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JP2004007312

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DESCRIPTION JP2004007312
A compact shape and sufficient sound pressure can be obtained. SOLUTION: In an inner space of
a casing CA, via a buffer plate 5B, between a permanent magnet plate 2 consisting of bond
magnets formed of banded magnets alternately forming N-poles and S-poles in strip form on the
plate surface, and the permanent magnet plate 2; A vibrating film 4 is provided in which an
electric wiring 41 extending along the boundary region between the N pole and the S pole is
formed on the film surface. The permanent magnet plate 2 is provided only on one side of the
vibrating membrane 4, and the buffer plates 5A and 5B are formed into a frame shape along the
circumferential edge 43 of the vibrating membrane 4. Set up. [Selected figure] Figure 2
Thin type electromagnetic converter
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
thin electromagnetic transducer having a structure in which a vibrating film on which electrical
wiring is formed is disposed along a permanent magnet plate. [0002] A thin electromagnetic
transducer which can be used as a speaker, a microphone or the like is disclosed in Japanese
Patent Application Laid-Open No. 9-331596, and an example of its specific structure is shown in
FIG. FIG. 6 shows an application of the electromagnetic converter to a thin speaker, and its casing
CA is constituted by substantially rectangular metal plate members 1A and 1B arranged
symmetrically in the vertical direction. That is, each of the metal plate members 1A and 1B is
formed into a container shape in which the inner peripheral portion 12 is shallowly recessed
except for the outer peripheral flange 11 having a predetermined width. These metal plate
members 1A and 1B are used as container open ports. A casing CA in which a substantially
rectangular gap space is formed inside is configured by facing each other and abutting with each
other at the outer peripheral flanges 11 and screwing and coupling with mounting holes 111
provided at a plurality of locations. In addition, many ventilation holes 13 are formed in the plate
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surface of metal plate 1A, 1B. A permanent magnet plate 2A, a buffer plate 3A, a vibrating
membrane 4, a buffer plate 3B, and a permanent magnet plate 2B are arranged in this order from
above in the gap space of the casing CA. The electrical wiring 41 is formed by printing on the
front and back film surfaces of the vibrating film 4, and the electrical wiring 41 comes out from
the feed terminal portion 42 provided at the center of one side of the vibrating film 4 and is
folded over the entire film surface. , Return to the feeding terminal unit 42 again. The upper and
lower permanent magnet plates 2A and 2B are bonded magnets formed by mixing magnetic
powder in a resin material, and as shown in FIG. 7, N poles and S poles are alternately formed in
a strip shape on the plate surface There is. The electric wiring 41 on the vibrating film 4 extends
alternately in the opposite direction along the boundary region of the N pole and the S pole, and
when an AC signal is input to the feed terminal portion 42, it goes from the N pole to the S pole
Under the magnetic flux, according to Fleming's left-hand rule, upward or downward force in the
same direction acts on the electric wiring 41 extending in the opposite direction according to the
polarity of the alternating current signal to vibrate the vibrating membrane 4 to generate sound
waves. Will occur. In the permanent magnet plates 2A and 2B, vent holes 21 are formed in the
boundary area so as to coincide with the vent holes 13 of the metal plates 1A and 1B, and sound
waves pass through these vent holes 13 and 21 efficiently to the casing CA. It is sent out. The
ventilation holes 13 and 21 also guarantee smooth vibration of the vibrating membrane 4.
[0005] By the way, for the above-described thin electromagnetic converter, further reduction in
thickness is required to further expand the application field, and therefore, a pair of upper and
lower parts is provided. It is conceivable to omit one of the permanent magnet plates.
However, according to this, it is not possible to obtain the effect that a pair of permanent
magnets are repelled and curved in opposite directions and a sufficient vibration space of the
vibrating membrane is secured therebetween, so that only one permanent magnet is provided.
