REW Alignment tool - Guides or Manual?

[JStewart]

Sorry my question not clear.
Post 169
Were you were saying that when combining the two subs with the alignment tool and align sum it should match the measured two subs graph this is a sign that measurement is ok.

Thanks

Yes. Its a confirmation that nothing has inadvertently been messed up by the user in the process, which can be surprisingly easy to do.

The alignment tool calculations are 100% accurate so when you find the best alignment save the aligned (summed) measurement. Next enter the alignment tool delay into the DSP (minidsp, AVR, whatever). If you now take a measurement of the combined subs and the mic has not been moved and no other settings anywhere have been changed, then the REW actual measurement will match the Alignment tool calculated results, EXACTLY.

When using the .mdat provided and the two measurements I believe to be the measurements for each sub separately and combined them with a 9.5ms delay, the measurement tool Calculated Result did not match a measurement in the .mdat that I assume was an actual measurement of the combined subs also with a 9.5ms delay added to the DSP. Until that can be explained an analysis of the .mdat by others may be invalid insofar as this exercise is concerned.

 

[Harrycr]

Yes. Its a confirmation that nothing has inadvertently been messed up by the user in the process, which can be surprisingly easy to do.

The alignment tool calculations are 100% accurate so when you find the best alignment save the aligned (summed) measurement. Next enter the alignment tool delay into the DSP (minidsp, AVR, whatever). If you now take a measurement of the combined subs and the mic has not been moved and no other settings anywhere have been changed, then the REW actual measurement will match the Alignment tool calculated results, EXACTLY.

When using the .mdat provided and the two measurements I believe to be the measurements for each sub separately and combined them with a 9.5ms delay, the measurement tool Calculated Result did not match a measurement in the .mdat that I assume was an actual measurement of the combined subs also with a 9.5ms delay added to the DSP. Until that can be explained an analysis of the .mdat by others may be invalid insofar as this exercise is concerned.

Thank you.
One sub is up front inside left main and center and back one is inside right rear surround (diagonally) behind the couch.
Does this mean that the polarity on the back sub should be reversed?

When measuring combined response with NO delay added and polarity reversed on back sub the graph looks better. Does this mean that go with this setup when phase aligning the 2 subs?

Thanks again

 

[JStewart]

Thank you.
One sub is up front inside left main and center and back one is inside right rear surround (diagonally) behind the couch.
Does this mean that the polarity on the back sub should be reversed?

When measuring combined response with NO delay added and polarity reversed on back sub the graph looks better. Does this mean that go with this setup when phase aligning the 2 subs?

Thanks again

If I measures better then it probably a lot closer.
Only way to know for sure is with a measurement of each sub separately with a timing reference and check with alignment tool. Remove any delays or polarity inversion before measuring. Set XO as high as allowed by your gear.

Option B is to Keep changing the delay of one sub in increments of 1ms and re-measuring after each. Tedious but doable.

 

[mattel]

Agree and you've got a good starting point for EQ.

Ok, I eq’d both subs. There is a substantial improvement in sound quality. Bass is more robust, tighter and really thumps.
Thank you so much!
For sub/main alignment:
measure each sub w/o any delay and with xover
measure FR and FL individually with xover
use center for timing reference
sum sub1+ sub2
sum FR+FL
use alignment tool to align the two summed responses by placing the cursor at the xover freq. and click “align at cursor”

Is this correct?

Thanks again. You have been a great help.

 

[JStewart]

Almost. Actually a little easier.

with XO set
with no other DSP modes set that might alter the signal (upmixers, downmixers, etc.)

measure each sub w/o any delay and with xover

These measurements are not needed. The already aligned subs group will be aligned with the mains.

measure FR and FL individually with xover

Yes.

use center for timing reference

Yes

sum sub1+ sub2

Measure the already aligned subs group.

sum FR+FL

Yes

use alignment tool to align the two summed responses by placing the cursor at the xover freq. and click “align at cursor”

I'd recommend using the slider. If you click on the slider you can then use arrow keys to move it which, for me at least, offers more precise movement.

