I'll bet
@ryanosaur has looked into Table Tuba subwoofers already, but just in case...
I know he's been looking around for something nutty like this. I'M interested in something nutty like this!
I have a coffee table right now I could replace with one of those. It's a good sized coffee table. I can imagine what an 18" in a horn loaded cabinet that size could do. Hell, I'll bet you could get below 20 hz from a 12" with some room gain.