I started in speaker building. Eventually built some "good enough" . Additionally, I am old enough my hearing is not as good as it was so I have built my last.
But, I have a lot of parts and my laboratory equipment if anyone is interested. I also have the AES anthologies 1-4 and many other books no longer available. I have a pretty good idea which measurement and CAD software works.
Speaker building ( done well) is an engineering practice. The woodworking part is trivial. All those folks who build beautiful boxes, and yea some are fantastic, don't spend the engineering time, numerous prototypes, measurements etc. I have learned a bit in over 40 years of speaker design. As an example, the serious design issues with diffraction with the picture Martin posted, let alone there is no way woofers that large can reach a tweeter that small. Never mind what happens when an OB is that close to a wall. Di-pole speakers are extremely difficult without serious DSP. Better off just buying Maggie's. Do you know what a 1/2 dB hump at 4300 sounds like? Hint, listen to any Billy Joel terribly mastered CDs.