# A few time alignment questions



## Twolions (May 21, 2014)

Hey all,

So thanks all for your help some weeks back. Since then I've had pretty decent results with using excess group delay via REW (in combination with impulse alignment near crossover) as per some of the guides made by the folks here (for aligning subs to mains). 

I have a few questions however (for mids to tweets alignment):

1.) Pasting here how I've aligned mids with the tweeters. Specifically, I'm trying to figure out if I'm aligning the BEGINNINGS of the impulses correctly. Hoping someone can clearly indicate to me what the beginnings of the impulses are here (for the peaks I'm aligning).

https://drive.google.com/file/d/0B0lmEib2rH9TSWhHdDdZejdSaW8/view?usp=sharing

2.) Another thing is, I am turning off PEQs (I set through the DSP) near the crossover point when aligning and then re-enabling after alignment. I don't know what the correct method is here for getting the best results in terms of phase/time alignment of drivers when using digital PEQs across the entire frequency range.


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## jtalden (Mar 12, 2009)

1. That graph is not helpful to me. The test conditions do not appear be properly configured for the process I follow. 
Have you:
> Placed the mic on the listening axis? (it's easiest with it about 1m distant.)
> Selected "Keep in/out Stream Active"?
> Selected "Start Stream"?
> Selected "Time zero locked"
> Set "Lockled Offset"/value such that the measurement of the TW falls near 0cm?
> Confirm that repeated measurements of the TW has the IR repeatedly fall at that same position?
> Then measure the MR to see the alignment of IRs and the Phase tracking. Adjust the delay as needed to achieve the correct timing.

Below is a MR-TW properly timed to provide good phase tracking. Note that there is also good SPL support throughout the entire XO range.









2. It's okay to have the PEQ filters active when doing this timing alignment so long as they are reasonably near the final needed values. If you have large boost or gains I would remove those until the alignment is established. Chances are that more modest setting will be needed with good timing. Adding filters to the *input channel* will effect both drivers identically so changing PEQ will not disrupt phase tracking.


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## Twolions (May 21, 2014)

Hi, thanks for the reply. For 1, I can confirm all, except for the fact I measure at the listening position. For 2, that makes a lot of sense. The only thing I'm noticing is that heavily PEQ-ing the input channels rather that individual drivers puts more strain on the DPS, and I think I can hear audible differences. At least with the Dynacord DSP 600 (ElectroVoice Dx46 is ghe US equivalent).


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## jtalden (Mar 12, 2009)

1. There is no problem measuring at the LP. The only issue is that strong reflections can sometimes makes the direct sound phase response more difficult to read.
2. Again I don't think that choice is a problem. With reasonable PEQ filters the difference should be insignificant. If the drivers are reasonably in phase in the XO range the filter gain would be expected to be slightly less working on both drivers rather than one and the relative phase between the 2 should remain unaffected. This is likely more of a theoretical difference, rather than a practical one, in terms of sound quality.


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## Twolions (May 21, 2014)

In regards to one, very true. In fact, I have an odd room acoustically speaking (clapping produces very distinct, fairly high pitched echo), meaning, yes, I have issues with severe reflections (for so many reasons I can't even begin to explain), but this being the living room and with WAF in mind, no real options as far as getting things in order via room treatment. This makes the phase response reading portion literally a nightmare.

For two, it doesn't hurt at all to try. I certainly have a ton of PEQs available per input channel, so I'll give this a try. It makes sense to me what you're saying.

Also, as a quick FYI, I use Kaiser-Bessel FIR filters across the entire frequency range. Still gives better results than using Linkwitz, etc., although with only 512 taps available in the DSP, naturally, I'm having issues with the < 200hz region.


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## natehansen66 (Feb 20, 2011)

Any reason you can't get the speaker up in the air in the middle of the room to get a gated measurement? Trying to interpret the speaker phase response from that of the room can be quite difficult.


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## IslandHydro (Mar 13, 2014)

<EDIT> nevermind I just found what I was looking for by looking at Twolions post from a couple weeks back. Time to go to school! 

