This might help with some ideas. http://www.stevemeadedesigns.com/board/topic/135451-hot-girls-oh-and-alphasig293s-rebuild-6-aa-mayhem-18s-2-cactus-k12-30k-rms-f150-pics-fixed/page__st__280
Actually yes there is.
so what is the difference?
Sub will run cooler and more efficient when wired in parallel as opposed to series with both having the same final impedance.