Well....it depends. If you are having truoble with the lead vocalists mic, for example, then you should try to use the eq on the board for that particular channel. Why would you change the eq on all of the mix when just one channel is the problem? For instance, why change the sound of the saxaphone when it isn't the problem.
In all reality this doesn't always work well. With only three or four bands to change, you are affecting too much of the sound. Changing the eq on the board, especially with limited eq control, can leave the signal sounding harsh and not at all lifelike.
So...... you are left with a dilema. The best thing to do is to try simple fixes first, such as becoming more proficient with mic and monitor placement and educate the vocalists on mic usage and positioning. Then, try to pick up another eq. They can be found for about $100 and put it on the offending channel output. This will give you greater control of the signal and you can make small alterations as necessary.....leaving a lifelike and clear sound.
This can be a very difficult and stressful part of any sound engineers job. It takes hours of fine tuning and most bands and performers don't realize that you need to rehearse, too. Also, if you have to move from venue to venue, everything changes in your mix.
For great answers to hundreds of questions about setting up a great mix, take a look at Recording Magazine. They are about finished with a 20 or so part series on how to set up a great mix, including all of the parts of the gear and how they work.
Well think about it. If you're going to ring out an entire SYSTEM, wouldn't you ring out the system? Not the individual channel. For taming feedback the typical channel strip eq is surgical enough, cuts too much. Even most built in parametric/sweeping cut a little a bit more. Usually the problem isn't in your channels, but your loudspeakers aren't tuned/rung out. One of the most overlooked details in sound reinforcement is setting proper gains. Gain is often set higher than it needs to be, so when a ring or two occurs the amatuer engineer will began cutting from the channel. As things get more dynamic, the system begans to ring again, and the amatuer keeps cuttin' and cuttin'. He eventually gets to the point where he has cut so much he struggles to make the channel audible. Because of all the cutting, he lost quite a bit of output. He could have made it easy on himself and notch down the channel's gain a tad bit. Not only does ringing out a system involve cutting, but it involves boosting to better hear what freqs are causing the problem. Just don't cut too much, it'll shrink your output. Causing you to push your inputs harder, which only make the problem worse. As a general rule of thumb, if you cannot achieve a decent level/tone after ringing out your system, then you probably cut too much. Esepecially if your gains are properly set and you're dynamically processing your trouble sources. However if you continue to receive rings, the problem isn't you, it's the source. Sometimes some mics are just a bad idea. Some rooms just absolutely suck. Some systems just don't work with some rooms and stages. Obviously you can manipulate some of those problems with what has been discussed, but you're not directly solving the probem. You're masking it more so than anything. But start with the source, you're only as good as your weakest link. Garbage in, garbage out.
I understand what you guys have said. I am going to change this a bit and see what you guys think. I have been running sound for a bit over two years now. I have designed for three or four shows with out problems and continue to be asked back. It was with this last show that I had the most feedback/ring problems ever. They never came from the housesystem unless you went above 0 on the fades for everything. It is a small venue 300 seats. (I will try to get several pictures later) But our music director had a little self powered deskmonitor, they work great for most orchestras because only the one person needs to hear the stage and everyone else takes thier cue off of them. Well she decided that it would be best if she cranked it to maximum so everyone back there could hear (a 8' x 8' square area or so). At times you would hear the ring/feedback come from her monitor and her monitor alone. I think part of that was because the mics feeding it were on prefade send, but that has never been a problem for us before.
So the band had the mics for their instruments going through their monitor? I take it you were mixing these mics? Next time, don't put band mics through the band monitor. There is no need for that, the band is probably loud enough as is, so I'm sure they can hear themselves. Putting vocal mics, wireless mics, etc through the band monitor is OK. Or, set the monitor to the max and ring out, set gains, etc. so that way she can only turn it down.
What things have you change from the show that you are getting the rings in and the other show that the sound was fine. If the rings are only in one or two channels and the rings sound different (because the mic’s are different or the placement of the mic’s is different), Then you should eq it out the best you can (without losing the life that it has) on the 4 band channel eq. If every channel gets a ring that is close to the same Freq, then you should eq it out on the 31 band eq. Most Sound systems always has couple of freqs that ring. That you can tune out in the 31 band eq. Some people are lucky and have everything just right so they never get rings. (when I say just right I don’t mean just the sound system, I mean everything the the stage set up to the people using the mic to the systemetc) Everything else is from the mics and where they are place or how loud they are. I don’t know how big you band is or how the sent up is or even who needs to or wants to here what in the monitor. So i cant say anything about not putting the mics back in the monitors, but that if you do it right should not be a problem. I have had a lot of different monitor problems with rings and stuff and every time me and my crew has been able to fix it. Something to think about is how are the mic's place with the speakers. Could you either move one or the other and make the sound still good but help stop the ring. Sometime just moving the mic a few inch’s in one direction could stop a ring. You can find stuff online, if you need to about where to mic stuff or how to set a monitor to a relationship of a mic. Another thing is (if it is a Vocal mic) How loud are they singing into the microphone. I use to have problems with a girl not singing loud enough so i would get to much background noise. So i would talk to her about singing louder. Now she is great at singing into the mic. I Never have any problems with her not being loud enough anymore.
Try and keep as little as open mics as possible at any given time. High-pass filters are your friends. Once you have the most amount of gain as possible and you need that extra more, you'll need to start cuttin freqs.
I agree a channel strip wil be a bit short if its not parametric, so a 1/3 octave graphic EQ wil be better. If the boundary mics are the only feeding back, put them on a subgroup and insert the EQ onthe group. Don't cut from the whole system if only 1 or a few mics are feeding back.
Also check ow linear the system is, you may have some spikes that may be inducing the ringing.
Try taking out the mics that are closest to the speaker for the instrumentalists. This will reduce feedback and they should be able to hear enough without one or two of the problem mics. If all else fails, try getting headphones from them all. You can try going to a reading teacher in an elementary school to see if they are still using the headphone distribution boxes that we used to use to allow many kids to listen to one book on tape or something like that.
I'm currently mixing a musical with a similar setup - 5 CrownPCC floor mics & 3 hanging mics plus 10 wireless mics. Running the monitor mix for the pit orchestra, I'm not sending the floor mics as they tend to still pick up a lot of the orch...only sending them the hanging mics & wireless. For the stage monitors obviously they are only getting the orchestra mics. I just has "shields" made for the floor mics - an L shaped section of plexiglass for each floor mic to try to keep the orchestra from bleeding into those mics. Hope that helps!
One thing you should also do with PCC160's and other boundary mics like them is to remove them from the vibrations by putting a mouse pad or foam underneath them and/or taking them off the stage and putting them on a music stand, or like I did, taper a dowel so it fits in a mic stand and screw a flat board on top for the microphone. That gives you a little bit of tilt of the microphone to remove the orchestra and focues on the actors.
The pit was behind the set, they had one speaker there was a curtain dividor and walls the only direct access to them from the stage was through the door way with no doors. it was thier monitor that fed back. the housesystem is setup so that it is almost imposible to feed back.