I'm doing a lot of work in a relatively old theatre this year. The space is part of a church that probably hasn't put any money into maintenance and upgrades for the theatre (except for light bulbs, which we sometimes have to beg for anyway) in over a decade.
Part of the space's oldness is antiquated wiring. I'm told by veterans of the space that electrical noise will come through the power system and get into the sound system. I've heard it, and sometimes it's impossible to tell where it's coming from. Supposedly, a hair dryer plugged in at the other end of the building can cause interference in the theatre.
The biggest problem, though, seems to be the lighting system. When I turn the sound system on before a show (following dimmer check, but before any lights are brought up), there's no noticeable buzz in the speakers. As soon as I hit the pre-show light cue, though, a buzz shows up.
When the lights cross-fade, the buzz modulates. I haven't been able to figure out what to do about the problem—not that I have much sound experience, but the guy who's been doing it for years just chalks it up to the space.
His normal setup includes a large umbilical cable running from the mixing board in the booth to the speakers and amps on- and backstage. That cable runs along a wall about ten feet up; on the other side of the wall are the two Strand CD80 dimmer racks that house the theatre's 48 dimmers. There are also usually power and signal cables for the amps and speakers running across the floor near the racks.
I've managed to mitigate most of the buzz in the house by turning down the speakers and boosting the amplification (so the overall output is reduced, but the signal is stronger compared to the noise). But there's still a noticeable buzz during silences, and it comes through quite loudly over the monitors.
Are there any mixing techniques that can further reduce or eliminate (ha!) the audible component of the interference, or do I need to recommend an overhaul of the equipment inventory and standard setup procedures?