Yeah, 20 Hz = 17 m wavelength, so move the microphones to be at least 17 meters apart, or a bit more if you think the sound is below 20 Hz, which should be doab

Yeah, 20 Hz = 17 m wavelength, so move the microphones to be at least 17 meters apart, or a bit more if you think the sound is below 20 Hz, which should be doable. And yes, I don't expect comparing amplitude to be useful--sound localization almost always uses TDOA/phase difference for that reason.