Edit: Link to example https://www.avnirvana.com/posts/46617/

 

[mattel]

Thanks for the corrections. I will proceed and post results.

 

[mattel]

@JStewart Please see post below.

 

[mattel]

Almost. Actually a little easier.

with XO set
with no other DSP modes set that might alter the signal (upmixers, downmixers, etc.)


These measurements are not needed. The already aligned subs group will be aligned with the mains.


Yes.


Yes


Measure the already aligned subs group.


Yes


I'd recommend using the slider. If you click on the slider you can then use arrow keys to move it which, for me at least, offers more precise movement.

Edit: Link to example https://www.avnirvana.com/posts/46617/

Hi, it has been a while since I had a chance to get back to alignment, so I apologize. Emergency eye surgery and not allowed to use my computer for a couple of months, holidays, etc.

I have moved one of my subs so first, I am starting again with trying to align my two subs (HSU's; one ported and the other sealed). I have a Emotiva UMC-1 processor, with a 5.2 setup and minidsp 2x4HD.

Measurements of the subs, mains and center are attached.

This is what I understand to perform 2 Sub alignment:

1. Use R sub base 200Hz XO and L sub base 200Hz XO (measurements with XO set to max =200Hz).
2. Use the slider to find the smoothest response, preferably with the summed output above the individual subs output. Question: while doing this, what should I be looking for from phase response, all 3 lines to converge and overlay each other?
3. Once I find the correct delay, click on align sum.
4. Re-measure both subs with XO's set to max to verify it and the aligned sum measurement are the same.


This is the measurements before delay applied. Except for the dip between ~35-50 Hz. I thought it looked okay.

View attachment 38412

3 sec delay set on slider. Smoother response, however SPL is below individual sub measurements at some frequencies. Not sure what the phase is telling me, though.

View attachment 38409

-16.34 sec delay set on slider. Not as smooth, but good SPL. This seems strange since the right sub is closer to MLP (~7ft. vs. 15.6ft for the left sub. Is the graph indicating the 3 lines are in phase (or close to it, from 40 - 120Hz?

View attachment 38410

I appreciate any help in sorting this out for me. Once I get the subs aligned properly, I will move on to aligning mains with subs.

 

[alexF40]

Hi @mattel did you manage to time align your subs properly using the alignment tool?

I'm currently really struggling trying to do the same thing and can't find any actual guides on how to use the time alignment tool, hoping for some help to get me started.

Cheers

 

[Exponential]

Hi @mattel did you manage to time align your subs properly using the alignment tool?

I'm currently really struggling trying to do the same thing and can't find any actual guides on how to use the time alignment tool, hoping for some help to get me started.

Cheers

All the information you need is contained within this thread.

 

[mattel]

Hi @mattel did you manage to time align your subs properly using the alignment tool?

I'm currently really struggling trying to do the same thing and can't find any actual guides on how to use the time alignment tool, hoping for some help to get me started.

Cheers

Sorry AlexF40 for not replying sooner. I do believe they are aligned at this point, however, I have not verified it with the impulse response. I am basing it on the substantial improvement in bass I am hearing. See if the link below is helpful.
Are you familiar with REW?

Dual Sub Alignment - Affirmation with Procedure

Hi, I posted this in another thread but did not receive a reply. So, I am trying it in a new thread. I have relocated one of my subs, so I am trying again to align my two subs (HSU's; one ported and the other sealed). I have an Emotiva UMC-1 processor, with a 5.2 setup and minidsp 2x4HD. I...

www.avnirvana.com

 

[gregw]

I've read most of this outstanding thread thanks to jtilden for all the good info. I was wondering if my receiver only has one sub out and I would like to add a 2nd subwoofer, is there a predictive tool in REW I could use to try to align them by changing the polarity and phase on one or both of them? Is only a trial and error method possible by making phase changes in say 10 degree increments through 180 degrees? Or is the best option purchasing a new receiver with 2 independent sub outs or a minidsp so that I can use the alignment tool to align them? The same question could be applied if one had 3 subwoofers without a way to change delay on each one. How would one go about it or is it impossible without a minidsp?

