Just FYI - I found a great thread by an audio technician explaining how tone-stacks work - the guy really puts it into simple language without all the math - making it clear to understand (especially for you folks who already get it more than I do). But even I can follow what he says...
Just follow this thread (just posted last month). By the way, if you missed it, Gibson Guitars bought Harmony Central and Craig Anderton is back there as editor/moderator. He did not write the post I am linking to, though....
http://www.harmonycentral.com/forum/forum/Forums_General/acapella-94/31438726-baffled-by-the-tonestack