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Seeking advice about speaker time alignment with REW

zerocrack

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I been going down the rabbit hole with the whole room correction/REW/Dirac ever since I got my 2nd sb2000 and DDRC-24 during last Christmas. Prior to purchasing Dirac this week. I was using alignment tool in REW and set up proper delay time in minidsp to get 2 subs to play nice with each other. And then I create an EQ in REW to smooth out all the bump in the subwoofer response up until crossover point, which I am setting at 60hz for Kef R7. That works out pretty well as I get much smoother bass response and I was happy until I deiced to get Dirac and use it full range. My living room is an L shape with vaulted ceiling so not very ideal room and I am hoping Dirac would get the best out of my system.

After I run calibration using couch settings (9 measurements), I see that there is a huge null at 300hz. This null is visible before Dirac as well but not too bad at -6dB but with Dirac the null is at -9dB. this null is at its worst at MLP. I decided to measure each L and R speaker separately at MLP but both doesn't seem have to this null so I am guessing there is phase/cancellation between the 2 speaker due to the room layout? I played around with alignment tool in REW but this time with left and right speaker and I find that if I put 25ms delay on left speaker, I get much better result throughout entire FR.

Is it normal/recommend to put delay on 1 speaker in a stereo setup? Is there any other approach I can take to get rid of the null? Measurement for L/R speaker included
 

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ernestcarl

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I been going down the rabbit hole with the whole room correction/REW/Dirac ever since I got my 2nd sb2000 and DDRC-24 during last Christmas. Prior to purchasing Dirac this week. I was using alignment tool in REW and set up proper delay time in minidsp to get 2 subs to play nice with each other. And then I create an EQ in REW to smooth out all the bump in the subwoofer response up until crossover point, which I am setting at 60hz for Kef R7. That works out pretty well as I get much smoother bass response and I was happy until I deiced to get Dirac and use it full range. My living room is an L shape with vaulted ceiling so not very ideal room and I am hoping Dirac would get the best out of my system.

After I run calibration using couch settings (9 measurements), I see that there is a huge null at 300hz. This null is visible before Dirac as well but not too bad at -6dB but with Dirac the null is at -9dB. this null is at its worst at MLP. I decided to measure each L and R speaker separately at MLP but both doesn't seem have to this null so I am guessing there is phase/cancellation between the 2 speaker due to the room layout? I played around with alignment tool in REW but this time with left and right speaker and I find that if I put 25ms delay on left speaker, I get much better result throughout entire FR.

Is it normal/recommend to put delay on 1 speaker in a stereo setup? Is there any other approach I can take to get rid of the null? Measurement for L/R speaker included

Both sets of measurements have strong early reflections at ~1ms and 2 ms which could be from bad positioning and/or room acoustics.

There is also a general phase mismatch between 200-300 Hz (likely from boundary interferences) causing the null you observed. Presuming both sets of measurements were to behave moreso in a minimum phase fashion, the summed/aligned response would be more even and have zero cancellation dips.

BTW, no, I would not apply 25 ms worth of delay on the left speaker -- that would completley ruin the LR time difference balance i.e. imaging -- rather, I would endevour to fix the room acoustics first.


*not that it's important -- only noticed now -- but polarity appears (maybe ?) to be inverted for the pair.
 

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Dumdum

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Put simply you have a standing wave (or combination of standing waves) that is presenting 180 out of phase at the mlp and it’s dominating the phase trace, you can add an all pass to whichever channel doesn’t have the phase invertion and that will help summation, but no adding delay to one channel is not a good idea as while it corrects the phasey dip it will throw everything else out of phase and create terrible comb filtering

It’s down to the position of the speakers in relation to reflective surfaces, put the mic in a static location at the mlp (play pink noise while moving the speaker) and move the speaker and inch outwards or inwards or forwards or back, you will see the response change and you’re looking for the smoothest response with the least dips and peaks Essentially your looking to fill nulls with peaks and kill peaks with nulls to get a flat response by adjusting the speakers location

Don’t stress if one speaker ends up closer than the other, your in an asymmetrical environment… it may offend ocd but if the response is good and you apply time alignment correctly and adjust levels the imaging and staging will be lots better and will snap into place

As for Ernest carls comment about phase being inverted I wouldn’t worry as long as both have the same polarity, that’s far more important and with 12db crossovers it’s not unusual to invert the polarity of one driver so polarity with regard to each other is more important
 
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