Abstract: A piezoelectric vibrator having excellent shock resistance and high reliability is offered. The centers of first and second piezoelectric vibrating plates are supported by pillars on a main surface of an enclosure and nearly or substantially parallel to the main surface of the enclosure. Spacers having a Young's modulus of less than 2 GPa are mounted on both end sides of the second piezoelectric vibrating plate to prevent contact between the vibrating plates, thus preventing damage. Other spacers are mounted on the main surface of the enclosure in positions corresponding to the first-mentioned spacers to prevent contact with the main surface of the enclosure, thus preventing damage to the second piezoelectric vibrating plate.

Abstract: Electro-dynamic loudspeakers typically include a diaphragm having a conductor applied to one of its surfaces. The diaphragm is secured to a frame. The conductor is connected to a power supply for providing electrical current through linear traces of the conductor that interact with magnetic fields generated by magnets that are mounted to the frame. The diaphragm is driven by a motive force created when current passes through the conductor within the magnetic field. The electrical current is varied to create an acoustical output from the electro-dynamic loudspeaker. Different frame structures are provided for simplifying the manufacturing process and defining a reduced cost electro-dynamic loudspeaker.

Abstract: Apparatus is disclosed for steering a directional audio beam that is self-demodulated from an ultrasound carrier. The apparatus includes means for modulating a carrier signal with an audio signal and means for adjusting the amplitude and phase of at least one of the audio signal and/or the carrier signal to steer the audio beam to a desired direction. The apparatus also includes means for generating an ultrasound beam in the desired direction driven by the modulated carrier signal. The apparatus may include means for weighting the audio and/or carrier signal by a zeroth order Bessel function to synthesize a Bessel distribution source. A corresponding method for steering a directional audio beam is also disclosed. A harmonic generator may be used to generate harmonics of low frequencies in the audio signal. The harmonics may provide (upon demodulation) a psycho-acoustic impression of improved perception of low frequencies.

Abstract: A loudspeaker module in the form of a ribbon element, where the module can be equipped with a membrane, 50 millimeters in width or narrower, and with any length from 50 millimeters to 2500 millimeters. The magnet system is equipped with so called booster-magnets in order to reduce loss of magnetic flow in the soft iron pole pieces and in order to equalize and in order to even the magnetic flow at the magnet ends. The signal-feed is designed in the form of passive current-feeding, whereby the inductance's negative impact of the frequency response up to the 1/f point is eliminated. Above the 1/f point, the ribbon membrane is compensation fed from a separate circuit consisting of R and C, whose values have been chosen in such a way that the resulting frequency response is flat over the whole operating area.

Abstract: A sonic actuator including a multi-layer membrane having a non-metallic elastomeric dielectric polymer layer with a first surface and a second surface, a first compliant electrode layer contacting the first surface of the polymer layer, and a second compliant electrode layer contacting the second surface of the polymer layer. The actuator further includes a support structure in contact with the sonic actuator film. Preferably, the non-metallic dielectric polymer is selected from the group consisting essentially of silicone, fluorosilicone, fluoroelastomer, natural rubber, polybutadiene, nitrile rubber, isoprene, and ethylene propylene diene. Also preferably, the compliant electrode layer is made from the group consisting essentially of graphite, carbon, and conductive polymers. The support structure can take the form of grid having a number of circular apertures.

Abstract: An electrostatic speaker system is provided wherein a multitude of speakers are provided in the system, each speaker having a thin electrically conductive film membrane sandwiched between a pair of stator plates. The film membrane is directly coupled to a high voltage AC audio signal emanating from a power amplifier for reproducing an audio signal. The high voltage AC audio signal is not applied to the stator plates but instead indirectly coupled to the pair of stators by a plurality of condensers (in a voltage multiplier circuit) of a electrical circuit contained within each speaker of the system. By applying the high voltage AC audio signal to the film membrane, approximately one-quarter of the voltage typically used to drive an electrostatic speaker is required.

