A tweeter is a loudspeaker that reproduces only higher audio frequencies. Because it is limited to high frequencies, it must be combined with speakers that reproduce other frequencies in order for the full range of recorded audio to be audible. The average tweeter outputs frequencies from approximately 2,000 hertz (Hz) and above. 20,000 Hz is considered to be the upper limit of human hearing, but some tweeters can produce frequencies even higher.
A full-range stereo or home theater system uses at least one other speaker in conjunction with each tweeter to produce a full range of sound. In a 2-way speaker, the high frequencies, also called treble, are paired with a speaker known as a woofer that reproduces low end or bass frequencies. More complex speakers use other drivers in addition to the woofer and tweeter to reproduce midrange frequencies. In home stereo speakers, drivers usually share a common enclosure. In some car stereo systems, however, each component may have separate housing to provide additional flexibility in directing the sound.
There are several different types of tweeter available. A cone tweeter has the appearance of a typical loudspeaker — a paper speaker within a metal frame — but is made with a lighter, thinner cone that can move rapidly and has a firmer suspension to repress movement at lower frequencies. A dome tweeter uses a light voice coil, the center of the speaker, within a light dome made of coated cloth or thin metal such as neodymium or titanium. The cone type is more economical, while the costlier dome tweeters have more accurate sound reproduction.
Less common is the piezo tweeter, which operates by flexing a piezo-electric crystal in response to voltage applied. Unlike other forms of speaker, it uses no magnets. An electrostatic tweeter has front and back elements with holes in them, over which electrostatic charges are used to make the speaker pulsate with the music. These are more expensive and less efficient than a dome type.
The treble frequencies reproduced by a tweeter are highly directional. Therefore, tweeters are evaluated based on their dispersion characteristics, or the size of the area they can effectively cover. This is often referred to as off-axis frequency response, and in an effort to improve this response, some devices are coupled to a horn. A horn tweeter directs output in a specific direction. By contrast, a dome tweeter disperses sound over a full 180— area, but can distort more easily.
The two most popular types for home stereo use are dome and horn tweeters. Each has its own unique characteristics, and the right device for a particular listener depends on the individual application and personal taste.