parts that make a speaker?

I'm interested in knowing the difference in all the different materials used to make a speaker, for example why should I choose a particular tweeter or why this woofer is the right one for my needs or even the cabinet design.
thanks in advance.
The short answer to your question is, loudspeaker design is all about tradeoffs, with a given target market in mind. Seldom is there an absolute "best" tweeter or woofer or cabinet, but there may be one that better suits a particular application at a particular price point.

A complete response to your question would require a book. It might be worth your while to find a copy of "High Performance Loudspeakers", by Martin Colloms.

Finally, go shop-hopping with a few of your favorite CD's in hand, and start discovering your own preferences!

Best wishes,

There is a website that is dedicated to speaker building. They have a forum to ask questions like yours, and they sell all of the parts.

Lots of info here and here. Also look at the parts express speaker diy pages.
Use the links from these sites to expand further. Lots of info on the net!