If my understanding is correct noise canceling is an additive process. The external microphone records the back ground, the electronics invert it and it is played over the music. Noise - noise + music = music
My Bluetooth headphones have this feature and it works. I can see the microphones outside the speakers, the units are 1/2 of an inch deep and about the same across the widest part. Definitely not comfortable under a helmet.
On a device in the ear canal I think there are two issues, where the microphone and processor goes on a tiny device and if the tiny microphone would pick up the extraneous noise burried so deep.
Andy
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