I have used many different types of subs. I think once you reach a certain level of bass quality the sound becomes more alike than different. Good quality bass is good quality bass. The big difference is between extension and power. I have owned SVS subs, the best being 3 16-46cs+ cylinders(Have not heard the ultra), M&K subs(many but their best was the MX-5000), klipsch THX ultra 2 subs, the madison pro subs previously mentioned, and now DIY 18 inch ported and sealed subs. My favorite were a combination of both. The sound and power of the pro subs were just amazing and made me realize what reference levels were all about without compression. The 3 SVS cylinders and Klipsch subs made me realize what extension was about so I thought. The SVS subs would shake my room more than the pro subs so I thought they had better extension. What the real difference was the sound and power. I will give 2 examples that happened in my room(others could very well have different results). I played the infamous Pulse movie scene with the 15-19 hz pulse wave and sonic bliss. The Svs subs again would shake things more(at least that is what it sound like). I took out my spl meter and the SVS subs were at 110 db's and the pro subs were also at 110 db's so it was not more extension but rather just a different sound. I then put in WOTW pod emerge and the SVS would peak out at 112 db's and the 2 pro subs would peak out at 123 db's, again with the Svs sounding like it had more shake. They were just different sounding. The midbass was no contest as the pro subs would just slap you in the face. I have since built DIY sealed 18's. To be fair I will give you the numbers with all at the same cost(around $1200), up front location(12 feet away from the LP), with all the same amps except the SVS. 1 SVS pb12/plus/2(was $1200 for me) would get me 110 db's on pulse, and 112 db's on WOTW. 2 pro subs, dual Madison subs($1360) would get me 110 db's on pulse and 123 db's om WOTW. My four ported 18 inch sono's($1700) would get me 120 db's on pulse and 126 db's on WOTW. The Svs subs still sound like they rattle things or shake things more and the other 2 sound more alike. I don't know what that means but clearly the more shaking is not because of its power but its sound. The DIY subs were much more visceral on the body. Now I have about $3200 worth of DIY sealed subs and I pin the meter past 126 db's no matter what scene(heavy bass) I play. Just my experiences with different types of subs. BTW, it is close in midbass between the DIY and the pro subs giving the slight nod to the pro subs(thanks to the dual horn subs). I had 4 pro subs and now 8 DIY sealed subs for the comparison.