Q: I’m familiar with the 3:1 rule for mic placement, but I don’t get how it works. How does the 3:1 ratio fix phase problems when each frequency has its own wavelength?
A: Technically, the 3:1 rule doesn’t fix anything with regard to phase. Instead, the “rule” works because of the way that volume drops with distance. (Check the inverse square law, for example.) The volume level of the signal at the distant mic is substantially lower than the volume level at the close mic, so any phase cancellation is reduced enough in level to not be an audible problem.