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Excess group delay and mismatched phase response

pollock0424

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Hello,
I have moved my system to the longwall + 15inch Subwoofer and found out that major issues in the bass region have been solved. To get some perspective here is my old thread. In this new setup, I am trying to figure out measurements such as excess group delay (GD) and minimum phase ([1],[2]). Here are some plots for my current setup:

phase_plot_left_with_sub.jpg


phase_plot_right_with_sub.jpg


As you can see phase response of the left speaker is approximately constant from 600hz to 20khz as opposed to the Right speaker. What is going on ? Should I be concerned that phase responses are not matching ? My guess is that I could experience cancellations ? Also, in the left speaker 600hz to 20khz, waves seem to be having same delay, how will this influence the perceived sound ?

Also, I am trying to see the excess group delay so that I can set the delay on my sub. Here are the plots, why is the "Excess group delay" option greyed out ?
excess_gd__plot_left_with_sub_excess.jpg


excess_gd__plot_right_with_sub.jpg


Also, you might have noticed a massive dip at 100hz, I think I can correct for that. It was probably because my work bench was put up as I have an amp on the bench, currently waiting to be fixed. I will re do the measurements again.

FIR_at_100hz_Th36_with_Sub.jpg


Any explanation of what's going on in the phase response will be greatly appreciated.
I am also looking for suggestions on setting the delay for the sub.
I feel like the treble response is not as good as before, is this my expectation bias or do you see something in the plots ?
 
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ernestcarl

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As you can see phase response of the left speaker is approximately constant from 600hz to 20khz as opposed to the Right speaker. What is going on ? Should I be concerned that phase responses are not matching ? My guess is that I could experience cancellations ? Also, in the left speaker 600hz to 20khz, waves seem to be having same delay, how will this influence the perceived sound ?

Whether or not you should be concerned depends on how you measured.

The right speaker's (blue trace) inclining phase to the right of the graph means that its upper-half of the FR is playing earlier than whatever is your set timing reference. If this is accurate, it could lead to a perceived image shift towards that side as well as cause some additional unnecessary comb filtering when both speakers are playing simultaneously.

Also, I am trying to see the excess group delay so that I can set the delay on my sub. Here are the plots, why is the "Excess group delay" option greyed out ?

You need to let REW calculate/generate those curves:

1702907642538.png


Also, you might have noticed a massive dip at 100hz, I think I can correct for that.

Likely caused by boundary interference reflection which you can either only partially compensate with EQ or move slightly via repositioning.

I am also looking for suggestions on setting the delay for the sub.

Try searching/skimming through previous threads or posts that discuss subwoofer and mains speaker alignment or the REW alignment tool.
 
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pollock0424

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@ernestcarl
Thanks for your response. I was able to generate minimum phase and look at the excess phase, I varied the phase knob on my subwoofer to achieve the best possible excess GD and RT60 decay. Soon, I will take a measurement of the subwoofer and speaker and get the time alignment value from REW and further fine tune the system. I was wondering if I should align my sub to left speaker or to the right or align it to L+R?

Regarding the phase mismatch, when I swapped the acoustic reference to the right side then the phase plot was also swapped, now the right speaker phase plot looks constant from 500hz to 20khz just like the left speaker when the reference was the left speaker.
 

ernestcarl

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I was wondering if I should align my sub to left speaker or to the right or align it to L+R?

It is always going to be time adjusted/aligned relative to the speaker channel that you’ve chosen to be the time reference.

BTW, I sometimes do L+R just for convenience.

For example, speaker A is 1 meter away from the mic MLP and speaker B is 1.2, and speaker C is 2 m away. Let’s also say the sub is in one of the far corners of the room. If you cannot reasonably get all channels to be symmetrical in distance through positioning, you should use the channel that is the farthest as the reference — applying delays to rest of the other speakers so that they all have synchronized arrival times to the mic — more important for the HF.

If the difference in distance is relatively tiny (couple of mm), then it does not matter all that much.

When phases significantly do not match around the crossover, you might need to apply additional filters, for example, an all pass to rotate the phase a bit in either of the speakers.
 
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pollock0424

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Agreed, it is all relative to a reference. Dirac on minidsp used to introduce delay/gain sometimes depending on the placement. I think that might impose restrictions on seating.. critical for me is time aligning sub bass frequencies with L+R. I might do a sweep on L+R and use that as a reference. This is all new to me and I'm still learning.
Nowadays, I use Integra drx 8.4 and I tried DLBC on it and I was less than impressed with the alignment of the subwoofer. Dirac full range however does an awesome job for a 7.1.4 system. I'm planning to redo the DLBC and if it doesn't work out, I will ditch it and put my minidsp shd back into the signal chain for handling the xover and time alignment between main L+R and sub..this way I will have a good 2.1 setup and that will also serve my HT. I think that DLBC also optimizes between satellites and subwoofer..but I'm not interested in that.
 

ppataki

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I tried DLBC on it and I was less than impressed with the alignment of the subwoofer.
I came to the same conclusion with Dirac and also with DLBC - the sub alignment was really poor
What I did to overcome that is that I manually mixed the sub into the signal (=setting the delay and the crossover in Jriver and using VST plugins) and fed Dirac with it - so Dirac did not 'see' the sub
The sound got waaaaay better (both objectively and subjectively)
 
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pollock0424

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@ppataki
I am moving a few things out of my office to clear some space. I will wait until then to redo all of it. I have a mode at 50hz and I will use PEQ to mitigate that, although it is not audibly disturbing with subwoofer crossed at 55Hz. I plan to set the system to 7.0.4 setting in my AVR and send full band signal to minidsp SHD and I will handling the crossover to the sub there. All this is to hide my SUB from Dirac lol... this is my continegent plan if DLBC fails utterly again!
 

ppataki

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@ppataki
I am moving a few things out of my office to clear some space. I will wait until then to redo all of it. I have a mode at 50hz and I will use PEQ to mitigate that, although it is not audibly disturbing with subwoofer crossed at 55Hz. I plan to set the system to 7.0.4 setting in my AVR and send full band signal to minidsp SHD and I will handling the crossover to the sub there. All this is to hide my SUB from Dirac lol... this is my continegent plan if DLBC fails utterly again!
So essentially you are doing the same as I did :)
 
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