I am searching for a technically accurate answer. I just calibrated my system with the help of a friend, and he asked me why I got a new sub (JBL PB 12). I told him that the frequency response was better, it has a larger woofer, and more power than the old one (an 8" 100W Kenwood HTB sub). The question came up - if you're calibrating the system to specific listening levels, than why does it matter what sub you have, provided it can reach those listening levels and be balanced with the rest of the system. I couldn't come up with a technically correct answer, but I know that my new sub sounds better than the old one. Can someone help me? I'm being totally serious, here. Knowing this answer will help me when I upgrade to a better sub in the future.