Room correction/DSP

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MartinC

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When room boundaries affect frequency response do they not also affect phase?
Yes, which is absolutely key to what I posted above. My whole point revolves around the phase response being affected by the room, not just the amplitude response.

 

MartinC

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I don't agree.

Unless the speakers are positioned in such a way that their response below 300Hz is identical, applying the same EQ correction to two speakers with a different response will neither make the individual nor the combined sound flatter at the listening spot. See below at 64Hz, 87Hz, 100Hz...

What are you attempting to demonstrate with the RMS average there? It does not represent the response for the two speakers played at the same time.

 

tuga

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Yes, which is absolutely key to what I posted above. My whole point revolves around the phase response being affected by the room, not just the amplitude response.
And in what way does measuring and EQ the response of both speakers simultaneously more effective than EQ'ing the responses individually?

 

tuga

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What are you attempting to demonstrate with the RMS average there? It does not represent the response for the two speakers played at the same time.
I am attempting to demonstrate that the response of both speakers playing simultaneoulsy will produce a combined response that when EQ'ed will not correct either speaker.

 

rdale

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I am attempting to demonstrate that the response of both speakers playing simultaneoulsy will produce a combined response that when EQ'ed will not correct either speaker.
According to Earl Geddes you need to EQ a first sub, and then add a second Sub and derive a different EQ for the second sub while the first sub is playing. Then repeat for a third differently EQ’d sub while the first two are playing. How that translates to EQing a pair of full range speakers I don’t know, as you wouldn’t want to do something similar for mid and treble.

 

MartinC

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With apologies to @flak monkey if you feel this is derailing your thread, but let me have a go at quickly proving what I've said to try to wrap this up.

As a very quick demonstration, here are measurements of each of my main speakers individually (run full range rather than with a subwoofer):

L and R Individual.jpg

Below is a comparison of what I get if I measure the two speakers simultaneously in black, compared to what I get by calculating the sum of the two individual measurement in red. To achieve this I used the acoustic timing reference option in REW which is good enough that the sum is very accurate for all but the highest frequencies, where frankly there is no point looking at the sum anyway. (@Camverton note that this is a demonstration for an asymmetric setup, as shown by the different responses for the two speakers.)

Measured and Calculated Sum.jpg

For the sake of demonstration I then produced an EQ filter based on the calculated sum, targeting a flat response below 200 Hz at 78 dB. Measuring the result of applying this filter to both speakers, with both speakers playing together, I got the result in purple below (with the uncorrected combined response in black for reference). 

EQed Sum.jpg

Finally, here's what the left and right speakers measured individually with the EQ applied look like. Note that the individual responses are far less flat below 200 Hz than the combined result above is.

EQed L and R Individually.jpg

 
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MartinC

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And in what way does measuring and EQ the response of both speakers simultaneously more effective than EQ'ing the responses individually?
Please re-read my long post from this morning, and earlier posts in this thread. I'm not going to keep repeating myself.