I had a 21” EV woofer mounted to the floor through a hole in the living room, using the wine cellar as the enclosure. That was during the early 80s and DSP was not a thing. It wasn’t doing a great job. The B&W 801 that I purchased later was doing a better job in sub frequencies.Now that's what I call a SubWoofer!
I could mount it in a hole on an outside wall and support it with a couple large timbers going down to a concrete slab.
Hummm, the brain's firing off ideas already. LOL
I now own a pair of Salon2 and they can produce the entire audio spectrum, at levels that are well over unhealthy levels. They only have 8” drivers!