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DESCRIPTION JPS61158299

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DESCRIPTION JPS61158299
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
piezoelectric speaker using a bimorph diaphragm which is formed in a corrugated shape in cross
section as a vibrator. [Prior Art] Conventionally, two polarized piezoelectric films are laminated
and attached to each other, and a bimorph diaphragm in which these films are alternately bent in
opposite directions with a predetermined interval is used as a vibrator. The piezoelectric speaker
used is known. This type of speaker is disclosed, for example, in Japanese Utility Model
Publication No. 54-10918, and by expanding and contracting the above-mentioned vibrating
body in the surface direction, compression waves are generated on the front side and the rear
side of the vibrating body to generate a signal voltage. It is designed to convert sound pressure.
That is, as shown in FIGS. 8 and 9, this kind of piezoelectric speaker laminates and sticks two
different piezoelectric films 21.22 with different polarization directions p, p2 and p2, and these
films 21.22 The bimorph diaphragms formed by providing the opposing electrodes 24.25 ...
facing each other through the piezoelectric film 21 ° 22 to the respective bending portions 23a
and 23b while vibrating into a shape are vibrated. It is used as the body 30. In addition, as shown
in FIG. 9, a − bent portion 23a. The pair of opposite electrodes 24.25 provided on the side 23b
and the pair of opposite electrodes 24.25 provided on the other bent portions 23a, 23b... Are
connected in parallel to the signal source 26, respectively. A potential difference corresponding
to the signal voltage Vo of the alternating current applied from the signal source 26 is generated
between the counter electrodes 24. 25. The curvature of each of the bent portions 23a, 23b,...
Are driven in opposite directions to each other by changing the level according to the signal level
of the signal generator and the direction thereof, to the front side and the rear side of the
vibrating body 30. Perform an air volume exclusion operation to generate compression waves.
Note that this air volume eliminating operation is an intake operation, that is, an operation for
shifting from the state shown in FIG. 10 [C] to FIG. 10 CB) and an exhaust operation, that is, FIG.
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An operation to shift to the state shown in C1), and a compression wave is generated by
repeating such an intake operation and an exhaust operation. Thus the signal V of said
alternating current. Is converted to sound pressure. By the way, the piezoelectric speaker as
described above has a structure in which the piezoelectric film 2-1.22 which is a dielectric is
sandwiched between the opposite electrodes 24.25 in each of the bent portions 23a, 23b,.
Therefore, a capacitor is formed between the counter electrodes 24 ° 25, and a capacitance is
generated between the counter electrodes 24 ° 25. With respect to the high frequency
component of the signal applied to the piezoelectric speaker due to the capacitance, the
impedance of the piezoelectric speaker is lowered and the efficiency is deteriorated. In addition,
the drop in the impedance causes a great load on the amplifier in the output stage, and an
excessive current may flow in the piezoelectric speaker to cause electrode breakage. For example,
when the capacitance is 30 nF and the signal voltage obtained by boosting the output of the
amplifier by 30 times with a transformer is applied to the piezoelectric speaker, the impedance
viewed from the primary side of the transformer is approximately 4 Ω at a frequency of 1.5 KHz
This is almost the limit for the above amplifier. Therefore, in the case of a signal whose frequency
is higher than 1.5 K'Hz, the impedance becomes smaller than 4 Ω and an excessive current flows
in the amplifier and the piezoelectric speaker. Do not add. Here, if the boost ratio of the
transformer is lowered, the impedance rises, but in the case of a piezoelectric film currently
obtained, for example polyvinylidene fluoride, the output sound pressure level is also lowered
due to the decrease of the boost ratio, the boost ratio is 30 times Is necessary. As described
above, since the piezoelectric speaker has a capacitance, it is difficult to reproduce from the low
band signal to the high band signal by one piezoelectric speaker. Therefore, it has been practiced
to reproduce the entire band of the above signal as a multi-way speaker system such as a socalled 2-way system or 3-way system by using piezoelectric speakers having different
capacitances for each signal band. [Problems to be Solved by the Invention] As described above,
it is difficult to reproduce the entire band of a signal by one piezoelectric speaker conventionally,
so a so-called multi-way using separate piezoelectric speakers for each signal band A speaker
system is configured to reproduce the entire band. Since separate piezoelectric speakers are used
in this way, there is a problem in terms of manufacturing and cost to make a speaker system for
reproducing the entire band into a limited space. The present invention aims to solve such
problems. [Means for Solving the Problems] In the present invention, two piezoelectric films are
adhered to form a bimorph diaphragm, and the bimorph diaphragm is divided into two or more
regions, and each region is also different from each other at different intervals. It bends so that a
cross section may become wave shape, and counter electrodes are provided in the front and back
of this fold bending part.
