Surround Sound Specifications

The description of surround sound specifications brought here is categorized using the number of discrete channels encoded in the original signal and the number of channels available for playback. Each channel may refer to a group of speakers. The graphics shown here denotes the number of channels, not the number of speakers.

3.0 Channel Surround (Dolby Surround)
Three audio channels are produced from a specially encoded two-channel source:

• Two channels for speakers at the front-left (L) and right (R).
• One channel for surround speaker or speakers at the rear-surround (S).
  

Placement: Three identical speakers placed equidistant around a central listening position. If two rear speakers are used they should also be placed above ear height, slightly behind the listening position, and should be of bi-polar construction.

4.0 Channel Surround (Quadraphonic)
Four audio channels are produced either from a specially encoded two-channel source or a four-channel source:

• Two channels for speakers at the front-left (L) and right (R).
  
• Two channels for surround speakers at the rear-surround left (LS) and surround right (RS). Some newer receivers support the LFE channel.
  

Placement: Quadraphonics is a system designed for music only. All speakers should be at an ±45˚. All speakers should be above ear height.

5.1 Channel Surround (3-2 Stereo) (Dolby Pro Logic II)
Five audio channels are produced either from a specially encoded two-channel or a stereo source:

• Two channels for speakers at the front-left (L) and right (R).
• One channel for speaker at the centre-centre (C).
• Two channels for surround speakers at the rear-surround left (LS) and surround right (RS).
• One low-frequency effects channel (LFE).
  

Placement: 5.1 speaker layouts should conform to the ITU-R BS.775 standard, despite the myth that music and video content require different placements. The ITU standard states that the left and right speakers are located at ±30˚, while the rear speakers should be positioned approximately ±110˚. There is speculation that rear loudspeakers at ±150˚ provide "more exciting surround effects".

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Surround Sound Systems

Surround sound systems use multichannel audio to enrich the sound reproduction quality of an audio source using additional audio channels reproduced by additional discrete speakers. the three-dimensional space of human hearing can be achieved using audio channels above and below the listener. Surround sound technology is used in cinema theatres, home theatre systems, video game consoles, personal computers, and so on.

Low Frequency Effects (LFE) Channel
The Frequency Effects channel (LFE) is originally developed to carry extremely low (sub-bass) sound effects such as thunder or explosions on a separate channel. This allows the theatres to control the volume of sound effects to suit the size of their sound system and the acoustic environment of their cinema. However, home system may not have a separate subwoofer that can handle such effects. Therefore, modern surround systems often incorporate a bass management system that allows bass on any channel to be fed only to speakers than can handle low-frequency signals.