JPH01135300A - Piezoelectric loudspeaker - Google Patents

Abstract

PURPOSE:To obtain a piezoelectric loudspeaker with a good quality by using a radiant successive oscillation with wave wrinkles to be expanded from a center to a outer circumference, setting a driving point in the peripheral vicinity, and applying a vibromotive force from the outer periphery of a piezoelectric element through a combining ring. CONSTITUTION:A constitution is so made that an inclusion angle alpha1 of wave wrinkle 2 of a diaphragm 1 is made approximately uniform, a wave height value (h) of the wrinkle is made maximum at the outer circumference and made lower as it goes to the center, and the orientation character of a surface rigidity distribution is made large at a outer circumference part and made lower as it goes to a central part. For the diaphragm 1, a paper pulp manufactured paper, etc., which has a proper internal loss is used, and a driving point 15 of the diaphragm 1 is properly set. A piezoelectric oscillating element 9 is combined through a combining gum ring 13 to the driving point 15 of the wrinkle 2 in making a outer periphery 14 into a driving terminal. When the dimensional ratio of the diaphragm 1 and piezoelectric oscillating element 9 is properly selected, an active piston movement is executed in a low sound band by the principle of a lever a valid mass is decreased by the reducing effect of an oscillating area due to a dividing oscillation in intermediate and high sound bands, and the output sound pressure in the all hands can be reinforced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a piezoelectric speaker including a piezoelectric vibrating element using a piezoelectric vibrating plate made of ceramic or the like.

[Prior Art] Moving coil type dynamic speakers have been the mainstream and widely used speakers for a long period of time, over the past half century. During that time, many improvements have been made, mainly due to advancements in permanent magnet materials, but it seems that they have already reached a saturation point. On the other hand, due to the development of technology such as integrated circuits, electronic devices are progressing endlessly in terms of diversification of functions and miniaturization of form, and speakers as built-in components are becoming thinner, lighter, and smaller. It is required in many ways.

As a speaker that meets the above requirements, a piezoelectric speaker including a piezoelectric vibrating element using a piezoelectric diaphragm made of ceramic or the like is known.

In recent years, strong piezoelectric ceramics mainly made of zirconium lead titanate have been developed, and piezoelectric ceramics are created by bonding this thin piece with an electrode surface to one side (unimorph type) or both sides (bimorph type) of a metal plate base. As diaphragms are now produced in large quantities and costs have been significantly reduced,
It has come to be widely used as an excitation source for electro-acoustic transducers.

Now, the applicant of the present invention first used a strong piezoelectric ceramic as described above to connect a weight to the center of the piezoelectric diaphragm through a viscoelastic layer, thereby restraining the center of the piezoelectric diaphragm. , Japanese Patent Application No. 59-18697 to propose a piezoelectric vibrating element configured to extract excitation force from its outer edge.
No. 9). According to the piezoelectric vibrating element having such a configuration, it is possible to significantly reduce problems caused by the stiffness of the piezoelectric vibrating plate due to the high elastic modulus inherent to ceramics.

[Problems to be Solved by the Invention] The conventional piezoelectric vibrating element as described above is an extremely convenient material for constructing a small piezoelectric speaker because it is flaky and lightweight as an excitation source. However, due to the miniaturization of the speaker, the radiation area is too small, resulting in insufficient output sound pressure and a narrow reproduction range.

This invention was made to solve this problem, and has the function of expanding the band and increasing the output sound pressure in a relatively small diameter diaphragm, and has the function of expanding the band and increasing the output sound pressure, and achieves a practically satisfactory output sound pressure and reproduction range. The purpose is to obtain a high-quality piezoelectric speaker with

[Means for Solving the Problems] A piezoelectric speaker according to the present invention uses a radially continuous corrugated diaphragm that gradually expands from the center toward the outer periphery as a flat diaphragm, A driving point is set near the edge that serves as the fulcrum, and the vibrational force of the outer edge of the piezoelectric vibrating element is applied via the coupling ring set at this driving point, increasing the amplitude by cantilever action and increasing the driving point. The diaphragm is configured to effectively excite and energize the diaphragm by matching the mechanical impedance of the diaphragm.

[Function] In the piezoelectric speaker of the present invention, the diaphragm performs a vigorous piston movement in the low frequency range due to cantilever action, and in the middle and high frequency range, the effective mass is reduced by the effect of reducing the vibration area due to divided vibration, and the entire range is reduced. Since the output sound pressure can be increased,
A practically satisfactory output sound pressure and reproduction range can be obtained.

