I have an Ampeg PF-115HE. This is an 8 ohm cab. It has a 15" speaker + a tweeter. Each of these is labelled as "8 ohms". Given that resistances in series add and resistances in parallel divide, how do they get the cab to come out as 8 ohms? I suspect the crossover has something to do with that but I'm not sure. Can anyone enlighten me? Also, if I were to remove the tweeter, how would that affect the resistance? Would it be the same as just turning the tweeter off?