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Is it possible to automatically correct the phase using REW arithmetics?

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AudioBoy

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If your subs and speakers are out of time you can get dips because they are cancelling each other at those frequencies (like comb filtering). You don't fix it by trying to "overpower" it. You fix it by time/phase aligning them.
When I bought the subs I adjusted their phase to best match the main speakers. By measuring the sub separately from the main speaker, you can see that the frequency response of the sub does not change in the area for which it is responsible.

1696178467942.png

So how exactly is your system connected? You mentioned RME Babyface Pro, so if you have that connected via XLR to the subwoofer, then the RME is controlling the volume.
RME ADI 2 DAC FS -> XLR -> Neumann KH 750 (L) -> XLR -> Topping LA90 (L) -> Dynaudio Contour 2.0i (L)
_____________________-> XLR -> Neumann KH 750 (R) -> XLR -> Topping LA90 (R) -> Dynaudio Contour 2.0i (R)

I'm using Babyface Pro for measurements only.

Do you have 1 channel to 1 sub to 1 speaker?
Yes, sir

So by remote control mode you mean with an app? And manual is with the switches?
Yes

But do you still have the "Control Mode" switch set to "Local"?
I know this and of course change these settings accordingly.

I'm not sure what the "Bass Management" switch does either.
It controls sub bypass mode. Signal transferred to main speaker at full range and sub does not play anything.

only get up to 315° at 80Hz, which is only 11msec, which might not be enough?
This is sufficient because the main speaker is on a stand that sits on top of the subwoofer.

But I'm not sure how you will achieve this considering the speakers signal comes from the sub?
it's very easy using sub bypass mode. So no problem

Or maybe you can mute the subs in the app, but still let the speakers play?
The Remote Control App has Base Management button also, so yes, it's possible.

which shows that "Digital Delay" can be set, but who knows how?
Only The Remote Control App has that option but I don't use it because there is no need to compensate for microseconds.

1696187106986.png


more info about the app

Today I tested the THD level of the subwoofer in local and network mode and got some interesting results.
I noticed that the curvature of the straight section of the transient response directly depends on the volume of the signal supplied to the subwoofer.

Babyface Pro Settings

1696180287936.png


REW using ASIO driver from RME.
No FIR filters were used.

Subwoofer settings in Local mode does not changed. (94dB, 0 phase degree, subwoofer gain ~ -6dB, low cut - 0 (off), stereo mode using single channel, 80Hz crossover)
Subwoofer settings in Network mode the same as in local except gain which is 0dB. HiPass and LoPass filter at 80 Hz.

The THD will be better if I lower the volume, the current THD is already the best I can get I guess.

1696182129657.png


I noticed that the curvature of the straight section of the transient response directly depends on the volume of the signal supplied to the subwoofer.

1696181153071.png


For more info please download mdat.

To be continued...
 
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ernestcarl

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I wonder if it is because you are sweeping so low (from 0Hz), and noise is getting in to the measurements (and is not being distinguished as noise by the calculations)?

I'm guessing much of the fluctuations will be from the room interaction with the sub.

I've measured my sub from 0-24kHz many times and it's almost always flat with no fluctuations prior t=0 (absent any EQ).

BTW, the spectrograms ernestcarl posted in #7 show decent room mode ringing at ~60Hz and ~120Hz. His FIR EQ seems to have sorted out ~60Hz, but not so much ~120Hz. Because peaking room modes can be cancelled with high-Q IIR filters, I wonder if applying some IIR EQ before moving to FIR correcting is a good idea? I've not got around to testing this myself yet. And no I don't mean putting some min-phase EQ in the FIR because that doesn't give the same results when using reasonable tap/IR-length limits (because it's Finite, not Infinite).

What is a reasonable tap count? All depends on the use-case. When dealing with the very low frequencies, it's actually better to do the min phase EQ correction first, and thereafter remeasure because the "simulation" or predicted phase change post EQ sometimes doesn't quite much up exactly with the actual measurement verification.

We could use 15 cycles instead and get a slightly better result:

Wavelet spect: 1/5 smooth, 40dB scale
1696209130219.png 1696209135946.png


The skew on the right channel is milder and more amenable to "correction":

1696209962977.png
 
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ernestcarl

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Another thing I plan to deal with is the huge distortion in the bass (about 10 percent in the 20-30 Hz region). My main speakers without a subwoofer are cleaner (about 5 percent) at the same region. This is weird.

Some of that distortion you are seeing with these in-room measurements already include distortion coming from the room. You could try measuring your sub outdoors away from wall boundary surfaces at the same level and see how much of a difference it makes. While your at it, you might as well include your mains -- so we can see what's it's like without all the comb filtering. *But, yeah, only if it's not too inconvenient.

BTW, what are your main speakers? And could you upload a measurement of just them without the sub and EQ (or crossovers) too, thanks!
 

neRok

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By measuring the sub separately from the main speaker, you can see that the frequency response of the sub does not change in the area for which it is responsible.

1696178467942.png
Yep, that looks like all sub problems. Is that 1 or 2 subs though?

