AVS Special Member
Join Date: Nov 2003
Location: Derwood, Maryland
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Almost every home electrical system runs at either 55 or 60 Hz. Long cables have a tendency to pick up extraneous signals in these frequencies. The signals tend to be faint, but they exist. For short connections, like say between a CD player and an amp, this likely won't be an issue. But longer connections, like between a speaker and a receiver it can be.
Regular speakers don't play 55 or 60 hz very well and they don't amplify the signal so the faint 55 or 60 Hz signal doesn't effect the overall sound much. Subwoofers, on the other hand, amplify the signal and they play 60 Hz really well.
Coaxial cable is shielded and hence the 60 Hz signal doesn't make it to the central conductor. RCA cable isn't and the signal does make it to the conductor(s).
In most cases, you can get away with a regualr RCA cable or even regular speaker wire, but in some cases, you'll get a constant 60 hz hum unless you use a coax cable.