Do speaker cables need a burn in period?

That’s the wrong question. The correct question is, why is directionality so audible when the difference in resistance is so small one direction vs the other? I don’t think anyone really knows. Physically, in microscope photos, there does appear to be non symmetrical distortion of the wire crystal structure caused by being pulled through the die. 

I disagree. It’s the right question because electricity is not mumbo jumbo and there must be a physical characteristic that accounts for it. By avoiding the question and calling it wrong (there are no wrong questions, only wrong answers!) you admit there is no such thing as directionality.

What do you mean by resistance in one direction is different from the other? Do you mean a reproducible difference in resistance as measured but is within the noise parameters of an Ohmeter? Because if we’re talking thousanths of an Ohm, that’s noise. For single crystal wire, there are very few breaks in the structure along the length of cable that would significantly contribute to DC based resistance, if it does exist at all. For AC, directionality goes both ways. In my research, I can’t seem to find any evidence for directional resistance effects. In microphotographs, is one able to tell the direction the wire was pulled? I’m asking these questions because it’s about time we get to the bottom of things and stop the handwaving and deception.

Whoa! Hey, chill, I just explained why *electrically* there’s a difference. Do I have to draw you a picture?

Do you mean a reproducible difference in resistance as measured but is within the noise parameters of an Ohmeter? Because if we’re talking thousanths of an Ohm, that’s noise.

A good DMM can measure DC resistance down to nano-Ohm. 

In the famous HiFi Tuning measurements of electrical characteristics of fuses of many brands including stock fuses, the lower resistance direction was always consistent with the direction that sounded the best, both for DC circuits and AC circuits. But as noted on the HiFi Tuning data sheets, the rather small differences measured did not account for the relatively significant differences heard in listening tests of “directionality.” And as fate would have it that’s how directionality can be controlled, by controlling the manufacturing process starting with the wire as it comes off the final die. I.e., it’s predictable. Hel-loo!