I've had to do my research on these as I'm not an expert in this field. These were left behind in a box full of audio equipment in the loft of an ex-rental house we've just bought.

I've checked online and can safely say these are Sennheiser HD25, and they appear to be the HD 25-1 version. It looks as if they have an upgraded cable and pads, the cable has the Custom Cans logo.

The only thing I have with a headphone jack in to test these with is an old minidisc player, and plugged into that these things create great sound but the volume on the minidisc player was never that loud so I've not been able to play anything really loud through them and check for any distortion.  My phone has a USB type C input and my TV, laptop and portable speakers are all either USB type C or HDMI inputs. So whilst I can say that these things definitely work and create great sound, I can't tell you exactly how well they push out music at full tilt.

They come with a spare driver unit that was opened but appears to be unused. From what I can see, these things are all modular so if any one part is not working, a spare seems to be readily available.

I've priced them lower than I can see other sets have sold for given that I've not been able to test them fully,  so someone could get a bargain here.

Sold as seen given all of the above, so please bear this in mind when bidding.

Good luck with the auction.