This stuff. A manufacture lists what the drivers are capable of reproducing, not what an individual can hear. The more frequencies and range a speaker can play, the better. It is known as head room. No, it is not marketing hype. Sennheiser is a very capable and experienced co.
The HD598s are really great sounding headphones.
I have both the 598s and the HD 600s. Two different types and they don't compare.
Make sure you understand what what the HD 598s are. Sound quality is excellent and the price has come way down on them making them a real bargain..
Somebody else will chime in to whine about what they don't understand here soon. Sheesh.
W.P.