I'm about to get a TC Electronic RH 450 head. http://www.tcelectronic.com/rh450/ Can someone explain to me like I'm a 6 y/o the whole bit about impedance? The suggested cab combinations on the TC website completely baffle me. Are they saying that I can't use that head with just one of those cabs? I must use more than one cab? In fact, I currently own a TC RS 210, which I'm using with a GK MB 210 combo as an extension cab - it works great. I'm thinking of getting a different 2 X 10 (I want a lighter one) and either a 1 X 12 or a 1 X 15 to go with my new amp head. So, my second question is - is that a good idea? Aren't bigger speakers slower, hence potentially causing phase problems? I'm pretty sure I've seen combinations like that (bigger and smaller speakers), but I'm still curious. THANKS in advance!