JPH02141096A - Piezoelectric loudspeaker - Google Patents

Abstract

PURPOSE:To weight respective piezoelectric vibrating parts, to directly input each bit signal of a digitized audio signal, and to reproduce audio by making the respective numbers of the piezoelectric ceramic layers of the plural piezoelectric vibrating parts different to each other. CONSTITUTION:Plural piezoelectric vibrating parts 13-16 driven by each bit signal of the digital input signal are stuck on a diaphragm 11 composed of an elastic body. Further, the respective numbers of piezoelectric ceramic layers 12 interposed between electrodes are made different to each other so that the respective piezoelectric vibrating parts 13-16 can generate sound pressure corresponding to the weight of each bit digit of the digital input signal. Thus, the respective piezoelectric vibrating parts 13-16 can be driven for every bit digit, and a PAM wave, namely, the continuous waveform of an original sound can be reproduced by inputting each bit signal of a binary code to the respective piezoelectric vibrating parts 13-16.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a piezoelectric speaker, and particularly to a digital speaker that 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 modulated into a digital signal by a PCM modulator 1, which is then passed through a transmission, recording, and playback system, and then re-transmitted to a PCM demodulator 2. It was converted into an analog signal and inputted to the speaker 3. As the speaker 3, various electric-to-sound conversion types such as an electromagnetic type, an electrostatic type, or a piezoelectric type are used.

In digital audio systems, analog audio signals are converted into digital signals for transmission, recording, and reproduction, so it is possible to achieve a very high S/N ratio and a large dynamic range.

[Technical Problems to be Solved by the Invention] In conventional digital audio systems, the original sound cannot be reproduced unless an analog audio signal is input to the speaker 3.

Therefore, it was necessary to connect a demodulator such as the PCM demodulator 2 having A/A conversion capability between the transmission/recording/reproduction system and the speaker 3. As a result, since a very expensive PCM demodulator is required, the cost of the entire system becomes quite high, and this becomes a factor that prevents the system from being made smaller, lighter, and lower in power consumption.

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

[Means for solving technical problems]

The present invention is a speaker that utilizes bending vibration caused by piezoelectric effect, and can be driven directly by digitized audio signals.
A plurality of piezoelectric vibrating parts are attached to a diaphragm made of an elastic body, and are driven by each bit signal of a digital input signal.

Each piezoelectric vibrating section may be a single-plate piezoelectric vibrating section configured by forming electrodes on both main surfaces of a piezoelectric ceramic plate, or at least two internal electrodes formed within the piezoelectric ceramic plate. It consists of a laminated piezoelectric vibrating section configured such that a plurality of electrodes are overlapped with each other via a piezoelectric ceramic layer. The number of piezoelectric ceramic layers sandwiched between the electrodes of the plurality of piezoelectric vibrating parts is made to be different from each other so that each piezoelectric vibrating part generates a sound pressure corresponding to the weight of each bit digit of the digital input signal. There is.

[Effect]

The digitized audio signal is in the form of a binary code, and in the present invention, each piezoelectric vibrating part is driven for each bit digit by inputting each bit signal of this binary code to each piezoelectric vibrating part. be done. Each piezoelectric vibrating section is configured to have a different number of piezoelectric ceramic layers interposed between electrodes, so that each piezoelectric vibrating section generates sound pressure corresponding to the weight of each bit digit. has been done. Therefore, the plurality of piezoelectric vibrating parts are directly driven by the digital input signal, and as a result, the continuous waveform of the PAM wave and, ultimately, the original sound is reproduced.

[Explanation of Examples]

FIG. 1 is a perspective view schematically showing a piezoelectric speaker according to an embodiment of the present invention. This embodiment is applied to a digital speaker directly driven by a 5-bit PCM signal.

