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How important in phase control on a subwoofer?

dasdoing

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I have never found the phase plot to be usefull for anything. it is usefull for anechoic speaker meassurements only.
you want to look at time, look at group delay.

now in terms of sub alignment I think you need to keep it as simple as possible. if you use regular 2nd or 4th order crossover all you realy have to do is to trail and error with delay until you get the flattest you can get. besides that just make sure you are not a cycle too early/late on excess group delay
 

ernestcarl

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How do you time align the sub with mains in a stereo set up?

If aligning phase is something you want to explore, make sure to have the appropriate clock timing reference set-up if you're using REW. Cheap USB measurement microphones like the UMIK-1 are popular, but they suffer from clock drift.

1646400300103.jpeg


1646400306299.jpeg


I use the left or right main speaker (sub is nearly equidistant between LR) as the reference for my sub/LFE channel sweeps. Alternatively, if you know the amount of offset to apply to each channel, you could set this manually as well.


I've attached some example sweeps -- equalized and unequalized -- of my summed (BM) bass-managed L+R mains with the subwoofer response separately. What one gets after clicking the "aligned sum" button is near identical to the real actual summed bass-managed L+R+Sub sweep.


1646400454035.jpeg

*phase difference is greatest between 125 -135 Hz, consequently we see much less of an SPL amplitude sum in that range.

But before doing that disable the frequency dependent windowing (which incidentally also greatly helps compress the size of the mdat file!)

1646400459221.jpeg




Wavelet spectrograms of the actual bass-managed LR summed response (w/ JRiver's 'pseudo-surround' option enabled):

1646401351021.png 1646401355367.png 1646402397014.png


Additional confirmation would be by checking with the moving microphone measurements (MMM) at the MLP and other seats elsewhere.
 

Attachments

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Bombadil

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Subs are integrated because the room screws up your full range speakers. In every room.
my point is that subs are not easy to integrate and can have a negative effect if not done properly. Room EQ systems can be very helpful in tuning the mains with or without subwoofer(s).
 

peanuts

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here is a funny interview of the owner of Goldenear technology speakers. he says he doesnt include phase adjustment on a subwoofer because "it is set correctly by our ingeneering"
my god. this shows you can be en employee for various audio companies for decades, own one etc but yet not understand the fundamental basics of a speaker at all. he also says s speaker needs to be about the same width of a human head, because the ears are on opposite sides of the head and therefor will sound more natural (!) (in a different interview on hometheatergeeks i believe)
 

gnarly

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If aligning phase is something you want to explore, make sure to have the appropriate clock timing reference set-up if you're using REW. Cheap USB measurement microphones like the UMIK-1 are popular, but they suffer from clock drift.



I use the left or right main speaker (sub is nearly equidistant between LR) as the reference for my sub/LFE channel sweeps. Alternatively, if you know the amount of offset to apply to each channel, you could set this manually as well.


I've attached some example sweeps -- equalized and unequalized -- of my summed (BM) bass-managed L+R mains with the subwoofer response separately. What one gets after clicking the "aligned sum" button is near identical to the real actual summed bass-managed L+R+Sub sweep.


*phase difference is greatest between 125 -135 Hz, consequently we see much less of an SPL amplitude sum in that range.

But before doing that disable the frequency dependent windowing (which incidentally also greatly helps compress the size of the mdat file!)




Wavelet spectrograms of the actual bass-managed LR summed response (w/ JRiver's 'pseudo-surround' option enabled):

View attachment 190312 View attachment 190313 View attachment 190321


Additional confirmation would be by checking with the moving microphone measurements (MMM) at the MLP and other seats elsewhere.

Very nice guide you offered. Good pointers.
I agree that few people go to the trouble of careful indoor sub alignment. Plus, it's dang hard to get good, consistent measurements down low, especially indoors.

I know i don't go to the trouble indoors, and i go to great pains when aligning outdoors.
But once i get indoors, i let the out outdoor phase alignment suffice as is.
A little EQ to knock down room modes is all i ever do once inside. Plus, i'm always moving subs and mains around the room/house, as well as trying entirely different DIY projects.

