Feedback occurs when an audio signal "hears itself" on an nearby speaker, creating a loud noise at a specific frequency.
Following these steps, you'll learn how to eliminate feedback onstage.
- Have the right equipment. Aside from your mixer, monitors, and amplifiers, you'll need a graphic equalizer (EQ) on every channel. You'll wire the send from the board into the EQ, and then into the amplifier. You need to be able to access the EQ from your mix position. If you're working in a studio environment, be aware of what effects the EQ will have on both wedge mixes and your headphone mixes.
- Identify the frequency feeding back, and why. Usually, feedback starts as a hollow, echo-like sound, then graduating to a piercing, high-volume squeal at a specific frequency or set of frequencies. Also, figure out where it's coming from -- if it's a specific microphone, sometimes some easy EQ on the individual channel can clean up the mix.
- Is it in the monitors, or in the house? Sometimes, feedback occurs in the house mix. If you suspect feedback in the house, turn the overall house volume down until it goes away; then, follow the upcoming steps to remove the feedback. If it's still there, chances are it's in a monitor mix.
- Identify the frequency. If you're bad at this, you might want to buy a handheld RTA (real-time analyzer). However, if you can, find the frequency with your knowledge of what frequencies are which. Typically, monitors will feed back in the 1.2, 3.5-5kHz range on the high end, and around 630Hz on the mid-low end.
- Now, using the graphic EQ, reduce that frequency range in few decibel increments. If you've found the frequency, and reducing it introduces another range of feedback, you need to look at your gain structure again. Normally, any hot-spots can be eliminated quickly; if it's continuing after your first sweep of EQ, it's something that can't be fixed by EQ.
- If EQ will not stop feedback, or you're finding it hard to EQ enough out to eliminate your feedback, your channels going into the monitors may have their gain too hot. Re-do your gain structure, paying careful attention to what signals are going where, and how hot the signals are in your channel meters, and your problem will, more than likely, go away.
What You Need
- Monitor Speakers
- Graphic Equalizers (EQ)
- Monitor Mixer or FOH Mixer with Aux Sends
- A good ear and/or RTA