JPH10126885A - Piezoelectric sound generator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the diameter of a piezoelectric vibrator and to miniaturize a piezoelectric sound generator by placing a mass member at the center part of the piezoelectric vibrator to increase the equivalent mass and then to shift the secondary resonance frequency to a lower level and accordingly preventing reduction of the sound pressure in an area of high frequency characteristic and to control the frequency characteristic in an area of high frequency. SOLUTION: A piezoelectric vibrator 8 includes a piezoelectric ceramic element 8b which is bonded to a plate-shaped metallic diaphragm 8a, and the fringe part of the diaphragm 8a is supported by the insulating cases 6 and 7. The front and rear air chambers are prepared at both sides of the vibrator 8 respectively. A mass member 8c is attached at the center part of the diaphragm 8a to control the frequency characteristic. Thus, it's possible to prevent reduction of the sound pressure in an area of high frequency characteristic and also to control the frequency characteristic in a range of high frequency by increasing the equivalent mass and then shifting the secondary resonance frequency to a lower level.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric sounder for obtaining a desired frequency characteristic by utilizing resonance between a front air chamber and a rear air chamber.

[0002]

2. Description of the Related Art In a piezoelectric sounding device that obtains a desired frequency characteristic by utilizing resonance between a front air chamber and a rear air chamber, a resonance frequency based on the vibration of a piezoelectric vibrator, a resonance obtained from the front air chamber, and a rear frequency The frequency characteristic is determined by overlapping with the resonance obtained from the air chamber.
The piezoelectric vibrator is configured by joining a piezoelectric ceramic element to a plate-shaped metal vibration plate, and a peripheral portion of the metal vibration plate of the piezoelectric vibrator is supported by an insulating case. As schematically shown in FIG. 11, a front air chamber 103 is formed on one side of a piezoelectric vibrator 102 supported by an insulating case 101, and a rear air chamber 104 is formed on the other side of the piezoelectric vibrator 102. Formed. Generally, as shown in FIG.
01 is partitioned by a piezoelectric vibrator 102 to form a front air chamber 10.
In many cases, both the rear air chamber 3 and the rear air chamber 104 are formed. However, the front air chamber and the rear air chamber are housed inside the electronic device and only when the case of the electronic device and the insulating case of the piezoelectric sounder are combined. May be formed.

The frequency characteristic (sound pressure-frequency) obtained by the vibration of the piezoelectric vibrator 102 is, as shown in FIG. 12, a peak P1 of the primary resonance frequency and a peak P1 of the secondary resonance frequency.
And 2. When the diameter dimension of the piezoelectric diaphragm is large (for example, 20 mm), the resonance obtained from the front air chamber 103 is emitted such that the sound pressure peaks in a frequency region higher than the secondary resonance frequency in FIG. The area of the hole 105 is set, and the area of the sound emission hole 106 is set so that the resonance obtained from the rear air chamber 104 has a sound pressure peak in a frequency region lower than the secondary resonance frequency. Then, the frequency characteristics obtained from only the piezoelectric vibrator 102 and the resonances from the front air chamber 103 and the rear air chamber 104 overlap to determine the frequency characteristics of the piezoelectric sounder.

[0004]

FIG. 13 shows, for example, the receiving frequency characteristics of the standard of a receiver set by the Telecommunications Industry Association of Japan for the telephone call quality. When a piezoelectric sounding device is used as a telephone receiver, it is required to satisfy the receiving frequency characteristics. According to this standard, when the sound pressure at 1000 Hz is 0 dB,
In the frequency range of 300 Hz to 3400 Hz, it is required that the frequency characteristics of the receiver fall within an allowable range between an allowable limit (lower limit) D and an allowable limit (upper limit) C. However, the smaller the diameter of the piezoelectric vibrator (piezoelectric vibrating plate), the higher the secondary resonance frequency tends to be. Therefore, if the diameter of the piezoelectric vibrator, that is, the diameter of the metal vibrating plate is reduced in accordance with the demand for miniaturization, the secondary resonance frequency becomes 3400 Hz or more, and as a result, the frequency characteristic of the piezoelectric sounder becomes high. The sound pressure in the frequency domain decreases,
The above-mentioned standard will not be satisfied. Therefore, an attempt was made to increase the sound pressure in the high frequency region by adjusting the number or size of the sound emission holes in the front air chamber or the rear air chamber, but could not obtain a sufficient result.

