I'll be glad when anti-feedback devices are common.

I just went to Amazon and looked for a book such as "Sound Systems for Dummies". Found nothing. There might have been books that would help the beginner or the interested auditor, but I had no way of knowing which ones. Many of the books were quite expensive, and who knew how technical they were.

I have the feeling that there are simple guidelines to preventing feedback, but so far I haven't found them. At a concert of Irish music with four players, we were hit by feedback 5 or 6 times. I'm convinced the room was so small that no amplification was needed.