Abstract: The invention relates to a method for the manufacture of a sensor element and to a sensor element. In the method, both surfaces of a sensor film are provided with metallic electrodes. The sensor element is produced by cutting it from a larger amount of sensor element material. In the manufacture of the sensor element material, the electrodes are produced as a continuous process from roll to roll and the sensor element material is formed by laminating as a continuous process from roll to roll. At least the signal electrode consists of repeated electrode patterns which are at least partially connected to each other via one or more narrow connecting strips, and a sensor element of a desired length and/or shape is produced by cutting the material across the region of the connecting strips.

Abstract: A sonic emitter, horn array with enhanced emitter-to-air acoustic coupling, with particular application to ultrasonic frequencies. The emitter comprises a plate support member having opposing first and second faces separated by an intermediate plate body. The plate body includes a plurality of conduits configured as an array of acoustic horns, with a small throat opening at the first face and an intermediate horn section which diverges to a broad mouth opening at the second face. An emitter membrane is positioned in direct contact with the first face and extends across the small throat openings. The emitter membrane is biased for (i) applying tension to the membrane extending across the throat openings and (ii) displacing the membrane into a non-planar configuration.

Abstract: A method of manufacturing a loudspeaker comprises: continuously forming diaphragm portions and alignment portions on a band resin film; positioning one of a frame and a protector at an upper die or lower die; aligning other alignment portions formed on the frame, the protector, or the upper or lower die having the film disposed thereon, with the alignment portion formed on the film; bonding the frame and the resin film that is to form the diaphragm; and cutting a diaphragm out of the resin film. A position of bonding the diaphragm to the frame or the protector can be easily determined by aligning the alignment portion formed on the band resin film with another alignment portion provided on the frame, the protector, or the lower or upper die on which the frame or protector is disposed. Further, a conventionally-indispensable ring can be eliminated to reduce a number of components.

Abstract: A smaller, less expensive, parametric audio amplifier system configured to be conformable to cable routing requirements that are no more stringent than that of conventional loudspeaker systems. The parametric audio amplifier system includes an amplifier assembly for amplifying an ultrasonic carrier signal modulated with a processed audio signal, an acoustic transducer assembly for projecting a sonic beam corresponding to the amplified ultrasonic signal through the air to regenerate the audio signal, and a low voltage connection for carrying the amplified ultrasonic signal from the amplifier assembly to the acoustic transducer assembly. The amplifier assembly includes an amplifier for receiving the modulated ultrasonic signal and generating an amplified ultrasonic signal having a low voltage level, and a voltage source for generating a voltage level.

Abstract: An electrostatic speaker is constructed using a thin flexible membrane as the active member. This membrane is uniformly positioned against at least one printed circuit board containing at least one stator fixed in the PCB. Variations in structure are provided, all including at least one PCB and a membrane. In a preferred embodiment, intermeshing opposing ridges on the PCBs are adjacent to a central vibrating area of the membrane, and serve to position and tension the membrane. Attachment means connect the PCBs together, and electrical connections permit the passage of current to bias the membrane and to drive the stators to vibrate the membrane, producing acoustical output in the sonic or ultrasonic ranges. The invention also relates to the electrostatic speakers produced by this method of manufacture.

Abstract: A method for manufacturing a speaker apparatus that includes fixing a magnetic circuit to a frame so that the magnetic circuit is positioned around a central hole of the frame; positioning a coil with respect to a center pole of the magnetic circuit; connecting a damper to the coil and the frame; positioning a jig in the central hole of the frame; projecting the jig from a center hole of the center pole; engaging a positioning portion provided on a diaphragm with the jig to position the diaphragm at a predetermined position with respect to the center pole, the positioning portion being removably connected with the jig positioned in the central hole of the frame to secure the position of the diaphragm relative to the magnetic circuit during the installation; and connecting the positioned diaphragm to the coil and the frame.

