My friend Dave Stagl posted a great article on how to eliminate feedback from your spoken word mics. As is Dave's style, it's a bit geeky and he breaks out the big guns to make some measurements to help validate what he's hearing and then help fix it. Even if you don't own an FFT measurement system (or know what one is), there are still plenty of concepts in his article that will help you fight one of the soundman's fiercest foes; feedback. Here's the intro, click on the link to read the full story.
Feedback drives me nuts. It turns my hair gray. I hate it, but unfortunately it is an ongoing issue in live sound.
The biggest gain before feedback challenge for me has always been and still remains spoken word mics. 99% of our spoken word mics are presently head-worn Countryman E6?s, and even though they are head-worn I still refer to these types of mics as lav’s; whether it’s on the side of someone’s head or clipped to a lapel, the capsules are basically the same type of electret microphones. And unfortunately, they all tend to be omnidirectional mics. I have tried directional mics in the past and found them to be more trouble than omni’s.