Schematic Diagram shows How a Buzzer make a sound

The principle that how the buzzer make a sound is consisted of oscillating device anf resonant device.And buzzers can be classified as passive buzzer and active buzzer.

Principle of passive buzzer: Square wave is input into the resonant device.Then it transferred into sound signal and is output.

Schematic Diagram is shown as the following picture.

Principle of active buzzer: After the direct current is input, the direct current is amplified and sampled through the oscillating system. Then the circuit produces sound signal 

under the effect of resonant device.Schematic Diagram is shown as the following picture.