JPH02158300A - Piezoelectric loudspeaker - Google Patents

Abstract

PURPOSE:To prevent sound quality in the output of a high tone from being deteriorated by fixing the peripheral edge part of a diaphragm on a case or a metallic plate via a flexible and porous fiber face material in which an adhesive is filled. CONSTITUTION:The loudspeaker is the one in which two bowl shape bimorph type piezoelectric sounding bodies (bowl shape piezoelectric sounding body) 10a and 10b are arranged symmetrically with a flat diaphragm 11, and furthermore the peripheral edge part of the flat diaphragm 11 is stuck on resin cases 12a and 12b. Here, the bowl shape piezoelectric sounding bodies 10a and 10b and the flat diaphragm 11 are stuck and fixed by using the flexible and porous fiber face material 20 in which the adhesive is filled, and the fiber face material 20 functions as a cushioning material with uniform thickness. In such a way, it is possible to obtain a piezoelectric loudspeaker with high sound quality in which a high frequency is prevented from occurring and no distortion and chattering is generated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a piezoelectric speaker whose sound source is a piezoelectric sounding body in which a piezoelectric element is bonded to a diaphragm.

[Conventional technology]

There are two types of piezoelectric speakers: a type in which a piezoelectric element is coupled to a diaphragm made of paper cone, etc., and the diaphragm is driven by the vibration of the piezoelectric element, and a piezoelectric sounding body in which a piezoelectric element is bonded to a diaphragm is coupled to a case by some means. This is a type that creates a cavity space and converts the bending motion of the piezoelectric sounding body into air vibrations to produce sound. The present invention is directed to the latter type of device that uses a piezoelectric sounding element as a sound source, but in this type of device, acoustic design is performed based on the thickness of the case, the boundary conditions for fixing the piezoelectric sounding element, and the sound emission holes of the case. Do this. Among these, the boundary conditions that fix the piezoelectric sounding element are particularly difficult to design. Even if the geometric dimensions can be designed, parasitic sound may occur, and many elements must be determined experimentally.

[Problem to be solved by the invention]

As illustrated in FIG. 4, there are various structures of the piezoelectric sounding body and various types of connections between the piezoelectric sounding body and the case. A piezoelectric sounding body is formed by bonding a piezoelectric element to one or both sides of a metal diaphragm. FIG. 4(a) shows an example in which a double-sided piezoelectric sounding body 1 is attached to a resin case 2, forming two cavity spaces. Figure 1) combines two dish-shaped double-sided piezoelectric sounding bodies 3a and 3b on both sides of a flat diaphragm 4 having a sound emitting hole in the center to form a composite piezoelectric sounding body. Attach 4 to resin case 2. This forms three cavity spaces.

It is known that piezoelectric speakers using a piezoelectric sounding body as a sound source are susceptible to distortion in the low frequency band of 400 to 550 Hz due to the method of fixing the piezoelectric sounding body. Especially when high sound pressure is generated, the sound quality deteriorates as a rattling sound. This phenomenon is thought to be due to mutual interference between the vibrations of the piezoelectric sounding body and the vibrations of other parts of the piezoelectric speaker due to the coupling between the piezoelectric sounding body and the case or the metal plate. Experience has shown that by making the adhesive at the joint relatively thick, the adhesive buffers vibrations and prevents distortion. However, when fixing a piezoelectric sounding element, it is extremely difficult to form and fix an adhesive layer with a uniform thickness, and the uneven local thickness of the adhesive layer may result in distortion. The outbreak may become large.

In view of the above-mentioned circumstances, an object of the present invention is to provide a piezoelectric speaker with high sound quality that does not produce distorted sounds or chattering sounds by improving the means for fixing the piezoelectric sounding body.

[Means to solve the problem]

The present invention provides a piezoelectric speaker whose sound source is a piezoelectric sounding body in which a piezoelectric element is bonded to a diaphragm, the diaphragm comprising:
Its peripheral end is fixed to a case or a metal plate via a flexible, porous fiber face material filled with adhesive.

Alternatively, it may be fixed with a plastic tape having adhesive layers on both sides.

[Effect]

