The reason I asked is that I have seen folk mentioning their X subs sound great there but the new Y subs at the exact same locations did not impress and that they had to do a new sub crawl all over for the new subs and the result is new subs at different locations did impress them after all. I remember reading about a guy who had a pair of PBUltra's and replaced them with a pair of VTF15-mk2's that he had to move his VTF subs to obtain great sound/output. He was disappointed with them where he had them at his PBultra locations.