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Manually time-aligning subwoofer(s) to mains - how to

Daverz

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imo people are overcomplicating.
play around with rough delay jumps until you get excess group delay close to zero (use dirac impulse for audible pre-delays).
from there play around with finer delay steps until you get the flattest in the crossover region

This is even more obscure to me than the OP. Excess group delay of which measurement (sub or main or both?) I don't understand the comment about Dirac impulses. Actually play them through the speakers?
 

dasdoing

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Excess group delay of which measurement (sub or main or both?)

both. in this example you can see the sub is about 25ms too late:

excess_gd.jpg


you want to bring it close to zero in the first step,

and if you overshoot a little (in the negatives) you have to check for audible pre-delay. a small spike of 5ms or so in the subwoofer range wont be audible.

Actually play them through the speakers?

yes, it makes pre-delay pretty obvious down there. I also like to use MJ Billie Jean; the first seconds reveal pre-delay pretty good (though I use this more for checking DRC filters which can cause audible predelay above 1000Hz).

In this first step we make sure we don't align fase in multiples of 360 degrees. If we don't do this we end up phase aligned but still have delay.

the second step is the real alignment. here our goal is to not have any cancelations in the crossover overlap. the easiest way is to look at the FR graph and adjust the delay in small steps. after a little trail and error the best value becomes obvious, because it causes the smallest dip
 
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fluid

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The sub (measured to the driver dustcap) is only about 1 meter further away from the listening position
I must have missed this before the microphone needs to be in the same position for measuring both speakers to set any relative delays.

In the mean time I have another doubt with the above spectrogram plots below 50 Hz: as you can see, the peak energy arrives ~60 ms later than the energy above 50 Hz. Reading about the wavelet spectrogram, I saw that in an ideal plot the peak energy needs to arrive at about the same time for all the frequencies, is it correct? In my <50 Hz region the sub is 'soloist', so this 60 ms delay is due to a not ideal interaction between the room and the sub? Are our ears sensitive to these different delays in the spectrum? I also tried to do some 'blind' tests between the aligned system and the not aligned one but I couldn't hear any differences, maybe my ears are just bad :) (or maybe I didn't test it with the appropriate audio materials)
It is hard to say as it takes a number of cycles at bass frequencies for the ear to recognise their existence the lower in frequency the less the problem. It can be hard to test for these issues with music because the music may not have much of those frequencies in it. I would suggest a slow sweep of a sine wave from REW's generator and see if any frequencies sound like they are missing or wrong.

There are many different ways to align drivers and look at measurements use whatever works or is easiest for you. All of these graphs are just different ways of looking at the same data.

It doesn't have to be excess group delay it can just as easily be the group delay.

Article from Charlie Hughes here
https://audioxpress.com/article/Subwoofer-Alignment-with-Full-Range-System
 

dasdoing

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about audibility of delays in the subrange: it depends on the music. percussive music will lose "punchyness". audiofile music on the other hand wont reveal it much. also it seams a delayed bass is percieved as less loud. all those effects are subtle though
 

dasdoing

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if you think about it, a delayed bass will act kind of like a limiter with fast atack. the atack of the kick will be masked (cause it is not isolated anymore). that's why the punch is lost
 

ernestcarl

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@ernestcarl Can you please have a look at my alignment just to see if I missed anything? (Or anyone willing to provide some feedback for that matter).

https://drive.google.com/file/d/1f1hYANWiVOkU9PsYnvLLZeZErT0KqHQw/view?usp=sharing

Your summed measurement looks fine.

Using the alignment tool, the delay I arbitrarily picked was 7.45 ms (a bit more conservative than yours).

1624602194223.png


WAVELET SPECTROGRAPHS
1624602202526.gif

linear peak, 100% scale, 1/5 res, normalized

*I shifted the IR of both mains and sub using the same time offset to get them to start correctly at 0.

IMPULSE RESPONSE
1624602441429.gif


I can't say that you'd be able to hear a whole lot of difference with either delay settings. You'd have to test it out for yourself. However, if I were to apply FIR correction, I would maybe pick the one where the sub's IR peak starts closer to the mains.
 

ernestcarl

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I'm very curious about how you figured out the delay I dialed in without me providing measurements without the delays? (which was a stupid move from me I must admit).

Just looking the at time axis. That simple. ;)
 

abdo123

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Just looking the at time axis. That simple. ;)

btw I'm super impressed by how smooth you can get your response (across one axis at least) even with just two subwoofers without EQ, I mean I went from 40dB error rate to just that 10 dB dip at 90 Hz that was fixed when summed with mains anyway.
 

ernestcarl

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btw I'm super impressed by how smooth you can get your response (across one axis at least) even with just two subwoofers without EQ, I mean I went from 40dB error rate to just that 10 dB dip at 90 Hz that was fixed when summed with mains anyway.