There's a lot of ringing at ~21Hz, and -EQ can fix it nicely. It's probably the same at ~15Hz, but the alignment tool doesn't go below 20Hz so I didn't bother testing.

~61Hz has a little ringing and can be improved with -EQ too.

~44Hz is a problem. Can you try the sub in a different position? Otherwise it seems a little +EQ either side of 44Hz can help it a bit.

Here's some quick examples;
IRs.jpg

When fiddling with the EQ's, it seems that smoothing the GD is the goal;
EQs.jpg

BTW, the GD is strange, because it seems the sub is ~37ms early (negative delay)?
GD.jpg

This is sufficient because the main speaker is on a stand that sits on top of the subwoofer.
The crossover filters and ported config of speakers or subs can add significant delay. My sub is 38.7ms late for example, and its between the speakers, so technically closer to me than the speakers.
 
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AudioBoy

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BTW, what are your main speakers?
Dynaudio Contour 2.0i
And could you upload a measurement of just them without the sub and EQ (or crossovers) too, thanks!
Sure, I will

Is that 1 or 2 subs though?
One, left.

Can you try the sub in a different position?
Wish I could, but alas no

BTW, the GD is strange, because it seems the sub is ~37ms early (negative delay)?
I noticed this too. I never set a delay, perhaps the sub's electronics do it, I don't know
The crossover filters and ported config of speakers or subs can add significant delay. My sub is 38.7ms late for example, and its between the speakers, so technically closer to me than the speakers.
I agree. I need to check this

my current system equalization variant. The left side is a little dominant and the voice lacks brightness due to the dip in the 1 kHz region, I guess. (mdat
)

1696230225203.png


GD (Psy)
1696230251863.png


Step
1696230269360.png
 

ernestcarl

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the GD is strange, because it seems the sub is ~37ms early (negative delay)?

Something that you should ignore as it likely is just an artifact of the limited passband. The phase goes wonky beyond that which REW seems to have trouble with.

I will only use it to check the linearity of the GD.
 

neRok

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my current system equalization variant. The left side is a little dominant and the voice lacks brightness due to the dip in the 1 kHz region, I guess. (mdat
)

1696230225203.png
Were those filters made by REW auto EQ? I think the ones <100Hz could be a bit more aggressive for a bit less ringing, but they're pretty good. I didn't pay attention to the higher ones, but above your room Schroeder freq (say 200Hz) you need to be more careful because the ringing the EQ introduces might be audible.

Those 2 big dips at ~105Hz and ~215Hz are not nice. Are you sure each speaker and sub is phase aligned?

The jagged response 1000-1500Hz is not good. Maybe it's something to do with the speakers reflecting off the subs, like an extra baffle? You might try sweeping close to the speakers mid drivers to see if it is a problem with the speaker itself, or something room/position related. Alternatively you might try using pillows and blankets as sound absorbers and put them over the subs to see if killing those reflections helps. Or maybe its a problem with nearby furniture?
 
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Were those filters made by REW auto EQ?
mostly. I didn't save them during processing, but one of them can be seen by opening the EQ window in REW for the graphs L VA/R VA.

1696237512108.png


I think the ones <100Hz could be a bit more aggressive for a bit less ringing, but they're pretty good.
Thank you, but for me there’s already a lot of bass :) Or maybe I didn’t understand you correctly.

you need to be more careful because the ringing the EQ introduces might be audible.
That's why when I creat a FIR I'm testing it on a drum kick (Klein + Hummel Subwoofer Test Signals - Kick drum train) and if I don't hear any artifacts I do next tests. If I hear a pre-ringing I'm starting all over again. This method works fine for me.

Those 2 big dips at ~105Hz and ~215Hz are not nice. Are you sure each speaker and sub is phase aligned?
Today I plan to measure the speakers separately and then you guys will help me answer this question I hope :)
But I guess It's my room modes and it is what it is. Will see.

The jagged response 1000-1500Hz is not good. Maybe it's something to do with the speakers reflecting off the subs, like an extra baffle?
Agree. I did some test with damping materials on walls and desk previously and its helps a lot. I plan to do this again and share my results here.

You might try sweeping close to the speakers mid drivers to see if it is a problem with the speaker itself

Near field measements (port, mid and tweeter)

1696238660255.png
 

neRok

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Thank you, but for me there’s already a lot of bass :) Or maybe I didn’t understand you correctly.
The ringing is the because of the bass bouncing around the room. See the second half of this post. So you can see your EQ#3 at 21.2Hz has stopped a lot of the ringing, just like the quick test one I did in post #65.
IRs - Copy.jpg

Today I plan to measure the speakers separately and then you guys will help me answer this question I hope :)
But I guess It's my room modes and it is what it is. Will see.
Cool. Only thing is, if you turn off the subs bass management then it might cause processing delay to the speakers, so the time could be off anyway. You really need to mute the speakers.

Or you could just do a quick sweep 50-200Hz and try every setting on the sub for phase and see which looks the best. That shouldn't take long.
 
