"Does this mostly apply to carpeted floors?"
No, every room and every floor has a different sound. When you set cables on that floor the floor becomes part of the dielectric. Some wood floors actually sound nice with the cable sitting on it, but I have found this to be rare. It has a lot to do with how the floor is constructed.
Keep this in mind though, according to the 4 fundamental force interactions your cables are affected sometimes up to 15meters away from the physical wire itself for some forces.
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