In my years of experience in sound, I have learned that it is important to eq your system. The problem is, I have never learned a good way to eq a system. How does everybody else eq their system? Which technique is the best?
Depends what I have around. I rather like the way the peavey CEQ eq's a system on an RTA. If I am doing strickly voice I EQ to someone standing onstage talking into a mic. Otherwise a piece of music that has good vocal quality as well as decent music quality. I try to choose music that resembles what the PA will actually be used for. For most events I usually do a bit of Rent, a bit of Wicked, and a bit of Sting. If i have a 31 band I drop all the frequinces to as low as the will go and slowly add stuff in.
I would say there are two ways to EQ a system. You can EQ it for best audio quality and most gain before feedback. EQing for quality is certainly the more difficult of the two. Perhaps the easiest way is to use a flat response microphone and some Real Time Analysis software with white noise to get the system as close to flat as possible. The goal here is to account for imperfections everywhere down the line, and it is only as reliable as the microphone, the preamp the microphone for RTA goes through, and the purity of the white noise (the output device may have aberrations in its output). EQing for Gain before Feedback is EQing to take out frequencies where a feedback is more likely to occur allowing for more gain. Here quality is something that is desirable, but it takes second place to volume.
This is one of those seemingly simple questions that could turn into a very very long thread.
First a slightly different perspective than the two earlier posts.
There are two different uses of eq, one is for monitors, were you are to get the most GBF (gain before feedback). Here an rta hardware of software helps, very experienced folks learn to be able to detect the frequency by ear and make the slight adjustment. The RTA helps to identify the frequency. All the work here should be done with the mic being used on stage, NOT a rta dedicated mic and you need to check for mic positioning, cupping your hand around the mic etc, all those actions that the mic user is likely to use. Typically this is called ringing out the system. You can have several options of how to do this
There are automatic systems, like Sabine Behringer etc, which detect the offending frequency and have a very narrow filter that they use. In a pinch these work, but you loose control, and you can very well wind up with a sound in the monitoring system that has good GBF, BUT poor audio quality.
You can use a parametric eq or a 1/3 octave graphic. Graphics are typical, but you need to realize that the marked band is the center of the frequency area being affected, that there is quite a bit of overlap and the tool is not as fine as you might suspect. A 1/3 octave does NOT mean that only a 1/3 octave is affected, but rather that the center point is at a third octave point, Subtle but major point. A parametric gives you more precise control, and with a rta can be quite effective. Most of the auto systems use parametric technicques, and they argue for their effectiveness based on this.
IMO it is NOT a good idea to simply drop all the 1/3 octave faders and then boost. First, as I mentioned each fader has quite a bit of influence on the adjacent frequencies, and for feedback elimination you should be reducing frequencies, not boosting the ones around them. Sometimes this idea comes from the technique that IMO you rarely ever want to boost a frequency about the zero line, but simply reduce the frequencies, SO in an extreme this could be interpreted as supporting the bring all the faders down to the minimal setting.
House eq is a different matter. Unfortunately a lot of people thing you just get a good ref mic, set the mic up and use the analysis to "level out" the room. The joke is the way to level out a room is with a bulldozer ;-)
Problem with the set the rta mic up is that you are doing it in a room where the reflections from the floor etc will have a dramatic effect on performance, and you typically have really extreme effects. In most cases these days people now look at really not using Rta systems to alter the room, but rather too correct the speakersystem for its non linearities.
SO you are looking for smooth transitions at the crossover points, you are looking at time alignment combing etc. Problem is that these are usually a combination of some graphic but typically a DSPsystem like Driverack or BSS . IN addition a lot of the settings should have been properly set during installetc.
So graphic eq on FOH is something to be approached carefully, listening to music you know is very helpful, moving around in the room etc. making small changes and then going back and checking from the previous location etc.
An experienced person typically when the see a graphic set up on mains that has dramatic all over the lot adjustments knows that it has been done incorrectly mainly based on a simple rta mic with an auto or semi auto set up.
The other thing to realize is that the frequency performance in a audience space is related to humidity and temperature, and also absorption. I know people selling auditorium seats talk about same absorption characteristics as people but that is just a minor part of all of it.
So imo look at eq on the main system as correcting the speakersystem NOT THE ROOM. There are some cases where you have a horrible room with massive reflections, or an apparent standing wave problem. IN most cases you are better correcting these with physical techniques if at all possible rarely will the graphic fix this.
One technique is to set the graphic for fohflat, and play some music that you are familiar with, and then go thru and carefully boost the various frequence bands one at a time, and hear the increase of NEGATIVE effect, and then use
the eq to reduce these areas.
Another reason not to use the boost is that here again is where you can cause distortion or over driving in the system with expensive results (blowing the driver/speaker). For instance you have a multi way system, with a cross over system if you boost the signal around the crossoverpoint you could overide effectively the cross over frequency and for instance put too low a frequence into a high freq driver, remember crossovers typically have 12-18 db roll offs, and you could off set this easily with the graphic.
There are some cases when you need to look at feedback elimination on main speakers, but if the system was installed properly this should be less of an issue as the speakers should not be placed so that the output feeds into the mics. Improper install or placement can lead to problems, most of the time you should first try to move the speaker or the mic.
