a small high frequency drive unit, mounted in a special casing, designed to sit on top of, and drawing its input signal from, existing speakers
A tweeter designed to reproduce the very highest frequencies above the 2-15 kHz range normally handled well by a good standard tweeter. Supertweeters are usually found in four- or five-way systems and are sometimes placed on the back of a cabinet, facing the wall behind the system. Note that a decent conventional tweeter should be capable of doing everything important that a supertweeter should do, because the highest frequency most people can hear distinctly (particularly if they are past the teen years) is about 15 kHz, and most music and film sound does not have significant energy past 12 to 13 kHz. The only way a supertweeter would offer an advantage would be if its radiating-surface diameter was very small-say one-half inch or less. This would result in improved dispersion above 10 kHz, compared with that of a typical 1-inch dome tweeter. Some supertweeters are said to have strong response to well above 20 kHz, but CDs, videodiscs, and videotapes do not reproduce that range, and nobody can hear up that high, anyway.