Frequency Response/Contour EQ in full range systems.

Jan 19, 2011
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Lately I've been experimenting with tonal shape/frequency response/contour equalisation of sound systems. I got this idea last year while attending a L-Acoustics seminar, they talked a lot about tonal shape/contour of their sound systems. Example can be found here:
http://drbentsen.no/wp-content/uploads/2010/12/Full-range-modular-systems-contour-bandwith.pdf

To my big suprise, I found that if I eq a sound system so it sounds pleasing to my ear for full range playback, I end up with a contour nearly identical to what L-Acoustics calls Reinforced Contour, +1dB/oct from 1K and downwards, and a "flat" level from 1K and upwards. It's also suprisingy easy to mix on, although I have to use a bit more lo-mid eq on my input channels, but not as much lo-cut as I used to do.

What's your experience with this kind of equalisation/contour response?
Do you have a preferred way of doing this? Genre/venue/audience spesific maybe?

"enquiring minds want to know" :)
 

Bennett Prescott

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Re: Frequency Response/Contour EQ in full range systems.

Helge,

Overall system tonality is one of the last little "secrets" I pull out of my bag, I'm sure anyone who regularly measures has a curve they shoot for. Sometimes it comes down to where it is acceptable to you to let the response get a little soft at FOH in order to provide more consistency elsewhere, and sometimes it comes down to what the PA system can do. I certainly have a slightly different strategy when I have a PA system that will do 50Hz solid all day, or when I have a sub system that will do 30Hz solid all day, than when I can only get to 80 or 90Hz in the mains and 35 or 40Hz in the subs.

However I think you will find that, if you offer a curve as you have suggested, few engineers will go messing around with the mains EQ much in the LF. Often I will shoot for a slightly softer HF, especially if I am trying to cover a very long distance and want the nearer seats to more closely approximate the response that is possible at 400'.

I have met one engineer in my life, ever, who wanted a truly flat PA (although even he appreciated a 6dB bump in the subwoofers). He had many excellent reasons for desiring it, and had the measurement chops to get it.
 

Tim McCulloch

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Jan 11, 2011
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Re: Frequency Response/Contour EQ in full range systems.

Yeah, 6db. Probably because the BE used the input strip EQ to make the sounds, not the PA system.

It's an odd thing, voicing a PA. Some guys want to play their favorite tracks flat and hear/feel what they want their show to be. This approach requires minimal strip EQ but frequently results in a lot of GraphiHacking® to get the mids and HF to play nice with the vox (esp GBF). Others want a reasonably "linear" PA, where what comes out of the console is what comes out of the loudspeakers. This approach tends to require less house EQ intervention and is appealing to BEs that have studio chops; it also requires that the BE have a solid grip on his/her bands input sounds and be able EQ/process accordingly.

As the system guy, my job is to make the PA work the way the headliner's BE wants it to work. I've done lots of different things over the 30 years I've been in audio and very little surprises me any more.

Have fun, good luck.

Tim Mc
 

John Roberts

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Re: Frequency Response/Contour EQ in full range systems.

The word contour is usually linked to "loudness" as our hearing's frequency response depends on SPL in the room.

The contour to sound good at easy listening levels will probably be different than for full tilt boogie.

One pretty well respected recording guy (IMO) makes a point of normalizing the SPL of the studio monitors while mixing to get consistent results.

JR
 

Ivan Beaver

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Re: Frequency Response/Contour EQ in full range systems.

With the exception of a "bump" down below 100hz (and that varies with the type of system-subs on aux or not-user style of music etc) I prefer to provide as clean a palate as possible for the "artist" (FOH operson) to work with. That mean as flat as possible (phase and amplitude)

In a live situation (not DJ playback-that is a different story), the FOH person will (should anyway) make the adjustments needed for a particular instrument in a particular freq range.

For example if the vocals are screaming at 4Khz, then that needs to be reduced in the vocal channel. Not pulled out of the overall PA EQ, becuase other instruments may need that level.

