JPH0241986Y2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to a piezoelectric speaker that uses a bending diaphragm made by bonding a piezoelectric ceramic plate to an elastic thin plate as a sound source, and aims to improve the sound pressure in the mid-low range and flatten the frequency response. That is.

The method of bonding a piezoelectric ceramic plate to an elastic thin plate to generate flexural vibration and use it as a sound source has many advantages such as no contact, long life, low current operation, and thinness, and it is better than conventional methods. Widely used as a piezoelectric buzzer.

However, in the past, the frequency of the generated sound was often 2KHz or higher.
On the other hand, as synthetic sound generation and synthetic melodies have recently been realized using LSI, their application as speakers has attracted attention, and it has become essential to obtain high sound pressure over a wider sound range than before. In particular, it is most important to improve the sound pressure in the low frequency range, which has been difficult with conventional piezoelectric buzzers.

FIG. 1 shows an example of a diaphragm (hereinafter referred to as a piezoelectric sounding element) in which a piezoelectric ceramic plate 2 is bonded to an elastic thin plate 1. In addition. 3 is a lead wire for applying a driving voltage to the electrodes 4 provided on the front and back sides of the piezoelectric ceramic plate 2. As shown in FIG. Further, FIG. 2 shows an example of the sound pressure frequency characteristic when this element is supported around the periphery. As described above, conventional piezoelectric sounding elements lack the sound pressure of 500 to 1300 Hz, which is essential for the reproduction of voices and melodies, and it is most important to improve the sound pressure in this frequency range.

Therefore, there is generally a method of lowering the natural resonance frequency of the piezoelectric sounding element by increasing its radius, decreasing its thickness, or decreasing its Young's modulus, and various ideas have been made to realize this. There is.

However, this method currently has many constraints such as the shape, material, and manufacturing of the piezoelectric sounding element, and it has not been possible to make significant improvements.

The piezoelectric speaker according to the present invention improves the sound pressure by electrically lowering the impedance of the piezoelectric speaker, rather than improving the sound pressure by mechanically improving the piezoelectric sounding element as in the past. In other words, the piezoelectric sounding element has capacitive impedance except in the vicinity of its resonance frequency, and by connecting an inductance in series with this, the impedance in the vicinity of these series resonance frequencies can be reduced, and the drive current of the piezoelectric sounding element can be increased and the sound pressure can be improved.

FIG. 3 shows an example of the configuration of a piezoelectric speaker according to the present invention. In FIG. 3, 1, 2, and 4 are the same as in FIG. 5 is a coil connected in series to the piezoelectric ceramic plate 2, 6 is a lead wire connecting the piezoelectric ceramic plate 2 and the coil 5, and 7 and 8 are lead wires to which voltage for driving the piezoelectric speaker is applied. Here, coil 5
The value of the inductance is determined by the capacitance of the piezoelectric ceramic plate 2 and the frequency for improving the sound pressure.
Furthermore, by using a coil 5 having a relatively large loss of around 10%, the frequency band in which the sound pressure can be improved becomes wider, and the sound pressure level can be flattened by reducing its height.

FIG. 4 is a sectional view showing another example of the structure of the piezoelectric speaker according to the present invention. This embodiment uses a parallel bimorph vibrator in which piezoelectric ceramic plates 2 are bonded to both sides of an elastic thin plate 1 as a piezoelectric sounding element. It is possible to further improve the sound pressure.

FIG. 5 shows an example of the sound pressure frequency characteristics of the piezoelectric speaker according to the present invention shown in FIG. This characteristic is obtained when a piezoelectric sounding element exhibiting the sound pressure frequency characteristic shown in FIG. 2 is used as peripheral support, and a 280 mH coil is connected in series with this. It can be seen that the sound pressure from 500 to 1300 Hz has improved and is flattened compared to the conventional model. In addition, the piezoelectric speaker according to the present invention not only improves the sound pressure in the low frequency range, but also can improve the sound pressure in any frequency range by using the inductance of the coils connected in series, and can also flatten the sound pressure. It can be measured.

In addition, Fig. 6 is an example of the sound pressure frequency characteristics of the piezoelectric speaker of the present invention shown in Fig. 4. By using parallel bimorph oscillators in this way, the effects of the present invention can be utilized more effectively, and the sound pressure can be improved. It is possible to achieve flattening.

As explained above, according to the present invention, by electrically connecting the coil in series with the diaphragm, it is possible to improve the sound pressure, especially in the low frequency range, and to flatten the sound. Note that it is also possible to improve the sound pressure in any frequency band and flatten the sound pressure by using the inductance of the coil.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a configuration example of a piezoelectric sounding element used in a conventional piezoelectric speaker, Fig. 2 is a diagram showing sound pressure frequency characteristics when the element in Fig. 1 is used with peripheral support, and Fig. 3 The figure is a diagram showing an example of the configuration of a piezoelectric speaker in an embodiment of the present invention.
The figure shows an example of the configuration of a piezoelectric speaker according to the present invention using a parallel bimorph vibrator as a piezoelectric sounding element. Figure 6 is the fourth
FIG. 3 is a diagram showing sound pressure frequency characteristics of the piezoelectric speaker according to the present invention; 1... Elastic thin plate, 2... Piezoelectric ceramic plate, 4... Electrode, 5... Coil.

Claims (1)

[Scope of utility model registration request] In a piezoelectric speaker in which a piezoelectric ceramic plate is integrally bonded to a thin elastic plate such as a metal plate to constitute a diaphragm that induces bending vibration, and this diaphragm is used as a sound source, the sound pressure of the piezoelectric speaker is A coil having an inductance that electrically resonates with the electrostatic capacitance of the diaphragm in a frequency range where the diaphragm is insufficient is electrically connected in series with the diaphragm between an input end to which a piezoelectric speaker driving voltage is applied and the diaphragm. Piezoelectric speaker configured by connecting.