JPH09307996A - Piezoelectric speaker - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain excellent sound quality with a wide band by suppressing a sound volume of a high frequency band for the piezoelectric speaker so as to increase the sound volume at a low frequency band. SOLUTION: A auxiliary diaphragm 20 is arranged in a case with a diaphragm 14 to which a piezoelectric ceramic plate 10 is adhered. The auxiliary diaphragm 20 is arranged closely nearly in parallel with the diaphragm 14. The surrounding of the diaphragm 14 and the auxiliary diaphragm 20 is supported by elastic bodies 17, 18, 23. The diaphragm 14 is vibrated by a voltage applied to the piezoelectric ceramic plate 10 and the auxiliary diaphragm 20 is vibrated in resonance therewith and a sound at a low frequency band which is unable to be obtained only by the diaphragm 14 is sounded.

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 a structure of a piezoelectric speaker capable of improving sound quality.

[0002]

2. Description of the Related Art Generally, a speaker which generates vibration electromagnetically is used as a speaker, but a piezoelectric speaker which generates vibration by a piezoelectric element is also used for the purpose of miniaturization and low-current driving. This piezoelectric speaker generates a sound by applying a voltage to a piezoelectric ceramic plate attached to a diaphragm to generate vibration. There is also an advantage that magnetostriction does not occur, for example, when used in combination with a liquid crystal display device.

[0003] A diaphragm made of piezoelectric ceramic has a problem that the sound quality is poor and harsh because the natural vibration frequency is located at a higher frequency than the audible frequency. In order to solve this problem, attempts have been made to reduce the thickness, to make the shape rectangular, and to make corrections by selecting an attachment method and a material, but none of them has been satisfactory. Further, if the size is increased, the sound quality in a relatively low frequency band is improved, but there is a problem that it is not suitable for a speaker of a portable device or the like.

[0004]

SUMMARY OF THE INVENTION The present invention provides a piezoelectric speaker which can be miniaturized and can improve the sound quality in a low frequency band.

[0005]

DISCLOSURE OF THE INVENTION The present invention solves the above problems by placing an auxiliary diaphragm along with a diaphragm in a housing and vibrating the auxiliary diaphragm.

That is, a piezoelectric speaker in which a vibrating plate having a piezoelectric ceramic plate with electrodes formed therein is arranged in a housing is characterized by including an auxiliary vibrating plate arranged in parallel with the vibrating plate.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION An auxiliary vibration plate such as polycarbonate is arranged in parallel with a vibration plate having a piezoelectric ceramic plate attached inside a housing. A spacer such as an elastic body is pressed against at least a part of the periphery of the diaphragm and the auxiliary diaphragm to fix them in the housing. Wiring for driving is connected to the electrodes of the piezoelectric ceramic plate, and vibration is generated by the input voltage. The displacement of the piezoelectric ceramic plate vibrates the diaphragm, and the auxiliary diaphragm vibrates in resonance with the vibration. By vibrating the auxiliary diaphragm, a low frequency sound is generated and the frequency band is broadened as a whole.

[0008]

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

FIG. 1 is a partial front sectional view showing an embodiment of the present invention. The overall shape is such that the vibrating element is fixed in a thin rectangular metal case as shown in FIG. The metal case includes an upper plate 11 having a storage space for elements and a lower plate 12 of a flat plate. The upper plate 11 has a through hole 13 through which sound passes. After housing the elements and the like, the projections formed on the upper plate 11 are bent, swaged and fixed. The through holes may be formed in the lower plate 12. Even when a case other than metal is used, almost the same structure can be obtained.

In this example, the diaphragm 14 can be made of a 42 alloy or the like having a size of about 0.1 mm, and its size is about 30 mm × 25 mm. A piezoelectric ceramic plate of 13 mm x 16 mm and a thickness of about 0.1 mm is attached to the center part. Electrodes such as silver are formed on both sides of the piezoelectric ceramic plate, and lead wires are attached to each electrode.
Connect 15. The connection of the electrodes on the surface to be attached to the diaphragm 14 can be performed by soldering lead wires to the diaphragm 14. It is also possible to adopt a structure in which a metal plate is adhered to the diaphragm using polycarbonate or the like, and a piezoelectric ceramic plate is disposed thereon.

The vibrating plate 14 is sandwiched by elastic members 17, 18 at its peripheral portion. Silicon rubber or the like is suitable for the elastic bodies 17 and 18, and the thickness thereof is preferably about 0.7 to 1.1 mm. In order to hold the diaphragm 14, it is necessary to have 1.5 to 3.0 mm inward from the position where it contacts the upper plate 11.

