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".

(to be continued)

Home Cinema

Home Cinema (a.k.a. Home Theatre) is basically an entertainment system that reproduces movie-theatre quality video and audio at homes. The first home cinema systems were 8mm film projector equipment which was replaced by laser discs. In mid 1990's, a typical home cinema would have been a laser disc or VHS videocassette player fed to a large rear-projection television. In late 1990's, DVD players with Dolby Digital (5.1 channel audio) were introduced along with high definition televisions. Nowadays the term home cinema includes a wide range of systems. The display might be a 60" HDTV and for audio, several thousand watts of power fed into a 12" (or more) subwoofer with five or seven surround sound speakers. The price on these equipments can go as high as $100,000.

Basically a home cinema is composed of the following components:

1. Input Device: Any audio/video source that can include high quality formats such as blu-ray. Others include VHS player or video game systems. Some of the newer models include a home theatre PC that acts as a library for video and music content.
2. Processing Device: Input devices must be processed for complex surround sound output.
3. Audio Output: Normally systems come with two speakers but can have up to 10 speakers and an additional subwoofer.
4. Video Output: A large High Definition display that can be LCD, plasma, video projector, rear-projection television or a traditional CRT television.
5. Atmosphere: High-end home theatres have sound insulation to prevent noise from escaping the room and a specialized wall treatment to balance the sound within the room.