JPS60148299A - Piezoelectric speaker with mechanical coupling transformer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to piezoelectric loudspeakers, and more particularly to structures for coupling a diaphragm to a piezoelectric drive element.

Prior Art U.S. Pat. Nos. 3,548,116 and 3,786
It is well known to attach the tip of a conical diaphragm directly to the center C of a circular piezoelectric drive, as described in US Pat. A loudspeaker with a coaxially mounted piezoelectric element and a corresponding attached diaphragm is disclosed in U.S. Pat.
It is proposed in No. 57.

A loudspeaker consisting of a plurality of aligned and regularly spaced diaphragms connected together by a rond and driven by an acoustic transducer is disclosed in U.S. Pat.
No. 039,044 and No. 4.107.479. U.S. Pat. No. 4,246,447 C: In one disclosed embodiment, a plurality of regularly spaced connecting ronds are coupled to each other and to a diaphragm. One diaphragm is driven by a piezoelectric motion device, and in another embodiment two diaphragms are coupled to the piezoelectric drive device by an O-ring.

The piezoelectric speaker in US Pat. No. 4.3E3S,241 has a piezoelectric drive coupled to a diaphragm by a cylindrical coupling member. In order to achieve a wide frequency range (1) the patent teaches that the ratio of the diameter of the cylindrical coupling member to the diameter of the electro-electric drive should be in the range 0.65-0.8. .

SUMMARY OF THE INVENTION It is a general object of the present invention to provide a piezoelectric speaker having a mechanical transformer such that a dome-shaped diaphragm and a flat diaphragm can be driven by a piezoelectric transducer.

Another object of the invention is to provide a piezoelectric speaker with a mechanical transformer that minimizes loss of high frequency response.

In one embodiment of a piezoelectric loudspeaker according to the invention, the diaphragm is coupled to a piezoelectric transducer by means of a mechanical transformer, which is typically centered at its smaller diameter end. It consists of a truncated cone which is similarly attached to the center of the piezoelectric transducer and whose larger diameter end is attached to the diaphragm.This conical transformer is designed to minimize its mass. It is preferably hollow and preferably made of a rigid material to enhance the mechanical bond.

DETAILED DESCRIPTION Referring to FIG. 1, a piezoelectric transducer 10 is coupled by a conductor 12 to a signal generator (not shown).

Although transducer 10 is shown as bimorph, monomorphs can also be used. Transducer 10 is preferably a circular disk having a center 14. The conical diaphragm 16 is truncated to define a smaller diameter end 18.

A piezoelectric transducer 10 is connected to a mechanically coupled transformer 20 with a diaphragm 16 (
-It is combined. Transformer 20 may be generally described as a truncated cone having a smaller diameter end or ring 22 and a larger diameter end 24 .

Conical shape of transformer 20? = The extending surface has a continuous C2 conical shape (which can also be formed as a solid wall extending from the smaller diameter circular end portion 22 to the larger diameter end portion 24C). Preferably, a plurality of regularly spaced support members or rods 26 are used to minimize energy transfer.
, transformer 20 should be made of a high stiffness, low mass material such as polycarbonate. The use of a plurality of regularly spaced apart rods 267a allows the creation of a transformer having a mass that is less than the mass that would be achieved if a solid wall were used. Preferably, the material chosen to make the rescue device has a high Young's modulus to density ratio y2.

Ends 22 and 24 of the transformer are attached to end 1B of piezoelectric glide device 10 and diaphragm 16 using adhesive such as epoxy resin.
may be fixed respectively. The diameter of the small φ end of the transformer 20 (22) has a significant effect on the high frequency response of the piezoelectric speaker. The diameter of the end 22 is effective as a low-pass filter. , the high frequency response of the piezoelectric speaker decreases as its diameter increases. Therefore, to achieve a large high frequency response, the diameter of the end 22 should be small compared to the diameter C2 of the piezoelectric reverberator 10. For example, if the outer diameter of the end 22 is approximately 0.1 inch, then the high frequency response that should be added by 14, or 20
It has been shown to provide a high frequency response of KHz and above.

Ideally, the diameter of end 22 should be as small as possible to achieve maximum high frequency response, but as the diameter approaches a certain point (2) the transformer 20 and piezoelectric transducer 10 will not move. It becomes difficult to connect the end 22.
If the diameter of the capsulator is 0.15 inch (2), the ratio of the 10th diameter of the capsulator to the diameter C of the end 22 should be greater than 1, and should be about 6 or more. The ratio of the diameter of end 22 to the diameter C of end 22 is greater than or equal to 1, and may be about 1 or greater, depending on the size and configuration of the diaphragm C.

In FIG. 2, a diaphragm 16 is shown secured to the large diameter end 24 of the unit 20. The assembled piezoelectric transducer 10, transformer 20 and diaphragm 1 can now be attached to the enclosure by means of the circumferential tabs 28 of the diaphragm 16, so that this assembly can be independently supported by it. or the piezoelectric transducer 1o is mounted on a conventional peripheral support structure C.
; Therefore, it can be supported.

Since mounting the assembly by attaching the transducer to a support would result in undesired damping, it is advantageous to support the assembly solely by the edges of the diaphragm.

6 and 4 illustrate one of the major advantages of the present invention, that is, a flat diaphragm 30 while maintaining a favorable cylindrical frequency response.
Alternatively, the ability to drive the dome-shaped diaphragm 62 with the piezoelectric transducer 10 is shown. Larger diameter end 2 of transformer 20
4 provides a substantially effective dispersion area for coupling energy to the diaphragms 30 and 52. The efficiency of embodiments of the present invention is increased because the mechanical impedance of each diaphragm is changed to a greater impedance than would be the case if ends 22 and 24 of the transformer were of the same area. Therefore, the mechanical transformer is coupled to the transducer at its center C2 and at the same time transforms the mechanical motion induced by the displacement C2 into a wider distributed area on the diaphragm.
Second, the high frequency response characteristics of the piezoelectric speaker are maintained. In the embodiment C2 shown in FIGS. 3 and 4, the piezoelectric speaker assembly can be mounted to the enclosure near the periphery of the diaphragm, or the piezoelectric transducer can be directly mounted in a conventional manner. can be supported.

Having described and illustrated embodiments of the invention, the scope of the invention is defined by the following claims.

[Brief explanation of the drawing]

FIG. 1 is an exploded view of a pressure speaker according to invention C2. FIG. 2 is an isometric view of one embodiment of a piezoelectric speaker with a conical diaphragm. FIG. 5 is an isometric view of another embodiment of a piezoelectric speaker having a generally flat diaphragm. FIG. 4 is an isometric view of another embodiment of a piezoelectric speaker having a dome-shaped diaphragm. Patent Applicant Motorola Incorporated Agent Patent Attorney Tamamushi Gobe = 72 1 = = 4

Claims (1)

[Claims] t. A piezoelectric speaker comprising a piezoelectric transducer and a diaphragm that generates air flow, comprising: coupling the motion generated by the piezoelectric transducer (2) to the diaphragm; Relatively small area near the center 1;
a piezoelectric device comprising a mechanical transformer having a first end attached to the diaphragm C2 and a second end having a substantially larger area than the first end attached to the diaphragm C2; speaker. 2. The mechanical transformer means comprises a rigid truncated conical structure, diaphragm (: a piezoelectric speaker according to claim 1, which effectively transforms the motion generated by the piezoelectric transducer with respect to the diaphragm). 3. A piezoelectric loudspeaker according to claim 2, wherein the transducer and mechanical transformer means are supported by the diaphragm.