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BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1a and 1b are side views showing the operation of
a piezoelectric ceramic, and FIG. 2 is a perspective view of the device of the present invention. □
-21 is a support, 23.24 is a lead wire.
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the improvement
of a direct emission speaker having a piezoelectric ceramic. Piezoelectric ceramic performs the
function of piezoelectric body by performing a polarization operation to align the polarization
direction of each domain by applying a direct current type IE in the thickness direction as is well
known. And by applying an electric field in the thickness direction, the shape is changed, and an
electro-mechanical or: mechanical-electrical conversion action is performed. In order to use such
a piezoelectric ceramic as a speaker vibration) 3) 12 plate, as shown in FIG. 1 (a), two
piezoelectric ceramic element f plates 1.1 are opposed to the same pole. It is suitable to use a
laminated bimorph-type piezoelectric ceramic, or a structure in which a piezoelectric ceramic
element plate l is adhered to a metal plate 2 as shown in FIG. 1 (b). 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 / resist refers to those of the
two configurations. When adopting such a piezoelectric ceramic for a direct radiation type
speaker, the following drawbacks must be solved. That is, since the piezoelectric ceramic has an
extremely sharp Q at its resonance frequency, the reproduction bandwidth is extremely narrow,
and it may be adopted as a speaker for reproducing the extremely limited frequency band of the
tweeter-1 or the spout eater. Have difficulty. 3) Attempts have been made to attach an elastic
material with large internal loss to one surface of the piezoelectric ceramic to lower Q at the
resonance frequency and thereby expand the reproduction band, but the drawback is that the
acoustic radiation efficiency is low There is. This invention combines a plurality of piezoelectric
ceramics having different resonance frequencies to solve the above-mentioned disadvantages of
the prior art, and staggers the resonance frequencies of the respective piezoelectric ceramics,
thereby losing acoustic radiation efficiency. The embodiment shown in FIG. 2 will be described in
detail below, which is capable of reproducing a wide band without any problem. In FIG. 2,
reference numeral 21 denotes a support, which is suitably made of a relatively hard material
such as plastic. Reference numerals 22a, 22b and 22c 122d denote piezoelectric ceramics
attached to one surface of the support 21 with a rubber adhesive or the like, and the dimensions
of the respective piezoelectric ceramics are different from each other. Reference numerals 23
and 24 denote lead wires for applying an audio signal to each of the piezoelectric ceramics 222
to 22d. In the figure, the respective piezoelectric ceramics are connected in parallel, but they may
be connected in series.
Then, when an audio signal is input to the lead wire 23.24, each piezoelectric ceramic vibrates
and emits a sound wave corresponding to the audio signal to the atmosphere. According to such
a configuration, the smaller the size of the resonant frequency of the piezoelectric ceramic, the
higher the resonant frequency, ie, the higher the resonant frequency than the piezoelectric
ceramic 22a. Then, if the dimensions of each piezoelectric ceramic are determined so that the
resonance frequency of each piezoelectric ceramic is generated continuously in a staggered
manner, the reproduction frequency band can be expanded by generating the resonance
frequency continuously. It becomes. The shape of the piezoelectric ceramic is not limited to the
square as shown in the embodiment, but can be various shapes such as circular, short and the
like, and the resonance frequency is different depending on the shape, so the piezoelectric
ceramic of the various shapes described above Can also be combined. Also, as shown in the
embodiment i'c, the respective rice-ceramics are not limited to being disposed in a plane, and
when the curved surface or 5 is disposed in a spherical shape, the directivity can be improved.
Furthermore, although the configuration of this invention makes low-frequency reproduction
possible without lowering the acoustic radiation efficiency, the use of an elastic material such as
butyl rubber for the support 21 can further flatten the frequency characteristics. Although some
efficiency losses occur, it is possible to make it even flatter. As described above, according to the
present invention, by arranging a plurality of piezoelectric ceramics different in size or shape on
one support, the resonance frequencies of each clay dragon ceramic are coupled in a staggering
manner, and if broadband reproduction is possible. It has a very good advantage in practical use.
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