[Embodiment] FIG. 1 is a plan view showing a diaphragm of a piezoelectric speaker according to an embodiment of the present invention, and FIG. 2 is an enlarged perspective view showing a part of the diaphragm of FIG. 1. In the figure, 1 is a diaphragm,
A plurality of arrow-shaped wave folds 2 gradually expand from the central dome part 3 toward the outer periphery, and are radially spread over the entire surface to form a regular chrysanthemum-patterned uneven surface. As shown in FIG. 2, the wave folds 2 have an included angle α1 of approximately 90° to
It has a substantially constant angle in the radial direction of around 120 degrees, and the wave height changes successively so that the wave height h1 at the outer circumference is the maximum and the wave height h2 at the center is the minimum. usually,
The wave height changes linearly in the radial direction, but in some cases, a part of a quadratic curve such as a parabola is adopted. With such a configuration, it is possible for the diaphragm 1 to adjust the surface stiffness distribution from the outer circumference toward the center to a desired state. Each wave fold 2
The outer circular arc portion 4 of the triangular slope 5 at the outer end, the edge portion 6 of the U-shaped groove that serves as the hinge (fulcrum), and the flat portion 7 that serves as the adhesive surface are continuous and integrated, and wave folds 2
The central end portion of is connected to the outer periphery of the central dome portion 3, and each corrugation 2 has a cantilever action with the edge portion 6 as a fulcrum, and the surface stiffness distribution of each portion can be completely controlled as desired. It constitutes a single flat diaphragm.

FIG. 3 is a sectional view showing the structure of a piezoelectric speaker formed using the diaphragm of FIG. 1. In the figure, 9 is a piezoelectric vibrating element, which is made by laminating piezoelectric plates such as ceramics of the same thickness on one or both sides of a thin metal plate, with a viscoelastic layer 11 interposed near the center of the piezoelectric vibrating plate. A weight 10 having a small mass (approximately 1 to 3 g) is coupled to the piezoelectric diaphragm to restrain the vicinity of the center of the piezoelectric diaphragm, and the vibratory force is extracted from the outer edge of the piezoelectric diaphragm. The piezoelectric vibrating element 9 is connected to a driving point 15 near the outer edge of the wave folds 2 of the diaphragm 1 via a coupling rubber ring 13, using an outer edge end 14 as a drive terminal.

Here, when the coupling rubber ring 13 couples a highly rigid ceramic vibrator and a much softer diaphragm,
This is a matching element to alleviate the difference in mechanical impedance between the two, and is loosely coupled along the uneven surface on the back side of the wave folds 2. In FIG. 3, 8 is a frame, 12 is a fixed end of the diaphragm 1, and 16 is a terminal plate to which an external signal voltage e is applied.

FIG. 4 is a schematic diagram for explaining the operation of the piezoelectric speaker of FIG. 3, and FIGS. 5 and 6 are equivalent circuit diagrams and output sound pressure characteristic diagrams of the piezoelectric speaker of FIG. 3.

Next, the operation of the piezoelectric speaker which is an embodiment of the invention described above will be explained. Now, when a signal voltage e is applied to the terminal plate 16 from the outside, the piezoelectric vibrating element 9 (zt) is restrained near the center by the action of the weight 10 (Z2) attached via the viscoelastic layer 11, and the piezoelectric vibrating element 9 (zt) The vibration element 9 is in a concave lens-shaped curved vibration mode as shown by the dotted line in FIG.
The primary vibration velocity Vl that bypasses 3(Z,) circulates. Furthermore, the diaphragm 1 (Zo) has a secondary vibration velocity ■.

flows in, is excited, and emits an output sound pressure po. In this case, the position of the driving point 15 on the wave fold 2 is set in consideration of the urging effect of vibration as a cantilever. For example, if the radius of the piezoelectric vibrating element 9 is made larger with respect to the diaphragm 1 and the driving point 15 is moved closer to the edge portion 6 that serves as the hinge (fulcrum) on the left side of FIG. While the vibration displacement in the vicinity increases, the driving impedance also increases, making it impossible to obtain a sufficient biasing effect, and conversely, the piezoelectric vibrating element 9
If the driving point 15 is moved closer to the center on the right side of FIG. 4 by decreasing the value, the opposite will occur. Therefore, the dimensional ratio of the diaphragm 1 and the piezoelectric vibrating element 9 is determined by finding the best harmonious point while taking into consideration the physical properties of both and the mechanical impedance of the driving point 15.

Here, as an example, the radius of the piezoelectric vibrating element 9 shown in FIG. 4 is r 1 = 13.5 mm, and the effective radius of the diaphragm 1 is r
= 20 mm, it becomes X-6,5 in Figure 4, and r, )/x = nζ3, so the amplitude at the center of the diaphragm 1 is simply expanded to about three times, The radiated sound pressure near the frequency fo of the −th order resonance point increases by approximately 10 dB. On the other hand, the impedance Z at the driving point 15 of the diaphragm 1. Z increases to nearly n2 -32-9 times and approaches the large output impedance Z1 of the piezoelectric vibrating element 9. ≦
It will be 71. This improves the transmission loss and standing wave reflection of vibration energy transfer at the driving point 15, and has a synergistic effect on improving the sensitivity and sound pressure response of the piezoelectric speaker. In this case, the coupling rubber ring 13 is connected to the piezoelectric vibrating element 9
The impedances Z1 and Z are interposed between the outer edge 14 of the diaphragm 1 and the driving point 15 of the diaphragm 1. It has a function as a viscoelastic element that adjusts the differences between
Close attention is paid to the rubber quality and shape of No. 3.

