Feedback Tuning.m4v

In a live sound reinforcement gig, feedback is to be avoided at all costs. So before the show, the mix engineer will spend as much time as necessary to feedback tune or "ring-out the room". Here's how...

A mic is turned up until the sound takes off, in other words, starts to feedback. The mix engineer uses a device called a real time analyzer (RTA) to determine the frequency of the feedback. Then that frequency is attenuated using an equalizer, until the feedback stops. The mic is then turned up again until feedback. The feedback could occur at the same or a different frequency. In any case the RTA is again used to determine the frequency, and the equalizer is notched down at that frequency until the feedback stops. This process is repeated until the sound system reaches it's target sound pressure level.

Ideally, if there are different types of mics to be used as well, each different mic would be feedback tuned as well. In most cases, the mics would be grouped by type and routed to a submaster that would mics.

The EQ pattern that results from the feedback tuning is usually the reverse of the sum of the natural resonances in the room and the non-linearity of the sound system. In any case, once the room has been tuned this way, the chances of feedback are greatly reduced.