In the vat, the molecular
velocity U of air as it passes through the hole 6. For most part, the through hole 9 is bypassed to
make the back chamber 8 (compliance C2) K, I, U, << U2, and the vibrating membrane 1 is hardly
excited and the output is small. If you choose nl, the resonance point of C2 and a frequency of 4
as f, in the low frequency range of f1 or more, it almost passes through the acoustic impedance
Z1, as shown in the characteristic curve diagram of FIG. At f, a cutoff of about 6 dB per octave is
obtained. Next, considering the high tone range, as shown in FIG. 2, the inertance of the sound
introduction hole 6 (monovalent mass m1, acoustic resistance molecule) leading to the front
chamber 5 and the front chamber 5 (compliance C,) The capacitance operates as a low-pass filter
in a half section, and the sound pressure potential at the point a decreases sharply, and the
driving force of the vibrating membrane 1 decreases significantly, as shown by f2 in FIG. It
(6) Because of this operation, the frequency band of the microphone can be determined by
providing two acoustic circuit elements indicated by reference numeral 1.9 in FIG. 2 in parallel,
as shown in FIG. It is possible to obtain the desired characteristics by narrowing the range of In
the case of a microphone for bamboo chopsticks, fl is 300 to 400 Hz, f 2 is 3 to 4 KHz or
appropriate, and the reduction grade is adjusted by adjusting the inherent Q (resonance
sharpness) of the acoustic element to a desired fit. I can do that. The band adjustment type
capacitor microphone according to the present invention is a so-called interruption bias type,
which applies a DC voltage of row electrodes K of 50 to 200 V, and a vibrating film itself which is
called electret type electret. Whether it is a film or an h-type having an electret film coated on a
back-shape lfi is adopted. Further, if the through hole 9 is opened and closed from the outside by
a shutter or the like, the bass cut-off frequency f1 can be adjusted in movement (7). (The L band
adjustment means is not limited to the condenser microphone, and can be applied to, for
example, a moving coil microphone. However, in this case, it is possible to set the resonance
point of the vibrating membrane to the desired 11 even if it has low-cut characteristics, or it is
possible to make adjustment to a wider range by applying the adjustment means of the present
invention is there. Furthermore, the through hole 9 can be immersed in the thick insulating main
body 3 so that it is easy to set the characteristics, and it is possible to make the back room case 7
pierce and allow the back room 8 to directly communicate with the outside air. Compared to the
conventional structure of the present invention, there is less risk of ingress of moisture from the
outside, and it is effective as a microphone capable of clearly transmitting voice.
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jps5769381, description
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