Abstract: A microphone array-based audio system that supports representations of auditory scenes using second-order (or higher) harmonic expansions based on the audio signals generated by the microphone array. In one embodiment, a plurality of audio sensors are mounted on the surface of an acoustically rigid sphere. The number and location of the audio sensors on the sphere are designed to enable the audio signals generated by those sensors to be decomposed into a set of eigenbeams having at least one eigenbeam of order two (or higher). Beamforming (e.g., steering, weighting, and summing) can then be applied to the resulting eigenbeam outputs to generate one or more channels of audio signals that can be utilized to accurately render an auditory scene. Alternative embodiments include using shapes other than spheres, using acoustically soft spheres and/or positioning audio sensors in two or more concentric patterns.

Abstract: A microphone array-based audio system that supports representations of auditory scenes using second-order (or higher) harmonic expansions based on the audio signals generated by the microphone array. In one embodiment, a plurality of audio sensors are mounted on the surface of an acoustically rigid sphere. The number and location of the audio sensors on the sphere are designed to enable the audio signals generated by those sensors to be decomposed into a set of eigenbeams having at least one eigenbeam of order two (or higher). Beamforming (e.g., steering, weighting, and summing) can then be applied to the resulting eigenbeam outputs to generate one or more channels of audio signals that can be utilized to accurately render an auditory scene. Alternative embodiments include using shapes other than spheres, using acoustically soft spheres and/or positioning audio sensors in two or more concentric patterns.

Abstract: A microphone array-based audio system that supports representations of auditory scenes using second-order (or higher) harmonic expansions based on the audio signals generated by the microphone array. In one embodiment, a plurality of audio sensors are mounted on the surface of an acoustically rigid sphere. The number and location of the audio sensors on the sphere are designed to enable the audio signals generated by those sensors to be decomposed into a set of eigenbeams having at least one eigenbeam of order two (or higher). Beamforming (e.g., steering, weighting, and summing) can then be applied to the resulting eigenbeam outputs to generate one or more channels of audio signals that can be utilized to accurately render an auditory scene. Alternative embodiments include using shapes other than spheres, using acoustically soft spheres and/or positioning audio sensors in two or more concentric patterns.

Abstract: A microphone array-based audio system that supports representations of auditory scenes using second-order (or higher) harmonic expansions based on the audio signals generated by the microphone array. In one embodiment, a plurality of audio sensors are mounted on the surface of an acoustically rigid sphere. The number and location of the audio sensors on the sphere are designed to enable the audio signals generated by those sensors to be decomposed into a set of eigenbeams having at least one eigenbeam of order two (or higher). Beamforming (e.g., steering, weighting, and summing) can then be applied to the resulting eigenbeam outputs to generate one or more channels of audio signals that can be utilized to accurately render an auditory scene. Alternative embodiments include using shapes other than spheres, using acoustically soft spheres and/or positioning audio sensors in two or more concentric patterns.

Abstract: A microphone array-based audio system that supports representations of auditory scenes using second-order (or higher) harmonic expansions based on the audio signals generated by the microphone array. In one embodiment, a plurality of audio sensors are mounted on the surface of an acoustically rigid sphere. The number and location of the audio sensors on the sphere are designed to enable the audio signals generated by those sensors to be decomposed into a set of eigenbeams having at least one eigenbeam of order two (or higher). Beamforming (e.g., steering, weighting, and summing) can then be applied to the resulting eigenbeam outputs to generate one or more channels of audio signals that can be utilized to accurately render an auditory scene. Alternative embodiments include using shapes other than spheres, using acoustically soft spheres and/or positioning audio sensors in two or more concentric patterns.

Abstract: Method and apparatus for the active cancellation of broad band noise and/or single frequency tones emanating from rotating machinery, such as an air moving device, by detecting related mechanical and acoustic signals therein and causing canceling vibrations to be applied directly to the rotating machinery by a transducer.

Abstract: A method and apparatus for providing a differential microphone with a desired frequency response are disclosed. The desired frequency response is provided by operation of a filter, having an adjustable frequency response, coupled to the microphone. The frequency response of the filter is set by operation of a controller, also coupled to the microphone, based on signals received from the microphone. The desired frequency response may be determined based upon the distance between the microphone and a source of sound, and may comprise both a relative frequency response and absolute output level. The frequency response of the filter may comprise the substantial inverse of the frequency response of the microphone to provide a flat response. Furthermore, the filter may comprise a Butterworth filter.

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 method and apparatus for providing a differential microphone with a desired frequency response are disclosed. The desired frequency response is provided by operation of a filter, having an adjustable frequency response, coupled to the microphone. The frequency response of the filter is set by operation of a controller, also coupled to the microphone, based on signals received from the microphone. The desired frequency response may be determined based upon the distance between the microphone and a source of sound, and may comprise both a relative frequency response and absolute output level. The frequency response of the filter may comprise the substantial inverse of the frequency response of the microphone to provide a flat response. Furthermore, the filter may comprise a Butterworth filter.

Abstract: Second-order gradient (SOG) toroidal and unidirectional microphones derived using a first-order gradient sensor (FOG) and a reflecting plane are described. The FOG is positioned with its axis illustratively orthogonal to and suspended a few centimeters from a large acoustically reflecting surface. The resulting sensor image is phase reversed resulting in a transducer that is a linear quadrupole. The linear quadrupole can be described by two dimensions, the distance corresponding to the FOG's dipole distance and twice the distance from the reflecting plane. If the reflecting surface is large enough or if the wall of an enclosure is used, the resulting microphone becomes a SOG unidirectional microphone. The perfect match between the sensor and its image from a good acoustic reflector results in an ideal SOG microphone with 3 dB beam width of .+-.33.degree. and no grating lobes below about 3 kHz for a spacing from the reflecting plane of about 2.5 cm.

Abstract: A back electrode has a plurality of ridges on one surface. An electret foil is spaced from the ridged surface of the back electrode. In the absence of applied pressure, a gap remains between the foil and the surface of the back electrode between the ridges. Above one applied pressure, the foil collapses between the ridges. Below a second applied pressure, the foil returns to its original position.

Abstract: A directional acoustic transducer includes a plurality of acoustic paths each having first and second ends. The second end of each path terminates in the atmosphere. An electroacoustic device is attached to an acoustic cavity and the acoustic path first ends are coupled to the said acoustic cavity through an acoustic arrangement adapted to produce a predetermined transducer directional response pattern.