(The original version of this article was first published on the Mp3 Backing Trax website circa 2006 – 2012)
Why you get microphone squeal/feedback
Microphone squeal is caused by feedback. Feedback happens when the microphone picks up the output sound from your speakers which it then re-amplifies causing a loop. The loop is caused by the microphone picking up the original amplified sound and amplifying it again, then again, then again, then again, until the sound can’t be amplified any more and something has to give.
Feedback has the capacity to blow your speakers or amplifier, although it has to be said that most modern amplifiers these days have protection built in to protect it from any lasting damage.
Nevertheless, feedback is a serious problem. Even if it doesn’t blow your amplifier or your speakers, it WILL drive you (and your audience) to despair.
Feedback usually presents itself in the form of a bassy boom or a high pitched ear-piercing sqeal depending on whether your microphone is picking up low frequencies or high frequencies.
What your microphone should and should not pick up
The only sound your microphone should pick up is your voice. It should then send your voice to your amplifier which, in turn, amplifies the sound and puts it out through your speakers. But if your microphone picks up any other sounds other than your voice, especially sounds coming from your speakers, it will then amplify and re-amplify those sounds in a never ending loop until something gives (usually your audiences ears)!
Feedback is a common problem when singing live. It’s more common in small venues where the microphone can easily pick up the sound from the main PA speakers. This is because in small venues you will usually have your main PA speakers fairly close to you. Your microphone picks up the sound from the speakers and, hey presto, the microphone starts to squeel and you have a feedback problem.
Also, in general, the more microphones you have on a stage at any one time switched on, the more feedback you are likely to get. This is because microphones will often feedback with each other.
How to cure microphone feedback – Tip 1
Fortunately there are a couple of ways to reduce microphone feedback when singing live. First, switch off microphones when they are not in use. For example, if the compere has a microphone he uses to introduce your act, switch it off as soon as he’s introduced you. If any others in your band are NOT singing a part in the song that’s curently being performed, tell them to switch off their microphone during that song.
A microphone which is not in use but switched on is like a sitting duck – it’s just waiting to pick up any rogue feedback frequencies and cause you problems. The golden rule is if it’s not in use, switch it off!
How to cure microphone feedback – Tip 2
When singing live, keep your microphone as close to your lips as possible but without actually touching your lips. Keeping your microphone close up to your mouth when singing live will allow you to reduce the overall volume of your microphone slightly at the mixing desk end and this is often just enough to stop the feedback.
I often see singers holding their microphone 6 inches to a foot away from their mouth when singing and then they can’t figure out why they are getting so much feedback. Holding a microphone far away from your mouth is only possible when you have an exceptionally big powerful voice, the premise being that if you DO have a big powerful voice, then you won’t need so much volume on your microphone and you won’t have feedback problems anyway.
Most male and female singers do not have a big powerful operatic type voice…more than 90% of singers have normal strength voices. This means that in most cases the microphone needs to be set at a reasonably high volume level to pick up their voice and that means feedback can be a problem. So if you find yourself in a live music venue where the EQ hasn’t been set by a professional sound engineer specially to suit that room prior to you singing in it, then keep the microphone closer to your lips. This will allow you to reduce the volume of your mic a little and therefore help reduce any feedback.
Just let me expand a little bit to be clear on this point. I know you’ve probably watched singers on TV holding the microphone quite far away from their mouth so maybe wonder why I’m telling you that you can’t do this. You see, if you are in a professional recording studio, a TV studio, or some theatres, you can often get away with holding a microphone at arms length because the acoustics in these places have been professionally set by professional sound engineers and the speakers have been carefully placed and EQ’d so that feedback is not a problem.
But you, as a gigging singer/entertainer, are unlikely to be in the same venue every night and even if you are, your PA has not been set up by a professional sound engineer. So for everyday types of live music venues that you will be singing in with your own PA system, keep your microphone fairly close to your mouth (except when you hit those big high notes of course) or feedback WILL be a problem.
How to cure microphone feedback – Tip 3
Another way to reduce feedback is to adjust the EQ on your microphone channel and take a little off the top-end (i.e. turn down the treble). This is because most microphone feedback tends to occur more commonly in the upper/treble frequencies (although bass feedback does happen too).
Bass feedback is more of a loud booming sound whereas high frequency feedback is more of a high pitched squeal.
Just be careful when using your EQ to cut frequencies though. If you take too much treble away from your microphone you could end up with a muffled vocal sound. Take too much bass frequencies away and you may be left with a tinny or thin sound to your vocals.
Higher end, expensive, mixing desks will have more comprehensive EQ settings than most standard gigging mixing desks. With a really good mixing desk you can scroll through the frequencies till you find where the feedback is occurring and “cut” that frequency without affecting any of the other frequencies. This is without doubt the best way to cure feedback problems. However this is more the realm of professional sound engineers so it’s probably not the sort of thing a normal singer would want to spend time learning to do. The process of “ringing out a microphone” is quite an involved process with quite a large learning curve, although in my opinion it is worth learning about if you really want to be guaranteed a good sound everywhere you perform.
Using a Feedback Destroyer
Another option may be to invest in a hardware device called a “Feedback Destroyer” which pretty much does what its name suggests. I had one of these in my live music gigging rack a few years back and it does a great job.
The only reason I stopped using it was because I prefer to find the feedback frequency myself and fix it rather than letting the machine do it for me. I just felt the machine took away a few unnecessary frequencies in its attempts to fix the problem. I felt that doing it manually gave me a bit more control over my sound.
But for anyone who doesn’t know how to find feedback frequencies, set Q factors, and cut them by the right amount of dB’s etc, a Feedback Destroyer machine will do most of all that work for you and could be an easy-to-use alternative to doing it all manually.