Because watching a DVD is barely worth the effort if you can’t hear it in surround sound, most media rooms disperse the sound with two front speakers, a center, two rears, and a subwoofer—what is known as a 5.1-channel system. While five-channel sound may be the norm today, in the not-too-distant future you should decide whether to upgrade to 7.1 or better.
In the most basic sense, surround sound is produced by surrounding the audience with speakers. However, simply increasing the number of speakers in a room does not create surround sound; the source material must be recorded for surround output, and the processor must know how to distribute the sound. So far, no DVDs are encoded to provide more than 5.1 discrete channels of sound, but some processors can output five separate channels and give the auditory illusion of more. With the first five-speaker arrangements, which also included a subwoofer, only the left and right front speakers provided the full frequency from low to high. Dolby exploited the possibilities with Dolby Digital 5.1. The 5.1 refers to five full-frequency main channels: front left, front center, front right, rear left, and rear right; the .1 indicates the subwoofer. (Another format, dts 5.1, provides the same number of channels, but many people say it sounds better because it doesn’t compress the sound as much.)
To understand the potential of more channels, you need to know the evolution of surround sound. Dolby, the first to respond to moviegoers who wanted the surround effect at home, created a format in which the sound from the rear channels was separated from the front pair. It filled the space behind the listener, but it was a synthetic fix. Dolby Stereo begat Dolby Surround, which preceded Dolby Pro Logic, and each time, Dolby more clearly defined the sound from the rear channels.
As the film industry pushed for more channels, home video enthusiasts followed. Lexicon, a company that produces digital audio processing equipment, and others developed side channels to provide sound between the front and rear speakers in large rooms, creating 7.1 systems. Two new technologies—Dolby EX and dts ES—provide sound to fill the space between the two rear speakers. If you add EX or ES capability and install two speakers in the back to create a mono channel, you have 9.1 channels. (If you have ES or EX capability without adding speakers, you are still listening to 5.1 or 7.1.)
Although DVDs aren’t designed for more than 5.1 sound, you can create a facsimile of more channels with the latest processors. Lexicon’s MC-12, for example, allows you to have two speakers at the front, two at the sides, two at the back, two more behind the back speakers for ES or EX, a main subwoofer, separate left and right subwoofers, and a front center channel. Add them up, and you have a dirty dozen. Alas, that DVD comes only in two-channel Dolby.