system
Given the following post, respond as if you're commenting on Reddit:
human
Why can noise cancelling headphones only cancel at low freqs?

Can anyone explain why exactly noise cancelling headphones are only able to cancel reasonably low frequency sounds?  Is it more of a practical limitation or a scientific limitation?

Bonus: Is it at all related to why low frequencies tend to travel through walls, while higher frequencies do not?
gpt
It's a problem with electronics. To cancel a wave you need to be able to synthesize an identical but opposite one. If you have a 100 Hz wave the Whole wave is 10 ms long. So, if you sample the signal, invert it and reproduce it with a lag of less than 1 ms or so you're almost set. If you have a 1 kHz wave (which is "mid range" in audio) the Whole wave is 1 ms long. You'd have to reproduce the signal identically in less than 0.1 ms. Which is basically impossible. Also, mantaining phase coherence is not that easy at higher frequency.