An object of the present invention is to provide a piezoelectric sounding device capable of adjusting frequency characteristics in a high frequency region.

Another object of the present invention is to provide a piezoelectric sounding device capable of adjusting frequency characteristics in a high frequency region when the diameter of a piezoelectric vibrator is reduced.

Another object of the present invention is to provide a piezoelectric sounding device capable of adjusting a frequency characteristic in a high frequency region by adjusting a secondary resonance frequency.

Another object of the present invention is to provide a piezoelectric sounding device capable of preventing a decrease in sound pressure when a mass member is attached to a piezoelectric vibrator using an adhesive to adjust a secondary resonance frequency. Is to do.

Another object of the present invention is to provide a piezoelectric sounding device that can effectively adjust the secondary resonance frequency by attaching a mass member to a piezoelectric vibrator.

[0010]

SUMMARY OF THE INVENTION A piezoelectric sounder to be improved by the present invention is a piezoelectric vibrator in which a piezoelectric ceramic element is joined to a plate-shaped metal vibrating plate. A front air chamber is formed on one side of the piezoelectric vibrator supported by the insulating case, and a rear air chamber is formed on the other side of the piezoelectric vibrator. I have.

In the present invention, a mass member for adjusting the resonance frequency is attached to the center of the metal diaphragm to adjust the frequency characteristics. In the present invention, the frequency characteristic in a high frequency region is improved by attaching the mass member to the metal diaphragm and moving the secondary resonance frequency to the lower frequency side. The present invention is particularly preferred when the secondary resonance frequency obtained from the configuration of the piezoelectric vibrator alone is smaller than the predetermined upper limit frequency when the diameter of the metal diaphragm is smaller (for example, the diameter of the metal diaphragm is 14 mm or less). in the case of)
It is effective for As described above, when the diameter of the metal diaphragm is large to some extent, the frequency characteristics can be easily adjusted by adjusting the number and size of the sound emission holes. However, as the diameter of the metal diaphragm becomes smaller,
It is difficult to improve the reduction in sound pressure in a high frequency region only by adjusting the number and size of the sound output holes. The inventor has conceived of improving or adjusting the drop in sound pressure by changing the secondary resonance frequency (by shifting to a lower frequency), which causes the drop in sound pressure in a high frequency range. Was.

The primary resonance frequency (f) of the diaphragm is f =
(1 / 2π) (1 / mc) ^1/2 . Where m is the equivalent mass and C is compliance. The secondary resonance frequency appears along with the primary resonance frequency. The equivalent mass is not the mass of the diaphragm itself, but a mass that actually participates in the vibration when vibrating, and the equivalent mass changes depending on the supporting structure of the diaphragm, the supporting conditions, and the like. The compliance C is a constant indicating the softness of the vibrating body, and the larger C means that the diaphragm is softer. In order to lower the secondary resonance frequency (shift to a lower frequency side), m or C may be increased. However, even if C is increased, if C is increased too much, the diaphragm cannot be supported and the shape cannot be maintained. In reality, the thickness of the metal vibrating plate of the piezoelectric vibrator is almost reduced to a state close to its limit, and it is impossible to further increase the C (softness) of the metal vibrating plate. Therefore, the inventors have considered reducing the secondary resonance frequency by increasing m (equivalent mass). A simple way to increase m (equivalent mass) is
The purpose is to increase the thickness of the metal diaphragm and increase the mass of the metal diaphragm. However, if m is increased in this way, C will be reduced, and consequently, it is difficult to lower the secondary resonance frequency. Therefore, in the present invention, m (equivalent mass) is increased by attaching the mass member to the piezoelectric vibrator. In the present invention, the mass member is disposed at the center of the piezoelectric vibrator in order to most effectively increase m (equivalent mass) with a light and small mass member. If the mass member is not disposed at the center, the mass of the mass member becomes heavy, resulting in an increase in the size of the mass member and a decrease in the C of the diaphragm. Such a problem does not occur if it is arranged at the center of the.

