One of the most awful and embarrassing situations for an audio engineer is microphone feedback during an event. Not only is it painful for our ears, but it can interrupt the flow of an entire performance or event. Audience members may become skeptical of your abilities and event planners will look for someone to blame. Essentially, feedback is the last thing you want while running sound. Here are a few tips to help prevent feedback.
1. Microphone Position & Polar Pattern
Different microphones have differently shaped areas from which signal can be picked up. It is essential to know your microphone’s specific polar pattern before you use them live. Knowing your microphone's polar pattern helps you to adjust where you will place stage monitors to avoid signal feedback into the microphone.
2. Know the “Point of Feedback”
Once you have adjusted and set your gain, slowly ride your mixer's fader up until you begin to hear feedback. Make a mental note or even use a piece of console tape to depict where feedback will ensue visually. If this level is too low, the microphone position or monitor position may need adjustment. This line is your limit and should only be crossed when required during certain moments when headroom has increased. Always make sure you bring it back below the line as soon as possible. Remember, feedback is acceptable during soundcheck. This is when you are feeling everything out and learning how the sound sources and stage configuration interact.
3. Use EQ
Using your ears or a real-time analyzer (RTA), determine which frequencies are spiking and feeding into each other. To do this, set all faders just below the point of feedback and raise the stage monitor levels up one at a time until they begin to feedback. When a frequency starts to spike, use a parametric or graphic eq to notch out the troublesome frequency pre-fader on the monitor output. Be careful not to tweak the EQ after this.
4. Carefully Watch Your Stage Volume
The louder your stage volume is, the higher the chance for feedback gets. Try keeping your monitor levels as low as possible. Once a musician is happy with their mix and level, you can usually get away with turning the volume down slightly when they are not looking. Furthermore, consider using in-ear-monitors when possible. This reduces stage volume drastically which in turn reduces the chance for feedback.
5. Always Mute Unused Microphones
It is a good idea to mute microphones that are not in use at any given time. This helps to reduce the amount of pickup from the stage, which in turn allows you to push the unmuted microphones louder. Additionally, unused microphones pick up bleed which can only muddy up a mix.
6. Teach Performers Proper Mic Technique
It is often not the equipment but the performers that increase your chances of feedback. When an inexperienced performer does not have a proper projection technique, feedback can often leak in. Always remind them that it is ideal for them to be as close as possible to the microphone.
7. Use Direct Boxes Instead of Amps
Use a direct box instead of an amp as much as possible. Instruments like keyboards or bass guitars usually do not depend on an amplifier for their tone. Using a DI box eliminates having another microphone on stage. Going direct will also reduce stage volume, and you will have a cleaner signal.
8. Always Be Alert and Ready to Mute
Keep an eye on all live microphones at all times and their position on stage. A singer walking in front of a PA stack or an MC waiving a microphone near a stage monitor are all common causes of sudden feedback. If this happens always be ready mute the affected channel or quickly throw a fader down, your audience will thank you.