The price difference vs performance is indeed something I'm looking at. Parts Express has a sale going on now, 10% off everything, so two NSW 21" will be $1,350. On the other hand, I might be able to get two used Ipal21 for around $1,900, or a $550 difference vs the NSW. The sealed box that Ricci uses at Data-bass is 23" x 23" x 20", around 4.5cf internal. My sealed box is actually a little bigger, 22" x 22" x 24", around 4.7cf internal. Correct me if I'm wrong, but it looks like on the Data-bass, in terms of distortion, motor strenght, linearity and sensitivity, the Ipal21 is a little better, right? I don't know that I would even notice that during my home use, maybe if I push them to their limit. Also, it seems to me that the amp I have is more tailor made to drive two Ipal21 vs two NSW since it puts out a little more power at 2ohm vs 3ohm. According to Ricci, he seems to like the NSW suspension better, not as stiff. Also, is easier to drive with most 4ohm amps out there and of course, is cheaper. In terms of how they sound, they should be very similar, no? Overall, they seem to be similar to each other and better than any other pro woofer out there. Same weight, size, power handling, similar xmax, voice coil, SPL, etc.