JPH0520956B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a piezoelectric receiver including a piezoelectric diaphragm having a structure in which a piezoelectric plate having electrodes on both principal surfaces is bonded to a metal diaphragm.

[Prior Art] A piezoelectric receiver equipped with a piezoelectric vibrator having a structure in which a ceramic piezoelectric plate having electrodes on both main surfaces thereof is attached to a metal diaphragm is known. In addition, an air chamber with a sound emission hole is provided on the front surface of the piezoelectric vibrator, and an air chamber with an acoustic leakage hole is provided on the rear surface to create a structure with three degrees of freedom, achieving high sensitivity in the entire reproduction frequency band. It is also known to widen the upper limit of the reproduction band and flatten the frequency characteristics.

[Problem to be solved by the invention] However, the upper limit of the band of the conventional piezoelectric handset is limited to a frequency that is approximately three times the fundamental resonance frequency of the piezoelectric diaphragm used in the receiver, so it is difficult to obtain the necessary reproduction band. In this case, the fundamental resonant frequency cannot be lowered unnecessarily, and this has been a major hindrance to achieving higher sensitivity and higher sound quality by lowering the fundamental resonant frequency.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a piezoelectric handset with high sensitivity and/or wideband.

[Means for Solving the Problems] The present invention for achieving the above object is characterized in that a piezoelectric plate having a first electrode on one main surface and a second electrode on the other main surface is a metal diaphragm. A piezoelectric diaphragm is attached to the piezoelectric diaphragm, and an air chamber is obtained that supports the edge of the metal diaphragm and has sound emission holes on the front surface of the piezoelectric diaphragm, and an air chamber is also provided on the rear surface of the piezoelectric diaphragm. In the piezoelectric receiver, the sound pressure of the piezoelectric diaphragm has a secondary resonance frequency that is approximately four times the primary resonance frequency of the piezoelectric diaphragm, and a sound pressure of a frequency sufficiently lower than the primary resonance frequency. Using a piezoelectric diaphragm that is higher than -6 dB with respect to pressure, the primary resonant frequency is set at the upper limit of the frequency band determined by approximately three times the primary resonant frequency of a piezoelectric receiver configured with three or more degrees of freedom. Adds a secondary resonance sound pressure approximately 4 times that of the
This invention relates to a piezoelectric receiver characterized by extending the next resonance frequency to about four times as high. That is, the diameter ratio of the piezoelectric diaphragm, for example, the piezoelectric ceramic plate and the metal diaphragm, is selected in advance so that the secondary resonance sound pressure is high, and the secondary resonance sound pressure obtained thereby is applied to the piezoelectric receiver. This relates to a piezoelectric receiver that is characterized by increasing sensitivity or widening the band by reducing resonance by adding the above frequency band to the upper limit of the frequency band.

[Function] In conventional piezoelectric handsets, it has been important to suppress the high-order resonance level, because it is thought that the high-order resonance of the piezoelectric diaphragm leads to a deterioration in speech quality. In contrast, the present invention actively utilizes the second-order resonance. That is, if the sound pressure near the second-order resonance frequency can be added to the upper limit of the reproduction band, the first-order resonance frequency can inevitably be lowered. In order to lower the first resonance frequency, sensitivity can be increased by increasing the areas of the piezoelectric plate and metal diaphragm, for example, without changing the area ratio S1/S2. As a result, a piezoelectric handset with high sensitivity and high quality can be obtained without reducing the band.

If the configuration is configured so that the primary and secondary resonance frequencies are not lowered, there will be little improvement in sensitivity in the band up to the primary resonance frequency, but the sensitivity at and around the secondary resonance frequency will increase. , it becomes possible to use the second-order resonance frequency, which has not been used in the past, and its vicinity as a reproduction band, and a wide band can be achieved.

[Embodiment] Next, a piezoelectric telephone receiver according to an embodiment of the present invention will be described with reference to FIGS. 1 to 6.

The piezoelectric receiver is constructed by attaching a piezoelectric diaphragm 1 to a container 2, as shown in FIGS. 1 and 2. The piezoelectric diaphragm 1 consists of a disk-shaped ceramic piezoelectric plate 3 and a disk-shaped metal diaphragm 4 to which it is attached. Although omitted in FIG. 1 for convenience of illustration, the ceramic piezoelectric plate 3
As shown in an enlarged view in FIG. 3, one main surface 3a
It has a circular first metal electrode 5 on almost the entire surface of the other main surface 3b, and has a circular second metal electrode 6 on almost the entire surface of the other main surface 3b. It is attached to the metal diaphragm 4.

The peripheral edge of a metal diaphragm 4 made of a brass disc is fixed to the container 2. A container 2 serving as a support means for the piezoelectric diaphragm 1 and an air chamber forming means is used to support the piezoelectric diaphragm 1.
A first air chamber 9 having a sound emission hole 8 on the front side is obtained, and a second air chamber 1 having an acoustic leakage hole 10 on the rear side is obtained.
1. Note that the acoustic leak hole 10 is closed with a damping material 10a.