FIG. 6 shows an embodiment of the piezoelectric speaker according to the present invention in which n=3 as described above, and the outer diameter of the diaphragm 1 is 5.
It shows the output sound pressure characteristics of a thin (6 mm thick) piezoelectric speaker with a small diameter of 0 mm diameter, and its operation has the expected biasing effect as described above. Almost satisfactory performance was obtained for a small piezoelectric speaker.

In the piezoelectric speaker according to the present invention as described above, the included angle α1 of the wave folds 2 of the diaphragm 1 is substantially uniform, and the wave height is maximized at the outer circumference and gradually decreases toward the center. The diaphragm 1 is designed so that the orientation of the surface stiffness distribution of the diaphragm 1 is large at the outer periphery and gradually decreases toward the center. Therefore, if the diaphragm 1 is made of a material such as paper pulp or plastic film that has an appropriate internal loss, and if the driving point 15 of the diaphragm 1 is set appropriately, the dimensional ratio of the diaphragm 1 and the piezoelectric vibrating element 9 can be By choosing an appropriate value, active piston movement will occur in the low range due to the lever principle, and in the middle and high range, the effect of reducing the vibration area due to split vibration will reduce the effective mass and increase the output sound pressure over the entire range.
This results in a practically satisfactory output sound pressure and reproduction range.

In the above embodiment, the cross-sectional shape of the wave folds 2 is triangular, but it may also be semicircular. They may be arranged tangentially, and the same effect as in the above embodiment can be achieved.

Further, in the above embodiment, the outer shape of the diaphragm 1 is the seventh
It is also easy to modify the shape into an elliptical shape or other shapes as shown in the figures.

Furthermore, the diaphragm 1 with corrugations 2 can be manufactured using processing methods such as the paper pulp mizusho molding method or the vacuum molding method of plastic films, making it possible to supply uniform, high-quality products in large quantities at low cost. It is. Furthermore, as shown in the output sound pressure characteristic diagram shown in FIG. 6, the piezoelectric speaker according to the present invention has a
It has particularly excellent high-frequency reproduction characteristics between 20 KHz and 20 KHz, and has the advantage of having essentially no external leakage magnetic flux, so it is useful as a tweeter for left and right front mounts of a large color television with an audio multiplexing system.

[Effects of the Invention] As explained above, the present invention uses a piezoelectric speaker in which a diaphragm with radially continuous corrugations that expands sequentially from the center toward the outer periphery is used, and an edge portion that serves as a fulcrum is used. A driving point is set near the driving point, and an excitation force is applied from the outer edge of the piezoelectric vibrating element through a coupling ring set at this driving point, and the vibration plate is excited and energized by cantilever action. , a thin, lightweight, and compact piezoelectric speaker can be constructed easily and inexpensively, and compared to conventional speakers of this type, despite its compact and flat configuration, it is possible to use a small-diameter diaphragm. On the other hand, the output sound pressure over the entire region can be increased, and a piezoelectric speaker having a practically satisfactory output sound pressure and reproduction range can be obtained, which is an excellent effect.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing a diaphragm of a piezoelectric speaker according to an embodiment of the present invention, FIG. 2 is an enlarged perspective view of a portion of the diaphragm shown in FIG. 1, and FIG. 3 is a plan view of the diaphragm shown in FIG. 1. 4 is a schematic diagram for explaining the operation of the piezoelectric speaker of FIG. 3, and FIGS. 5 and 6 are equivalent diagrams of the piezoelectric speaker of FIG. 3. FIG. 7 is a perspective view showing a diaphragm of a piezoelectric speaker according to another embodiment of the present invention. In the figure, 1... diaphragm, 2... wave folds, 3...
- Central dome part, 4... Arc part, 5... Triangular slope, 6... Edge part, 7... Flat part, 8... Frame, 9... Piezoelectric vibrating element, 10.・Weight, 11...
Viscoelastic layer, 12... fixed end, 13... binding rubber ring, 14
... Outer edge end, 15... Driving point, 16... Terminal board. In addition, in the figures, the same reference numerals indicate the same or equivalent parts. Patent applicant Kaibara Seisakusho Co., Ltd. (2 others) Is
1 Figure 1: Handling failure 4: TX: Jl extension 2-front fold '5-triangular slope 3: Central dome section 6: Ethos section Figure 2 7: Plain arch

Claims (1)

[Claims] In a piezoelectric speaker whose vibration source is a piezoelectric vibrating element made of piezoelectric ceramics, etc., each wave fold of a diaphragm is made up of a diaphragm with continuous wave folds that expand sequentially from the center toward the outer periphery. In order to act as a cantilever using the outer edge of the plate as a fulcrum, the outer edge of the piezoelectric vibrating element is connected to a driving point near this fulcrum via a coupling ring, and the diaphragm is excited by the action of a lever. A piezoelectric speaker characterized by being configured as if it were a powerful force.