A live mix is one thing, DJ playback, movie playback etc have different needs in terms of eq that also vary with intended playback level.

The problem is people often try to use what is good for one usage and apply it to another, which often ends up with results that are not desired.

In sound-one size does not fit all.
 
Re: Frequency Response/Contour EQ in full range systems.

With the exception of a "bump" down below 100hz (and that varies with the type of system-subs on aux or not-user style of music etc) I prefer to provide as clean a palate as possible for the "artist" (FOH operson) to work with. That mean as flat as possible (phase and amplitude)

In a live situation (not DJ playback-that is a different story), the FOH person will (should anyway) make the adjustments needed for a particular instrument in a particular freq range.
As much as I respect your opinion and knowledge of audio I still think the FOH person should be allowed to mix however he wants without systems people saying THIS is the way you SHOULD do it. As long as he/she isn't breaking anything, right?

For example if the vocals are screaming at 4Khz, then that needs to be reduced in the vocal channel. Not pulled out of the overall PA EQ, becuase other instruments may need that level.
Ah, the real world: What if that screaming vocal is needed in the monitors that are run from FOH and there is no EQ instrted on the vocals buss? FOH dude has to do SOMETHING to not burn the audience's ears - one way is to tame the vocals with the FOH graphic and just add that range with channel strip EQ on the instruments that end up lacking 4 kHz. Just saying that there are several legitimate "roads to salvation" - even if I generally try to mix the way you suggest here.





A live mix is one thing, DJ playback, movie playback etc have different needs in terms of eq that also vary with intended playback level.
It seems to me that if we are using the logic that the sound system response should be flat and the mixerperson is "doing it wrong" if the mix needs a adjusted FOH graphic to sound right, then we are saying that all the major movie studios are "doing it wrong" because their mix doesn't sound right on a flat system. Do you see what I mean?



In sound-one size does not fit all.
Which is what I'm saying also. If it sounds good and doesn't break anything I kinda don't care how the mixerdude got there. :)
 
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Jay Barracato

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Re: Frequency Response/Contour EQ in full range systems.

The funny thing is in my world of small clubs and bars, listening rooms, PACs, and festivals, every system engineer refers to their "preferred" frequency contour as "flat" regardless of the way it measures.
 

Bennett Prescott

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Re: Frequency Response/Contour EQ in full range systems.

The funny thing is in my world of small clubs and bars, listening rooms, PACs, and festivals, every system engineer refers to their "preferred" frequency contour as "flat" regardless of the way it measures.
Jay, in my experience nobody wants to mix on a flat PA. Also in my experience, only measurement folks understand that the PA is not flat. At almost every level of the industry.
 
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Re: Frequency Response/Contour EQ in full range systems.

I have a curve I aim for, its fairly similar to the l'acoustics example and it is "flat" in a way. Its roughly the shape of music. Run all of your favorite tunes through an RTA with really slow averaging, you will see a very common shape that resembles the l'acoustic curve and the curve I use as a guide for tuning concert PA's .
 

Ivan Beaver

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Re: Frequency Response/Contour EQ in full range systems.

I have a curve I aim for, its fairly similar to the l'acoustics example and it is "flat" in a way. Its roughly the shape of music. Run all of your favorite tunes through an RTA with really slow averaging, you will see a very common shape that resembles the l'acoustic curve and the curve I use as a guide for tuning concert PA's .
Let's look at that statement a little bit deeper.

First of all, you are describing the average response of the music that is going INTO the system No argument there at all. But you will find that different styles have some very different relaionships and different producers of the same style will have different relationships-but let's forget that for a little bit

HOWEVER-If you want to HEAR that music the same way-you HAVE to run it through something that does not CHANGE the relative level relationships.

If you run it through a system what has a different response (as you suggest the same level differences) and then measure it AGAIN, you will see that the response that you are hearing no longer has the same "shape" as what went into it. The new "shape" is added to/subtracted from the origional.

Hence my reason for a flat/neutral system.

