Speakers: For Movies and Music
You'll need a minimum of six speakers for your home theater systemfront left, front center, front right, surround left, surround right, and a powered subwoofer. You can purchase speakers separately, or buy prepackaged home theater speaker systems; this latter approach ensures that you'll get matching speakers across the entire sound field.
When you're shopping for speakers, keep in mind that the center channel speaker is especially important, as this is where virtually all movie dialogue is reproduced. The center channel speaker typically goes on top of, or in some instances just underneath, your television set. It's best to get it up near ear level, so that the dialogue seems to come from the television screen. For that reason, most center speakers are shielded, so that the magnetic speaker drivers don't affect the television screen or electronics.
The front left and right speakers should match the center speakers, with a similar sound response, so that dialogue moving across the front sound field sounds the same from speaker to speaker. These speakers should be placed on either side of your television screen. Ideally, all three front speakers should be the same distance from your main listening/viewing position, and at the same vertical level.
The two surround speakers are best placed on the side walls of your room, slightly behind your main listening/viewing position. It's a common mistake to put these speakers directly behind you, but that's not how they're designed to work; technically, these speakers are for surround channels, not rear channels. Putting them to the side or slightly back is fine, but directly behind isn't proper. However, since there's less directionality in the surround channels, you have some flexibility in vertical placement; it's okay to hang them from the ceiling, if necessary.
Finally, the subwoofer is unique among all your speakers in that it isn't powered by your A/V receiver. Instead, it's fed a line signal that contains the movie's low-frequency effects (LFE) channel. The subwoofer contains its own amplifier, which is why it costs a little more than the other speakers. The subwoofer is also unique in that it's not directional, which means that it can be placed just about anywhere in the room. It's okay to place it out of the way, which is good because it's an ugly little bugger. That said, you get a little bit better bass response when you place it in a corner.
If you go with a 6.1 or 7.1 Dolby Digital ES system, add one or two more speakers directly behind your main listening position. These true rear-channel speakers should be of the same make and model as your side surround speakers.
Speaker size is entirely subjective. Many small "satellite" speakers deliver surprisingly good sound these days, although old-school audiophiles might still prefer the wider range of floor-standing speakers. Satellite and bookshelf speakers work in a home theater system because they don't have to carry the bass load; the subwoofer does that. So you don't need big multi-speaker floor-standing systemsalthough there's nothing wrong with that approach.
If you listen to a lot of music, demo the speakers with a full-range music CD. Believe it or not, movie soundtracks are far less demanding than music CDs; speakers that do a good job reproducing explosions might be less acceptable in reproducing a violin concerto.
The price range for speaker systems is incredibly wide. You can find complete low-end systems for as little as $300, while super-high-end speakers might go for $5,000 or more for a full set. Let your ears be the judge.