So i was looking for vintage Sennheiser headphones and a friend offered this rather new hd540 ref (with aftermarket pads) to me.
Although to be fair none of us have any extensive knowledge about the hd540 and I would love to know if this is a early/mid/or late 300 or 600ohms version.
https://www.superbestaudiofriends.org/index.php?threads/fun-with-vintage-headphones.9934/ “The impedence is denoted by…”