By now, your vocal should be sounding great — nice and punchy with just the right frequency balance and the perfect amount of space. But people have short attention spans these days, so you’ve got to shake things up if you want to keep them interested for three whole minutes.
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).