Is there any kind of FAQ on time alignment? So far my only effort is to reverse phase on one driver, and then adjust timing to get maximum null at XO between that driver and the next. In reading this post it appears there is more to do, and I'd love to do it. But at this point most of what this post discusses is greek to me. Any pointers?


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## Twolions (May 21, 2014)

I feel your pain. On one hand it was a rewarding experience to read through so much great stuff I've learned from the posters here, but on the other hand, it's hard to sort of collate all the important good stuff for people who don't have the time to go through and understand the great threads that are available here on the subject.

The most straightforward (although not completely accurate) guide on doing time alignment (with HolmImpuls software) was actually this:
http://www.diysubwoofers.org/misc/holmimpulse/ta.html

I absolutely don't recommend doing this for aligning subs to mains though. You may have some success aligning your mids to tweeters however. 

For aligning subs to mains, check out what is said about excess group delay here:
http://www.roomeqwizard.com/help/help_en-GB/html/minimumphase.html

You might also need to use REW to look at impulse responses at a fairly narrow range around the acoustic xover between your subs and mains. There is a post about this on this forum.

When trying to understand the alignment of subs to (everything else), you should really check out this article. It's awesome in explaining how you should approach the task altogether. There are some very important concepts stated here that have proven quite effective for me (when applied):

http://soundoctor.com/whitepapers/subs.htm


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## jtalden (Mar 12, 2009)

IslandHydro said:


> Is there any kind of FAQ on time alignment?


 It's a confusing subject. There is lots of info around, but I don't have a link that covers it well. The best answers often depends on the situation. I may be able to help if you have specific questions.



> So far my only effort is to reverse phase on one driver, and then adjust timing to get maximum null at XO between that driver and the next. In reading this post it appears there is more to do, and I'd love to do it. But at this point most of what this post discusses is greek to me. Any pointers?


 > That null method is an accurate way to confirm that the 2 drivers are in phase at the XO point. Note that it does not indicate if the 2 sounds arrived at the same time however. One driver can be 1, 2, 3, etc. wavelengths ahead or behind the other and still be 'in phase'. Given a reversed polarity of one of the drivers, then the timing could be off 1/2, 1-1/2, etc. 

> In most cases the distances/timing of the 2 drivers would be reasonable and the timing would be no more than 1 wavelength away from the best setting. 1 wavelength is not too likely to have a significant audible effect for most listeners.

> Anything beyond this level of adjustment is more for the hobbyist who enjoys fine tuning and has the provision to adjust the relative timing of the 2 drivers.

> What the null method doesn't clearly show is the phase tracking between the 2 drivers. When the phase tracks closely throughout the entire XO range then both drivers are launching each XO range frequency at the same time so the 2 travel directly to the listener and arrive there at the same time. The frontal lobe is therefore stable at all XO frequencies. 

> If the phase crosses at the XO frequency at a significant angle, it will still creates a null there when the polarity of one driver is reversed, but the launch/arrival times of other frequencies in the XO range will differ between the 2 drivers. This causes a tilt to the frontal lobe at those other frequencies in the XO range. Very poor timing can create several nulls in the XO range. The greater the timing error the more likely it is to be noticeable.

Unless you just like playing with XO settings it is sufficient to use the null method. It is best to also confirm that the 2 IRs are in close alignment with each other.

The settings shown in post 2 above are just to show an ideal situation where the phase tracking has been adjusted so that the phase closely matches throughout the entire XO range. It is an idealized situation. It is not a required one when taking a practical perspective.


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## IslandHydro (Mar 13, 2014)

Thanks for the info, I actually do like playing with the XO's so I'll probably do some more poking around on this. I have a 2x4 minidsp on my subs, and a 4x10 on my mains so I have lots of electronic 'knobs' to turn. I need to do some more reading to figure out how to do the impulse response work and then I'll dive in. I just finished doing some room treatments (superchunks) and so I need to do some sweeps on the low end anyway. Thanks again!


