The Line Array Project #3: Literature & Resources Review

In this post I want to present a brief review of some of the best sources of literature and training concerning line array currently available. This is not going to be exhaustive, but will include a number of resources I have found to be useful myself whilst trying to further my own understanding of line array.

One of the things I feel our industry has always been a bit poor at is academia. What we do sits on the divide between science and art, leading to a delicate balancing act between the objective and subjective when informing our understanding and design approaches. Sometimes we get this balance wrong. One of my major passions is to foster greater standards of excellence both personally and within the wider industry, and that means getting better at this. It shouldn’t be enough to know just a few rules of thumb and to let a clever bit of software do all the hard work for us – that’s not engineering, it’s just laziness – we should understand the systems we are deploying intimately in order to appreciate the complexities of the decisions we make as sound designers.

Line array is probably one of the toughest areas in this respect. When I began my own investigations into line array I found the available resources to be scant, unreliable and inconsistent. Finding rigourous research is challenging; there is information out there, but much of it is shallow and of dubious quality – in the best cases accurately presenting only a partial understanding of the phenomena, and in the worst cases actually promulgating untruths. There are one or two nuggets of gold out there however, and I present these below.

Literature

Please note that this is not really a thorough literature review, rather you should view it more as a directory of useful resources on the topic along with a few guiding comments to contextualise each.

Elements of Acoustical Engineering – Second Edition (1957), Olson, Harry F. – The original line array paper; in fact there is a lot more than line array in here, but readers will find several chapters on line-source and various array configurations in section “II: Acoustical Radiating Systems”. Olson was mainly interested in directivity and describes equations for generating polar plots based upon each configuration. As I’ll discuss in a later post, the concept of a polar plot for a line array is somewhat flawed as the array does not posses linear directivity characteristics in the same way that a point source will do, but none-the-less we need to recognise the value of Olson’s work as an important early contribution to the field. I’m not sure of the legality so I won’t link directly here, but Google returns several copies of the full text on PDF for interested readers.

Sound Fields Radiated By Arrayed Multiple Sources, 92nd Convention of the AES (1992), Heil, C. & Urban, M. – The 1992 AES convention paper in which Christian Heil and Marcel Urban first introduced their “criteria for arrayability”. The math is quite heavy, but it is worth it for the introduction of several key ideas. Heil and Urban describe the Fraunhofer and Fresnel zones* (more on this in a later post), as well as defining the border between the two and highlighting the frequency dependency. At the end of the paper the authors define several conditions for arrayability which were later adopted as part of L-Acoustics’ Wavefront Sculpture Technology (WST) criteria.

Wavefront Sculpture Technology, 111th Convention of the AES (2001), Urban, M., Heil, C. & Bauman, P. – A development of the 1992 paper, Heil et. al go on to describe further WST criteria and the DOSC waveguide. The requirement for an isophasic wavefront (acheived via the waveguide) is defined, a critical stage in controlling the behaviour of an array at shorter distances/higher frequencies.

TI 323: C4 System Specifications and Configurations, d&b audiotechnik – I’ve long been big fan of the guys at d&b, I find they have a particular knack for explaining difficult concepts in comprehendible language. d&b’s C-Series includes a number of arrayable cabinets; although I wouldn’t describe these as true line array speakers as they lack isophasic waveguides which d&b later introduced with the Q-Series. The TI323 document for the C4 system offers some great introductory discussions of line array topics.

Training

Hands on training on line array seems to be quite rare and my experience is that most engineers are still doing the majority of their learning on the job. Several of the top end manufacturers do offer training courses, often (with some exceptions) at a fairly substantial cost and with a strong product focus. I’ve obviously not attended all of these, but here are two I wish to highlight for UK based readers.

d&b audiotechnik Line Array Workshop – d&b host a line array workshop at their UK facilities in Nailsworth. Although delivered by a manufacturer and with some leaning towards a focus on their product, there is also a lot of really good generic theory covered during the earlier part of this training course before it moves on to practical rigging and demonstrations using products from across d&b’s range. It is free to attend, though numbers are limited and there is regularly a waiting list for spaces. Steve Jones and Oran Burns who (at the time of writing) run the course are both excellent communicators and engineers whom I have massive levels of respect for. My one criticism of the course when I attended would be that there is a strong focus on the Fresnel model which I did not feel was fully contextualised with an explicit discussion of its limitations*.

SFL Line Array Training – As I work for SFL I cannot make any claim to impartiality here, however SFL’s Mark Payne runs an excellent line array course. I believe this course to be unique as the only non-manufacturer affiliated line array course in the UK. The course runs over 2-days; looking at line array theory and design on day one, and rigging and practice on day two. There is also a preceeding day covering a more general background in acoustics/electro-acoustics, and a follow up day covering digital systems networking including amplifier control networks. The course involves hands-on practice with current line array products from both d&b audiotechnik and L-Acoustics and is very reasonably priced at just ¬£30 per day.

 

Footnote:

*At several points in the post I have referred to Fresnel analysis. For reasons I will discuss fully in a later post, I am wary of the Fresnel approach to understanding line array. The Fresnel model is very useful and I will use it at points during my investigations, however it is important to appreciate that the Fresnel model is a simplification of the reality (a very useful one that has been used to good effect by several pivotal researchers); it has its limitations and I am interested in taking my investigations  beyond this. The model describes array behaviour quite accurately but does not in itself explain that behaviour on the level at which I want to understand it.

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