The other eq is for the individual signals to get the correct tonal balance you want based on the mic performer etcetc. That is where you tend to do more individual tweaking.
So in general, monitors get rung out for feed back elimination\
Mains get eq'ed to smooth out the response of the speakersystem
mics get eq'ed for tonal support
Often it is good to avoid a feedback destroyer as Sharyn advised. I'm of the thought process that a well set up system does not need them. And also like I said, using RTA software and a flat mic is probably the easiest way to EQ for quality. Doing it by ear is something I'm not experienced enough to do.
In addition defining a few words might help. When I found out what these all meant it helped a lot. An octave is double the frequency. One octave would be like from 1kHz to 2kHz, or from 50Hz to 100Hz. In addition the ear hears the difference from octave to octave to be the same, so from 100 to 200Hz sounds like the same gap as from 1kHz to 2kHz. So a 1/3rd octave EQ will have 3 sliders per octave. The "Q" function on a parametric EQ will change how wide the area affected by an adjustment is, from fractions of an octave, to octaves. Also an octave in music is the same, so from C to C (C2 to C3 for example) is doubling the frequency.
You might see "cents" used with octaves. They are simply one 1200th of an octave. Very small measurement, not really dealt with in audio for the most part, but good to know of.
Also a parametric EQ is an EQ with 3 adjustments per band, one changes the frequency of the center, one changes the width of the frequencies changes, and one changes the amount of gain added or reduced.
I've used any and all of the above, but here's the short format of my two cents. In any situation you can simply throw on a CD, and listen on a good pair of cans, adjusting the FOH graphs until the room sounds as close to the cans as you can get it. That works best for situations where playback is the main concern.
For vocal reproduction, you've got to address the feedback situation before tailoring the room to suit the program. When an RTA is lacking, you just have to make the room ring and try sliders on the graph until you find the right one. When an RTA is available, don't rely on it too much just as you shouldn't rely on an automatic feedback eliminator. Any monkey can look at the RTA and level the room out, that doesn't mean things will sound good after he's done.
I have an RTA in my rig, it's actually a retired DEQ2496 digital EQ that I used to use FOH. I usually don't plug in the calibrated mic anymore. I just rest it on the dog house of my console and plug the wedge output into the left input. That way, what ever is solo-ed reads on the RTA display. It's higly useful for finding what frequencies to notch in a hurry, and the more I use it the less I need it, my ears are becoming more and more trained. But even when I can pick up on what's wrong with FOH by ear and tweak those graphs, when I'm doing six or eight monitor mixes from 150 feet away it can be difficult to tell which wedges are squealing. Sometimes too, I'll ring the system to within an inch of its life at three in the afternoon and run all day like that, and after seven the air will change and I have to fix the monitors, remotely, on the fly, quite a lifesaver.
Be a bit careful with using cans, since phasing errors tend to be masked but it does give you an idea of what the music should sound like minus room/speaker "alteration"
As he points out, over time you do learn to know what it should sound like, like a musician knowing when the instrument is in tune
Patchable rta for monitor mixes controlled from foh, can be a big help for quick find. As Jon points out, remember that temp and humidity have a significant effect on the sound. Dave Rat of RAT SOUND and Band Engineer for Red Hot Chili Peppers just wrote an article on this for "live sound"
Number one, i dont beleive in the auto systems. They may come close, but im never really happy with the sound that comes off of it, but it may just be because of my music background. Now, i know that for alot of people doing EQ can be kind of difficult, but the first thing i do is go for nothing but making the actually pitches correct. To do that, there a few things you can do, depending on how perfect you want it. As a musician i have a good ear for tuning and just play a very good copy of anmazing grace my buddy recorded and use it as abase for the pitches and different instruments for different pitch ranges and frequencys. If im in a really perfectionist mood or if the systems going to be set up for awhile, i will run different pitches and adjust untill each pitch matches up with a tuner in the house. Also works good when working with mics. I like to do each mic individually like this with a standard pitch to give them all an equal center. Its amazing how off some mics are. And once you have the nitty gritty down for proper pitches and such, everything else pretty much falls into place.
On the low end cutting off low frequencies that your speakers cannot reproduce is usually a good idea, it reduces the work load on the amp and adds a degree of protection for the speakers. Reason being that many times the speaker is actually attempting to move to support the frequency but is not able to generate that frequency, SO in general a low frequency cut off will improve things a bit.
A trick that is used in a lot of pro setups is what is called AUX subs, here what you do on your mixer is only assign those inputs that actually have low frequency content that you want to reinforce to that aux feed in addition to your normal out, you then take your normal mixer/rack out and feed that to your crossoverdspsystem that covers everything above your subs (typically in big systems above 80hz or so) you then only feed the aux sub feed to a crossover/dsp that only send the 80hz and below to the sub FROM the inputs that you want. This can really clean up you system quite a bit, keeps a lot of low end rumble out of the system and gives you more control.
On the High end I would not cut out the frequencies, freq response of speakers is measured in terms of a response curve, with a roll off, so if you cut the hign end frequencies you are going to also effect the frequencies below the cut off based on the slope of the crossover.
