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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
piezoelectric speaker, and more particularly to a structure of a piezoelectric speaker capable of
improving sound quality.
2. Description of the Related Art Generally, a speaker that generates electromagnetic vibration is
used, but a piezoelectric speaker that generates vibration by a piezoelectric element is also used
for the purpose of downsizing and low current driving. This piezoelectric speaker generates a
sound by applying a voltage to a piezoelectric ceramic plate attached to a diaphragm to generate
a sound. When used in combination with a liquid crystal display device, there is also an
advantage that no magnetostriction occurs.
The diaphragm made of piezoelectric ceramic has a problem that the sound quality is bad and it
is offensive because the frequency of the natural vibration is located at a higher frequency of the
audio frequency. In order to solve this, attempts have been made to reduce the thickness or to
make the shape rectangular as well as to make corrections by the method of attachment and the
selection of materials, but none have been sufficient. In addition, if the size is increased, the
sound quality in a relatively low frequency band is improved, but there is a problem that it is not
suitable as a speaker of a portable device or the like.
SUMMARY OF THE INVENTION The present invention provides a piezoelectric speaker which
can be miniaturized and can improve the sound quality of a low frequency band.
SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems by
disposing an auxiliary diaphragm together with a diaphragm in a housing and vibrating it.
That is, a piezoelectric speaker in which a diaphragm provided with a piezoelectric ceramic plate
having electrodes formed in a housing is disposed in a housing, characterized in that it comprises
an auxiliary diaphragm arranged in parallel with the diaphragm.
polycarbonate is disposed in parallel with a diaphragm in which a piezoelectric ceramic plate is
pasted in a housing, in proximity to the diaphragm.
A spacer such as an elastic body is press-contacted to at least a part of the periphery of the
diaphragm and the auxiliary diaphragm to fix the inside of the casing.
Wiring for driving is connected to the electrodes of the piezoelectric ceramic plate, and the input
voltage causes vibration.
The displacement of the piezoelectric ceramic plate vibrates the diaphragm, and the auxiliary
diaphragm vibrates in resonance with the vibration. The vibration of the auxiliary diaphragm
generates a low frequency sound to widen the frequency band as a whole.
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a partial front cross-sectional view showing an embodiment of the present invention.
The entire shape is a structure in which a vibrating element is fixed in a thin rectangular metal
case as shown in FIG. The metal case comprises an upper plate 11 provided with a storage space
for elements and a lower plate 12 of a flat plate. The upper plate 11 is formed with a through
hole 13 for passing sound. After the elements and the like are accommodated, the projections
formed on the upper plate 11 are bent and crimped and fixed. The through holes may be formed
in the lower plate 12. Even when a case other than metal is used, substantially the same structure
can be obtained.
In this example, the diaphragm 14 can use 42 alloy or the like of about 0.1 mm 2, and its
dimension is about 30 mm × 25 mm. A piezoelectric ceramic plate of about 13 mm × 16 mm
and about 0.1 mm in thickness is attached to the central portion thereof. Electrodes of silver or
the like are formed on both sides of the piezoelectric ceramic plate, and lead wires 15 are
connected to the respective electrodes. The connection of the electrodes on the surface to be
attached to the diaphragm 14 can be performed by soldering a lead wire to the diaphragm 14.
Alternatively, a metal plate may be adhered to the diaphragm using polycarbonate or the like,
and a piezoelectric ceramic plate may be disposed thereon.
The diaphragm 14 is held by elastic members 17 and 18 at its peripheral portion. Silicon rubber
or the like is suitable as the elastic bodies 17 and 18, and the thickness thereof is suitably about
0.7 to 1.1 mm. In order to hold the diaphragm 14, it is necessary to be about 1.5 to 3.0 mm
inward from the position in contact with the upper plate 11
The auxiliary diaphragm 20 is disposed between the diaphragm 14 and the upper plate 11. The
diaphragm 20 is suitably made of polycarbonate or the like, and its thickness may be about 0.1
to 0.5 mm. The dimensions are the same as the diaphragm 14 and fixed so as not to move into
the case. The through holes 21 may be formed in the auxiliary diaphragm 20.
An elastic body 23 is disposed between the auxiliary diaphragm 20 and the upper plate 11. The
elastic body 23 is made of silicone rubber or the like as the elastic bodies 17 and 18 and has a
thickness of about 0.3 to 0.5 mm, and the other dimensions are the same. A rigid spacer may be
used instead of this elastic body.
The elastic body 23, the auxiliary diaphragm 20, the elastic body 17, and the diaphragm 14 are
sequentially stored in the upper plate 11. Lead wires are connected to the diaphragm 14 and are
drawn out from the through holes in the side surface of the upper plate 11. Next, the elastic body
18 is accommodated and held by the lower plate 12, and the projection of the upper plate 11 is
bent and assembled. Therefore, the process of adhesion etc. becomes unnecessary at the time of
an assembly.
In addition, if the structure which withdraw | draws a part of diaphragm 14 outside so that the
upper plate 11 may not be contacted is employ | adopted, the man-hour of penetration of a lead
wire and soldering can also be reduced.
If a through hole is formed in the auxiliary diaphragm 20, distortion generated at the time of
large input can be reduced.
However, if it is too large, vibration efficiency is reduced, so it is desirable to minimize it.
The present invention is not limited to the above example, and materials and dimensions can be
arbitrarily selected according to the application. Further, the auxiliary diaphragms may be
arranged on both sides of the diaphragm, or the number of the auxiliary diaphragms arranged on
one side may be plural, and the material and thickness thereof may be different. Also, the
diaphragm and the auxiliary diaphragm may be arranged not parallel but with a predetermined
angle. And fixation of a diaphragm and an auxiliary diaphragm can also be performed by another
method. Alternatively, the auxiliary diaphragm may be used as a housing.
When the piezoelectric speaker of the above-mentioned example was used, it was also confirmed
that although the sound of the frequency band of 1.5 kHz or more was obtained by the
conventional one, the sound of a low frequency of 0.7 to 0.8 kHz was obtained.
In addition, it was also confirmed that when the through holes are formed in the lower plate, the
improvement on the lower region side is further achieved.
This is because the inherent vibration of the substrate or the like to which the piezoelectric
speaker is attached can also be used.
According to the present invention, it is possible to improve the sound quality of the low range
which has not been obtained conventionally while maintaining the small size. Conventionally, the
high frequency side was strong and unpleasant, but the high frequency side is relatively
suppressed, and a wide band and good characteristics can be obtained.
In addition, if the auxiliary diaphragm is provided with a through hole, there is an advantage that
distortion at the time of large input can be prevented, and the sound quality can be improved
also in that aspect.
Furthermore, since the assembly can be performed only by housing the diaphragm and the
elastic body in the housing, the number of assembling steps can be reduced.
Not only the advantage that the process of adhesion etc. is unnecessary but it is advantageous
also in terms of reliability.
Brief description of the drawings
1 is a partial front sectional view showing an embodiment of the present invention
(A) is a plan view showing an embodiment of the present invention, (b) is a front view
Explanation of sign
11:Upper plate 12: Lower plate 14: Vibrating plate 20: Auxiliary vibrating plates 17, 18, 23:
Elastic body
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