A speaker includes a holder forming a hollow space, a magnetic system received into the hollow space and defining a magnetic gap, an elastic plate assembled with the holder and defining a first surface and a second surface opposite to the first surface, a diaphragm defining a dome part connected with the first surface of the elastic plate and an edge part connected with the second surface of the elastic plate, and at least a coil defining an end suspended in the magnetic gap and an another end connected with the dome part. The edge part defines an arcuate portion depressed toward the magnetic system.