A piezoelectric speaker generates a sound by a piezoelectric element (transformed by a voltage) and a diaphragm (it is called “shim material”) for piezoelectric element attached thereto. For example, it is used for a beeping sound of a personal alarm, an electric device, and so on. The piezoelectric element is non-magnetic material as itself. Accordingly, it is expected to be used under a strong magnetic field environment in which a general dynamic type-speaker cannot be used, for example, inside MRI (magnetic resonance imaging) device.
However, as to an earphone and a headphone including the piezoelectric speaker, the sound quality is poor.