[Operation] In the piezoelectric speaker of the present invention, a plurality of areas having a
corrugated cross section are formed at different intervals on one bimorph diaphragm, so that
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each area can be made to correspond to a specific signal band. it can. Therefore, the multi-way
speaker can be constituted by one bimorph diaphragm, and the reproduction of the entire band
of the signal becomes possible. The piezoelectric speaker according to the present invention will
be described below with reference to the drawings. FIG. 1 is an external perspective view
showing a structure of an embodiment of a piezoelectric speaker according to the present
invention. In this figure, in the piezoelectric speaker 1, a single bimorph diaphragm 3 is formed
and disposed in a so-called accordion pleat shape in a frame 2. The bimorph diaphragm 3 is
composed of a region 3A with a large interval of rotation of the waveform of the cross section
and a small region 3B, and the electrode pattern 12A on the front and back of the ridge and
valley of the waveform. 12B is formed by vapor deposition. The lower end 8 of the bimorph
diaphragm 3 is bonded to the frame 2. In this embodiment, the voice band is divided into a low
band and a high band, the low band is reproduced in the area 3A, and the high band is
reproduced in the area 3B. That is, a signal such as voice is supplied to the terminal 4, and a low
band signal is applied to the electrode pattern 12A of the area 3A through the low pass filter 5,
the transformer 6 and the electrode introducing portion 9, The signal is applied to the electrode
pattern 12B through the transformer 7 and the electrode introducing unit 10. The ground line is
common to the electrodes in the above regions 3A and 3B, and is connected to the electrode
introducing portion 11. By the way, in order to form a plurality of regions having different wave
repetition intervals of the cross section on one bimorph diaphragm 3 as described above, the
electrode pattern 12A. As shown in FIG. 2, 12B is formed by vapor deposition with a change in
intervals ll and 12 in a comb shape in which T-shapes are connected. The electrode patterns 12A
and 12B are formed on the front and back of the bimorph diaphragm 3 so that the comb-like
direction is opposite. The electrode pattern is divided into the electrode pattern 12A of the area
3A and the electrode pattern 12B of the area 3B, but the ground lines are commonly connected.
In the present embodiment, the area of the electrode pattern 12B in the area 3B is set to 115 of
the area of the electrode pattern 12A in the area 3A, and the electrostatic capacity of the
electrode pattern 12A is 30 nF while the electrostatic capacity of the electrode pattern 12B is 30
nF. The capacitance is 6 nF. The area 3B is used to reproduce a bass signal, but when applying a
signal boosted 30 times by the transformer 6 as described above, a signal whose frequency is
higher than 1.5 KHz is applied between the electrodes of the area 3B. must not.
Therefore, a signal whose high range has been attenuated by the low pass filter 5 is applied
between the electrode patterns 12A through the transformer 6. The electrode pattern 12B in the
area 3B for high-frequency reproduction has a small electrostatic capacitance, so the problem
does not occur even if the entire band of the signal is applied. In this embodiment, the signal
boosted 15 times by the transformer 7 is the electrode It is applied between the patterns 12B.
