Concerning subwoofers, I may be splitting hairs here but I have heard the HSU 15" subs before. In comparison to my own subs (which are all hand made by myself), the HSU cabinets will resonate/vibrate/rattle with the strong bass signals. This may be an unfair comparison -- my subs are about 175lbs each, massive internal bracing, use 12" woofers and the vent is tuned to 24Hz. Cabinet walls are two layers of different thickness MDF with a Dynamat separation layer between them. They truly play flat down to 20Hz and are insane. I've done measurements with REW!
The HSU subwoofer cabinets are not constructed as well as the JL Audio and SVS subs. They are larger cabinets and don't have the internal bracing required for this much energy. What happens is that the walls of the cabinet will resonate/vibrate with the woofer and you will hear "rattling" as part of the subwoofer tones. I have heard this.
The JL Audio and SVS subs are much heavier with smaller drivers. I know the JL Audio cabinets are well braced and the cabinet itself is smaller so it is much more resistant to cabinet wall resonance. JL Audio and SVS are definitely much more expensive, so in the end I guess you get what you pay for.
That being said, I would probably agree that HSU is definitely a good value sub. The HSU 15" might play a little bit lower (into the 20hz area) than the JL/SVS because it's a larger driver and cabinet. However, I would say the most effective bass is going to be in the 40-80 Hz area anyways.
