Patent ID: 7016515

Claim:
A speaker apparatus, comprising: a primary coil arranged on a fixed pole piece and disposed in a vicinity of a gap of a magnetic circuit and to which a current corresponding to an input audio signal is supplied; a one-turn cylindrical ring forming a secondary coil, arranged on a movable bobbin and disposed in the gap for having induced therein a current corresponding to a current that flows in said primary coil, and being movable relative to said primary coil; and a vibrating plate attached said bobbin and vibrated by said secondary coil with an interaction of the current induced by said secondary coil and a magnetic flux in the gap, wherein the following relation is satisfied L 1 /L 2 =R 1 /R 2 Wherein R 1 is a DC resistance of said primary coil; L 1 is an inductance of said primary coil; R 2 is a DC resistance of said secondary coil; and L 2 is an inductance of said secondary coil.