Do Cables Wear Out?

I knew that my diatribe would start some controversy. BobP needs to llok at a chart of elements and electrical characteristics thereof - silver oxide is a better conductor than copper. He should also refrain from making comments like "no corrosion happen at the outside of wire if it is insulated". This is completely untrue - I tried to explain in some detail that oxidation starts immediately on the surface of the copper wire when the raw conductors are pulled and only coatings like enamal(Litz) are able to slow this process down significantly. To comment that insulation ( which in cable-talk is called dielectic) "cures" this process is completely false and misleading. No cable company that I am aware of vacuum seals their cables to prevent oxidation - it just isn't a good resolution for the problem. In my experience ( and I have a LOT), most non-litz-coated copper wire will have some audible effects from oxidation of the copper somewhere around the 6-7th year after being manufactured. For those that took the time to read these posts- I hope that my time in writing them was worthwhile for you.

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/