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## subterFUSE (May 10, 2014)

Twolions said:


> When trying to understand the alignment of subs to (everything else), you should really check out this article. It's awesome in explaining how you should approach the task altogether. There are some very important concepts stated here that have proven quite effective for me (when applied):
> 
> http://soundoctor.com/whitepapers/subs.htm



Very interesting information. So, if I understand this correctly, he is suggesting that even if the subwoofer is actually the nearest speaker to the listener, it might need to be treated as the furthest while the mains are actually delayed?

In my car, the subs are the nearest speakers to the listening position. Subs are approx 38" from the LP.
The horns are 68" and 72" from the LP. I have always been tuning by setting the right side horn as the 0 delay speaker, and then matching everything to it. Possibly this has been wrong, and it might be necessary to delay the entire group of horns and midbass to the subwoofer?


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## jtalden (Mar 12, 2009)

It all depends on which alignment you want to implement. There are tradeoffs either way. 

> To achieve close phase tracking the SW IR will start to rise near the same time as the MW IR starts to rise. That way the sound from both drivers will arrive at the listener at the same time for each frequency in the XO range. There will be the same phase rotation and GD in both drivers across the frequency range, but the frontal lobe will be stable.

> Less total GD can be achieved when the peaks of the IRs are more closely aligned. That way the arrival timing of frequencies away from the XO range is more nearly the same. The SW sound at the XO frequency will arrive 1/2, 1, or 1-1/2 WL early relative to the MW (depending on the XO filter Slope). 

Assuming a 70-120Hz XO range then the overtones then a 70Hz fundamental from the SW will arrive at the listener at more nearly the same time as its 140Hz/210Hz second/third and harmonics from the MW. Close to the XO point however there will be a 90° phase shift and the staggered arrival time. The harmonics of the XO frequency will thus be delayed. The frontal lobe will shift up and down 45° through the XO range. 

> Either way the null at the XO point with one driver's polarity reversed will indicate proper timing for that alignment. The SPL support through the XO range will still be good, but of course the most support is achieved with the phase tracking alignment.

I have used both types of alignment often in my experiments with good results. I think most listeners will find either method to be very satisfactory. Some may prefer one over the other.


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## ajinfla (May 10, 2009)

jtalden said:


> It's a confusing subject. There is lots of info around, but I don't have a link that covers it well.


This is the best one that I know of, unfortunately archived format


cheers


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## jtalden (Mar 12, 2009)

Thanks for that. 
I like the helpful definitions there. The charts and concepts are also helpful and technically accurate. Like many other articles it understandably doesn't address the flexibility provided by DSP XO units or how to measure, adjust and confirm the desired result.


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## jtalden (Mar 12, 2009)

Here are some additional thoughts in case they are helpful to those fine tuning their DSP XO unit.

There is this good advice from Linkwitz Lab at: http://www.linkwitzlab.com/crossovers.htm

1. "The best electrical crossover filter is one that maintains the acoustic polar response of a loudspeaker throughout the crossover frequency range as output shifts from one driver to the next."

[I think that "a stable frontal lobe" is just another way to state the same concept.]

2. "The sum of acoustic lowpass and highpass outputs must have allpass behavior without high Q peaks in the group delay." 

[I think this is just a recognition of the condition that will result if "1." is achieved (and the SPL each of the 2 drivers individually at the XO point is -6dB).]

I believe it follows that the easiest way to measure, adjust and confirm this condition is to achieve close phase tracking of the 2 drivers throughout the XO range. An acoustic LR-4 is a good example and often targeted, but given a DSP flexible filter/delay settings, it is not the only solution. I would think that any set of XO settings that results in the measured acoustic condition of close phase tracking is in the "Best" category.

By this definition the optional alignment mentioned above is not in the "best" category. I concur with that from a theoretical perspective. The optional alignments are often used however and there a many highly regarded speakers designed that way so we could think of them as in the "better" category.


