US Patent 7394913 Speakers

A voice coil bobbin coupled to a damper is allowed to vibrate in its axis direction within a magnetic circuit including a magnet and a plate supported by a yoke. A range extending between a neutral position of an end of the voice coil bobbin and a portion of the yoke opposing the end of the voice coil bobbin is longer than a range extending between the plate and a neutral position of a portion where the voice coil bobbin is coupled to the damper. A damper ring is fitted around the voice coil bobbin in a position closer to the plate within the portion where the voice coil bobbin is coupled to the damper. A rear face of the damper ring opposing the plate is shaped in face-geometry parallel to a face of the plate opposing the damper ring.