A couple of months ago while at a Networking Event, a speaker got up and about 5 times in their 20 minute talk, feedback happened. As most of the audience looked perplexed as to what was going on, the speaker said "I guess the microphone just doesn't like me." That wasn't the case. As he moved around the 'stage' area, there were specific spots he moved into that before it even happened the first time, I was prepared for it. After the event, I spoke to the organiser and mentioned a very quick fix to cutting out the problem of feedback. But, it reminded me how over the years, just how little people know about feedback, especially with how common it is.
We've all been there. When you go to an event, whether it's a gig, a seminar or anything else that requires a microphone and a speaker. Somebody is at the front, and all of a sudden a piercing, screeching sound comes out across the room. Your face screws up like you're listening to the phattest of Dubstep tunes, your head turns away like you've been caught peaking at your mum and dad wrapping your Xmas presents and your hands cover your ears like my mum did when I listened to the phattest of Dubstep tunes as a teenager... and an adult!
If you're at a large enough event, it seems to be the automatic response for everybody to turn their heads to the back and stare at the sound engineer, sometimes shaking their heads, maybe even tutting. As a sound engineer who spent most of their early career working live gigs in multiple different scenarios, it feels that way. Everybody staring, waiting for you to come up with the magical fix and telling you with their eyes that you better not do that ever again. It's daunting.
Feedback, and that whole rigmarole of misplaced blame can be avoided. Feedback is not a complicated thing. I'm going to discuss what feed back is, why it happens and then I will give you a couple of tips on how to avoid it. These all apply to all, whether you're a musician or a speaker, hopefully this will help you to avoid arguably the most common mistake in sound.
What Is Feedback?
We're not talking about someone letting you know what they think - we're talking about that high-pitched screech coming through the speakers (not my mum's interpretation of what the phattest of Dubstep tunes sound like).
In basic terms, feedback is a continuous loop of energy that spins round through a sound system. It's very easy to come across, very easy to fix but feels almost impossible to avoid.
How Does Feedback Occur?
As mentioned before, feedback is a loop of energy. The 2 main components are the speaker and the microphone. First off, to make it clear, we'll look at what exactly a mic and speaker do.
A microphone serves the purpose of taking in acoustic energy (your voice, an instrument etc.) and turning it into electrical energy.
A speaker's purpose is taking electrical energy and turning it into acoustic energy.
Once the sound leaves the speaker, it makes its way into your ears.
So, when you speak into a mic, sound travels through cables, gets turned into electrical energy, and back out of a speaker being turned back into acoustic energy. Feedback occurs when sound leaves the speaker and goes back through the microphone. Which, in turn, goes back through the system, out the speaker, into the microphone and so on. That is feedback. When using a microphone and speaker, the system amplifies the signal. Even when you don't speak, the speaker emits the signal which the microphone picks up.
When going through a sound system, the speaker, microphone and other pieces of equipment pick up certain frequencies better. The reason behind the high pitched, screeching sound is that the signal going round the system is being picked up and amplified slightly more at specific frequencies, especially higher frequencies.
Usually, when you are speaking or performing, you aren't near the speaker. Speakers are facing towards the crowd and not you. If you are performing on a stage with monitors, performing on a small stage or performing on a large stage but move around a lot with bad speaker placement, the chances of feedback are much higher.
How Can I Stop It?
Avoiding feedback is pretty simple. Some situations are more prone to feedback than others, but I'm going to give you three tips to avoid feedback in most situations. These tips come from the main 3 causes of feedback.
1) If you are an engineer, or the person who's responsible for plugging the microphone into the system - don't turn the microphone up all the way. The less you are boosting the signal, the less feedback. Try and get the person speaking to hold the mic closer to their mouth or speak louder.
2) If you can, keep away from direct contact with speakers then do. Normally, you will find speakers are either side of the stage and at the front with the source of audio behind them, but that's not always the case. Sometimes speakers are further back the stage, sometimes are tilting or turning more centrally, sometimes there are on-stage monitors facing directly into the stage and at the source. But, whenever you get up on stage, make sure you know where the speakers are and what parts of the stage to avoid.
3) Mic technique. Beware of the mic technique. This is a very, very common cause of feedback. A few years ago, while at University, I was covering a gig as part of an assignment. A small performers college in London was teaching their students about touring as an artist and put together a UK tour. One gig was at Band on the Wall where I was doing work experience and shadowing. One specific performer, a rapper, when not rapping, put his arm down and pointed the mic directly at the on stage monitor. Like, maybe a foot apart but directly in there. This, as we've figured, caused feedback constantly. There were 4 sound engineer students, the in-house sound engineer and our live engineer tutor all at the back of the room behind the desk flailing our arms around like we were signalling down a passing ship on a desert island. Signalling 'NOOOOO STOOOOOOOOP', but he didn't listen and we caught HELL until we all went mad and told them why it was their fault.
Another mic technique problem comes with how you hold the mic. Now, bare with me while we get pretty technical.
Chances are, if you are performing or speaking, you will have an SM58 or another mic exactly like that. Otherwise know to some as a 'Lollipop mic' for its lollipop shape. These mics have a 'polar patterns' which explains a microphones ability to pick up sounds coming from different angles. We will look at 2
Your microphone comes naturally with a 'Cardioid' polar pattern, given the name because of the pickups resemblance to a heart.
As you can see in image above the microphone primarily picks up what's in front of the mic, but will pick up a little bit from behind and to the side. Note that the pattern starts at the silver line going across the head.
The handle of the mic is not just there to protect the parts inside, it's there for you to hold. It's very important that you hold the mic there and not half on the head, but too many people hold the mic covering the bottom half of the head.
When the bottom half of the microphone head is covered, it confuses the diaphragm and this turns the mic from a 'Cardioid' pattern to an 'omnidirectional' (omni for short) polar patter. Omnidirectional means all directions.
As you can see in the image above, the mic picks up on the sides and behind, equal to what it was picking up from the front. So should the microphone be close enough in any direction to a speaker, it will pick up whatever's coming from the speaker. Once the energy comes from the speaker, back into the mic, the feedback starts.
Feedback is a simple issue with simple solutions, but more often than not, our natural instincts to move in particular ways, or hold the mic a certain way, will cause feedback to occur. If you are speaking, or performing, you need to be aware of what you can do to minimise the risks. Some venues and spaces are more prone due to the layout and limitations but it's pretty much avoidable.
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