> I noticed that most of their “noise-cancelling” was actually passive and consisted of good noise suppression from the good seal created by the headphone ear c

> I noticed that most of their “noise-cancelling” was actually passive and consisted of good noise suppression from the good seal created by the headphone ear cups. This is absolutely not the case, you can turn the cancelling on and off while still wearing them and it makes a huge difference to background noise. Many years ago they had a demo where you stand in the store and they blast a low-pitched white noise roar (like a jet engine) at you, and have you turn the cancelling on and off -- it's something ridiculous like a 45db drop. I bought a pair on the spot. It's certainly the case that the cancelling is less effective at higher frequencies like voices than it is at low-pitch background noise, which does decrease their effectiveness in an office environment. I have mixed opinions about build quality -- the originals were solid, I wore these around town most days for a few years, and they are now about 6 years old and still working. The replacement cups that I bought were garbage and disintegrated within 6 months of only at-desk wearing. So perhaps construction is not what it used to be. Interestingly I heard that Bose patented the physically optimal geometry for noise-cancelling microphones, which would mean that their competitors are necessarily inferior at pure noise cancelling; don't know if that's true though. I also find it annoying that these headphones require batteries to function even if you aren't using the noise cancelling feature; makes it very unreliable for carrying around town, but not a problem at my office desk. Without knowing anything about the electronics involved, it seems like it would be much better to have it degrade to being non-noise-cancelling powered headphones, instead of bricks, when the battery dies.