Why use a graphic equaliser
Feedback is probably the most common problem a church will face with their PA system. This, however, does not need to be the case. With the careful setting up of a graphic equaliser this problem can be greatly reduced if not virtually eliminated.Feedback occurs when amplified sound from a loudspeaker re-enters a microphone and is re-amplified. Feedback occurs at specific frequencies, sometimes referred to as peaks, in a system. A graphic equaliser allows you to cut these specific frequencies and therefore remove the peaks. You'll notice that most graphic equalisers have either 15 or 31 "bands". These ˜bands", each with their own slider, control a range of frequencies within the audio spectrum. With a 31 band unit (also referred to as a 1/3 octave EQ), the frequency range of each slider, or band, is smaller which therefore gives more precise control.
Setting up your graphic equaliser
For simplicity, firstly we'll discuss how to set your graphic if you have a Peavey equaliser with FLS (Feedback Location System). FLS is a great help to the user who is unfamiliar with setting up graphic equalisers. Not only that, it saves time too! Equalisers with FLS have an LED above each band slider. When feedback occurs the light glows above the band at which the system is feeding back. This allows the operator to locate and cut the band quickly and easily. The method outlined below is a relatively simple way of reducing feedback in your system.
Firstly make sure all the sliders on the graphic equaliser are set to the centre position, ie flat. This means that there is neither boost nor cut on any of the bands.
Raise the fader of, for example, your lapel radio mic (lapel radio mics tend to be very prone to feedback). Continue doing this until the system starts to feedback, or ˜ring". Do this carefully so as not to induce more than one or two feedback frequencies at a time.
The FLS light above the band at which the feedback is occurring should now be lit. Cut this band, ie move the slider down from its central position until the feedback is eliminated.
Repeat this process of raising the mic level and cutting the feedback frequencies until the first frequency you cut starts to feedback again. You should stop here because if you continue you will just be cutting the same frequencies and reducing what's known as headroom.
This process can be repeated with the other mics in your system which are prone to feedback (there is no need to do this for mics of the same type).
You should be able to achieve far higher levels with your system without it feeding back after this process is complete. You have successfully rung out your system!