What the hell are you talking about. 40 Hz is 40 Hz whether it is an 8 or an 18 or a **** 36 inch sub. My 15s hit just as tight and responsive as a 12, 10, 8, or 6.5. And there are 6.5" subs that will play just as low into inaudible tones as any 18. The 18 just does it with more authority becasue of much more displacement. I think people get confused when they hear the difference in 10s and much larger subs. Since the smaller ones don't move as much air as the larger they get a reputation for being punchier and large subs get labeled sloppy. This is not the case, fact is they all work the same and the difference in air displacement is what causes it to sound/feel different.