Someday, i hope to get serious about indoor sub management...
 

gnarly

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I have never found the phase plot to be usefull for anything. it is usefull for anechoic speaker meassurements only.
you want to look at time, look at group delay.

now in terms of sub alignment I think you need to keep it as simple as possible. if you use regular 2nd or 4th order crossover all you realy have to do is to trail and error with delay until you get the flattest you can get. besides that just make sure you are not a cycle too early/late on excess group delay
I think reality is that trial and error, like you suggest, is the norm for indoor sub tuning.

I do find phase is useful though. In fact, i value frequency magnitude and phase far above any of the derivative measurements that come from them, like group delay.
Why not go straight to the source is my thinking. I know if i have flat mag and phase, i'll have no group delay until i have mag and phase roll-offs, very nice impulse and step response, spectrograms, waterfalls, etc etc.
 

dasdoing

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Why not go straight to the source is my thinking.

it's just so unintuitive in a room meassurement. actualy worse than unintuitive. you can't create a perfect impulse while looking at it, since a totaly flat room phase whould mean heavy pre-rining in the low-end.
 

ernestcarl

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it's just so unintuitive in a room meassurement. actualy worse than unintuitive. you can't create a perfect impulse while looking at it, since a totaly flat room phase whould mean heavy pre-rining in the low-end.

I do not believe a "totally flat room phase", group delay or even perfect looking step/IR should be the goal if one is using phase manipulating FIR filters like you and me. As long as one is able to get a good enough summation with minimal added time distortion you're basically set. I also find it beneficial to be able to separate FIR corrections done for each channel unlike with DRC-FIR wherein it is recommended to correct the impulse response of the already summed sub+mains "system". This isn't how it is done with my Sceptre S8 monitors: or at least I'm almost certain that FIR & IIR correction is applied to each individual driver plus the summed overall total system response. But, again, I'm not an expert here!

Hmmmn... say, if I wanted to eliminate or reduce the dip seen in my mains+sub response specifically around 130+ Hz using the more "basic" or manually-oriented rePhase approach -- using as few taps as possible -- and at the same time easily avoid potential ringing, I'd just use very mild phase filters.

Quite incidentally, in the course of my experiments of just fooling around, I kind of figured out that if I applied 12dB/octave linearizing filter to the mains around 94Hz or so (though also unfortunately causing additional FIR time delay and some small increase in GD), then I could potentially fill-in that narrow dip around 130 Hz a tad bit more. Yet, ultimately, I decided against it since the processing time and GD cost to achieve the "improvement" in that small specific cancellation area doesn't seem particularly obvious to me -- kind of maybe(?) also looks somewhat a bit "worse" after checking out the resulting summed response's wavelet graph.

1646437006263.jpeg



1646440024464.png


The difference after my FIR phase EQ simulated "test revision", if any at all, is negligible.
 
Last edited:

Galz

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If a phase knob is pure delay so a receiver's distance does similar but better, with multiple subs wouldn't it be useful to have delay on the subwoofer for receivers that don't support separate subwoofer delays? Or will the improvement from minidsp with MSO still be huge? Assuming that global eq can be done by the receiver's DRC so that the minidsp only benefit is (to my understanding) the more precise delay and individual sub PEQ filters?
 

Chromatischism

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If a phase knob is pure delay so a receiver's distance does similar but better, with multiple subs wouldn't it be useful to have delay on the subwoofer for receivers that don't support separate subwoofer delays? Or will the improvement from minidsp with MSO still be huge? Assuming that global eq can be done by the receiver's DRC so that the minidsp only benefit is (to my understanding) the more precise delay and individual sub PEQ filters?
With multiple subs you definitely need individual delay control. Some subs give you this, many do not. Often times a device like a MiniDSP is needed with multiple subs anyway because most receivers don't support them.
 

