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Coaxial Flat-Plane Loudspeaker with Polymer-Graphite Honeycomb Sandwich Plate Diaphragm

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The coaxial flat-plane loudspeaker is a new approach to direct-radiator plane diaphragm loudspeakers and provides improved performance not obtainable from conventional designs. 1) Sound imaging is enhanced by keeping the broadening of the sound source to a minimum. This feature was realized by coaxially monting four flat-plane diaphragm loudspeakers, each handling a portion of the total sound spectrum from near subsonic frequencies up to superosnic frequencies so that the acoustic centers of all four radiators are aligned in one plane. This causes the arrival times and sources of sounds from all diaphragms to be equal. The time delays between all frequencies can therefore be held to a minimum. 2) A flat and smooth frequency response has been obtained by eliminating the conventional cone diaphragm's cavity with its inherent resonances and break-up frequency characteristics. 3) Piston motion over a comparatively wide range of frequencies has been realized by adopting a sandwich-type construction consisting of two polymer-composite sheets with an aluminum foil honeycomb core bonded in between. The polymer-graphite skin material is designed to have a high internal loss factor, while the core material ensures high flexural rigidity. This construction yields a plane diaphragm which maintains piston motion over a wide range of frequencies with flat frequency characteristics and excellent transient response.

JAES Volume 29 Issue 11 pp. 800-807; November 1981
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