Few things are capable of ruining a live performance like the screeching
sound of microphone feedback. In this video, I'm teaching
you a five-step process to eliminate microphone feedback before it happens,
but if this is our first time meeting my name is Kyle. Welcome to Audio University.
Anytime there's a microphone sending signal to a speaker in the same room, there's a chance that
a feedback loop will be created. The signal can only be amplified up to a certain point before
feedback will occur. The microphone signal is amplified through the speaker then the sound from
the speaker is picked up by the microphone and amplified through the speaker again.
Imagine a vocalist singing into a microphone on stage. The point at which the sound from
the speaker becomes louder at the microphone than the sound from the vocalist, feedback will occur.
The amount of amplification that's allowed before this point is called the maximum
gain before feedback and by following these five steps,
you'll drastically increase the maximum gain before feedback of your system.
The most effective way to increase your system's maximum gain before feedback is to provide
more space between the microphone and the speaker. The main speakers are the speakers
that point toward the audience. It's best to get as much distance as possible between the
microphones on stage and the main speakers. This will allow the sound to attenuate so much that
it won't cause a feedback loop by the time it reaches the microphone.
Stage monitors are the speakers on stage pointing toward the musicians. The signal from a microphone
will be sent to probably a monitor wedge that will allow the vocalist to hear his or herself sing.
It would be counterproductive to put the stage monitors as far away from the microphone as
possible because the vocalist is right next to the microphone and that would just mean that
the speaker has to be turned up more. Instead try to get the speaker as close to the vocalist
and as on axis with the vocalist as possible so that less amplification is required. Remember that
the closer a speaker is to the listener, the quieter it can be. That's why IEMs (or in-ear
monitors) are so useful for live sound production because they can be inside the musician's ears
and, therefore, can be extremely quiet while still providing adequate level to the person listening.
Not only that, but if you can convince musicians to use in-ear monitors it will quiet down the
level on stage which will probably lead to a cleaner, easier-to-mix front of house experience.
Using directional microphones and speakers is another way to increase your system's
maximum gain before feedback. This will allow the speakers and microphones to be
in closer proximity to one another without causing a feedback loop.
The most common polar pattern for microphones in live sound reinforcement is cardioid. One reason
cardioid mics are so popular in live sound is that they reject the sound coming from the
speakers and therefore increase the maximum gain before feedback of the system. When placing the
microphones on stage, consider the microphone's polar pattern. This graph shows that cardioid mics
reject sound best from the rear. If a microphone has a cardioid pattern such as the Shure SM58,
in theory you should place it so that the rear rejection point faces toward the speaker.
Depending on the size of the stage, the spacing between the microphones and speakers,
and the types of microphones and speakers you're using,
certain frequencies will tend to feedback sooner than others. For each instrument,
set a high pass filter as high as you can without affecting the instrument's sound.
To learn more about high pass filters, how to use them, and how they work you can watch this video.
Ringing out speakers is the process of finding and eliminating feedback with EQ. Using an equalizer,
you can eliminate the first frequencies that feed back without affecting the other frequencies.
A graphic equalizer is a great tool for working quickly. It's important to understand that less
is more during this process. If you follow these steps, you'll make sure that you're not doing more
harm than good. First ensure that the vocal microphone preamp is set as low as possible.
Next send the vocal microphone to the nearest monitor at unity gain.
This means that the auxiliary send to the monitor is set to 0 dB.
Start to bring up the microphone preamp slowly. When you hear a frequency starting to feedback,
reduce that frequency by 6 dB on the graphic EQ. Repeat this process for the next four frequencies
that feedback. Then do the same thing but only reduce the next few frequencies by 3 dB. After
you've found about six frequencies, reduce the microphone preamp gain by 6 dB and speak into the
microphone to determine if the microphone is loud enough without feeding back. It's really important
that you don't overdo this. If you find yourself removing seven, eight, or more frequencies,
you're effectively just turning everything down and degrading the frequency balance of the signal.
Instead, reduce fewer frequencies with the EQ and just reduce the preamp gain you're applying to the
signal. That will usually yield better results for both you mixing and for the musicians on stage.
In a recording studio you sometimes set the preamp gain before anything else,
but while mixing monitors I prefer to use as little preamp gain as possible. To accomplish
this, I recommend setting all auxiliary master faders to unity or 0 dB. In general, each musician
will want to hear their own instrument more than anyone else will. Start with the kick drum sent
to the drummer at unity and set the preamp gain based on how much the drummer needs.
Start with the guitar microphone sent to the guitarist at unity and set the preamp gain based
on how much the guitarist needs, and so on. Once you've set the preamp gain for each instrument
based on how much the musician playing that instrument needed in their monitor, go ahead and
use the aux sends to the other monitors to give the other musicians what they need. The reason I
make this recommendation is to avoid unnecessary amplification. If you add a ton of preamp
gain only to send a tiny amount to the monitor wedges, then that preamp gain was unnecessary.
How you place microphones on stage will play a large role in reducing feedback.
Keeping the microphone in close proximity to the sound source will help reduce feedback. The
further a vocalist is from their microphone, the more gain you'll need to use to get an
adequate level. If the vocalist stays close to the microphone less gain will be required, reducing
the chances of feedback. I already mentioned the microphone polar pattern earlier, but did you know
that the way you hold the microphone can actually change the polar pattern of that microphone?
A common mistake in microphone technique is to cup the microphone. This mistake can turn a cardioid
microphone that picks up sound from the front into more of an omnidirectional microphone that picks
up sound evenly from all directions. If you've got any experience working with musicians you
know that you can only really control this up to a certain point. The musician's microphone
technique will either make your job as an audio engineer much more difficult or much easier.
And while you can't directly control the musicians, the equipment, or the environment,
if you follow these steps you'll set yourself up for success. Here's another bonus tip.
Choosing the right speakers for the situation will help reduce the chances of feedback. If
you want some help choosing the best speakers, check out the free speaker specifications guide
at audiouniversityonline.com/speaker-specs-guide/. Hit the "Like" button if you found this
video helpful and subscribe to Audio University for more content like this.