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## Niick (Jan 2, 2015)

Jtalden,

the method you describe for adjusting the timing relationship between two drivers at crossover really grabbed my attention. I've been using this same exact method (measuring the acoustic phase response and adjusting timing to achieve good phase tracking thru crossover) for a while now in my job as a car audio installer. I learned the method from the pro sound guys, this seems to also be the preferred method for pro sound techs. My question is, in order to be able to get a useable phase reading in a car environment between a tweeter and mid for example, I have to use really tight windowing, although the windowing type I'm using is SysTune's TFC window, which has a timing length that is freq. dependent. So far the results have been nothing short of stunning. However, since you are the first person outside of the pro sound forums I've seen so far that directly describes this method, can you think of any theoretical disadvantages to using this method in a car environment? Also, I'm using delay, adjustable in .02 ms increments, to achieve desired phase tracking. Are there any disadvantages to using delay as opposed to AllPass filters for this? The processors that we sell have adjustable delay per channel but not AllPass filters. Any further thoughts or suggestions/comments would be much appreciated dde00


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## subterFUSE (May 10, 2014)

Gennelle51187 said:


> Jtalden,
> 
> the method you describe for adjusting the timing relationship between two drivers at crossover really grabbed my attention. I've been using this same exact method (measuring the acoustic phase response and adjusting timing to achieve good phase tracking thru crossover) for a while now in my job as a car audio installer. I learned the method from the pro sound guys, this seems to also be the preferred method for pro sound techs. My question is, in order to be able to get a useable phase reading in a car environment between a tweeter and mid for example, I have to use really tight windowing, although the windowing type I'm using is SysTune's TFC window, which has a timing length that is freq. dependent. So far the results have been nothing short of stunning. However, since you are the first person outside of the pro sound forums I've seen so far that directly describes this method, can you think of any theoretical disadvantages to using this method in a car environment? Also, I'm using delay, adjustable in .02 ms increments, to achieve desired phase tracking. Are there any disadvantages to using delay as opposed to AllPass filters for this? The processors that we sell have adjustable delay per channel but not AllPass filters. Any further thoughts or suggestions/comments would be much appreciated dde00



I'm using a Helix DSP Pro in my car. It has .01ms time delay increments, and also has phase angle adjustment in 11.5 degree steps (based on 2nd order all-pass filters).


I would be very interested to know how to properly use the phase angle adjustments. Thus far, I have not had good success with them... so I have been ignoring the phase controls and just using time delay.


The phase angle adjustments are based on a 2nd order all-pass filter with variable corner frequency. The corner frequency is automatically adjusted by the DSP, and is relative to the high-pass filter cutoff. The only exception is the subwoofer which uses the low-pass frequency as the basis for the variable corner frequency of the all-pass filter. The owners manual says the consequence of this is that if adjusting the phase angle, you must begin with the lower freq drivers and move up to the higher ones.



What I am most interested in knowing is how to go about using the phase angle adjustments? Are they do be used instead of time alignment? Or used together with time alignment?


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## Niick (Jan 2, 2015)

So my understanding of all pass vs. delay is that quite simply all pass delays a group of frequencies, very much like intentionally induced group delay, where as delay adjusts the delay of all frequencies equally. So with delay, a .01 ms setting will change the phase of lower frequencies much less than it will change the phase of higher frequencies, since the higher the frequency, the shorter the wavelength. Clear as mud, right? 

I wold love to get my hands on a processor of that caliber. We only sell Rockford Fosgate 360.3 and Audison bit one and bit ten. 

I asked this same question of delay vs. all pass on the rational acoustics (Smaart) forum, and the answer I got was that in pro sound scenarios where the delay is so great that sound is already having a hard time correlating the the visual performance, because of huge stage to audience distances, then to add even more delay isn't desire able, so to phase align your acoustical crossovers in this scenario all pass would be a better way to go. Which makes me think, that if the delay increments of your processor are fine enough to to achieve good alignment, then in a car scenario delay is more than acceptable. I think maybe all pass filters, used in conjunction with delay, would be ideal. 

Like maybe use delay to compensate for the positional offset inherent in a car, and then all pass filters to adjust crossover phase alignment. Maybe??

