Turn the city off.
That's a normal commute. Move through it, then switch noise cancelling on.
How it hears the room.
- Six microphones listen. Four on the outside of the cups hear the train; two inside hear whatever still reaches your ear.
- The chip answers. It plays the same sound back, flipped upside down, thousands of times a second.
- The two cancel out. What is left is your music, or nothing at all.
A simplified picture of active noise cancelling. Figures on this site are illustrative.