With regard to speaker cables, the claims which are made for some types I have grave doubts. I can do no more than quote Peter Walker, HiFi Engineer and founder of the Acoustical Manufacturing Company.
"There are only two requirements a speaker cable should satisfy.
The first is that it should be long enough to reach between amplifier and speaker.
Then having done that, the only other requirement is, ideally, the colour of the insulation should match that of the surface on which it lays."
