The transition distance is not the system’s maximum throw. It is the distance that the
system’s near-field characteristic will reach – or, if you prefer, the 3dB per doubling
of distance attenuation range (ignoring air absorption). Beyond this distance the
attenuation rate will increase to 6dB/doubling of distance (ignoring air absorption).
The transition distance can be thought of as the distance that the line array’s
advantageous low attenuation rate will reach.
The distance from the stage to the furthest seats in a typical football stadium is in
excess of 120m. The line array advantage (the effect of moving the near-field
characteristic closer to the audience) will be proportional to frequency and the square
of the line length so it will be less for short arrays at low frequencies.
It is very important that you use a line array that is long enough for the low-mid
frequency projection to follow the superior mid and high frequency projection
out far enough for mid-high air absorption to have a balancing effect.
The following curves show the spectral balance of 4 and 12 W8L cabinets vs distance
taking air absorption into account for about 40% relative humidity.
The 4 x W8L system low mid projection is less efficient than its upper mid projection
because too few cabinets have been used for the line to be effective at low
frequencies. The smaller system would project clean vocals but it would sound thin –
lacking warmth and authority.
The 12 x W8L system 200Hz, 600Hz and 6KHz responses are closer together (and,
obviously, at a higher amplitude). The longer line has "kicked" the low-mid
frequencies out further so that they can keep up with the mid and high frequencies.
A 12 x line array provides excellent spectral tracking over typical stadium distances
whilst providing the extra high frequency headroom required to partially counter air
absorption.
Note that, as air absorption increases, upper mid frequency characteristics tend to
track lower mid characteristics with high frequencies tailing off.
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