Positioning of the monitors in a surround sound installation
The audio presentation is only created correctly if the monitor orientation (angle) is correct. The monitor locations are usually specified as angles relative to the listener facing forward.
For stereo and conventional multichannel systems the monitors are assumed to be at the listener’s ear height. If the monitor height is higher or lower, sound perception will change and this will affect the sound image.
3D or immersive sound reproduction systems also use monitors at multiple layers at various heights or above the listener. Then also the vertical orientation angle must be considered and should be correct.
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.
All the monitors should be vertically 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°
The acoustical axis should be angled horizontally and vertically towards the listening position for the best flatness of the frequency response.
All of the monitors are positioned at 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. The Smart Active Monitoring (SAM) products contain an electronic delay to enable accurate distance alignment even in cases where the monitors cannot be located physically at the same distance from the listening position.
The distances from the monitors should be aligned precisely. The timing difference between the two monitors in a stereo system should be smaller than 0.1ms. Sound travels in air 340m/s, so in 0.1ms sound travels 34mm.
Make sure that the monitors are positioned at the same distance from the listening position, i.e. the monitors should be placed in a circle with the listening position at the centre.
Time delay formula
tdelay = (dmax - dmon) / c
Explanations for the symbols: tdelay is the time delay needed to ensure that the monitor sound arrives at the same time as the others
dmax is the maximum distance of any of the monitors to the listening position
dmon is the distance of the closer monitor to the listening position
c is the speed of sound in air at 20°C at sea level = 344m/s
The centre channel monitor is 2.12m from the listening position. The left and right monitors are both 2.46m from the listening position. The time delay required on the centre channel is
tdelay = (2.46 - 2.12) / 344 = 988µs (so set the delay unit to 1ms)