Galz

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With multiple subs you definitely need individual delay control. Some subs give you this, many do not. Often times a device like a MiniDSP is needed with multiple subs anyway because most receivers don't support them.
What I mean is how much benefit would be in a minidsp when you have variable phase knob on a PB-2000 and an XT32/ Arc/Dirac (assuming no DLBC for Dirac, and for XT32 assuming it doesn't set the optimal delay) receiver? Would the phase knob do a "close enough" job to get the delay right? How much is there ti gain with individual sub PEQ filters?
 

Chromatischism

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I'm not sure how SVS does their subs, but since they are DSP-based, it is more likely a delay than a phase adjustment.

Usually though with room correction you leave the subwoofer delay controls set to zero.

So, why get a MiniDSP? I would get one if:

1. My AVR doesn't support independent subwoofers, or if it supports 2 and I have more than 2 subs
2. If I don't have Room EQ: I couldn't get the results I wanted with the subwoofer's built-in controls alone
3. If I did have Room EQ: I could improve on my results (to touch up)
4. If I wanted to implement MSO
5. If I wanted to implement BEQ
 

Galz

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In a case of an AVR that doesn't support 2 subs, would the delay from the "phase" knob suffice?
 

gnarly

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it's just so unintuitive in a room meassurement. actualy worse than unintuitive. you can't create a perfect impulse while looking at it, since a totaly flat room phase whould mean heavy pre-rining in the low-end.

The only things that can be successfully EQed are minimum phase, which means when magnitude is flattened with EQ, phase is also flattened.
Those corrections will not pre-ring. Nor will complementary linear phase xovers between the sub and main speaker.

The only things that will cause pre-ring are flattening the phase response of the subs low end mag roll-off, or excessive phase manipulation beyond minimum phase EQ corrections, in the sub's pass-band. Neither of which are good practice..

So really.. looking at phase is still all that's needed for good sub alignments/tunings.. imo/ime.
 

gnarly

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I do not believe a "totally flat room phase", group delay or even perfect looking step/IR should be the goal if one is using phase manipulating FIR filters like you and me. As long as one is able to get a good enough summation with minimal added time distortion you're basically set. I also find it beneficial to be able to separate FIR corrections done for each channel unlike with DRC-FIR wherein it is recommended to correct the impulse response of the already summed sub+mains "system". This isn't how it is done with my Sceptre S8 monitors: or at least I'm almost certain that FIR & IIR correction is applied to each individual driver plus the summed overall total system response. But, again, I'm not an expert here!

Yes, correction of individual drivers is totally the way to go. This give best quasi anechoic response.
Then when the speaker is placed in whatever room, global correction of the entire system is OK. But global correction for the speaker itself is very sub optimal ime. Best to tune speaker first, then adjust to room.
Hmmmn... say, if I wanted to eliminate or reduce the dip seen in my mains+sub response specifically around 130+ Hz using the more "basic" or manually-oriented rePhase approach -- using as few taps as possible -- and at the same time easily avoid potential ringing, I'd just use very mild phase filters.

Pls see my reply to dasdoing re pre-ring.
If you are wanting to use FIR around 130Hz, a very few taps will not work. The frequency resolution will be so low as to be totally ineffective.
Look at the slippage in rePhase down low when you try to reduce to a few taps.
Quite incidentally, in the course of my experiments of just fooling around, I kind of figured out that if I applied 12dB/octave linearizing filter to the mains around 94Hz or so (though also unfortunately causing additional FIR time delay and some small increase in GD), then I could potentially fill-in that narrow dip around 130 Hz a tad bit more. Yet, ultimately, I decided against it since the processing time and GD cost to achieve the "improvement" in that small specific cancellation area doesn't seem particularly obvious to me -- kind of maybe(?) also looks somewhat a bit "worse" after checking out the resulting summed response's wavelet graph
View attachment 190465


View attachment 190471

The difference after my FIR phase EQ simulated "test revision", if any at all, is negligible.

It looks like its just a timing difference causing the glitch in the spectro at about 180Hz....like the speaker needs a little more simple delay relative to the sub.

