Do Cables Wear Out?

I haven't read all the responses, so this may be redundant.

When a cable's insulation changes (due to exposure to humidity/high temperature/contact with liquids, etc.), the cable's impedance changes. For example, airplane mechanics can tell whether a wire has been damaged due to exposure to humidity or hydraulic fluid just by measuring the impedance of the wire. In fact, they can tell not only whether a cable has been damaged, but also the starting point, length, and type of damage, just by measuring the impedance. Obviously insulators that resist environmental effects can reduce the problem.

The impedance changes are observable in the audio-frequency spectrum. So the impedance characteristic of the wire affects the signal and the sound.

Does this lower the sound quality? I don't know. Perhaps it makes it better.

By the way, the tarnish that forms on silver is sulfide not oxide.

http://educ.queensu.ca/~science/main/concept/chem/c03/C03DEEA1.htm

Scroll down to "EXPLANATION".

OK, JWP, tell us how much the measured resistance of 8 feet of 12 AWG speaker wire changes over 7 years. You've made the claim, and you've told us you have a LOT of experience, so show us what you've got.

By the way, litz is not a coating but rather a type of wire configuration composed of a bundle of smaller wires, each coated or not.

http://www.litz-wire.com/

JWP, just because you are older than me (you have a lot of experience) doesn't mean that you understand oxidation nor corrosion in metals. Silver oxide or sulphide which someone thoughtfully pointed out might conduct better than copper, but not better than silver. Insulated wire is not exposed to the atmosphere and thus does not coorode there, but at the exposed ends. I too would like to know the increase in resistance in a piece of wire after 10 years.
Salut, Bob P.