**I like Science!!!**
Just a nerdy interlude:

Impedance is the term applied to a 'complex' resistance (

link).

**Z** =

**R** + i

**X** where Z is the impedance, R is the resistance and X is the reactance. If you have a DC source, then all you measure is resistance (eg: like in a resistor), for any device however that stores energy (like a capacitor or inductor) you have to take into account the change in inductance due to changing

*phase* and

*frequency* of your AC source.

Series inductance follows the rules of Z = (R1+R2)+i(X1+X2), which means that inductive loads wired in series produce an equivalent inductive load

**greater** than either of the individual loads.

Parallel inductance follows the rules of Z = 1/{(1/R1+1/R2)+i(1/X1+1/X2)}, which means that inductive loads wired in parallel produce an equivalent inductive load

**less** than either of the individual loads.

Since sound waves are produced by your driver moving forwards and backwards in its cage, you require an AC source to produce the changing magnetic fields that move the driver forwards and backwards. This means that the drivers have an inductive load, and that it changes based on the frequency and phase of the source (eg: your music).

The purpose of a crossover circuit is to break up the frequency range of the source into discrete intervals that drive specific loads, as well as to balance the phase of the drivers. EG: so you don't send a 16kHz tone through your 15" subs, or worse send a 200Hz tone through your 1" tweets. Other scenarios would be say sending the same 200Hz signal to two 15" subs in the same cabinet, but have one driver be out of phase with the other by about 10 degrees... Mmmm... warbly...

Now, your power load is P = (V**2)/Z, so if your impedance (Z) drops down really low, your voltage (V) stays more or less the same, and your power consumption jumps up. This power is dissipated by your driver into sound energy, heat energy and motion, based on your driver's efficiency. Usually speakers in cabinets have a pretty low efficiency (heat to motion), and a pretty high power rating. If you run them in excess of their power rating you run the risks of: a) melting the voice coil, b) tearing the surround or spider cone(s), both of which more or less turn your driver into a fancy magnetized paper weight.