Sennheiser HD558 (modded) Frequency Response and CSD Waterfall Plots.
The mods consist of the single foam strip (right behind the driver) removed from inside the housing. I have my doubts the changes are significant (moar bass, etc.) I re-applied the strips and felt the stock sounded slightly more midrangy. That was about it. Maybe I'll measure the stock headphones one day. I'm not really that interested.
These are good headphones though, especially for the price.