Posted to please review these in the thread "Review Request" here on IF.
These appear to have wood backs and a single Heil AMT folded ribbon driver. The earlier prototype in 2015 was I think a hybrid arrangement of the same Heil with a dynamic driver, maybe ? Not sure.
ESS did make a Heil headphone, single driver, back in 1976 model called - ESS Mark I Heil Air-Motion Transformer Stereophones (AMT). They either had a 1/4" plug end(fotos I saw)or ran off the back speaker outs of a loudspeaker amplifier (per a different owner), and were rare, but lacked bass. I think they were open-back and noticeably had a large Y-yoke metal piece holding the very large oblong (? plastic ?) cups. I think the frequency response rolled off on both ends. Have only seen fotos of 1 set of these, owned by the Heil family. May not have been just a single prototype, because fotos of the retail box were also shown and are up on head-fi.
Interested to read about the brand new ones, and if closed back, should have good bass just considering frequency response only.