Dear Jonah:

I’ve heard about and experienced microphone cables that actually make a sound when moved around the floor, when no mic is connected. Is this just a phenomenon of phantom power on the cable? Are some brands of cable known to have this problem more than other brands? I can’t believe that voltage is being generated by the cable itself, so is it just cable resistance varying when the cable is moved? – Bill S.

Hey, Bill. You’re talking about handling noise. The Triboelectric Effect (which is a fantastic Scrabble word) is a fancy name for the fact that static electricity can build up inside cables when they’re moved.

The motion rubs the conductive shield against the rubber insulation, and this creates a charge just like the one you get when you shuffle across a carpet in your socks.

Turning to basic electronics, we know that a capacitor consists of two electrically conductive surfaces separated by an insulator. One of the variables that determines the amount of capacitance is the distance between the conductors.

Now back to mic cables: there are two internal conductors wrapped in rubber insulation, and all of that is surrounded by a shield, so it’s functionally a capacitor. When the cable is moved, it can flex in a way that changes the distance between the shield and the internal conductors, which changes the cable’s capacitance. The varying capacitance can generate small fluctuations in the voltage created by the static buildup mentioned earlier; actually, this is exactly how condenser mics work. This phenomenon is called microphonics.

Both of these effects are usually just lumped into the term “handling noise” because they’re so similar, both in sound and in cause. If you do a bit of online searching, you’ll find more or less the same explanation of this effect on various audio websites, but very little information on what to do about it.

Here’s the scoop: handling noise is usually an indicator of inferior cable construction. If you’ve ever stripped back the insulation on a high-quality mic cable, you’ve probably seen bits of string or nylon thread woven in there.

It’s filler, but unlike sawdust in hot dogs, it’s good filler. Cable manufacturers call these packing strands, and they help keep the cable in shape. This, in conjunction with quality build materials, means that well-designed, modern cables are pretty well-behaved when it comes to charge buildup, so if you’re having problems, the cable is probably old, cheap, or both.

My thanks to the folks at CBI Professional Wiring Systems in Oriskany, NY for confirming the accuracy of this answer.

Got a question? Send it to Jonah via email at askjonah@livesoundint.com.