Piezoelectric speaker, piezoelectric audio device employing piezoelectric speaker, and sensor with alert device attached

A piezoelectric audio device comprising:

• a piezoelectric vibrator comprising:
• a piezoelectric body formed of a piezoelectric element;
• and
• a plate-shaped body which has a larger diameter than the piezoelectric body and which is attached to a surface of the piezoelectric body in a concentric form;
• a film-shaped body that is provided around the piezoelectric vibrator so as to elastically hold the piezoelectric vibrator;
• a frame that supports the outer periphery of the film-shaped body;
• and
• a resonator configured to resonate with a radiation sound emitted by the piezoelectric vibrator,
• wherein the film-shaped body comprises a coarse and dense portion in a circumferential direction thereof, which has a physically coarse portion which can become a mountain portion or a valley portion or both, and which is disposed so as to correspond to a natural frequency of an in-phase mode in which antinodes and nodes are formed in a concentric form,
• wherein the frame is formed of a bottomed cylindrical body which has one open end and which has an inner wall configured to support a periphery of the film-shaped body so as to define a posterior air chamber between the film-shaped body and a bottom surface of the frame, and
• wherein the resonator is provided so as to cover the opening of the frame, and defines an anterior air chamber between the film-shaped body and the frame.