JPH0777478B2 - Piezoelectric speaker - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric speaker, and more particularly to a digital speaker which can be directly driven by a digitized audio signal such as a PCM signal.

[Conventional technology]

As shown in FIG. 2, in a digital audio system, an audio signal in the form of an analog signal is converted into a PCM modulator 1
Was modulated into a digital signal, passed through a transmission / recording / playback system, and again converted into an analog signal by the PCM demodulator 2 and input to the speaker 3. As the speaker 3, various electro-acoustic conversion types such as an electromagnetic type, an electrostatic type and a piezoelectric type are used.

In a digital audio system, an analog voice signal is converted into a digital signal for transmission / recording / reproduction, so that a very high S / N ratio and a large dynamic range can be realized.

[Technical problem to be solved by the invention]

In the conventional digital audio system, the original sound cannot be reproduced unless an analog audio signal is input to the speaker 3. Therefore, a demodulator with D / A conversion capability such as the PCM demodulator 2 can be transmitted, recorded, and
It was necessary to connect between the reproduction system and the speaker 3. As a result, a very expensive PCM demodulator is required, which considerably increases the cost of the entire system, and is a factor that hinders downsizing, weight reduction, and power consumption reduction of the system.

An object of the present invention is to provide a digital speaker that can directly input a digitized audio signal and reproduce an original sound.

[Means for solving technical problems]

The present invention is a speaker that utilizes flexural vibration due to the piezoelectric effect, and can be directly driven by a digital audio signal. In the speaker of the present invention,
A piezoelectric vibrating element is attached to the elastic vibrating plate, and the piezoelectric vibrating element has a plurality of piezoelectric vibrating portions that are driven for each bit signal of a digital input signal. Further, the thickness of the plurality of piezoelectric vibrating portions is different from each other so that each piezoelectric vibrating portion generates a sound pressure corresponding to the weight of each bit digit of the digital input signal.

[Action]

The digitized audio signal is in the form of a binary code, and in the present invention, by inputting each bit signal of this binary code to each piezoelectric vibrating section, each piezoelectric vibrating section is driven for each bit digit. To be done. The thickness of each piezoelectric vibrating portion is different from each other so that each piezoelectric vibrating portion generates a sound pressure corresponding to the weight of each bit digit. Therefore, multiple piezoelectric vibrating parts are directly driven by the digital input signal, and as a result, PA
The M wave and then the original sound waveform is reproduced.

[Explanation of Examples]

1 (a) and 1 (b) are a sectional view and a plan view of a piezoelectric speaker according to an embodiment of the present invention.

The present embodiment is applied to a digital speaker for direct driving with a 5-bit PCM signal.

First to fourth piezoelectric vibrating bodies 12 to 15 are attached to a rectangular elastic vibrating plate 11 made of a metal material such as brass using a conductive adhesive (not shown). The first to fourth piezoelectric vibrating bodies 12 to 15 respectively constitute the piezoelectric vibrating portion of the present invention.

The piezoelectric vibrators 12 to 15 are made of the same piezoelectric ceramic material and have a structure in which electrodes are formed on both main surfaces of the piezoelectric ceramic. As clearly shown in FIG. 1 (a), the thicknesses of the piezoelectric vibrating bodies 12 to 15 are different from each other. This difference in thickness is provided so that when each piezoelectric vibrating body 12 to 15 is driven for each bit digit of the digital input signal, a sound pressure corresponding to the weight of the bit digit is generated as described later. This is to enable That is, in this embodiment,
Sound pressure ratio of the first to fourth piezoelectric vibrator 12 to 15 when it was driven by a alone, 2 ^0: 2 ^1: 2 ^2: to be 2 ^3, respective thicknesses are selected.

A lead wire 21 is connected to the elastic diaphragm 11.
The lead wire 21 is connected to the piezoelectric vibrating body 12 via the elastic vibrating plate 11.
Are electrically connected to the electrodes 12a to 15a on the lower surface of.
Further, the lead wires 22 to 25 are electrically connected to the electrodes 12b to 15b on the upper surfaces of the first to fourth piezoelectric vibrating bodies 12 to 15, respectively.

The elastic diaphragm 11 may be made of an insulating material, or the piezoelectric vibrators 12 to 15 may be attached to the elastic diaphragm 11 using an insulating adhesive such as an epoxy resin. The electrical extraction from the electrodes 12a to 15a on the lower surface of the piezoelectric vibrating bodies 12 to 15 may be performed individually and a common potential may be given by connecting the lead wires.

Next, the driving method of the above embodiment will be described. As shown in FIG. 3, the MSB of the 5-bit PCM input signal
The (sign bit) is inverted by the inverter 26 and input from the lead wire 21 to the electrodes 12a to 15a on the lower surface of the piezoelectric vibrating bodies 12 to 15. On the other hand, the electrodes 12b-1 on the upper surface side of each piezoelectric vibrating body 12-15
Bit signals (LSB bit, bit 2, bit 3, bit 4) of each bit digit are input to the lead wire 5b through the lead wires 22 to 25.

Each of the piezoelectric vibrators 12 to 15 has a sound pressure ratio when driven independently.
Since the thickness is made different so that it becomes 2 ⁰ : 2 ¹ : 2 ² : 2 ³ , by inputting each bit signal as described above, the piezoelectric vibrators 12 to 15 are set to the weight of the bit digit. Generates a corresponding sound pressure.

Therefore, the sound pressures generated by the first to fourth piezoelectric vibrating bodies 12 to 15 are combined to convert the digitized sound signal into a sound wave.

