Used the Fostex 31.5" woofer I have designed many bass systems inc sum used in military simulators. I also have designed many monitors. Small is just small if your going small in loudspeakers you are compromising performance so you can have a small speaker. Think about the wavelength sizes your trying to replicate. Are real-life musical performances the size of a loaf of bread?
Physics Question: Why does cabinet volume matter so much to bass response?
If you put the same 8' woofer into a bookshelf speaker or a floorstander, you will get a different frequency response. Does anyone know what's happening with the air pressure on the inside of the cabinet to cause this to happen? Does the woofer in the bigger cabinet have greater excursion, and therefore produce more amplitude?