JPH0525238B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a piezoelectric electroacoustic transducer used in telephone handsets and the like.

Conventional configurations and their problems Piezoelectric electroacoustic transducers using piezoelectric vibrators constructed by bonding ceramic piezoelectric bodies to metal diaphragms are widely used as piezoelectric buzzers and piezoelectric sounding bodies. Recently, they are being used as telephone receivers and transmitters.

Generally, this piezoelectric vibrator is constructed as shown in FIGS. 1 and 2. That is, a circular flat ceramic piezoelectric body 2 having electrodes made of silver or the like formed on both surfaces is bonded to one side of a diaphragm 1 made of a circular flat metal using an adhesive.
Furthermore, the electrodes on the attachment surface of the ceramic piezoelectric body 2 and the diaphragm 1 are electrically connected.

A piezoelectric electroacoustic transducer using this piezoelectric vibrator is constructed as shown in FIG.

That is, a step 5 is provided inside the case 4 having the sound emitting hole 3 on the top surface, and the peripheral edge of the diaphragm 1 of the piezoelectric vibrator 6 is brought into contact with the step 5.
A back air chamber plate 8 having a support ridge 7 on the outer periphery is incorporated into the bottom surface of the diaphragm 1, and the periphery of the diaphragm 1 is fixed by the support ridge 7 of the back air chamber plate 8 and the stepped portion 5 of the case 4. was.

Further, an acoustic leak hole 9 is provided in the center of the back air chamber plate 8, and an acoustic resistor 10 is attached to the acoustic leak hole 9 so as to block it. Terminals 11 and 12 are provided, and the input terminal 11 has a lead wire 13 connected to the electrode of the ceramic piezoelectric body 2 of the piezoelectric vibrator 6.
However, a lead wire 14 connected to the diaphragm 1 is connected to the input terminal 12.

Note that the case 4 was provided with a stepped portion 5 and the back air chamber plate 8 was provided with a supporting protrusion 7 to serve as a fixed portion for the piezoelectric vibrator 6;
A fixing ring may be used as a fixed part separately from the case 4 and the back air chamber plate 8.

In a conventional piezoelectric electroacoustic transducer of this type, the fixed part of the piezoelectric vibrator 6, in this example the stepped part 5 and the supporting protrusion 7, have a circular ring shape, and the shape of the receiver of a telephone using this is circular. The frequency characteristics of the sound pressure level are generally measured by attaching the coupler to a coupler of a predetermined volume, but it is required that the coupler be located in the shaded area shown in FIG. 4, for example. In other words, 3,
Above 4KHz, it is necessary to attenuate at least 18dB/octave.

However, in general, when the peripheral edge of the circular flat piezoelectric vibrator 6 is fixed in the shape of a circular ring, many higher-order resonances occur in addition to the basic resonance. Figure 5 shows a piezoelectric vibrator 6 whose peripheral part is fixed in a circular ring shape.
In the example of the sound pressure frequency characteristic of a single unit, ₁ is the fundamental resonance frequency, ₂ , ₃ , and ₄ are the 2nd, 3rd, and 4th, respectively.
This is the next resonant frequency. However, in the case of a telephone handset, only the vicinity of the fundamental resonance is used, and higher-order resonances are not only unnecessary but also have an adverse effect. In other words, as shown in curve A in Figure 4, the sound pressure peaks (sensitivity peaks) B and C are located at the necessary parts above 3.4KHz.
occurs, making it impossible to achieve the necessary high-frequency attenuation characteristics.

OBJECTS OF THE INVENTION An object of the present invention is to provide a piezoelectric electroacoustic transducer that can suppress unnecessary sound pressure peaks in high frequencies.

Structure of the Invention In order to achieve the above-mentioned object, the present invention has a piezoelectric vibrator configured by bonding a ceramic piezoelectric body to a metal diaphragm, and a piezoelectric vibrator that is installed in a case having a sound emission hole on the top surface, which is flush with the top surface of the case. Incorporate it so that it has a spacing of
A back air chamber plate having an acoustic leakage hole is connected to the piezoelectric vibrator at a constant distance on the bottom of the case, and at least one of the fixed portions of the circumferential edge of the piezoelectric vibrator is made non-circular. This configuration is intended to prevent high-order resonance of the piezoelectric vibrator from occurring and suppress unnecessary high-frequency sound pressure peaks.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described using FIGS. 6 to 12 of the drawings.

First, the structure of the piezoelectric resonator and the structure of the piezoelectric electroacoustic transducer are substantially the same as those shown in Figs. Therefore, we will explain its characteristics.

Basically, as shown in FIG. 6, the fixed portion 15 at the peripheral edge of the piezoelectric vibrator 6, which is made of a metal diaphragm 1 to which a ceramic piezoelectric body 2 is bonded, is made non-circular as shown with diagonal lines. At the point.

Specifically, as shown in FIGS. 7 and 8, the stepped portion 5 of the case 4 having the sound emitting hole 3 on the upper surface is shaped like an ellipse.

Further, as shown in FIGS. 9 and 10, the support protrusion 7 of the back air chamber plate 8 may have an elliptical shape.

Note that the shapes of the step portion 5 of the case 4 and the supporting protrusion 7 of the back air chamber plate 8 may be oval instead of oval.

