This post is a request from my lighting guy Steve. He's a freelance lighting guy in the Western New York area and also one of the house engineers at a club in Rochester, NY.
Steve wanted to know if I had any links to articles about ringing out monitors and EQing front of house. There's a million of em out there but I thought I'd add my own to the pile. Let's start off with monitor world.
Until you get so you're really a crack shot at ringing out though, you should probably just arrive early and try to work on it when nobody else is around to be annoyed by the repeated squealing. Start with flat graphs and open up all the vocal mics on stage. If it's a really volatile stage you can EQ the mics about like you would for a show. Then just start turning up till things squeal. An RTA is kind of a crutch but a useful tool when you're learning what each frequency sounds like. Notch and turn up, repeat.
When you've got it fairly bullet proof go up on stage yourself and talk on the mics to see if you can excite any further feedback. Wave the mic around, point it right at a wedge like some singer is sure to do later in the evening, cup the mic, all that stuff. You're likely to get a few more notches.
If you get to a point where you're using more than half of the sliders on your graphs you should probably stop, flatten them, move the wedges around and start over. If you EQ too much you're removing so much level from the program that nobody on stage is going to be able to hear anything. So look for wedges that are making reflections off of things, pairs that are both pointed at the same spot, etc. It also probably isn't necessary to push each slider on the graph all the way to the bottom. Experiment a little to find out how much it takes to kill the squeal and then take out just a little more.
The last thing to consider is gain structure. If you have to EQ pretty drastically then you'll be removing quite a bit of level from your monitor mixes. If you start out by rolling off all the lows below 100Hz or 120Hz then you can go ahead and turn up the post gain on the EQ, this will keep the gain structure happier in your console rather than raising the gain there and getting hiss. It'll be quieter and also make sure that you don't "run out of knob" on the aux sends. Once you've finished notching, turn up that EQ post gain a little more and you should be in good shape.
For front of house it's a common practice to find out what EQ needs to be done to make up for the room. The room is a huge player in how your system sounds. A great sounding system in one room can sound like garbage in another. That kind of EQ, to fight ringing in the house, or to take care of some aesthetic issues is often done in the lousdpeaker management department. That way guest engineers can't get into trouble as easily. Then it's nice to have a pair of 31 band EQs on hand to shape the sound for each particular performer. Since your corrective EQ is already in the box, you can start out with these flat.
Tweaking for ringing in the house can be accomplished just like you would with the wedges on stage. Although in the house you're more likely to get very low resonances, below 250 Hz from things like kick and low tom mics, or very high ones from guitars or singers waving vocal mics around. Once you're ring proof, take a walk around your crowd area and see what you think. Is there a build up of mids in the center? Are the highs dying off in the back? Those might be things that you want to try and fix by moving speakers around but you can't always do that so apply some corrective EQ.
Lastly, you'll want to sculpt the sound to enhance what you'll be mixing that night. An easy way is to get some play back going and compare the sound in your headphones to what you're hearing in the room. Match the material to what you'll be seeing on stage later. Don't set up for Van Halen if Bjork is coming in. If you get good at this you can really help yourself out later on.
If you've got the room and your cans (headphones) sounding pretty close. You can line check your band in the cans without blasting away in the house. You need to have a pretty good understanding of your gain structure but with a little practice you'll know about where stuff needs to sit. If a guitar mic sounds good in the cans, then when you push it up in the house you shouldn't have much work to do in achieving you final mix. This can really save your butt if you're stuck in a festival style event and either don't have the time or aren't allowed to check your band in the house.
I hope that helps and feel free to chime in one and all. Let us know what tricks you use.