Well I have no real basis for comparison, since I went from never having a sub to my DIY project:

http://bhavesh.0catch.com/DIY%20sub.htm

Even powered with a mediocre mini stereo amp, it still performs very well on listening tests and using LFE sweeps. The 12'' driver is equivalent to the original SVS driver, so I'd put it on at least the level of a 10'' STF-2.