The term "multichannel audio" refers to the use of multiple audio tracks to reconstruct sound on a multi-speaker sound system.
Two digits separated by a decimal point (2.1, 5.1, 6.1, 7.1, etc.) are used to classify the various kinds of speaker set-ups, depending on how many audio tracks are used.
The first digit shows the number of primary channels, each of which are reproduced on a single speaker, while the second refers to the presence of a Low Frequency Effect (LFE for short), which reproduced on a subwoofer. Thus, 1.0 corresponds to mono sound (meaning one-channel) and 2.0 corresponds to stereo sound.
For any given number of audio channels, there is an optimal physical setup for the speakers that produces the best effect possible. For this reason, special icons are placed on surround sound equipment to symbolise the number of channels and the physical placement of the speakers. Small black squares (one for each channel) are placed in a square that represents a room to indicate how to set them up:
The physical configuration of the speakers in a 5.1 surround system is of utmost importance, as it directly influences sound quality and the realizm of audio effects.
For best results, there are a number of rules to follow when placing each speaker:
- Front speakers should preferably be placed at the height of the ears of a seated listener. The rear (surround) speakers must be positioned slightly above this height.
- The left and right front speakers must be placed one on each side of the television set, both at the same distance. In practice, they should each form a 25Â° to 45Â° angle with the listener.
- The central speaker must be placed directly above or below the TV set, as it is primarily used to relay the main actors' dialogue.
- The subwoofer may be placed anywhere in the room, but preferably on the ground, so as to better transmit the vibrations. It is best to try out different locations in the room.
- The optimal position for the rear speakers is a short way back from the listener, forming a 90Â° to 110Â° angle with him or her.
6.1 setup is similar to a 5.1 configuration, as it only adds a rear central speaker in order to compensate for the gap between the two rear speakers.
A 7.1 setup bridges the gap between the two rear speakers, using not one, but two speakers.