Editing Tweeter (section)

===Piezo tweeter===
{{Further|Piezoelectricity}}

A [[Piezoelectricity|piezo]] (or piezo-electric) tweeter contains a piezoelectric crystal coupled to a mechanical diaphragm. An audio signal is applied to the crystal, which responds by flexing in proportion to the voltage applied across the crystal's surfaces, thus converting electrical energy into mechanical.

The conversion of electrical pulses to mechanical vibrations and the conversion of returned mechanical vibrations back into electrical energy is the basis for ultrasonic testing. The active element is the heart of the transducer as it converts the electrical energy to acoustic energy, and vice versa. The active element is basically a piece of polarized material (i.e. some parts of the molecule are positively charged, while other parts of the molecule are negatively charged) with electrodes attached to two of its opposite faces. When an electric field is applied across the material, the polarized molecules will align themselves with the electric field, resulting in induced dipoles within the molecular or crystal structure of the material. This alignment of molecules will cause the material to change dimensions. This phenomenon is known as [[electrostriction]]. In addition, a permanently polarized material such as [[quartz]] (SiO<sub>2</sub>) or [[barium titanate]] (BaTiO<sub>3</sub>) will produce an electric field when the material changes dimensions as a result of an imposed mechanical force. This phenomenon is known as the [[piezoelectric effect]].

Piezo tweeters rarely get used in high-end audio because of their low fidelity, although they did feature in some high-end designs of the late ‘70s, such as the Celef PE1 in which they were utilised as a super tweeter in combination with a conventional dome tweeter. They are often used in toys, buzzers, alarms, bass guitar speaker cabinets, cheap computer or stereo speakers and PA horns.{{Citation needed|date=September 2018}}