I have noise canceling headphones (Bose QC 35), that also have microphone built-in. If the microphone is active, noise canceling doesn't work, they just pass through ambient sounds (this is by design. I suppose, they did it so you wouldn't feel that you're in "vacuum" when you are talking).
Anyway, the problem is that whenever I connect my headphones to macOS, the system switches from internal microphone to headphones' one. Therefore, noise canceling doesn't work, unless I go to system settings and switch microphone back to the internal one.
This is very annoying, especially considering that I have to do that every time I connect headphones.
Is there any way to force macOS to always use internal microphone, or not to use the specific headphones' one?
Update from 10/2017:
So I found out that "headphones' microphone is being used" only happens when Skype is running. But ever since I stopped using Skype (or having it running all the time), the problem was gone!
This is not the solution for the original question, I'm just leaving it here for the future reference.