High Frequencies
Practical line array systems act as line sources only in the low- and mid- frequencies. For the high frequencies, some other method must be employed to attain directional characteristics that match those of the lows and mids. The most practical method for reinforcement systems is to use wave guides (horns) coupled to compression drivers. Each horn must have a very narrow vertical and a very wide horizontal dispersion.
Rather than using constructive and destructive interference, horns achieve directionality by reflecting sound into a specified coverage pattern. In a properly designed line array system, that pattern should closely match the low-frequency directional characteristic of the array. If the array's vertical dispersion is 60 degrees and there are 12 boxes, then each horn would need to have 5 degree vertical coverage. (Narrow vertical coverage has the benefit that it minimizes multiple arrivals, which would harm intelligibility.) If this is achieved, then the wave guide elements can be integrated into the line array and, with proper equalization and crossovers, the beam from the high frequencies and the constructive interference of the low frequencies can be made to align so that the resulting arrayed system provides consistent coverage.
Read more about this topic: Line Array
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