What is feedback?
That screech you hear from the sound system when you hold the mic wrong? That’s Audio Feedback.
No, no, not negative comments -- Audio Feedback is when sound from the loudspeakers comes back into the microphone, creating a “feedback loop” and causing an awful howl.
Here's a graphic explaining what feedback is and how it works, and you can watch a video explanation here:
So I know what it is, but how do I prevent it?
If you have a sound technician in the room, it’s their job to keep the screech away, but how do you prevent it when you’re on your own? Read on for some of the most useful tips to prevent microphone feedback at your events.
Use directional microphones to your advantage
Most microphones you’ll encounter at venues are “Unidirectional” - microphones that pick up sound from the front, and reject sound from the back. Make sure you keep the microphone on stage and that the microphone is behind the main speakers - Feedback is caused when the microphone picks up the amplified audio from the speakers, so make sure the mic can’t “hear” the sound from the speakers.
Speak close to the microphone
If you speak closer to the microphone, it will pick up more sound from your voice compared to the background noise, increasing the clarity of your voice and reducing the chance for feedback. If you’re going to shout or belt out a loud note, make sure you back away a bit to avoid overpowering the microphone or sound system, which can cause distortion, and possibly damage.
Turn off unused mics
You get a lot more volume from your sound system without the risk of feedback when you have one mic on than if you have 4, or 20 mics turned on. Make sure you limit the number of microphones in use at one time by turning off or muting unused microphones. If you’re on a panel where you take turns speaking, you might mute your mic in between comments.
(We sound geeks call the amount of volume you can get without problems "gain before feedback," and it is reduced with every additional open microphone. See a more technical explanation on Wikipedia here: https://en.wikipedia.org/wiki/Gain_before_feedback.)