The speed of sound is constant. Frequency and wavelength are not. That means a low frequency sound occupies more physical space and time than a high frequency one.
And because time is also a constant, when we move one microphone, we delay it by some distance that corresponds to some wavelength. And what that means is when you combine these two signals together, half that wavelength is going to operate destructively and that particular frequency is prone to get cancelled out. And this is also a good time to clear up another misconception, which is just because that wavelength occupies a physical space, you do not need to be that far away from it to hear it.
The sound pressure is going to rise and fall wherever you are. Oh yeah, share that with somebody who belongs in a big kitchen class.
