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Equalising a system
As discussed before, the fundamental benefits of equalisation are:
• Improved intelligibility and natural sound of the sound system.
• An increase in the gain available in the system before feedback.
In some circumstances, it may not be possible to achieve a natural sounding system
that is completely intelligible due to poor acoustics or high levels of background noise.
In such cases, a compromise must be struck by the engineer depending upon the use to
which the system will be put. It may be argued that in the case of a vocalist,
intelligibility must be sought at all costs. However, for dance music reproduction a
more natural approach, with no real concern for intelligibility of the individual lyrics,
may be preferred.
Please remember, the equaliser is not a 'cure all' device and will not solve the
problems of a poor sound system, installation or venue acoustics but, when used
carefully, can bring out significant improvements in the quality of reproduction of a
system.
Preparing for equalisation
Before starting to equalise the system, it is worthwhile checking that the system is
performing correctly. Listening to the system without any equalisation may reveal
underlying distortion or artefacts of the room, for example, lengthy reverberation,
which may need to be rectified before trying to equalise the room.
It may also be worthwhile using a sine tone sweep so that problems at certain
frequencies, which may not be immediately noticeable with pink noise, can be detected
and corrected before equalisation. Especially, check the system's crossover points as
these may reveal problems with the system. Note that poor coverage cannot be
rectified through the use of equalisation.
When you are satisfied with the basic system performance, equalisation can begin.
Equalisation using an RTA
The measurement microphone should, ideally, have a flat response or be calibrated to
the RTA and placed in a sensible position where it will not be affected by nearby objects
that may interfere with the local acoustics, such as within one metre of a rear or side
wall, or in a balcony opening.
Using the RTA and a pink noise source, adjust the level of the frequency bands on the
graphic equaliser inversely to that shown on the RTA display. Do it so that the peaks in
frequency response are reduced to the level of the other bands and, conversely, the
deficient bands are increased. You will need to perform the test at a reasonable level
approaching normal usage volume so that the equalisation can take into account the
response of the loudspeakers at normal operating level (versus low level). It may also
be desirable to take measurements at points throughout the area. Although it may not
be possible to get perfect equalisation throughout an entire area, it may be preferable
to obtain a good equalisation of the whole area rather than a perfect equalisation at a
single point with poor performance at all other points. A compromise may need to be
made in an effort to equalise the sound for the whole area rather than just the centre
FOH position.
Chapter 11: Graphic Equaliser (GEQ)
XL8 Control Centre
Operator Manual
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