Scott's PA System Tutorial: Running Sound

Page 4

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Signal Adjustment and EQing

EQ Defined

An EQ (short for equalizer) is a device used to filter out or boost specific frequencies in a PA system or any other amplification system (such as a guitar amp, home stereo, TV set, etc). In a sound system, it has two primary purposes. One is to help control feedback, and the other is to help achieve the specific sound you are looking for when you are performing.

If set correctly, an EQ helps in the control of feedback by making each frequency coming out of the speakers reach the threshold of feedback at as near the same time as possible. . .

Did I just hear someone say, "Huh?"

Let me explain. . .
First, we need to understand what a frequency is. A frequency is a tiny piece of sound that, based on its pitch, can be pinpointed at a specific spot in the entire spectrum of sound. Frequencies can be separated electronically and then assigned to different individual controls on the equalizer. On most graphic EQs (The ones with sliders), the lowest frequency will be assigned to the leftmost slider, and the second lowest to the second from the left, and so on all the way up to the highest frequency range which is assigned to the rightmost slider. These sliders will be marked in hertz. Hertz (cycles per second) is a measure of frequency where the lower the number, the lower the tone. Therefore 20 hertz would be a really low frequency, and 20K (20,000)hertz would be a really high frequency. It's not absolutely necessary that you know this, but it can definitely help out when trying to identify problems in the equalization or specific instruments.

In a PA system, or any system that creates sound, some frequencies will tend to dominate the sounds leaving the system. In the case of PA systems, we are mostly concerned with the way the different frequencies are proportioned as they leave the speaker. If a PA system is used without an equalizer, some frequencies will come out of the speakers much more prominently than others. These frequencies, since they are in essence louder, will be the first frequencies to feedback as the system is turned up to higher volumes. This is one reason why we need an EQ. An equalizer makes it possible to, well. . . "equalize" all the frequencies so that they all reach the threshold of feedback at the same time. In other words, you can use the EQ to make it so the highs will feed back at exactly the time as the lows as you increase the volume of the entire system. You do this by using the individual sliders on the EQ to turn the naturally louder frequencies down to the same level as those frequencies that are naturally a little quieter and vice versa.

Adjusting the EQ

Although you can start with either the mains or the monitors, I prefer to set up the EQ for the monitors first. This is because, due to their proximity to the microphones, monitors are much more likely to feedback. That means EQing them is a more delicate operation than EQing the mains and will require a little more time and attention. At gigs, time is not always a luxury, and you may have to start before you are completely done adjusting things to your satisfaction. I find that since they aren't responsible for most of the feedback, the mains are a lot easier to adjust "on the fly" after the band has started if it becomes necessary. Monitors aren't so easy to adjust once the band has started playing, so I like to adjust them first to ensure that the greatest source of feedback will get EQed. This helps keep my feedback problems to a minimum.

"Ringing Out" the Monitors

To adjust the EQ in the monitors, follow the steps outlined below. Since this procedure involves listening for small amounts of feedback "ringing" in the speakers, it is sometimes referred to as "ringing out" the monitors.

1) First make sure there is no one on the stage that will be making any noise that will go into the PA. Ringing out the speakers will require you to increase the volume level of the system until it is right on the edge of feeding back. If someone yells into a microphone while you are doing this, all kinds of uncomfortable things that may cause ear damage could result. Not to mention, you may want to beat the guy up. This of course could lead to the band breaking up. Then you might have to cut your hair off and go get a day job. You don't want that, so it's best to just keep everybody clear during this part of setting up.
2) Now, if you haven't already done so, adjust the levels of the mic and instrument channels (in the monitors) to approximately where they will be set during the performance. (See Input Signal Adjustment)
3) Adjust the sliders on the graphic equalizer so that they are all just a little low of center as illustrated in the diagram below. You will be individually adjusting these upward as you adjust the EQ, so you need to have a little extra room to slide them up while still leaving some room to adjust them downward if necessary.

[Monitor EQ]

This is where it gets tricky. . .

