[Vinyl]

I own those old phones from the early '90s, if my memory is correct. I've always enjoyed them, but I can't remember anything about the specs. The impedance should be fairly high, for I've never been able to decently drive them out of a portable player -- not to mention how wierd they look when coupled to an mp3 player several times smaller than themselves!
I also wonder how they compare with today's models, from Sennheiser or other brands. As far as I know, Sennheiser models starting with a 5 are the low end of audiophile grade, but I'm not sure about older models. My phones are "made in Germany", if that helps.

 

[Freetrademan]

I also have the HD520 II, and I've enjoyed it for the last two decades. One drawback is that it isn't quite efficient enough to drive my iPod/iPhone at ample volume. Hoping new technology would improve on that old design, I recently bought the Sennheiser HD598. In all my store evaluations, I found it to be the best-sounding (and most comfortable) headphone in town. Also works well with my portable devices (although it has only a large 1/4" plug- clearly not intended for mobile use). But back at home, side by side with my old HD520, I found the HD598 to be a little too thick in bass, but the HD520 just right. They're very similar.