According to the present invention, the equivalent mass is increased by disposing the mass member at the center of the piezoelectric vibrator,
By shifting the secondary resonance frequency to a lower frequency side, it is possible to prevent a decrease in sound pressure in a frequency region having a high frequency characteristic and to adjust the frequency characteristic in a high frequency region.

Although the shape of the mass member is arbitrary, it is preferable to make the mass member plate-shaped in order to reduce the thickness. Since the metal diaphragm is usually in a disk shape, it is ideal that the mass member is also formed in a disk shape and arranged substantially concentrically with the metal diaphragm. In this manner, the frequency characteristics can be adjusted by minimizing the mass and size of the mass member. Specifically, the frequency characteristics are adjusted by adjusting the secondary resonance frequency obtained from the piezoelectric vibrator by setting the mass and the shape and dimensions of the mass member. If the mass and the shape of the mass member are set so that the secondary resonance frequency approaches a predetermined upper limit frequency, the mass characteristics of the mass member can be minimized and the frequency characteristics can be effectively adjusted. The predetermined upper limit frequency is an upper limit of a frequency that requires a sound pressure equal to or higher than a predetermined value that is naturally determined according to a use. If the frequency characteristics are adjusted to conform to the above-mentioned standard of the reception frequency characteristics of the Communication Machinery Manufacturers Association, the upper limit frequency of 3400 Hz is the predetermined upper limit frequency. Therefore, in this case, the mass and the shape and dimension of the mass member may be set so that the secondary resonance frequency approaches 3400 Hz. It goes without saying that the number and size of the sound emission holes are also adjusted so that the resonance frequency of the front air chamber is slightly lower than the upper limit frequency.

When the mass member is joined onto the piezoelectric ceramic element of the piezoelectric vibrator, a silicone rubber-based adhesive having elasticity in a cured state is used as the adhesive. This is to prevent the mass member from alienating the deformation of the piezoelectric vibrator. If an adhesive exhibiting little elasticity after curing is used as an adhesive, the movement or deformation of the piezoelectric ceramic element is alienated due to the presence of the mass member, so that sufficient vibration may not be generated and the sound pressure may decrease. is there. The same applies to the case where a mass member is adhered to the center of the surface opposite to the surface of the metal diaphragm to which the piezoelectric ceramic element is joined, and in this case, an adhesive having elasticity in a cured state is used as the adhesive. When used, there is an effect that the compliance of the metal diaphragm can be prevented from being reduced. In particular, when the mass member is bonded to the surface opposite to the surface of the metal diaphragm to which the piezoelectric ceramic element is bonded, the thickness of the case on which the piezoelectric ceramic element is disposed can be reduced.

Preferably, the peripheral edge of the metal diaphragm is supported on the insulating case by a support structure that does not substantially reduce the substantial diameter of the metal diaphragm. This is because when the substantial diameter of the metal diaphragm is substantially reduced, it is necessary to further increase the equivalent mass of the mass member.

It is preferable that the mass member be as soft as possible so as to minimize the compliance of the metal diaphragm. However, in order to obtain a certain mass, a metal plate is inevitably used. In this case, it is preferable to use an inexpensive material having a specific gravity as large as possible, such as an iron-nickel alloy.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic partial cross-sectional view of a handset of a mobile phone in which a piezoelectric sounder (or a piezoelectric speaker) according to an embodiment of the present invention is disposed, and FIG. 2 is an embodiment of the present invention used in FIG. It is a schematic sectional drawing of the piezoelectric transducer of an example. In FIG. 2, the thickness of each part is exaggerated for easy understanding.

