A speaker includes a circuit board, a peripheral wall, a diaphragm, at least one support member and at least one piezoelectric actuator. The peripheral wall is located on a surface of the circuit board. The diaphragm has an outer boundary attached to the peripheral wall. The diaphragm, the peripheral wall and the circuit board collectively form a chamber. The at least one support member protrudes from the surface of the circuit board and is located within the chamber. The at least one piezoelectric actuator is located on a top of the at least one support member and electrically driven to cause a vibration of the diaphragm under applied electrical bias.