I would love to test this theory, I certainly have the measurement equipment to do so, you're not in NW Oregon are ya?


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## jtalden (Mar 12, 2009)

Gennelle51187 said:


> Jtalden,
> ...However, since you are the first person outside of the pro sound forums I've seen so far that directly describes this method, can you think of any theoretical disadvantages to using this method in a car environment?


 No, not so long as you can read the direct sound phase. If the reflections prevent that then another method must be used.



> Also, I'm using delay, adjustable in .02 ms increments, to achieve desired phase tracking. Are there any disadvantages to using delay as opposed to AllPass filters for this?


There are no disadvantages that I know of. I only use delays. The unit I use provides for 0.01ms increments. It also has a "phase" setting option in 5° increments, but my experiments show it to be functionally identical to adjusting the delay setting for that driver, so I am unclear what, if any, value is provided by that feature.


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## jtalden (Mar 12, 2009)

Gennelle51187 said:


> ...I asked this same question of delay vs. all pass on the rational acoustics (Smaart) forum, and the answer I got was that in pro sound scenarios where the delay is so great that sound is already having a hard time correlating the the visual performance, because of huge stage to audience distances, then to add even more delay isn't desire able, so to phase align your acoustical crossovers in this scenario all pass would be a better way to go.


 To me that suggests that in that case they don't bother with Phase tracking and instead just adjust the delay/phase such that the phase crosses at the XO frequency. That is the optional "good" XO settings that were mentioned above. 

Whether this is done using the Phase control or delay control the result is the same. The phase control though would automatically pick the delay increments in much larger and more appropriate step sizes. That is probably the advantage; to provide much faster and more convenient adjustments to get "acceptable" results.

-Just my guesswork from your comments.


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## Lumen (May 17, 2014)

jtalden said:


> It's a confusing subject. There is lots of info around, but I don't have a link that covers it well. The best answers often depends on the situation. I may be able to help if you have specific questions. > That null method is an accurate way to confirm that the 2 drivers are in phase at the XO point. Note that it does not indicate if the 2 sounds arrived at the same time however. One driver can be 1, 2, 3, etc. wavelengths ahead or behind the other and still be 'in phase'. Given a reversed polarity of one of the drivers, then the timing could be off 1/2, 1-1/2, etc. > In most cases the distances/timing of the 2 drivers would be reasonable and the timing would be no more than 1 wavelength away from the best setting. 1 wavelength is not too likely to have a significant audible effect for most listeners. > Anything beyond this level of adjustment is more for the hobbyist who enjoys fine tuning and has the provision to adjust the relative timing of the 2 drivers. > What the null method doesn't clearly show is the phase tracking between the 2 drivers. When the phase tracks closely throughout the entire XO range then both drivers are launching each XO range frequency at the same time so the 2 travel directly to the listener and arrive there at the same time. The frontal lobe is therefore stable at all XO frequencies. > If the phase crosses at the XO frequency at a significant angle, it will still creates a null there when the polarity of one driver is reversed, but the launch/arrival times of other frequencies in the XO range will differ between the 2 drivers. This causes a tilt to the frontal lobe at those other frequencies in the XO range. Very poor timing can create several nulls in the XO range. The greater the timing error the more likely it is to be noticeable. Unless you just like playing with XO settings it is sufficient to use the null method. It is best to also confirm that the 2 IRs are in close alignment with each other. The settings shown in post 2 above are just to show an ideal situation where the phase tracking has been adjusted so that the phase closely matches throughout the entire XO range. It is an idealized situation. It is not a required one when taking a practical perspective.


Please chase me away with something other than silence if I'm off topic...
I am just beginning to learn about relative phase/delay, but in the context between mains and sub. The article referenced in Post #8 offers excellent explanations of time alignment, but doesn't help me derive the steps needed to align through the crossover region (80 Hz). I've used and understand REW for FR and waterfall plots. Any insights would be much appreciated and apologies if this is a hijack.

