I did a few sinewave sweeps..
It's more or less flat all across; there seems to be a bit of a dip around 7kHz but that is it.
Extension in the treble is better than HE500/400, it goes closer to 15kHz before petering out. I'm not sure if that's just my ears though.
Bass is a bit interesting.
Ok thanks :]
You got my full attention now...