Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Having electrostatic element
Reexamination Certificate
1998-01-07
2001-10-16
Le, Huyen (Department: 2643)
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Having electrostatic element
C381S174000
Reexamination Certificate
active
06304662
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to capacitive or electrostatic sonic emitters and more particularly to emitters which include a stator element and associated, movable emitter film useful for generating sonic output as a speaker device in response to an applied variable voltage.
2. Prior Art
The science of acoustics has long known of the utility of a movable electrostatic membrane or film associated with and insulated from a stator or driver member part of as a speaker and/or microphone device. Typical construction of such devices includes a flexible Mylar(tm) or Kapton(tm) film having a metalized coating and an associated conductive, rigid plate which are separated by an air gap or insulative material. An applied voltage including a sonic signal is transmitted to this capacitive assembly and operates to displace the flexible emitter film to propagate the desired sonic compression wave.
Two primary categories of electrostatic speakers exists, depending on the application and frequency of the sonic output. Single-ended speakers comprise a single plate, typically having holes to allow the sound to pass through. The film is suspended in front or behind the plate, and may be displaced out of contact with the plate by spacers. With ultrasonic emitters, the film has been biased in direct contact with an irregular face of the plate, whereby the film is allowed to vibrate in pockets or cavities. An insulative barrier of either air, plastic film or similar nonconductive material is sandwiched between the film and plate to prevent electrical contact and arcing. Typically, the plate and diaphragm are coupled to a dc power supply to establish opposing polarity at the respective conducting surfaces of the metalized coating and the plate. The capacitive relationship resulting from this configuration enables the electrostatic speaker to convert a variable voltage into sonic output as a compression wave.
The second primary category of electrostatic speakers is represented by the push-pull configuration. In this case, the speaker has two rigid plates which are symmetrically displaced on each side of a conductive membrane. With applied voltage, one plate becomes negative with respect to the membrane while the opposing plate assumes a positive charge. The transmission of a variable voltage to this capacitive assembly results in the reinforcing effects of push and pull on the membrane, thereby enhancing power output. Further details of theory and construction of common electrostatic emitter designs is found in
Electrostatic Loudspeaker
by Ronald Wagner, Audio Amateur Press, 1993.
Many years of directed research have developed a variety of technical improvements to this basic system, but the component definition has remained substantially the same. In particular, the rigid plate which operates as the stator or static element generally provides support to the film and supplies a conductive medium for application of the desired sonic signal. Typical materials used for plate construction include aluminum, copper plated circuit board, and similar materials well known in the art.
Although this pattern of material choice has generally served the purposes required for electrostatic speaker, the absence of substitute compositions has limited the variation in speaker applications. For example, audio systems are usually large in size to accommodate development of lower frequencies. Therefore, weight and geometric configuration become significant design factors. Furthermore, the requirement for rigidity and the known stiffness of accepted plate materials typically results in construction of the plate element as the load-bearing component of the speaker system. Taken together, the traditional limitations adopted by this history of plate development has diverted attention from exploring other options for electrostatic speaker design.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to provide alternate component materials to the generic electrostatic speaker configuration which offer new variations in structural and acoustic properties.
It is a further object of this invention to enable reduction in weight and stiffness requirements by utilizing a foam material as the stator element of the speaker system.
Yet another object of this invention is to develop a variety of plate or stator compositions which offer selective degrees of sound transmittance based on open/closed cell structure.
A still further object of the present invention is to provide a plate or support member capable of operating in single or push-pull configuration, and within the full range of sonic output, including both audio and ultrasonic frequencies.
Another object of this invention is to provide an inexpensive foam stator or plate which has little weight and is capable of being formed in a variety of geometric configurations which offer both economy and performance enhancement.
A specific object of the present invention is to provide an electrostatic speaker for audio applications which offers substantial reductions in manufacturing costs and simplified structural design.
These and other objects are realized in a speaker device comprising an electrostatic emitter film which is responsive to an applied variable voltage to emit sonic output based on a desired sonic signal and a first foam member having a forward face, an intermediate core section and a rear face. The forward face is composed of a composition having sufficient stiffness to support the electrostatic film and conductive properties which enable application of a variable voltage to supply the desired sonic signal. The surface of the forward face includes small cavities having surrounding wall structure defining each cavity which terminates at contacting edges approximately coincident with the forward face of the foam member. The film is applied to the forward face of the foam member and biased in direct contact with the contacting edges of the forward face such that the film is directly supported by the forward face. A signal source is coupled to the speaker device for supplying the variable voltage which includes a sonic signal The invention can also be configured with the first forward face as an insulating member, with the intermediate core and /or rear face operable as the conductive element.
In another embodiment of this invention, a push-pull configuration is developed, using a second foam member of similar construction positioned on an opposing side of the electrostatic emitter film from the first foam member. The electrostatic emitter film is sandwiched between the respective foam members and includes a conductive layer in noncontacting relationship with the respective first and second foam members for enabling the film to capacitively respond with the first and second forward faces to the variable voltage in a push-pull relationship.
Another variation of this invention includes an electrostatic emitter film operable in the, audio range with a support member having a forward face, an intermediate core section and a rear face, wherein the forward face is composed of a composition having sufficient stiffness to support the electrostatic film and includes conductive properties which enable application of a variable voltage to supply the desired audio signal. The electrostatic film is applied to the forward face of the support member and is biased in direct contact with the contacting edges. Here again, the system may be adapted for push-pull operation with a second support member, and can also be modified to have the insulative layer interchanged at the forward face.
An additional embodiment of this invention comprises an electrostatic emitter film which is responsive to an applied variable voltage to emit sonic output and a first foam member having a forward face, an intermediate core section and a rear face. The foam member is again composed of a composition including conductive properties which enable application of a variable voltage to supply the desired sonic signal from the foam member t
Croft, III James J.
Norris Elwood G.
American Technology Corporation
Le Huyen
Thorpe North & Western LLP
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