Altering the response (as you suggest) reminds me of a guy I knew in college who used Marshall amps and 4x12 cabinets for his stereo system. His reason was that is what his favoirte band (Led Zeppelin) used and he wanted it to sound as close to the origional as possible.

Yet what he was really doing is altering-again-the sound of the recording. And I would argue that the drums and vocals weren't run through a Marshall guitar amp.

Just something to think about.
 

Ivan Beaver

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Re: Frequency Response/Contour EQ in full range systems.

As much as I respect your opinion and knowledge of audio I still think the FOH person should be allowed to mix however he wants without systems people saying THIS is the way you SHOULD do it. As long as he/she isn't breaking anything, right?

If it sounds good and doesn't break anything I kinda don't care how the mixerdude got there. :)
I agree that as long as they aren't breaking anything, they should be allowed to do as they wish-sometimes it is very much a part of the "style" of the music.

I just relate that a flat system (more on "flat" in a second) is like a white canvas to a painter. If the canvus is already "colored", then the artist has a harder time creating the image they want to.

FLAT-WHAT DOES IT MEAN?

Flat is a term that is thrown around, without any other association. Hence I think a lot of the confusion.

What does the term "flat" used? Back in the old days of dedicated RTA's, if a system was made "flat" nobody liked it. It was edgy, lacked warmth and so forth.

HOWEVER-if the same system was measured and adjusted (properly-another issue altogether) with any of the various transfer function measurement systems, then "flat" will sound very different.

They are both "flat", but measured with different tools.

To be honest I have not compared a transfer function measurement to an RTA measurement using the same measurement system-with a system in a real room.

I suspect that they may be closer today than they used to be.

I think "flat" is just another one of those terms that are thrown around, without people really knowing what it means (as Bennett suggested), such as phase, impedance, pattern, combfiltering and many other terms.
 
Re: Frequency Response/Contour EQ in full range systems.

Ivan makes some good points, as usual.

Something else one should keep in mind is whether the target response curve, and the measurements being made to see if the target has been achieved, is the direct field of the loudspeaker system or the in-room response of the system. If we're talking about the direct field in an outdoor setting I would venture to say that something like Reinforced Contour from the L'Acoustics graph might sound better. However, if we're inside, but still talking about the direct field of the loudspeaker, one would also do well to consider the power response of the loudspeaker system. Typically this will have a primary effect on the perceived sound quality in the frequency region below 500 Hz. Of course this is room dependent. A direct field measurement that resembles something closer to the Flat contour curves may sound better than the other two, but this will depend on the power response of the system, the placement of the loudspeakers, and the reflective surfaces of the room.

When measuring the system response in a room below 300 Hz or so I think it's a good idea to do so with a longer, or no, time window so that reflections from the room actually get into the measurement. Of course an RTA would show the entire reverberant field. In this frequency region such a measurement may actually be more indicative of the perceived response of the loudspeaker system because the power response and room effects are included.

Sometime these distinctions are overlooked. I don't think they should be because they are not subtle.
 

Jay Barracato

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Re: Frequency Response/Contour EQ in full range systems.

Jay, in my experience nobody wants to mix on a flat PA. Also in my experience, only measurement folks understand that the PA is not flat. At almost every level of the industry.
Actually given the acoustic nature of bluegrass, I am looking for a flatter response than most techs down low, but like you, I also like a fairly strong roll off up high. Somehow, not needing +16 db under 100 has translated to not needing anything under 100 (if you were to go back and hunt some of my posts from 5 years ago, I bet you could find me saying the same basic thing).

I also found it humorous that I think I fit Tim's description of a mixer, but he attibutes that to studio folks, something I have had minimal experience with.

Anyways, the nicer the voicing of a PA, the less eq I find I use in general. My basic philosophy is put a good sounding mic on a good sounding source and let it rip. Drastic eq needs seem to me to be treating a symptom not the basic problem, but that is another thread I have been considering.

