>> Active noise cancelling still adds to the absolute volume, doesn't it?
Noise canceling works by playing back the exact environmental frequencies through the headphones, 180 degrees out of phase. So from the perspective of your ears, noise canceling does lower the absolute volume.
The phase-shifted signal from active noise canceling electronics only actually achieves physical cancellation if the signal it's attempting to cancel hasn't changed. By the time the phase-shifted response to a dynamic signal like speech comes out of the speaker, the signal it's trying to cancel is gone, and there is in fact more sound coming to your ears.
Noise canceling works by playing back the exact environmental frequencies through the headphones, 180 degrees out of phase. So from the perspective of your ears, noise canceling does lower the absolute volume.