Sent from my iPad using HTShack


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## Niick (Jan 2, 2015)

So, as I understand it, yes you can use REW to align a sub/main system. Although I have not done this before with REW, I do align sub/main systems probably more than any other type of alignment. And I've done this process both in rooms and in vehicles, because the company I work for has demo systems in the showrooms as well. So it is with your question in mind that I post these pictures. These pics were from an email presentation I put together for my former boss (he's now retired), they were in NO WAY EVER INTENDED TO BE SHOWN TO PEOPLE ON THIS FORUM, I don't want it to be taken the wrong way, these pics were put together to try and explain why a processor would be beneficial to someone with no real technical knowledge of audio systems and acoustics. The people on this forum are, in general, wayyy more advanced than I am, and so it is with the utmost humility that I present to you the following:


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## Niick (Jan 2, 2015)

So basically just replace the software in the pics with REW and you'll have accomplished the same thing. Jtalden showed an example of the same concept in his post (this thread, post #2) that contained the Holmimpulse pic. Also, note the scale, both x and y axis, in each of the pics. Again, this was meant to be a demo of what a simple delay alignment could do for the sub to mains transition. It isn't meant to be a "look at my awesomely flat response" example. I'll be off work tonight and all day tomorrow, if I can answer any more questions I'll try to help however I can, plus I have one of my laptops from work at home with me, and it has REW on it, although I don't have any stored measurements in REW, I do have some .wav files in SysTune that I can load into REW and maybe come up with a working model for how this would be done in REW. 

Have you used REW to measure the acoustic phase response of a loudspeaker system yet?


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## jtalden (Mar 12, 2009)

A little dated at this point, but still a reasonably good guide.
http://www.hometheatershack.com/for...g-driver-phase-rew-v5-example.html#post341732


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## Niick (Jan 2, 2015)

jtalden, thanks for the link! Phase alignment can be such a pain the butt, especially in a car, that I love it when I find new material to read on the subject. Its definitely not your common topic, at least that's been my experience. Just before I read your post just now I was actually playing with unwrapping the phase to try and see it more easily. I learned to phase align crossover regions using Smaart, but I now own a different program (SysTune Pro), which while admittedly "expensive", i use it as a tool for work, and it has paid for itself many times over at this point. There is a function within the program called "delay analysis" that is supposed to make all this "reading the phase trace" business totally unnecessary. what you do is take a trace of your sub, take a trace of your mid/hi system, load the two traces into delay analysis, and BAM, DONE! 2 seconds. it will give you a graph and delay time necessary for 4 different possible outcomes: 
#1 maximum summation positive polarity 
#2 maximum summation with one system inverted polarity 
#3flattest summation thru crossover (and whether or not that requires a polarity inversion) 
#4 a "custom" choice that allows you to input any delay time and has a check box for inv. polarity 

Ive only had a couple opportunities to try it so far, but all be damned if it didnt work exactly as promised! what a time saver this is! If anybody is interested, there is a free 30 day trial version avaiable


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## jtalden (Mar 12, 2009)

BlueRockinLou said:


> Please chase me away with something other than silence if I'm off topic...
> I am just beginning to learn about relative phase/delay, but in the context between mains and sub. The article referenced in Post #8 offers excellent explanations of time alignment, but doesn't help me derive the steps needed to align through the crossover region (80 Hz). I've used and understand REW for FR and waterfall plots. Any insights would be much appreciated and apologies if this is a hijack.
> 
> Sent from my iPad using HTShack


SW to mains can be difficult sometimes using this method as the room modes can make the direct phase hard to determine.

I can answer questions for those working through the process. Given the needed REW measurements, I can also do the analysis for you and suggest what delay is needed to approach the "best" alignment (closest phase tracking for the XO filter settings). 

Optionally, the alignment can be determined by entering delays/distances such that they approximate measured distances and also provides a null at the XO freq when the polarity of the SW is reversed. Just adjust he SW delay/distance to adjust the freq of the null.

Another method is entering delays/distances set such that they approximate measured distances and then fine tune the SW distance as needed to maximize the SPL using the RTA.

