I began writing this article a few months ago, as I sat in my office here in the Pacific Northwest, looking out the window at the rain making it obvious that, at least in this corner of the world, another summer had come and was long gone.
Another year of street fairs, festivals, music in the park, shed lawns, barbeque catering and tarping the arrays to keep them from being waterlogged by the imminent thunderstorm was in the books, and it was time to go back indoors for the winter.
And moving a sound system inside of an enclosed space presents a whole different range of acoustical challenges.
Something a younger practitioner of the art and science of live sound reinforcement had said caused me to think that perhaps a review of general acoustical principles was in order. As he walked the venue, he was experiencing lots of reverberation as well as some slap-back echo from a large concrete wall. He asked if we could “turn up the system so that the direct sound would override the slap.”
I explained to him that the reverb and slap levels would increase at a 1:1 ratio to the level of the energy generating it. The only ways to mitigate the echo were absorption, diffusion or changing the cluster geometry and using the directivity of the loudspeaker hang so that we didn’t excite the wall as much.
Much of the evolution in equipment, especially on the loudspeaker front, is intended to help us cope with difficult acoustic circumstances. New concepts in providing directivity seem to appear every week. Line arrays, beam steering, coverage mapping software and new horn topologies are just some of the tools that can be used to improve the system/room interface. But like any tools they must be used properly to provide maximum benefit.
An old salt once told me “Put sound where the people are, don’t put sound where the people aren’t,” and in many cases this sums up what we try to achieve with our loudspeaker toolbox. An ideal system would cover each member of the audience at an equal volume level with identical frequency response.
Depending on the type of event it might also provide a perfect stereo (or surround sound) image at every seat, excellent intelligibility for spoken word, and seamless localization of the apparent audio source. It would not excite the walls, ceiling, balcony face or any other potential source of destructive flutter echo, but rather would tickle them just enough to create a nice, well balanced but not overbearing reverberant field. That’s not too much to ask, is it?