As shown in FIG. 1, this telephone receiver has a structure in which a piezoelectric transducer 2 which is combined with the housing 1 to form a piezoelectric sounder is mounted on a housing 1. The housing 1 integrally has a fitting portion (projecting portion) 4 for attaching a piezoelectric transducer to an inner wall portion of the housing body 3.
The projection 4 has a cylindrical shape, and has a cutout recess 4a into which the positioning projection half 7f of the piezoelectric transducer 2 is fitted. The housing body 3 has one or more sound emission holes 3a formed in an inner portion surrounded by the protruding portion 4. A ring-shaped spacer 5 is arranged on the inner periphery of the protrusion 4. The projection 4 has a positioning projection half 7f.
The end of the front case 6 of the piezoelectric transducer 2 is fitted via the ring-shaped spacer 5 in a state where the notch recess 4a is fitted. Specifically, the piezoelectric converter is arranged such that the opening 6c of the front case 6 faces the sound emission holes 3a formed in the housing main body 3, that is, the opening 6c is covered by the wall of the housing main body 3. 2 is fitted to the protrusion 4. In this state, a front air chamber R1 is formed between the wall of the housing body 3 and the piezoelectric vibrator 8 of the piezoelectric transducer 2.

As shown in detail in FIG. 2, the piezoelectric transducer 2 is constructed by fitting a front case 6 forming a first case half and a back case 7 forming a second case half. The housing has a split storage case (insulating case) in which a piezoelectric vibrator 8 that vibrates according to an electric signal is stored. In this embodiment, the fitting portions are joined by welding or the like in order to prevent air leakage from the fitting portions of the front case 6 and the back case 7. Front case 6 is shown in FIGS.
As shown in detail in (C), the bottom wall 6a and this bottom wall 6
a peripheral wall portion 6 extending from the outer peripheral portion so as to surround the outer peripheral portion
b, and is integrally formed of an insulating resin material made of PPO resin containing glass. FIG. 3 (A)
(C) are a plan view, a sectional view, and a back view of the front case 6. A circular opening 6c that partially exposes the metal vibration plate 8a of the piezoelectric vibrator 8 is formed in the bottom wall 6a. The diameter of the opening 6c is so small that the finger does not touch the metal diaphragm 8a during the assembling work of the telephone and large enough not to cause resonance. A positioning projection half 6d having a rectangular parallelepiped shape is integrally provided on the outer peripheral portion of the bottom wall 6a. The peripheral wall portion 6b
It has a substantially cylindrical shape with a notch 6e. The notch 6e is formed at a position corresponding to the positioning projection half 6d. The notch 6e is provided with the lead wires 10a, 10b when the back case 7 is fitted to the front case 6.
Is finally formed, and the inside thereof is sealed with a sealant 11. Surrounding wall 6b
An annular rib 6f extending continuously in the circumferential direction is formed integrally with the inner wall at a position near the opening 6c. An inclined surface, that is, a first tapered portion 6g is formed on the outer surface of the inner wall portion of the rib 6f. The first tapered portion 6g is formed so as to expand radially outward (that is, expand in diameter) as the distance from the opening 6c increases.

The back case 7 constituting the second case half
Is shown in detail in FIG. 2 and FIGS. 4 (A) to 4 (C),
A peripheral wall portion 7b rising from the bottom wall portion 7a so as to leave a disk-shaped bottom wall portion 7a and an edge portion 7a1 of the bottom wall portion 7a.
And, like the front case 6, a glass-filled P
It is integrally formed of an insulating resin made of PO resin. 4A to 4C are a plan view, a cross-sectional view, and a back view of the back case 7. A leak hole 7c is formed in the bottom wall 7a. The leakage hole 7c is formed at the center of the bottom wall 7a, and a braking cloth 9 is joined or bonded to an opening at one end located inside the rear case 7 of the leakage hole 7c so as to cover the leakage hole 7c. It is pasted (Fig. 2). Reinforcing ribs 7d are formed on the inner surface of the bottom wall 7a facing the front case 6. The reinforcing ribs 7d are formed in a lattice shape, and have a shape and dimensions that can increase the strength of the back case 7. A positioning projection half 7f is formed on the outer periphery of the bottom wall 7a. The positioning projection half 7f is composed of two rectangular parallelepiped projecting pieces 7f1 and 7f2, and a plate-like portion 7f3 connected to the bottom wall 7a. When the back case 7 is fitted to the front case 6, the positioning projection half 6d of the front case 6 is fitted to the positioning projection half 7f while being sandwiched between the protruding pieces 7f1 and 7f2. It should be noted that, with the back case 7 fitted to the front case 6,
A gap in which a and 10b are led out of the piezoelectric transducer 2 is formed between the positioning protrusion half 6d and the plate-like portion 7f3. The lead-out portions 10a and 10b can be easily led out and the sealing agent can be easily injected into the plate-like portion 7f3.
, 7f2 are formed with semicircular notches 7f4 so as to increase the strength of attachment to bottom wall 7a.