The ratio of the major axis and minor axis of this elliptical or oblong shape is
1.05/1 to 1.25/1 is desirable. The solid line in Figure 11 is the sound pressure frequency characteristic when the ratio of the major axis to the minor axis is 1.05/1, and the broken line is the sound pressure frequency characteristic when the ratio of the major axis to the minor axis is 1.25/1. As the ratio increases, the unnecessary sound pressure peaks in the high range become larger, and as the ratio increases, the unnecessary sound pressure peaks in the high range become smaller. The diameter ratio is 1.05/1~
A range of 1.25/1 is preferred.

Further, the stepped portion 5 of the case 4 and the supporting protrusion 7 of the back air chamber plate 8 may both have a non-circular shape, but a sufficient effect can be obtained just by making either one of the shapes non-circular.

Further, a fixed portion 15 at the peripheral edge of the piezoelectric vibrator 6
In addition to the above-mentioned ellipses and ellipses, it may also be a flower shape consisting of continuous unevenness as shown in Figure 12, and although not shown, all non-circular shapes such as squares and polygons can be targeted and have the effect. .

Further, in the above embodiment, the stepped portion 5 of the case 4 and the supporting protrusion 7 of the back air chamber plate 8 are made non-circular, but the case 4 is cylindrical and the back air chamber plate 8 is made non-circular.
In order to fix the peripheral edge of the piezoelectric vibrator 6 as a simple disc-shaped piezoelectric vibrator 6, a non-circular support ring such as an ellipse or an ellipse may be placed above or below the piezoelectric vibrator 6 and fixed.

The reason why the peripheral fixed portion of the piezoelectric vibrator 6 is made non-circular is as follows.

The vibration mode of the circular piezoelectric vibrator 6 when it resonates is:
The resonance frequency is determined by the inner diameter of the fixed part 15 in a flexural vibration mode in which the center of the piezoelectric vibrator 6 is an antinode and the inner side of the fixed part 15 is a node. Therefore, when the fixed portion 15 is in the shape of a circular ring, clear resonance occurs at a specific frequency, and as shown in FIG. 5, the high-order resonance level also becomes high.

However, if the fixed portion 15 is made non-circular as in the present invention, the fixed diameter of the piezoelectric vibrator 6 is not constant from the center but differs in the circular direction, so that the resonance energy is dispersed into a plurality of frequencies. Therefore, the fundamental resonance, where the resonance energy is the largest, is not affected much, but the resonance energy is dispersed in the higher-order resonances, and the second-order, third-order, and fourth-order resonances become less likely to occur.

The sound pressure frequency characteristics of the piezoelectric electroacoustic transducer of the present invention are as shown by the solid line in FIG.
Compared to the conventional example shown by the broken line, unnecessary high-frequency sound pressure peaks are significantly reduced, indicating flat and good high-frequency attenuation characteristics.

Effects of the Invention As described above, in the piezoelectric electroacoustic transducer of the present invention, since the fixed portion of the peripheral edge of the piezoelectric vibrator is made non-circular, high-order resonance can be efficiently suppressed, and unnecessary high-frequency sound pressure peaks can be suppressed. It has the effect of eliminating the occurrence of noise and creating a flat sound pressure frequency characteristic, and when used in telephone receivers and transmitters, it enables extremely clear voice transmission and reception, and has great industrial value. It is what it is.

[Brief explanation of the drawing]

Figure 1 is a top view of a general piezoelectric vibrator, Figure 2 is a front view of the same, Figure 3 is a sectional view of a piezoelectric electroacoustic transducer using the same piezoelectric vibrator, and Figure 4 is the invention of the present invention. and a sound pressure frequency characteristic diagram of a conventional piezoelectric electroacoustic transducer, FIG. 5 is a sound pressure frequency characteristic diagram of a single piezoelectric vibrator with a conventional piezoelectric vibrator fixed structure, and FIG. An explanatory diagram showing an example of a fixing structure of a piezoelectric vibrator in an acoustic transducer, FIG. Figure 9 is a top view of the same back air chamber plate, Figure 10 is a half-sectional front view of the same, and Figure 1
FIG. 1 is a sound pressure frequency characteristic diagram based on the ratio of the major axis to the minor axis of the same embodiment, and FIG. 12 is an explanatory diagram showing a fixing structure of a piezoelectric vibrator of another embodiment. DESCRIPTION OF SYMBOLS 1... Metal diaphragm, 2... Ceramic piezoelectric body, 3... Sound emission hole, 4... Case, 5... Step part,
6...Piezoelectric vibrator, 7...Support protrusion, 8...Back air chamber plate, 9...Acoustic leak hole, 10...Acoustic resistor,
11, 12... Input terminal, 13, 14... Lead wire, 15... Fixed part.

Claims (1)

[Claims] 1 A piezoelectric vibrator composed of a ceramic piezoelectric body coupled to a metal diaphragm is installed in a case with a sound emission hole on the top surface at a constant distance from the top surface of the case, and a sound source is attached to the bottom of the case. A piezoelectric electroacoustic transducer in which a back air chamber plate having a leakage hole is coupled to the piezoelectric vibrator at a constant distance, and at least one of the fixed portions of the peripheral edge of the piezoelectric vibrator is made non-circular. .