JPS5929039B2 - piezoelectric speaker - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a piezoelectric speaker using a bimorph type piezoelectric vibrator, and more particularly, to a piezoelectric speaker that achieves a wider band of reproduced sound by improving the fixed portion of the vibrator.

Due to the characteristics of the piezoelectric vibrator used as the drive source, piezoelectric speakers are thin and have low power consumption.As integrated circuits for generating melodies and synthesized voices have come into practical use in recent years, their uses have expanded. Demand has been expanding.

However, until now, piezoelectric speakers have low reproduction efficiency in the bass range, making it difficult to reproduce important range widths, and have only been put into practical use for high-pitched sounds.

2. Description of the Related Art Conventional piezoelectric speakers designed to reproduce low frequencies include those having a structure using a cantilever-shaped piezoelectric vibrator.

That is, as shown in FIG. 1, the piezoelectric vibrator 1 has a piezoelectric plate 3 attached to a rectangular metal plate 2, one side of which is inserted and fixed into the fixing part 4 of the case, and the metal plate 2 at the other end is inserted and fixed. The center point of the diaphragm 5 is connected to the diaphragm 5.

Note that the circumferential end of the diaphragm 5 is made of polyurethane foam 6, for example.
It is fixed to the opening 7 of the case through.

Although this cantilever beam structure inherently has a large amplitude, its reproduction efficiency in the low frequency range was low and could not be put to practical use.

SUMMARY OF THE INVENTION Therefore, the present invention aims to improve the reproduction efficiency particularly in the low frequency range and widen the frequency band of reproduced sound in a piezoelectric speaker using a cantilever-shaped piezoelectric vibrator.

The present invention was developed through intensive research aimed at improving the reproduction efficiency in the low frequency range of cantilever structure piezoelectric vibrators, and found that in the conventional case there was a problem with the vibration node position of the vibration mode, I found out that it is not being utilized.

In other words, the flexural resonance frequency (,fn) of a piezoelectric vibrator with a cantilever structure can be obtained from the following equation, where l is the effective length of the vibrator, t is the thickness, and αn is the constant determined by the vibration order. .

fncx-αn2·t/12 Here, the first-order resonance (fl), which is the lowest frequency resonance, determines the reproduction limit in the bass range, and the value of α1 in this case is about 1.9.

Therefore, the larger the resonance force of the first resonance, the higher the reproduction efficiency in the bass range and the wider the band.

Specifically, in the vibrator, the piezoelectric plate must be composited up to the metal plate surface at a position beyond the vibration node position of the vibration mode.

However, in the case of the speaker with the conventional configuration described above, even if the first end of the metal plate is ideally fixed with the fixing part 4, the position of the vibration node of the first resonance is indicated by the black dot in Figure 2 a. Since the pressing force at the fixed part 4 is actually limited, the vibration node position moves further inside the fixed part 4, and the composite part of the piezoelectric plate 3 was away from the vibration node position, and the first resonance was not effectively utilized.

Therefore, in this invention, by bending the metal plate on the fixed side of the vibrator, a vibration node in the first resonance is generated in the piezoelectric plate composite part of the metal plate, and the vibration force of the first resonance is reduced. This greatly improves reproduction efficiency in the bass range.

That is, in this invention, one metal plate of a piezoelectric vibrator is bent, the bent tip is fixed to a speaker case, etc. to form a cantilever structure, and a diaphragm is connected to the other tip of the metal plate that is not fixed. It is a piezoelectric speaker.

To explain this invention in detail based on FIG. 3, piezoelectric vibrator 1
, a piezoelectric plate 3 of a predetermined size is stuck to the outer surface of a metal plate 2 whose one end is bent into an L-shape from approximately the bending point, and the tip of the bent portion of the metal plate 2 is inserted into a fixing part 4. It is a fixed configuration.

Therefore, the vibration displacement and the vibration node position in the first resonance occur in the metal plate 2 portion to which the piezoelectric plate 3 is attached, as shown in FIG. All of the next resonances are effective for driving the diaphragm coupled to the tip of the metal plate 2.

The shape of the bent portion of the metal plate 2 may be bent at any other suitable angle in addition to the above-mentioned right angle bending, and in addition to making the bent portion flat like the L-shape described above, the same effect can be achieved by making it a curved surface. is obtained.

Also, fold it into an L shape and then fold it again.
The cross section of the bent portion may be U-shaped or crank-shaped.

The shape of the metal plate 2 or piezoelectric plate 3 of the vibrator 1 can be any shape that can be used for a vibrator with a cantilever structure, such as a rectangular shape or a trapezoid, and the same effect can be obtained.

Furthermore, the same effect can be obtained even when two piezoelectric plates are bonded to the upper and lower surfaces of a metal plate.

In addition, the length of the metal plate 2 having a composite part of the piezoelectric plate 2 from the vibration tip of the vibrator 1 to the bending point is 11), and the effective length of the bending part from the bending point to the fixed part 4 of the vibrator 1. (referred to as 12), if there is even a slight bend, the reproduction efficiency in the bass range can be improved, but the effective length 12 of the bend is the length 11 of the vibrating part where the piezoelectric plate 2 is combined. If the relationship is 0.05 or more, the sound pressure level in the bass range necessary for a practical speaker can be obtained, and to some extent IJl! The larger the number 1, the greater the effect.

