Humming Speakers

Client
Our client recently built a new church and asked us to install a sound system. The installation went well until we noticed some buzzing from the center loudspeaker array, which is mounted to the ceiling. The funny thing is that even without any power to the amplifiers the speakers still hum. Even without the speaker wires plugged in on the amplifier side the loudspeakers hum. Only after we sent men up in a lift and unplugged the wire from the loudspeakers did they stop humming. Should I re-run the cable? I need to know within the next few days.

Thanks,

Name Withheld For Fear Of Mockery

TIP
Is the loudspeaker cable in conduit?

Client
Yes

TIP
Your loudspeaker wire in conduit is definitely running in parallel with some electrical circuits. I would guess ceiling lighting with a decent DC component like a ballast or dimmers. This is obviously induction given your description. Do you have to run the cable again? Maybe… Did you by any chance run stranded electrical wire – TFFN – in these conduits?

Client
Yes. Twelve runs of #12 in a 1 _" conduit.

TIP
OK. Now we are getting somewhere. You can try one thing first. Trace the route of your conduit run and try to determine where it might be running parallel with lighting/dimmer etc. and see if you can separate the speaker and lighting conduit enough to eliminate the hum. Another possible fix (though a long shot) is to get one of your guys on each end of the conduit. Hook one end of the wire to a drill while the other guy holds the other end of the wire and SLOWLY twist the pairs of wire. If the conduit run is straight enough and short enough this twisting could do the trick. It’s worth a try if re-pulling the cable is a major job.

If this doesn’t work, yes, you will have to run the wire again but using a completely different route this time and watch out for electrical conduits running next to your speaker wire for any significant span. And you might want to consider twisting it as the wire is pulled through the conduit off of the spools. There is a jig for this on the market. Contact TIP and we will provide you with the name of a few vendors for it or rent you one of ours. Just a side note from your Uncle TIP – Speaker wire is twisted for a reason.

Hope one of these works for you,

This sort of thing happens all the time believe it or not. And for all of you speaker cable nerds out there that pay attention and do the math to make sure that their speaker cable is the proper size for the distance and load, you will be happy to know that my second suggestion for twisting the wire actually worked. Problem solved in less than two hours.

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