| 摘要 |
PROBLEM TO BE SOLVED: To solve the problem wherein improvement in the efficiency of a magnetic circuit by equipping a repulsive magnet cannot be achieved satisfactorily, since the outside diameter of the repulsive magnet equipped on a pole piece must be decreased, when magnetic distortion is reduced through equipping of a short ring. SOLUTION: An inner magnet type magnetic circuit 51 for driving a voice coil 44, connected to a diaphragm 42, is equipped with the repulsive magnet 57 both faces of which are magnetized to polarities that are respectively reverse to those of a magnet 55, located on the surface of the pole piece 56 at its side of the diaphragm 42, and the copper-made short ring 58 is fitted coveringly to the inner periphery part at the tip of cylinder portion 52b of a pot yoke 52. Thus, the repulsive magnet 57 can have the outside diameter to be nearly equal to that of the pole piece 56 regardless of whether the short ring 58 is equipped. COPYRIGHT: (C)2007,JPO&INPIT
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