A speaker, which includes a basket holding an exciter, a holding down ring fastened to the basket to hold down a diaphragm, which has an annular suspension and a cone fastened to the inner diameter of the annular suspension and coupled to the exciter, and a locating plate capped on an annular positioning portion of the exciter and pressed on the center area of the cone with a beveled outer bearing surface to hold down the center area of the cone against vibration in transverse direction to prevent a distortion of sound.