The peripheral wall 7b has a substantially cylindrical shape having a cutout 7g. The notch 7g is formed at a position corresponding to the positioning projection half 7f. The notch 7g forms a gap for leading out the lead wires 10a and 10b when the back case 7 is fitted to the front case 6;
The inside thereof is filled with a sealant 11 made of a silicone rubber-based adhesive. An inclined surface, that is, a second tapered portion 7h is formed on the outer surface of the inner wall of the peripheral wall 7b. This second
The first tapered portion 6g of the front case 6 is
Similarly to the above, it is formed in such a direction that it spreads radially outward (that is, expands in diameter) as it moves away from the bottom wall portion 7a.

As shown in FIG. 2, the peripheral walls 6 b, 7 b of the front case 6 and the rear case 7 are fitted so that the end surface 6 b 1 of the peripheral wall 6 b contacts the edge 7 a 1 of the rear case 7. It is configured in combination. As described above, the groove G is formed on the inner wall of the peripheral wall of the insulating case in a state where the peripheral walls 6b and 7b are fitted to each other. This groove G
Opens inside the insulation case (towards the center)
In other words, the cross-sectional shape of the piezoelectric vibrator 8 is a substantially V-shaped groove that expands toward the center and extends along the peripheral wall of the insulating case to receive the peripheral edge of the metal diaphragm 8a of the piezoelectric vibrator 8. The shapes of the inner wall portions (or the shapes of the first and second tapered portions) of the peripheral wall portions 6b and 7b are each configured to form such a groove portion G.

As shown in the schematic views of FIGS. 5A and 5B, the piezoelectric vibrator 8 has a plate-shaped metal vibration plate 8a and a first electrode portion 8a1 on an outer peripheral portion of the metal vibration plate 8a. And a mass member 8c provided on the piezoelectric ceramic element 8b. FIG.
5A is a schematic cross-sectional view of the piezoelectric vibrator 8 and FIG.
FIG. 3 is a schematic plan view of the piezoelectric vibrator 8. Metal diaphragm 8
“a” is made of a circular metal plate having a thickness of 0.03 mm and a diameter of 14 mm made of an iron-nickel alloy. The piezoelectric ceramic element 8b includes a piezoelectric ceramic 8b1 and a bonding electrode layer 8b2 and a non-bonding electrode layer 8b3 provided on both surfaces of the piezoelectric ceramic 8b1, respectively.
It has a thickness of 0.05 mm and a diameter of 11.3 mm. The joining electrode layer 8b2 is joined so as to be electrically connected to the metal diaphragm 8a. The first electrode portion 8a1 and the non-bonding electrode layer 8b3 have lead wires 10a and 10a, respectively.
0b is connected by soldering, and the piezoelectric vibrator 8 vibrates according to an electric signal given between the first electrode portion 8a1 and the non-bonding electrode layer 8b3.

