# How to generate EQ curve from one measurment to match another ?



## rjay (Jan 20, 2013)

I have measured my Left & Right speakers separately. I now want REW to suggest settings for a generic EQ so that the left speaker matches the right. But I can't see how to do that and the help file doesn't explain it. For a start I can only see one measurement at a time - if I could see both then I'd manually make EQ adjustments on the Left measurement, but it seems you can't.


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## jtalden (Mar 12, 2009)

If you want to try the same EQ for both L and R and have that EQ based on the average of the 2 that can be easily done.

Assuming you are interesting in full range EQ then:
Just average the 2 measurements to get another curve and then open the EQ tab for that calculated "measurement".

You should use the "Average the Responses" button at the bottom left corner of the "All SPL" tab. 

[In this case don't use the math function "(A + B) /2" in "All SPL/Controls" dialog. It is not intended for this purpose as it carries the phase data with it an thus the HF results will be misleading.]


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## rjay (Jan 20, 2013)

Thanks, but that's not what I'm trying to do.

I want to use the Right spkr measurement as a benchmark and then get REW to generate suggested EQ settings on the Left spkr measurment so it becomes as close the Right as possible.


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## fusseli (May 1, 2007)

You won't be able to do exactly what you want. REW is designed to match a response target, which is generally flat but you can add in slopes and gradual rise in the HF or LF. If you open EQ you will see where you setup the target and setup your EQ. If that won't get your L to match your R, you'll have to proceed manually.


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## Wayne A. Pflughaupt (Apr 13, 2006)

It’s not a good idea to apply independent filters to the front L/R channels above ~300 Hz. It does wacky things to your imaging. Best to use matching filters down to that point; below 300 Hz you can apply per-channel filtering.

Regards, 
Wayne


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## weverb (Aug 15, 2008)

Wayne A. Pflughaupt said:


> It’s not a good idea to apply independent filters to the front L/R channels above ~300 Hz. It does wacky things to your imaging. Best to use matching filters down to that point; below 300 Hz you can apply per-channel filtering.


Wayne,

Can you expand on the "wacky things"? I currently go to 800 Hz and have not heard anything "wacky". Or maybe I have missed it. :huh:


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## Phillips (Aug 12, 2011)

I have experienced this, now i try to use shelf filters first, then stereo filters (identical for both channels). This has proved to be beneficial and also to a second listener being my fiancee.

The imaging is lost and sounds, muddled unnatural etc, well that's what mind sounded like. 

Wayne will have better wording.


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## JohnM (Apr 11, 2006)

rjay said:


> I have measured my Left & Right speakers separately. I now want REW to suggest settings for a generic EQ so that the left speaker matches the right. But I can't see how to do that and the help file doesn't explain it. For a start I can only see one measurement at a time - if I could see both then I'd manually make EQ adjustments on the Left measurement, but it seems you can't.


There are a couple of ways you can do that. For the manual approach, look at the Predicted graph in the overlay window, you can see post-EQ graphs for both measurements there. To see the target on the EQ window first use the Add Offset to Data control from the main SPL&Phase graph to shift your target measurement curve so that it sits at 0 dB at some reference point (e.g. 1 kHz), then export that measurement as text and load it as a house curve. Set the target shape to Full Range with an LF cutoff of 0.


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## Wayne A. Pflughaupt (Apr 13, 2006)

weverb said:


> Wayne,
> 
> Can you expand on the "wacky things"? I currently go to 800 Hz and have not heard anything "wacky". Or maybe I have missed it. :huh:


Despite Phillips’ confidence in my ability to give an eloquent description, I really can’t! All I can say is that I noticed that things didn’t sound right, something slightly but noticeably weird about it, and it went away with the EQ’s bypassed. I was going to mention that Phillips has also claimed to have encountered the same situation, but I see he’s already done that.

