Here is my comparison from my own SVS 20-39 with the ISD and a 500 watt ARS500 amp to a Hsu VTF3 that I heard at a dealer's place. Mind you, that this comparison was not done side to side, so room acoustics may have played a large part in what I heard, but i will give you a grading scale as to what I thought about each unit. 1-10 for each criterion, and add them up in the end. 1. Extension (from how low to how high) HSU: 10 SVS: 10 I really couldnt tell which one of these could go lower. I was using a frequency sweep (AVIA for the HSU, THX for the SVS) and I could not tell which one of these really got down to the floor better 2. High Bass (70-120 Hz) HSU: 9 SVS: 8 What I mean by high bass is bass that ranges from 70-120 HZ. The Music that I used for this was the bass line from Alice In Chains Would, Incredible Bongo Band, Gypsey Kings greatest hits, and some others I cant remeber. In other words, the bass that approaches the midrange. For the HSU, the bass seemed a little more natural, in other words, the bass blended with the rest of the music. While this bass on the SVS was very accurate, it was always in synch with the rest of the music, but at times it seemed to domintate the music a little bit, even after adjusting the levels. But to be fair with the SVS, it is only rated to 80 hz 3. Mid Bass (40-70 Hz) HSU: 10 SVS: 9 This is where the Hsu really shines. Listening to really mid-bass heavy music, like Mirwais, Madonna's Music, Beastie Boys, some Phish, Some really bass-heavy Led Zeppelin, Primus, stuff like that. I cant really explain it, it just felt right. The bass came out clean and was never ever boomy. With the SVS, much the same, but at some times the bass seemed to linger on a note for a fraction of a second, if you know what I am saying. But altogether, a great showing 4. Low Bass (40 Hz and below) HSU: 9 SVS: 10 Now this is where the SVS really shined. For this test, I pulled out some of the best bass-thumping music, like more Beasties, some 2 live crew, some old pipe-organ stuff, as well as some movie listening, like Matrix, T@, U571, MIB, stuff like that. Man, was this amazing listening to these two subs. In terms of how low the bass goes, it was almost impossible to tell. but interms of extension and volume, the SVS took the cake. i am not sure if it was because of the amp, or whatever, but on scenes like that one MIB part (where the bass goes really, really low as they take the elevator down) or the end of Hoochie Mama, the SVS really pumped it out, almost to the point of breaking glass. So the totals are: HSU: 38/40 SVS: 37/40 Really close race, and these are worthy competitors.