Crossover Questions

My apologies to any to you who have read this post elsewhere first:

I am probably going to be replacing my crappy subwoofer amp soon, along with adding a two channel amp for the front speakers.

In researching the amps, I find that most have a high-pass filter @ 120Hz, and a low pass filter @ 80Hz.

The question is: what happens to the frequencies between 80Hz and 120Hz?? If I purchase two identical amps (which I am probably going to do), and set one with the HiPass for the door speakers, and bridge the other one and set it with the LoPass for the sub, what about the "lost" Hz range?

Why would crossovers be set so as to possibly eliminate any frequencies like this? Am I nuts? Could I use the one amp at full-range to eliminate the dropped frequencies, or will I blow up my door speakers (they will most likely be good quality 6x8s when the amps are installed)??

What gives?

The crossover doesn't just cut the frequecies above or below the x-over point it tapers them off. So even with the high cut at 120 and the lows at 80 they will still have some overlap in between. when added together in the car they keep the middle range between them at approximately the same level as the rest of the fequencies.

Gregs right on. Most amps with just a switch crossover(on or off) also have a 12db crossover. a 12db high pass crossover set to 120hz has a 3db down point at 105hz and a low pass crossover set to 80hz has a 3db down point of 100 hZ. This means that when each is 3 db less they add to each other which effectivly gives you back 3 db so their is no loss in this range at all.

Of coarse this is all theoretical different audio equipment will have different results.

I knew it couldn't be as ridiculous as it sounded - thanks for the info.