With this logic you might as well get a sub with 3MM of Xmax since it does not seem to matter. All I'm saying is that the TC2000 will have the ability to move 50% more air which is a large difference. Why do the subs that I have owned reach their Xmax in ported boxes at many frequencies? I know that it is not the most important spec on a sub but when comparing two similar subs you might as well go with the one that has more potential. He is going to want it loud and low, otherwise he would not be getting a 15inch sub in a ported box.