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OPTIMISED GROUND STACKING
WLA-25 rigging doubles up as an optimized ground stacking system, using the WLA-25SUB subwoofer as a base. Arrays
of WLA-25 line array elements can be aimed downwards by as much as 10° to cover audience areas close to a stage, as
well as upward by as much as 10° in order to better cover distant balcony seating areas.
AIR ABSORPTION
The high frequency performance of the medium and long throw sections of the line array will be limited by air absorption.
As the distance from the source increases, the mid and high frequencies will be reduced. The amount of absorption at a
given frequency is function of pressure, temperature and relative humidity. By far the most important factor is the relative
humidity, although temperature does have a significant effect.
To achieve minimal spectral variance across the coverage of the array, the groups of loudspeakers covering the middle to
rear of the venue will require equalization to compensate for this effect. Air absorption is difficult to predict with any great
accuracy, and in any case the relative humidity of the venue is likely to change when the audience arrive or the weather
changes. It is important that the venue is monitored during the event as the equalization applied during the design stage
with an empty venue may not be suitable during the event.
As a general guide, boost above 8kHz for a long throw group of loudspeakers and 12kHz for a medium throw group of
loudspeakers.
The chart overleaf shows attenuation in dB/m for a given frequency and humidity. It is important to note that the effects of
air attenuation are linear, unlike the level of attenuation from distance from the inverse square law. For example, at 100m
a source would be 40dB down compared to it's SPL at 1m. Assuming 50% relative humidity and 20° the level at 10kHz
will be an additional 16dB below this (approximately 56dB down).
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