Line Array Directionality
Somewhat opposite to the concept of arraying groups of predominantly horn-loaded loudspeakers in the quest to ultimately generate large-system pattern control, the modern line array is a mixture of horns (or waveguides as many manufacturers name their devices) combined with various sizes of cone drivers.
The pursuit is clear: improved directivity and the benefit is delivering sound to the seated audience areas while minimizing ‘acoustic overflow’ into unseated regions of a venue. By eliminating unwanted reflections from walls and ceilings, the direct sound should be clearer and cleaner.
However, line arrays tend to excel at sending coherent sound over long distances which makes the reflections more of a discreet echo instead of the scattered reverb effect of less coherent systems. The trick, it seems, is to focus the line array very, very carefully to avoid discreet reflections.
There’s an easy way to explain what happens in a line array formation. The multiple sources in the line generate acoustical addition with one another, mostly because they are closely arrayed in the physical plane, while they simultaneously generate cancellation lobes off-axis. This factor forms a line array’s exceptional ability to provide tightly defined directionality in the long axis of the line.
As you walk towards a well designed line array and then walk directly under it, it will sound like the level was attenuated by a very large number. And that’s a good thing when dealing with feedback and other stage-related contamination.
Line ‘em up: subwoofer and full-range line arrays.
Let’s look at it like this: stack up a bunch of acoustic sources in a line – curved or not – and there will be a measure of acoustic addition and a measure of cancellation. Account for the band-limited parameters that always exist in relation to the transducer sizes and shapes (with DSP no doubt), and one can create a system that ultimately provides broad-band directional control.
But it’s not so easy. Combining conical sources, such as 6- or 8-inch cone drivers in the MF range, so that they acoustically mate with HF waveguides that are designed to keep high frequency output as narrow as possible, does not make for an easy outcome.
All sorts of things are then done to try to get vastly different dispersion patterns to roughly agree with each other. Angling the cone drivers is usually the first step. The next is to provide various forms of physical baffles that interrupt the cone driver’s native dispersion characteristics. Finally, DSP is used in an attempt to manage pattern control.
The good news is that almost anything that produces sound, when combined in a closely coupled line, will take on a measure of vertical control all on its own. Thus, most line arrays, whether carefully engineered and tested – or not – will exhibit a measure of useful pattern control.
As the world of professional audio continues to grow and develop, it’s likely that a steady rate of product improvement will be on the menu. The job of the end user is to separate idle claims from demonstrable benefits. And that’s something we, as a group, do pretty well.
Senior technical editor Ken DeLoria has mixed innumerable shows and tuned hundreds of sound systems with an emphasis on taming difficult acoustical environments, and as the founder of Apogee Sound, developed the TEC Award-winning AE-9 loudspeaker.