I've done a fair bit of reading about this in the last year, and to the best of my understanding, the predominant factors are the impedance curve of the loudspeaker and the amplifier design that create an
"interaction" that the speaker cable must be capable of dealing with. I used to naively think that speaker cables were simply "big wires" that carry current to the speaker drivers, but I've come to realize its considerably more complex than that. For one thing, certain loudspeaker impedance curves can cause an amplifier to become unstable and oscillate, and in this situation, the design configuration & complexities inherent in the speaker cable design and geometry as well as he amplifier design plays an influential role. My understanding is the worst kind of geometry are parallel wires, that is, "zip cord" style speaker cables.
Also, some folks think that the current in a speaker cable flows through the conductors like "water in a tube", and that is absolutely not what happens; its quite a bit more complex than that. What speaker cables actually carry is an electromagnetic wave which propogates along the cable, and thus is subject to "summations" and "cancellations" that any series of waves is; they are also subject to "reflections" which are influenced by the cable length. Further, velocity of propogation (Vp) of this EM wave varies by frequency. These different "Vps" are part of the why speaker cables and their design are amongst the most complex and also important cables in a stereo system (next to power and digital cables).
Couple of last points: speaker cables are subject to current resonance modal distortions as well as RF from gigahertz computer CPUs and GPUs, where, for these bandwidths, they can function literally as antennas, picking up the RF and feeding it
backwards into the amp, only to be re-amplified as noise.The latter is why it's
really a bad idea to a computer or any high-bandwidth CPU functioning as a music server anywhere near your main audio rack and speaker system.
So, yeah, there's a lot going on that a speaker cable must deal with...
