JP2551813B2 - Piezoelectric speaker - Google Patents

Description

TECHNICAL FIELD The present invention relates to a speaker using a thin plate piezoelectric element as a drive source.

(Prior Art) As a supporting structure of a piezoelectric element in a conventional sounding device using a thin plate piezoelectric element, there is one shown in FIGS. 5, 6, 7, and 8. In FIG. 5, the thin plate piezoelectric element 1 is attached to the metal thin plate 2, and the peripheral edge thereof is fixed to the step portion of the case 3. A cavity 4 ′ is provided on the front side of the case, and the sound pressure generated by the vibration of the thin plate piezoelectric element 1 propagates through the sound output hole 5 provided on the front side of the case 3.
In the structure shown in FIG. 6, the metal thin plate 2 to which the thin plate piezoelectric element 1 is attached is fixed to the case 3 via the support member 6 at the node point of the thin plate piezoelectric element 1, not at the periphery thereof. A cavity 4'formed between the case 3 and the support member 6
The sound pressure generated inside propagates through the sound output hole 5. However, these are used for the purpose of generating sound of a single frequency, that is, for the buzzer.

The piezoelectric speaker shown in FIGS. 7 and 8 is used. In FIG. 7, the metal thin plate 2 to which the thin plate piezoelectric element 1 is attached is fixed to the bottom of a plastic film 7 molded in a pot shape.
Secure the periphery of the to the flat front plastic film 8,
A closed cavity 4'is formed between both plastic films 7 and 8, and at the time of use, their peripheral portions are perforated by a spacer 9 and a perforated portion 11 of a perforated board 10 is formed.
Install facing the.

In the structure shown in FIG. 8, the metal thin plate 2 to which the thin plate piezoelectric element 1 is attached is extended, and the peripheral edge thereof is fixed to the fixing ring 13.
The fixing ring 13 is attached to the perforated board 10 for use.

(Problems to be Solved by the Invention) As shown in FIG. 7, when the input becomes large,
As shown in FIG. 10, the front plastic film 8 is distorted by its natural vibration and reproduces a distorted sound. Also,
The frequency characteristics are those shown by the solid line in Fig. 13 when measured with the back open as shown in Fig. 11, and
As shown in the figure, when the measurement is performed in the back closed state, the characteristics shown by the dotted line in FIG. 13 are obtained, and in the back closed state, the bass is significantly reduced and the sound quality is deteriorated.

As shown in FIG. 9, the input shown in FIG. 8 is distorted and the distorted sound is reproduced when the input becomes large. In addition, the frequency characteristic becomes severe as shown in Fig. 14, and the characteristic in the open rear state shown in Fig. 11 is shown by the solid line, whereas the characteristic in the closed back state shown in Fig. 12 is As indicated by the dotted line, the valley becomes large and the high level level rises, deteriorating the sound quality.

Therefore, the frequency characteristics shown in FIGS. 7 and 8 depend on the back space of the mounting case, and there is a problem that it is difficult to use, for example, an ultra-thin case with a closed back surface.

The present invention aims to solve these problems.

(Means for Solving Problems) The present invention has an object to solve the above problems, and a step portion is provided in the middle of a plastic film whose peripheral edge is fixed to a fixing ring, and a concave portion is formed in the central portion. , A thin disk peripheral edge is adhered to the peripheral edge of the recess to form a closed cavity,
A thin plate-shaped piezoelectric element is adhered to a thin disk facing the cavity,
Attach a perforated board to the front of the plastic film,
It is characterized in that the sealed cavity and the entire plastic film are vibrated by the vibration of the thin plate piezoelectric element.

(Operation) According to the present invention, the laminated body of the thin plate piezoelectric element and the thin plate having the above-described structure can perform the bending-free bending movement as shown in FIG. 3 due to the existence of the cavity behind it. Even if the input becomes large, the deformed state becomes as shown in FIG.

 The frequency characteristic is as shown in FIG.

(Embodiment) FIG. 1 shows an embodiment of the present invention.

Reference numeral 13 denotes a fixing ring on the outer periphery, which fixes the peripheral edge of the plastic film 7. A step portion 12 is provided in the middle of the plastic film 7, and a dish-shaped recess 7a is further formed in the central portion of the plastic film 7. A cavity portion is formed by adhering the peripheral edge of the metal thin disk 2 to the peripheral edge of the recess portion 7a. 4 is formed and the thin plate piezoelectric element 1 of the thin disk 2 facing the cavity 4 is attached.

 Next, the operation will be described.

When a signal voltage is applied to the thin piezoelectric element 1, the cavity 4 is formed.
Vibration occurs, and the entire plastic film 7 further vibrates. The vibration state becomes as shown in Fig. 4 even if the input becomes large, and since the irregular vibration as shown in Fig. 9 and Fig. 10 does not occur, the sound is not distorted, and the cavity 4 at the center of the plastic film 7 is Since it vibrates, the entire plastic film 7 having a larger diameter vibrates greatly, and its frequency characteristic is smooth with little undulations as shown by the solid line in FIG. 2, and the step 12 is provided in the middle of the plastic film 7. The frequency characteristic can be further improved.

(Effect) According to the present invention, a step portion is provided in the middle of the plastic film whose peripheral edge is fixed to the fixing ring, a concave portion is formed in the central portion, and the thin disk peripheral edge is attached to the peripheral edge of the concave portion. A closed cavity is formed, a thin-plate piezoelectric element is attached to a thin disk facing the cavity, a perforated board is attached to the front surface of the plastic film, and the closed cavity is formed by vibration of the thin-plate piezoelectric element. Since the parts and the entire plastic film are vibrated, the impedance of the piezoelectric element becomes lower than that of the conventional piezoelectric speaker when an input signal is applied, the bending movement becomes easier, and the sound pressure level rises. In the central part of the characteristic, the rise is significant, the frequency characteristic is less uneven, the sound pressure level in the high frequency part is low, the clarity of the voice is high, and the level of the high frequency is lowered. Sound with no harsh can be obtained.

[Brief description of drawings]

FIG. 1 is a plan sectional view showing an embodiment of the present invention, FIG. 2 is a graph showing its frequency characteristic, FIG. 3 is a plan sectional view showing a vibrating state of a thin plate piezoelectric element in the present invention, and FIG. FIGS. 5 to 8 are plan views showing vibration states of the speaker of the present invention.
FIG. 9 is a plan sectional view showing a conventional technique, FIG. 9 is a plan view showing a vibrating state of a thin plate piezoelectric element in the conventional technique, and FIG. 10 is a plan view showing a vibrating state of a conventional speaker.
Figure 12 is a plan view showing the state of the speaker characteristic test.
13 and 14 are graphs showing the characteristics of the conventional speaker. 1 ... Thin plate piezoelectric element, 2 ... Metal thin disk, 4 ... Cavity 7 ... Plastic film, 13 ... Fixing ring

Claims (1)

(57) [Claims] 1. A hollow portion in which a step portion is provided in the middle of a plastic film whose peripheral edge is fixed to a fixing ring, a concave portion is further formed in the central portion, and a thin disk peripheral edge is adhered to the peripheral edge of the concave portion to seal it. A thin plate-shaped piezoelectric element is adhered to the thin disk facing the hollow portion, a perforated board is attached to the front surface of the plastic film, and the sealed hollow portion and the plastic film are vibrated by the vibration of the thin plate-shaped piezoelectric element. A piezoelectric speaker that vibrates the whole body.