An auxiliary diaphragm 20 is arranged between the diaphragm 14 and the upper plate 11. Polycarbonate or the like is suitable for this diaphragm 20, and its thickness is preferably about 0.1 to 0.5 mm. The size is the same as that of the diaphragm 14, and is fixed so as not to move into the case. In addition, it is preferable to form the through hole 21 in the auxiliary diaphragm 20.

An elastic body 23 is provided between the auxiliary diaphragm 20 and the upper plate 11.
Place. The elastic body 23 is made of silicon rubber or the like similarly to the elastic bodies 17 and 18, and has a thickness of about 0.3 to 0.5 mm and the other dimensions are the same. A rigid spacer may be used instead of the elastic body.

The elastic body 23, the auxiliary vibration plate 20, the elastic body 17, and the vibration plate 14 are sequentially housed in the upper plate 11. A lead wire is connected to the vibration plate 14 in advance, and this is pulled out from the through hole on the side surface of the upper plate 11 to the outside. Next, the elastic body 18 is housed, pressed by the lower plate 12, and the projections of the upper plate 11 are bent to assemble. Therefore, a step such as bonding at the time of assembly becomes unnecessary.

By adopting a structure in which a part of the vibration plate 14 is pulled out so as not to contact the upper plate 11, it is possible to reduce the man-hours for inserting lead wires and soldering.

If a through hole is formed in the auxiliary diaphragm 20, it is possible to reduce the distortion generated at the time of a large input. However, if it is too large, the vibration efficiency decreases, so it is desirable to minimize it.

The present invention is not limited to the above examples, and the materials and dimensions can be arbitrarily selected according to the application. Also, arrange auxiliary diaphragms on both sides of the diaphragm,
The number of sheets arranged on one side may be plural, and the material and the thickness thereof may be different. Further, the diaphragm and the auxiliary diaphragm may be arranged not at parallel but at a predetermined angle. Then, the diaphragm and the auxiliary diaphragm can be fixed by other methods. Alternatively, the auxiliary diaphragm may also be used as a housing.

Using the piezoelectric speaker of the above example,
It was confirmed that the conventional one could only obtain sounds in the frequency band of 1.5 kHz or higher, but could obtain sounds in the low frequency range of 0.7 to 0.8 kHz.

It was also confirmed that forming a through hole in the lower plate improves the lower frequency band. by this,
This is because the vibration peculiar to the substrate on which the piezoelectric speaker is mounted can also be used.

[0020]

According to the present invention, it is possible to improve the low-frequency sound quality, which has not been obtained conventionally, while maintaining a small size. Conventionally, the high-frequency side is strong and uncomfortable, but the relatively high-frequency side is relatively suppressed, and good characteristics can be obtained in a wide band.

Further, if the structure in which the auxiliary diaphragm is provided with a through hole is adopted, there is an advantage that distortion at the time of a large input can be prevented, and in that respect, the sound quality can be improved.

Further, since the assembly can be performed only by housing the diaphragm and the elastic body in the housing, the number of assembling steps can be reduced. This is advantageous not only in that the step of bonding or the like becomes unnecessary, but also in terms of reliability.

[Brief description of drawings]

FIG. 1 is a partial front sectional view showing an embodiment of the present invention.

FIG. 2A is a plan view showing an embodiment of the present invention,
(B) is a front view

[Explanation of symbols]

 11: Upper plate 12: Lower plate 14: Vibration plate 20: Auxiliary vibration plates 17, 18, 23: Elastic body

Claims (5)

[Claims] 1. A piezoelectric speaker in which a vibrating plate having a piezoelectric ceramic plate formed with electrodes formed therein is arranged in a housing, the piezoelectric speaker comprising an auxiliary vibrating plate arranged in parallel with the vibrating plate. 2. A piezoelectric speaker in which a diaphragm having a piezoelectric ceramic plate with electrodes formed therein is disposed in a housing, the piezoelectric speaker includes an auxiliary diaphragm arranged in parallel with the diaphragm, and A piezoelectric speaker characterized in that at least a part of the piezoelectric speaker is fixed in the housing through a spacer. 3. A piezoelectric speaker in which a diaphragm having a piezoelectric ceramic plate with electrodes formed therein is arranged in a housing, the piezoelectric speaker includes an auxiliary diaphragm arranged in parallel with the diaphragm, and A piezoelectric speaker characterized in that at least a part of the piezoelectric speaker is fixed in the housing through an elastic body. 4. A piezoelectric speaker in which a diaphragm having a piezoelectric ceramic plate with electrodes formed therein is disposed in a housing, the auxiliary speaker having a through-hole arranged in parallel with the diaphragm. Piezoelectric speaker. 5. The piezoelectric speaker according to claim 1, 2, 3, or 4, comprising a plurality of auxiliary diaphragms.