Speaker Wire material

Could someone please explain this to me. I have heard that using speaker wires made out of different materials will have different sounds such as using silver would sound differnt than say using copper. I have a background in electronics and don't quite understand this. If both wires have the same load carrying capacity (silver being a better conductor the wire could be smaller diameter than the copper) what would cause the the sound to be differnt. When it comes down to the physics of it aren't you just pushing electrons along the wire?