Peter Strassacker interviewed by
Frank Kleiber (4/2006).
Peter, the original system was 5.1. What's important to know about it?
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
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.
When should direct sound transducers be used, and when dipoles?
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.
Does this mean that most home cinema users should buy dipoles?
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.
What's important to know about the front speakers?
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.
What's different in 6.1 systems?
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
Finally the 7.1 system...
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
Well, that should have covered everything.