Patent attributes
Ring magnets (5) are concentrically placed with certain spacings (6) on a magnetic frame (4). The magnetic members on the magnets (5) are removed, and the magnets are arranged so that the polarities of adjacent magnets (5)are alternately opposite to each other, thus forming a magnetic circuit. Ribs (7) are provided to a planar vibrating plate (1) and a voice coil (2) fabricated by vertically stacking conductive wires annularly is attached to the planar vibrating plate (1). The planar vibrating plate (1) is secured to a frame (4) through a gasket (3). The voice coil (2) is inserted into magnetic gaps of spacings (6). Since no magnetic body is placed over the magnets (5), the height of the magnetic circuit can be low, and an increase of the reactance due to provision of the magnetic body of the voice coil (2) does not occur. Since the rigidity of the planar vibrating plate (1) is high, it is unnecessary to secure the planar vibrating plate (1) to the frame (4) while applying a tension.
