does anyone have a good resource on the web for learning about resistance as it pertains to car audio?

The best website I have ever come across dealing with car audio, from the absolute basics ("...what is an electron...") to subjects so deep that I don't even begin to have the math to comprehend them, (for example, look here) is:

http://www.eatel.net/~amptech/elecdisc/caraudio.htm

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This is really a fantastically good website, done as a hobby and labor of love by a man who I believe is retired from the electronics industry. I would actually go so far as to say it is the best website (on any topic) I have ever visited. While the more you know about car stereo the more you will get out of it, even if you know nothing at all it is well enough presented that you can give yourself an education* to equal or surpass that of any installer you are likely to come across in any stereo shop. It is that good. I highly recommend that you bookmark this site.
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tanstaafl.

*by education, I mean theory, not practice. A good installer knows "tricks of the trade" that would amaze you!