The rectangular diaphragm 11 is made of an elastic material such as a metal material such as brass. A piezoelectric ceramic plate 12 is attached onto the diaphragm 11 using a conductive adhesive (not shown). The piezoelectric ceramic plate 12 has first to fourth piezoelectric vibrating parts 13 to 16 formed in four equal-area areas by forming electrodes on both main surfaces and inside the piezoelectric ceramic plate 12, which will be described in detail below. Each of the piezoelectric vibrating parts 13 to 1
6 is configured to be driven for each bit digit of the digital input signal.

FIGS. 3(a) to 3(d) show the first to fourth piezoelectric vibrating parts 13.
16 is a sectional view showing the configuration of FIG.

As shown in FIG. 3(a), in the first piezoelectric vibrating section 13, electrodes 13a to 13b are formed on both main surfaces of the piezoelectric ceramic plate 12. As shown in FIG. That is, this piezoelectric vibrating section 13 is in the form of a single-plate piezoelectric vibrating section in which grooves are formed only on both main surfaces of the piezoelectric ceramic plate 12.

On the other hand, as shown in FIG. 3(b), the second piezoelectric vibrating section 1
No. 4 has a structure in which an internal electrode 14a is formed at the center in the thickness direction of the piezoelectric ceramic plate 12, and electrodes 14b and 14c are formed on both main surfaces. electrodes 14b formed on both main surfaces;
14c are electrically connected to each other by a connecting conductive portion 17 shown in FIG. Therefore, the second piezoelectric vibrating section 14 is a laminated piezoelectric vibrating section having two piezoelectric ceramic layers 12a and 12b separated by an internal electrode 14a.

The third and fourth piezoelectric vibrating parts 15 and 16 are also in the form of a laminated piezoelectric vibrating part, similar to the second piezoelectric vibrating part 14. That is, as shown in FIG. 3(c), in the third pressure T4 vibrating section 15, three internal electrodes 15a to 15c are formed in the piezoelectric ceramic plate 12, and electrodes 15d, 15e is formed. The internal electrodes 15b are connected to the electrodes 15 on both main surfaces by the connecting conductive parts (see Figure 1).
d.

15e. Internal electrodes 15a, 1
5c are electrically connected to each other by a connecting conductive portion (formed on a side surface not shown in FIG. 1) and drawn out. Therefore, in the third piezoelectric vibrating section 15, four piezoelectric ceramic layers are constructed by interposing three layers of internal electrodes 15a to 15c within the piezoelectric ceramic plate 12.

Similarly, in the fourth piezoelectric vibrating section 16, seven internal electrodes 16a to 16g are formed within the piezoelectric ceramic plate 12, and eight piezoelectric ceramic layers are configured within the piezoelectric ceramic plate 12. Although not particularly shown, the internal electrode 16
a to 16g are electrically connected to each other every other layer, and among them, internal electrodes 16b, 16d, and 16f are electrically connected to electrodes 16h and 16i on both main surfaces.

In the first to fourth piezoelectric vibrating parts 13 to 16 shown in FIG.
and two piezoelectric ceramic layers are formed. Therefore, when each of the piezoelectric vibrating parts 13 to 16 is driven independently, the sound pressure ratio generated by these parts is 2° l':2''
, 23. This sound pressure ratio was set because
This is to weight the sound pressure of the piezoelectric vibrating sections 13 to 16 in accordance with the weight of each bit digit of the PCM signal.

Next, the driving method of the embodiment shown in FIG. 1 will be explained with reference to FIG. 4. The first to
Electrodes 13b, 14b, 14C connected to one potential of the fourth piezoelectric vibrating parts 13 to 16115b, 15d, 15e
and 16b, 16d.

As shown in FIG. 4, the signal MSB (sign bit) of the maximum bit digit of the 5-bit PCM signal is inverted by an inverter 21 and input to 16f, 16h and 16i.

