oxided copper is not as good of a conductor as regular copper, it may even drop down to a semi-conductor. that is why people use gold plating a lot on ics, etc. having said that i dont know how much that oxidation affects the sound. its nice to get some speaker cables that are pre-terminated so that they should never oxidize on you. i use bare wire on my speakers (at the moment) and just trim off the ends every year or so to expose some fresh copper, eventually ill get some different speaker cables where i wont have to worry about oxidation though.