Equalisation is one of the best ways to make the most of your equipment and get things sounding perfect. However, in untrained or inexperienced hands it can prove to be your biggest nightmare.
This article is going to teach you how to use your graphic equaliser to eliminate unwanted feedback and give you a head start when it comes to the sound check. Follow these simple steps and learn the easiest way to “ring out” your PA.
Before we get carried away and start running, lets learn to walk first and find out what EQ is and what it does.
Equalisation (EQ) is basically a way to reduce (cut) or increase (boost) certain frequencies in an audio signal. As I’m sure you are aware, sound is a wave form. We can use EQ to alter this wave form by restricting how much of the signal is allowed to pass thorough. It’s a bit like a sieve, we can set how small the holes are in the sieve by how much we want to cut the signal. The more we cut, the smaller the hole and therefore less of the signal gets through.
The opposite is true of boosting a signal, when you increase a frequency the amount is raised. The problem with boosting signals is that you are artificially boosting them, in other words you’re adding what wasn’t in the original source. This isn’t normally too noticeable with small increments, but you should be wary of adding too much. You are far better to use good quality equipment at the source with the frequency response you want, rather than trying to add it in afterwards.
EQ can be used for a number of purposes including noise reduction to remove rumbles or hiss. It can be used for placement to bring a certain instrument forward in the mix. For example increasing bass and treble helps something jump out. Cut them and boost the mid range to sit something back in the mix.
Then there is the entire mix, where you can shape the sound as a whole to bring out the characteristics you want. Perhaps by boosting the bass to bring out the rhythm, or more commonly to account for the room you are in and give it a more natural sound.
The subject of equalisation is massive and this article cannot hope to do the entire subject justice. The idea is to help you prevent feedback on your PA by using EQ.
First of all you should try and set up your equipment suitably. That means sensible microphone placement so you don’t have your vocalist standing right in front of the speakers. You should also be using the correct mics for the job at hand, using an omni-directional mic capsule will be more sensitive to feedback that a Cardioid for example. Look at the images below to see how to pick up of a omni-directional mic could potentially give you more problems than a Cardioid.
Once you are all set up turn the master volumes down for both your front of house (FOH) and monitor mixes and centre all tone controls on each of the channels you are using on your desk. You can use these at a later date to adjust each channel as required, but you don’t want them to effect the frequency response while ringing out. You should also centre all the sliders on you graphic EQ, you will be able to feel the slider click into place when it reaches the detente.
Mute all channels and increase the gain until you are getting a good signal level usually depicted by LEDs to the side of the fader, or possibly a needle on a VU meter at the top of the desk. You certainly want to avoid it peaking out, but you want enough level so that you aren’t turning up your amps too high to compensate. If the source of your signal is weak to begin with you will be fighting a losing battle from the start.
With the mic channel now live, set its fader to 0db. Slowly (and I mean slowly) increase the master volume for either your FOH mix or monitors until you start to hear the feedback. As soon as you hear it stop and pull them back very slightly until it is gone, be careful here because not only can excessive feedback damage your equipment, but it can also do some serious damage to your hearing. Your PA should now be sitting on the verge of feedback, but not actually ringing.
At this point turn your attention to the graphic equaliser and starting from one end, carefully increase each fader slightly. If it doesn’t feedback, return it to the centre and move on to the next one. Eventually you’ll hit the right frequency that is causing the feedback, this time instead of re-centring it move it down further to roughly the middle of its bottom half. Do this for all the frequencies repeating the same process, if you find one that is particularly sensitive then pull it down a bit further still.
Once you have completed this return to your mixer and slowly increase your faders again. You should find the feedback has gone now, if you can get the level high enough then you’re all done. On the other hand if you still need more level you can repeat the entire process. I wouldn’t recommend doing this more than a couple of times, if you’re still getting lots of feedback try looking at other potential factors discussed above.
Now that you have a “safe” working level you can use the tone controls on the mixer to achieve your desired sound. It’s all fairly simple really, and with practise you’ll learn what the different frequencies sound like and be able to jump straight to the right fader. You’ll also learn how much you need to cut the signal by, it probably won’t be as much as I’ve told you in this article.
Of course there are other options out there, you could for example employ the use of a “feedback destroyer”. This is essentially a graphic equaliser hidden inside a box with some clever circuitry that can detect feedback automatically. As soon as it discovers any, it will cut the offending frequency for you it’s a great and lazy way of getting the hard work done for you. Another advantage of these systems is they will generally make a much smaller notch in the frequncy spectrum, just where the feedback occurs. You shouldn’t actually notice any difference to the sound. which cannot always be said for a graphic EQ because they effect a much larger portion.
Of course they are a lot more expensive, but if you can afford it then get one. It will save you a lot of time and hassle and will more than pay for itself in the long term.