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How to EQ Your PA

Well, I finally saw one. One what, you ask? Let me tell you. Many, and perhaps most people misuse the EQ on their PA by immediately and automatically setting it in what I call the Smiley Face configuration. Mids cut, highs and lows boosted, with the resultant curve of the EQ sliders looking like a smile. I have been known to comment that the manufacturer of the EQ unit could have saved a lot of money by simply putting a button on the unit that accomplishes the same thing: boosts highs and lows, and cuts mids. Well, what I saw was exactly that; a button that does this. It was on the back of a powered Mackie speaker that belongs to a friend of mine. I am unsure as to why Mackie would wish to do this, but I can tell you why many people do this with their EQs. They are assuming that their PA speakers put out plenty of mids, but do a poor job of putting out lows and highs. While this may have been true in the 60s and 70s, it is no longer safe to assume this. Speaker design has come a long way in the last thirty or forty years. In fact, many less expensive speakers are too good at reproducing the upper mid to high end, as they have horns to do this job. Horns are often more efficient than cone speakers, and the higher the frequency, the less wattage it takes to produce the same db level. Put these two factors together, and you may find it is actually more desirable to cut the higher frequencies than to boost them

Equalizers, or EQs as they are commonly referred to, come in several different configurations. The two most common are "Graphic", and "Parametric". Another is a unit that will automatically locate an offending frequency, and pull out a narrow slice of the program right where it is needed, leaving the rest alone. These are commonly called "Feedback Exterminators", and for good reason. They are the kind to have, but are unfortunately fairly pricey.

We'll take a look at Feedback Exterminators and Parametric EQs later; right now I wish to discuss the Graphic EQ, as these are by far the most common in the real world.

Graphic EQs
Graphic EQs are called "Graphic" because they look like a bar graph. When you use them, you can see at a glance which frequencies have been boosted, cut, or left alone. They usually have a row of sliders, placed one next to the other, each handling its own specific frequency range. The ones in charge of the lowest frequencies are on the left, and the farther right you go, the higher the frequency that will be affected by the sliders. (I once had a bass amp that had an EQ section with about 7 rotary knobs with different frequencies listed under them, and a label that said "Graphic Equalizer. I'm sure the only difference between this and your typical graphic EQ was that it had rotary knobs instead if sliders, but was it really a Graphic EQ?)

Some Graphic EQs are built right into a mixer or powered PA head. Others are available in rack-mount units, usually one or two space. They vary in the number of sliders they employ to boost or cut frequencies, or bands; most common are the 7 band, 15 Band, and 31 Band, or "Third Octave". 7 band EQs have seven sliders, 15 band 15, and so on. The 31 band is also called a "Third Octave", because that is approximately the width of frequencies one of its sliders affects, one third of an octave. As you may see, that is really quite a wide range. If you wish to lower a frequency that is feeding back, you not only pull out that frequency, but also quite a wide swath above and below it too. Also, the less sliders you have to cover the entire range, the wider the hole they must put in your program in order to remove an offending frequency. Therefore, where a 31 band EQ will pull out a third of an octave, a 7 band will pull out better than an octave and a half! So, you can probably see the need for taking care when using one of the smaller EQs. Usually rackmount EQs are either 31-band single space, or dual 31 band 2 space, or dual 15 band single space. I have seen some older 2-space dual 15 band EQs as well. There may be some rackmount 7 band single or dual EQs; I have never seen one, and I wouldn't advise buying one unless you are on an extreme budget, don't have any type of EQ, and find one for about twenty bucks. I guess they are better than no EQ at all, but barely. With the extreme width of frequencies they affect per slider, really they are no more than 7 band tone controls. They are so imprecise; trying to use them to control feedback really is like using a sledgehammer to swat flies. Usually they are only found on self-contained PA heads, the kind you plug a Mic into the front, and the speakers out the back.

As I said before, many people automatically set their Graphic EQs up with the middle frequencies cut, and the lower and upper frequencies boosted, the sliders forming a curve that starts high on the bottom, makes a graceful curve down to the middle, and then another graceful curve up to the top. It looks pretty, but in most instances, this is the wrong way to do it. The only way I can think that this would actually be proper is if someone has speakers that do midrange well, but do a really crummy job of putting out low and high frequencies. Then, in order to flatten out the frequency response of the speakers, one would want to boost the lows and highs, and cut the mids. This would in theory flatten the frequency response, but in practice still wouldn't work very well, as it is usually not whole frequency ranges that are too soft or loud, but all too often specific frequencies within a range.

Why, you ask? Well, it depends on a number of things. The shape and size of a room, the amount and hardness or softness of furniture in a room, the amount and hardness or softness of the people in a room (well, really the difference between hardness or softness of the people make an infinitesimal and probably inaudible difference, but you get the idea.) Also your microphones and speakers (and possibly your mixer and/ or power amp) have frequencies they produce really well in relation to the other frequencies.

Hard surfaces reflect sound, soft ones absorb it. Try yelling with your mouth a couple of inches from a painted wall, then a couple of inches from your pillow, and you will see what I mean.

If the back wall of the stage where you are playing is just a painted, sheet rock wall, you may have trouble getting your monitors as loud as you would like without encountering pesky feedback. Ditto if you are playing a club like some I've played where the room is long and narrow, and you're at one end playing across the room the short way, aimed right at the opposite wall. In this instance it is probably your mains that are the problem, though.

Varying voltage can affect the way your gear reproduces frequencies, as well. I've noticed this problem mostly in industrial areas. You may have noticed something like this before. One night, everything sounds great, and the next night, even though youve changed nothing everything sounds like... well, not so great.

