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BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows an embodiment of a piezoelectric alarm
according to the present invention, FIG. 1 is a plan view thereof, and FIG. 2 is a cross-sectional
view taken along the line AA 'of FIG. FIG. 3 is a sound pressure waveform diagram of the
piezoelectric alarm device shown in FIG. 1 and FIG. 1 ... 1st piezoelectric vibrator, 2 ... 2nd
piezoelectric vibrator, 3 ... 1st piezoelectric element, 4 ... 2nd piezoelectric element, 5 ... 1st metal
Plate 6 6 second metal plate 7 first diaphragm 8 'second diaphragm 10 reflector 10.
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a piezoelectric
alarm that causes a piezoelectric vibrator to be bent and vibrated in an electric circuit to produce
sound, and the purpose of the invention is to use a large volume and low frequency, cp (1) An
object of the present invention is to provide a piezoelectric alarm that emits an audible sound to
be felt. The piezoelectric alarm that senses a large volume and a low frequency as mentioned
here is, for example, a horn such as a car horn whose sound pressure is about 1 meter ahead and
whose fundamental frequency is several hundred Hz, or 1 m ahead. It refers to something with
similar performance. Conventionally, a piezoelectric alarm is generally known as a piezoelectric
buzzer, but the volume of the generated sound is at most 100, II * at 1 m ahead, and the timbre is
a simple tremor with a resonance frequency of 2 touch to 4 touch. Therefore, in the prior art,
there has been no piezoelectric alarm that can be put to practical use as the automotive horn. In
order to achieve the above object, the present invention improves the sound generation structure
with respect to sound pressure, and uses the beat phenomenon generated by each single
vibration audible sound by bending and vibrating two piezoelectric vibrators with respect to
timbre. It is An embodiment of the present invention will be described with reference to the
drawings. In the figure, reference numerals 1 and 2 denote composite piezoelectric vibrators
(hereinafter simply referred to as vibrators) for efficiently converting radial vibration energy of
the piezoelectric element into sound (2) echo energy. The vibrators l and 2 are piezoelectric
elements 3.4 obtained by polarization processing of porcelain such as zircon and lead titanate in
the thickness direction, and radial expansion and contraction due to the electrostrictive effect of
the piezoelectric elements 3.4 oil for thickness direction It consists of a metal plate 5.6 for
vibration and a diaphragm 7.8 for sound pressure amplification, and they are integrated by
bonding with an adhesive via the metal plate 5.6. In the electroacoustic transducer of such
structure, the inserted metal plate 5.6 acts as a mechanical impedance matching device, and the
relatively small royal element 3.4 can also drive the large diaphragm 7.8. . In the present
embodiment, the diaphragm 7.8 is drawn and curved in the peripheral portion in order to
prevent the reduction of the sound output due to the phenomenon of the phenomenon. The
difference between the vibrator 1.2 is that the sizes of the diaphragm 7 and the diaphragm 8 are
slightly different, which is a feature of this invention. An electric circuit 9 vibrates the vibrators 1
and 2 at their respective (3) natural bending frequencies. A reflector 10 for increasing sound
pressure is formed with a recess at the center of the front surface, and after the electric circuit 1
is accommodated in the recess, the reflector 10 is closed so as to fill the recess with a light
plating agent.
The shape of the reflector 10 may be a flat plate or a horn, but a curved shape similar to the
diaphragm as shown in the figure, that is, the peripheral portion is concave toward the front, is
preferable. 12 is a support for coupling the vibrator 1 and the reflector 10, and 13 is a support
for coupling the vibrator 1 and the vibrator 2 and is adhered to the inside of the portion at the
time of resonance of the vibrator. It becomes an elastic body such as a sponge body. In the above
component, the first vibrator l is supported on the front surface of the reflector 10 with an
appropriate interval determined by the 14 bending frequency such that the peripheral curved
shape is concave toward the front surface. And the second vibrator 2 has a suitable interval
determined by the bending frequency such that the curved shape of the peripheral portion is
concave toward the front, and the front surface of the first vibrator 1 is disposed. (4) The first
vibrator l is disposed via the support 13 so as to also serve as a reflector of the second vibrator 2.
Regarding the sound pressure in the above configuration, first, the first oscillator l is a
modification of the structure of the oscillator itself, the effect of the reflector 10, and the outer
diameter of the second oscillator 2 is smaller than that of the first oscillator 1 (The second
vibrator 2 is disposed to cover the front surface of the first vibrator 1), but the sound pressure
emitted from the first vibrator l is large enough to achieve the original purpose. It can be
reached. (The value is substantially the same as when the second vibrator 2 is not disposed on
the front. The sound pressure emitted by the second vibrator 2 is large due to the structural
improvement of the second vibrator 2 and the function and effect of the first vibrator l as a
reflector. (In spite of being smaller than the first vibrator 1) is approximately the same as the
sound pressure emitted from the first vibrator l. It is important to the tone described next that
the central sound pressure is almost the same level. When the timbre is described, the first
vibration (5) moving element 1 and the second vibrator 2 have different diameters of
diaphragms, so their natural frequencies are different. And the sound which each emits alone is a
high frequency single treble noise. However, when it vibrates at the same time, due to the beat
phenomenon produced by each single tremor, it is felt to human auditory sense as a sound with a
low frequency difference of each frequency. Furthermore, what is important here is that the
sound pressure emitted from the two transducers is almost the same level. If this level is
different, the beat phenomenon will not be felt as the distance from the sound source is
separated, it will become one single treble sound with high sound pressure level. However,
according to the present invention, as described above, since the sound pressure levels emitted
from the two vibrators are substantially the same value, it can be perceived as a sound having a
low difference in frequency regardless of the position from the sound source .
One numerical example of the present invention is shown as a piezoelectric element 3.4 obtained
by polarizing a zircon-shaped lead titanate ceramic with an outer diameter of 361111B and a
thickness of 0.5ff in the thickness direction, an outer diameter of 5QwmB as a metal plate 5.6,
Thickness 0.51 III brass plate, outer diameter 92 mfll as diaphragm 7 (6) Flat plate portion 59
mg (peripheral portion is curved shape), brass plate of thickness 0 ° 3 N, and as diaphragm 8,
outer diameter 35 mB, flat plate portion 50 鰭 (peripheral portion is curved shape), brass plate of
thickness 0.3 ff , Which are bonded with an epoxy adhesive to form the vibrator 1, 2, and the
reflector 10 with an outer diameter of 95 mB (the peripheral part is a curved shape) through the
5 N thick support 12 on the front surface In the case where the first oscillator 1 is disposed and
the second oscillator 2 is further disposed between the first oscillator 1 and the support 13
having a 3ff thickness, the electric excitation input is 2 W and 1 m forward The maximum sound
pressure reached about 117 when the first vibrator 1 was used alone and the 114 dB% of the
second vibrator 2 alone was used. In addition, each natural frequency is 280 (Hb, 3100 H 2, and
therefore, it is perceived as low frequency sound of 3100 nz-2800 H 2-300 H 2 to human
hearing. As described above, according to this invention, improvement of the sound generation
structure and bending vibration of the two vibrators are used (7) to utilize the beating
phenomenon generated by each single tremor, so even in the piezoelectric alarm device The
effect is that I can emit an audible sound that feels at high volume and low frequency. Therefore,
the practical and excellent effect that the application of the piezoelectric alarm can be extended
to fields such as automotive horns? Play.