Abstract: A speaker interconnection block with two voice coils to be driven with separate amplifiers, or to use one amplifier to drive the two voice coils in series or parallel without having to reinterconnect the voice coils. This is achieved by locating the negative voice coil terminals next to each other and the positive voice terminals next to each other on the connection block. When two amplifiers are used to drive the voice coils, the sequence of connections of the amplifiers matches those of the voice coils mentioned above. When only one amplifier is used, that amplifier is connected between the two amplifier terminals farthest from each other. To connect the voice coils in series a single jumper is used to interconnect the two terminals in the center, and for parallel connection two jumpers are used to connect to two terminals at the ends of the sequence together separately.

Abstract: A method and system for adjusting the frequency response characteristics of a transducer assembly (312) is disclosed. The transducer assembly (312) includes a modifiable buffer circuit (100) being generally enclosed within a housing (314). Electrical signal connections for modifying the operating state of the modifiable buffer circuit (100) are accessible outside the housing (314). The modifiable buffer circuit (100) further includes a plurality of signal inputs (234) and outputs (230), the plurality of signal inputs (234) are accessible from outside the housing. A predetermined relationship exists between the plurality of signal inputs (234) and the plurality of outputs (230). A resistor network (224) is operably connected to the plurality of outputs (230) wherein a portion of the resistor network (224) is operably disconnected from a filter network (218) in response to the plurality of signal inputs (234).

Abstract: A semiconductor integrated circuit includes a capacitor element which defines a prescribed decay time constant with one or more resistors, an MOS transistor connected to the capacitor element via its gate, and a constant current generating element which generates a constant current. The capacitor element is charged with the constant current so as to create a linearly changing voltage. The linearly changing voltage is applied to the gate so that the MOS transistor can accordingly output a smoothly changing current.

Abstract: An ultrasonic transducer having a reduced cost of manufacture. The ultrasonic transducer includes a first insulative retaining layer, a second insulative retaining layer, and a vibrator film layer sandwiched between the first and second retaining layers. The first retaining layer includes a first plurality of apertures formed therethrough, and the second retaining layer includes a second plurality of apertures formed therethrough, in which the second apertures are substantially in registration with the first apertures. The ultrasonic transducer further includes a first cover portion having a plurality of spring/backplate assemblies connected thereto, and a second cover portion. The combination of the first retaining layer, the vibrator film layer, and the second retaining layer is sandwiched between the first and second cover portions of the ultrasonic transducer.

Abstract: Apparatus for use with a loud speaker with a volume control function, the apparatus having a recess for releasably receiving an audio device, a first connector on the apparatus for electrical connection with a second connector of the audio device to enable functional connectivity between the apparatus and the audio device, the apparatus including: (a) a volume control for controlling the volume of the loud speaker, (b) an electrical power connector for supplying electric power to the audio device, and (c) at least one functional connection for functional connection with the audio device for establishing a functional relationship between the first control means and the audio device, the recess being sized and shaped to receive therein the audio device, the recess being of dimensions such that the audio device does not extend beyond edges of the recess when the audio device is functionally engaged in the recess and the first connector and the second connector are engaged.

Abstract: A sound generator circuit configured for a handheld computer is disclosed. A method of producing a tone with a sound generator and handheld computer is also disclosed. The sound generator circuit includes a low pass filter having an input and an output. The input is coupled to a pulse width modulated (PWM) signal line. The sound generator circuit also includes a switching circuit coupled to the output of the low pass filter and being controlled by the output of the low pass filter. Further, the sound generator circuit includes a sound generator having a first and a second terminal. Further still, the sound generator circuit can include a high-pass filter coupled across the first and second terminals.

Abstract: An electrostatic loudspeaker requires a high voltage DC bias power supply to bias the stators and diaphragms of electrostatic speakers. A self biased power supply eliminates the need for an external power supply by deriving a high voltage bias from the stator AC signal voltages which have been rectified and run from a high voltage tap and/or through a voltage multiplier which has a voltage limiting means.

