This is a review and detailed measurements of a Sennheiser HD 598 SE with replacement "leather" pads.
I have a HD595 (same shape, older top model of this range) and when I replaced the pads with very similar ones to the original ones, the sound was
ruined.
so I suggest never ever measuring any headphones with replacement pads
before measuring the original.
Not in my book. These pads are not significantly different either. If there is such massive difference due to pads, then measurements need to use calibrated pressure as to keep their shape in certain manner. And you best use them the same way. You think these are safe assumptions?
in my case it was just a different foam and maybe slightly different velour, and the sound was drastically changed.
I am 100% sure that if you measure this headphone with original pads, the difference will be huge.
also, 598 and 598SE are the same except for the colour.
also pretty sure the difference between 595 vs 598 vs 599 would be
much smaller than same pair with original vs these pleather pads. don't know why but you may be underestimating the influence of pad material on the sound.
consider this: 598Cs is widely considered to be horrible compared to other models of the series. why? because it has pleather pads + it's closed, not open.
as for the the exact pads, these might be the ones
https://dekoniaudio.com/product/choice-leather-for-sennheiser-hd598-headphones/
they measured the difference vs stock on another Sennheiser model, it's pretty significant.