If these easier methods don't happen to result in the "best alignment they should result in a "good" alignment and are likely to be indistinguishable from the "best" alignment in terms of sound quality.


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## Niick (Jan 2, 2015)

jtalden said:


> SW to mains can be difficult sometimes using this method as the room modes can make the direct phase hard to determine.


So, I've definitely heard this before, that the HF region is often easier to phase align, due to the shorter wavelengths not exciting room modes like the LF. For me though, it's definitely the HF region that is wayyyyy harder to read than the LF, due to the interior of a car having such short reflection times. The pics in the above posts where I'm using Smaart to align a sub to mains were done in the showroom of our store, I was setting up a display, the sub was a JL W6 12" and the mains were 2 way 6 1/2 components mad by Hertz. The showroom is quite large compared to most living rooms, I have yet to try this method in an actual home, and I have no doubt what you say is accurate, I just wonder why the LF was so easy to get a phase reading for me. Do you think it could have something to do with Smaart's Multi Time Window?


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## jtalden (Mar 12, 2009)

I have seen the HF XO problem in a car application. I only looked at one car application for subterFUSE found HERE. I also was not able to use REW with the phase tracking process to align the MR-TW due to all the reflections. I was able to do it for the SW-MW XO where the wavelengths are much larger.

My experience is only with my room setup and in helping a few others here to align their setups via them posting the needed measurements. 

The program used to align the phase tracking makes a big difference. The various features and controls available can make the job must easier or even automated as you indicated above with SysTune Pro. My only experience is with REW and HolmImpulse. The particular features and controls favor Holm for phase alignment. REW is a little less friendly for this task, but is still very capable. REW is my main program. I use it to determine EQ settings (where it really excels) and also all other analyses. Holm comes in handy for phase alignment when there is a difficulty due to a peculiar situation.


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## Lumen (May 17, 2014)

Gennelle51187 said:


> So basically just replace the software in the pics with REW and you'll have accomplished the same thing...
> ...I'll be off work tonight and all day tomorrow, if I can answer any more questions I'll try to help however I can, plus I have one of my laptops from work at home with me, and it has REW on it, although I don't have any stored measurements in REW, I do have some .wav files in SysTune that I can load into REW and maybe come up with a working model for how this would be done in REW.
> 
> Have you used REW to measure the acoustic phase response of a loudspeaker system yet?


Wow, that really helped from a purely layman's perspective. I think it's a really good place for any layman to grasp the overall concept, and some detail to boot! Thank you for that, and for offering your time on seemingly moment's notice. The crowd here at The Shack sure are special!!



jtalden said:


> A little dated at this point, but still a reasonably good guide.
> http://www.hometheatershack.com/for...g-driver-phase-rew-v5-example.html#post341732





Gennelle51187 said:


> jtalden, thanks for the link!


Ditto!


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## Niick (Jan 2, 2015)

jtalden said:


> I have seen the HF XO problem in a car application. I only looked at one car application for subterFUSE found HERE. I also was not able to use REW with the phase tracking process to align the MR-TW due to all the reflections.


Great link, I was checking out the impulse responses in the link and that brought up a question, how the hell do you see the (what I consider) "normal" linear view of the impulse response, my curiosity got me to playing with REW last night to take a look at the viability of using the program to phase align, and I found that I could only see the ETC view of the impulse response, I'm used to the linear view like in the measurements for the car application you linked to. The ETC just doesn't work as well for me, plus you can't see relative polarity between drivers with ETC like you can with linear. What am I missing, obviously this view of the IR is available in REW, I just don't know how to find it!


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## Lumen (May 17, 2014)

jtalden said:


> SW to mains can be difficult sometimes using this method as the room modes can make the direct phase hard to determine.


Wonderful :sweat: :R



jtalden said:


> I can answer questions for those working through the process. Given the needed REW measurements, I can also do the analysis for you and suggest what delay is needed to approach the "best" alignment (closest phase tracking for the XO filter settings).


