Here’s what my TD15M pair calls “home”.
5 cubic feet of net internal volume, golden ratio dimensions and bottom vent to get a bit of vertical quarter-wave mode reinforcement. Initial Fb=32Hz, but might be adjusted after a subjective evaluation. All 18mm BB-ply with double-thick front and rear baffles. Simple finish with 8 coats of wipe-on poly. I just got done building these and will do the crossover actively via a 2×4 miniDSP.
They’ll look even better once I get the phase plugs. 😉