I’ve long had thots about using the Newform Ribbons with some Accoustat panels for lower down.
They can be used as low as 1k can’t they?
All jokes aside, i once made a subwoofer out of concrete. Actually, it was two subwoofers together in one box, each side had two 10" isobaric arranged woofers. Total of four woofers per sub. It took two people to move it. Its still in use, for some 20+ years, by my brother.
Wow, hope there is enough support under the floorboards! These sound like they would warp the base boards with that much weight in one point.