Target Based Full Frequency Room Correction

dallasjustice

Member Sponsor
Apr 12, 2011
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Dallas, Texas
I have tried a couple of the top computer room correction products. I've never been satisfied with the sound. The only room correction I've ever thought worked well is narrow band low frequency filters. The only success I've had is with filters less than the room's transition frequency which is about 250hz in my case. I've talked to some very smart folks and I am now understanding why the so called "target curve" approach may be deeply flawed. It's my conclusion that this target based approach cannot achieve it's stated goals.

Paul Hales articulates the shortcomings with modern day target based room EQ as well as anyone I've heard. The interview really begins at the 17:00 mark. Enjoy:
[video]http://twit.tv/show/home-theater-geeks/164[/video]

"If you have good loudspeakers, EQ above 200hz is a bad idea."

"The only way to change the acoustic space, is to change the acoustic space."
 
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amirm

Banned
Apr 2, 2010
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Seattle, WA
That's a very good video and worth a watch. I will go ahead and post it in the video tutorial section.

On the specific, yes, you always want to listen to make sure any correction -- below or above transition frequencies -- makes things subjectively better. They do sometimes and we have proof of that in subjective double blind listening tests. But many EQ products screw things up as was shown in the same tests.

This is an advantage of "Pro" products where you can fine tune things after correction. On my JBL Synthesis EQ for example, I can turn any correction filter on and off on each channel and do a quick AB. I even do it with my eye closed to make it blind. One-button EQs are not helpful in this regard.
 

Nyal Mellor

Industry Expert
Jul 14, 2010
590
4
330
SF Bay Area, CA, USA
That's a very good video and worth a watch. I will go ahead and post it in the video tutorial section.

On the specific, yes, you always want to listen to make sure any correction -- below or above transition frequencies -- makes things subjectively better. They do sometimes and we have proof of that in subjective double blind listening tests. But many EQ products screw things up as was shown in the same tests.

This is an advantage of "Pro" products where you can fine tune things after correction. On my JBL Synthesis EQ for example, I can turn any correction filter on and off on each channel and do a quick AB. I even do it with my eye closed to make it blind. One-button EQs are not helpful in this regard.

The other big big big advantage of the JBL approach is that they have already measured the speakers anechoically, know their power response, and so they know what target to correct to. Every other speaker and room correction system out there you are pretty much guessing at the target curve.
 

dallasjustice

Member Sponsor
Apr 12, 2011
2,067
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Dallas, Texas
You only need a large crane, an open field and an earthworks mic to get anechoic speaker measurements. How hard is that? :p
The other big big big advantage of the JBL approach is that they have already measured the speakers anechoically, know their power response, and so they know what target to correct to. Every other speaker and room correction system out there you are pretty much guessing at the target curve.
 

Nyal Mellor

Industry Expert
Jul 14, 2010
590
4
330
SF Bay Area, CA, USA
You only need a large crane, an open field and an earthworks mic to get anechoic speaker measurements. How hard is that? :p

I guess that depends where you live!

Does Yoav have anechoic measurements incl. power response? That would be one way to start I guess.
 

dallasjustice

Member Sponsor
Apr 12, 2011
2,067
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Dallas, Texas
Yes. Yoav does get anechoic measurements of all speakers that go out. I saw it myself in the factory. The factory is very large with a very high ceiling. And, yes, he does have a big liftgate machine to get the speaker off the ground.

I don't know what kind of measurements they are. He says that he saves them on his computer. Maybe I could ask.

I guess that depends where you live!

Does Yoav have anechoic measurements incl. power response? That would be one way to start I guess.
 

Wayne A. Pflughaupt

Well-Known Member
Oct 15, 2012
100
38
268

I have tried a couple of the top computer room correction products. I've never been satisfied with the sound. The only room correction I've ever thought worked well is narrow band low frequency filters. The only success I've had is with filters less than the room's transition frequency which is about 250hz in my case. I've talked to some very smart folks and I am now understanding why the so called "target curve" approach may be deeply flawed. It's my conclusion that this target based approach cannot achieve it's stated goals.
I’d suggest ditching the “computer room correction products” and make your adjustments manually, using a measurement program like Room EQ Wizard.

IMO it’s poor form to refer to EQ correction above the transition frequency as “room correction.” Above the transition frequency what you’re correcting is the speaker.

I don’t know what Mr. Hale’s idea of a “good speaker” is, but I see reviews for expensive speakers all the time in Home Theater Magazine with severe frequency response deviations. For instance, here’s the quasi-anechoic response graph the magazine posted for a couple of them.



Legacy Classic HD (purple trace) - $4400/pair




B&W 802 Diamond (purple trace) - $24,000/pair


I have a hard time believing that a speaker with a 5 dB hole two friggin’ octaves wide wouldn’t sound better with that problem corrected, no matter how “good” it is. If the speaker has an inherent frequency response problem, there’s nothing you can do to the room that’s going to fix that.

Granted, manually equalizing above the transition frequency can be tricky. You have to be able to look at your response graph and recognize which issues are audible and can be fixed via equalization, and which can’t reasonably be dealt with. However, a basic “rule of thumb” is to go after the broader response deviations, as they are the most audible – IOW, correction that will get an audible improvement. Typically this means problems / filters 1/3-octave or wider, as opposed to the narrow filters often used for equalizing bass response (although I’m not generally in favor of that either, but that’s a topic for another thread).

Here’s a good read on a successful full-range EQ project:

Spridle’s Experiment

Regards,
Wayne A. Pflughaupt



 
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