what happens to the impedance on the m80s if you bi-amp?does it stay 4 ohms?or will that change?just something running through my head....thanks

Ron, the impedance essentially stays the same. The woofer and mid/high impedances are each 4ohms and when driven by separate amps each amp sees a 4ohm speaker section.

Actually JohnK, I don't think that is the case. I would assume that both sections are roughly 8 ohms (assuming that the mid/tweeter section and the woofer section have the same nominal impedence). This is because when the bridges are in use, thus creating a circuit that runs the parts in parallel (not a series), it is a 4 ohm speaker.

When you run two identical speakers (or anything else that adds resistance, for that matter) that are a certain impedence in parallel, you half the impedence. Thus, going the other way around (seperating the woofers from the mids/tweets), you would double the impedence.

No, Will, the effect of the crossover on impedance has to be taken into account. At say 50Hz the woofer impedance would be about 4ohms, but the crossover would have the tweeter impedance much higher at that point so as to roll off its response. If for example the tweeter impedance that the amp "saw" at that point was 100ohms rather than its normal 4ohms (because of the crossover) the net parallel impedance would be 1/R=1/4+1/100 or 1/R=26/100 or 3.85ohms. The parallel connection doesn't result in a halving of impedance since the impedances seen by the amp aren't the nominal equal ones of the drivers.

Ahh, I forgot to account for how the crossovers will react differently at different frequencies. I just incorrectly assumed that they were identical circuits; can you blame me? I posted at 5 am. I am just happy that I was coherent - heh.