JPS6360400B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention utilizes Helmholtz acoustic resonance,
This invention relates to a piezoelectric buzzer that allows easy adjustment of resonance frequency over a wide band.

Buzzers that utilize resonance include the electromagnetic type, which has been widely used in the past, and the piezoelectric type, in which a piezoelectric vibrator is fixed to a metal plate. This figure shows the basic structure of a piezoelectric vibrator, which is used as a sound source in small portable devices such as wristwatches and electric desktop calculators to reduce size, thickness, and power consumption. 1 is a piezoelectric vibrator. . 2 is a circular diaphragm made of a thin elastic metal; 3 is a piezoelectric vibrator having a smaller diameter than the diaphragm 2 and has electrodes 4 and 4' on both sides and is polarized; It is fixed to the diaphragm 2 via the diaphragm 2. 6 and 6' are fixed to the diaphragm 2 and the piezoelectric vibrator 3 by lead wires, respectively. When an alternating current is applied to such a piezoelectric vibrator 1, the piezoelectric vibrator 3
expands and contracts in response to the alternating current, and the diaphragm 2 also causes bending vibrations corresponding to the expansion and contraction of the piezoelectric vibrator 3.

Piezoelectric buzzers, which are generally small and have good electroacoustic conversion efficiency, utilize the resonance effect of a diaphragm, but they are composed of a resonant space and a sound emission opening, each part of which is sufficiently small compared to the wavelength of the sound wave emitted. The use of Helmholtz cavity resonance is extremely efficient. However, the Q value of the resonance of these diaphragms and the acoustic resonance caused by the sound emission holes in the resonant space is relatively high, and there are also variations in the resonant frequency due to manufacturing, making it difficult to match the resonant frequency and the drive frequency. . Therefore, these piezoelectric buzzers whose resonant frequency cannot be changed, although they utilize an efficient resonant space, result in products with a large variation in volume, and their characteristics are not fully utilized.

Next, a conventional example that improves the above-mentioned problems will be explained according to the figures. In Figs. 3 and 4, 1 is the above-mentioned piezoelectric vibrator in which a piezoelectric vibrator 3 is fixed to a diaphragm 2. . Reference numeral 7 denotes a storage box having a cylindrical shape with an open bottom end, a sound emitting hole 7a is provided on the top surface, and a step 7b is provided at a predetermined position inside, and the piezoelectric vibrator 1 is supported and fixed around the step 7b. Reference numeral 8 denotes an adjustment plate for adjusting the opening area of the sound emission hole 7a, one end of which is connected to the storage box 7.
It is rotatably supported on the shaft. 9 is a resonant space formed by the storage box 7 and the piezoelectric vibrating body 1.

In such a configuration, when an alternating current is applied to the piezoelectric vibrator 1 via the lead wires 6, 6', the piezoelectric vibrator 1 vibrates and the air in the resonance space 9 vibrates. In this case, there was a drawback that the sound pressure decreased as the opening area of the sound emitting hole 7a became smaller due to the movement of the adjustment plate 8.

Figure 5 shows a second conventional embodiment, in which reference numeral 11 denotes a cylindrical storage box with openings at both ends, and a threaded portion 1 around the outside of the storage box.
1a, a convex portion 11b is provided at a predetermined position on the inside, and the piezoelectric vibrating body 1 is supported and fixed around the stepped portion 11b. 12 is a cylindrical outer box with an open bottom end, and a sound emitting hole 12 in the center of the top end.
a, and a threaded portion 12b is provided on the inside to be screwed into the storage box 11. 13 is a resonant space formed by the outer box 12, the storage box 11, and the piezoelectric vibrator 1.

In such a configuration, when an alternating current is applied to the piezoelectric vibrator 1, the piezoelectric vibrator 1 vibrates and the air in the resonance space 13 vibrates. In this case, when the outer box 12 is rotated, the volume of the resonant space 13 changes, making it possible to match the resonant frequency and the driving frequency, but since the external dimensions change, it is difficult to store it in a limited device. However, there was a drawback that the overall frequency was also distorted.

The present invention solves the above-mentioned drawbacks, and the present invention rotatably engages an adjustment box provided with a sound emission hole in a resonance box so that the sound emission hole of the resonance box provided with the sound emission hole is located inside, To provide a piezoelectric buzzer in which resonance frequency is adjusted by mutually rotating a box and an adjustment box, and sound pressure at resonance can be stably obtained.

