Edited by vid - 10/15/13 at 4:30am
According to many sources, this headphone was a real flagship when they came out. I heard a pair one month ago, a friend bought a pair on ebay. They sounded good but to my ears (and to my friend's ears) a pair of AKG k701 sounded quite better. His pair is mint and stock configuration. I hope that the above mentioned mods can elevate it to a higher level. Of course it is always nice to try new things if you can buy them cheaply.
Today's Unipolar 2000 auction (phones sans power unit) ended at 35.60 €. Hopefully went to someone on here and who can source an HER 2000.
These are the uncompensated raw measurements for the two channels modded. I keep forgetting which is left and which is right, so I've simplified the naming.
You can check out a basic example, roughly, of one type of compensation curve here, i.e. a curve that would be reduced from raw measurements to arrive at an estimation of how the response would be perceived. The Unipolar has the 3 kHz peak and some of the lead-in upwards slope, but both measure about 5 dB lower than they 'should', and the rest beyond that is abnormally flat. I'm not sure whether this is a problem with my measurement setup - as I've mentioned earlier, I've had much trouble getting conventional-looking measurements out of the Uni unlike with most other over-ears I've tried - or whether it is that Sennheiser used an odd equalization curve for these phones. The drivers were meant to sit in what would basically have been free air, slightly angled towards the ears, acting as tiny speakers of sort.