“I have an annoying hum with my DJ setup right now. The hum doesn’t happen at all volume levels. Once I turn up the volume to a level where the hum starts and I turn it up a little after that, the hum gets real loud, bass heavy, and overtakes the sound. I immediately have to turn it down so I don’t blow my speakers or my eardrums. It seems to only happen when I have my turntables on though, a CD works just fine. I have balanced lines from my mixer to my crossover, and from the crossover to each amp running 2 speakers and a sub.”
There are several things that will cause turntables to hum. Like any audio equipment there is the danger of ground loops, but turntables are especially prone to hum when poorly grounded. To that end most have a separate ground wire that must be attached to the mixer. If you don’t do this there is a good chance you will get hum. Also, having motors, fluorescent lights, and other devices that generate powerful magnetic fields in close proximity to a turntable’s sensitive cartridge will cause hum through induction. However, in your case it sounds like you’re experiencing a form of feedback. Record players work mechanically in that the stylus is vibrated by grooves in the record. If your turntable is situated in close proximity to your subwoofer(s) they will cause it to vibrate. This vibration is picked up by the turntable and transferred through the cartridge and back to the mixer and amplifier where it is amplified more. In these situations you don’t have to turn things up too loud before you can start to hear the results, and as you turn it up the problem gets exponentially worse. There are a few solutions to this (in no specific order):
- Turn down the bass on your equalizer
- Move the subs further away from the turntable
- Isolate your turntable from vibrations – sometimes a thick piece of soft foam underneath the turntable will help. Also note that some turntables are inherently much, much better at reducing this problem than others.
- Flip the polarity on your main balanced signal cables between your mixer and crossover. This will change the phase relationship between the turntable and the PA, which will either make the problem better or worse. Try it.
Best overall results are likely to come from some combination of these tips. You’ll need to experiment to see what works best for you.