Jose wrote:

In my experience with the David Clark HS10-13X ANR headset, the passive
noise reduction is excellent, and more than once I have forgotten to
turn on the ANR, and didn't notice until halfway through the flight.
(and turning the ANR on made another big difference)

Aren't DC's known for their passive noise reduction?

In any event, I agree with Newps: The only time you will fly without the
Bose ANR activated is when you fail to have a replacement set of batteries
nearby. Otherwise you will always use ANR.

--
Peter