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Dealing with feedback problems; Graphic versus Parametric Equalizers

Feedback on feedback.

“Our band has been having problems with feedback in our PA and monitors. I’ve worked with our graphic equalizers quite a bit to improve things, but the problem remains. A monitor engineer recently told me to use a parametric EQ. Can you shed some more light on this?

Minimizing feedback while maintaining a modicum of sound quality isn’t easy. It’s basically an exercise in compromise. First thing’s first. If you turn up any mic/speaker system enough it will feed back, no matter how much equalizing you do. That said, there are all kinds of tricks good engineers use to minimize feedback. The positioning of the monitors in relation to the microphones is critical. Make sure you know the polar pattern of both. Spend some time experimenting. There are more exotic things you can experiment with, like running your monitors out of polarity with the mains, or reversing the polarity of the horn or woofer in the monitors, but you probably don’t need to take it quite that far to realize an improvement.

The most likely reason the engineer recommended a parametric EQ is because a good parametric can better able you to dial in to the exact problem frequency and very tightly notch it out without a significant compromise to the overall sound quality of the system. Graphic equalizers are great; they generally just don’t get in tight enough for this type of precise work. You have to experience the results yourself to fully understand the benefit of being able to very accurately zoom in on a hot frequency like this, but it does take some skill. Further, in a typical live situation these problem frequencies can move around a bit. You don’t notice it that much when using graphic equalizers because they affect a broader band of frequencies, but with the small frequency ranges affected by a tightly dialed parametric things like moving a microphone stand a few inches, or the room filling up with people, or even a change in the relative humidity can change the hot frequency enough to render the parametric useless. If you have a full time monitor engineer (or a sound guy who can stay on top of the monitors) this is no problem, but if your band has to set and forget you need to be careful. A good alternative in those circumstances are the feedback eliminators. These automatically chase ringing frequencies and make EQ adjustments accordingly. Sabine and several other companies make them, and they actually work wonders when used properly under realistic circumstances. Talk to your Sweetwater Sales Engineer for more information on those.

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