We're not saying that they rolloff on an audible level, the both of us are far too seasoned to make that mistake. We're saying they rolloff energy wise. HE-400 can't quite put off as much pressure as the LCD2 at 30hz, as an example. Square waves will confirm that as well.
I could see that.
But I think square waves are a little silly to look at though. They're basically really cryptic FR graphs(they have harmonics that extend throughout the audible range, they don't represent only bass), and inaudible things can totally mess one up.