A speaker, or speaker system is an electromechanical device (transducer) that converts an electrical signal into sound. The term loudspeaker can refer to individual devices, or to complete systems consisting of an enclosure with one or more speakers and additional electronics inside. Loudspeakers are the most variable elements in any audio system, and are responsible for significant differences between otherwise identical sound systems. Speaker performance (i.e., their accuracy in reproducing a signal without adding distortion) is significantly different than that of other audio equipment. The frequency response of a speaker is often indicated as being within 3 dB of perfect linearity (though many speaker designs fall far outside this range), whereas an amplifier may vary less than 0.1 dB.
To reproduce a wide range of frequencies, most speaker systems require more than one speaker, particularly for high fidelity (quality). Individual speakers are used to cover different frequency ranges. Subwoofers are speakers for very low frequencies; woofers, for low frequencies; mids or high-mids, for middle frequencies; tweeters, for high frequencies; and super-tweeters, for very high frequencies.
These terms for different speaker applications/ranges can differ widely depending on the application. Home theater speakers (consisting of four satellite speakers, a center channel speaker, and typically a powered subwoofer) connected to home theater amplifiers or stereos use the designation "tweeter" for high frequencies whereas professional audio systems for concerts typically designate all types of high frequency speakers simply as HF or "highs". High frequency compression speaker units are also called "horns" in cases where the professional loudspeaker's lower frequency drivers are front-loaded.
A "filter network", called a "crossover" separates the incoming signal into different frequency bands appropriate for each speaker. A speaker system with 'N' separate frequency bands is described as "N-way speakers": a 2-way system will have woofer and tweeter speakers; a 3-way system is a combination of a set of woofers, mid-range speakers, and tweeters.
Speakers are made for almost every use: for computers, iPod speaker systems, Home Audio, Professional Audio, Wireless, Auto, and Headsets. Speakers are design in different form factors, like bookshelf speakers, floor standing speakers, as well as for outdoor use. Computer Speakers typically are 2-way, 3-way, and surround sound speaker systems. Leading speaker system manufacturers include: Altec Lansing, Creative Labs, Cyber Acoustics, JBL, Logitech, Yamaha, and others.