I have a very trained ear and have been around for a long, long time I own the Hsu STF2 and it is a superb sub. I cannot find a weakness with it. Dr. Hsu's tech support is second to none.
IMHO the Hsu is the only entry level audiophile grade cube sub. I have mine in my NAD/ JM Labs/Arcam system and it keeps up perfectly. The tightness of bass and fast response are unriveled in its price range and quite a few steps above. The only thing I would have done differently is to choose the STF3 as Dr. Hsu sugested to me before I bought the sytem. This is to say by no means is the STF2 underpowered, Hitting 110db in my 12x14 room.
I have had Paradigm, CSW, Klipsch, Velodyne and other mid market models and the Hsu is a different ball game- the bass is so forceful, clean and tight. With the other subs I noticed muddy transients especially in movie explosions. The Hsu hits like a sledgehammer and blends perfectly.
If you would like another suggestion I also was very interested in the PSB 5i which is said to be a great sub as well. Also many here love SVS but I personaly don't like Cylinder subs as big as refrigerators in my living room.