An embodiment of the present invention will be described below with reference to the drawings.
In Fig. 6, reference numeral 21 denotes a cylindrical resonance box with an open bottom end, and a stepped portion 21b is provided at a predetermined position on the inside and a stepped portion 21c is provided at a predetermined position on the outside.The side wall has a rectangular (or circular) opening area. Sound emission hole 21 of approximately 0.8cm ²
A is provided. The piezoelectric vibrating body 1 has a diameter of approximately
The periphery is supported and fixed to the step part 21b with a length of 4.5 cm,
A resonance space 23 of about 10 cm ³ is formed inside the resonance box 21 . 22 is a cylindrical adjustment box with one end open;
A rectangular (or circular) sound emitting hole 22a with an opening area of approximately 3 cm ² is provided on the side wall, and the opening end is engaged with the outer step 21c of the resonance box 21 without any gap and is rotatably engaged. and the sound emission hole 21 of the resonance box 21
A sound guide space 24 of approximately 10 cm ³ is formed surrounding the space a. In this case, a sound guiding portion 24a is formed between the sound emitting hole 21a and the sound emitting hole 22a. 6 and 6' are lead wires.

In the above configuration, when an alternating current is applied to the piezoelectric vibrating body 1 via the lead wires 6, 6', the piezoelectric vibrating body 1 vibrates and vibrates the air in the resonance space 23 and the sound guiding space 24. In this case, when the resonance box 21 and the adjustment box 22 are rotated relative to each other, the length of the sound guide portion 24a changes, and the resonance frequency changes. Also sound emission hole 21
There are various possible paths for the sound guiding part 24a within the sound guiding space 24 from a to the sound emitting hole 22a, but one is possible because the dimensions of the resonance box 21, adjustment box 22, etc. The phase difference between the sounds is small, and there is almost no cancellation of each other. This relationship is shown in FIG. 7 through experiments. The vertical axis represents the resonance frequency and the horizontal axis represents the rotation angle, and the sound emission hole 21a of the resonance box 21 and the adjustment box 22
The point where the sound emission hole 22a of the
It shows how symmetrical characteristics are obtained with 180° as the boundary. FIG. 8 is a diagram showing the frequency characteristics of the piezoelectric buzzer, in which the vertical axis represents the sound pressure and the horizontal axis represents the frequency. The solid curve represents the resonance frequency f _R of the piezoelectric vibrator 1,
The relationship between the resonance frequency f _O 〓 when the sound emission hole 21a of the resonance box 21 and the sound emission hole 22a of the adjustment box 22 are aligned is shown, and the resonance box 21 and adjustment box 22 are rotated relative to each other. Accordingly, the resonant frequency f _O of the resonant box becomes low, and the resonant frequency when it reaches its lowest value at a rotation angle of 180° is defined as f _p 〓, which is shown by a dotted curve. When the frequencies of the sound pressure amplified by the resonance box, which are at the same level as the sound pressure P at the resonance frequency f _R of the piezoelectric vibrator 1, are f ₁ and f ₂ , the resonance frequency f _R of the piezoelectric vibrator 1 is
In the case of designing a composite sound consisting of two sounds amplified by a resonant box, a frequency equal to or higher than the sound pressure P of the resonant frequency f _R of the piezoelectric vibrator 1 can be arbitrarily set in a wide range from f ₁ to f ₂ . You can easily obtain a distinctive complex sound that is pleasant to the ear.

Next, the second embodiment will be described according to the drawings. In FIG. 9, numeral 31 is a cylindrical resonance box with an open bottom end, and a stepped portion 31b is located at a predetermined position on the inside and a stepped portion 31c is located at a predetermined position on the outside. A sound emitting hole 31a of a predetermined size is provided at a predetermined position eccentrically on the upper end wall. The piezoelectric vibrating body 1 has a stepped portion 31b
Its periphery is supported and fixed to form a resonance space 33. Reference numeral 32 denotes a cylindrical adjustment box with an open bottom end, the inner diameter of which is approximately equal to the outer diameter of the resonance box 31;
A sound emitting hole 32a of a predetermined size is provided eccentrically at a predetermined position in the upper end wall, and the lower end of the opening is engaged with the outer step portion 31c of the resonance box 31 without a gap so as to be rotatably engaged. A sound guide space 34 is formed.

In the above configuration, when an alternating current is applied to the piezoelectric vibrator 1, the piezoelectric vibrator 1 vibrates and the resonance space 3
3. Vibrate the air in the sound guide space 34. In this case, by mutually rotating the resonance box 31 and the adjustment box 32, the length of the sound guide formed between the sound emission hole 31a and the sound emission hole 32a changes, so that an appropriate resonance frequency can be obtained. The resulting effect is similar to that of the first embodiment.

