They are very traditional open headphones with almost no sub-bass. They start to fall off below 80Hz. The bass could be a bit tighter too as there is a bit of mid-bass emphasis to make up for their lack of sub-bass. For me, they sound fine with almost all music, but I do miss the sub-bass after listening to more "fun" headphones. For the most part, I wouldn't have known what sub-bass is missing, but when I listen to music with strong sub60-80Hz content on my home theater system which is flat to 20Hz, I can tell the 600 are holding back the bass.
This applies to everyday items as well as high end items that I don't really need.