Electrical signals can be converted into sound using devices like loudspeaker, Piezo buzzer etc. We use a buzzer because available loudspeakers have a low impedance and require more current.
Generate sound from electrical signals, using a Piezo-electric buzzer.
When you change the frequency of the voltage that excites the Piezo, both the frequency and the intesity of the sound changes. The intensity is maximum near 3500 Hz, due to resonance. The resonant frequency of the Piezo buzzer is decided by its size and the mechanical properties.