However, the waveform of the sound reproduced as it is becomes a PAM wave. Therefore, in order to bring the sound closer to the original sound, it is preferable to combine a low-pass filter that passes a band of 1/2 or less of the sampling frequency, or arrange an acoustic low-pass filter in front of the speaker. That is, by combining such a low-pass filter or an acoustic low-pass filter, the PAM wave can be made into a continuous sound pressure waveform.

In the embodiment shown in FIG. 1, the piezoelectric vibrating element is composed of a plurality of piezoelectric vibrating bodies.
Although it is composed of 12 to 15, a piezoelectric vibrating portion having a plurality of thicknesses may be composed of the integral type piezoelectric vibrating element 31 as shown in FIG. That is, the piezoelectric vibrating element 31 shown in FIG. 4 has a plurality of steps 31 on the upper surface side of one piezoelectric ceramic.
Parts 32-35 that form a-31c and are separated by steps 31a-31c
, Each of which constitutes a plurality of piezoelectric vibrating portions. The other structure is the same as that of the embodiment shown in FIG.

Further, in the embodiment shown in FIG. 1, a plurality of piezoelectric vibrating bodies 12 to 15 each having a rectangular planar shape are pasted on the rectangular elastic vibrating plate 11, but the planar shapes of the elastic vibrating plate and the piezoelectric vibrating body are also as described above. It is not limited to those. For example, FIG.
As shown in (b) and (c), a disk-shaped elastic diaphragm 41
Piezoelectric vibrating parts 42 to 45 may be formed on the upper surface of the piezoelectric vibrating parts 42 to 45 divided into four shapes such as a fan shape and a triangle.

Also in the modification shown in FIGS. 5A to 5C, each piezoelectric vibrating body 42 to 45 may be formed by using a separate piezoelectric vibrating body, as in the embodiment of FIG. You may comprise using the integrated piezoelectric diaphragm.

Further, as shown in FIG. 5 (d), a disc-shaped first piezoelectric vibrating body 42 is arranged at the center on a disc-shaped elastic vibrating plate 41,
The second to fourth piezoelectric vibrating bodies 43, which are annularly concentric with the periphery,
It may be a structure in which 45 is formed.

That is, as is clear from FIGS. 5 (a) to (d),
The planar shapes of the elastic vibration plate and the piezoelectric vibration element in the present invention can be changed to any shapes as needed.

Further, in the above-described embodiment, the case of performing acoustic conversion of a 5-bit PCM input signal has been described, but it is also possible to reproduce a digital signal having another number of bits such as 8 bits and 16 bits other than 5 bits. The present invention can be applied.
In that case, it is possible to directly convert the digitized voice signal into voice just by changing the number and weighting of the piezoelectric vibrating portions according to the number of bits.

The present invention can be applied to the case of converting a digital signal of a modulation method other than PCM modulation into voice.

〔The invention's effect〕

As described above, in the present invention, the thicknesses of the plurality of piezoelectric vibrating plates are different from each other and are weighted, and each bit signal of the digitized audio signal is directly applied to the plurality of weighted piezoelectric vibrating portions. By inputting, the sound can be reproduced. Therefore, a high-quality reproduced sound can be obtained and the expensive PCM demodulator can be omitted simply by connecting directly to the amplifier that outputs the digital signal. Therefore, the price of the digital audio system can be effectively reduced, and the size of the system can be reduced.
The weight and power consumption can be reduced.

Furthermore, because it has a relatively simple structure in which multiple piezoelectric vibrating parts are arranged on the elastic vibration plate and the thicknesses of the vibrating parts are different from each other, it is excellent in mass productivity and therefore low in price and excellent in reliability. It is possible to realize a digital speaker.

[Brief description of drawings]

1 (a) and 1 (b) are a sectional view and a plan view of an embodiment of the present invention, FIG. 2 is a block diagram showing an outline of a digital audio system, and FIG. 3 is an embodiment of FIG. FIG. 4 is a block diagram for explaining a driving method, FIG. 4 is a sectional view for explaining another embodiment of the present invention, and FIG.
(D) is each top view for demonstrating the modification of the planar shape of an elastic diaphragm and a piezoelectric vibrating part, respectively. In the figure, 11 and 41 are elastic bodies, and 12 to 15 and 42 to 45 are piezoelectric vibrating bodies forming the first to fourth piezoelectric vibrating portions.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yo Yo Ando Tenjin, Nagaokakyo City, Kyoto Prefecture 26-26-10 Murata Manufacturing Co., Ltd. (72) Inventor Hiroshi Tamura 2-26-10 Tenjin, Nagaokakyo City, Kyoto Stock Company Murata Manufacturing Co., Ltd. (56) Reference Japanese Patent Laid-Open No. 2-113797 (JP, A) Japanese Patent Laid-Open No. 58-121897 (JP, A) Japanese Utility Model Sho 59-122000 (JP, U)

Claims (1)

[Claims] 1. A speaker using flexural vibration due to a piezoelectric effect, comprising: an elastic diaphragm, and a plurality of piezoelectric vibrating sections driven for each bit signal of a digital input signal, and on the elastic diaphragm. And a piezoelectric vibrating element attached to the piezoelectric vibrating section, wherein each of the piezoelectric vibrating sections generates a sound pressure corresponding to the weight of each bit digit of the digital input signal, the plurality of piezoelectric vibrating sections have different thicknesses. Piezoelectric speaker characterized by being