The frequency characteristic of the piezoelectric speaker 1 of this embodiment configured as
described above is, as shown in the characteristic diagram of FIG. 3, the frequency characteristic
of reproduction by the area 3A in the low band and the reproduction by the area 3B in the high
band. The frequency characteristics H are synthesized and become substantially flat over the
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entire band of the signal. Although the impedance characteristic of the piezoelectric speaker 1
exhibits the characteristic as shown by the thick line in the same figure, the frequency is 1.5 KHz
and 20 KHz and it is about 4 Ω, and it does not overload the amplifier of the output stage. In this
manner, a so-called full range speaker capable of reproducing the entire band of the audio signal
can be realized by the piezoelectric speaker using one bimorph diaphragm. In this embodiment,
when the interval 11.12 of the electrode patterns 12A and 12B formed on the bimorph
diaphragm 1 is a constant value, and the accordion pleat shape is formed, the period and
amplitude of the wave shape of the cross section are constant. However, these may be changed.
For example, in the region 3B of the bimorph diaphragm 1, the directivity of the frequency
characteristic in the high region of this piezoelectric speaker can be changed by giving
characteristics to the amplitude of the wave shape of the cross section. That is, as shown in FIG.
4, when the amplitude of the wave shape of the cross section of the region 3B is formed to have a
convex characteristic, as shown by a broken line in FIG. In the case where the frequency
characteristic at the position of is periodic and the amplitude is constant (indicated by a dashed
dotted line). Improved compared to). That is, directivity is improved. Alternatively, if the
amplitude of the wave shape of the cross section of the region 3B is formed to have a concave
characteristic as shown in FIG. 6, the frequency characteristic of the piezoelectric speaker at the
45.degree. Position is as shown by the broken line in FIG. Although the directivity is lowered and
the directivity is deteriorated, it is the optimum speaker when listening to music in a narrow
range such as a desktop type speaker. Further, in the regions 3A and 3B, an effect of flattening
the frequency characteristic is also produced by changing the period interval of the wave shape
of the cross section or the curvature of a part of the corner. [Effects of the Invention] As
described above, according to the present invention, a single bimorph diaphragm is used to form
a plurality of areas having different rotation intervals of the wave shape of the cross section to
constitute a piezoelectric speaker, thereby forming a signal band. Since reproduction is divided
into each area, it is equivalent in appearance to reproduce the entire band with one piezoelectric
speaker.
Also, by simultaneously forming the electrode pattern of each region on one bimorph diaphragm
by vapor deposition, processing such as forming into a wave shape, mounting to a frame, etc. can
be performed in one process, and the effect on cost reduction is large. Become.
[0002]
Brief description of the drawings
[0003]
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FIG. 1 is an external view showing an embodiment of a piezoelectric speaker according to the
present invention, FIG. 2 is a schematic view showing an electrode pattern of a bimorph
diaphragm constituting the piezoelectric speaker, and FIG. 3 is the piezoelectric It is a
characteristic view showing the frequency characteristic and impedance characteristic of a
speaker.
FIG. 4 is a schematic view showing an example of the cross-sectional shape of a bimorph
diaphragm applicable to the above embodiment, and FIG. 5 is a frequency characteristic diagram
of a piezoelectric speaker in which the bimorph diaphragm is formed in the shape of FIG. FIG. 6
is a schematic view showing another example of the cross-sectional shape of the bimorph
diaphragm applicable to the above embodiment, and FIG. 7 is a frequency characteristic of the
piezoelectric speaker in which the bimorph diaphragm is formed in the shape of FIG. FIG. FIG. 8
is an external perspective view of a bimorph diaphragm of a conventional piezoelectric speaker,
and FIG. 9 is a schematic view showing the configuration of the above-described inmorph
vibrator and the relationship between each electrode and a signal voltage applied. FIG. 10 is a
schematic view for explaining the operation principle of this piezoelectric speaker. DESCRIPTION
OF SYMBOLS 1 ... Piezoelectric speaker 2 ... Frame 3.30 ... Bimorph diaphragm 4 ... Input terminal
5 ... Low-pass type filter 6.7 ... Transformer 9.10.11 ... Electrode introducing portion 12A, 12B:
electrode pattern 21.22: piezoelectric film 23a, 23b-bending portion 24. 25: electrode! Applicant
Applicant Sony Corporation Attorney Attorney Koike Atsuko Tamura-
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