A high-quality multi-channel audio system surrounds the listener with realistically lifelike sounds from all directions. These systems are used to:
The same fundamental principles of a stereo system also apply to a surround sound system, except that you need, four, five or more channels of audio, rather than just two. Obviously a surround system can be quite a bit more expensive than a 2-channel stereo system of equivalent quality.
In addition to the usual front left and right speakers, a 5.1 surround system adds a center front (or "dialog") speaker, rear left and right speakers, and a subwoofer. Space and budget considerations aside, you would ideally have five identical floor-standing speakers optimally positioned equidistant from the preferred listening position.
When cost precludes five identical best-quality speakers, our recommendation depends upon your priorities:
You may have heard recommendations to use special-purpose "bipole" speakers positioned at the sides of the room, rather than regular speakers positioned in the rear. With the advances in surround technology brought by Dolby Digital and DTS, we no longer favor bipole side/rear speakers.
In addition to 5.1 there are other configurations such as 4.0, 4.1, 6.1, and 7.1 systems. A 4.0 system is two front and two rear speakers with a phantom center channel; a 4.1 system just adds a subwoofer to a 4.0 system. A 6.1 system adds a rear center speaker to a 5.1 array, whereas a 7.1 system adds 2 more side-rear surround speakers. You can do other arrays such as an 8.4 system if you wish which would mean 8 full range audio channels and 4 subwoofer channels. Generally speaking most people are doing 5.1 systems these days, although some people are doing 7.1 systems instead. All things being equal 5.1 systems are of course less expensive than 7.1 systems.
Update: Some BluRay discs now come with 7.1 soundtracks, so now there is more of a reason for installing 7.1 surround systems than before.
Update: The main point of Dolby Atmos, DTS:X, and Auro 3D is that they add height information which is properly delivered by having speakers overhead—as opposed to trying to bounce those overhead channels off the ceiling from floor-standing speakers.
Update: Dolby Atmos is an object-oriented surround sound mode and is designed to be backward compatible. Starting in late 2014 there are now some Dolby Atmos encoded Blu-ray discs which have been released. For Atmos the design for most home theaters will start with either a 5.1 or 7.1 speaker set-up with the proviso that the height of those speakers ideally should not exceed 1˝ times the head height at the listening positions. To that array then add either 2 or 4 speakers at ceiling level in order to deliver a periphonic soundfield. Typical set-ups are 5.1.2 or 5.1.4 or 7.1.2 or 7.1.4. Note that the last number in these examples represents the number of ceiling-level speakers. If you have a very large room and a more or less unlimited budget with which to do proper justice to them then other set-ups with more channels are possible, up to a 24.1.10 array (24 floorstanding and 10 ceiling speakers), as you can have up to 32 audio channels in your home theater. For most home theaters a recommended practical implementation of Atmos is a 7.1.4 configuration which once again that last number means having 2 front and 2 rear ceiling-level speakers for a total of 4. Alternatively if you are doing an x.x.2 Atmos configuration then the 2 ceiling level speakers will be postioned at the front of the room. Note that though the lower level speakers may have lossless audio, the overhead speakers get a signal that is lossy compressed. For more info see the Dolby Atmos White Paper as well as a listing of Dolby Atmos commerical movie releases.
Update: Announced in April 2015, DTS:X is an object-based audio codec which is positioned as the next-generation successor to DTS-HD Master Audio and offers a Dialogue Control Feature which allows a sound "object" such as a dialogue track to have its volume raised independently. It is backward compatible with other DTS bitstreams. DTS:X supports lossless encoding for high quality audio. Although in situations where there are bitrate concerns, DTS:X can be used in lossy mode. DTS:X supports sampling rates up to 96k/24 bit for object mixes—and also supports up to 192k/24 for stereo and multi-channel mixes. As for speaker placement, it is flexible to accommodate a variety in the number of speakers as well as of room shapes and sizes.
Update: Auro 3D is another new surround sound mode which has been introduced. However as of 2015 because the list of initial Auro 3D titles is relatively small compared to that of Dolby Atmos it is questionable if it will be widely adopted or not.
The acoustics of the room will also greatly affect the performance of the surround system. If you are custom building a room, we suggest that you consider acoustics when you choose the size of the room and the listening position. The primary listening position should usually not be located halfway back into the room as this position has anomalies that will interfere with the sound from the speakers.
As in a 2-channel stereo system, the electronics and cabling that you use with the speakers will greatly affect the system's overall performance. If you are listening to movies, the dynamic contrasts in the loud passages may dictate a somewhat larger amplifier than usual.
Instead of a preamplifier, a multi-channel audio system employs a surround-sound processor which:
Surround sound processors vary considerably in sound quality and capabilities. In addition to the sonic merits of the equipment, you may wish to consider ergonomics, as some processors are considerably easier to use than others.
If 2-channel stereo listening is very important to you, then you may wish to consider a separate high-performance stereo preamplifier. With the surround processor's left and right front channels connected to the preamplifier via a unity-gain input, the system then utilizes the front left and right power amplifiers and speakers for multi-channel use. With a high-performance CD player, turntable, music server or other source connected directly to the preamplifier, this type of system design bypasses all the surround equipment during stereo use. We have found that this configuration is the optimal design for high end stereo listening.
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