The speaker as disclosed by the present invention includes a lower plate carrying an outer magnet assembly and an inner magnet assembly. The outer magnet assembly and the inner magnet assembly form a magnetic gap. The speaker further includes a suspension received in the magnetic gap for supporting a voice coil. The outer magnet assembly includes an outer main magnet, a top plate stacked on the outer main magnet, and an auxiliary magnet stacked on the top plate. The outer main magnet and the top plate are such configured that the magnetic gap has an inner diameter, along a direction from the diaphragm toward the lower plate, gradually increasing and then gradually decreasing. The suspension locates at the region having the greatest inner diameter.