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Furukawa Review No.21

Development of a Diaphragm for a Planar Acoustic Transducer

Takeshi Nishimura , Kenji Iizuka , Hideharu Yonehara , Katsutoshi Sakai , Motohiro Yamane


A diaphragm has been developed to meet the need for ultra-thin acoustic transducers (less than 1 cm thick) for use in liquid-crystal TV sets and in slimline lightweight equipment for automobiles. The diaphragms, which have a voice coil formed over the whole of both surfaces of the base resin film, achieve a high level of sound quality by means of circuit design techniques using magnetostatic analysis. From the physical properties and configuration of the materials (base resin, copper coil and edges) making up the diaphragm, bass reproduction characteristics of better than 65 dB at 100 Hz were achieved through the development of band design techniques using eigen-value simulation to predict the reproduction band in the bass range. In planar acoustic transducers incorporating these diaphragms, driving force is generated over the whole surface of the flat diaphragm, which acts as a planar wave radiator, providing flat phase characteristics and sharp directionality. Other outstanding advantages are that, unlike conventional cone speakers, these acoustic transducers use no paper, resulting in superior resistance to heat and moisture and making underwater operation feasible, and that the individual sound cells are smaller, reducing howling.

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