The difference is plain as day. I currently use the closed back Beyerdynamic DT770 with an amp for listening to music, but exclusively the Bose QC25 for work an

The difference is plain as day. I currently use the closed back Beyerdynamic DT770 with an amp for listening to music, but exclusively the Bose QC25 for work and commuting. The main difference between my Beyerdynamic DT770 and the Bose QC25 are: 1. Without any music playing but with active NC on, the QC25 feel like open-back headphones. The feel is airy and like a weight is lifted from your ears in the QC25 vs. muffled/dull/pressured in the DT770. You can sort of hear your the blood in your ears pumping in the closed-back DT770, a bit like what you would hear in a seashell. If you turn off the NC, the QC25 is about the same as the DT770 without sound. If you go back to your HD202s after having used NC for an hour or so, you'll immediately notice the difference. 2. Sound quality is much worse in the QC25, it's not even close. No rich lows, no clear highs, it's just a mess. Still, it's usable. 3. However, the killer feature is that with the QC25 you can listen at extremely low volume (think 1 bar on the iPhone) and still hear the music clearly. On the DT770 you have to play the music louder, and I find that very quiet music is better for focusing.