How do the attributes of a room affect the EQ?

Ben Lagman

Ben Lagman

Freshman
Jan 11, 2011
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Shrewsbury, Massachusetts, United States
Apologies if this is a 'n00b'-ish question. I'm curious though, what attributes of a room affect the changes made into the sound coming out of the mains/outfills/etc? Like for example,
what would be differently be done in terms of EQ when doing a concert inside of an arena with let's say 20,000 fans, versus a concert done outdoors with the same amount of audience. I know there could be a huge amount of variables in this situation, but I'm talking about general things that are usually done (ie. what's adjusted in order to fit the rooms shape and such).
 
It's all about reflective and absorbent surfaces outside you don't have "normally" many reflective surface so the sound travels away creating a need to get stronger speakers for a smaller area , nothing to reflect back into the audience means they generally only get a single source. Sorry for the short post but I'm on my phone.

Sent from my ADR6300
 
Re: How do the attributes of a room affect the EQ?

Generally speaking, enclosed spaces will have reflections and room modes to deal with. You'll be dealing with the phenomenon of "critical distance", trying to maximize the area of direct sound and minimize the area of reverberative sound. You'll also be dealing with rising humidity over the course of the time with a bunch of people breathing out moist air, so the HF will tend to get absorbed more as the humidity rises. Outdoors you'll have to deal with wind blowing your HF around. But other than compensating for rising humidity and perhaps a few transient phenomena, these issues are generally dealt with by arraying for coverage and DSP. "EQ" is perhaps a misnomer.
 
Re: How do the attributes of a room affect the EQ?

Bennett Prescott said:
Higher humidity causes better HF transmission, not worse.
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That is a problem I recently 9as in the last year or so) became all to familiar with.

I am used to high humidity and the HF loss over distance is no where near as bad as in low humidity climates.

During one install I was 700' away and could not only not hear any real HF, but the measured response at 10K was like 60dB down. WOW! No amount of boost is going to make that up. And jsut think of the pour little HF devices that would die trying.

I could get out to about 5-6Kz at that distance and then it dove like a rock.

Not the loudspeakers problem-but rather the low humidity was killing it.

At least that is one good reason for living in the "liquid air south". We have better highs. And I'm not saying anything else-----------------------------
 
Re: How do the attributes of a room affect the EQ?

I wonder if that humidity/HF phenomenon is reflected in regional preferences of brighter EQ settings or boxes in drier climates and less bright EQ/boxes in more humid climates. Anyone have any actual anecdotal or statistical info on regional preferences?
 
Re: How do the attributes of a room affect the EQ?

Basically you would use EQ to reduce frequencies that will "over-excite" the room. In the case of the room I do sound in mostly, I'm usually hacking a lot of 400-500Hz out as an example. Every room is different. Outdoors with the same rig, I'd probably add that stuff back in on the graph.

Greg
 
Re: How do the attributes of a room affect the EQ?

Ben Lagman said:
For example, let's say somebody was put into a room with bad acoustics. Not being too specific here, but what would usually be changed in order to (partially) compensate because of the the reverb produced?
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One thing you can do is to set an RTA to a fast decay. Put pink noise into the system-fairly loud. Now mute the nosie and watch the display decay. You may see one area/freq that decays slower than the rest-ie hangs around a bit longer.

PUt an EQ cut in that area.

Yes the response of the system will be altered. But if you don't energize the room as much at that freq, then those freq will not stand out as much-or interfer as much.

You ahve to be careful how much you cut, but it can offer a measure of help.
 
Re: How do the attributes of a room affect the EQ?

George Friedman-Jimenez said:
I wonder if that humidity/HF phenomenon is reflected in regional preferences of brighter EQ settings or boxes in drier climates and less bright EQ/boxes in more humid climates. Anyone have any actual anecdotal or statistical info on regional preferences?
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That is exactly what I have come to realize.

Over the years I have argued about important having HF extension is. I have come to the realization that it depends on where you live. In a low humidity area-having a system that goes up high is not really that big a deal-unless you are fairly close to the system.

In a high humidity area, having the extra HF extension can really help add to the music.

So as usual-"it depends".
 
Re: How do the attributes of a room affect the EQ?

Ivan Beaver said:
One thing you can do is to set an RTA to a fast decay. Put pink noise into the system-fairly loud. Now mute the nosie and watch the display decay. You may see one area/freq that decays slower than the rest-ie hangs around a bit longer.

PUt an EQ cut in that area.

Yes the response of the system will be altered. But if you don't energize the room as much at that freq, then those freq will not stand out as much-or interfer as much.

You ahve to be careful how much you cut, but it can offer a measure of help.
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Alternatively, you can go back to the "58 in the middle of the room" method I first learned to use. Put an SM58 on a stand in the middle of the room pointing straight up and about 7' in the air. Turn the gain up nice and hot on the input, then raise the channel fader until you hear the first "hot" frequency start to ring. Back off the fader a bit, then (starting at the LF end of your graphic) raise each slider one at a time, noting which ones set off the "ringning". When you find a hot slider, notch it down a bit. You'll learn how much over time. Lather, rinse, repeat.

Primitive, but it works. The more you do it, the better you get.
 
Re: How do the attributes of a room affect the EQ?

Ben Lagman said:
For example, let's say somebody was put into a room with bad acoustics. Not being too specific here, but what would usually be changed in order to (partially) compensate because of the the reverb produced?
Click to expand...
As Greg and others noted, you may be able to compensate with EQ for some environmental acoustics issues but you can't alter the room acoustics with equalization, the best you can do is to try to minimize the negative interactions of the system with the room.

