OMNI OR UNI?

I recently happened to catch Curtis Salgado blowing harp and singing up a storm out in the mosh pit in front of the stage, out in front of his band, out in front of the monitor line, out in front of the main PA speakers -WITH NO FEEDBACK!

He was using two high quality unidirectional vocal mics -a SHURE BETA58 for voice and an EV RE10 for harp. Both have the benefit of picking-up audio signal from a small well-defined heart-shaped ("CARDIOID" pattern) area on-axis with the front of the mic's grill. No squeals -even when only partially cupping the EV for harp.
UNI and OMNI. You'll see these words in the description of various microphones. It describes the nature of the mic's pick-up pattern: UNI denotes 'one'. The mic is sensitive in a single direction -as are most high-end vocal mics; OMNI means 'all', it's sensitive in all directions -or simply non-specific, non-selective -as are most mic elements commonly associated with harp. For most applications (such as on stage with your amp & your band) your typical OMNI-equipped harpmic will work fine. When you're working with extreme dB levels or in the combat zone out in front of the main PA, feedback hazards may be minimized by blowing through a Unidirectional "CARDIOID" dynamic mic. Yet another tool in the arsenal...