Well, I figured out why we have bad humming.

[CSCTech]

Well, even if there is no audio being played through the speakers we always get a pretty loud hum that we have lived with. We never knew why, and then we found the reason.
The wires running from the amps to the speakers have no shielding. And since these wires run right next to all the houselights wiring, when the houselights come on the noise gets louder, and when they are off it gets a little softer.
You can hear the spotlights turned on, heh.

 

[DuckJordan]

hmm... sounds like the contractor cut a few too many corners... to fix this issue would be to run new wire that is shielded. which may become very expensive depending on how it was run.

 

[venuetech]

the houselighting wires are not within conduit?

it is normal practice for the speaker wires to be unshielded.

but it also best to avoid placing audio cabling near higher voltage AC.

try unplugging the audio input at the amp, then check for buzz.

 

[TimmyP1955]

With RFI, I've seen the noise get into the amp via the speaker cables picking it up and feeding it into the negative feedback loop. Seems off that it could happen with 60Hz, but ya never know.

Do NOT replace the speaker cable with shielded cable - some amps get very unhappy when driving shielded cable.

 

[Footer]

Its not the shielding.... its the power feeding your amps. Follow the power. Odds are you have the same power feeding your dimmers as you do feeding your amp rack. It is the mortal sin of installing power to a theatre, but it happens fairly often.

 

[SHARYNF]

Why does this sound like Millbury Auditorium or is it just that part of Mass?

There is no way that the power to the lights is not in conduit unless it is left over from the days of ceramic stand offs. It might be BX cable or something else.

Speaker wires are NEVER SHIELDED.

As Footer says it is a power problem feeding the amps.

Sharyn

 

[museav]

If you have not already done so, the first step might be to find out where the hum is actually getting into the system. Direct monitor the amp output with the house speakers disconnected and see if the hum is there, if it is then that pretty much nixes the idea of it being induced in the cable run. Monitor the input of the amp, is the hum there? Work your way back through the system until you can verify where the hum is actually introduced. Or do the inverse, start at the mixer output and disconnect one connection at a time through the signal chain until you find the one (or ones) that relate to the hum. However, until you verify the actual source of the hum you'll just be making guesses at the cause and possible solutions.

 

[rwhealey]

Another question:

Are the wires in the same conduit?

If so, isn't it against code to run the low voltage speaker wires along with the lighting stuff?

 

[BillESC]

Are all of your audio components plugged into the same electrical supply?