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Placement Of Home Cinema Speakers

Peter Strassacker Dr. Peter Strassacker
involved in loudspeaker design since 1977
Books on material and field research
speakers like Lagrange 98, Pascal, Sub 10-60

Peter Strassacker interviewed by
Frank Kleiber (4/2006).
 

Frank:
Peter, the original system was 5.1. What's important to know about it?
 

Heimkino

Peter:
If the home cinema system takes up only a part of a room, then only this part is going to be discussed here:

The front speakers are placed left and right of the screen. Not all viewers in a cinema are sitting inside the optimum triangle in between the front speakers. Therefore, the film industry introduced the Centre C speaker. The main purpose of this speaker is to acoustically stabilise the centre.

All bass comes form the subwoofer (S). Consequently, the front speakers are cleared of all bass information; bass is the produced only by a specialist that may initially be located anywhere in the room. Especially suited are locations in between the two front speakers (F).

The rear speakers (R) are placed behind the viewer. Either direct sound transducers or dipoles may be used.

Heimkino

Frank:
When should direct sound transducers be used, and when dipoles?

Peter:
If the system is mainly used for hi-fi, especially in surround sound, then I recommend direct sound transducers picture above); but it also depends on how far the rear speakers (R) are away from the listener: are they away less than 1 metre, then direct sound transducers are unsuitable. Dipoles are the way to go (picture left) and they should be placed in such a way the sound reaches the listener indirectly.

Like illustrated in the picture, a dipole radiates at least in two directions; a dipole's main task is to generate a diffuse sound (the source location should not identifiable). Therefore, a dipole radiates out of phase to front and rear. Lower frequencies are often radiated directly towards the listener (then we have a third direction), since the source lower frequencies cannot be located.

Heimkino

Frank:
Does this mean that most home cinema users should buy dipoles?

Peter:
Not necessarily.

A diffused sound is also possible by tilting a direct sound transducer towards the side wall. A disadvantage is that a tilted speaker is difficult to attach to the wall. Otherwise, the result of a tilted speaker is similar to a dipole, since there is a direct radiation plus many different reflections, establishing a diffuse sound characteristic.

An advantage is that the listener can play around with the positioning of the speakers until the required sound characteristics has been found.

Heimkino

Frank:
What's important to know about the front speakers?

Peter:
The front speakers should produce a sound where every source can be located. The centre speaker helps achieving this. In systems without timing compensation front and centre speakers could be arranged slightly circular around the listener.

In this case the front speakers should not be placed too close to the side walls, room conditions permitting. The distance A should be at least 80 cm. Otherwise, the indirect sound (i, now on the right in the picture) follows the direct sound (d) in less than one metre distance. This cannot be detected by the human ear, resulting in less three-dimensional sound and difficulty to locate the sound source.

Heimkino

Frank:
What's different in 6.1 systems?

Peter:
Well, the rear sound has the same problem as the sound coming from the front: if the rear sound comes straight form the back, then only the listener sitting dead centre is able to hear that. Therefore, the rear centre (C) was introduced, stabilising the centre.

The two other rear speakers (R) are the same as in a 5.1 system; they could be either direct sound transducers or dipoles.

Ideally, the rear centre should have the same height as the other rear speakers.

Heimkino

Frank:
Finally the 7.1 system...

Peter:
In a 7.1 system, all sound sources are practically around the listener.

The same applies here: If the distance between listener and speaker is less than one metre, then dipoles would be the answer. However, also direct sound transducers that are tilted towards the side or rear wall, are suitable. The ideal height is somewhere between 1.5 m and 2 m.

Otherwise, direct sound transducers may also be used. They should ideally have the same height as the front speakers. The distance between the neighbouring speakers and between the listener and the speakers should be similar. If the distance between the listener and the rear speakers is too high or to low than the timing should be corrected using the AV receiver.

Frank:
Well, that should have covered everything.

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