DIY speakers of solid/reclaimed wood?

These look very nice, small and worth trying.

In general though, no, you don't want to go getting 3/4 knotty pine for your speakers.

Previous works I've seen used a 2 layer system, with the internal 3/4" or thicker MDF, and an outer shell of raw wood. They can be gorgeous.

Too lively a cabinet creates a speaker that only works in some circumstances.

When I was considering building a pair myself my plan was to make the structure out of MDF and then "skin" it with local red cedar, which I already have. I built the countertops in my cabin with it. It is old growth and quite hard. Very pretty with tongue oil or even just mineral spirits. Would not use it by itself though.

I still might build a pair just for the fun of it. But that will be a ways down the road after a few other wild hares have been tamed.

Those speakers should be fine. They are small enough that even if they did very very slightly change shape (swell/shrink) you wouldn't hear a difference. I doubt you would see any effect on the joinery.

Speaking of stable woods to use for speakers. I had a pair of monstrous 4-way speakers custom built for the Alice Cooper Billion Dollar Babies tour as "side fill" speakers- whatever that is. The guy I bought them from was a roadie for the tour. I used them for a few years for rock music and they rocked.... they could mix concrete. Layout and driver compliment was close to a JBL 4345 but used mostly GAUSS drivers. I sold the drivers but kept the massive custom crossovers- just in case....All I know is the crossovers were made by Fergitron of N.J.. Exactly who made those speakers is still a mystery.

They were built with 1" thick 22-ply Russian Baltic Birch plywood. Heavily braced internally. Very heavy and extremely stable. Not the prettiest, but probably the best-constructed speakers I have ever owned. I have always kept the idea that someday I would build a good looking pair using the Russian Birch as a foundation and veneer with Rosewood or something easy on the eye.