One needn't be a Metallurgist to understand that when copper(or any other metal) is drawn through a die to form it into wire, it's crystal structure takes on a chevron shape. Apply a modicum of electrical theory and it's not a stretch to say that same chevron formation JUST MIGHT be affecting the musical signal like a diode. Musical signals are much more complex that "just" AC current, sine waves or test voltages, containing a plethora of cues including harmonic, ambient, frequency, distance, time and SPL information(the list could go on). When I was introduced to the Wood Effect on a test CD, I was able to discern exactly when the phase was reversed, though I couldn't explain the precise reason. It just sounded "wrong" somehow. I'm guessing the psychoacoustics of it are that the ear/brain connection can tell when sounds are SUPPOSED to generate compressions rather than rarefactions, and the consciousness responds accordingly. To me it's not a stretch to believe it possible for the chevron/crystal structure of a drawn piece of metal to affect the positive portion of a very complex musical/electrical signal in such a way as to disturb the balance of it's components. It doesn't take much of a trained ear to know something is "wrong" with a signal, when a direct comparison is made with an uncompromised one.