Patent ID: 7907742

Claim:
An exciter comprising: an outer yoke comprised of a side wall and a bottom; a permanent magnet attached to said bottom; an inner yoke placed on said permanent magnet and provided with a clearance from said side wall; a coil wound around a cylindrically shaped bobbin and inserted into said clearance; a coupler member fastening said bobbin, attached to a board member, and vibrating due to said coil being supplied with a drive signal so as to make said board member vibrate; an elastic member elastically supporting said outer yoke and said coupler member; a sealing member partitioning a clearance between said outer yoke and said coil from an outside space; at least one passage provided at said bottom of the outer yoke at the outer circumference of said permanent magnet for communicating air between a closed space formed by said sealing member and the outside space; wherein said coil is formed between said coupler member and the at least one passage; and wherein the at least one passage comprises a number of passages inversely related to the size of the closed space.