The mass member 8c is formed of a circular metal plate having a thickness of 0.1 mm and a diameter of 5.6 mm made of an iron-nickel alloy, and is adhered so as to be arranged substantially concentrically with the metal diaphragm 8a. It is bonded to the non-bonding electrode layer 8b3 by the agent. The adhesive used for joining the mass member 8c is such that the mass member 8c does not alienate the deformation of the piezoelectric vibrator 8.
It is preferable to use a material having elasticity in a cured state. In this example, a silicone rubber-based adhesive was used. The mass member 8c plays a role of adjusting the secondary resonance frequency of the piezoelectric vibrator 8 to adjust the frequency characteristics of the piezoelectric sounder, and sets the secondary resonance frequency obtained from the piezoelectric vibrator 8 to a predetermined upper limit frequency. It has a configurable mass and shape. In this example, the secondary resonance frequency of the piezoelectric vibrator 8, which was 4000 Hz by setting the diameter of the metal diaphragm 8a to 14 mm, becomes 3400 Hz (the upper limit frequency of the standard established by the Telecommunications Machinery Industry Association). Mass member 8c
Was set to 20 mg.

The piezoelectric vibrator 8 has the first and second tapered portions (wall portions surrounding the groove G) 6g and 7h so that the mass member 8c faces the inside of the storage case (toward the rear case 7). It is fixed (FIG. 2).

When assembled in the above configuration, the contact state between the peripheral portion of the metal diaphragm 8a and the first and second tapered portions 6g and 7h is any one of the states shown in FIGS. The states are mixed. This is based on the processing accuracy of the insulating case and the metal diaphragm and the dimensional error caused by the expansion and contraction of the material. In design, the dimensions of each part are determined so as to be in the state shown in FIG.

In the contact state shown in FIG.
The peripheral edge of the metal diaphragm 8a is received in the groove G such that a slight gap is formed between the peripheral edge of the metal diaphragm 8a and the groove G in the contact state shown in FIGS. G and is received in the groove G. In the example shown in FIG.
End 6g of enlarged diameter of first tapered portion 6g of front case 6
1 is separated from the enlarged end 7h1 of the second tapered portion 7h of the rear case 7 by the thickness of the metal diaphragm 8a,
Between the end 6g1 and the end 7h1, the first wall of the peripheral wall 6b is provided.
The contact inner wall portion 6h that is continuous with the tapered portion 6g is exposed. In the example shown in FIG. 8, the enlarged end 6g1 of the first tapered portion 6g of the front case 6 is in contact with the enlarged end 7h1 of the second tapered portion 7h of the back case 7.
Actually, since the metal diaphragm 8a is made of metal and the tapered portion is formed of resin, the corner portion of the metal diaphragm 8a is in a state of being cut into the tapered portion.

In the contact state shown in FIG.
a and the inner wall 6g of the first case half 6 and the second case 6a.
Between the inner wall 7h of the case half 7 and the space (front air chamber R1) located on the front side of the metal diaphragm and the space (rear air chamber R2) located on the back side. An airtight seal portion (insulating resin melt-cured portion) K is formed. FIG.
In the contact state shown in FIG. 7, the front air chamber R is located between the peripheral edge of the metal diaphragm 8a and the inner wall 6g of the first case half 6.
An airtight seal portion (insulating resin melt-cured portion) K for preventing communication between 1 and the rear air chamber R2 is formed. Hermetic seal part K
Is formed by dissolving the wall portion of the first tapered portion 6g with a solvent (for example, dichloromethane) that dissolves the PPO resin of the first tapered portion 6g, and then evaporating the solvent to disappear.

Next, the piezoelectric transducer of this embodiment and the mass member 8
c, a piezoelectric transducer of the comparative example having the same structure as that of the present embodiment is made, and each piezoelectric transducer is mounted on the housing 1 as shown in FIG. Examined. FIG. 9 shows the relationship between the sound pressure of each piezoelectric sounder and the frequency of the piezoelectric vibrator. In the figure, A, A1 and A2 indicate the characteristic curve, the peak of the primary resonance, and the peak of the secondary resonance of the piezoelectric sounder of the present invention.
B, B1, and B2 show the characteristic curve, the peak of the primary resonance, and the peak of the secondary resonance of the piezoelectric sounder of the comparative example. From this figure, in the piezoelectric sounding device of the comparative example, the secondary resonance frequency is the upper limit (3400H) of the standard established by the Telecommunications Industry Association.
z) is surpassed. On the other hand, the mass member 8c
In the piezoelectric sounder of the present invention provided with
It can be seen that the frequency can be set to 400 Hz.