The fiber facing material filled with adhesive acts as a cushioning material with a uniform thickness. This prevents the generation of high frequencies and eliminates distortion and chatter. A similar effect exists for plastic tapes with an adhesive layer.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1(a), in this embodiment, two dish-shaped bimorph piezoelectric sounding bodies (hereinafter referred to as dish-shaped piezoelectric sounding bodies) lOa and fob are arranged symmetrically with respect to a flat diaphragm 11. Furthermore, the peripheral edge of the flat diaphragm 11 is
It is formed by adhering to the resin case 12a12b. The electrical wiring that drives the dish-shaped piezoelectric sounding bodies TOA and TAB is as follows:
It is omitted in this drawing. The flat diaphragm 11 is a metal plate made of brass, stainless steel, etc., and has a sound emitting hole 13 in the center, so that cavity spaces are formed between the plate-shaped piezoelectric sounding bodies 10a and 10b, respectively. Since this type of piezoelectric speaker is a composite type having two sound sources and three cavity spaces, it is a high output type and can have a wide frequency characteristic. In the present invention, in order to take advantage of this excellent characteristic, the dish-shaped piezoelectric sounding bodies 10a, 10b and the flat diaphragm 11 have a flexible porous fiber face material filled with an adhesive or an adhesive layer on both sides. Adhesively fix it using plastic tape. Dish-shaped piezoelectric sounding body 10a, 1
The entire circumference of the edge of 0b is flanges 15a and 16b, and as shown in FIG.
, and are adhered via plastic tape 21. In the embodiment, the fiber facing material 20 is a mesh # made of nylon (registered trademark).
200 impregnated with a flexible silicone rubber resin was used. In addition, in the case of the plastic tape 21, a polyester film of about 38 μm is used as the base material,
The adhesive layer 21a was uniformly provided on both sides. The adhesive layer 21a uses a urethane-based adhesive, an acrylic-based adhesive, a nitrile rubber-based adhesive, etc., and does not necessarily have to be the same on both sides. Since the adhesive layer 21a is firmly adhered to the base material, the thickness of the adhesive layer does not locally change when bonding the dish-shaped piezoelectric sounding elements 10a and 10b.

Hereinafter, data for experimentally confirming improvement effects will be illustrated for examples according to the present invention and conventional examples. First, regarding the case using the fiber facing material 20, Fig. 2 (ta) (bl) is the data of the conventional example, and is the frequency spectrum when driven at the fundamental wave (a 1425 Hz and (b) 600 Hz, respectively. In the data in the figure, the frequency scale is 0.5K)Iz, and the gain scale is 10 dB.As shown in the figure, in case (a), the 2nd to 4th harmonic waves are at the same level, There is a difference of about 6 dB from the fundamental wave level.In the case of (b), the tertiary wave is particularly large, but there is a difference of about -14 dB from the fundamental wave.This implementation corresponds to this. An example is shown in Figure 2 (C) (
Shown in d). When the fundamental wave of fc) is driven at 425 Hz, the second-order wave is hardly seen, and the third-order wave is -14 dB with respect to the fundamental wave. is negligible.

Next, regarding the data for Plus Deck Tape 21,
As shown in Figure 3, Figure 3 (at, (bl is the fundamental wave 525
1 (z) (al is the conventional example, fbl is the deheter of this embodiment.

In the conventional example (al), the secondary wave was small, but the tertiary wave was only -3.4 dB different from the fundamental wave.

On the other hand, in this embodiment (bl), the tertiary wave had a remarkable effect of -20.8 dB with respect to the fundamental wave.

These effects are due to the fact that when fixed with adhesive, the thickness of the adhesive locally varies on the bonding surface, and because the thickness is not sufficient, there is no buffering effect, and the vibration of the piezoelectric sounding element and the vibration of other parts. This is because the defects caused by vibration and interference can be eliminated.

Note that in the example explained above, measures were taken for the part where the dish-shaped piezoelectric sounding element is adhered to the flat diaphragm, but it is unlikely that the same effect will be obtained even if measures are taken for the part where the dish-shaped piezoelectric sounding element is adhered to the resin case. Not even.

〔Effect of the invention〕

As explained above, in combination with a flat resonator plate, a resin case, etc. using a piezoelectric sounding element, 1. In a piezoelectric speaker that forms an acoustic cavity space, as a means for fixing and bonding the piezoelectric sounding element. By using a flexible porous fiber surface + A filled with adhesive or a plastic tape having an adhesive layer on both sides, it has become possible to reduce the generated distortion in the low frequency band.

Particularly in the low frequency range of 400 to 55011z, the deterioration in sound quality that caused chatter when the output was high was eliminated, and good characteristics were obtained.

[Brief explanation of the drawing]

FIG. 1 (al is a vertical cross-sectional view of an embodiment of the present invention, tb),
fc) is an enlarged view of the adhesively fixed part between the piezoelectric sounding body and the flat diaphragm, and Fig. 2 shows the piezoelectric speaker with the adhesively fixed part as shown in Fig. Fig. 3 (a) is a characteristic comparison diagram of the piezoelectric speaker with the adhesive fixed part shown in Fig. 1 (C) and a conventional piezoelectric speaker. It is a figure illustrating the format of fixing a sounding body. ioa, 10b -- dish-shaped piezoelectric sounding body, ll - flat diaphragm, 12a, 12b - resin case, 16a, 16b - flange (of dish-shaped piezoelectric sounding body) , 20...Fiber surface material, 21-Plastic tape.

Claims (2)

[Claims] 1. In a piezoelectric speaker whose sound source is a piezoelectric sounding body in which a piezoelectric element is bonded to a diaphragm, the diaphragm is made of flexible, porous fibers filled with adhesive and whose peripheral edge is attached to a case or metal plate. A piezoelectric speaker characterized in that it is fixed through a face material. 2. 2. The piezoelectric speaker according to claim 1, wherein a plastic tape having an adhesive layer on both sides is used in place of the fiber surface material.