ORIGINAL: PReal

Its quite simply due to the magnetic field a pulse of electical current creates. The magnetic field induces changes in most low voltage wires within the magnetic field the pulse created, sort of like an eddy current. The voltage difference also plays a key role. You can run power wire next to speaker wire all day because they are both high voltage and high voltage can resist the changes. Running a power wire next to a signal wire is bad because the low voltage in the signal wire is easily manipulated. A speaker wire and a signal wire will have little to no reaction because even thought the speaker wire is high voltage the current pulses are not high enough to create a strong enough magnetic field to induce interference.

Thats at least what my engineering degree has led me to beleive. I am one of the engineers that canusuallyapply thier learnings to everyday life, but sometimes I still nerd out.