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Justin Grealy: An absence of balance in reinforcement installations

Justin  Grealy
Justin Grealy: An absence of balance in reinforcement installations

Revered FOH engineer and Audio Pro International columnist Justin Grealy takes an insightful look at the challenges faced when searching for 'middle ground' in the world of installed sound reinforcemnet...

As a working live sound engineer, I am regularly asked to specify and install PA systems for all sorts of different venues and applications. Until relatively recently, the audio marketplace could provide virtually any kind of loudspeaker system, from very small passive cabinets, through point source boxes with any dispersion from 20 to nearly 180 degrees, to large line array systems. This cornucopia of audio choice meant that it was relatively easy to find the appropriate type of cabinet for the venue.

However, recently I have been trying to source appropriate systems for several “difficult” smallish (under 1000 capacity) venues for both temporary and permanent installations and I seem to be finding the same problem with most of the major loudspeaker manufacturers, in that there doesn’t seem to be any middle ground between the small point source “infill’ type cabinet and the larger flown line array systems. Unfortunately, line array technology is often unsuitable for small rooms, particularly rooms that are asymmetrical, deeper than their width, or massively reflective. I know that there are some products, for example the L-Acoustics Kudo that have variable waveguides (they call it  the K-louver) which allow the user to adjust the horizontal dispersion each side of the array independently. However, it seems to me that the marketplace is very line array orientated, and in much the same way as engineers are being forced by the market into using digital consoles, (see last month’s tirade) the overwhelming majority of manufacturers (and therefore PA companies) who offer large format systems are only supplying line array.

Certainly there is a profusion of different systems available, from tiny to gargantuan, but the principles remain the same. Most decent sized concert venues can be serviced excellently well with line arrays and the predictive software combined with new sub-bass deployment technologies (cardiod arrays, for example) give the modern sound engineer more flexibility and personal choice than ever before. I offer no argument against the ever greater use of both material and physical technologies thus empowering us, but I do catch myself feeling that on occasions I’d rather be flying some point source boxes that I could, in a single vertical plane, point away from the brick wall half a metre from the hang or to better cover that awkward, odd-shaped room.

Obviously this is a market driven thing and the major suppliers of, for example, d&b or Nexo, have disposed of their presumably no longer serviceable point source systems in favour of line array. I would contend that there was a flexibility available from the d&b C4/C7, the Nexo Alpha, Turbosound’s Flash/Floodlight and several other similar systems that isn’t really there anymore. Comparatively inefficient; big; heavy; and awkward to rig are all sustainable arguments for this, I agree, discounting the cost issues, and I know that this is an unfashionable view, but I should like to have the choice.

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Please, feel free to correct me here, people, if I’m missing something obvious, at justingrealy@gmail.com. I’d love to be wrong.

This line of thought brings me to consider some of the more fundamental issues regarding reinforcement, which I feel are ripe for review in consideration of the new technologies available. There are two major issues that I think merit serious consideration. The first is what I refer to as ‘The Proscenium Wave’ dilemma. The traditional method of reinforcing, for example, an arena rock show is by hanging a large stereo speaker system close to the downstage edge and pointing it at the rear wall of the venue, projecting a wave down the room and reinforcing it on its way with extra delayed loudspeakers where necessary. This approach produces many impediments (unpleasant reflections, comb filtering, high frequency dispersion issues) to flat and consistent coverage throughout the venue, as well as making the whole stage monitoring situation untenable in terms of achieving acoustic clarity over the massive room reflections (hence the in-ear revolution).

Surely now we have the technology and the vision, at least theoretically, to reconsider this method. In large-scale applications, such as arenas, one could consider dispensing with the traditional left/right proscenium system in favour of a number of smaller hangs evenly distributed over the length of the arena, aimed specifically at the audience and not at any reflective surfaces i.e. the walls. This would, of course, dispense with the need to delay any of the speaker systems, as the distance from the source to the listener will be consistent throughout the venue.

‘Impractical’, I hear you cry. Yes, indeed it is, but only because nobody has yet evolved any practical method or infrastructure, although several sound designers and companies have used this method with varying degrees of success. It will surely require some radical redesigning of rigging and cabling, but in these days of intelligent amplifiers, the whole processing and equalising experience could be joyfully simple. Especially as one could, by choice, only deploy the systems that actually cover the audience, so in the event of a half full arena for example, one simply turns off the speakers that are pointing at empty seats or floor, thus eliminating any real reflection problems. Any reflections caused by the walls of the venue will naturally be at 180 degrees to the stage and therefore inconsequential to the stage sound.

Issue number two is of a similar nature but with regard to sub bass. I’m really talking about sub (80hz and below) rather than bass. Not a large bandwidth and until relatively recently a fairly inexact science with little regard for wavelength or provision for accurate adjustment. Mostly the major issues with sub reinforcement are of containment and consistency versus amplitude. Again, although considerable advances in sub design and deployment have been made recently, these issues could easily be resolved by the deployment of several smaller sources evenly dispersed around the room. The crucial issue with sub bass is to remove and acoustically decouple the speakers from the stage. This would prevent the massive sympathetic resonance caused by stages (and often the airspace underneath) vibrating at unpredictable frequencies and at considerable amplitude, thus adversely affecting all the instruments and microphones placed on it.  Again, one could reduce the amplitude required from a proscenium left/right sub array substantially and still deliver the same acoustic effect or better by deploying the subs in this way.  

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Tags: Installation, Live Sound, turbosound, l-acoustics, d&b audiotechnik, Justin Grealy, nexo alpha

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