Abstract: A transformer includes a bobbin having a cavity, a primary winding wound around the bobbin, and a secondary winding wound around the bobbin and magnetically coupled with the primary winding. In the transformer, at least one of the primary winding and the secondary winding is divided into at least two portions which include a portion wound at an inside region of the transformer and a portion wound at an outside region of the transformer. Also, at least a portion of the other one of the primary winding and the secondary winding is wound between said at least two portions obtained by dividing the one of the primary winding and the secondary winding, and at least a portion of the cavity of the bobbin is used as a space to dispose another member therein.

Abstract: This disclosure relates to a design for the circuit required to drive electrostatic loudspeakers. Such speakers require a high voltage audio signal, typically generated using a wideband, high power step-up transformer. The design eliminates the requirement for such a transformer by mixing the audio frequency signal with a high frequency carrier. This modulated signal may then be amplified and transformed to a high voltage signal using a much more modest transformer operating at the carrier frequency. A simple detection circuit then recovers the original audio waveform from the modulated signal and drives the electrostatic loudspeaker. Such a circuit may be cheaper than a wideband transformer and may also improve the frequency response of the driving electronics.

Abstract: A capacitor microphone includes a case having an end wall defining an opening for a sound hole, a capacitor portion comprising a diaphragm, a back plate and a spacer, the diaphragm opposing to the back plate via the spacer, the capacitor portion being accommodated in the case in such an manner as the diaphragm is placed on the side of the end wall, and a substrate accommodated in the case farther from the end wall than the capacitor portion, the substrate having an impedance conversion element mounted on a surface thereof facing the capacitor portion. A communicating opening is provided around the back plate in a position opposing to the impedance conversion element for communicating spaces on the front and back sides of the back plate. The communicating opening has a larger area than that of the top of the impedance conversion element to allow the spaces on both sides of the back plate to communicate with each other.

Abstract: A member for producing an audible sound in a vehicle including a speaker area having an upper surface and a lower surface, the speaker area being located on the member. A piezo bimorph is attached to the speaker area, the piezo bimorph including a first piezoelectric element attached to the upper surface of the speaker area, and a second piezoelectric element attached to the lower surface of the speaker area. An amplifier in electrical communication with the piezo bimorph, the amplifier supplying an electrical field to the piezo bimorph, the piezo bimorph causing the speaker area and the member to vibrate, causing an audible sound.

Abstract: In a first aspect the present invention provides a compact high efficiency driver suitable for driving a loudspeaker, such as a miniature loudspeaker for mobile phones or hearing aids. The driver comprising an interface for receiving an input signal, a three-level modulator, and a three-level H-bridge. The interface may be adapted to receive a digital input signal. In a preferred embodiment of the driver the H-bridge is controlled by a correction circuit which is operated by a Return-To-Zero scheme. In a further preferred embodiment the driver comprises a supply voltage step-up circuit for increasing a voltage supplied to the H-bridge. In a second aspect the present invention provides a miniature loudspeaker assembly having a built-in driver. In a third aspect the present invention provides a mobile device with a built-in miniature loudspeaker assembly.

Abstract: A system for distributing a source voltage from a signal source to a number of drivers or loudspeakers is disclosed. The system includes at least one autotransformer for connection to the signal source, and a number of drivers electrically connected to the autotransformer. The autotransformers distribute the source voltage across each of the drivers. The autotransformers produce an output voltage across each of the drivers, such that the sum of the output voltages is substantially equal to the source voltage multiplied by the number of drivers.

Abstract: The invention relates to an acoustic element and method for sound processing. The acoustic element (1) is made of a porous stator plate (2) which is either electrically conductive or plated on at least one of its surfaces to be conductive. A moving diaphragm (3, 3a, 3b) has been attached to the stator plate (2). To measure as well as produce sound pressure and particle velocity, the equipment comprises two pairs of aforementioned acoustic elements (1). Elements serving as sensors control elements serving as actuators to attenuate and absorb sound.

