So you wanna learn to design speakers huh? Well I can't help you with every single aspect, but what I can do is lay down the basics to the not-so-basics. What I do know plenty about (at least I think so) is subwoofers and general low-frequency enclosure designing. I'll try to post as much information as I can remember, quoting my sources as necessary. Below you'll find links to the various types of enclosures that I know how to design in which you can find lots of useful info for designing them.

General Loudspeaker Theory

1. Sealed Enclosure

2. Vented Enclosure

3. Single Reflex Bandpass

4. Parallel-Tuned Dual Reflex Bandpass

5. Series-Tuned Dual Reflex Bandpass

6. Triple Reflex Bandpass

Triple Reflex Bandpass Simulation Program