The present invention relates a speaker having a diaphragm around the rim of a frame on the speaker for disposing a magnetic member at the center of the diaphragm along the direction of a resonant space enclosed by the diaphragm and the frame. When a winding in the center of the frame is excited, the resonant space generates varying magnetic lines and an attraction-repulsion effect is generated in the center of the winding or a reserved space at the position of the periphery to vertically slide the magnetic member and cause the diaphragm to vibrate and generate sound. The present invention can effectively reduce the space occupied by the components such as the seat, core, and magnetic member, and greatly reduce the thickness of the speaker.