Anybody who has been to a big concert or performance will have seen line arrays in action. Apart from the loudspeakers themselves, the way they are configured plays a huge role in the quality, throw and overall clarity of the sound. In this edition, we will be discussing the different configurations of line arrays and the reasons behind it.
A line array is a loudspeaker system made up of a number of loudspeakers. Sounds simple enough right? Wrong, this where factors such as phase come into play. Timing differences from different sources when combining identical signals may sometimes result in phase cancellation, leading to loss of audio information. Thus, the speakers of a line array system need to be mounted in a line and fed in phase, to create a uniform source of sound. The distance between adjacent speakers need to be close enough to ensure that they constructively interfere with each other to result in a louder, more evenly distributed sound output pattern.
The need to focus the sound at the audience has resulted in vertical line arrays becoming the norm. They provide a very narrow vertical output pattern without wasting output energy on ceilings or empty air above the audience. A vertical line array displays a normally wide horizontal pattern useful for supplying sound to the majority of a concert audience.
Two lesser-used configurations are the straight and curved array configurations. The problem with curved arrays is that they are not very well suited to most venues as the bottom half will be angled down to provide extra coverage at locations close to the front of stage, the top half will be angled upwards at the ceiling. The problem with straight line arrays is that the beam is far too narrow at high frequencies. A solution to utilise the best features of both arrays is to use a curvilinear or ‘J’ array. Comprised of a straight line portion and a curved portion at the bottom. This provides a long throw straight line component for people relatively far away, while the curve at the bottom acts as an in-fill for the area directly in front of the array.
Spiral arrays, on the other hand, are curved all the way along the array, but the curve is progressive. This means that the top of the array is almost straight with angles of 1° between boxes, and increases to about 6-10° at the bottom. A well designed spiral array could have an almost constant directivity pattern and uniform throw that delivers sound to the audience away from the array as well as ones that are directly under it.