4) Now very gradually slide the master monitor slider (or knob) up until you hear the faint beginnings of feedback. Don't turn it loud enough to allow that feedback to take over, but you want it to be right on the edge. If it is feeding back continuously, pull it back just a hair until it stops. Don't let it get out of control, or it can damage the speakers.
5) Very carefully and slowly slide the far right slider on the monitor EQ (highest frequency) up until you begin to hear faint high frequency feedback coming from the speakers. This is the "ringing" part of ringing out the monitors. Once you hear that sound, pull that slider down very slightly until the feedback subsides. Don't slide it up any farther. That would cause continuos loud feedback that could damage both speakers and ears. Even worse, it could make the early arrivals in the audience shout out rude and annoying things at you. That of course could cause you to shout rude and annoying things back at them which could in turn cause you to lose the gig, and again you could be looking at a haircut and a day job. So be careful with that slider.
6) Now, move over to the next slider to the left and follow the same procedure described in step 5. The only difference is that the pitch or frequency of the ringing feedback will be a little lower since you are adjusting a lower frequency slider.
7) Working your way from right to left (high to low), perform the procedure outlined in step 5 for the remaining sliders on the EQ. Some of these will go all the way up without feeding back. It's OK for a couple of them to do that. When that occurs, just return the sliders that don't feedback back down to halfway (flat), and adjust them by ear (until they sound right) after you are done ringing out the rest of the EQ. If a lot of them are going all the way up without feeding back, you need to slide the ones that do feedback down even farther than they were when you started and then begin the whole thing over again from step 4. That will make those frequencies that you pulled down lower feed back at a higher level on the master slider thus allowing the overall volume to increase. This increase in volume will get the frequencies that weren't feeding back to a higher level thus helping them to achieve enough volume to reach feedback levels, then those frequencies can also be "rung" out.

Note:
As your ear gets used to hearing these different frequencies, you should get to a point where you can identify the approximate frequency of the feedback you are hearing and then match it to the corresponding slider on the equalizer. Once you learn to do this, you will be able to hear feedback and then, by ear, pinpoint the slider you need to adjust (turn down) in order to eliminate that feedback. This will make ringing out the monitors easier, because instead of starting all over as described in step 7, you could simply turn the master monitor slider up and identify (by ear) which frequency feeds back and turn it's slider down. In essence, you would be doing the procedure in reverse. You'd be making the feedback happen with the master slider and then reducing the offending frequency at the EQ instead of finding the upper feedback threshold by increasing the individual frequencies with the EQ.

8) Once you have all (or at least most) of the frequencies as high as they can go without feeding back, then turn the master monitor volume slider or knob back down to the level you will be using during the performance.
9) Now, check a microphone and see what you think? If it sounds good, then finish adjusting the individual levels of the individual input channels (mics and instruments), and you will be ready to move on to adjusting the mains. If it doesn't sound the way you want it to, you can now adjust the monitor equalizer's sliders to your personal preferences. The thing to remember, however, is that if at all possible, you should make your adjustments by reducing frequency levels rather than raising them. This is especially true of the sliders that did cause feedback as you adjusted them in step 5. The ones that didn't cause feedback can be adjusted all the way up or down without causing any feedback problems in the monitors so you may want to concentrate your efforts there.
10) Pat yourself on the back and move on to adjusting the mains.

EQing the Mains

In smaller rooms,, the mains can be EQed by applying the same procedures described for the monitors to the mains. Whether to leave the monitors up while I do the mains is something that I still haven't decided. I see good points and bad for each way. If you turn the monitors down while you work with the mains, you know you are getting sound that is coming from nowhere but the mains, but on the other hand, if you leave the monitors on while you do the mains, you get a full blown picture of what things will be like once the whole system is running. It's a hard call. I'm not sure which is best, but I usually leave the monitors up and running while I do the mains so that I won't get any surprises when I have everything on later. I'll leave this one up to you.

In larger rooms, and outdoors, ringing the mains out isn't very practical. Oftentimes, not enough sound will come back to the stage from the speakers to cause much, if any, feedback to occur, and if some sound does make it back to feedback, it won't necessarily be an accurate representation of what is really coming out of the speakers. I know of only two ways to EQ the mains. One is very scientific and requires the use of some expensive equipment involving a microphone on the dance floor and some funky "pink noise" generating device. It also takes a little extra time to do it this way. Most people don't really have either the time or the money to spend on this system, so they have to resort to the old fashioned way of doing things. That way relies primarily on your ear and a lot of common sense. In other words, you have to listen to the speakers and see if they sound right to you and then, if they don't, you have to know how to adjust them to sound like you want them to. Try as I might, I can't think of a step by step method of adjusting the mains, so instead, I've listed (in no particular order) some tips and ideas below.