Abstract: A hearing aid and method for stimulating the tympanic membrane of a patient via an input of acoustic signals into the middle ear cavity. The hearing aid includes an acoustic signal receiver, a signal processor, and an implantable transducer. In one aspect of the invention, the impedance of the implantable transducer is matched to a characteristic frequency range of the human tympanic membrane to acoustically couple the transducer with the tympanic membrane. In another aspect of the invention, the impedance of the implantable transducer is matched to a measured impedance of a patient's tympanic membrane to achieve the acoustic coupling. In either case, the acoustic signal receiver receives acoustic sounds and generates frequency response signals for the signal processor. The signal processor, in turn, processes the frequency response signals to generate transducer drive signals for the implanted transducer. The acoustically coupled transducer receives the drive signals to generate acoustic signals, e.g.

Abstract: A power supply assembly (10) specifically designed to supply a bias voltage to a diaphragm (34) located on an electrolytic or electrostatic speaker(s)(32). The assembly (10) produces the bias voltage from an audio signal derived from an audio amplifier (30). Thus, a direct connection to a utility power source is not required. The assembly (10) is comprised of five major circuits: a rectifier and filter circuit (12) which converts the input audio signal to a regulated d-c current, an adjustable regulator circuit (14) which is applied the regulated d-c current and produces a regulated direct-current voltage, a d-c to a-c inverter circuit (16) which receives the regulated d-c voltage and produces a high voltage a-c, an eight-times multiplier and rectifier circuit (18) which receives the high-voltage a-c and produces a regulated high voltage d-c, and a current limiter circuit (20) which receives the regulated high voltage d-c and produces the bias voltage which biases the diaphragm (34).

Abstract: An non-hybrid electrostatic speaker system is provided. Each electrostatic speaker contains a diaphragm positioned between pair of electrically charged stators. A central unit is provided having a plurality of slots for receiving a plurality of printed circuit boards. Each speaker employed within the system has a printed circuit board assigned thereto and is mounted within the central unit slots. A single DC power source within the central unit supplies a constant DC voltage to each electrostatic speaker. All electronics needed to operate the speakers are “de-coupled” from the speaker and located within the central unit. The central unit couples to an audio amplification device which is coupled to an audio sound producer.

Abstract: The present invention intends to provide a piezo-electric speaker which can generate a sound from the low frequency range to the high frequency range as well as transmit the acoustic vibration to a sound-board with a high efficiency. This is achieved by providing a piezo-electric speaker comprising a piezo-electric member generating a strain according to an electric signal applied thereto; a piezo-electric vibration plate converting the strain to the acoustic vibration; and a sound-board resonating to the acoustic vibration; the piezo-electric plate being supported on the sound-board; the acoustic vibration caused by the piezo-electric vibration plate being propagated from the sound-board to the ambient air to generate a sound.

Abstract: This invention provides an analog audio amplifier having both excellent linearity and high efficiency, which is combined with digital amplifier. The analog-digital combined amplifier comprises a class A, class B or class AB type analog amplifier serving as an independent voltage source; and a class D type digital amplifier serving as a dependent current source in which the analog amplifier and the digital amplifier are connected to each other.

Abstract: A sonic actuator including a multi-layer membrane having an elastomeric dielectric polymer layer with a first surface and a second surface, a first compliant electrode layer contacting the first surface of the polymer layer, and a second compliant electrode layer contacting the second surface of the polymer layer. The actuator further includes a support structure in contact with the sonic actuator film. Preferably, the dielectric polymer is selected from the group consisting essentially of silicone, polyurethane fluorosilicone, fluoroelastomer, natural rubber, polybutadiene, nitrile rubber, isoprene, and ethylene propylene diene. Also preferably, the compliant electrode layer is made from the group consisting essentially of graphite, carbon, and conductive polymers. The support structure can take the form of grid having a number of circular apertures.

