Patent ID: 8798309

Claim:
A speaker device comprising: a magnet formed in a ring shape; a yoke having a center pole portion inserted in a center of the magnet; a plate formed in a ring shape and arranged on an outer circumferential surface of the center pole portion of the yoke while being attached to the magnet; a coil bobbin formed in a cylindrical shape and movable in an axial direction of the center pole portion while being partially fitted on the center pole portion of the yoke; a voice coil wrapped around an outer circumferential surface of the coil bobbin, at least part of the voice coil being arranged in a magnetic gap formed between the plate and the center pole portion of the yoke; a diaphragm having its inner circumferential portion connected to the coil bobbin, the diaphragm being vibrated as the coil bobbin moves; and a magnetic fluid filled in the magnetic gap, wherein a magnetic gradient is formed that is adapted to change a magnetic force acting on the magnetic fluid by changing a magnetic flux density in a circumferential direction of the center pole portion and changing the magnetic flux density in the axial direction of the center pole portion, and the lowest magnetic flux density in the circumferential direction is greater than half the highest magnetic flux density in the axial direction.