The bane of all live performers that require open microphones is, of course, feedback. It's the electronic version of fingernails on a chalkboard, but it doesn't have to be a major problem. Today, there are several ways to battle our arch enemy. The first is to use a feedback supressor. These start at about $299 (from both dbx and Peavey) and go up to almost $600 (for a Shure DFR22). This is the easiest fix, as the user interfaces of these devices are quite user-friendly. Basically, they analyze your audio, detect which frequencies are causing the feedback and automatically (or manually) supress them. Another simple method is by using a 31-band EQ (which every good PA system should have in any case). These start at a modest $109 (for the ART EQ-351). It's usually a simple task to turn up the mics to the point of feedback and then use the equalizer to cut the frequency that's causing the problem. Don't let feedback ruin your live performances when there are easy ways to eliminate the problem before it becomes a problem.