Abstract: An electrostatic speaker device, comprising a first foam stator having an interior surface, and a second foam stator having an interior surface positioned adjacent to the interior surface of the first stator. The interior surfaces of the first and second foam stators include electrically conductive cellular structure sufficiently small in cell size to develop a substantially continuous electrostatic charge dispersion across the respective first and second interior surfaces. At least one diaphragm is disposed between the first and second foam stators and includes an electrically conductive layer responsive to electrostatic forces developed by the respective first and second stators.

Abstract: An ultrasonic emitter device for converting electrical signals to audio output by acoustic heterodyning of ultrasonic emissions. The device comprises a rigid core member having a top surface which includes an array of cavities of predetermined size and means for enhancement of at least one resonant frequency operable as a carrier frequency within an ultrasonic frequency range. An electrostatic field is generated at the top surface of the core member, and operates with respect to a resilient, dielectric diaphragm disposed in tension along the top surface and across the cavities to allow an intended range of orthogonal displacement of emitting sectors of the diaphragm positioned over the cavities and within a strong portion of the electrostatic field. A conductive medium is applied to one face of the diaphragm and is electrically isolated from the core member.

Abstract: An ultrasonic capacitance transducer having a sealed membrane supported above a conductive substrate by thin insulating material to form a sealed evacuated cavity whereby the transducer can operate immersed in fluid.

Abstract: A broadband microfabricated ultrasonic transducer which includes a plurality of resonant membranes of different sizes and/or shapes supported above a conductive substrate.

Abstract: A system for attenuating noise which can be sensed by the auditory nerve comprising a microphone positioned in a first sound region for sensing noise present in the first sound region for creating a first electrical signal having a frequency and amplitude corresponding to the noise sensed in the first sound region. Circuitry is provided for processing the first electrical signal to create a second electrical signal having the same frequency but of opposite amplitude and sign of the first electrical signal. A speaker is provided for converting the second electrical signal to anti-noise for attenuation of the sensed noise in a second sound region spaced from the first sound region. A microphone is disposed in the second sound region for detecting any noise above a predetermined noise level in the second sound region to provide an error correction signal.

Abstract: An electrostatic ultrasonic transducer formed on a semiconductor substrate by micro-machining wherein the transducer includes a silicon nitride membrane supported above the surface of the substrate by insulating supports; and the substrate and membrane define the electrodes of the transducer.

Abstract: An electrostatic loudspeaker has electrodes 24 and 26 arranging multiple plate electrodes 24A to 24D, 26A to 26D insulated each other on both sides of movable electrodes 12, thereby being capable of efficiently producing a large sound pressure level.

Abstract: An electret transducer array and fabrication technique are disclosed. The array comprises a foil having a layer of insulating material and a layer of metal in contact therewith. The layer of metal comprises one or more discrete areas of metal which define the active areas of one or more transducers in the array. Electrical leads are coupled to the discrete areas of metal. By means of these leads, electrical signals produced by each transducer in response to incident acoustic signals may be accessed. The areas of metal may be formed by selectively removing metal from the foil, or by selective metal deposition. The layer of insulating material is electrostatically charged. The electret transducer array further comprises a porous backplate of sintered metal. The backplate further comprises a rough surface in contact with the layer of insulating material. The backplate serves as a common electrode for transducers of the array.

Abstract: A device for electronically generating a sound according to the present invention includes an integrated circuit chip producing electronic signals corresponding to a desired melody, a switch controlling the ON and OFF states of the integrated circuit chip, a battery powering the integrated circuit chip, a sound generator having a dish-shaped vibrating plate and producing sounds responsive to the electronic signals, and a circuit pattern section having a plurality of lead portions interconnecting the integrated circuit chip, the switch, the battery and the sound generator. The circuit pattern section is formed by punching a conductive metal sheet in a press. Selected ones of the lead portions can advantageously be formed by punching into the battery holder or the switch. According to one aspect of the invention, an acoustic chamber is defined by the sound generator and a cover formed by potting or injection molding.

