JPH09327094A - Piezoelectric speaker - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the small sized piezoelectric speaker in which a change in a sound pressure from a low sound frequency region till a high sound frequency region is small and a distortion factor is small even at a high sound frequency region. SOLUTION: The piezoelectric speaker 10 includes a flat vibrator 12 made of a piezoelectric material. Electrodes 14, 16 are formed respectively to both sides of the vibrator 12. The electrode 14 is split into 5 electrode parts 14a-14e. A circuit network 18 is used to give a signal between the electrodes 14 and 16. A signal is given to the electrode parts 14a, 14e via an inductor 22 of the circuit network 18 and a signal is given to the electrode parts 14b, 14d via an inductor 20 of the circuit network 18. A signal is directly given to the electrode part 14c. As the frequency of the input signal gets higher, the impedance of the inductors is increased and the electrode parts receiving the signal are limited and the vibrating area of the vibrator 12 is decreased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric speaker, and more particularly to, for example, a piezoelectric speaker for reproducing wide band sound.

[0002]

2. Description of the Related Art As a conventional speaker, there is one that emits sound by driving a cone formed of, for example, paper. Then, there is a speaker box in which a plurality of speakers having different diameters are attached, and these speakers are driven by using a circuit network, a multi-amplifier or the like to achieve a wide band and a low distortion rate. Further, there is one in which a corrugation is provided in one speaker, frequency division is mechanically performed, and a vibration area is changed according to frequency. In such a speaker, the area of the vibration region of the cone in the high frequency region is reduced to prevent the distortion rate from being deteriorated due to the divided vibration. Further, there is a piezoelectric speaker in which electrodes are formed on both surfaces of a vibrating body formed of a piezoelectric body and a signal is input to the electrodes to vibrate the vibrating body.

[0003]

A speaker using a cone is usually attached to a speaker box. If a speaker is attached to such a speaker box, the size becomes large. The piezoelectric speaker has a structure in which electrodes are formed on both sides of a piezoelectric body and has a capacitance C. When the angular frequency of the signal is ω, the impedance of the piezoelectric speaker is 1 / ωC.
Therefore, as the frequency increases, the impedance of the piezoelectric speaker decreases, and a large current is input. Therefore, as shown in FIG. 9, the sound pressure of the emitted sound increases as the frequency increases. That is, in the piezoelectric speaker, the sound pressure is different between the low tone range and the high tone range. Further, in the high-pitched sound region, the divided vibration occurs in the vibrating body, and the distortion rate increases.

Therefore, a main object of the present invention is to provide a small-sized piezoelectric speaker having a small change in sound pressure from the low tone region to the high tone region and a small distortion rate even in the high tone region.

[0005]

The present invention includes a vibrating body formed of a piezoelectric body and an electrode formed on an opposing surface of the vibrating body. At least one of the electrodes is divided and the vibrating body A piezoelectric speaker in which a signal having frequency characteristics is input to the divided electrodes so that the vibration area changes. In this piezoelectric speaker, a circuit network formed by an inductor is connected to the divided electrodes in order to input a signal having frequency characteristics to the divided electrodes.

The vibrating area of the vibrating body changes depending on the frequency of the input signal, and the amplitude corresponding to the frequency can be obtained. When the sound in the treble region is emitted, the vibration area of the vibrating body is set to be small, whereby divided vibration of the vibrating body can be suppressed and the distortion rate can be reduced. Further, when the sound in the low-pitched sound region is emitted, the vibration area of the vibrating body increases, and a large amplitude can be obtained.

Furthermore, if a circuit network formed of inductors is used, the impedance of the inductor increases as the frequency increases, and no signal is input to the electrode connected to the inductor section. Then, the electrodes to which signals are input are limited, and the area becomes small. When the electrode area becomes small, the substantial capacitance C of the piezoelectric speaker becomes small, and even if the frequency becomes high, the impedance 1 / ωC does not become so small. Therefore, even if the impedance of the entire piezoelectric speaker decreases as the frequency increases, the substantial change in the combined impedance of the piezoelectric speaker and the circuit network becomes small. Therefore, even if the frequency changes, the change in the current input to the piezoelectric speaker is small, and the change in the sound pressure of the radiated sound can be reduced.

