Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Having electrostatic element
Reexamination Certificate
1999-08-16
2002-05-21
Tran, Sinh (Department: 2743)
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Having electrostatic element
C381S423000, C381S426000
Reexamination Certificate
active
06393129
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to electrostatic emitters used in speaker systems. More particularly, the present invention involves the use of paper as the stator member of an electrostatic emitter.
BACKGROUND ART
Although the concept of electrostatic loudspeakers has been in development for about a hundred years, commercial applications were not realized until the late 1940's. Since then, a standard construction for electrostatic loudspeakers has dominated the state of the art. This standard utilizes two conductive, stationary, planar stators positioned such that they are in parallel, coaxial relationship with a specific displacement gap between them. A tensioned diaphragm, usually made of metalized polyester, is positioned between the stators in a non-contacting, suspended configuration. Two polarities of an AC audio signal are sent from the output of a step-up transformer to the two respective stators. A high voltage, low current DC bias voltage is concurrently applied to the diaphragm to enable vibration for an audio output.
Despite the advantages of electrostatic speakers, commercial acceptance over dynamic speaker systems has been nominal. Magnetically driven cones and related dynamic speakers have secured over 99% of the market share. This is due in part to the high cost of producing quality electrostatic systems, the space requirements for obtaining low range frequency response, and the difficulty in obtaining structures which are suited for long term stability and dependable operation. The tensioning and spacing requirements for suspending the diaphragm in noncontacting condition between stators has severely limited the speaker shape and configuration. The prior art has used relatively expensive materials for stators which supply strength and durability such as plastics, metals, woods and other strong composites. Accordingly, prior art electrostatic speakers have traditionally been expensive, flat, large in size, and generally unattractive.
U.S. Pat. No. 2,872,532 to Buchannan et al.; U.S. Pat. No. 2,935,575 to Bobb; and U.S. Pat. No. 4,439,642 to Reynard are representative of numerous prior art references which teach the basics of electrostatic speaker design. These references illustrate the conventional tensioned diaphragm suspended over a stator which includes openings or some other form of acoustic transparency. Numerous design variations have been attempted to realize other uses and arrangements for electrostatic speakers systems. For example, U.S. Pat. No. 1,782,278 teaches the use of organic matter, such as paper, combined with a conductive covering for producing an electrostatic diaphragm. Another example is U.S. Pat. No. 5,287,331 to Schindel et al, which shows the modification of a rigid stator including a roughened surface with peaks and valleys to facilitate high frequency response useful for ultrasonic emitters. U.S. Pat. No. 2,855,467 to Curry and U.S. Pat. No. 3,544,733 to Reylek et al. illustrate flexible dielectric diaphragms in combination with flexible conductive films which provide marginal audio output for specialized applications. Other advances have covered anchoring or attaching the diaphragm between along its surface area to avoid the difficulty of broad surface tensioning as discussed above. In addition, attempts have been made to develop electrostatic speaker output from layers of alternating spacer and thin film diaphragm material. These efforts have not provided the conventional stiff vibrating diaphragm necessary for low frequency response and even marginally acceptable audio output.
None of the prior art references have developed commercially acceptable solutions to providing an inexpensive electrostatic speaker which can be used in general audio applications. Nevertheless, the demand for inexpensive high quality sound systems continues to grow as electronic devices which incorporate sound systems become even more prevalent.
Accordingly, it would be an improvement over the state of the art to provide electrostatic transducers which use paper based stators. It would also be an advantage to provide paper based electrostatic emitters which are inexpensive, virtually disposable, and produce high quality acoustic output.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to provide an inexpensive electrostatic transducer which may be used generally within the speaker industry.
It is an object of the present invention to provide paper based electrostatic emitters which are virtually disposable.
It is an additional object of the present invention to provide an electrostatic transducer wherein the stator member is an inexpensive paper material.
These and other objects are realized in an electroacoustic transducer or emitter which includes at least one stator member with an operating surface positioned adjacent an emitter diaphragm. The stator member is comprised of at least one stiff sheet of paper having perforations for acoustic transparency. The stator also includes a means to develop electrical conductivity and to receive an applied voltage. An emitter diaphragm is suspended adjacent to and spaced a sufficient distance from the operating surface of the stator member to enable diaphragm oscillation in response to an applied signal voltage. This arrangement permits diaphragm movement within at least one emitter section without creating restrictive contact on the operating surface of the stator member.
In an alternative embodiment, the diaphragm is a composition of paper having electrical conductivity sufficient to receive an acoustic signal voltage from a voltage source and to vibrate as an acoustic emitter with respect to electrostatic forces applied at the stator member. Electrical contacts are also positioned on the stator member and the emitter diaphragm for coupling to appropriate voltage sources.
These and other objects, features, advantages and alternative aspects of the present invention will become apparent to those skilled in the art from a consideration of the following detailed description taken in combination with the accompanying drawings.
REFERENCES:
patent: 1609760 (1926-12-01), Massolle
patent: 1782278 (1930-11-01), Vogt
patent: 2922851 (1960-01-01), Manley
Conrad Terry J.
Croft, III James J.
Norris Elwood G.
American Technology Corporation
Dabney P.
Thorpe North & Western LLP
Tran Sinh
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