Are there any quality subs that are designed to be placed underneath a coffee table? Obviously most of the subs discussed here are ones that are too tall to fit. I haven't measured it but I would imagine a height of 8 or 10 inches would probably fit.
That's not a lot of room. Is that the only place for the sub? If so check out the Paradigm Millenia sub. It's expensive but will fit and seems to perform pretty well. Check out HomeTheater.com and Sound and Vision.com for reviews.