Time to address some fallacies about the HD800 6khz peak and new production units.  After listening to Max's HD800 alongside my own and comparing both of our Sennheiser supplied charts with various measures purrin and myself took there are four things I've come to conclude.


1-The 6khz peak and bass response is roughly the same among units from 11xxx-16xxx despite what our charts show is a discrepancy of a few dB at 6khz.  The rumour about 6khz being shelved by Senn are false
2-My older unit has ever so slightly more midbass but it's marginal enough to unit variation, not revision.  Talking around .25-.5Db at around 100hz.
3-We were able to replicate the Sennheiser chart discrepancy in the 6khz treble peak via slightly misaligning cup placement.  It seems to be user error on the part of one of the 16 lab techs used on each Senn chart.  A millimeter or two only effects this treble area discrepancy, no other part of the spectrum.  Despite this narrow that appears to be an outlier compared to other Senn graphs, there is strong correlation between Sennheiser's own measurements and purrin's.
4-While taming 6khz is useful to taming fatigue w/ the HD800 it is not the most important factor.  Elevating the midrange a few dB from 1-3khz does more to improve overall listening fatigue than just taking on the 6k peak alone. 


Number 4 is the greatest area of discrepancy between mine and Max's HD800.  As a result it's easier to listen to his for longer duration.  Mine has a bitmore extended trebel past 12khz which seems to improve air a bit.