If you've ever been to a live music performance or anywhere else a PA system is being used, there's a good chance you've heard feedback at some point. That awful high-pitched whine often occurs while setting up or checking the system, or, if you're really unlucky, in the middle of a performance or speech.
Luckily, feedback can normally be prevented, or at least the chances of it happening severely limited. If you're using a PA system yourself, feedback is definitely something you'll want to avoid, as it can really spoil your event and cause everyone a lot of discomfort to boot. Follow these tips and you'll hopefully enjoy a screech-free event.
Understanding what causes feedback
Feedback can occur when you're using any speaker with a microphone's sound coming through it live. As its name suggests, the noise happens when the sound from the speakers gets fed back into the microphone, which creates a loop of sound.
This feedback loop happens so fast that a high-pitched frequency is generated, and it will continue until the loop is broken in some way. This can be done either by cutting the power to the PA, disconnecting or switching off the mic, or moving it into a position where the speaker output is no longer being fed directly into the mic.
Positioning your microphones
One of the simplest ways to limit feedback is to just make sure the microphone is as far away from the speakers as possible while it's in use. You should also try to avoid having it pointed directly towards them.
This can be a challenge in small areas, and when you have a performer or speaker moving around as they use the microphone. Try to work out a safe area and encourage people to stay within it, perhaps marking it with tape.
If you have multiple microphones on the go, the principle is the same, but there's a higher risk so more careful planning is needed to stop feedback from happening.
Perfecting your PA setup
If you find you're struggling with microphone feedback despite taking care over your mic and speaker positions, try switching to a unidirectional mic. This will only pick up sound from one angle, limiting its potential for picking up stray noises.
A good quality graphic equaliser is also a useful bit of kit for any professional PA. When you're setting up a microphone, by carefully increasing the volume of its channel until feedback occurs, you can push it back down slightly and stop feedback.
If all else fails, automatic feedback eliminators are available that can be plugged in between the mic and the mixer, dealing with feedback the easy way.