Next, an example of a piezoelectric speaker using a vibrator according to the present invention will be described. As shown in FIG. The vibrator 1 is fixed by being inserted into the support part 7 in the speaker case, and the diaphragm is coupled to the vibrating tip of the vibrator.
A piezoelectric speaker that does not require the fixing part 4 described in FIG. 1 can be obtained.

In addition, as shown in FIG. 5, the vibrator 1, whose bent portion is L-shaped, is fixed by the supporting portion 7 of the diaphragm 5 in the same manner as described above, and in order to make the speaker thinner, the vibrator A piezoelectric speaker can be obtained by providing a stepped portion at the vibrating tip of the vibrating tip and coupling the vibrating plate 5 to the tip.

In addition, as described above, vibrators having bent portions of various shapes can be incorporated into the piezoelectric speaker.

Next, an example according to the present invention will be shown to clarify its effects.

The metal plate 2 is made of a phosphor bronze plate with a width of 15 mm, a thickness of 0.2 vtrtt, and a length selected as appropriate, and a zircon-lead titanate pressure-holding electromagnetic ceramic with a length of 20 mm, a width of 15 ynm, and a thickness Q of 2 mm. The piezoelectric plate 3 was glued, the length 11 from the vibrating tip to the bending point was 25 mrft, the length inside the fixed part 4 of the L-shaped bent part was 5 mrIL, and the length 12 of the bent part was varied. Created.

In addition, there is no bending part and the effective length of the vibrator is 257f.
A conventional vibrator was manufactured which was the same as the vibrator of the present invention except for using trIL.

These vibrators were fixed to the fixed part 4 of the speaker case with a length of 5 cages, and the effective diameter was 50 mm at a part 1 mm from the tip of the vibrating part.

The center of a diaphragm made of a polyimide film with a thickness of 100 μm was joined together, and the diaphragm was fixed to the supporting part of a speaker case via foamed polyurethane with a thickness of 1 mm, thereby assembling a piezoelectric speaker.

A sine wave voltage of an effective value of 1■ is applied to each of the conventional piezoelectric speaker and the piezoelectric speaker of the present invention incorporating a vibrator with various lengths of bent portions, so that the first resonant frequency of the vibrator is adjusted. The sound pressure level was measured at a position in front of the speaker 10c1'IL in this case.

The results are plotted on the horizontal axis, which is the effective length 1 of the folded part of the vibrator.
The graph of FIG. 6 shows the value obtained by dividing 2 by the length of the vibrator, 11, and plots the sound pressure on the vertical axis.

As is clear from FIG. 6, in the case of the conventional piezoelectric speaker of 12/11-0 in which the vibrator does not have a bent part, virtually no sound pressure is obtained, and in the case of the present invention, the sound pressure is 12/11-0.
/11-0.05 or more indicates that sufficient sound pressure is obtained as a speaker.

In other words, the reproduction efficiency in the bass range is significantly improved, and the ig
As the value of 2/11 increases, the sound pressure increases.

On the other hand, piezoelectric speakers are characterized by being thin as mentioned above, but if the value of 12/11 exceeds 0.4, the effective length of the bent portion in the above embodiment is 1.
This means that 12/It exceeds 0 m11 L, and in consideration of making the speaker thinner, 12/It is preferably a value of 0.05 to 0.4.

As is clear from the above embodiments, the piezoelectric speaker according to the present invention has a bent part on the fixed side of the vibrator, so that the reproduction efficiency in the low frequency range is significantly improved, and the piezoelectric speaker according to the present invention has a high reproduction efficiency over the practically necessary range width. This is an excellent piezoelectric speaker that can reproduce sound at a sound pressure level.

[Brief explanation of the drawing]

Fig. 1 is a vertical cross-sectional view of a conventional piezoelectric speaker, Fig. 2 is an explanatory diagram showing the vibration node position of the first resonance of a conventional vibrator, and Fig. 3 is a longitudinal cross-sectional view of a conventional piezoelectric speaker.
The figure is an explanatory diagram showing the vibration displacement and vibration node position of the first resonance of the vibrator according to the present invention, FIGS. 4 and 5 are longitudinal cross-sectional views showing an embodiment of the piezoelectric speaker according to the present invention, and FIG. It is a chart showing the relationship between IL; z/IJ1 and sound pressure in Examples. In the figure 1... Vibrator, 2... Metal plate, 3
...Piezoelectric plate, 4...Fixed part, 5...
... Vibration plate, 6... Polyurethane foam, 7.
...Support part.

Claims (1)

[Claims] 1. One metal plate of a piezoelectric vibrator, which is a combination of a metal plate and a piezoelectric plate, is bent, and the vibrator is fixed at the bent tip,
A piezoelectric speaker with a diaphragm coupled to the other side of a metal plate. 2. The effective length from the bending point of the metal plate to the fixed part is
2. The piezoelectric speaker according to claim 1, wherein the value divided by the effective length from the bending point to the tip on the diaphragm side is 0.05 to 0.4.