mark,
when I was a small boy (hindi pa ganun katagal yun ha!), my brothers who were into (like most of us here) building their own speaker systems. after choosing their drivers for a two-way system they hit a problem much like what you are asking now. so what they did was solicit the help of my father and uncle who were also into audio during their time. what they had in mind was to build a passive crossover that would render the flatest response from the woofer and the tweeter, now since the tweeter has (almost always) the higher sensitivity they had to attenuate it so it won't overpower the woofer or something in those lines.
from what I remember, they used a signal generator, an oscilloscope, and something that resembles a mic and put the finished speaker inside a bigger box laced with foam and then seal it for testing. I don't know where they got that idea for testing speakers but that speaker sure sounded great.
oh well, I guess now we have better tools and formulas for determining that.
cheers
