Green = Shure SRH 1840
Red = Sennheiser HD 800
So the HD 800 has a mid-bass boost and a dip at the mid range. Both the HD 800 and Shure SRH 1840 seems to roll off the sub bass, but since the HD 800 has a mid-bass boost, it is not as apparent from the frequency graph.
The HD 800 doesn't look as flat as headphones like the Shure SRH 1840. It is a bit coloured with boosted and dipped frequencies.