Ok I burned in the k100 driver for 24 hours. I could have burn in more, bur this is the impression:
As packaged, they are over damped, with muted bass.
I opened 2 circumference holes and bass increase ridiculously. I ended up using configuration that was much more opened than my hd800 driver, and still got rumbling bass. However there is very annoying peak in the upper mids and doesnt go away with different damping and mod I made. The center part is metal vapour film so it is light and rigid, and surrounding white plastic must be softer, and it indeed move like a piston. But the upper mid and high screwed up, and not that much detail or sense of space. It also sounds harsh, not smooth in these region
Then I desoldered them and swap in the berrylium 300 ohm and damn. Not as smooth sounding as the hd800 driver but like 95% and sounds quite smooth without any peak. This is almost the same case with hd800 driver when i first got them. The high peak of hd800 is mostly due to the thin metal panel they use to create resonance and produce more detail in the high . Detail retrieval of the BE driver is on par with hd800. Interesting because they are both very stiff and fixed edge. On Hd800 its plastic but stiffness is increased by the fixed inner circumference. On the berrylium, the whole diaphragm is plated with what is supposed to be the stiffest and luglight metal. As a result they sound a bit similar, detailed but less bass ( not piton like movement like those rubber mounted fostex biocellulose drivers)
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