On the other hand, the lower bit signal is input to the electrode connected to the other potential of the piezoelectric vibrating section that generates the sound pressure corresponding to the weight 211 of the pick finger. That is, the lowest bit signal L
SB is input to the electrode 13a of the first piezoelectric vibrating section, and signals of bit 2, bit 3, and bit 4 are input to the electrode 14a of the second piezoelectric vibrating section and the electrode 14a of the third piezoelectric vibrating section, respectively. 15a, 15c and the electrode 1 of the fourth piezoelectric vibrating section 16
6a, 16c, 16e, 16g.

As a result, when the first to fourth piezoelectric vibrating parts 13 to 16 are driven individually, the sound pressure ratio is 2°:2I:21.7:
2, each piezoelectric vibrating section 13 to 16 generates a sound pressure corresponding to the weight of the bit digit.

Therefore, the sound pressures generated in the first to fourth piezoelectric vibrating sections 13 to 16 are synthesized, and the digitized audio signal is converted into a sound wave.

However, as it is, the waveform of the reproduced sound is PAM
It becomes a wave. Therefore, in order to get the sound closer to the original sound, it is preferable to combine a low-pass filter that passes the sampling frequency band of 172 or less, or to place an acoustic low-pass filter in front of the speaker. That is, by combining such low-pass filters or acoustic low-pass filters, a continuous sound pressure waveform can be obtained.

In addition, in the said Example, the electrodes 13b, 14c, 15e of the lower surface of the 1st - 4th piezoelectric vibrating part.

16i does not necessarily need to be formed separately as shown in FIG. 1, and may be a common electrode.

Next, an embodiment will be described in which the areas of the plurality of piezoelectric vibrating parts are also made different to weight the sound pressure generated by each of the eight moving parts in one pressure layer.

As shown in FIG. 5, in the second embodiment, a piezoelectric ceramic plate 12 is attached to a diaphragm 11 made of an elastic material.
, first to fourth piezoelectric vibrating parts 23 to 26 whose areas are not necessarily equal are formed.

The electrode configuration of the first to fourth piezoelectric vibrating parts 23 to 26 is
They are shown in Figures (a) to (d), respectively. In addition, Fig. 3(a)
Parts corresponding to the structures in ~(d) will be given corresponding reference numbers and their explanation will be omitted.

In this embodiment, the first and second piezoelectric vibrating parts 23 and 24 are constructed in the same manner as in the embodiment shown in FIG. That is, although the first and second piezoelectric vibrating parts 23 and 24 are configured in areas of equal area (see FIG. 5), in the second piezoelectric vibrating part 24, by forming the internal electrode 24a, , weighting is performed by changing the number of piezoelectric ceramic layers in both.

On the other hand, the third piezoelectric vibrating section 25 has only one internal electrode 25a like the second piezoelectric vibrating section.

However, the area of the third piezoelectric vibrating section 25 is twice as large as that of the second piezoelectric vibrating section 24 (see FIG. 5). Although the number of layers is the same, the third piezoelectric vibrating section 25 is capable of generating twice the sound pressure as the second piezoelectric vibrating section 24.

Furthermore, in the fourth piezoelectric vibrating section 26, two internal electrodes 2
6a, 26b are formed, and the piezoelectric ceramic plate 12 is
The layers are divided into piezoelectric ceramic layers. Furthermore, the fourth
The piezoelectric vibrating part is configured to have eight layers and three times the area of the first and second piezoelectric vibrating parts ζ (see FIG. 5).

Therefore, the fourth piezoelectric vibrating section 26 weighted by both the number of laminated layers and the area ratio can generate a sound pressure (3X8/3)=2' times that of the first piezoelectric vibrating section 23. has been done.

As described above, in the second embodiment, in order to make the sound pressure of each piezoelectric vibrating part 2° l':2'':2', the number of piezoelectric ceramic layers of the plurality of piezoelectric vibrating parts is changed. Not only that, but its area has also changed.

As described above, in the present invention, in addition to weighting by changing the number of piezoelectric ceramic layers, a method of weighting by changing the area ratio may also be adopted.

