US Patent 9154884 Electro-acoustic transducer

An electro-acoustic transducer includes a frame, a magnet circuit unit accommodated in the frame, and a vibration unit engaging with the frame. The magnetic circuit unit includes a lower plate, a main magnet positioned centrally on the lower plate, a pair of auxiliary magnets positioned spaced from the main magnet for forming a magnetic gap, and a pair of upper plates attached to the auxiliary magnets, respectively. Each upper plate includes a base body integrated with the frame, and a restricting part extending from the base body and engaging with an inner surface of the auxiliary magnet facing the main magnet.