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Setting EQ's

Discussion in 'Sound, Music, and Intercom' started by 09astephens, Dec 22, 2007.

  1. 09astephens

    09astephens Member

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    I realize it is hard to explain over a computer how to set EQ's. But would it be possible for someone to try to explain how to correctly set them. Our school has a very large auditorium, and we get very bad feedback. We know that some of the problem is that the chorus uses mics in the pit. Which when they are in the pit they are in front of the subs. We have a Mackie cfx-20, and the only eq we have in the one in the board. I've heard that you can set the eq according to the pitch of the feedback. But I don't know much more than that.

    I sincerely thank you for any responses!!
     
  2. soundman1024

    soundman1024 Active Member

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    I hate to say it, but I don't think you're going to have too much luck. Most of the time you want a 1/3rd octave EQ for that kind of purpose. These EQs have 31 sliders for 31 different frequencies along the audible spectrum.
    Another alternative is a parametric EQ, but graphic is easier to begin with.


    With the graphic EQ on the board I would suggest only making one cut for the frequency the feeds back most often. If you start trying to hit several frequencies you'll end up just cutting most of your audio down.

    With your mics in the pit, just use the low cut button by the white knob on top. That should help if you aren't doing that already. Typically this would be done on most inputs unless you do want lows out of it, like a CD player, or a kick drum. With mics near subs definitely use this low cut.

    With the EQs on each channel you have a fixed high and low adjustment. On many vocal mics you may find it helps to bring the lows down for theatre, but for musicals you may need to keep them. Your mid adjustment has a white knob by it that is handy. It allows you to change where the center of the cut/boost is. Say you're having trouble with feedback at 800Hz, just turn your white knob there and cut some.

    If you don't know what frequencies sound like try this.
    http://sft.sourceforge.net/
     
  3. derekleffew

    derekleffew Resident Curmudgeon Senior Team Premium Member

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    Here's a fairly comprehensive thread on the topic. Type "equalizer" into the search tool for much, much more.
     
  4. wolf825

    wolf825 Senior Team Emeritus Premium Member

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    Most feedback problems are the result of a improper gain structure (in otherwords--too high a gain or improper level setting) and also for poor or non-ideal placement of microphones in relation to the speakers.

    EQ adjustments can only go so far in fixing some problems like this if the rest of things are not set properly. If you are placing your mic's in front of your speakers then start there--and if that is not possible to move them or move the speakers, and they are in front of yoru Subs only--a High Pass Filter (or low cut adjustment) would be your first course of action. What that will do is basically eliminate the low frequencies that are passed thru those mics--if they are chorus mics or area mic's for a stage or orchestra--you don't need the low end anyway. So if your console has a HPF (high pass filter) set it to around 200-250hz for starters if its adjustable--if not just turn it on as a fixed setting may be around 80 hz. This control, if you have one, is usually labeled HPF or LOW CUT, and is next to or near the GAIN/INPUT knob or next to your EQ knobs on each channel. Go ahead and start with it ON as listed above...

    Second would be to re-adjust your gain structure on those mics and in your system... For mics--you may have one mic gain that is wide open and the rest may not be, so you need to make sure they are all similar to start--the idea being that to start your gain structure you want the mic's to work collectively and equally, and not have one mic try to do the work of 3 or 4. The GAIN is simply how 'sensitive' your microphone is to what is around it and how much of that sound you allow in to be mixed. A Mic is just an electronic "ear" and it picks up everything and it is often made to pick up specific or a range of frequencies depending on its type and application--but what you let come in to your system to be mixed is what you adjust with your GAIN knob and other controls. The higher the gain--the more sensitive the mic picks up and more the room noise and frequencies you let in--and the more prone to feedback you will be. In an example (depending on your equipment), at a low gain your mic may able to pick up well only sounds that are within say a foot or two..if you turn that gain up to around 12 or 2-o-clock, your gain may pick up sounds very well that are 5 feet away--anything closer will be really really loud and strong and anything further will sound distant...and you will also notice a definite "air" about the sound as it picks up more and more. When setting your gains you want to listen but you also want to look at your channel indicators--for level. You do not want to be in the RED or else you will overload the signal you let in, and you will get "mush" and distortion. Again without hearing or seeing your set up--its difficult to describe. After you get the mics' balanced for gain inputs, you can adjust for mix levels later. Your GAIN control is usually the very FIRST knob at the top of the channel--says GAIN or INPUT....start with them all the way down and experiment from there with adjusting them up so they all balance out. Another thing you could try is to lower your gains on the mic's closest to the speakers and raise it more on the ones furthest away from the speakers.. There are many things you can try--without seeing or hearing your situation all this advice is just starting off points...

    Another thing to consider and check while you do your gain structure set on the mics--you also have gain structure on the rest of your system to consider..again you want to ensure that everything is balanced. The way to start is setting a gain on a mic is to turn all your gains DOWN. Bring your MASTER fader up to nominal -0db- or close to it, bring your channel fader up to or close to nominal, and then open your channel gain until you get feedback on that mic--once you do back off your gain to lose the ringing. Do the same with each channel or mic. As you add more mics, you will need to back the gains down as you are collectively increasing things in your mix. After you get a couple of mics--you should have a general point for your gains to be set at.. After you get this gain structure started--then consider your EQ's... Again--this is a very rudementary starting point and explanation...there is much more to this and any other sound guy will tell you of another dozen things to check too.. This is to give you starting points--not try to teach you sound....

    Make sure ANY EQ that you have on that channel or in your system is not boosted to start with. For CHANNEL EQ & system EQ--start FLAT--no boost or cut, and do NOT boost any frequency to start....this could be another factor to check in those mics and in your set up. Occasionally someone will turn the BOOST/CUT to a full BOOST thinking they are making things sound better or are adjusting a frequency and they grab the wrong knob--seen it a billion times in schools...and suddenly that channel is boosted at 2k or 800hz or whatever and no one knows why they are suddenly getting feedback or why things sound like butt. So flatten out any EQ you have to begin with on all your channels. Once you ensure your EQ's are flat--finish setting yoru gain structure as above to where you have sensitivity but not feedback.

    You may wish to purchase the Yamaha Sound Reinforcement Handbook which is a very helpful guide. It gets a bit technical for non technical folks and beginners--but its topics and sound related suggestions is thorough enough to explain how things work in great detail so you can get a much better grasp on things... You may find it helpful.

    I hope this helps get you started...I'm sure others will have more to add which you can try.
    -w
     
    chausman, miriam and (deleted member) like this.

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