In the embodiments described above, each piezoelectric vibrating part was constructed by forming the electrodes and internal electrodes as described above on one piezoelectric ceramic plate, but each piezoelectric vibrating part was constructed by forming the above-mentioned electrodes and internal electrodes on a single piezoelectric ceramic plate. It may also be composed of a piezoelectric vibrator. That is, the piezoelectric speaker of the present invention can also be constructed by separately attaching the laminated or single-plate piezoelectric vibrators constituting the piezoelectric vibrating section to the diaphragm 11.

Furthermore, in the above embodiment, the 5-bit PCM signal is
Although we have explained the case of acoustic conversion, 8 bits other than 5 bits
The present invention can also be applied to the case of reproducing digital signals of other bit numbers such as 16 bits and 16 bits. In that case, the digitized audio signal can be directly converted into audio in the same way as described above by simply changing the number and weighting of each piezoelectric vibrating section according to the number of bits.

In addition, the present invention can be applied to converting a digital signal using a modulation method other than PCM modulation into audio.

Further, the planar shape of the piezoelectric vibrating portion and the elastic body is not limited to the rectangular shape shown in the drawings, but may be any shape such as a disk shape.

〔Effect of the invention〕

As described above, in the present invention, by making the number of piezoelectric ceramic layers of a plurality of piezoelectric vibrating parts different from each other, each piezoelectric vibrating part generates a sound pressure corresponding to the weight of each bit digit of a digital input signal. Since each bit signal of the digitized audio signal is directly input to a plurality of weighted piezoelectric vibrating sections, audio can be reproduced.

Therefore, you can obtain high-quality playback sound just by connecting directly to an amplifier that outputs digital signals, and you can
It becomes possible to omit the M demodulator. Therefore, the price of the digital audio system can be effectively reduced, and the system can be made smaller, lighter, and consume less power.

Furthermore, since it has a relatively simple structure in which multiple piezoelectric vibrating parts are arranged on a diaphragm made of an elastic material, and the number of piezoelectric ceramic layers is different from each other, it is excellent in mass production, and is therefore low cost and A digital speaker with excellent reliability can be realized.

[Brief explanation of the drawing]

FIG. 1 is a perspective view for explaining the outline of the first embodiment of the present invention, FIG. 2 is a block diagram for explaining the digital audio system, and FIGS. 3(a) to (d) are , respectively, are cross-sectional views for explaining the structures of the first to fourth piezoelectric vibrating parts, FIG. 4 is a block diagram for explaining the method of driving the embodiment of FIG. 1, and FIG. The plan view and FIGS. 6(a) to 6(d) for explaining the second embodiment are sectional views of the first to fourth piezoelectric vibrating parts of the second embodiment, respectively. In the figure, 11 is a diaphragm, 12 is a piezoelectric ceramic plate,
13 to 16 are first to fourth piezoelectric vibrating parts, 12a to 12
b is a piezoelectric ceramic layer, 13a, 13b, 14a to 14
c, 15a to 15e, and 16a to 16i indicate electrodes. Figure 1 Figure 2

Claims (1)

[Claims] A speaker that utilizes bending vibration caused by piezoelectric effect, comprising: a diaphragm made of an elastic body; and a diaphragm attached to the diaphragm and driven by each bit signal of a digital input signal. Each of the piezoelectric vibrating parts includes a single-plate type piezoelectric vibrating part in which electrodes are formed on both main surfaces of a piezoelectric ceramic plate, or at least one internal electrode is formed in the piezoelectric ceramic plate. It consists of a laminated piezoelectric vibrating section in which a plurality of electrodes are overlapped via two piezoelectric ceramic layers, and the plurality of piezoelectric vibrating sections are arranged such that each piezoelectric vibrating section generates a sound pressure corresponding to the weight of each bit digit of the digital input signal. A piezoelectric speaker characterized in that the number of piezoelectric ceramic layers sandwiched between electrodes of a vibrating part is different from each other.