Why Different Sounds Are Different

To discover the operational differences between electro-magnetic and piezo-ceramic transducers, let's return to the design process of each and then determine how each device will vary the sound. The first operational difference between the two devices exists in how the base material is made to deflect.

The electro-magnetic device creates the deflection by applying an oscillating voltage to a coil that,
during the positive half cycle, pushes away or deflects the thin base material which is mounted on top of the magnet. The base material is then brought to its original position during the magnetic half cycle by a magnetic field. Thus, the base material vibrates at the frequency of the applied signal, causing vibrations in air pressure, or sound.

Piezo-ceramic devices deflect with the application of an oscillating voltage. The piezo crystal is
mounted to a metal base within a sound chamber. The drive circuitry supplies an oscillating signal to the crystal which causes it to deflect. As previously mentioned, the deflections of the piezo cause changes in the air pressure within the sound chamber, creating the audible sound. The sound output will be at the frequency of the oscillating signal supplied by the drive circuit. No electro-magnetic or RF noise is created with piezo devices.

The popular Mallory Sonalert® is a good example of a piezo-ceramic audible alarm. It is simple to
operate because it is self-contained, with the drive circuitry supplied within the device. In addition, it is effectively sealed for use in harsh environments. Models are available which operate at various voltages ranging from 1 VDC to 250 VAC.
Which is the right device for you? It depends entirely on your application and the sound you anticipate it will take to accomplish your objective.