Although there are better headphones out on the market, these are one of the best for the price. Studio-Reference standard, and one of the very few headphones that passed the broadcast standards set by the Institute of Radio Technology in Munich.
These are from the same family as AKG's K240S (the new consumer version) and the K240M (the original version)... the DF takes the M version higher by calibrating the drivers to sound like you were in a mixing studio (instead of listening from a headset)
These aren't for your average iPod though, (you get AKG's K240S for that) these require a decent headphone amp to power the high impedance drivers.
For those that are starting a home studio... these are the best substitute for near-field monitors.... specially for portable studios.