How Do Line Arrays Work?
Line arrays achieve directivity through constructive and destructive interference. A simple thought experiment illustrates how this occurs.
Consider a speaker comprising a single twelve-inch cone radiator in an enclosure. We know from experience that this speaker’s directivity varies with frequency: at low frequencies, it is omni-directional; as the sound wavelength grows shorter, its directivity narrows; and above about 2 kHz, it becomes too beamy for most applications. This is why practical system designs employ crossovers and multiple elements to achieve more or less consistent directivity across the audio band.
Stacking two of these speakers one atop the other and driving both with the same signal results in a different radiation pattern. At points on-axis of the two there is constructive interference, and the sound pressure increases by 6 dB relative to a single unit. At other points off-axis, path length differences produce cancellation, resulting in a lower sound pressure level. In fact, if you drive both units with a sine wave, there will be points where the cancellation is complete (this is best demonstrated in an anechoic chamber). This is destructive interference, which is often referred to as combing.
A line array is a line of woofers carefully spaced so that constructive interference occurs on-axis of the array and destructive interference (combing) is aimed to the sides. While combing has traditionally been considered undesirable, line arrays use combing to work: without combing, there would be no directivity.
Kilde:
http://www.meyersound.com/mseries/m3d/l ... theory.htm
