A line array is a line of adjacent loudspeakers that coherently couple together creating a line source. A true line source will create a cylindrical wave-front propagating perpendicularly to the line source. This is instead of the spherical wave-front emitted from a point source.
A line array has a narrow dispersion at each end of its cylindrical wave-front. This helps to reduce room reflections and improves sound intelligibility. The narrow dispersion also allows the line array to throw (project) further than a simple point source system.
A point source loudspeaker will loose 6dB with every doubling of distance. A line source will only loose 3 dB with every doubling of distance, showing a major improvement of throw. This means that a point source starting at 130dB at 1m will be 88dB at 128 meters compared to a line source starting at 130dB will be 109dB at the same distance.
An accepted approximation is that the source centres need to be less than ½ a wavelength apart. So for 100Hz this would need to be 1.715 meters apart and for 5kHz just 0.0343 meters.
The source needs to be at least four times as long as the wavelength. This means that for a 100Hz Line Array you need a source 13.72 meters long. At 5kHz the source only needs to be 0.274 meters long.
Technically this is a curvy-linear array often implemented as a ‘J-array’. It works in a similar way to a line array and is a more common solution. Often people use the term line array to describe a curvy-linear array.
The theory behind line arrays was first published by Harry Olson in 1957 and was initially used to develop column loudspeakers (which are line arrays). Modern Line Arrays have been used at large scale events since the mid eighties.
Usually line arrays are vertical and flown either side of the stage. However, a line array will work at any angle. The angle should be set for best coverage. For example larger live events may have the bass bins across the front of the stage to create a horizontal line array (Glastonbury) or hung directly above the stage (Metallica).
Line arrays can be the best and the worst sounding systems. Short line arrays can be ‘plug and play’ systems, but with large commercial line arrays it is important to equalise each box (block or sector) correctly to the manufacturers specification.
If you put your head right next to the centre speaker of a line array you will (almost) only hear that one speaker. As you move away you will be influenced by the surrounding speakers but the furthest part of the line reduces the sound. Once you are at a greater distance (maybe 20m away from a 4m line) you will hear all of the line in unison.
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