Surround channels

They primarily serve to deliver ambience and diffuse sounds in a film or music soundtrack.

It and its successor, Dolby Pro Logic (1987), used a single rear surround channel, but often using two speakers connected in anti-phase or a dipole radiator, as shown in the speaker configuration diagram to the right in gray.

Unlike most typical speaker placements, surround speakers are often intended to radiate such that the sound reflects off walls so that the sound arrives at the listening position indirectly as a reflection rather than a direct wave.

In commercial cinema, where there is a large area to cover, it would be impractical to use a single speaker for each surround channel.

JBL states that surround speakers should be spaced evenly along the side and back walls, starting at no closer than 1/3 of the room length from the screen (so the surrounds do not interfere with the front channels) and should be located at about 10–12 feet high and angled down to face the opposite wall-floor boundary.