[jdsully]

Yes but perfect destructive interference isn’t possible unless everything remains fixed in place which is difficult on a living human head. Its quite possible to get temporary constructive interference for short periods, and also plausible the brain would filter the spurious noise out.

[davidgould]

Not quite following this argument. The distance between the microphone and speaker is fixed (and small compared to the wavelengths of interest) because they are part of the AirPod.

[jdsully]

The distance between the speaker and ear drum.

[davidgould]

Assuming the the canceling wave is timed to cancel at the speaker this should not matter as the external wave and the canceling wave would have the same distance to the ear drum.