-----One good bet for getting the mains to sound good is to start from a consistent setting on the EQ. Some schools of thought say that you should start by setting the EQ in a smiley face and others say that you should set it up to look like a sine wave. Through a lot of experimentation, I've found that (for me at least) the best starting place for the EQ is to set it up something like the diagram of the EQ below. I came up with this setting through experimentation before anyone had told me about the sine wave or the smiley face way to do things, but by comparing, you can see that my method falls somewhere in between the two. You can experiment on your own to find the starting place that is best for you. Don't forget, though, that it is only a starting place. Once everything is up and running, you will most likely need to make adjustments and changes to some frequencies in order to make the front of house speakers sound as good as possible.

-----The most common problem feedback frequency I've discovered is the 2K band. It may be a good place to check when you are hearing a high end squealing feedback. Don't forget that more often than not, feedback problems will occur in the monitors before the mains.

-----Each input channel can be individually EQed to some degree by adjusted the EQ knobs (high, mid, low, etc.) assigned to that channel. This is a tremendous aid when dealing with different brands of microphones and different vocal tones. For instance, some singers and some microphones will naturally have a lot of lower tones. Instead of fixing the problem of too many lows in that mic by changing the main equalizer and thus changing the whole mix, try adjusting some of the knobs assigned to that channel alone.

-----In any equalization situation, it is always preferable to turn something down rather than to turn something up. For instance, if your system sounds too rumbly and muddy, rather than trying to turn the highs and mids up to get a crisper sound, try turning selected frequency bands in the lower ranges down to achieve the same end. You cannot cause feedback by turning something down, but turning things up can easily set your speakers to squealing.

-----If you are having troubles hearing the vocals, rather than simply turning them up try adjusting the EQ so that there are a little less lows and mid lows and a little more high mids and highs. Most of the clarity in the vocals comes from the higher midrange frequencies. If they are pulled way down, you will never hear the vocals very well no matter how loud you turn up the volume. Think of it like this, if you put a pillow over a boom box speaker, you would be able to hear the rumble of the low end (some guitar, bass guitar, and drums), but you wouldn't be able to distinguish the words of the song being sung. That is because the low frequencies can resonate through the shell of the box, but the mids and highs can't. Move the pillow, and all the highs and mids come out fine, and you can again hear the vocals. Think of the pillow as if it was the slider controls for the highs and mids. Turn those mids and highs up, and you get vocals, turn them down and they go away.

-----When adjusting the EQ, you may want to play a CD through the system. Choose music you are familiar with so that you know how it is supposed to sound. Also choose something that has a similar sound to the band that is about to use the system. Use the Equalizer to make that CD sound great, and it won't take much adjustment to make things sound good once the band starts playing. I personally prefer to use thick heavily produced music like Kansas or Floyd. That way, I'm sure I'm using a good well EQed CD.

-----The goal when adjusting the mains is to achieve a good fullrange sound. Be careful not to over do it on the lows or the mids. Too many mids will wear your audience out (ie. "my ears hurt") and may even run them off, and too many lows will give you a distorted rumbly sound that makes it impossible to hear the nuances of the music.

-----If possible, find someone who can give you a second opinion on how it sounds. Just a casual, "How's it sound?" can yield an opinion that might just point out something you hadn't noticed.

A Final Word on EQ

In my observation, improperly adjusting the EQ is probably the most common mistake made by soundmen in local venues. It is very tempting, especially when you are pressed for time, to skimp in this area. It's also a very huge mistake. The EQ is essential to getting a good sound in the front, and it is the only real weapon you have against feedback. This is especially true in the monitors. Properly using an equalizer can double your potential volume and clarity on stage, and can virtually eliminate feedback. If you get it all set right before you start, you won't have to worry about that feedback at all, and you can spend your sound engineering time doing things that are much more fun like playing with the effects and sculpting the sound to each particular song. This brings us to the next and final section of this tutorial. Click on "Next Page" and we will take a look at adjusting and operating the effects.

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