Rather than two-channel sound, a home theater boasts multichannel surround sound. Two-channel sound gives a left and a right speaker effect, while multichannel surround sound adds a front center speaker between the front left and right speakers — plus two surround speakers for the sides of the room.
Newer versions of surround sound add even more rear speakers and side surround speakers to enhance your surround-sound field. A subwoofer is part of almost all home theater setups, but a subwoofer is more a part of the bass management of the collective speakers than part of the surround-sound system itself.
To understand the impact of the concept of surround sound on your home theater, you need to understand a bit about encoding and decoding sound:
When the master mixers at the movie studios create the audio track to go with the movie, they encode the music in very specific ways. They designate which channel (you can read speaker into that if you like) the specific sound goes through. In addition, each different channel is designed to provide spatial sound effects — meaning that the channels can work together to make sounds come from different locations relative to you, the listener. The goal is to decode those signals onto the correct channels to replicate the studio’s intent.
So, let’s say that a squadron of jets in a scene from Top Gun is doing a fly-by of the carrier command bridge. If you were in the command bridge, you'd hear the jets come in from the left, sweep across in front of you, and then disappear to the right and the rear as they turn off to the starboard side of the ship. If you're sitting in a well-tuned home theater, you should hear no differently. And as the bridge shakes, your subwoofers provide you with the vibrations to make you feel as if you’re actually there.
The encoders have to designate on the movie or TV program soundtrack the specific sounds that, at specific times, are to be sent to specific channels in your system. The speakers connected to those channels are given those signals by your surround-sound-equipped A/V receiver, which properly decodes those tracks from the DVD or other video source. A home theater audio system needs to have it all correct from beginning to end.
In a two-channel system (also known as stereo), you might hear some of that sound effect, in that it might get the left and right parts right. A two-channel system can’t help with the front to back movement, however, and that’s the critical part of a surround-sound system — it surrounds you!
