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BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view showing an example of
an electret microphone according to the present invention, FIG. 2 is a plan view of its back
electrode holder, and FIG. 3 is a perspective view of a shielding plate. 11: Capsule, 16:
diaphragm, 17: spacer, 18: back electrode plate, 19: back electrode holder, 22: shield plate, 21:
cushion, 24: impedance conversion unit, 25; housing hole, 29: input terminal, 31: Output
DETAILED DESCRIPTION OF THE INVENTION This invention relates to a microphone in which an
electret is used as a diaphragm, 41! Because of the diaphragm and the electret microphone that
was designed to reduce the size in the vertical direction. Conventional electret! In the case of
Ikroho 7, in order to miniaturize, k is forced to make the radius of the diaphragm small, and the
size of (1) b (i /; '7g) is perpendicular to the diaphragm. Not too small and nine. However, the
diameter of the diaphragm is reduced, and the sound quality is deteriorated, and the sensitivity is
also reduced. The present invention is to provide a thin electret microphone having high
sensitivity, stability, and good sound quality by reducing the size of the diaphragm in the radial
direction and reducing the size in the direction perpendicular to the diaphragm. Next, an
embodiment of an electret microphone according to the present invention will be described with
reference to the drawings. In the figure, reference numeral 11 denotes a capsule, which in the
same way as the prior art consists of a metal cylinder. One end face of the capsule 11 is
controlled by a front plate 12, a central hole is opened at the center of the front plate 12, and a
cross 14 closing the central hole 13 is attached to the front of the front plate 12 . Inside the
capsule 11, it is attached to a ring 15, and the front and back moving plate 6 is converged, and
the ring 15 side is in contact with the front face I [12. The vibrating plate 16 is polarized, and a
metal foil is deposited on one surface of the thin film 9, that is, the surface of the ring 15 @. (2) in
contact with the edge portion of the diaphragm 16-The back electrode plate 18 opposed to the
vibration I [16] is accommodated in the shell 11 via the spacer 17. The back electrode [18 is held
by the back electrode hole / -19. At the back of the holder 19 there is 1 lli of a masking plate 22
via a ring-shaped cushion 21 and the rear end of the capsule 11 is folded against the back of the
masking plate 22) * crimped. As a result of vibration I [16, the back electrode plate 18, the back
electrode holder 19, and the marking plate 22 are mechanically fixed in the cover 11. In the
present invention, the impedance converter 24 is accommodated in the peripheral wall of the
back electrode holder 19. That is, the front electrode holder 19 is a short i cylindrical body of a
shaft of a synthetic resin material having a relatively large thickness, the accommodation hole 25
is formed in the peripheral wall thereof, and the impedance conversion 1124 is inserted into the
accommodation hole 25. In the figure, the back pole holder 19 is formed eccentrically with
respect to its axial center so that a ring-shaped step 26 is formed on the back pole & 18 ', the
back pole plate 18 is inserted into the step 26 and held. Ru. The ventilating hole 27 is penetrated
through the back electrode i [i 81 'c, and the portion between the back electrode plate 18 and the
layer covering plate 22 and the portion between the back electrode plate 18 and the
micromotion plate 16 (3) is the air hole 27. To communicate with the wolf.
The in-bimens transformation 114240 input terminal 29 is connected to the back face 1 [1 g on
the back surface by, for example, a robot] Lll1 C, and the output terminal 31 passes through the
through-hole 32 formed on the side surface of the cab ring 110 without contacting this throughhole 32 External Km is released lnJ +. In order to prevent air leakage in the back chamber 28
through the accommodation hole 25, the impedance conversion portion 24 is covered with an
elastic material such as rubber cloth and inserted into the accommodation hole 25. Alternatively,
after inserting the impedance conversion unit 24, the portion K11 is filled with the material. As
shown in FIG. 3, the bell cover plate 22 has a part of the side edge thereof extended at right
angles to # 1 of the plate surface of the shield plate to construct the insert piece 34 integrally.
The insert piece 34 is inserted between the impedance converter 24 and the capsule 1120. At
this time, a notch 35 wider than the end edge of the insertion piece 34 is formed so as not to
contact the output terminal 31. The connection between the shielding plate 22 and the ground
terminal of the impedance converter 1134 is formed with a narrow cut 36, and the contact with
the ground terminal is sufficient to make the contact k (4) 7-+ 1. In the conventional electret
microphone KTh−, although it is accommodated in the impedance conversion unit 24 # i backfill
3 $, the rounding vibration INI @ and the Kttl 11 degree for reducing the size in the direction
perpendicular to the angle are reduced, but the electret microphone according to this invention
For example, since the impedance 9 is accommodated in the front pole $ 81-19, the size in the
direction perpendicular to the vibration I [16] can be reduced accordingly, and the thin 11 can be
formed. It is possible to reduce the diameter of the vibration 1 [16 by 9] so that the sound quality
is good and the feeling k can be stabilized. That is, it is not necessary to reduce the thickness of
the diaphragm to a large degree for rounding feeling, and it is not necessary to reduce the
thickness to 17%, and the feeling is very stable. Production of each part is good quality, and it is
easy to assemble and assemble, without the size definition becoming too sharp. However, it is
desirable to make the microphone thin, that is, to reduce the length of the cast iron's axial
porcelain *), and such desires can be enjoyed. It is possible to form the hole of the weir device
into which the output terminal 31 is collected and which is formed in the cub dragon 11 (5) and
the through hole 32 of the capsule is cut at the back edge O of the capsule). . Such an
arrangement would make the assembly operation more weighty, and make the capsule difficult
to shape when the capsule 11 is crimped. クッション21としては4! It is desirable to use an
air-permeable one that does not affect the air pressure between the inside and outside of the
capsule to always be the same.
At the same time, if the cushion 21 is made elastic, the capsule and the value cover will be
elastically deformed IIC II, and the contact will be mourning. As the ceramic cushion 21, it is
possible to make the inner surface of 11111 [22 an unevenness or the like by using an elastic
one without air permeability and to provide air permeability to the outside through the
unevenness. Although the back electrode plate 18 and the back electrode holder 19 are
eccentrically combined, they may be combined concentrically. Further, the impedance conversion
portion 24 is inserted in the housing hole 2s without being fixedly provided in the station size 25
of the back electrode holder 19, and electrically connected with the back electrode plate 18 by
the plug and the jack vII% K. There is no way to connect, and it is a storm even if the impedance
converter is configured in the body of the hook or the jack (11). Further, the back electrode
holder is divided into two in the axial direction to form an integral part with the front electrode
plate 18 and the value plate 2! Position the screw on the back cover of the fore pole holder 19
and use that screw, which may be integral with the integral part! It is also possible to attach an
electric microphone.