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LISTENING
AT HOME
There
are over 200 million DTS 5.1 surround systems in the world. How many are set up
correctly? Most people use their system solely to play movie sound on, and see
surround sound as an 'effect'. So they put the front left and right speakers close
to the sides of their TV, and the rear speakers go wherever they will fit - usually
right behind the listener. This can be fine for film sound, and many music producers
like the rear speakers to be well behind, as it compensates a bit for the lack
of a rear centre speaker. (This deficiency in 5.1 has resulted in the new improved
6.1 or EX system - which does have a rear centre speaker.)
The
correct arrangement for 5.1 speakers is crucially based on them being arranged
on a circle that has the listener at its centre. This means that all five speakers
are sited at an equal distance from the listener. The subwoofer can be placed
wherever is convenient, as such low frequencies cannot be accurately located.
The front left and right speakers should each be placed at 30° from the centre
line. The rear left and right should be at 110° from centre. The official
5.1 spec actually states 'between 100° and 120° from centre'. Another
important factor is the distance of the speakers from walls. To cancel out early
reflections, each speaker should be placed two feet from the walls. One foot would
be acceptable. Or maybe put cushions behind the speakers? All of this is very
important for listening to transaurally-processed sounds. Some of he delays used
in the technique are tiny: less than half a millisecond. If the speakers are not
placed correctly, a further delay will be added, and this will disturb the spatial
imaging. SETTING
UP A 5.1 SURROUND SYSTEM
Bilocation has a 5.1 template printed onto the disc. A printable A4 template
can also be downloaded HERE
The
templates can be used for setting the angle of the speakers, but measurement is
also important. Remember that each speaker must be the same distance away from
the listening position. Speaker stands are best for placing the speakers at ear-level.
Here's how to set up a 5.1 system for a notional 14ft x
12ft room:-
5.1 surround is based on a circle with the listening position
at its centre, but some of the rear of the circle isn't used. The idea is to make
as big a circle as possible, as this increases the size of the 'sweet spot'.
A
very rough 'rule of thumb' is to make the diameter of the circle 2ft less than
the longest side of the room. In a rectangular room, the listener should be facing
one of the long sides. If the room measures 14ft x 12ft, then a 12ft diameter
circle will be the absolute maximum - but the centre of the circle won't be the
centre of the room: it will be 18" to 2ft back from the centre. Remember
all five speakers must be at least one foot from the walls (and preferably two
feet) to cancel early reflections.
The
best way to start is find the centre line, and position the centre speaker on
the line, and a compromised 18" from the front wall. If your system is also
used for film sound, this is often dictated by the position of the TV, with the
centre speaker on top of it. From the centre speaker measure whatever is to be
the radius of the required circle - in this case 6ft. This is the listening position.
You need to mark this spot.
Then
place the front left and right speakers. These are both at 30° from the centre
line, and so form an equilateral triangle with the listening position. Each side
of the triangle is the length of the radius of the circle, and a piece of string
makes it very easy to set up. Stretch the string from the listening position to
the centre speaker. This length can be halved to give the distance from the centre
speaker to each of the left and right fronts. All three of the front speakers
should sit on the outer edge of the circle though, and should form an arc.
You
could just place the template on the floor at the listening position, and stretch
the string out at each of the angles printed on the template. This is the easiest
way of positioning the rear speakers. The rear speakers should properly be placed
at between 100° and 120° from the centre line, so start at 110°.
For
a 12ft diameter circle this puts the rear speakers at about two feet behind the
listening position. Note that the rear speakers are almost twice as far apart
as the fronts. Again, check the distance from each speaker to the listening position
by measuring with the string.
The
subwoofer can be placed anywhere convenient, as the very low frequencies it generates
are impossible to locate spatially. At the front is best though, as subwoofers
occasionally rattle, which gives away their position. The
five surround speakers should be mounted at ear-level, or at least at the same
height. They could of course suspended from the ceiling. All must point directly
at the listening position, and all must be placed at the same distance from it.
Finally,
take great care when wiring the speakers up. They absolutely must be in phase
(eg red on the amp to red on the speaker) - so only use cable that is properly
marked. | | | | |
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