The mk2.5s are a little bit more forward than the mk1s. The mk2s are definitely not dark sounding. Maybe slightly laid back or even too forward for those would prefer the mk1. These mk2s were modded with a partial 80% block of the vents and a full spring mod.

Nope - they are just shiney up there! These have a ton of air. This could be a characteristic of the mk2.5. Jude mentioned when he heard them that he actually heard treble - which he said wasn't the case with other 007s that he had heard in the past. Could be the amp though. Or could be the mods.

The 10khz-20hz region seems unique among the phones you've measured.  Even FR, fast but rough decay.  I wonder what causes the jaggedness and how it manages to be so clean despite.

I find that really interesting too.  The 009 CSD was similar too.  The ESP950 didn't have those tiny little ridges though.

I find that really interesting too.  The 009 CSD was similar too.  The ESP950 didn't have those tiny little ridges though.

It looks to me like a well controlled problem of some sort.  Something Stax saw in the driver's response and worked to minimize to the point of irrelevance.