The RTA decay or ringing out the system approaches are beneficial but some system-room interactions are listener/measurement location specific, so you may want to look at more than one location. Also keep in mind that the acoustical environment, from the ambient noise level to the absorption and diffusion present to the temperature and humidity in the space, may vary as the audience varies, so you sometimes may need to initially 'guesstimate' those effects and then tweak them later on.

What you might do may also be dependent on what tools you have. You can do some with an octave EQ and your ears, more with a one-third octave EQ, a RTA and your ears and even more with a parametric EQ, dual channel analyzer and your ears.
 
Re: How do the attributes of a room affect the EQ?

If you have access to a multiband dynamics package, often this is a better way to deal with room issues than relying just on EQ.

Many digital consoles have multiband comp (even smaller ones like LS9), and a BSS 901 or similar works for analog folks, as well you'll find this feature (sometimes called dynamic eq) in quite a few new DSP's

Applying compression to a frequency region where the room response is poor can help to prevent transients from "energizing" and becoming problematic. Of course it's not perfect, but it really can make a considerable improvement.
 
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Re: How do the attributes of a room affect the EQ?

Jeff Babcock said:
If you have access to a multiband dynamics package, often this is a better way to deal with room issues than relying just on EQ.

Many digital consoles have multiband comp (even smaller ones like LS9), and a BSS 901 or similar works for analog folks, as well you'll find this feature (sometimes called dynamic eq) in quite a few new DSP's

Applying compression to a frequency region where the room response is poor can help to prevent transients from "energizing" and becoming problematic. Of course it's not perfect, but it really can make a considerable improvement.
Click to expand...

IF you're in a situation where you're getting a high percentage of the sound out into the room with your system. Anything short of that and you're kinda stuck. As someone once said, "You can't EQ stage wash".
 
Re: How do the attributes of a room affect the EQ?

+1 on what everybody else said. You can even do the run the faders up on the house EQ ring out trick with some music if you don't have an analyzer or pink noise. Pick a song that has a good spectral balance (Earth Wind And Fire "September" always worked for me) Start flat then run each band up and listen to what is going on. Put it back to flat or pull it down as needed if you have to clear up something and go to the next band. If you move a fader a small amount and you get a huge change compared to the other faders you have a problem so cut as needed. As a general rule don't boost anything and keep the EQ as flat as possible, just cut to compensate for the major problems. You can do this to some extent during the performance as the acoustics change with people etc. Eventually you will learn your frequencies and not need to probe around as much. As Dick said, "The more you do it , the better you get." You can download "Simple Feedback Trainer" http://sft.sourceforge.net/ which is a series of sinewave tones (not the same as a third octave worth of broadband material but it will get you close and as a plus will help you determine feedback frequencies).

Positioning of the speakers can go a long way in taming some problems, especially in the upper octaves. If they are horn loaded try to aim so the pattern is less firing at a wall to eliminate reflections. Get the speakers up higher if possible. If anyone can't see the tweeter you can bet they can't hear it as well. You are trying to get as much direct sound from the speakers to the listeners as possible while at the same time eliminating as much reflected sound as possible.

If you have the capability delay the mains to or slightly behind the backline. Use your ears for the final amount. Like everything else it varies with temperature, humidity, position, etc. etc. This will tend to reinforce the sound of an instrument rather than fight with it. When I started many years ago this was not an option. Now I can hear the actual drum kit and guitars rather than a bunch of mud and slosh fighting with my lovely sound in the PA. The instruments will have 3 dimensional position as well as volume.

Above all else it starts on stage with the players and instruments. Sometimes a little more damping in a kik drum or a little tape on the outer edge of a tom to kill some of the overtone can go a long long way. Turning a guitar amp sideways and facing the player for those that absolutely positively feel the need to turn up to eleven can help as well. We are in Junior Varsity so I am assuming we are dealing with at least some local artists where it might be possible to help with the stage sound. Remember we are capturing and reinforcing a performance. Any "bad acoustics" here aren't going to get any better no matter how much processing is applied slight of the mute button.
 
Re: How do the attributes of a room affect the EQ?

Just be careful with how much you remove. Just because you see a 6dB boost doesn't mean you should remove all of it, you need to listen to determine how much of it sounds good and how much of it sounds bad. Conversely, you may hear something in the room that your analyzer doesn't show you. Cutting too much may make your system sound thin even though it measures good.
 
Re: How do the attributes of a room affect the EQ?

Exactly Bennett,
This is why I have always used music to do a final dial in even when I have measuring tools available. Never has a more true phrase been said in this business than, "If it sounds right, it is right."
 
Re: How do the attributes of a room affect the EQ?

Eric Cagle said:
Exactly Bennett,
This is why I have always used music to do a final dial in even when I have measuring tools available. Never has a more true phrase been said in this business than, "If it sounds right, it is right."
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But to different people "right sounds very different.

How many times have you heard a lousy mix and the "mixer" thinks it sounds good. Just because he has no idea what he is doing, does not make it "right".

What if he has to HF response and the highs are boosted so it sounds "right" to him? Does that make it right? Yes to him-but not to the rest of the crowd who has normal hearing. They are being punished because of what somebody thinks is "right".
 
Re: How do the attributes of a room affect the EQ?

Great point Ivan,
Lets hope the person in the mix position is capable enough so at least their version of right is close enough to everybody else's version of right to be listenable. If that is not the case I usually use the option that has always worked for me.............Leave :)
 
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