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RESONANCE DAMPER FOR
PIEZOELECTRIC TRANSDUCER
CROSS REFERENCE TO RELATED
APPLICATION
This application is a continuation-in-part of U.S. patent application Ser. No. 08/236,209. filed May 2. 1994.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to the field of audio loudspeakers using a piezoelectric device as a driver, and more particularly to a resonance damper for use on such a piezoelectric device.
2. Description of the Related Art
Modern piezoelectric devices are a very reliable and inexpensive means of converting electrical energy into physical motion and exhibit a high tolerance to environmental factors such as electromagnetic fields and humidity.
Accordingly, piezoelectric devices are a logical choice for use in audio transducers. However, to date no one has been able to construct a practical piezoelectric audio loudspeaker having good fidelity characteristics. Although piezoelectric devices have a good frequency response, designers have had limited success in coupling a piezoelectric device to an acoustical diaphragm for producing sound in the manner that produces a high fidelity speaker or microphone. Conversely, piezoelectric devices have been successfully used in audio transducer devices that produce a single or a limited range of frequencies, such as beepers and audio warning signals associated with electronic devices.
One aspect of audio loudspeaker quality can be quantified by its Q factor, which represents the degree to which the speaker components, such as the driver, diaphragm and enclosure, interact to control resonance. Lower Q factors indicate a lower resonant frequency amplitude which is desirable, particularly for high-frequency speakers. Improved audio quality, without degradation of other performance parameters, is always a goal of loudspeaker designs.
A common failure mode of prior art piezoelectric transducers is failure of the connection between the piezoelectric device and the diaphragm due to rough handling or highimpact loads on the speaker enclosure. Attempts to shock mount the piezoelectric device typically resulted in reduced frequency response and poor speaker fidelity.
What is needed then is a resonance damper that improves the Q factor and frequency response of the driver. It is also desirable to provide a means for shock mounting the piezoelectric driver used in audio loudspeakers without affecting the overall fidelity of the loudspeaker.
SUMMARY OF THE INVENTION
The present invention solves the above-noted deficiencies by providing a resonance damper for a transducer to improve frequency response and a means for shock mounting the piezoelectric driver.
The present invention uses a resilient membrane that is resiliently coupled to a piezoelectric device to dampen its resonance frequency, thereby lowering its Q factor and improving the frequency response of the piezoelectrically driven loudspeaker. In one preferred embodiment, the damper is a resilient membrane of closed-cell foam that is die-cut to be generally circular and to have a plurality of
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flaps. The flaps can be created by cutting a central opening and a plurality of slits, or an opening can be cut in a "daisy" pattern, thereby creating flaps between the lobes of the daisy. The flaps can then be arranged about the piezoelectric device
5 by locating adjacent flaps on opposite sides of the piezoelectric device so that the resilient properties of the flaps hold the device in place and provide the proper dampening characteristics. The significant advantages of the present invention are
10 that it provides a resonance damper that is inexpensive to manufacture and inexpensive to couple to the piezoelectric device because the membrane comprises a single piece of die-cut foam which can be coupled to the piezoelectric device without any adhesives or mechanical fasteners.
15 Additionally, speaker quality is improved as quantified by its Q factor. Preliminary testing indicates that the damper of the present invention lowers resonance frequency amplitudes by 5-10 dB.
Preferably, the resonance damper of the present invention
20 can be coupled to a loudspeaker that uses a diaphragm having two sheets supported by foam supports. The diaphragm sheets are configured in a convolute configuration which is generally referred to herein as a flat, curvilinear plane, defined as a surface formed by a straight line moving
25 transversely through space along a curved path. The sheets are connected to a bridge, which in turn is connected to a piezoelectric device. The diaphragm, foam supports, bridge and piezoelectric device are preferably mounted in an enclosure. The bridge is preferably a thin, lightweight, rigid
30 structure that transfers a point source of motion to a line, thereby transferring the piezoelectric's point source-ofmotion to a line source-of-motion for tangentiaUy driving the diaphragm. When the damper of the present invention is used in loudspeakers having the flat, curvilinear diaphragm
35 and bridge structure, it is preferable that the damper contact the edges of the bridge when it is coupled to the piezoelectric device.
The resonance damper of the present invention can also be used on piezoelectric loudspeakers using cone dia40 phragms to improve its frequency response and as a shock mounting to prevent failure of the piezo-to-diaphragm connection.
The foregoing and additional features and advantages of 45 the present invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an exploded, perspective view showing the 50 components of an audio transducer of the present invention. FIG. 2 is a cross-section, elevational view taken along line 2—2 of FIG. 1. FIG. 3 is a cross-section, elevational view taken along line 55 3—3 of FIG. 1.
FIG. 4 is a detailed elevational view of a bridge and piezoelectric device of the present invention.
FIG. 5 is an alternative embodiment of a bridge of the present invention further showing a pad located between the gQ bridge apex and a piezoelectric device wherein the pad acts as a low pass filter.
FIG. 6 is an alternative embodiment of a bridge of the present invention.
FIG. 7 is an alternative embodiment of a bridge of the 65 present invention.
FIG. 8 is an alternative embodiment of a bridge of the present invention.
