Question: How do I prevent microphone feedback?

Answer: Feedback, also known as the Larsen effect, occurs when the amplified sound from any loudspeaker reenters the sound system through an open microphone and is amplified again and again, causing a loop. We often tell customers that feedback is not the fault of the microphone because any microphone will feed back given the right conditions (or maybe in this context, wrong conditions). However, there are some steps that you can take to avoid or lessen the likelihood of feedback. Try some of these:

• Keep the microphone behind the main loudspeakers to minimize the sound that can reenter the microphone. If the microphone is in front of the speakers, then feedback is nearly guaranteed. You may notice this when a performer or presenter steps out into the crowd and finds themselves in front of the speakers. More often than not the result is that loud, ugly, screeching sound.

• Use a microphone with a unidirectional (cardioid) polar pattern. A cardioid microphone has its maximum sound rejection at the rear of the mic. Keep monitors or loudspeakers aimed at this area of maximum rejection. Please note that an omnidirectional microphone picks up sound equally all around the microphone and has no area of sound rejection. It is much harder to keep sound from reentering an omnidirectional microphone.

• Place the microphone close to the sound source. When you reduce the distance between the sound source and the microphone by half, you double the sound pressure level at the microphone. This is an application of the inverse square law. It increases your gain before feedback (i.e., it allows your sound system to produce more SPL before reaching a level that would induce feedback). In other, simpler words, if you move the microphone closer to the sound source (your mouth, for example) the sound will be louder, so you can turn down the volume at your mixer. This will greatly reduce the likelihood of feedback.

• Feedback will occur at different frequencies at different volumes. Use an equalizer or the EQ section of your mixer to find the offending frequency and cut back that frequency. There are commercially available feedback eliminators that automatically dampen the frequencies where feedback is occurring. You have to be careful when using these because sometimes they can go too far and notch out frequencies too deeply and make you sound a bit hollow.

Following these steps should help you avoid feedback. But if you continue to run into feedback issues while using your A-T mic, please contact our Audio Solutions Department so we can troubleshoot the problem. And, as always, be sure to check back next Wednesday for a new “Question of Week”!