Active buzzer with oscillation circuit built in, the sound frequency is fixed, but can only send out the voice of a single frequency. The passive buzzer working should with a driven current. The human ear can hear the sound from 20hz to 20kHZ. The driving signal of passive buzzer is AC signal , Passive buzzer can make sound under different frequencies. The most important difference between passive buzzer and active buzzer the required input signal，The active buzzer work signal is direct current (dc).While the passive buzzer not internal drive circuit, the most ideal work signal is a square wave.