Feedback in audio systems is a high-pitched ringing noise, usually caused by a microphone picking up sound from the speakers. To prevent it you can:
Reduce the volume of the speakers so less audio is picked up by the microphones.
Mute any microphones you aren’t using.
Position microphones away from speakers and avoid pointing them directly at the speakers. Most vocal microphones are directional and will reject more sound from the back
Adjust the EQ on the mixer to lower frequencies that are prone to feedback.
Our mixers have an Automatic Feedback Suppression system which is on by default. This works by automatically applying EQ to cut only the frequencies which are beginning to ring