Abstract: In a sound system having a sound source for generating sound signals, a low-impedance amplifier for amplifying the generated sound signals, and high-impedance loudspeakers for reproducing audible sound from the amplified sound signals, an impedance conversion device having a step-up transformer section is disconnectably connected between the amplifier and the high-impedance speakers. The output side of the low-impedance amplifier is also connected directly to low-impedance loudspeakers. Thus the sound system can be operated to selectively broadcast either monaural sound or binaural stereo music of high quality.

Abstract: An integrated amplifier and speaker system includes a speaker having an enclosure having a closed end and an open end; an electro-acoustic driver sealingly mounted in the open end; a reflex duct connected acoustically to the enclosure through a port and having a reflex duct open end proximate to the electro-acoustic driver means; and an amplifier assembly that has an inner surface defining an interior surface of the enclosure. The amplifier subassembly further includes a circuit board that extends within the enclosure. The amplifier is electrically connected to drive the electro-acoustic driver means.

Abstract: A method and apparatus for controlling the sound pressure levels of a substantially capacitive speaker. The controlling element is substantially capacitive and may be either fixed or variable.

Abstract: A device for converting an electric signal into an acoustic signal comprises an input terminal (1) for receiving an electric signal, an amplifier unit comprising N sub-amplifiers (13,15), and a transducer unit comprising N electrostatic transducers (2,3). The diaphragm (3,8) of the N electrostatic transducers forms part of a diaphragm which is common to all transducers. The input terminal (1) is coupled to the input (6) of the first transducer (2) via a first subamplifier (13). Further, the input terminal (1) is coupled to the input (11) of the (i+1)th transducer, i ranging from 1 to N-1 inclusive, via a series arrangement of an i-th low-pass filter (14) and an (i+1)th sub-amplifier (15) (in that order). The sub-amplifier is moreover of the feedback type. Further, for N>2 a low-pass filter having a higher sequence number i has a lower cut-off frequency.

Abstract: The present invention concerns a dielectric film for converting electromagnetic or electrostatic energy into mechanical work, and a procedure for manufacturing the film. The film of the invention consists of a homogeneous film layer foamed to be of full-cell type and which has been oriented by stretching it in two directions and coated at least in part on one side or on both sides with an electrically conductive layer. The film is manufactured by extruding the plastic which has been made to be foamable, into tubular shape, performing intermediate cooling of the tube and reheating it, expanding the heated tube in two directions, metallizing the outer surfaces and cutting the tube open to become a film.

Abstract: A network for matching an electrical source of audio signals to a piezoceramic driver for a high frequency loudspeaker. The network consists of all of the elements of a bandpass filter network, but with the parallel combination of an inductor and a capacitor in the output stage of the filter replaced by an autotransformer or autoinductor which transforms the input impedance of the piezoceramic transducer into an equivalent parallel capacitance and resistance which, together with the inductance of the autotransformer, supply the load resistance for the filter and replace the capacitor and inductor omitted from the output stage of the bandpass network. An additional shunt resistor may be placed across the output of the autotransformer to obtain the desired effective load resistance at the input of the autotransformer.

Abstract: A loudspeaker system includes at least one electromagnetic loudspeaker assembly having a single vibratory coil form to which a vibratory diaphragm is attached. Two or more voice coils are wound on the vibratory coil form, each operating within a magnetic field. Electronic circuitry includes a signal conditioning network and a pair of amplifiers, one amplifier for each of the voice coils. The signal conditioning network, possibly preceded by a filter, is arranged to feed the respective amplifiers, the latter being coupled to their respective ones of the voice coils. D.C. currents provide forces in each of the voice coils, such that these forces are caused to oppose one another. The signal currents in the voice coils are such that the difference in the forces developed by the voice coils produce a vibratory motion of the voice coil form and the diaphragm attached thereto. A power supply is provided. A variable impedance circuit is connected between the power supply and the voice coils for adjusting the D.C.