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user manual
TCS Compact series
tcs compact manual
page 15
Calculating the sound pressure level at a known distance from the PA
Sound intensity reduces rapidly as the distance from the source increases according to
the inverse square law which, predicts that a doubling of distance will result in a
reduction of ¼ the original, equal to a drop of 6dB, providing there are no reflections or
reverberation. For every 3dB increase of speaker output you need a doubling of input
power.
For example, in an open space where the front seats are 6 meters (20 ft) from the sound
source and the back seats are 60m (200 ft) from the sound source, you would expect the
sound pressure to drop by a factor of 100 (= 20 decibels) between the front seats and the
back seats.
In a ‘real world’ enclosed auditorium, this reduction is partially mitigated by the effects of
reverberation in the distant field and, in the near field, because the speaker looks more
like a wall source than a point source. Therefore the sound field in a room only behaves
according to the inverse square law in a relatively narrow distanced range.
It should be possible to make considered decisions regarding the particular models of
speakers that are required based on their sensitivity and SPL (sound pressure level) in
order to achieve the desired coverage and level.
Equalisation
TCS COMPACT series enclosures are designed to provide smooth and even frequency
response. They do not need excessive amounts of external equalisation to overcome the
sonic deficiencies often found in many lesser designs.
In order to compensate for room acoustics, TCS Compact series enclosures require only
minimal equalisation. As in any system, over-equalisation introduces phase shifts,
distortion and a reduction in headroom, usually causing more problems than it cures. It is
good practice to use as little equalization as possible, aiming to ‘cut’ frequencies rather
than adding large amounts of ‘boost’.
Most rooms will have resonances that will be excited at particular frequencies needing
some cut to help tame the sound. These problems are most pronounced at the lower
frequencies where loudspeakers generally exhibit very little directional control. Under
most circumstances a 1/3 or 1/2 octave graphic equaliser will generally be adequate, with
the fader settings applied smoothly and sparingly for the required room compensation.
If you find that the system needs a lot of boost at lower frequencies you probably need
additional sub-bass units.