JPH0410797B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a resonant piezoelectric speaker.

A conventional piezoelectric speaker uses a piezoelectric conversion mechanism to drive a diaphragm to generate sound waves. In this type of piezoelectric speaker, in order to obtain flat frequency characteristics, the resonant frequency of all the vibrating bodies including the diaphragm driven by the piezoelectric body is removed from the reproduction frequency range, making it a non-resonant type. The piezoelectric material was directly driven by a fundamental wave electric signal in the reproduction frequency band, and the acoustic output was obtained by air vibration based on this.

The piezoelectric speaker described above has low efficiency because it is a non-resonant type, and the overall structure of the speaker is complicated, including the piezoelectric body, the diaphragm support structure, and their coupling structure, and it is especially difficult to reproduce low frequencies. The diaphragm must be made larger in proportion to the wavelength, making the speaker large and making it difficult or impossible to put it into practical use.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a resonant piezoelectric speaker that is small, lightweight, highly efficient, and has sharp directivity, which is constructed without using acoustic radiation from a diaphragm as in the prior art.

That is, the present invention emits ultrasonic waves whose amplitude is modulated by an audible sound into the air using a piezoelectric material, and obtains an acoustic output by the nonlinear action of the air. A piezoelectric material having a structure is made to self-oscillate at a frequency in the ultrasonic range, and audio input is applied to the pair of main electrodes.

Embodiments of the present invention will be described in detail below with reference to the drawings.

In FIG. 1, P is a piezoelectric body, and the piezoelectric body P
Main electrodes are formed on both sides of the main electrode 11.
A return electrode 12 insulated from the main electrode 11 is formed on one surface including the main electrode 11 . Return electrode 12 of piezoelectric body P
The main electrode 13 on the other side is connected to the input terminals 3 and 4 of the amplifier A, respectively, and the output terminal 5 of the amplifier A is connected to the main electrode 11 of the voltage body P so that the piezoelectric body P self-oscillates. It is configured. Moreover, the piezoelectric body P and the amplifier A are set to self-oscillate at a frequency in the ultrasonic range. on the other hand,
The audio input terminals 1 and 2 are connected to main electrodes 11 and 13 of the piezoelectric body P via a low-pass filter F having an attenuation characteristic of -12 dB/octave and a variable resistor R.

Then, with the piezoelectric body P self-oscillating with ultrasonic waves, if an audio signal is applied from the input terminals 1 and 2 to the main electrodes 11 and 13 of the piezoelectric body P through the low-pass filter F and the variable resistor R, the amplitude will be determined by the audio signal. The modulated ultrasonic waves are emitted from the piezoelectric body P and propagate in the air, and audible sound is extracted due to the nonlinear effect of the air serving as a propagation medium.

In the above embodiment, the piezoelectric body P is composed of a bending vibration type piezoelectric body, such as a unimorph made by bonding a piezoelectric plate and a metal plate, or a bimorph made by bonding two piezoelectric plates. It may also be provided.

Since the present invention is configured as described above, various effects as described below can be obtained.

Since it uses a piezoelectric material with an ultrasonic frequency, it can be constructed in a compact size.

It is highly efficient because it uses the resonance frequency of the piezoelectric material.

It uses ultrasonic energy in the air, so it has sharp directivity.

Sounds in lower frequency ranges are easier to play.

It can be used for audio output from radios, tape recorders, electronic musical instruments, voice synthesis equipment, etc., and is compatible with conventional speakers.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram for explaining a resonant piezoelectric speaker according to the present invention. P is a piezoelectric body, A is an amplifier, 1 and 2 are audio input terminals, 11 and 13 are main electrodes, and 12 is a return electrode.

Claims (1)

[Claims] A piezoelectric body having a pair of main electrodes and a return electrode is caused to self-oscillate at a frequency in the ultrasonic range, and an audio input is applied to the pair of main electrodes so that ultrasonic waves whose amplitude is modulated by the sound are radiated from the piezoelectric body. A resonant piezoelectric speaker characterized by: