We promise we aren’t turning the TTOTD into a personal advice column so bear with us on the question. There is some technical stuff to learn here.
“I practice weekly with a small rock cover band in a guy’s basement. He has loads of awesome equipment, however he hasn’t learned how to use it properly and doesn’t like others to mess with it. Consequently, I sound better at home with my simple setup. The question is specifically about the EQ. Even if I secretly change it, every week when I return he has taken several EQ bands and pushed them all the way down to try and prevent feedback. In other words he keeps turning the gain up on the mics (about 10 mics) until it feeds back and then whichever band(s) are ringing he pushes down as far as they will go. We still never get the volume or clarity we should. I believe this EQ problem is the main reason it sounds like crap but I don’t know how to tell him technically that it doesn’t work to do this. Any feedback?”
Nice pun there. First, opening up 10 mics in a typical basement is an almost certain recipe for disaster. Do you guys really need to have 10 mics open to rehearse? If so, you may want to consider acoustically treating the basement to minimize reflections, which can make feedback problems worse. I also highly recommend finding a way to rehearse at a low volume. You should be wearing earplugs anyway (you’ll regret it later if you don’t), but lower volumes will make things more intelligible and require less volume from the PA/monitor systems, which will reduce feedback. We frequently say EQ is somewhat of a last resort, and that applies here too. Take care of these other issues as much as possible for addressing the EQ aspect.
Now, on to the EQ. Remember that EQ is simply a level control for different frequencies of the audio. If you lower everything between 100 Hz and 10 kHz by 10 dB you have effectively lowered the volume of your system by 10 dB, because there normally isn’t much information outside that range. Sure, the bass gets through, but the perceived ‘volume’ of the system will be much lower. Let’s say you lower everything between 1 kHz and 4 kHz by 10 dB. Again, you’ve done more harm than good in that you have simply taken the bulk of the important information (vocals, guitars, etc.) and turned it way down. The system will sound terrible, not be clear, and you’ll find yourself turning up the vocal channels to be able to hear them, which makes them more prone to feedback again (actually it’s worse, see below). This is a never ending cycle that leads nowhere if you allow it.
The principle of turning up a system to find the hotspots of feedback so they can be ‘dipped’ on the EQ is valid. But you should only dip it enough to get rid of the feedback. Once you’ve found the worst four to six trouble spots and have them under control you will find that you are starting to go in circles. You can turn it up, but the same frequencies will ring again, or you begin to dip everything down, which as pointed out above is similar to just turning the overall volume down. This is where you must stop. You can tell if you’ve let it go too far by listening to the system. If it sounds muffled and flat you need to undo some of what you did. If you still can’t get enough volume out of it you are going to have to try other things, like changing the mechanics of the system (‘the system’ in this context includes the room you are in). Move speakers, mics, change polarity of some mics, change the acoustics of the room, etc. Continuing to pull down EQ frequencies is not going to get it.
As mentioned above, pulling down a bunch of adjacent sliders on a graphic EQ makes little sense. You create all kinds of phase shift, group delay, and other anomalies. But it’s actually worse than you think. If you pull every slider on a graphic EQ to the bottom what do you think happens with the audio frequencies that are between the bands? For example, if you pull 1 kHz and 2 kHz down 10 dB how far down do you think 1.5 kHz is? The answer depends largely on the Q of the equalizer, but in most cases you’ll find that the frequencies between the bands don’t get pulled down nearly as far as the frequencies on the EQ centers. When fighting feedback this is a real problem because after a while it’s actually the frequencies in between the bands that are feeding back, and you just can’t get to them. One solution is to use a parametric EQ, but you can get good results with a graphic if you use it sparingly. Those automatic feedback eliminators work very well, and can do wonders for removing feedback without too much coloration to your sound. This is because they use very narrow filters that are precisely tuned to the feedback frequency.