Before I dive into the meat of this project I’m going to begin with a few posts introducing the topic and its history. These will help to set the context for the later explorations of line array behaviour.
Early Line Array History
The earliest known research into line array is thought to be the work for Harry F. Olson, an American electrical and acoustical engineer. Olson documented the basic directivity characteristics of line array configurations in Elements of Acoustical Engineering.
Olson’s work led to the development of column style loudspeakers which employed vertical stacks of mid-range drivers in a format that delivered highly directional audio propagation for vocal applications. Column speakers became a popular choice for speech reinforcement, particularly in reverberant spaces where the focussed directivity helps to minimise unecessary excitation of the reverberant field, resulting in an improved direct-to-diffuse ratio which is desirable for clarity and intelligibility. Column loudspeakers are still used for this purpose today, with class leading products from manufacturers such as Bose and K-Array among others.
Although the column loudspeaker became popular in certain applications, its use has always been restricted by inherent limitations regarding its performance. The line-source effect is observed to break down where driver spacing becomes significant relative to the wavelength. For low frequencies this is not problematic, however for higher frequencies it becomes impossible to locate drivers in close enough proximity to avoid destructive interference between them at some listening positions, resulting in the unwanted phenomena of comb-filtering. To improve high frequency performance smaller drivers in closer proximity are desired, however this simultaneously reduces low frequency performance for which larger drivers are preferable. The outcome is a trade off which limits the usable bandwidth of the system; we balance the high frequency requirement for small, tightly packed drivers, against the low frequency requirement for larger drivers, ultimately finding a compromise somewhere inbetween that performs well in the mid-range frequencies but tails off at high and low frequencies. This is acceptable for speech reinforcement in a reverberant environment, where the sacrifice in frequency response is balanced against the benefits of focused directivity, however it renders the column solution generally unsuitable for musical reinforcement where the reduced bandwidth and LF headroom represents a less palatable sacrifice.
Modern column speaker systems have come some way towards managing this trade-off, and there are a number of products that I have been really impressed by in recent years; delivering the directivity benefits of the column arrangement whilst performing well across enough of the frequency range to be practical for musical reinforcement in certain contexts. However, the frequency response does still remain more limited than for a genuine full range system, and the small column elements are limited in headroom. I consider it unlikely therefore that we are ever going to see the column loudspeaker performing on a level sufficient for its application in large scale sound reinforcement.
Modern Line Arrays
It was not until several decades later that Christian Heil, at the then fledgling L-Acoustics, revisited the concept of line array for larger scale audio reinforcement applications. Heil was interested in defining the criteria for a line array system that overcame the existing problems and presented a better solution than the cluster arrays that were commonly deployed for large events at the time. His 1992 paper comments:
Nowadays some concerts involve more than one hundred boxes. Unfortunately arraying boxes arises interference phenomenons which are not easily mastered. As far as linear frequency response, directivity control and power level at long distance are concerned, the results can be disastrous.
Large arrays of boxes, the characteristics of which are well known, lead most of the time to very surprising results. The question is to know whether or not it is possible to predict the behaviour of an array when the behaviour of each element is known.
Our purpose is to describe the sound field produced by arrays in such a way that criteria for arrayability can be defined.
This and later papers set out the basic criteria for L-Acoustics’ WST (Wavefront Sculpture Technology), which are the fundamental requirements at the heart of all modern line array systems.
In 1994 Heil turned WST into reality with the launch of V-DOSC, featuring the DOSC waveguide. Although met with initial skepticism, L-Acoustics’ V-DOSC line array rapidly cemented itself as the first in a new generation of loudspeaker systems; with many rival manufacturers subsequently releasing their own line array solutions. V-DOSC proved so monumental a turning point in the history of audio reinforcement that it went on to have a nearly 20 year production run, only recently taken out of manufacture and still used for major tours and concerts all over the world. In 2012, two decades after Heil’s original paper, V-DOSC was the main loudspeaker product deployed in the London 2012 Olympic Stadium, proving just how lasting and significant a development in live sound reinforcement it has been.
Line array has continued to develop since the launch of V-DOSC, with virtually all the leading manufacturers launching their own ranges of line array solutions. Line array speakers have become smaller and lighter, enabling the deployment of line array in smaller venues. Solutions have become cheaper, enabling greater access to the technology such that some form of line array can now be found in a very large proportion of productions. Line array has also become very fashionable – perhaps too fashionable – leading to a line array myth culture in which it is not always properly understood and is sometimes heralded as something more than it is.
In my next post I intend to present a review of available literature as well as other resources, ultimately setting the scene for my own research which I will go on to share over future posts.
- Elements of Acoustical Engineering – Second Edition (1957), Olson, H.F.
- Sound Field Radiated By Arrayed Multiple Sound Sources (AES 1992), Heil, C. & Urban, M