Next, the third embodiment will be described according to the drawings. In FIGS. 10 and 11, 41 is a cylindrical resonance box with an open bottom end, and a stepped portion 41b and a predetermined outer side are provided at a predetermined position inside the resonance box. A step portion 41c is provided at each position, and a sound emitting hole 41a of a predetermined size is provided at a predetermined position eccentrically on the upper end wall. Piezoelectric vibrator 1
is supported and fixed around the step portion 41b to form a resonance space 43. Reference numeral 42 denotes a cylindrical adjustment box with an open bottom end, the inner diameter of which is approximately equal to the outer diameter of the resonance box 42, and a sound emitting hole 42a of a predetermined size provided in the center of the upper end wall. partition wall 4 having a predetermined diameter and a predetermined height on concentric circles;
2b is integrally molded. The lower end of the opening of the adjustment box is connected to the outer step 41c of the resonance box, and the partition wall 4
The lower ends of the resonance boxes 2b are engaged with the upper end surfaces of the resonance boxes without any gaps, and the adjustment boxes are rotatably engaged with the outer sides of the resonance boxes to form the sound guide space 44, and the sound emission holes 41a
A sound guide portion is formed between the sound emitting hole 42a and the sound emitting hole 42a. In this case, the sound emitting hole 41a is arranged so as to be located outside the partition wall 42b.

In the above configuration, when an alternating current is applied to the piezoelectric vibrating body 1 via the lead wires 6, 6', the piezoelectric vibrating body 1 vibrates and generates sound, and the sound is amplified in the resonance space 43 and the sound emission hole 41a. and the sound guide section 44,
The sound is emitted to the outside through the sound emitting hole 42a. In this case, by mutually rotating the resonance box 41 and the adjustment box 42, the length of the sound guiding portion changes, so the resonance frequency also changes, and an appropriate resonance frequency can be obtained. The sound guide section is divided into two lines from the sound emission hole 41a of the resonance box 41 by the partition wall 42b of the adjustment box 42.
2a, the phase difference between the sounds passing through each sound guiding section is small because the dimensions of each part of the resonance box, adjustment box, etc. are sufficiently smaller than the wavelength of the sound wave, and they hardly cancel each other out. This effect is similar to that of the first embodiment.

As described above, in the present invention, by providing an adjustment box and rotating it mutually with the resonance box, the resonance frequency can be easily adjusted, and the yield of the product is also very good if it is fixed with adhesive at the best position. Furthermore, as shown in Fig. 8, a piezoelectric buzzer consisting of a complex sound in which frequencies f ₁ to _{f 2} are set in addition to the resonance frequency f _R is also extremely advantageous in terms of design because the resonance frequency can be adjusted.
It is highly effective for industrial use.

[Brief explanation of the drawing]

Fig. 1 is a plan view of the piezoelectric vibrator, Fig. 2 is a side view, Fig. 3 is a plan view of the first example of the conventional piezoelectric buzzer, Fig. 4 is a side sectional view, and Fig. 5 is the conventional piezoelectric buzzer. FIG. 6 is a side sectional view of one embodiment of the present invention, FIG. 7 is a diagram showing the rotation angle and resonance frequency of the adjustment box, and FIG. 8 is a diagram showing the frequency of sound pressure. 9 is a side sectional view of the second embodiment of the present invention, FIG. 10 is a plan view of the third embodiment of the present invention, and FIG. 11 is a side sectional view of the same. 1: piezoelectric vibrator, 2: diaphragm, 3: piezoelectric element,
6, 6': Lead wire, 21, 31, 41: Resonance box,
21a, 31a, 41a: sound emission hole, 22, 32,
42: Adjustment box, 22a, 32a, 42a: Sound emission hole, 23, 33, 43: Resonance space, 24, 34,
44: sound guide space, 24a: sound guide section, and the same reference numerals indicate the same parts throughout the figures.

Claims (1)

[Claims] 1 A piezoelectric vibrator is housed inside a resonance box provided with a sound emission hole to form a resonance space, and an adjustment box provided with the sound emission hole is rotatably formed with the resonance box to form a sound guide space. A piezoelectric buzzer, characterized in that the length of a sound guide portion that is engaged with each other and formed between a sound emission hole of the resonance box and a sound emission hole of the adjustment box is changed.