Surround sound is the idea of wrapping a listener in sound, just like a movie theater. There are several different formats to get this effect, like Dolby Digital and DTS, and higher-resolution formats like Dolby TrueHD and DTS-HD Master Audio. The lower resolution formats can be found on DVDs, while the high-rez formats are available only on Blu-ray.
In terms of number of speakers and placement, there are multiple options:
5.1 Surround Sound
5.1 Surround is the most common surround sound speaker configuration. The five channels alluded to in 5.1 surround include the front left and right speakers, a center speaker, rear left and right speakers. The "point one" channel is the subwoofer.
5.1 surround sound is the backbone of lossy surround sound formats like Dolby Digital and DTS and was at the core of the home theater movement in the 1990s, powered by the advent of DVD-Video. DVD-Audio and SACD often had 5.1 audio tracks for music but, with both formats basically dead today, 5.1 for music is increasingly difficult to find.
For home theaters that are physically deep, side channels are often added to create a 7.1 surround system. This requires 7.1 surround sound source materials such as a Blu-ray player, as well as an AV receiver and/or AV preamp to process the 7.1 surround sound formats. A single rear speaker is the 6.1 format. The best 7.1 surround formats include the lossless Dolby TrueHD and DTS Master Audio.
6.1 Surround Sound
6.1 Surround is the slightly less popular "surround back" configuration, somewhat overshadowed by its more elaborate 7.1 big brother. It is found in DTS ES and Dolby Digital EX surround formats. 6.1 configuration has three front speakers (left, right and center), as well as two side speakers and one speaker centered in the rear plus a subwoofer.
6.1 surround sound never really took off with home theater consumers, as 7.1 surround was better for bigger rooms.
7.1 Surround Sound
7.1 surround sound is the most popular surround sound configuration found in high-end home theater systems today. 7.1 surround features three front speakers (left, right and center), two side speakers (left and right), two rear speakers (left and right) and an LFE ".1" or subwoofer channel.
You need to have a 7.1 source, such as a Blu-ray player, and an AV receiver capable of processing 7.1 surround sound, as well as the above-mentioned speakers and amplification needed in order to enjoy 7.1 surround sound. Popular 7.1 surround sound modes include high-resolution, lossless Dolby TrueHD and DTS Master Audio.
10.2 Surround Sound
10.2 surround was developed by Tom Holman (creator of THX) at the University of Southern California to be "double" 5.1 surround sound with many more speakers and multiple subwoofers.
10.2 surround has been more of a concept than anything home theater clients are purchasing and/or installing, as there is a lack of source material and processors capable of reproducing this much sound. Moreover, the physical room needed for 10.2 speakers is often too much for even larger home theater rooms. 10.2 is better suited for cinema and or IMAX installations. 10.2 was first demonstrated at the Audyssey labs in Los Angeles.