FIG. 10 shows the sensitivity of each piezoelectric sounder and the frequency of the piezoelectric sounder (primary resonance frequency and secondary resonance frequency based on vibration, resonance obtained from the front chamber, and resonance obtained from the rear chamber). And the allowable range of the frequency characteristics of the receiver set by the Telecommunications Machinery Manufacturers Association. In the figure, A and B show the characteristic curves of the piezoelectric sounder of the present invention and the comparative example, and C and D
Indicates the allowable upper and lower limits. As shown in the drawing, in the piezoelectric sounder of the comparative example, the secondary resonance frequency is 3400 Hz.
In the piezoelectric sounder of the present invention in which the mass member 8c is provided while the frequency of the piezoelectric sounder falls below the lower limit in the frequency range of 300 to 3400 Hz, the secondary resonance frequency becomes 3400 Hz. It can be seen that the frequency of the piezoelectric sounder can be made to be within the allowable range in order to make them closer.

In this embodiment, the mass member is bonded on the piezoelectric ceramic element of the piezoelectric vibrator. However, the mass member is provided at the center of the surface opposite to the surface of the metal diaphragm to which the piezoelectric ceramic element is bonded. Mass members may be joined. Also in this case, when an adhesive having elasticity in a cured state is used as the adhesive, there is an effect that the compliance of the metal diaphragm can be suppressed from being reduced. If the mass member is bonded to the piezoelectric ceramic element in the rear air chamber side and the mass member is arranged in the front air chamber side, the thickness of the mass member is increased and the diameter of the mass member is reduced. And the reduction in compliance can be suppressed.

In this embodiment, the hermetic seal portion K is formed by using a solvent or an adhesive, but the hermetic seal portion is not necessarily formed.

[0034]

According to the present invention, the equivalent mass is increased by disposing the mass member at the center of the piezoelectric vibrator, and the secondary resonance frequency is shifted to the lower frequency side, so that the frequency characteristic is improved. It is possible to prevent a decrease in sound pressure in the frequency domain and adjust the frequency characteristics in a high frequency domain. Therefore, the size of the piezoelectric vibrator can be reduced by reducing the diameter of the piezoelectric vibrator while maintaining the desired sound quality.

[Brief description of the drawings]

FIG. 1 is a schematic partial cross-sectional view of a handset of a mobile phone in which a piezoelectric sounder according to an embodiment of the present invention is disposed.

FIG. 2 is a schematic sectional view of an example of a piezoelectric converter used in the embodiment of the present invention.

FIGS. 3A to 3C are a plan view, a cross-sectional view, and a back view of a front case used for the piezoelectric transducer of FIG. 2;

FIGS. 4A to 4C are a plan view, a cross-sectional view, and a back view of a back case used for the piezoelectric transducer of FIG.

FIGS. 5A and 5B are a cross-sectional view and a plan view of a piezoelectric vibrator used in an example of an embodiment of the present invention.

FIG. 6 is an enlarged view of a fixed portion between the piezoelectric vibrator and first and second tapered portions.

FIG. 7 is an enlarged view of another fixed portion between the piezoelectric vibrator and the first and second tapered portions.

FIG. 8 is an enlarged view of still another fixed portion between the piezoelectric vibrator and the first and second tapered portions.

FIG. 9 is a diagram showing the relationship between sound pressure and frequency of each piezoelectric sounder.

FIG. 10 shows the sensitivity and frequency of each piezoelectric sounder (frequency determined by overlapping the primary resonance frequency and secondary resonance frequency based on vibration, the resonance obtained from the front chamber, and the resonance obtained from the rear chamber). FIG.

FIG. 11 is a schematic partial sectional view of a conventional piezoelectric sounder.

