I got a newer pair of HE-500's from Hifiman and they seem to be voiced a bit differently from my older ones. The highs are smoother and there's a little more weight on the low end. I've also noticed that the pads have foam rings between the, um, pad parts and the cloth screening, which may account for this difference in voicing. I'm not sure if I like this or not! I mean, this FR is probably more "correct," but it's less unique. I don't want all of my headphones to sound "correct." I might mess with the pads later.
I am liking this, though: http://soundcloud.com/joyful-noise-recordings/talk-normal-cover .
I've been so damn tired lately and it seems to have nothing at all to do with my schedule or how much sleep I get.