Many of you will have heard about the Fostex T50RP series having vents letting pressure out to the ear-side of the driver. The result is less sub bass, and closing it off results in more sub bass. Most dynamic driver headphones have this white driver paper covering the baffle, which is like a spider web. Most of it is open. So this paper regulates the pressure being blasted back from the cup. So say you took a pair of HD600's and covered all of that paper with something completely airtight... What would change?