Your home theater system consists of many parts, from the audio/video receiver to the big-screen television to the DVD player and cable/satellite box. But of all these components, the ones that most affect the sound you hear are the speakersall 5.1 of them!
Basic speaker technology has remained essentially unchanged for almost fifty years. The only difference is the number of speakers in your system. Fifty years ago, a "hi-fi" setup consisted of onecount 'em, onespeaker. Then came the advent of stereophonic sound, and that one speaker became tworight and left. Today, to meet the requirements of surround sound movie soundtracks, your basic home theater setup needs six speakers: five (hopefully) identical full-range speakers for three front and two rear (surround) channels, and a separate powered subwoofer for the low frequency effects (deep bass) channel.
Each of the five full-range speakers in your system consists of a box-like enclosure and one or more individual speaker elements, called drivers:
A one-way speaker, like that found in many smaller "satellite" speakers, has a single driver.
Two-way speaker systems consist of two drivers: a larger one to reproduce bass and midrange frequencies, and a smaller one to reproduce the higher frequencies.
Three-way speaker systems consist of three drivers: large for the bass, midsize for the midrange, and small for the highs.
In a two- or three-way speaker system, the largest speaker (the one that delivers the bass) is called the woofer. The smaller one (the one that delivers the highs) is called the tweeter. In three-way systems, the driver in the middle is called, rather unimaginatively, the midrange. The single audio signal sent to the speaker cabinet is divided among the two or three speakers by means of a passive crossover circuit, which splits the sound according to frequency range.
Some larger speakers include more than three drivers. In fact, some tallish floorstanding speakers (such as the Polk Audio RTi12) incorporate multiple drivers of the same size. The thinking here is that multiple drivers deliver cleaner sound, at louder sound levels. (More speakers move more air, which makes for louder sound.) Or, depending on the configuration, several smaller woofers can be employed to do the job of a single larger woofer.
Some speakers incorporate a built-in powered subwoofer, and are thus classified as four-way speakers. A built-in subwoofer eliminates the need for a separate subwoofer elsewhere in your room, and thus results in a cleaner setup.
Speaker performance is measured in terms of frequency response. The best tweeters deliver frequencies up to or even exceeding 20 KHz. A good woofer delivers frequencies down to 40 Hz or lower. The better the speaker system, the cleaner the sound. Note, however, that high-quality sound is not necessarily dependent on a particular type of speaker system. A good two-way system can deliver better sound than a cheap three-way system. And you can't determine how a speaker sounds by its size; many smallish systems sound better than speakers with massive woofers. (However, you can somewhat reliably relate speaker quality to price; more expensive speakers do tend to sound better!)
While we're talking about size, let's examine the two most common types of speaker systemsthe larger floorstanding systems and the smaller bookshelf speakers.