FIG. 12 is a diagram showing the relationship between sound pressure and frequency of a conventional piezoelectric transducer.

FIG. 13 is a diagram illustrating a standard standard of a receiving frequency characteristic of a receiver set by the Telecommunications Industry Association.

[Explanation of symbols]

 2 Piezoelectric transducer 6 Front side case (first case half) 6a Bottom wall 6b Peripheral wall 6c Opening 6g First taper part 7 Back side case (second case half) 7a Bottom wall 7b Peripheral wall 7h Second tapered portion 8 Piezoelectric vibrator 8a Metal vibrating plate 8b Piezoelectric ceramic element 8c Mass member G Groove K Hermetic seal portion (insulating resin melt-cured portion)

Claims (7)

[Claims] 1. A peripheral portion of a metal vibrating plate of a piezoelectric vibrator in which a piezoelectric ceramic element is joined to a plate-shaped metal vibrating plate is supported by an insulating case, and the piezoelectric vibration supported by the insulating case is provided. In a piezoelectric sounder in which a front air chamber is formed on one side of a child and a rear air chamber is formed on the other side of the piezoelectric vibrator, the resonance frequency is adjusted at a central portion of the metal diaphragm. Wherein the frequency characteristic is adjusted by attaching a mass member for performing the operation. 2. A piezoelectric vibrator in which a piezoelectric ceramic element is joined to a plate-shaped metal vibration plate, a peripheral portion of the metal vibration plate is supported by an insulating case, and the piezoelectric vibration supported by the insulating case is provided. A front air chamber is formed on one side of the child, and a rear air chamber is formed on the other side of the piezoelectric vibrator, and a primary resonance frequency and a secondary resonance frequency based on the vibration of the piezoelectric vibrator, The resonance obtained from the front air chamber and the resonance obtained from the rear air chamber overlap to determine a frequency characteristic, and the secondary resonance frequency obtained from the configuration of only the piezoelectric vibrator is higher than a predetermined upper limit frequency. The piezoelectric vibrator in which the diameter dimension of the metal diaphragm is smaller as the height becomes higher, wherein a plate-shaped mass member for adjusting a resonance frequency is attached to a central portion of the metal diaphragm, and the piezoelectric vibrator to which the mass member is attached From Wherein the mass and shape of the mass member are determined so as to lower the secondary resonance frequency to be closer to the predetermined upper limit frequency and adjust the frequency characteristics. vessel. 3. A piezoelectric vibrator in which a piezoelectric ceramic element is joined to a disk-shaped metal diaphragm having a diameter of 14 mm or less, a peripheral portion of the metal diaphragm is supported by an insulating case, A front air chamber is formed on one side of the piezoelectric vibrator supported by the piezoelectric vibrator, and a rear air chamber is formed on the other side of the piezoelectric vibrator. A primary resonance frequency based on the vibration of the piezoelectric vibrator And a secondary resonance frequency, a resonance obtained from the front air chamber, and a resonance obtained from the rear air chamber are overlapped with each other to determine a frequency characteristic. The plate-shaped mass member is attached, and by setting the mass and the shape and dimension of the mass member, the secondary resonance frequency obtained from the piezoelectric vibrator to which the mass member is attached is adjusted to adjust the frequency characteristic. hand The piezoelectric sound generator according to claim Rukoto. 4. The piezoelectric sounding device according to claim 1, wherein said mass member is bonded onto said piezoelectric ceramic element using an adhesive having elasticity in a cured state. 5. The piezoelectric sound generation device according to claim 1, wherein said mass member is bonded to a center portion of a surface of said metal diaphragm to which said piezoelectric ceramic element is joined, opposite to a surface thereof. vessel. 6. The mass member has a disk shape,
4. The device according to claim 3, wherein the metal diaphragm is arranged substantially concentrically.
A piezoelectric sounder according to claim 1. 7. The metal casing according to claim 1, wherein the peripheral portion of the metal diaphragm is supported by the insulating case by a supporting structure that does not substantially reduce a substantial diameter of the metal diaphragm.
Or the piezoelectric sounder according to 3.