Maybe Home Theater Gurus or Gamer can do a new youtube video based on this good info. No one on youtube knows to set the FDW to 5 cycles or to manually adjust with the arrow keys and look at the phase and SPL graphs after clicking "Align phase at cursor." That is pretty key - I was getting a really high distance change for sub to mains that didnt make a lot of sense.

 

[jtalden]

One LFE output on an AVR is reasonably likely to work okay if 2 identical SWs are nearly the same distance to the LP. A difference less than 2 ft. is not likely to cause too much SPL trouble.

To find out in advance of another SW purchase:

• Place the existing SW in each potential location
• Set REW timing feature active
• Measure the existing SW at each location
• Use REW Trace Arithmetic A + B to see the resulting SPL of using those 2 locations.

If you have a variable phase on your SWs and you want a more detailed analysis of 2 locations, the following can be done. It is more likely to allow for larger differences in the distance to the LP. Measure each location with the phase control set to maybe; 0, 45, 90, 135 and 180°.
You will have 10 measurements, but all combinations probably don't need to be to be analyzed. The closer SW location needs all 5 settings the further location needs only 4 measurements as the 180° measurement is not really required. The following table shows the analysis combinations that are most likely to contain the best setting. We can use REW Trace Arithmetic as before to sum each combination and determine which combination results in the best SPL response.



This methodology is not as refined as using the REW Alignment Tool when the delay of can be adjusted between the 2 SWs, but it does still have a good chance of resulting in an acceptable SPL result.

 

[JStewart]

One LFE output on an AVR is reasonably likely to work okay if 2 identical SWs are nearly the same distance to the LP. A difference less than 2 ft. is not likely to cause too much SPL trouble.

To find out in advance of another SW purchase:

• Place the existing SW in each potential location
• Set REW timing feature active
• Measure the existing SW at each location
• Use REW Trace Arithmetic A + B to see the resulting SPL of using those 2 locations.

If you have a variable phase on your SWs and you want a more detailed analysis of 2 locations, the following can be done. It is more likely to allow for larger differences in the distance to the LP. Measure each location with the phase control set to maybe; 0, 45, 90, 135 and 180°.
You will have 10 measurements, but all combinations probably don't need to be to be analyzed. The closer SW location needs all 5 settings the further location needs only 4 measurements as the 180° measurement is not really required. The following table shows the analysis combinations that are most likely to contain the best setting. We can use REW Trace Arithmetic as before to sum each combination and determine which combination results in the best SPL response.

View attachment 44286

This methodology is not as refined as using the REW Alignment Tool when the delay of can be adjusted between the 2 SWs, but it does still have a good chance of resulting in an acceptable SPL result.

@jtalden , once this method is completed could the alignment tool be used to check alignment between the two subwoofers and possibly tweak the phase knob of the delayed sub to slightly improve it, if desired?

 

[jtalden]

I don't know how to convert an alignment tool delay change directly into a SW phase control change. I was just assuming that if the best setting for SPL appeared to be between the 45° phase control increments, the user would just measure one or two of settings in-between. I would not expect much change resulting from a 20° phase control change, but I don't have any practical experience doing it this way.

 

[andyc56]

@jtalden , once this method is completed could the alignment tool be used to check alignment between the two subwoofers and possibly tweak the phase knob of the delayed sub to slightly improve it, if desired?

From what I've seen by looking through the service manuals of sub amps having continuous phase controls, these phase controls actually implement a first-order all-pass filter using op-amps. A first-order all-pass filter has a flat frequency response magnitude, and a phase response that approaches zero at frequencies well above its center frequency, and approaches 180 degrees at frequencies well below the center frequency. The phase response is 90 degrees at the center frequency. The center frequency is determined by the phase knob, and it's not possible to calculate it accurately in general, because of the vagaries of pots and analog circuits. Unlike a pure delay, which has a phase shift vs. frequency that looks like a straight line when the frequency scale is linear, an all-pass filter's phase response vs. frequency is curved. Because of this fundamental difference between the phase response vs. frequency of an all-pass filter and that of a delay, there is no way of translating a delay found from the Alignment Tool to an equivalent all-pass filter - because no such equivalent all-pass filter exists.

