Figure 1: Typical electrical installation (showing ground wires only).
Figure 2: Single groundwire installation with single dedicated line.
Figure 3: Single groundwire installation with multiple dedicated lines.
FAQ: Pre-wiring an Audio Room
Pre-wiring a Home Theater: Eliminating Grounding Related Hums
When pre-wiring for a Home Theater, it is critical that the ground connections be wired in a very specific way. If you are planning to run a dedicated power line (or multiple dedicated power lines), proper grounding is critical to ensure that noise and hum are reduced to an absolute minimum.
Typically, when an electrician wires a home, each power outlet has a ground wire (along with the hot and neutral) that runs from the outlet, directly to the service panel (see figure 1). When multiple ground wires of different lengths are connected to the service panel ground, 'current eddies' are created due to the different lengths of the ground wires (differing Ground Potentials). These 'current eddies' create the infamous 60 cycle hum! Do not use hospital grade outlets in the dedicated power line, as hospital grade outlets require separate grounds and cannot be tied together.
The key to reducing hum and noise is to have the electrician wire only a single ground from the audio / home theater system to the electrical service panel (see figure 2). If you are installing a dedicated or multiple dedicated lines in the Home Theater it is critical that all outlets that will be attached to the A/V system be wired with the same single ground wire, and run directly to the service panel. 'Hot and neutral' wires are attached directly to the service panels dedicated power line. Do not attach anything other than the Audio and Video system to this special dedicated line. Be sure to plan for enough outlets for the electronics, speakers, sub-woofers, video and video accessories as well as the location of each outlet (subwoofers in the rear, etc). Lighting, fans and anything not directly related to the A/V system, should be attached to a separate circuit with it's own ground, connected to the service panel.
The net result will be noise and hum free power with a 'deep black background' in which to enjoy your audio and video presentation. Please note, before trying any of the above mentioned suggestions, please check your local electrical codes.