Primarily used in studio or hi-fi installations, dome speakers do not have a moving cone. The dome is fixed and is best for mid-range and higher frequencies. Speakers like these have a wide sound dispersion capability, spreading the sound through 180 degrees.
Horns
Horns draw upon some of the earliest principles of speaker design. They comprise the horn itself - usually a large, flared device - and a pressure-based driver. A thin sheet of metal vibrates on a pad of air to generate the sound waves.
The curves of the horns are precisely engineered to transmit the sound produced by the driver. They are best used for high and mid-range sound, and some may be equipped with more than one driver. Horns are rigid and have limited sound dispersion and range, and if badly designed they can impair sound quality by creating a kind of megaphone effect. Nevertheless, they are often used in larger sound system installations.
Piezo-electric speakers
You are most likely to find a Piezoelectric speaker in your watch or portable radio. Developed in the 70s, they offer a significant advantage in that it is almost impossible to overload them. However, they have a limited frequency range and tend to make sounds harsh and shrill - ideal for sonar or a miniature alarm, but no good for music.