BTW, there's a pretty good video tutorial about the Alignment Tool by Jeff Mery ("fattire" on AVS). I've included it below. Apologies if it's already been mentioned in this thread.

 

[gregw]

Thanks for the instructions on the phase adjustments and trials for a 2nd subwoofer. Great idea. will have to try out when i can find some free time

Thanks for the reference to the other youtube video as well

 

[gregw]

Can you point me to a link to access the REW help supplement for the beta versions that discusses the alignment tool?

 

[John Mulcahy]

All the REW help is available in the application (searchable) and online. Here is the Alignment tool topic, but it is brief and really only concerned with the controls.

 

[Foly83]

Hello

I have a general question regarding alignment. Would be happy if John comments on this as well.
Looking at the video #191. It is super explained and nice to see when a nice frequency response can be produced with the different subs.
Still, I'm wondering about the timing aspect in this example.
Isn't it better if all subs run together in phase at the respective Xo?
The time alignment is the most important thing. So that all subs together give the impulse to the MLP at the same moment. To generate a better dynamic in the bass to the MLP. Otherwise the bass feels imprecise.

 

[John Mulcahy]

The time alignment is the most important thing. So that all subs together give the impulse to the MLP at the same moment.

I don't agree with that. A subwoofer can't deliver anything that resembles an impulse, the impression of dynamics comes from higher in the frequency range. We can't even perceive the direction of subwoofer-range frequencies with any accuracy, given the wavelengths (almost 7 metres at 50 Hz, for example) that isn't surprising. We can easily perceive uneven frequency response, however, even at such low frequencies. As such I'd say getting an even response is much more important. Timing may help with that, phase tracking through the crossover region helps the response there, but I'd happily shift timing for a more uniform response.

 

[Foly83]

Thanks for the explanation
Impulse was expressed incorrectly. I mean wave front or pressure wave. It is difficult for me to translate.

 

[gregw]

Thank you John, The Help link at the top of the rew web site I was using only brings me to the regular help pages not the beta help pages. I was googling for rew beta supplement help and not finding it.

 

[fattire]

From what I've seen by looking through the service manuals of sub amps having continuous phase controls, these phase controls actually implement a first-order all-pass filter using op-amps. A first-order all-pass filter has a flat frequency response magnitude, and a phase response that approaches zero at frequencies well above its center frequency, and approaches 180 degrees at frequencies well below the center frequency. The phase response is 90 degrees at the center frequency. The center frequency is determined by the phase knob, and it's not possible to calculate it accurately in general, because of the vagaries of pots and analog circuits. Unlike a pure delay, which has a phase shift vs. frequency that looks like a straight line when the frequency scale is linear, an all-pass filter's phase response vs. frequency is curved. Because of this fundamental difference between the phase response vs. frequency of an all-pass filter and that of a delay, there is no way of translating a delay found from the Alignment Tool to an equivalent all-pass filter - because no such equivalent all-pass filter exists.

BTW, there's a pretty good video tutorial about the Alignment Tool by Jeff Mery ("fattire" on AVS). I've included it below. Apologies if it's already been mentioned in this thread.

Thanks Andy! I’m here too but this might be my first post :-). Tons of super smart people on this thread. If anyone has any corrections or feedback on that video, I’m all ears. I want correct, digestible information out there.

 

[gregw]

So I did some experimenting. I tried manually implementing a sub delay where the SPL looked good in the alignment tool and set not too far from the distance determined by YPAO (about 5 feet higher). But then if I click Align phase slope at cursor, it gave me a much larger distance of 18 feet above the original YPAO distance I think due to reflections in the room, as when I did the same with FDW to 6 cycles the number was about 5 feet higher. Then when I measured the actual response with both distances, the larger one looked better in the crossover region. What would be the downside of using a high delay like that on the sub if the frequency response looks the best? I'm not really noticing a lipsync error and the bass sounds good to me. Just confused because in Jeff's video I believe he alluded to not wanting the distance to be too far from the actual distance, but if the frequency response looks the best in one's room with a long delay and one is not seeing a lip sync error, what is the problem?