At one festival this summer we were the first band to take the stage with IEMS. When we started there was a bad buildup of 600ish under the tent over the stage caused by the FOH stacks which were outside but next to the tent. I would guess it had not been noticed before because the loudness of the stage monitors had been covering it up. I ended up cutting 600, 315, and 125 which seemed to be natural resonance frequencies of the stage and tent. Both of the bands following me had techs with them that I know. After each band the system tech would re"flatten" the house graph, only to have the next tech cut the exact same things.

I guess going back to flat is better than the usual festival setting where everything gets hacked further and further as the show goes on (I am usually the one trying to slide frequencies back in at that point), but in this case it was especially crazy as it was a two set a day festival, and all three of us went through the same thing twice.

On the other hand, there is a company that provides for a lot of festivals around the area, that provides the EASIEST rig to walkup and mix on that I have ever encountered. While I only had 2 sets on their stage this summer at one festival, I was also a guest of other bands at two other festivals. I have heard this rig in several different locations, with a variety of local problems/constraints to overcome, and it consistantly sounds good to me. While mixing on it, I never even looked at the system eqs, and only made a couple of really minor changes to channel eqs. The bulk of my mixing was setting my dynamics and the relative levels of effects that I wanted. After that the show was truely just riding a couple of vocal faders as the lead singer switches between songs. Since it was digital, I had even less to do the second set.

So I guess it goes back to perception and taste. In the first example, the system engineer was chasing his perception of flat (he did have a measuring system at FOH, but did not account for the buildup and bleed back through the mics under the tent on stage) regardless of the end result, while in the second example, because the system engineer's taste matched my own, I never even thought about how the system was tuned.

No doubt about which system was easier to work with. Also breaking with my traditional of keeping all the names out of where I have been and who I have worked with, system 2 (the easy one) was Jason M from Southard.
 

Ivan Beaver

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Re: Frequency Response/Contour EQ in full range systems.

I understand what you say, but that shape is a real thing, would you care to explain it?
I assume you are talking to me about this-if not, then ignore this.

First of all lets assume (which is incorrect-but is all we can do) that the system that the system the recording engineer was using was "flat". So the relationships of different freq to others is based on what he wanted you to hear-because that is the way he heard it when he mixed it.

Let's say the lows are 10dB hotter than the highs in his mix. So when you play it back in a system that has a 6dB bump on the bottom, and then measured again (using the same input source), you would see that the lows are now 16dB hotter than the highs. This is NOT how the engineer intended you to hear the music.

It may sound "better" (or not depending on what you like-some people like more bass than others-so who is "right"?), but it is not accurate or having the intended response as the origional recording.
 
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Re: Frequency Response/Contour EQ in full range systems.

Ivan,
Concert PA systems almost always have a curve similar to the l'acoustics curve. This is not new information. It is a reality. I attribute this to "shape" of popular music. You disagree. What is your explanation?
 

Tim McCulloch

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Jan 11, 2011
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Re: Frequency Response/Contour EQ in full range systems.

I agree that as long as they aren't breaking anything, they should be allowed to do as they wish-sometimes it is very much a part of the "style" of the music.

I just relate that a flat system (more on "flat" in a second) is like a white canvas to a painter. If the canvus is already "colored", then the artist has a harder time creating the image they want to.

FLAT-WHAT DOES IT MEAN?

Flat is a term that is thrown around, without any other association. Hence I think a lot of the confusion.

What does the term "flat" used? Back in the old days of dedicated RTA's, if a system was made "flat" nobody liked it. It was edgy, lacked warmth and so forth.

HOWEVER-if the same system was measured and adjusted (properly-another issue altogether) with any of the various transfer function measurement systems, then "flat" will sound very different.

They are both "flat", but measured with different tools.

To be honest I have not compared a transfer function measurement to an RTA measurement using the same measurement system-with a system in a real room.

I suspect that they may be closer today than they used to be.

I think "flat" is just another one of those terms that are thrown around, without people really knowing what it means (as Bennett suggested), such as phase, impedance, pattern, combfiltering and many other terms.
"FLAT" is pretty much meaningless, that's why I prefer Robert Scovill's term "linear."