A speaker that uses the inverse piezoelectric effect of piezoelectric materials to work is called a piezoelectric speaker. The phenomenon in which dielectrics (such as quartz, potassium sodium tartrate and other crystals) are polarized under pressure to cause a potential difference between the two ends of the surface is called the "piezoelectric effect." Its inverse effect, that is, the elastic deformation of the dielectric medium placed in the electric field, is called the "reverse piezoelectric effect" or "electrostriction".
Piezoelectric speakers are divided into piezoelectric high polymer speakers, piezoelectric crystal speakers and piezoelectric ceramic speakers according to different media.
Compared with electrodynamic speakers, piezoelectric speakers do not require a magnetic circuit, and do not require a bias voltage compared with electrostatic speakers. They are simple in structure and cheap, but they have many shortcomings, large distortion, narrow frequency band and unstable operation.
Piezoelectric speakers are mostly used for treble, and their bandwidth is relatively narrow, generally lower than 4 or 5kHz, it will drop quickly. Some trolley speakers often use piezoelectric speakers with horns for treble, which can simplify the crossover and save costs. There are also some piezoelectric speakers that add a coil behind the piezoelectric sheet to increase its sound pressure level.