Maybe it’s happened to you before — you’re on stage and ready to perform, but you hear a sudden, high-pitched sound. But then it gets louder. And louder. And louder. This dreaded sound is an assault on your ears and the ears of your audience members, but the good news is that you can prevent it.
What’s That High-Pitched Sound?
The high-pitched sound you hear coming from your microphone is most likely what’s known as feedback. It’s often a sharp, shriek-like sound that continuously gets louder (and very quickly becomes extremely loud). The mechanism that causes feedback is very simple.
If you spend a lot of time around PA systems or guitar amps, you know that they are not completely quiet. When the amp or system is switched on, it creates a low hissing sound. On high-quality speakers, the hiss is kept to a minimum, but it may be louder on low-end or damaged speakers. The volume of the hiss also depends on speaker volume — if a speaker is louder, the hiss will be louder, too.
Now normally, the hissing sound is very quiet compared to the music coming out of the speakers. It isn’t enough to be distracting to listeners. However, if your microphone is facing the speakers or amps (or even if it’s just turned a little too far in the direction of a speaker), you can experience feedback.
This is when the normally almost-unnoticeable hissing sound is picked up by the microphone. That signal is then amplified by the PA or amp and picked up again. The result is a powerful sound that rapidly becomes louder and louder. The constant re-amplification happens at the speed of electricity (just a little slower than the speed of light), so when you run into feedback, you’ll get hit by a near-instant shrieking sound. The process is called “feedback” because the microphone and speakers continually feed into one another, amplifying the signal.
If you’ve been unfortunate enough to run into this issue, you’ve probably seen someone rush to the stage to unplug the mic. It’s a lot better to prevent the feedback issue than it is to deal with it after it happens. Fortunately, there are several ways to prevent it.
How Do You Stop It From Happening?
The first way to prevent feedback noise involves being careful about angles. You’ll want to position the microphone and speakers so they don’t have the opportunity to start feeding into one another. The best position for feedback prevention has the mic positioned behind the speakers, with the speakers facing toward the audience.
Of course, this position isn’t always possible. If you can’t control the placement of the speakers, you can at least control their angles relative to the mic. Do your best to angle the speakers away from the microphone. So if you have two speakers and a microphone set up, you don’t want the mic pointing directly back and the speakers pointing directly forward. Instead, you can turn the speakers so they’re facing closer to the sides of the stage.
If you’re playing at an established venue, chances are good that the speakers and mic are already set up correctly. But when you need to set up your own PA, it’s important to know how to place your mic and speakers.
If you’re using your microphone and frequently experience feedback issues, you might want to look into purchasing a microphone or wireless mic system with built-in feedback reduction systems. While it’s still wise to make sure you’ve placed your mics and speakers in a way that reduces feedback risk, a feedback reduction system just adds that extra layer of protection.
If you don’t have an anti-feedback system, adding a little bit of delay (a very little bit — only a couple of milliseconds) to the microphone can achieve nearly the same effect. You might use an effect pedal to do this, or the PA system may have a built-in delay effect to use. Depending on your gear, this might not be possible. But if you have someone else managing your sound, chances are good that they’ve already taken this step.
You can also work with an experienced sound engineer. Most music venues have a sound engineer working, but in some cases, you may need to work with your own. A capable engineer will be able to stop feedback using EQ. To do this, they identify the exact frequencies that are causing problems and then effectively scoop them out.
What Other Issues Could It Be?
If your mic is making a high-pitched sound that doesn’t continually get louder, it likely isn’t a feedback issue. Sometimes, speakers and mics run into something known as “interference.” Cell phones radiate an electromagnetic field, and this field can enter the mic capsule and cause noise. Cell phone interference usually creates a stuttering sound that can vary in pitch. Interference can also sometimes be caused by a car engine, although this type of interference usually creates a high-pitched whining noise.
Typically, dealing with interference is fairly easy — ask everyone in the vicinity who has a cell phone to turn it off. This is part of why many movie theaters ask you to turn off phones. If car engine interference is an ongoing issue (and you own or are in charge of the performance venue), it may be worthwhile to invest in some soundproofing for the walls closest to the noise.
If you’re having trouble controlling interference around the microphone everywhere you go, it might be worthwhile to invest in ferrite rings. These are small rings that, when attached to a cable, help reduce interference. These little metal rings aren’t a perfect solution, but they can help you get interference under control. Ferrite rings are also very affordable, so they’re a helpful solution if you’re on a budget, too.
Hopefully, by the time you get to your next gig, you’ll know exactly how to deal with feedback or interference as they arise. Just remember to set things up carefully, and everything should go smoothly.