Symptoms
One of the most annoying -- but difficult to find and solve -- problems that can crop up in a home theater or stereo system, is a ground-loop subwoofer hum.
A ground loop is an electric difference of potential between various ground points throughout the system. Ideally, all ground points have zero volts between them.
Diagnosis
When a ground loop problem exists, you'll hear a low frequency hum when you plug any audio or video components -- including subwoofers -- in the electric outlet. This hum is caused by the ground voltage potential differences among the system components, power cords and audio/video cables.
Solution
Although some people like trying to stop subwoofer hum by using a power conditioner, in most cases it doesn't help Instead, try the following steps to stop subwoofer hum.
- If the subwoofer is plugged into its own outlet, plug the subwoofer's power cord into an outlet shared by the other components. Use an extension cord if necessary.
- If the hum persists, and your system includes a cable TV, disconnect the cable line. If the hum stops, install an isolation transformer on the cable.
- If the hum persists, disconnect the remaining component cables one at a time until the hum stops. Install a coaxial isolation transformer on that cable.
- If the hum persists, install a line-level ground loop isolator on the subwoofer's line-level feed cable. This usually solves most hum problems.
- If nothing helps, disconnect all the audio cables from the subwoofer. Leave the subwoofer plugged in and switched on. If the subwoofer hums, it points to a defective unit. Contact the company's customer service to technical support