Even if the magnetic force of the plate is strong, the vibration amount of the vibrating film does
not increase so much, and there is a problem that sufficient electromagnetic conversion
performance can not be obtained. Therefore, the present invention is intended to solve such
problems, and it is an object of the present invention to provide a thin electromagnetic
transducer having a compact shape and sufficient electromagnetic conversion performance. In
order to achieve the above object, according to the first aspect of the present invention, a
permanent magnet plate (2) comprising bond magnets in which N poles and S poles are
alternately formed in a strip shape on the plate surface ) And a permanent magnet plate (2) via a
buffer plate (5A, 5B), and an electric wiring (41) extending along the boundary region between
the N pole and the S pole is formed on the film surface In the thin electromagnetic transducer in
which the vibrating membrane (4) is disposed in the inner space of the casing (CA), the
permanent magnet plate (2) is provided only on one side of the vibrating membrane (4) and the
buffer plate (5A, 5A, 5B) are provided only on both sides of the edge (43) of the vibrating
membrane (4). In the first aspect of the present invention, only the peripheral portion of the
vibrating membrane is sandwiched between the buffer plates from both sides, and the inner
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peripheral portion of the vibrating membrane is not sandwiched, and a vibration space for the
thickness of the buffer plate Is formed on the upper and lower sides of the vibrating film, the
vibrating film vibrates sufficiently large by the action of the magnetic force of the permanent
magnet plate, and good electromagnetic conversion performance can be obtained. In the second
invention, the buffer plate (5A, 5B) is formed into a frame shape along the circumferential edge
(43). In the second aspect of the present invention, the frame shape makes it possible to easily
install the buffer plate in the casing. The reference numerals in the parentheses indicate the
correspondence with the specific means described in the embodiments to be described later.
DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an exploded perspective view
showing an example of the case where the electromagnetic converter of the present invention is
applied to a thin speaker, and FIG. 2 is a cross sectional view of the peripheral portion of the
container of the thin speaker. is there. In the present embodiment, only one permanent magnet
plate 2 is provided below the vibrating film 4 as compared with the conventional one (see FIGS. 6
and 7) already described. The shape of the buffer plates 5A, 5B located is different from the
conventional one as described below. The other structure is the same as the conventional one,
and the same reference numerals are given to the same parts. As shown in FIG. 3, one of the
buffer plates 5A, 5B is a rectangular frame having a fixed width along the inner periphery of the
metal plate 1A, 1B constituting the casing CA. An inner circumferential portion surrounded by
the portion 51 is a rectangular opening 52.
Such buffer plates 5A, 5B are respectively disposed along the inner circumferences of the upper
and lower metal plates 1A, 1B (FIG. 2), and the circumferential edge 43 of the diaphragm 4 is
held between them. There is. The frame width of the buffer plates 5A and 5B is preferably about
5 mm to 10 mm, and is a region (following) other than the vibrating film 4 region (active
vibration region) that generates a vibration force according to Fleming's left hand rule described
in the prior art Clamp the vibration area). As a material of the buffer plates 5A and 5B, it is
preferable to use a non-woven fabric in that it is less likely to inhibit the vibration of the driven
vibration area and a large number of holes through which sound waves pass. An example of the
plate thickness of the buffer plates 5A and 5B is a plate of about 100 mm square and the plate
thickness is about 0.35 mm. According to such a structure, only the circumferential edge portion
43 of the vibrating membrane 4 is sandwiched by the buffer plates 5A and 5B, and the active
vibration area of the inner circumferential portion is not sandwiched, and the buffer plate Since
the vibration spaces corresponding to the thickness of 5A and 5B are formed above and below
the vibrating film 4, the vibrating film 4 vibrates sufficiently large by the action of the magnetic
force of the permanent magnet plate 2, and good electromagnetic conversion performance, ie,
sound Pressure is obtained. The sound pressure characteristics are shown in FIG. 4, and the
sound pressure is improved particularly in the band of 1 KHz to 10 KHz as compared with the
sound pressure characteristics of FIG. 5 of the thin speaker using a flat buffer plate without an
opening. If an electrically insulating layer is formed on the surface of the vibrating film 4 or if an
electrically insulating resin plate is used instead of the metal plates 1A and 1B, the vibrating film
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4 contacts the casing CA wall. It is possible to prevent electrical shorting in advance. Further, the
buffer plates 5A and 5B do not necessarily have to be in a frame shape, and for example, only on
the return area (the edge of the front and rear ends in FIG. 1) of the electric wiring 41 on the
vibrating film 4 which hardly generates vibration force. It may be provided in correspondence
with As described above, according to the thin electromagnetic converter of the present
invention, sufficient electromagnetic conversion performance can be obtained with a compact
shape. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an exploded perspective view of a thin
loudspeaker showing an embodiment of the present invention. FIG. 2 is a cross-sectional view of
a container peripheral portion of the thin speaker. FIG. 3 is a plan view of a buffer plate. FIG. 4 is
a sound pressure characteristic diagram of the thin speaker of the present invention. FIG. 5 is a
sound pressure characteristic view of a thin speaker using a flat buffer plate. FIG. 6 is an
exploded perspective view of a conventional thin speaker. FIG. 7 is a partial cross-sectional view
of a conventional thin speaker. [Description of the code] 1A, 1B: metal plate, 2: permanent
magnet plate 4: vibrating membrane 41: electrical wiring 42: feeding terminal portion 43:
circumferential edge portion 5A, 5B: buffer plate, CA …casing.
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