All About Sound: Surrounded by Sound
Just as the "front axis" of left, right and center channel speakers in a home theater system deliver the front stage performance that anchors the action to your screen, rear audio ambiance is provided by loudspeakers placed around the sides and rear of the theater seating area.
Rear audio ambiance is important in home theater to reproduce "surround sound" effects. If it's raining on-screen, it should be "raining" in your home theater. If there are airplanes are flying around on-screen, they should be "flying around" in your home theater, also. Producing this illusion is the job of rear, or surround, loudspeakers. They add size and dimension to the soundstage and ensure a seamless transition when sounds and effects move from the front and center to side and rear speakers.
Specialized rear/surround speakers come in many different styles and arrays; conventional direct radiating, bipole/dipole, and reverberant dispersion. The kind of surround speakers you choose for your home theater will have everything to do with the size of the space and the position of your seating area.
While large-scale movie theaters use multiple arrays of direct-radiating surround speakers, direct-radiators are not as successful in smaller settings. Without exact placement and calibration, their direct delivery can call attention to them and distract attention away from the front stage.
Paradigm engineers recommend reverberant dispersion rear/surrounds. Reverberant soundfield rear/surrounds, placed to the sides and rear of the listening positions, envelop listeners in a less specific radiation pattern, creating more ambiance without explicitly drawing your attention.
Reverberant soundfield rear/surrounds work just as well for realistic reproduction of multi-channel music. Because of their ability to create a large non-localized sound field, they contribute multidimensional realism to the reproduction of the original recording’s acoustic space.
When choosing rear/surround speakers to fill out your home theater or music listening space, consider the size of the space and the position of the listeners. Then choose speakers that will not detract from the front-stage performance, but only deliver realistic rear audio ambiance.
Want more info? Here's an old article, dated sure, but full of excellent basic information about surround sound and choosing and placing surround sound loudspeakers in your home theater. We're showing our age with this, but good info is good info.