http://www.shure.com/support/technotes/app-eq.html
Good info on equalization and feedback
http://www.shure.com/support/technotes/default.htm
A whole bunch of stuff about sound pickup
http://www.webervst.com/sptalk.html
Extensive speaker discussion, (search for the word "nominal")
http://www.whirlwindusa.com/tech.html
Great articles, a little techhy but solid info (& another impedance/water analogy)
http://www.acousticdimensions.com
If you want to go headfirst into acoustics, this site will help
http://music1online.com/learningcenter.html
LOTS of in-depth articles on mics & sound
http://www.amptone.com/g068.htm
GREAT list of links, lots of info - You Must Check it!
IronMan Mike Curtis
I've got a lot of respect for this guy, he was my ALPHA test.