Abstract: The long term average broad band gains of a plurality of individual signal channels, associated with a corresponding plurality of microphone elements, are electronically and dynamically adapted to one another. This is realized by periodically and dynamically processing the signals from the individual microphone elements. More specifically, the processing is such that the long term average broad band gain of the signal channels of the individual microphone elements is dynamically adjusted, an energy estimate of each microphone signal channel is averaged over the long term and the difference in energy between the signal channels is used to readjust the long term average broad band gain of the microphone signal channels to minimize those differences.

Abstract: Full directional pickup coverage is realized by employing a pickup arrangement which provides a plurality of audio polar directivity patterns, i.e., directional beams. These polar directivity patterns are formed in a unique embodiment of the invention by generating a plurality of frequency independent time-delayed versions of a corresponding plurality of spatially sampled signals and by combining each of the plurality of spatially sampled signals with one or more selected ones of the time delayed versions to generate at least a similar plurality of polar directivity patterns. More specifically, the spatially sampled signals are combined with the delayed versions in such a manner that a greater number of polar directivity patterns can be considered than the number of spatially sampled signals. In a specific embodiment, the spatially sampled signals are acoustic (audio) and a plurality of microphones arranged in a predetermined spatial configuration is employed to obtain them.

Abstract: A speakerphone comprises an upper housing member and a lower housing member that are joined together to enclose a loudspeaker, a microphone, and a printed wiring board having electronic components mounted thereon that cooperate in the operation of the speakerphone. The upper housing member includes a continuous sidewall that is molded into its underside and extends downwardly toward the printed wiring board. The sidewall surrounds a group of sound apertures that are also molded into the upper housing member. A loudspeaker is attached to the underside of the upper housing member in such a manner that it completely covers the sound apertures. A sealed enclosure within the speakerphone is formed by creating a seal between the sidewalls and the printed wiring board. A compliant gasket is illustratively used to create the seal. As a result, the frequency response of the loudspeaker is improved, and acoustic coupling between the loudspeaker and the microphone is reduced.

Abstract: A directional microphone assembly is constructed from a first-order-gradient microphone element enclosed within a housing, molded from an acoustically-opaque, resilient material such as Ethylene-Propylene-Diene-Monomer. The microphone element includes a diaphragm which moves under the influence of sound pressures applied on its opposite surfaces to generate an electrical signal which is proportional to the differential sound pressure. The housing includes a first acoustically-transparent channel for communicating sound pressure from a first opening in the housing to one surface of the diaphragm, and a second acoustically-transparent channel for communicating sound pressure from a second opening in the housing to the other surface of the diaphragm. The housing supports the microphone element and forms a continuous seal around its perimeter so that sound pressure in one channel does not leak into the other.

Abstract: A loudspeaking telephone station (speakerphone) includes a loudspeaker and one or more microphones within the same housing. The microphones are directional, each having a polar response characteristic that includes a major lobe, one or more side lobes, and nulls between pairs of lobes. The loudspeaker is positioned in the null of the polar response characteristic that resides between the major lobe and an adjacent side lobe. The microphone apparatus is positioned so that its major lobe is aimed in a direction that is generally perpendicular to the direction that the loudspeaker is aimed. Means are provided for increasing the distance between input sound ports of a first-order-gradient (FOG) microphone and thereby improving its sensitivity. A pair of such improved FOG microphones are used in assembling a second-order-gradient microphone. Full duplex operation is achieved when a pair of echo cancelers are added to further reduce the coupling between the transmit and receive directions of the speakerphone.

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.