Excerpted paragraphs from an article entitled GLORIOUS ACOUSTIC GUITARS

By Brian Knave

POLAR REGIONS

The two most commonly used polar patterns are cardioid and omnidirectional. Obviously, the cardioid pattern is useful if you're recording other instruments in the same room simultaneously, because the pattern's rear rejection minimizes bleed from nonsource sounds. However, if there is no interference from other instruments, be sure to audition an omni mic. The omnidirectional pattern typically gives a bigger picture of the sound, which can be especially desirable if you're using a single microphone.

Of course, opinions vary about the use of cardioid versus omnidirectional microphones. Saltzman feels that using a cardioid pattern on an acoustic instrument produces a "pinched" sound, so he prefers to use omni mics. "A mic capsule is naturally omnidirectional," he explains. "To make the mic cardioid, a manufacturer has to do acoustical porting and other modifications. So a cardioid mic is basically a crippled omni. A cardioid doesn't capture all the sound coming from an acoustic guitar. When I put a mic on an acoustic, I want to pick up as much sound as possible, so I go with an omni."

Another advantage of omnidirectional mics is their lack of proximity effect, which means bass frequencies don't multiply like bunnies as the mic gets closer to the sound source. This attribute lets you position the mic closer to the sound hole without increasing boominess. A corollary benefit (for small-diaphragm models only, because they employ a single capsule that does not "hear" behind itself as well as a dual capsule, large-diaphragm condenser) is the relationship of mic-distance to ambient sound: the closer the mic is to the guitar, the less room sound it hears. This is an important consideration if all you have to work in is a crappy-sounding room. I recently recorded a vintage Lowden guitar with a single Earthworks TC30K (small-diaphragm omni) positioned only inches from the juncture of fretboard and sound hole. The result was a stunningly natural, in-your-face acoustic guitar track with no hint of room sound.