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JPS5633890

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DESCRIPTION JPS5633890
BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1a and 1b are side views showing the operation
of a piezoelectric ceramic, FIG. 2 is a perspective view of the present invention, and FIG. 3 is a
sectional view of the same. 21 is a support, 22 is a piezoelectric ceramic.
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the improvement
of a direct emission speaker having a piezoelectric ceramic. As is well known, the piezoelectric
ceramic is made as a piezoelectric body by performing a polarization operation in which the
polarization direction of each domain is aligned by applying a direct current electrode in the
thickness direction of the ceramic. And by applying an electric field in the thickness direction, the
shape is changed to perform an electro-mechanical or mechanical-electrical conversion
operation. In order to use such a piezoelectric ceramic as a vibration O2 plate of a speaker, as
shown in FIG. 1 (a) iC, two piezoelectric ceramic '7' element plates 1.1 are opposed to the same
poles. A bimorph-type piezoelectric ceramic bonded to each other or a structure in which the
piezoelectric ceramic element plate 1 is bonded to the metal plate 2 as shown in FIG. 1 (b) is
suitable. This is because the piezoelectric ceramic having such a configuration vibrates so that its
central portion is curved by applying an AC signal (audio signal) to both electrodes, and as a
result, it emits an acoustic wave. Therefore, in the following description, the piezoelectric ceramic
refers to the two configurations. When adopting such a piezoelectric ceramic for a direct
radiation type speaker, the following drawbacks must be solved. First, the piezoelectric ceramic
has an extremely narrow and sharp Q at its resonance frequency, so the reproduction bandwidth
is extremely narrow, and it is for re-tapping a very limited frequency band like a tweeter-1 or a
spout eater. It is also difficult to adopt it as a speaker. Second, the manual impedance of the
piezoelectric ceramic is extremely large (for example, in a bimorph type piezoelectric ceramic
with a thickness of 04 to 0.5), the manual impedance at 20 KH2 is about IK.OMEGA. And further
increases as the frequency decreases. Therefore, when connected to a conventional audio
amplifier, an adverse effect due to impedance mismatching occurs. And, to prevent this, it is
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necessary to intervene an impedance matching device between them. This invention solves the
drawbacks of the above-mentioned conventional example, and the embodiment of FIGS. 2 and 3
will be described in detail below. In FIG. 2, reference numeral 21 denotes a support serving as a
base for arranging and holding the piezoelectric ceramic 22 and is made of an elastic material
such as butyl rubber (thickness 6). Then, a plurality of mold ceramics 22 are attached to one
surface of the support 21 with a rubber adhesive or the like. One surface of each piezoelectric
ceramic 22 is electrically connected by a lead 4 wire 23, and the other surface of each L is
electrically connected by a lead 24.
That is, each piezoelectric ceramic 22 is connected in parallel to human power. Then, when an
audio signal is input to the lead wire 23.24, each piezoelectric element exhibits bending vibration
and emits an acoustic wave into the atmosphere. According to the above configuration according
to the present invention, since one surface of each of the piezoelectric ceramics 22 is in close
contact with the elastic member 21, the energy absorption action of the elastic member dumps Q
at the resonance frequency. This enables the reproduction bandwidth to be expanded even
though the reproduction level is reduced. Furthermore, since the back surface of the piezoelectric
ceramic 22 is in close contact with the support, the emission of sound waves from the back
surface of the piezoelectric ceramic 22 can be prevented. Also, by connecting the respective
piezoelectric ceramics in parallel, the manual impedance is reduced equivalently, and as a result
of the improvement of the impedance manner 5 with the audio amplifier, the acoustic conversion
efficiency is improved. As described above, while the in-transit piezoelectric ceramic can not be
applied as a direct radiation type speaker because of high Q of resonance and high human
impedance, this device dumps Q of resonance and input impedance As it could be made smaller,
it could be adopted as a diaphragm of a direct radiation type speaker.
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