well as previously noted i have a new 1x15 cab. i was wondering what kind of sound i would get by adding a 1x18? normally, i know the balanced thing to do is to add a 2 or 4x10. but i play metal, and so i'm guessing i'm eventually going to have to downtune...i only play 4 strings, but still, we might go to C. so, how would each cab modify my sound, generally? and which do you recommend?