When I first got into HiFi I came across this video... At the time I figured hey why not bi wire the speakers.
I just watched that video. It was, of course, nonsense. Uncle Paul comes across as a friendly humorous guy, kind of like a wise old neighbor. I think he knows better, but he's representing his business, PS Audio. He wants to sell his product. At least that video was only 6 minutes long. It could have been worse.
Here's the nonsense: He said no single wire does both bass and treble equally well. He's saying you can wires good for bass and wires good for treble, but not both in one wire. That's absolutely not true.
As frequency gets higher and higher, wires do begin to become more resistant (less efficient). As the frequency gets higher and higher, the electric current tends to travel near the outer surface of copper wire. This happens in both solid or stranded copper wire. It seems obvious that bass signals travel through all the wire, but treble signals are confined to the wire's surface. This well known phenomena is called the 'Skin Effect'. OK so far, right?
Here's what's wrong with this thinking. In copper wire, the skin effect occurs at much higher frequencies than any in audio. You need signals at frequencies of roughly 100,000 Hz or higher, before it becomes significant. At the upper end of the audio frequency range, 20,000 Hz, skin effect is only just beginning to happen. It's only a few percent of the total signal. In the megahertz frequency range (TV and FM radio carrier signals) the skin effect is major. That's why copper clad steel coaxial antenna cables work. All the signal travels through the thin copper layer at the surface.
I've heard other arguments that try to 'splain why bi-wiring or bi-amping is so good. All of them invoke a little physics – just enough to make sense to people who only know a little physics. But they all are wrong if you know more than just a little physics.
Here's the final reason why this kind of reasoning is nonsense. No physics is needed to understand it. If bi-wiring really made an audible difference, blinded listeners should hear a difference between bi-wired speakers and single-wired speakers. Unblinded listeners often believe they hear differences, but blinded listeners never do.