Tyll's already got that covered. His square wave measurements look good.
A nice square wave at 30Hz or 50Hz really doesn't say much. They are unique though to each headphone. I'm under the impression that some people think that a good looking square wave correlates with maintaining a low frequency or bass response. This is not necessary true! A square wave consists of the specified frequency and the summation of odd integer harmonics at successively lower levels, going on to infinity. Square waves do not happen in nature. You pull a third or fifth harmonic out of phase slightly, the square wave collapses. Other than determining how damped or over-damped a driver is, they are not that useful (at least from a speaker builder's point of view.)
I remember when the LCD2s first came out, and one of my first impressions was that they sounded slightly over-damped (meaning the signal had little ringing but probably didn't reach its theoretical high and low levels.) Of course someone would slap the perfect looking LCD2r1 square wave measurement in my face and tell me I was wrong. The funny thing is that square wave measurement definitely showed the LCD2r1 was over damped! IMO, a little bit of extra ringing in the square wave to allow the high and low level peaks to reach closer to their potential is preferable to nice almost perfect squares with little ringing.
Edited by purrin - 9/6/11 at 3:22pm