The 300 Hz thing I mentioned might just be a function of my particular room at the time I made the observation. Imaging as we know is based mainly on our perception of the direct signal from the speakers, and the lower in the frequency range you go, the more “omnidirectional” the sound becomes as the room enters in equation - as far as our ability to localize the signal source is concerned. I’ve never seen anything specifically on this, but my feeling is that the point in the frequency range where the sound source can no longer be localized is very much room-dependant: It will be lower in a relatively “dead” room than it will be in a “live” room. At the time my listening room was probably more on the “dead” side, with wall-to-wall carpeting, soft cloth-covered furniture, highly irregular wall surfacing behind the listening area, and a high, steeply-sloped cathedral ceiling to scatter sound pretty effectively. I haven’t checked things in my current room with hardwood floors, but I expect that the localizing frequency point would be well above 300 Hz.

So if you haven’t noticed any issues as high as 800 Hz with stereo filters, my gut feeling is that your room is more “live” than mine was – or like you said, maybe you just haven’t noticed it. I’d say try to find a recording that’s rich in frequency content down in that range – say, a saxophone ensemble recorded in stereo (and obviously it has to be stereo), and listen to the way imaging sounds when you switch the equalizer in and out.

Regards, 
Wayne


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## AudiocRaver (Jun 6, 2012)

Just another view point:

If the 2 speakers are poorly matched and it is the speakers themselves at fault, not room effects, them the imaging is probably already poor and might be improved by using eq to "match them up." I do agree with Wayne P. that such efforts are often more harmful than helpful, though.


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## Phillips (Aug 12, 2011)

> Despite Phillips’ confidence in my ability to give an eloquent description, I really can’t! All I can say is that I noticed that things didn’t sound right, something slightly but noticeably weird about it, and it went away with the EQ’s bypassed. I was going to mention that Phillips has also claimed to have encountered the same situation, but I see he’s already done that.


Hard to pinpoint and describe, yeah i thought you might be able to word it better than me.


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## AudiocRaver (Jun 6, 2012)

If you still want to try accomplishing the original goal, here is a way to get there. It will correct L speaker to match R speaker. There will probably some gain offset that you will have to adjust for manually.


Set 1-octave smoothing for L & R curves
In All SPL, generate A/B curve with A=L and B=R
Apply offset to A/B (with Add Offset to Data) to get it to range of L speaker curve
In EQ window for A/B, generate correction filters; Export the filter values to a file
In EQ window for L speaker, import the saved filter set
In Predicted SPL window (Overlays), you should see a pretty good match, probably with some gain offset


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## weverb (Aug 15, 2008)

Wayne A. Pflughaupt said:


> Despite Phillips’ confidence in my ability to give an eloquent description, I really can’t! All I can say is that I noticed that things didn’t sound right, something slightly but noticeably weird about it, and it went away with the EQ’s bypassed. I was going to mention that Phillips has also claimed to have encountered the same situation, but I see he’s already done that.
> 
> The 300 Hz thing I mentioned might just be a function of my particular room at the time I made the observation. Imaging as we know is based mainly on our perception of the direct signal from the speakers, and the lower in the frequency range you go, the more “omnidirectional” the sound becomes as the room enters in equation - as far as our ability to localize the signal source is concerned. I’ve never seen anything specifically on this, but my feeling is that the point in the frequency range where the sound source can no longer be localized is very much room-dependant: It will be lower in a relatively “dead” room than it will be in a “live” room. At the time my listening room was probably more on the “dead” side, with wall-to-wall carpeting, soft cloth-covered furniture, highly irregular wall surfacing behind the listening area, and a high, steeply-sloped cathedral ceiling to scatter sound pretty effectively. I haven’t checked things in my current room with hardwood floors, but I expect that the localizing frequency point would be well above 300 Hz.
> 
> ...


Interesting stuff this acoustic stuff is. I wonder if listening distance also plays a part. I would guess your listening position was further back from the speakers? I sit very close (basically 60" triangle leg lengths) plus my speakers are placed less than ideal to begin with. Might need to start a new thread as not to take the op's off topic.


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## weverb (Aug 15, 2008)

Phillips said:


> I have experienced this, now i try to use shelf filters first, then stereo filters (identical for both channels). This has proved to be beneficial and also to a second listener being my fiancee.
> 
> The imaging is lost and sounds, muddled unnatural etc, well that's what mind sounded like.
> 
> Wayne will have better wording.


Interesting suggestion. May need to revisit some of my filters and try this technique. Thanks Phillips.


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