Wait what. The orthodynamic headphone manufacturers advertise with a planar wavefront and Sennheiser advertises with a curved wavefront? And dome drivers already produce a curved wavefront... Crazy world.
I also don't see how any of those headphones other than the HD800 would produce an HD800-like wavefront, because afaik that's the only one with a ring driver and the others don't seem to have some sort of special waveguide either. Not more special than the "paper" with the hole in the middle as found in the HD515 and up anyway.
I stand honorably corrected, right, it's the ring driver thing (particularly good for Wagner!) that makes the difference.
I was thinking about Sennheiser's re-positioning of the angle of the transducers in relation to the ear that seems to be present in the newer 'phones. Everything turns to mush in my brain, cornmeal mush.