Although I don't own a pair of HD800 headphones, I want to chime in here regarding this frequency chart, as I have seen this before from Dekoni, but the pads ended up offering MUCH different results, basically, exact opposite. How can this be explained? I have no idea, but maybe someone else with some Focal cans can back me up on this if they tried or use them.
So this frequency chart for their custom Stellia style pads for the Focal lineup showed massive drop in the low end, however, when using them they actually increased the low end very nicely compared to stock pads. They were my go to pads for my Focal Elex HPs. I love low end and probably what some, okay maybe most would consider exaggerated low end, so if a pad would have reduced it this significantly I would have hated them.
https://dekoniaudio.com/product/dek...es-replacement-ear-pads-for-focal-headphones/
Again, I cant explain this but thought it might be relevant here. Will need some real world listening with these to get an actual idea of what they actually sound like.