Avoid this by following the 3:1 rule, which stipulates that the distance between multiple mics should be at least three times the distance between the close mic and the source. For example, if you have a close mic 8″ from the sound hole of your acoustic guitar, your ambient mic should be at least 24″ away from the other mic, or the same sound source. The big change in amplitude between the two signals will mitigate the comb filtering, and you can accentuate this by angling the mics in different directions (provided it sounds good).
So let’s do it. Let’s make a tuning system out of the harmonics of the C string. First, we should find the C, G, and E whose frequencies are as close to each other as possible. We’ve already got C at 1 Hz. We can bring our G at 3 Hz down an octave by dividing its frequency in half. This gives us a G at 3/2 Hz. We can also bring our E at 5 Hz down two octaves by dividing its frequency in half twice. This gives us an E at 5/4 Hz. When you play 1 Hz, 5/4 Hz and 3/2 Hz at the same time, you get a lovely sound called a C major triad. Cool!