Hmm... somethings probably not right if you have speakers that cannot produce certain frequencies... If that is truly the case you should look what the documentation for your speakers says to do with the signal your feeding them. If they have their own crossover or something like that, just feed them a non-shaped signal (dont try to do the crossover's job for it).
What is much more common to do (in my experience) is to pull out a frequency that a speaker produces too well. This frequency often has something to do with the speaker cabinet size and other design parameters. I know I use one set of speakers all the time, and I always have to notch out the same three frequencies and they sound about 100 time better, and I get a ton less feedback.
I am assuming that the OP comment was regarding speakers that either do not have the low end range or the upper end range which is pretty typical, A lot of speakers don't put out much below about 60hz or so and roll off dramatically about 12k or so
so it does not mean that there is something wrong with the speakers
Now, I am going to be eqing a system in a gym. I have worked a little bit with sound in there and I can't seem to get it to sound right. Are there any tricks, or is a room like that beyond making your system sound good? Our gym has an open balcony and is made of bricks, all flat of course. So echo and reflection is a real pain. Any suggestions?
Get your speakers up high, pointing DOWN at the audience, to reduce bounce back from the walls
If you can get drapes that you can hang around (commando 16 works great) it can make a big difference.
Lastly believe it or not if you can just borrow plastic wrapped bales of fiberglass insulation, and leave them all wrapped up and just stack them in the corners and in a few columns along a side wall it will help. Sometimes your local home improvement center will loan it to you, since you don't have to open them at all
Lastly, if you do this all the time, we on occasion use a series of curved panels that we hang from the ceiling, to reduce the reflections from the high areas of the gym, and keep the sound directed down to audience, sort of like a big band shell.
I know that the room is a problem. I think the problem is a little of both. We are using the older PV SP-3's and I recently had to replace the woofers in them because one of them had been damaged. I figured a basketball or something hit it. Now that that problem is fixed, I am working on the sound. I am going to be talking to a company in our area to see if they will donate some sound baffling materials to the school to use in the gym. I will see if I can get the speakers to be pointed down a little. They aren't right now.
Think of the speakers like lights, the need to point and shine where you want the sound, NOT around the rest of the gym. I have seen endless setups where the speakers are just pointed out at the audience, the problem is the sound goes over their heads, bounces off the walls especially the back wall. Get the up high pointing down on the audience, then the sound absorption of the people will make a difference.
in order to come back to the initial posting. In my experience the common RTA/pink noise measurement fails if the room is reverband or otherwise critical.
This happens because an RTA just averages over a longer period of time (which must be done to get stable results), but human hearing uses time to decide what sound is 'good' (which is the sound arriving first) and which is 'bad' (which is the sound arriving later). Because an RTA is 'timeblind' it can not decide which sound is good and which is bad.
There are a lot of useful aplication for RTA, like ringing out or checking frequency content of a signal or detect feedback, but it is not 'state of the art' for equing a speaker room combination.
Nowerdays I suggest a pc based system, like smaart(R) sim(R) or SATlive as the tool to use for speaker/room equing.
Nevertheless you must know what you're doing.
I also have a bit of a feedback problem in our little community theater. We hung the center cluster (for the first time ever) this past summer, and while it sounds pretty good in conjunction with the left and right wings (which I also just hung) it's about 10 feet back from the front of the circular stage front and we do get feedback from the actor's mikes from time to time. The "better" actors with louder, more level voices come out fine, it's the actors with the weaker voices that I have problems with. Currently without spectrum analyzer (RTA?) or EQ my only resource has been to pull down the center cluster volume momentarily as needed to squash the feedback, and live with lower-than-required mic volumes for these actors.
The reigning suggestion seems to be to balance the mic not the room. So I would want an RTA that I can move between input channels during a show to see how each input is balancing and where feedback problems are occuring. Then I need a good EQ for the output ....
Fyi, I'm using a Mackie CFX-20 ... analog, 20 input channels, 12-16 live mics.
1) RTA: any suggestions on what software (I will be able to get a PC if needed) or hardware to use for a spectrum analyzer? Preferably one that I can easily move between channels, or set up to several direct outs (we have inserts that can be used for this) or sub or aux outs, so I can quickly switch my monitoring between channels during the performance as needed?
2) EQ: For the output, do I plan to EQ the individual channels (we have 20), or the sub-outs to the speakers? I have four main house outputs (left, center, right, rears) so if the EQs work in channel pairs then presumably I would need two units.
are you satisfied with the sound of the vocals, and there is just a feedback problem, or is the sound not what you exspect?
If you have an anused aux, you can simply use the aux to feed the rta. Other posibility is to connect the RTA to the pfl signal, which might be done using the monitor output.
As the first step I'd assign an eq to the center cluster.
If you're using a digital controller, you might also try to adjust the time differences between left / right and center.
P.S. If you're sure that you only need an RTA then I'd go for a 19" RTA, otherwise I'd use a software solution (which also can help during EQ and delay setup). Threre are some software RTA's available. On the Allen&Heath pages there is a pure RTA software. Other software containing an RTA is smaart or SATlive (and a many other).