By configuring the piezoelectric receiver to have three degrees of freedom as described above, it is possible to flatten the frequency characteristics, widen the reproduction band by extending the upper limit of the reproduction band, and increase the sensitivity of the entire reproduction band. Note that the conventional piezoelectric receiver is also configured with three degrees of freedom, but even if the degree of freedom is simply three, the upper limit of the reproduction band is about three times the fundamental resonance frequency of the piezoelectric diaphragm 1.

A first elastic lead wire 12 is connected to the first metal electrode 5 of the ceramic piezoelectric plate 3, and a second elastic lead wire 13 is connected to the metal diaphragm 4.

Here, a concrete method for increasing the secondary resonance sound pressure may be, for example, changing the ratio of the diameter D1 of the piezoelectric ceramic plate 3 to the diameter (effective diameter) D2 of the area where the metal diaphragm is not fixed. A change in the vibration state due to a change in the ratio D1/D2 between the diameter D1 of the piezoelectric diaphragm 3 and the diameter (effective diameter) D2 of the metal diaphragm 4 will be explained with reference to FIG. The bending motion of the piezoelectric diaphragm 1 below the first resonance frequency occurs as shown by the dotted line in FIG. 6A, and the bending motion of the piezoelectric diaphragm 1 at or near the second resonance frequency occurs as shown in FIG. 6B. occurs as shown by the dotted line.
At or near the second resonance frequency, the nodes 14 of the bending motion occur at positions concentrically surrounding the piezoelectric plate 3 as shown in FIG. 6B and FIG. Dotted line 1 inside the node 14 in Figure B
It is determined by the difference between the amount of volume displacement that occurs at the portion indicated by 5a and the amount of volume displacement that occurs at the portions outside of the joint portion 14 and indicated by dotted lines 15b and 15c. Furthermore, the position of this node 14 changes depending on the diameter of the ceramic piezoelectric plate, and as shown in FIG. In this case, the sound pressure increases.

In order to include the second resonance frequency in the reproduction band according to the present invention, the diameter (effective diameter) of the metal diaphragm 4 is
D2 is set to 33mm, and the diameter D1 of piezoelectric plate 3 is 25mm.
is set to . Note that the thickness of the piezoelectric plate 3 and the metal diaphragm 4 are both 0.1 mm, and the primary resonance frequency is approximately 900 Hz, which is significantly lower than that of the conventional one. In the diaphragm used in the present invention, the diameter and area of the piezoelectric plate 3 and metal diaphragm 4 are larger than those of conventional piezoelectric diaphragms in order to lower the first and second resonance frequencies.
The ratio D1/D2 of both diameters is 25/33, which is smaller than the conventional one.

If the piezoelectric diaphragm 1 is configured as described above, the sensitivity frequency characteristic of the piezoelectric diaphragm 1 alone will be as shown in a of FIG. 4,
The first resonance P1 is obtained at 900Hz and approximately 3600Hz
A relatively high level of second-order resonance P2 is obtained at the point. If a piezoelectric handset with three degrees of freedom is constructed using the piezoelectric diaphragm according to this embodiment as shown in FIG. 1, the sensitivity frequency characteristic will be as shown in c in FIG. and high sensitivity are achieved. Therefore, the second resonant frequency and its vicinity can be used as a reproduction band, and the sensitivity in the low and high frequencies becomes higher than before.

For comparison, a piezoelectric diaphragm in which the diameter D1 of the piezoelectric plate 3 is 28 mm, the diameter (effective diameter) D2 of the metal diaphragm 4 is 33 mm, and the thickness of both is 0.1 mm was fabricated in the same manner as in the example according to the present invention. When I calculated this sensitivity, I found that
The sensitivity frequency characteristic shown in FIG. 4b was obtained, and when this was supported by the container 2 in the same manner as in FIG. 1 to create a structure with three degrees of freedom, the sensitivity frequency characteristic became as shown in FIG. 5 d. In the case of this comparative example, the diameter of the metal diaphragm was set to a relatively large 33 mm, similar to the example of the present invention, so the sensitivity in the low range up to the first resonance frequency was not as great as that of the example of the present invention. There is no difference. However, the sensitivity at and around the second resonance frequency is extremely low and has almost a single peak characteristic, so when a piezoelectric receiver is configured, the
The sensitivity in the region of 3 kHz or higher is lower than that of the characteristic line c of the example.

When the ratio D1/D2 between the diameter D1 of the piezoelectric plate 3 and the diameter D2 of the metal diaphragm 4 is reduced according to the present invention, the above-mentioned difference becomes large and the sound pressure level becomes high.