[0008]

According to the present invention, it is possible to obtain a piezoelectric speaker having a characteristic that a change in sound pressure is small in a low tone region to a high tone region and a distortion rate is small even in a high tone region. Moreover, like a speaker using a cone made of paper,
It is not necessary to attach it to the speaker box and can be made compact.

The above objects, other objects, features and advantages of the present invention will become more apparent from the following detailed description of the embodiments of the invention with reference to the drawings.

[0010]

1 is a perspective view showing an example of a piezoelectric speaker of the present invention, and FIG. 2 is a sectional view thereof. The piezoelectric speaker 10 includes, for example, a flat plate-shaped vibrating body 12. The vibrating body 12 is formed of a piezoelectric body such as a piezoelectric ceramic, and is polarized in the thickness direction. Electrodes 14 and 16 are formed on both surfaces of the vibrating body 12. Then, one electrode 14 has, for example, five electrode portions 14a, 14b,
It is divided into 14c, 14d and 14e.

In this example, the electrode portions 14a, 1 at both ends are
4e is formed to have the largest area, and the central electrode portion 14c is formed to have the smallest area. The electrode portions 14a and 14e at both ends are electrically connected, and the electrode portions 14b and 14 adjacent to the electrode portions 14a and 14e are electrically connected.
d is electrically connected.

In this piezoelectric speaker 10, the electrodes 14, 1
A signal is input between six. At this time, the circuit network 18 as shown in FIG. 3 is connected to the electrode 14. A signal is directly input to the electrode portion 14c of the electrode 14. A signal is input to the electrode portions 14b and 14d via the inductor 20. Furthermore, the electrode portions 14a and 14e include
A signal is input via the inductor 22. Here, the inductance of the inductor 22 connected to the electrode portions 14a and 14e is set to be larger than the inductance of the inductor 20 connected to the electrode portions 14b and 14d.

The inductance is L and the angular frequency of the signal is ω
Then, the impedance of the inductor is represented by ωL. Therefore, when the frequency is low, the impedance of the inductor is small, and as the frequency is high, the impedance is large. That is, a signal with a low frequency easily passes, and a signal with a high frequency hardly passes.

When a signal is input to the piezoelectric speaker 10 via the circuit network 18 as described above, the signal is input to all the electrode portions 14a to 14e in the low frequency region, that is, the low tone region. Therefore, almost the entire surface of the vibrating body 12 vibrates, and a large amplitude can be obtained.

Further, as the frequency of the signal becomes higher, the impedance of the inductor becomes higher and the signal is not input to the electrode portion. Here, the electrode portion 14
Since the inductance of the inductor 22 connected to a and 14e is larger than the inductance of the inductor 20 connected to the electrode portions 14b and 14d, first, the electrode portion 1
The signals input to 4a and 14e are limited. When the frequency of the input signal further increases, the electrode portions 14b and 14d
The signal that is input to is also limited, and the signal is input only to the electrode portion 14c. Thus, as the frequency of the signal increases, that is, in the high-pitched sound region, the vibration area of the vibrating body 12 decreases, and the vibrating body 1
The divided vibration of 2 is suppressed. Therefore, the distortion rate in the high tone range can be reduced.

As described above, in the piezoelectric speaker 10,
The vibrating body 12 has a large vibration area in the low-pitched sound region, and the vibrating body 12 has a small vibration area in the high-pitched sound region. Therefore, it is possible to obtain a large amplitude in the low tone region and suppress the divided vibration in the high tone region.

The impedance of the piezoelectric speaker 10 decreases as the frequency increases, while the impedance of the inductors 20 and 22 increases as the frequency increases. Therefore, the combined impedance of the piezoelectric speaker 10 and the circuit network 18 does not change much depending on the frequency, and the fluctuation of the current of the input signal can be reduced. Further, in the high-pitched sound region, a signal is input only to the electrode portion 14c, but in this case, the electrode area becomes small and the substantial capacitance C of the piezoelectric speaker 10 becomes small. Therefore, the angular frequency ω of the signal
Even when the value becomes large, the change in impedance 1 / ωC of the piezoelectric speaker 10 is smaller than that when signals are input to all the electrode portions 14a to 14e.

