Tech Tin Files: Regular Speaker Versus Piezo speaker

• A regular loudspeaker exploits the "motor/generator" effect of a coil of wire suspended in a magnetic field. When an electric current is passed through the coil a magnetic field is created around it. This field reacts with the field in which the coil is suspended (magnetic attraction and repulsion) and a mechanical force is exerted on the coil - which moves. The coil is attached to the 'speaker's diaphragm.
• The current through the coil comes from the amplifier which drives the 'speaker. The current is varying in magnitude and frequency, so the coil, and therefore the diaphragm, moves in the same manner, reproducing the amplitude and frequency of the recorded material. A piezo 'speaker exploits the piezoelectric effect which is exhibited by some crystals, notably quartz and Rochelle salts.
• If a voltage is applied across a piece of piezoelectric material it will flex, or change dimension in one direction. In a piezo 'speaker, a piece of piezoelectric material is attached to a diaphragm. When the signal voltage from an amplifer is applied across the piezo element, its flexure or dimensional movement is transferred to the diaphragm. The frequency response of piezoelectric material is not very good, particularly at the lower end, that's why they are used as high frequency transducers.