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How important in phase control on a subwoofer?

tecnogadget

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What about the Pro version of the SVS’s, the polarity setting isn’t a physical knob, you get a digital DSP variable setting by the means of an App. Is that still just a delay?
 

Bombadil

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If you are using the sub in a system with Room EQ a phase adjustment is not used and therefore not needed.

If you use it in a system without DSP, then it is essential.
The newer iterations of ARC include a phase matching tool, in addition to the Room EQ functionality. I have not seen any objective reviews of the phase matching feature, but have read in another forum that the AVM 90 is ready to go other than the addition of this phase matching feature to ARC Genesis.
 

My adventures in stereo

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Measuring using REW and umik, with svs pb 2000 pro dual, playing with phase settings, has helped me smooth out the frequency response in my room
I started out with the reccomended 0 degree on both but got better response with the following setting
Screenshot_20220303-214028_SVS.jpg
Screenshot_20220303-214043_SVS.jpg
 

Beershaun

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Here is a good paper that explains it.

Reiterating what others have said.
1)You use phase control to time align the subwoofer with the main speakers at the crossover frequency so they don't cancel each other out and create a dip in frequency response at the crossover point.
2)You need to adjust 2 things to do this depending on your systems capabilities. Adjust the delay or distance settings in your receiver so the subwoofer and main speaker soundwaves reach the listening position within a certain time window to be cohesive. Then adjust the phase to further dial in the SPL at the specific crossover frequency. Like playing an 80hz tone (crossover frequency) and reading an SPL meter at the listening position, then adjusting the phase knob until the SPL is at it's loudest.

This is what I took away from the paper I posted that walks through techniques on how to set your distances and phase to integrate a subwoofer into your system.
 

Bombadil

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I'm a fan of subs, and consider them essential for HT. However, threads like this one lead me to appreciate the view that a well designed "full" range speaker like the big Revel towers or the remarkable Genelec 8361A is the wiser choice when compared to main/sub integration that may well not be done properly.
 

My adventures in stereo

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How do you time align the sub with mains in a stereo set up?
Phase control seems to help, based on the REW measurements
 

ernestcarl

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naaah. it's just a delay, like all variable "phase" knobs. calling those knobs phase-anything is just a stupid idea someone once had and more stupid people copied.

While it does add delay -- I double checked and it appears to be about 4.5 ms if flipped to 180 degrees -- it's not like a pure digital time delay because the phase becomes "bent" or "mangled" or whicher description you prefer. The Rythmik subwoofer's variable delay/phase knob behaves more like an analog all-pass filter.
 

ernestcarl

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but a delay does just this

A pure time delay shifts the phase, yes, but it does not actually alter the shape of the phase selectively nor increase group delay in the manner I showed.

Diagram from Meyer Sound:

1646339915547.png
 
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Galz

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A phase angle between two signals from the same signal source indicates a delay between the two.

While that is correct, seems like when you also have a reflection, then you will have a phase and amplitude difference that depends on both the direct and reflected distances as well as the frequency. Also I couldn't find (at least not quickly) the formula to also account for what happens when the reflected signal's intensity is lower, but with equal intensity you get:
sin(A) + sin(A + phase) = 2 * sin((2 * A + phase) / 2) * sin(phase/2)

So when you measure for phase you won't necessarily get the phase of the actual direct signal when there are reflections.

I don't really know how all the phase/timing-related measurements are affected by it, as the direct signal still arrives at the same time and at the same phase regardless of reflections.
 

Chromatischism

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I'm a fan of subs, and consider them essential for HT. However, threads like this one lead me to appreciate the view that a well designed "full" range speaker like the big Revel towers or the remarkable Genelec 8361A is the wiser choice when compared to main/sub integration that may well not be done properly.
Subs are integrated because the room screws up your full range speakers. In every room.
 

Chromatischism

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While it does add delay -- I double checked and it appears to be about 4.5 ms if flipped to 180 degrees -- it's not like a pure digital time delay because the phase becomes "bent" or "mangled" or whicher description you prefer. The Rythmik subwoofer's variable delay/phase knob behaves more like an analog all-pass filter.
The subs are labeled Delay and go from 0-16ms. Are you saying you can't get 16ms of delay from them? In my experience in a 16 ft room I did, unless I just got lucky where things lined up.
 

gnarly

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Phase alignment, subs to mains, is a very common practice with prosound.
It's just a matter of getting phase traces to overlay.
This page 101 from Rational Acoustics Smaart manual describes it starting with Comparing Phase Traces ..
Manual is a great reference btw..
smaart phase traces.JPG



Irony is that even for subs with long wavelengths, like all phase alignments, once subs are further apart than 1/4 wavelength at summation frequencies , the phase alignments break down fairly rapidly.
So for example, take a sub crossing at 100Hz, the acoustic centers, sub to main, needs to be under 3ft for good phase overlay.
And that's just at the crossover frequency: if using a common 24dB/oct LR xover, acoustic center should be within 2 ft for summation good summation and low ripple down to -15dB.

It's kinda why so many folks go to multiple subs i think...it's not all that easy to get subs and mains truly phase aligned.
Because it requires pretty tight, adjacent co-location, sub to main.
For most folks, it appears easier to make a compromised, but smoother sound, with multiples.
 

Galz

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Irony is that even for subs with long wavelengths, like all phase alignments, once subs are further apart than 1/4 wavelength at summation frequencies , the phase alignments break down fairly rapidly.

Does this still apply with DSP with delay like most room correction systems? I thought it corrects just that, and the remaining phase issues are due to reflections?
 

gnarly

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Room correction systems can only fully correct to one spot. They may get lucky and hit a decent sized spot, but that's about it.

Phase trace overlay between sub and main, when within 1/4 wavelength spacing, will encompass all spots.

But, all that "all spot encompassment" has nothing to do with room modes and "virtual subs" formed by room reflections.

Indoors, it's a pretty big crap shoot.
Outdoors, with co-located subs and mains, and properly phase aligned...is about the only way i know to really hear the compelling virtue of good phase alignment.
 

ernestcarl

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The subs are labeled Delay and go from 0-16ms. Are you saying you can't get 16ms of delay from them? In my experience in a 16 ft room I did, unless I just got lucky where things lined up.

Perhaps for traditional analog speaker setups it would mean something. My monitors have some inherent DSP delay of their own, and the sub’s response is already mangled when it reaches the MLP requiring EQ before alignment. All my monitors also have different phase profiles — BTW, ever tried aligning three or four pairs of monitors that do not share phase profiles? It is difficult doing that manually in a multichannel setup. You need some kind of way of visualizing the phase traces, IR and/or step response, and frequency magnitudes on top of each other.
 
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Chromatischism

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I usually don't even measure phase if my frequency response is smooth.
 

ernestcarl

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I usually don't even measure phase if my frequency response is smooth.

It’s not necessary… but if one wants to be absolutely sure:

There is an alternative yet somewhat more “intuitive” way of checking how flat, smooth, and even the summed response is really in both frequency magnitude and time using a (zoomed-in and -out) wavelet type spectrogram. Not many people will be able to show you that they’ve even been able to come close to getting something resembling a perfect or at least very good summed response at their MLP. It’s worth checking out.
 
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