Anyway, as you can see, there are quite a number of things that can affect the way your gear sounds and performs. And, how your gear performs also affects the way you perform. So right now let's take a look at how a graphic EQ can help us, and how to bend it to your will and make it do so.

Setting Up a Graphic EQ
You may have used a graphic EQ before, and gotten less than stellar results. In fact, you may have wondered if it was really called a Graphic EQ because of the language that it inspired you to employ. Never fear, there is an easy way to work one of these things, and it doesn't require voodoo, perfect pitch, or even human sacrifice.

  1. Turn the master volumes for both the mains and monitors all the way down. This is very important.

  2. Center all tone controls on each if the channels you are using on your board. You can go back and adjust these later, but for now you dont want them influencing the frequency response while you are setting up your EQ.

  3. Center all of the sliders on the EQ. This means halfway between the top and bottom. Yes, every last one. Don't succumb to the temptation to leave that one slider down because "that frequency always feeds back.". Just do it. You with me? Okay. (Often you can feel the slider click into place when it reaches center; this is called a detente.)

  4. Carefully and slowly raise the master volume for the mains or monitors, whichever you are setting the EQ for on the board until you hear a little ring. Now lower it slightly, until the ring just stops.

    Note: When I say slowly and carefully, I mean it! Most of the frequencies that will really shriek if you are not careful are in the range and at a volume that can damage your hearing, or anyone elses that happens to be on stage at the time, or near your mains if you are setting them. It is a good idea to warn others to leave the stage when you are setting monitors, and to warn any others who may be in front of the mains when you set the EQ for them. Damaging SPLs can be avoided, however, if you work slowly and carefully at this point.

  5. Slowly and carefully slide each slider up, one at a time, starting with the lowest frequency. If nothing happens, slide it back down to center and leave it there. Go to the next slider and do the same. Keep going until you find one that rings. When you do, pull that one about halfway down between the middle and the bottom of its travel, or, in other words, about three quarters of the way down from the top of its travel. Continue up until you've repeated this procedure with all the sliders. Once in a while you will find one that really screams as soon as you move it. Pull these down farther than the others.

  6. Slowly and carefully raise the master volume on the board until you hear a little ring. Stop, and turn it back down a touch, and youre good to go.
That's it! Pretty simple, huh? Don't feel bad, it took me quite a while to figure this one out. Before that, I was hunting and guessing just like you.

Let me just say, though, that the idea here is not to keep turning the main volume up, and to keep pulling down sliders so it won't feed back. This would be defeating your purpose. Ideally, you shouldn't pull down more than a couple or three. More than about seven or eight, and it is probably already too loud enough, and you should quit while you're ahead. It won't get louder if you continue. Remember, each of those sliders turns down at least one third of an octave, and even more with the 15 and 7 band models.

Oh, the "halfway down" was just a rule of thumb. After a while you'll learn how far down to pull it, depending on how readily it feeds back when raised.

Parametric EQs
Parametric EQs only really need to have one control in order to function. The most basic is just a variable frequency notch filter. This means adjust it to a frequency, and it cuts a hole in the program there. Of course, they can get much more sophisticated than that, with controls to determine the "shape" of the notch, the depth and width of the notch, whether the notch is a cut or a boost, and so on. These are really easy to set: you just sweep the frequency of the notch from one end to the other until the feedback goes away. Most can have a much narrower band they affect as opposed to a graphic EQ, so youre not swatting flies with a sledgehammer. The only drawback is the amount of filters they have. Some have one, the more expensive ones can have five or so.

Feedback Exterminators
These are really nifty! To set them to control feedback, you just put them in set mode, crank up their input volume, and then raise your main volume until you hear a ring. ZAP! A filter finds that frequency, locks on to it, and that bit of feedback is exterminated! Then you repeat the process, until you've used up most of the filters, leaving at least one to "float" so it can eliminate any feedback that pops up during the show, and you're set. The coolest thing is that the filters in these take out a really narrow chunk, just exactly where the feedback was. This means that they don't affect the overall sound of your music, they just get rid of the feedback. After you set them you can turn the volume back down to below feedback levels, play some pre-recorded music through the system, and click the EQ between active and bypass mode. You won't hear a difference.

These units go from six or seven filter, stick 'em between your mic or acoustic guitar and the board types, to ultra sophisticated lots more filters than you really need and you could buy a pretty nice used car for what they cost types. Really.

You vocalists that are always having a hard time getting loud enough monitors should go right out and buy one of the personal, inline types. I mean like, run, do not walk, to your local music store and get your hands on one of these. It will make your microphone able to get much louder through the monitors, and the mains too. You'll be able to hear you, and the crowd will be able to hear you. (Assuming the rest of the PA is up to the task.) The cost? Oh, somewhere around three SM58s. Trust me, it's worth it, and how many toys do you vocalists get to buy, anyway?

Basically, EQs are not that tough, if you approach them from a logical point of view, and treat the volume controls with respect.

Kelly Marsh is an active player that has been playing live and professionally for about twenty years.
Add a Comment
Danny Myburgh (2) wrote:
Oct 11 2012
Robert Harewood (5) wrote:
Jan 23 2013
Hi Danny, The way bass frequencies bend increases bass response at walls and corners (apparently +3/+6db respectively) You will know that when you cup your hands around the mic, you get instant "proximity effect" bass boost. check: http://www.recordingmag.com/resources/resourceDetail/225.html skip down to "bass buildup"

Could this contribute to your bass feedback problem? google "basstrap" and "helmholtz resonator"