On the other hand, when the ratio D1/D2 of the diameter D1 of the piezoelectric plate 3 and the diameter D2 of the metal diaphragm 4 is increased as in the comparative example, the second resonance frequency and the sixth
As shown in FIG. decreases. Therefore, in the case of the comparative example, the second-order resonance frequency and its vicinity cannot be effectively used as a reproduction band.

In the comparative example, the diameter of the metal diaphragm 4 was set relatively large according to the example, so the sensitivity in the low range was relatively high.
When setting the next resonance frequency to about 1200 Hz to widen the band, it is necessary to reduce the diameter of the metal diaphragm 4, and the sensitivity in the low range becomes worse than the embodiment of the present invention. The frequency characteristic is the fifth
It becomes e in the figure.

As described above, according to the embodiment of the present invention, it is possible to increase the sensitivity by lowering the first resonant frequency, and it is also possible to use the second resonant frequency and its vicinity as a reproduction band. Therefore, there is no reduction in high frequencies. As a result, a piezoelectric handset with high sensitivity and high quality can be provided.

[Modifications] The present invention is not limited to the above-described embodiments, and, for example, the following modifications are possible.

(1) The number of sound emitting holes 8 in FIG. 1 may be reduced to one. Further, a portion of the plurality of sound emitting holes 8 may be closed with a damping material (damper material) to flatten the frequency characteristics.

(2) When electrically connecting the lead wire 13 to the metal diaphragm 4 at the fixed end or in the vicinity thereof, it is not necessary to use a telescopic lead wire.

(3) The dimensions, shapes, etc. of the piezoelectric ceramic plate 3 and the metal diaphragm 4 can be changed in various ways. however,
In order to include the secondary resonance frequency and its vicinity in the reproduction band, the piezoelectric diaphragm is designed so that the secondary resonance sound pressure is -6 dB or more higher than the sound pressure at frequencies sufficiently lower than the primary resonance frequency of the piezoelectric diaphragm. 3 diameter D1
It is desirable to set a ratio D1/D2 between the diameter D2 of the metal diaphragm 4 and the diameter D2 of the metal diaphragm 4.

(4) The effects of the present invention are significantly obtained when the primary resonance frequency is set to approximately 1000Hz or less;
In this way, it is also possible to have a structure in which it is not set particularly low. Even in this case, the diameter of the piezoelectric plate 3
When the ratio D1/D2 between D1 and the diameter D2 of the metal diaphragm 4 is decreased, the second resonance frequency and the node 14 of the bending motion in the vicinity thereof are shifted to the periphery of the metal diaphragm 4 as shown in FIG. 6B. Because they are close to each other, a high sound pressure level can be obtained. As a result, the second resonant frequency, which is about four times the first resonant frequency, and its vicinity can also be included in the reproduction band, and a wide band can be achieved.

[Effects of the Invention] As explained above, by using the second-order resonance frequency and its vicinity as a reproduction band, it is possible to achieve higher sensitivity and/or a wider band.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the principle of a piezoelectric receiver according to an embodiment of the present invention, FIG. 2 is a cross-sectional view taken along the line -- in FIG. 1 with the lead wires removed, and FIG. FIG. 4 is a sensitivity frequency characteristic diagram of the piezoelectric diaphragms of the example and comparative example, and FIG. Fig. 6 is a diagram showing the vibration mode of the piezoelectric diaphragm of the example at the primary and secondary resonance frequencies, and Fig. 7 is the secondary resonance frequency of the comparative example. FIG. DESCRIPTION OF SYMBOLS 1... Piezoelectric diaphragm, 2... Container, 3... Ceramic piezoelectric plate, 4... Metal diaphragm, 5... First metal electrode, 6... Second metal electrode.

Claims (1)

[Scope of Claims] 1. A piezoelectric diaphragm comprising a piezoelectric plate having a first electrode on one main surface and a second electrode on the other main surface attached to a metal diaphragm; and a container formed to support an edge of the diaphragm and to provide an air chamber having a sound emission hole on the front surface of the piezoelectric diaphragm, and to provide an air chamber on the rear surface of the piezoelectric diaphragm. In a piezoelectric receiver configured with three or more degrees of freedom, 2 times the primary resonance frequency of the piezoelectric diaphragm, which is approximately four times the primary resonance frequency of the piezoelectric diaphragm.
The primary resonance frequency of a piezoelectric receiver configured with three or more degrees of freedom, using a piezoelectric diaphragm in which the sound pressure at the next resonance frequency is higher than -6 dB with respect to the sound pressure at a frequency sufficiently lower than the first resonance frequency. A secondary resonance sound pressure of approximately 4 times the primary resonance frequency is added to the upper limit of the frequency band determined by approximately 3 times the primary resonance frequency, thereby extending the band upper limit to approximately 4 times the primary resonance frequency. Piezoelectric receiver.