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Only thing is, if you turn off the subs bass management then it might cause processing delay to the speakers, so the time could be off anyway. You really need to mute the speakers.
It's not a problem. I'll take two separate measurements. One through the sub, the other directly through the amplifier.
 
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I took the series of measurements requested. - mdat

No phase matching yet, because the remote control program only allows you to specify 0 and 180 degrees. For a full spectrum of phase measurements (0, 45, 90, 135, 180, etc.) I need to use the local mode and crawl around the floor until midnight. So I'll do it later.

But something interesting is already noticeable. The subwoofer changes the phase of the speakers by 180 degrees, although the application settings are set to zero.

1696249328465.png


Edit: I got a glitch and called Left Sub as Light :) Sorry
 
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palm

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That's why when I creat a FIR I'm testing it on a drum kick (Klein + Hummel Subwoofer Test Signals - Kick drum train) and if I don't hear any artifacts I do next tests. If I hear a pre-ringing I'm starting all over again. This method works fine for me.
If I remember correctly there is also a low pass dirac test to check if the sub isn’t off by multiples of 360°.

By the way I realize now that even if you use the analog input the DSP offers more possibility than my K+H O800, including delay correction so measuring a negative timing is possible (I’m not saying this is the case)
 
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Are you sure each speaker and sub is phase aligned?
Now I know it's not as perfect as it could be. :) mdat

1696275171613.png


I also discovered that my right subwoofer has a hardware issue when switching between 45-90 degrees. The phase does not change. I took the measurements twice to ensure there was no error on my part.

By the way I realize now that even if you use the analog input the DSP offers more possibility than my K+H O800, including delay correction so measuring a negative timing is possible (I’m not saying this is the case)
I wish Neumann's software was as good and reliable as its hardware. :). I chose local mode because network mode (which is much more convenient) is quite slow, and you never know what to expect the next time you turn on the subwoofer. Neumann devices are rumored to use the Sennheiser audio control protocol, and on github we can find third party DSP control tools for some Neumann hardware. I need to check this or write my own with blackjack and ladies... :)
 

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ernestcarl

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I took the series of measurements requested. - mdat

No phase matching yet, because the remote control program only allows you to specify 0 and 180 degrees. For a full spectrum of phase measurements (0, 45, 90, 135, 180, etc.) I need to use the local mode and crawl around the floor until midnight. So I'll do it later.

But something interesting is already noticeable. The subwoofer changes the phase of the speakers by 180 degrees, although the application settings are set to zero.

View attachment 316100

Edit: I got a glitch and called Left Sub as Light :) Sorry


It looks like having access to individual time delays only minimally improve the summation:

1696386363963.png 1696385677344.png

The subs' steep acoustic low pass FR slope and mains' deep null around ~100 Hz aren't positively complementing each other. This is just a consequence of your current room acoustics/setup.


If I vector average your LR measurements using the set 0 and 90 degrees phase adj., and thereafter compare that to my simple time delay compensation:

1696386051895.png
*Sub's gain in the "aligned sum" appears off a little bit.

With the unequalized vector averaged responses, 0 deg LR sum appears better. Then again, you are going to "phase" correct each channel anyway...
 

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No, I don't get any significant difference with Umik and its min phase version, either. I was only quite surprized to see a very different phase response with an analog XLR mic and an audio interface. I don't feel confident enough yet to make a point, correct loopback set up with these systems is quite complicated but I will share my results here soon. But my speakers' XO phase correction now seem to be 12dB/oct at each XO frequency rather than inverted polarity 24 and 12 dB/oct corrections I was applying based on Umik measruements.

But as I said, I don't want to make bold statements at this stage. I am still waiiting for some TRS cables delivery to compare them all simultaneously.


PS Earthworks wouldn't supply me with a phase calibration file, either (I asked for it!)
After many measurements and attempts to extract the correct calibration file for the sound card (and all the gear on the signal's way to the speaker), I came into the conclusion that the phase response is identical between a carefully measured (clock adjusted with acoustic timing reference) USB mic and an analog XLR mic with an audio interface. My variable 50Hz response from measurement to measurement due to dirty electricity was causing the confusion.
 
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OCA

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New REW beta release out today!!!

 
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New REW beta release out today!!!


These are my current settings and I don't like them. While the bass is rich, the female voice sounds flat and shrill. Partly because I compensated for the 3 kHz area, but I have settings without compensation. The same thing. Only the voice as a whole is even further away from me and dull.

When I turn off the FIR filter, that is, the system sounds without correction, the female voice returns beautiful harmonics that make it realistic and not squeaky. I also tried to create a VBA filter like you did in the last video, but it didn’t work out because my bass peak is located very low in frequency and I don’t want to boost bass frequencies, which are already sufficient. Just wanted to compensate for the dips.

An audiophile must suffer :) :(
 

OCA

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Only minimum phase version of an impulse response is invertable and only then the inversion filters will be causal and stable. The filter I shared below is not based on a target curve, just an inversion (but a correct one) below transient on a flat line:


Let me know if they DON'T sound great ;)
 

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30dB peaks are abnormal though (inversion couldn't cut all of it). Your sub volume maybe too much compared to the speakers.
 
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