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Configure the equalisers
Sensible correction of the in-room response requires the ability to measure the acoustic frequency response of
each speaker individually. The measurement microphone does not need to be expensive and suitable electret
microphones are widely available. If the appropriate measuring equipment is not available, we recommend that the
parametric filters be bypassed by setting Bank 2 Switches 2 & 3 to OFF. Setting of the low- and high-frequency
contour controls may be attempted by ear to the user’s preference.
Correcting for room resonances requires thought, skill and patience. It is not sensible to attempt to fully equalise
response dips, as this may lead to system overload. Fortunately, dips are less objectionable than peaks. For this
reason, each parametric filter allows just 4.5dB of boost but 12dB of cut.
It is also not advisable to make corrections to a single position measurement. The response of the speaker/room
combination can differ considerably throughout the room and it is all too easy to worsen the response in one position
whilst making it better in another. An average of several measurements taken at different positions throughout the
room should ideally be used to ensure an overall improvement in all listener positions.
The Method
We suggest taking measurements at each seat position and at several points outside the immediate listening area.
Point the microphone towards the speaker being measured.
The resonances change with height. Often seats will be at the same level, so put the microphone at a typical ear
height. If the home theatre room is like a mini cinema with regular rows of raked seating, measure at each seat at the
likely ear height. Do not hand hold the microphone during measurements. Use a tripod or other means of holding
it still. It is advisable to make the last measuring position n (the one used for subsequent equalised measurements)
the primary listening position.
21
The Theory
A number of response measurements R
1
to R
n
are taken and the average or mean
response R
m
is calculated.
The microphone is left at position n and further measurements are taken as
adjustments are made to the equalisation. If the measured equalised response at
position n (called R
neq
) is multiplied by R
m
and divided by the unequalised R
n
, one
can review the equalised mean response, R
meq
R
meq
=
R
neq
.R
m
R
n