Depends what you call small. Using room reinforcement (and if your speaker is in a room why aren't you?) you can get down to the 3.5-4 cubic foot range with useable response to 25Hz no problem. You do have to keep the pathway long, which means a small mouth, and you have to toss the 'old school' reliance on hypex tapers. When 'going by the book' doesn't work sometimes you just have to write a new book.