As described above, the piezoelectric speaker 10 can reduce the variation in impedance regardless of the change in signal frequency. Therefore, the piezoelectric speaker 1
The change in the current input to 0 is small. That is, in the piezoelectric speaker 10, the vibration area of the vibrating body 12 is changed according to the frequency, and the input current is made substantially constant, so that the sound pressure changes from the low sound region to the high sound region as shown in FIG. Can be made smaller. Moreover, the piezoelectric speaker 10 does not need to be attached to the speaker box unlike a speaker using a paper cone, and can be a small speaker, and can be manufactured at low cost.

In the piezoelectric speaker 10, as shown in FIG. 5, the electrode 14 has three electrode parts 14a and 14a.
It may be divided into b and 14c. In this piezoelectric speaker 10, the electrode 14 has the "U" -shaped electrode portions 14a and 14b.
And is divided into a central electrode portion 14c surrounded by them. And, in the bass region, all electrode portions 14a,
A signal is input to 14b and 14c, and the entire surface of the vibrating body 12 vibrates. Then, as it approaches the high-pitched sound region, no signal is input to the electrode portion 14a, and in the high-pitched sound region, no signal is input to the electrode portion 14b.

Further, the division of the electrodes is not limited to the three electrode portions, but as shown in FIG.
You may divide into b. In this case, a signal is input to both electrode portions 14a and 14b in the low tone region, and a signal is input to either one of the electrode portions in the high tone region. Of course, it may be divided into four electrode parts or six or more electrode parts, and by adjusting the signals input to many electrode parts,
The vibration area of the vibrating body 12 depending on the frequency may be finely adjusted. Further, either one of the electrodes 14 and 16 may be divided, or both of them may be divided. Both electrodes 14,1
When 6 is divided, the respective electrode portions are formed so as to face each other, and the signals input to the facing electrode portions are adjusted.

Further, as shown in FIG. 7, a vibrating body 12 having an arcuate cross section may be used. Further, as shown in FIG. 8, a cylindrical vibrating body 12 may be used. In these cases, the electrode portions 14a to 14e that are divided in the axial direction of the vibrating body 12 and extend in the circumferential direction are formed. In particular, when a cylindrical vibrating body 12 as shown in FIG.
Sound can be emitted toward 60 °, and the speaker can be an omnidirectional speaker. Of course, the shape of the vibrating body 12 may be another tubular shape such as a rectangular tubular shape.

[Brief description of drawings]

FIG. 1 is a perspective view showing an example of a piezoelectric speaker of the present invention.

FIG. 2 is a cross-sectional view of the piezoelectric speaker shown in FIG.

3 is an illustrative view showing a state in which a circuit network for inputting a signal having a frequency characteristic is connected to the piezoelectric speaker shown in FIG.

FIG. 4 is a graph showing a relationship between frequency and sound pressure when a signal is input to the piezoelectric speaker via the circuit network shown in FIG.

FIG. 5 is a perspective view showing another example of the piezoelectric speaker of the present invention.

FIG. 6 is a perspective view showing still another example of the piezoelectric speaker of the present invention.

FIG. 7 is a perspective view showing another example of the piezoelectric speaker of the present invention.

FIG. 8 is a perspective view showing still another example of the piezoelectric speaker of the present invention.

FIG. 9 is a graph showing the relationship between frequency and sound pressure of a conventional piezoelectric speaker.

[Explanation of symbols]

 10 Piezoelectric speaker 12 Vibrating body 14 Electrode 16 Electrode 18 Circuit network 20 Inductor 22 Inductor

Claims (2)

[Claims] 1. A vibrating body formed of a piezoelectric body, and an electrode formed on an opposing surface of the vibrating body, wherein at least one of the electrodes is divided so that a vibration area of the vibrating body changes depending on a frequency. A piezoelectric speaker in which a signal having a frequency characteristic is input to the divided electrodes. 2. The piezoelectric speaker according to claim 1, wherein a circuit network formed by an inductor is connected to the divided electrodes to input a signal having the frequency characteristic to the divided electrodes.