How can active noise cancellation be used in an interesting way? How well does it work?

Question

Headphones

Active noise cancellation is going to the masses (one of the first steps in this from Sony is complete headphones with such a feature), and of course, there have been many such solutions on the market for a long time.
Also on Habré, the announcement of a device with this technology for the home has recently slipped.
It is placed on the window and filters sounds at your request. Do you want to hear only the birds singing when there is a traffic jam under the windows? You are welcome!
And I wondered if it could be used on robots? Having just watched a video about hexapods on ros, I once again decided for myself that they are too noisy. And the sound is not pleasant.
It seems to me that I hung a microphone, a speaker on it - and a solution? Will there be an effect? Or maybe they already did that?

Answer 1

With active noise cancellation in reality, everything is not as smooth as in marketers' stories.
Roughly speaking, in a wide frequency range, this is fantastic, and if in headphones the problem is successfully solved in a complex way also due to the design, then in other applications everything is much more complicated ...

Answer 2

1) active noise reduction works well only for regular sounds
2) the emitter should be as close as possible to the source of noise or to the receiver
if the noise reduction emitter in the earphone is almost point-blank to the ear and the sound cannot be bypassed and by applying noise with antiphase it can be well muffled ,
then in the case of a hexacopter there will be a problem of interference and extinction will occur only in some directions - "beams" in other directions will gain amplification, but even this, if desired, can be used, for example, in copters for surveillance - the "extinguishing beam" is somehow combined with the direction of the camera.