| 摘要 |
PROBLEM TO BE SOLVED: To prevent a coil from being broken even when a large input is supplied to the coil so as to drive a diaphragm with large amplitude by arranging magnets so that a couple of magnetic poles is along with a drive direction of the diaphragm, fitting the magnets to the diaphragm, arranging a plurality of coils as magnetic field providing means so that the coil axes are along with a drive direction of the diaphragm and fitting them to a frame. SOLUTION: A ring shaped magnet 2 around a center axis X is fitted and fixed to a middle of a diaphragm 1 of nearly cone-shape. An upper face and a lower face of the magnet 2 correspond to a couple of magnetic poles. An outer circumferential part and an inner circumferential part of the diaphragm 1 are supported by an edge 4, dampers 5, 6 fitted to a frame 3 elastically in a direction of the center axis. Coils 8-11 using a center axis X coaxially are fixed between ring projections 7a of a yoke 7. A drive current supply means 12 detects a level of an audio signal and selects any of the coils 8-11 in response to the detected level to supply a drive current and to provide an alternate magnetic field in the drive direction of the magnet 2.
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