AUDIO TIPS by Jim Wilkens, A1 at AVFX
If you overhear your audio engineer using the phrase “gain before feedback” (or the Barkhausen Stability Criterion) they’re referring to how strong the microphone’s audio signal can be before the speakers start to ring. In other words: how loud can you turn up the sound before the loudspeakers start to screech and the audience begins to cringe?
The only one who feels worse than the presenter is the meeting planner.
Audio feedback is one of the worst things that can happen during a presentation and yet it’s probably the most common problem that meeting planners experience.
Microphones always “hear” the sound from the loudspeakers and that sound is fed back through the microphones and out to the speakers again. This situation is called a “feedback loop” and is present when the microphones and loudspeakers are in proximity. That horrible screeching sound occurs when the sound entering the microphone from the loudspeakers is actually louder than the original voice or source sound. Managing the gain before feedback is always one of the audio engineer’s top priorities.
Actually, in a live sound system, the ever-present “feedback loop” is always there even when the ringing is not present, other subtle problems might occur. When your presenters sound hollow, nasal, or boomy, the cause is often the feedback loop from microphone to loudspeaker to microphone.
Good system design minimizes issues of feedback by ensuring the correct placement and selection of speakers. Good system tuning, skillful live mixing and use of equalization all serve to minimize the effects of that ever-present feedback loop.
Don’t let the feedback loop upstage your prestigious presenter. Always trust your audio engineer.
SEE ALSO: The Physics of Audio