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I am currently enjoying a fantastic theater production as the assistant sound designer for a musical. The sound designer that hired me has moved on to another Tech rehearsal and has left me with the task of running the show. We normally discuss issues regarding the show. But one issue that we recently resolved still bugs me.

We had a monitor placed by the band so that band leader can follow the vocal performances on stage. But this monitor would frequently give out a loud buzzing sound. After changing several lines, I noticed that the buzzing would stop after jiggling the monitor's power cord plugged into a power strip. I noticed that the buzzing decreased but remained when plugged into a power strip with fewer plugs sharing the strip. Eventually, the buzzing disappeared entirely when plugged directly into its own outlet.

My question is this. Is this a common occurrence for powered monitors? Granted, it may be an old model. But since it's my first gig in theater production, I was wondering if power strips are notorious for causing problems like this.

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Yeah sounds like a grounding issue to me. When you jiggled the power cord, did you jiggle it on the speaker side or power strip side. If doing a home run to the power of the speaker solved your problem, then you have found the problem. I would avoid plugging a monitor into a power strip anyways, for many reasons, but mainly because artists can be clumsy and hit the off switch on the strip and make you look like an idiot when it was their fault. I try to always eliminate the possibility of things that can make me look stupid other than myself.

Get one of these in your kit, http://www.google.com/products/catalog?hl=en&client=firefox-a&hs=TNU&rls=org.mozilla:en-US:official&q=ground+tester&gs_upl=5980l5980l0l6115l1l1l0l0l0l0l73l73l1l1l0&bav=on.2,or.r_gc.r_pw.&biw=1678&bih=877&um=1&ie=UTF-8&tbm=shop&cid=6930323965348544694&sa=X&ei=z8SCTtnFE4aNsQLqg73_Dg&ved=0CEQQ8wIwAQ

sorry for long link but was from a quick google search.

If it is a powered speaker, are you feeding signal via balanced or unbalance input.

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  • The link is not working. Pls describe the kit.
    – wondering
    Jan 25, 2018 at 23:58
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Was it that 50Hz earth type buzz? It seems possible that there was a faulty earth wire or connection for the monitor's power supply or in the power strip.

One thing I can say for sure, you will get good at trouble shooting doing live sound, as there are so often noises that come from unexpected places. Even if you know the venue well, there are always new(old) instruments and gear brought in by performers.

Hey, it's character building!

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  • Definitely mid to low frequency. Definitely not 50 Hz low, tho! As Michael suggested, I'm going to keep that monitor on its own power source!
    – Hubert Campbell
    Sep 29, 2011 at 6:32
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it's not uncommon for other equipment to produce electromagnetic interference, or even introduce electrical noise back into the grid. in close proximity these things get picked up. classic example is fast switching power load without a snubber. http://en.wikipedia.org/wiki/Snubber ... from here it gets specialised and someone else could probably explain..

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maybe some of the lighting was plugged into the same power source? I'm not lighting expert, I'm just judging it from lighting dudes who've angrily told me that a bit of a buzz from lighting is impossible to get rid of.

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