If you meant there were two subs in that one measurement of yours, I couldn't tell as it looks already as if it were a single unit.

Phase induced dips due to non-optimal summing is probably common esp. for people who don't measure. I used to think it was difficult to get these to align right -- in fact, it's not too hard once one gets the hang of it. Though, it was very difficult manually applying different FIR filters in my couch setup (MCH surround). Different FIR filters had to be created for the fronts, surrounds, and the sub -- so as to achieve the greatest linear summation between the bass managed sub signal, the full-range LFE signal, and all the satellites (mains are linear phase coaxes, surrounds weren't).
 

ernestcarl

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Something curious I noticed... If we extract the excess phase versions of the summed responses and look at their individual spectrographs:

1624606257631.gif

linear peak, 100% scale, 1/6 res, normalized

The 7.45 ms delay for mains looks more linear across the board.

*actually, this was kind of already indicated within the GD graph views as well.
 

abdo123

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This is my current delay settings, Output 1 is Left main, Output 2 is right main, Output 3 is left sub, Output 4 is right sub. The subs (3 and 4) have an inherent electronic delay of 19.25ms.

1624606929036.png


I included a new set of measurements, everything is time referenced to output 2.

https://drive.google.com/file/d/1quIaU5q4dIY2sD6MKO1lcvtPeyx7HnrN/view?usp=sharing

The responses seem quite healthy to me, but my methods were very simple (just look at the alignment tool and keep scrolling till you find good alignment) please let me know if you think I am better off with any of these changed!
 
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ernestcarl

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This is my current delay settings, Output 1 is Left main, Output 2 is right main, Output 3 is left sub, Output 4 is right sub. The subs (3 and 4) have an inherent electronic delay of 19.25ms.

View attachment 137312

I included a new set of measurements, everything is time referenced to output 2.

https://drive.google.com/file/d/1quIaU5q4dIY2sD6MKO1lcvtPeyx7HnrN/view?usp=sharing

The responses seem quite healthy to me, but my methods were very simple (just look at the alignment tool and keep scrolling till you find good alignment) please let me know if you think I am better off with any of these changed!

It looks like you've centered the mic between the left and right front channels much better from these set of measurements: Delay 0.1537 ms with left as output source and the right as reference.

Were these individual channel measurements applied with all delays in the graphic in place?

The left and right subs look not quite aligned esp with the delay you added to the right sub (output 4):

1624647264998.png


1624647426020.png


It's better to align both subs first (functioning as mono) so that they optimally sum prior factoring in actual delays needed for the rest of the satellite channels. *Although, I suppose if you were making an admitted compromise for a more linear response across a broader area maybe some slight difference in the timing could be possibly beneficial if borne out by the measurements.
 
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abdo123

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It looks like you've centered the mic between the left and right front channels much better from these set of measurements: Delay 0.1537 ms with left as output source and the right as reference.

Good to know I guess? Don't think I did anything differently from usual.
Were these individual channel measurements applied with all delays in the graphic in place?

Yes, I thought I had a healthy summation but you disagree so perhaps I should give it an extra try. Keep in mind that output 3 has inverted phase, just incase you missed that.

What delay should I pick based on your analysis? You managed to generate much more glorious headroom than my setting.
 

ernestcarl

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Good to know I guess? Don't think I did anything differently from usual.

It might seem like so, but the timing in your current measurements looks different:

1624648571185.gif


Yes, I thought I had a healthy summation but you disagree so perhaps I should give it an extra try. Keep in mind that output 3 has inverted phase, just incase you missed that.

What delay should I pick based on your analysis? You managed to generate much more glorious headroom than my setting.

Oops... I forgot about the inversion! Factoring that in:

1624649458207.png

not 14 ms but 7 ms for the left sub (so remove the inversion)


As for the satellites with the current set of measurements you have shown in the red SPL magnitude trace and the delays of miniDSP in place: reduce it by ~9.5 ms
 

abdo123

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It might seem like so, but the timing in your current measurements looks different:

View attachment 137383



Oops... I forgot about the inversion! Factoring that in:

View attachment 137385
not 14 ms but 7 ms for the left sub (so remove the inversion)


As for the satellites with the current set of measurements you have shown in the red SPL magnitude trace and the delays of miniDSP in place: reduce it by ~9.5 ms

So to summarize + make sure, Output 3 / Left sub gets inverted back to normal (previously inverted) and receives a 7 ms delay, while output 4 receives no delay at all (originally 7.5ms).

the mains' delays is reduced from 24ms to 14.5ms.
 

abdo123

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