Terry,
I am not an expert on this, but crossovers are highly dependent on the drivers selected, the driver mounting locations in relation to each other, the enclosure size and many, many other factors. There isn't one universal crossover. For info I would read some of the interesting stuff at
www.zaphaudio.com and at
http://www.troelsgravesen.dk/Diy_Loudsp ... ojects.htm
This is both a science and an art. I have not done it myself although, I've built 4 sets of speakers so far that were designed by John Krutke at zaph.
I know this doesn't help much, but I hope the info on the sites helps. There is a ton more out there as well as books on the subject.
One could argue I guess that a simple crossover will work, but it won't be optimal in almost any case. However, parts express sells some standardized crossovers in their lineup maybe proving all this wrong; and then again, maybe not.
Regards,