Knowledgebase: Miscellaneous
Preventing Feedback
Posted by Rick Shao on 13 November 2015 06:26 AM

Q: Every time we think we have acoustic feedback licked, it seems to rear its ugly head again when we least expect it. We’ve even employed a “feedback eliminator” device among our equipment. Any suggestions?

Suggestion: Take heart. All your previous problem-solving steps are not in vain. Before you pull any more hair out, consider the following: do you have a team that gathers briefly for note-sharing immediately after your day’s work (or at least lingers for a few minutes while things are being tidied up)? If not, that can be a great starting point for process improvement. Actors in live theater almost always discuss notes immediately after a performance - while the director’s and stage manager’s observations are fresh. This will work in other areas, too! Oftentimes, everybody’s in such a hurry to get on with the rest of the day, that the details of problems are forgotten by the time a Monday or Tuesday staff meeting takes place.

It will especially help to note the conditions that appear to lead to your problem: which speakers and mics cause the loop? Is it related to one particular person? Does it involve a wireless lavalier mic? Does it appear to loop via monitor speakers or mains? Spending a little effort isolating the items of equipment involved can give you a basis to simulate the problem (i.e., cause it to happen - like a “forced-failure” test of a jet engine) when no one else is in the room. If you can simulate the problem, you can take steps to control or prevent the conditions that cause it.

Since lavaliers are almost always omni-directional (picking up signal equally from all directions in three dimensions), they tend to be the most frequent feedback culprit mic type. If a user walks into a “hot zone” (minimum distance between mic and primary dispersion region of overhead or monitor speaker) at random, feedback can be the unpleasant result. Educating the mic user (whether they are a preacher or actor) about these zones will help them to avoid these sonic “booby traps.”

Tip: A related issue is lavalier placement on the person’s robe, dress or suit coat. The farther it is from the speaker’s mouth, the higher the gain must be to obtain adequate signal. Unfortunately, the higher the gain, the greater the risk of feedback. Ideally, the mic should be centered, and no more than about five inches below the chin.

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