May i know what is SPC?
So copper will help with base? Isn't unique melody's cable a full copper already?
SPC is.. as what taeyonie has mentioned above.
and as to your question..
Copper has varying levels of purity and thickness and no. of strands in a wire and so much more details... to put it simply, Copper has different grades
copper normally (generally) brings out the lushness of vocals and adds more "oomph" or "kick" or slam bass.
and as for SPC, silver plater copper, means that the core cable is copper, but plated with a small amount silver.. the reason for this is mainly for a compromise between silver cables and copper cables. some people like the in between sounding of silver cables and copper cables... therefore there's SPC.
imho, 3DD would be best paired with either copper or SPC.