Preventing Microphone Feedback

There are so many parameters to juggle while mixing live and it’s easy to get stressed about the possibility of microphone feedback. Here are some things that can impact feedback:

• Room acoustics

• Speaker placement

• Speaker volume

• Speaker tuning

• Microphone placement

• Mic technique

• Singer/speaker volume when presenting

• Channel EQ

• Channel dynamics

• Channel volume

That’s not even an exhaustive list!

Feedback occurs when the microphone passes through the speaker system loud enough for the microphone to start amplifying the sound coming from the speaker system. This then creates a feedback loop which typically starts as a small ringing frequency and then grows louder and louder before it turns into a full constant tone.

When Feedback Occurs:

The first action for us to perform when there is feedback is to cease the feedback. This typically involves turning the volume of the channel down or, in serious cases of feedback, completely muting the channel. I personally prefer lowering the volume as it is less distracting than muting the channel.

After the feedback is gone, I will turn the channel back up to the point where it starts to feedback, and then I will pull it down by 1 or 2 dB. I will then take note of where the fader position is at.

Gain Before Feedback

We can talk about feedback with one main measurement and that is ‘gain before feedback.’ Gain before feedback explains how much a channel/microphone can be turned up before it starts feedback.

There are multiple actions we can take to increase the gain before feedback of a channel.

Use an EQ or Graphic Equalizer.

• Using an equalizer to find the frequency that is feeding back and either removing this frequency from the main PA, the monitor speakers, or the channel can help with increasing the gain before feedback.

• A graphic equalizer can be used to identify and reduce the frequency ranges that are most prone to feedback. Start by reducing the gain on the frequency band that is most prone to feedback (usually in the midrange frequencies), and adjust as necessary based on the specific situation.

Position the microphone properly.

• The position of the microphone can greatly affect the likelihood of feedback. Position the microphone as close as possible to the sound source (the speaker's mouth) while maintaining an appropriate sound quality distance. Also, make sure that the microphone is not pointing towards any loudspeakers or monitors, as this can increase the risk of feedback.

Use a directional microphone.

• A directional microphone, such as a cardioid or hyper-cardioid microphone, can help to reduce the amount of ambient noise and other unwanted sounds that the microphone picks up. This can help to minimize the risk of feedback, especially in noisy or reverberant environments.

Reduce the overall system gain.

• Feedback occurs when the microphone picks up sound from the loudspeakers, which is then amplified and fed back into the system. By reducing the overall system gain, you can reduce the amount of sound that is picked up by the microphone and therefore reduce the likelihood of feedback.

Use a feedback suppressor.

• A feedback suppressor is a device that is specifically designed to detect and suppress feedback. These devices use sophisticated algorithms to identify the frequency ranges that are prone to feedback and dynamically reduce the gain in those ranges.

Use a noise gate.

• A noise gate is a device that can be used to reduce the amount of ambient noise that is picked up by the microphone. By setting an appropriate threshold level, the noise gate can automatically reduce the gain of the microphone when it is not in use, which can help to reduce the overall level of ambient noise and reduce the likelihood of feedback.

The Biggest Impact on Gain Before Feedback

All of the listed actions above are great to use at the moment, however, the largest factor for controlling feedback is the speaker system design and placement of the speakers.

Make sure that the placement of the speakers is such that the presenter or singer is NOT in front of the speakers. Having the presenter or singer outside of the speaker coverage will have at least a 10-20 dB difference in gain before feedback.

In the case of using floor monitors, you would need to have the singer in front of the floor wedge to hear their required mix. In this case, it is best to use the directionality of the microphone in the best way and to place the floor wedge in the null of the microphone.

Lastly, be cautious of the volume needed by the band member from the floor wedge. If feedback is becoming an issue, and the steps above have been taken, then have a conversation with the artist and request that the monitor volume be lowered to give a better experience for the audience.

Watch my video below to see some of these tips in action!

Until next time,

Drew

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