Setting up Loudspeakers in a Room

Phenomenon of human acoustical perception

Where should the loudspeakers and the listener be placed in order to obtain excellent sound quality? Before answering this question, we would like to explain a few basic facts about human acoustic perception.

P.W. Klipsch, designer of the famous Klipsch horn, once said that God gave us two ears but only one mouth, so that we may listen twice as much as we talk. There is, however, a second reason to this. Based on different signals which are transmitted to our brain via our ears, we can determine the spatial information relating to a sound source.

Acoustical Perception 1

If the sound source is in front of us, the acoustic sound will reach both ears at the same time and with the same volume.

Acoustical Perception 2

If the sound source is 90 degrees to our right, the acoustic sound will reach the right ear approx. 0.7 milliseconds before it will reach the left ear. In this respect, our head can be regarded as an acoustic shadow for the left ear which causes reduced acoustical perception.

Acoustical Perception 3

If two loudspeakers send the same signal from different locations, our brain will calculate the mean value between the two locations. When listening to an old mono record of Maria Callas, we hear the soprano and the orchestra exactly in the middle between the two loudspeakers.

Acoustical Perception 4

Reflections from a wall cannot be easily distinguished from a direct sound source by our brain. When calculating the mean value, our brain will move the sound source away from the loudspeaker and towards the reflection.

However, we are glad to say that in the course of evolution our brain has developed a technique which allows us to shed some light on the dark chaos of reflections.

Acoustical Perception 5

The spatial information relating to a sound source is mainly detected by the brain in the first five milliseconds, everything which follows will at first be ignored. Sound travels at 1.7 metres (5.6 ft) in five milliseconds. If the sound of a reflection has to travel 1.7 m (5.6 ft) more than the direct sound of the source, then it will have no influence on our spatial perception.

This intelligent approach to acoustic perception is the reason why, in former times, we were able to run in the opposite direction from a sabretooth tiger, in the middle of a thick forest with many reflections rebounding from trees.