If you’ve been in the live sound business for any time at all, or working in any field related to sound, you’re quite likely to agree that the most maddening technical anomaly of all is the elusive “hum” or “buzz.” These two terms can be related or separate, but they’re both nasty business just the same.
We’ve all set systems – large and small – only to power up and discover the beast within. Is it 60 Hz? 120? 240? A combination? Is it mains? Monitors? Backline? Lights?
First, do no harm! (Yep, this applies to us too.) Don’t start undoing your stage work in a panic. Try to discern what frequency(ies) are the problem. A Real-Time Analyzer can come in quite handy – even a rudimentary online RTA app is worth the investment.
Let’s focus on the common 60 Hz hum.
Hopefully you’ve taken the time to verify the integrity of the house power. This is a must. A simple line checker from the hardware store is a cheap way to make sure the house is “keeping it clean” and feeding the proper line voltage – and with the hot, cold and ground in the right order.
Make sure (especially in small/medium house applications) to connect all PA power feeds, as well as backline, to the same source. Don’t mix and match! It’s a sure-fire ground loop headache waiting to happen.
Invest (wisely) in proper power conditioning and sequencing devices. These protect and catch big voltage issues long before they reach your gear. Also be sure to reduce any capacitive coupling by keeping parallel runs of audio and AC power separated as far as possible from one another. Do a little homework on parasitic coupling. It’s a fascinating subject and very important to us sound people who are prone to running lots of wire.
I know, I know, some of you are saying “go digital and clear up a lot of these issues.” True, some of this applies more to us old (and young) “analog dogs,” but digital offers its own sets of problems. I also don’t think I’m speaking out of turn in either case when I say that you’re only as good as what you’re being fed from the house.
Maybe you’ll get lucky and be able to isolate the problem to one or two input channels. And don’t forget the backline. Sometimes a bad filter capacitor in a backline amp can wreak havoc on your system and the stage audio as well. Use those DI ground lifts as needed. Keep XLR cables in mint condition. A few hours of work in the shop can save lots of headaches in the field.
There’s nothing wrong with older power amplifiers, but you might want to have a look inside. Change those old filter caps, or if you’re not budget-challenged, get some new amps. (They’re lighter weight too!)
Watch out for older small-venue fluorescent lighting or newer compact fluorescents. They and their respective ballasts have a way of getting into your wired (and wireless) systems. Most of the time the problem is a poorly grounded “main,” but nothing substitutes for a clean, stable and well-grounded source. (Not always possible, I well know.)
If all else fails, don a bee bonnet. (I always keep one handy in the gear box.) Convince your audience that the sound they’re hearing is a recent insect infestation, smile, and (try) to have a great show anyway!