Microphone feedback is a real issue during a live performance or presentation. It can be both loud and distracting. Here are a few tips on how to avoid this issue and ensure that your audience hears your voice loud and clear!
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- Keep the microphone behind the main loudspeakers to minimize the sound that can reenter the microphone. If the microphone is in front of the speakers, then feedback is nearly guaranteed. You may notice this when a performer or presenter steps out into the crowd and finds themselves in front of the speakers. More often than not the result is that loud, screeching sound.
- Use a microphone with a unidirectional (cardioid) polar pattern. A cardioid microphone has its maximum sound rejection at the rear of the mic. Keep monitors or loudspeakers aimed at this area of maximum rejection. Please note that an omnidirectional microphone picks up sound equally all around the microphone and has no area of sound rejection. It is much harder to keep sound from reentering an omnidirectional microphone.
- Place the microphone close to the sound source. When you reduce the distance between the sound source and the microphone by half, you double the sound pressure level at the microphone. This is an application of the inverse square law. It increases your gain before feedback (i.e., it allows your sound system to produce more SPL before reaching a level that would induce feedback). In other, simpler words, if you move the microphone closer to the sound source (your mouth, for example) the sound will be louder, so you can turn down the volume at your mixer. This will greatly reduce the likelihood of feedback.
- Feedback will occur at different frequencies at different volumes. Use an equalizer or the EQ section of your mixer to find the offending frequency and cut back that frequency. There are commercially available feedback eliminators that automatically dampen the frequencies where feedback is occurring. You have to be careful when using these because sometimes they can go too far and notch out frequencies too deeply and make you sound a bit hollow.
Following these steps should help you avoid feedback.