Diagnose and Eliminate Subwoofer Hum or Buzz

You've cabled up a new speaker to your system, placed the subwoofer for best performance, and even tweaked the audio equalizer so that everything sounds perfect to your ears. You sit down to relax and listen but notice that something is off. A conspicuous, persistent hum emanates from the subwoofer, and it shows no signs of going away.

Subwoofer hum or buzz is a low-level noise that can be present whenever a passive or powered subwoofer is turned on, whether or not it is playing. This 60-hertz hum is a direct result of being plugged into an AC wall outlet.

Sometimes the hum is obvious. Sometimes it takes some focused listening to notice. Either way, you can correct the situation without having to resort to filtering out the noise, which also ends up stripping out audio signals. Usually, all it takes is a change in the way the subwoofer connects to power.

You can take several approaches to get rid of the annoying hum. If the first suggestion doesn't work, try one of the others.

• Change the polarity of the subwoofer's connection. This is probably the simplest fix to try because all it involves is reversing the power plug's orientation. Sometimes, one of the prongs is wider than the other, which preventing the reversal. In such situations, use an AC ground adapter to reverse the polarity. Most of these adapters have uniform-sized prongs and are readily available at local home improvement stores.
• Reverse other plugs. When components share the same source, such as a power strip or surge protector, the culprit may not be the subwoofer at all. It could be some other two-prong AC plug. One by one, reverse the orientation of the other plugs to see if it makes a difference.
• Separate the cables. When you cluster power or audio cables in bundles, signals bleed over and create noise because of this proximity. Space cables apart so the fields created by moving current don't interfere with each other. If it's not possible to separate them a sufficient distance, upgrade the audio cables to ones with more effective shielding.
• Switch outlets. Sometimes the subwoofer hum is caused by a ground loop, which happens when it's fighting a second device for possession of the ground. If you have another three-prong piece of equipment sharing the same wall outlet, power strip or surge protector as the subwoofer, move the subwoofer to another AC circuit in the room. It may be necessary to use an extension cord to reach a wall outlet that is separate from the rest of the stereo system.
• Use an audio isolation transformer. If the previous grounding techniques haven't worked, you may need to purchase and install an audio isolation transformer. Many are designed for powered subwoofers and connect in line with the cables. They instantly resolve ground loops.