Here's a spectro of a 4-way i made indoors that shows both good point and bad points as they apply to this thread.
Note the smooth integration between sub and main at 100Hz. This was made with 96 dB/oct linear phase LR xovers at 100Hz, 650 Hz, and 6.3kHz. Non of those xovers produce any pre-ring, as complementary linear phase xovers cancel pre-ring.


4-way ground plane spectro.jpg


However, this spectro has phase flattening, and insufficient taps to flatten mag, on the very bottom end of the sub's roll-off.
Here's the mag and phase trace that goes with the spectro.
Note how phase stays flat below 40Hz, whereas mag (SPL) is rolling off.
A linear phase high-pass was used for the sub......and that will cause pre-ring, because there is no complementary off-set.
The HPF should have been minimum phase.

Hope this all made sense....
Bottom line is, sub to main integration is very doable....but best if done outdoors co-located, (stacked together etc) before being brought into room.

4-way ground plane SPL & Phase 1-12th.JPG
 

ernestcarl

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Yes, correction of individual drivers is totally the way to go. This give best quasi anechoic response.
Then when the speaker is placed in whatever room, global correction of the entire system is OK. But global correction for the speaker itself is very sub optimal ime. Best to tune speaker first, then adjust to room.


Pls see my reply to dasdoing re pre-ring.
If you are wanting to use FIR around 130Hz, a very few taps will not work. The frequency resolution will be so low as to be totally ineffective.
Look at the slippage in rePhase down low when you try to reduce to a few taps.



It looks like its just a timing difference causing the glitch in the spectro at about 180Hz....like the speaker needs a little more simple delay relative to the sub.

Here's a spectro of a 4-way i made indoors that shows both good point and bad points as they apply to this thread.
Note the smooth integration between sub and main at 100Hz. This was made with 96 dB/oct linear phase LR xovers at 100Hz, 650 Hz, and 6.3kHz. Non of those xovers produce any pre-ring, as complementary linear phase xovers cancel pre-ring.


View attachment 190562

However, this spectro has phase flattening, and insufficient taps to flatten mag, on the very bottom end of the sub's roll-off.
Here's the mag and phase trace that goes with the spectro.
Note how phase stays flat below 40Hz, whereas mag (SPL) is rolling off.
A linear phase high-pass was used for the sub......and that will cause pre-ring, because there is no complementary off-set.
The HPF should have been minimum phase.

Hope this all made sense....
Bottom line is, sub to main integration is very doable....but best if done outdoors co-located, (stacked together etc) before being brought into room.

View attachment 190563

Yes, I sort of already had an idea that it needs to be complimentary. During my examination of the individual driver component sweeps on my linear phase monitors (Sceptres), they pretty much showed the same: the pre-ringing or pre-causal ripple when both complementary linear phase responses combined essentially resulted in a perfectly clean response with almost no signs of ripple and a great looking step response — at all angles.

The use case I had in mind needed to work with streaming videos with as little visible lip-sync delay as possible. Essentially any more taps would cause unwanted delay.

Another issue was that I absolutely wanted to preserve SPL without boosting EQ, but the indoor responses and locations of the monitors (not to mention closed ports) already caused a big loss in the low end. This made it desirable for me to use broad overlapping crossovers. Even if it were something that could be done, the cost is not acceptable to me.
 

Chromatischism

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In a case of an AVR that doesn't support 2 subs, would the delay from the "phase" knob suffice?
It can give you more options, but if it's really phase and not a linear delay, it behaves differently than one done in an AVR.
 

Galz

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Anyone tried Anthem Arc phase and does using that feature (be it with automatic system or manually with REW) provide any improvement over just tweaking the subwoofer distance? Does that feature really give Arc an edge over other room EQ systems that only have delay/distances, or does it not really matter?

Supposedly I wouldn't expect much difference in integration between making the entire subwoofer signal arrive earlier as opposed to just making the frequencies around the crossover arrive earlier, as the effect on the crossover area would be the same? Or do I not understand the feature correctly?
 

Beershaun

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Gene talks about it in depth here on audioholics YouTube video.
 
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