Where to place Loudspeakers in a 5.1 Setup - Tip 8

There are recommendations from various organizations on the correct placement of loudspeakers for a 5.1 surround sound installation. In general, they all agree on the following positioning in the horizontal plane:


tip8 fig1


NOTES:

  • The front left and right loudspeaker angles can be pushed out slightly (5° max) as there is a real source (centre channel) and not a phantom image formed by a stereo pair. However 30° is the preferred angle.
  • The rear loudspeakers can be position will less restriction as human source positional perception is not so good to the rear.
Vertically all the monitors should be at the same height, however, if there is a viewing screen or window in the way, the centre channel can be raised by up to 7° - this is allowed due psychoacoustic limitations in the ability of humans to resolve vertical directions. Lowering the centre channel is not preferred as the negative effects of the floor reflection are increased. The monitors' acoustical axis should be placed at ear height or the monitors can be raised slightly to help reduce floor reflection effects and to give a less obstructed path from the monitor to the listening position. Remember to angle them down so that they still point towards the listening position.


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The rear channel angles can be raised by more than the front monitors as humans have poor positional perception of sounds from the rear but the standards do not agree with one another on this: 15º is perhaps sensible maximum here.

In all cases the acoustical axis of the monitor must be angled both horizontally and vertically towards the listening position to give the best on axis frequency response.

Finally, all of the monitors should be positioned the same distance from the listening position, i.e. the monitors should be placed in a circle with the listening position at the centre of the circle. Where this is not possible time delays must be used to ensure that sound from each of the channels arrives at the same time. Approximately 1ms is required for every 30 cm positional difference so a delay unit with a 10 µsec resolution is the minimum requirement to give a 3 mm positional resolution accuracy. If the rear monitors are further away from the listening position then all 3 front channels must be delayed by the same amount. If the centre monitor is closer to the listening position then only a single channel delay unit is required. If the monitors are not aligned properly so that the sound arrives at the same time then ripples will be experienced in the midrange range at the listening position.


tip8 fig3

ITU–R BS.775–1:
Multichannel stereophonic sound system with and without accompanying picture (Geneva, 1992-94)