It's a pretty subjective question. The Velo is a great sub. JimP is getting similar extention in his room to the PB13 and recently commented that he preferred the mid to upper bass performance of the HGS. However, the jury is still out. I've got limited experience with the DD15 and own the U13. There were a couple of years in between, but in my room, the bottom octave of the SVS is considerably stronger than the Velo and the musical performance above 30hz is on par. That doesn't mean that you or JimP won't prefer the HGS. As I said, it's an outstanding performer.