Awesome, you are a generous person! Which plots/measurements do you need? 



jtalden said:


> Optionally, the alignment can be determined by...
> Another method is...


All the stated methods involve manipulating the AVR's distance settings to achieve a corresponding time delay. Unfortunately, my AVR does not allow for changing distances when Dirac correction is used. Would inserting a miniDSP 2x4 processor between my AVR and sub solve that problem? The way I understan it, I should take care of speaker and sub position/orientation first, then room treatment, then auto-EQ, then tweak sub+mains time delays.



jtalden said:


> If these easier methods don't happen to result in the "best alignment they should result in a "good" alignment and are likely to be indistinguishable from the "best" alignment in terms of sound quality.


Very true! Dirac is doing a pretty decent job for me, but I'm a perfectionist and sweat the details! :sweat: :devil:


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## Niick (Jan 2, 2015)

BlueRockinLou said:


> Wow, that really helped from a purely layman's perspective. I think it's a really good place for any layman to grasp the overall concept, and some detail to boot! Thank you for that................


No problem sir! I often find that when trying to explain something, the act of forcing yourself to put it into words can help you yourself understand it better, so, the more questions I can answer the "more better" my own understanding will be. So in that respect, thank YOU!


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## jtalden (Mar 12, 2009)

Gennelle51187 said:


> ...I found that I could only see the ETC view of the impulse response, I'm used to the linear view like in the measurements for the car application you linked to. The ETC just doesn't work as well for me, plus you can't see relative polarity between drivers with ETC like you can with linear. What am I missing, obviously this view of the IR is available in REW, I just don't know how to find it!


Place your cursor in the red circle as shown below and the selection box shown will appear.


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## jtalden (Mar 12, 2009)

BlueRockinLou said:


> All the stated methods involve manipulating the AVR's distance settings to achieve a corresponding time delay. Unfortunately, my AVR does not allow for changing distances when Dirac correction is used.


I thought I read someplace that for the XMC-1 the user first sets the distances and then runs Dirac? If that can be done then there is no problem and no other equipment is needed.


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## Lumen (May 17, 2014)

jtalden said:


> I thought I read someplace that for the XMC-1 the user first sets the distances and then runs Dirac?


 I will check on that! It's not the first time I overlooked an XMC-1 feature, but in my own defense it IS a complex animal. I seem to remember that speaker size and crossover can be adjusted. I'll need to look for distance when I get home. Thanks for the quick replies!


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## Niick (Jan 2, 2015)

jtalden said:


> Place your cursor in the red circle as shown below and the selection box shown will appear.


Thanks!! I knew it was something simple like that?


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## Niick (Jan 2, 2015)

Awesome!! So THATS how you see the step response!! I've been wondering how the hell you see the step response like the ones described by John Atkinson. I've found that by playing the "speaker pop" signal from Studio Six Digital's speaker polarity app, you can directly observe the step response on a digital oscilloscope. This is extremely handy for testing the factory polarity of speakers in a car that you can't visually see because of panels/ grills. When I started to use this signal, picked up by a mic and analyzed on a scope, I quickly realized that this is the same "step response" signal as described by John Atkinson. But when I used REW to try and see the step response, to compare it to my direct method, it always looked way different. Now I know why, I didn't have %FS selected! Ahaa!! Thank you very much sir.......a whole new avenue of experimentation has just opened up for me!!


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## Niick (Jan 2, 2015)

JohnM said:


> Impulse and step responses are not measured directly using the corresponding signals because the signal to noise ratio of the result is poor. It is difficult to put much energy into an impulse or a step without exceeding the linearity and power handling limits of the device you are testing, whereas with a sweep a lot of energy can be delivered over the duration of the sweep giving a much cleaner result.


So this is what JohnM told me when I asked him about directly measuring the step response vs. acquiring step thru deconvolution via REW.........smart dude!


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## Niick (Jan 2, 2015)

Ok guys, I know I've probably carried this thread a little (a lot?) off topic, but does anyone know if JohnM has implemented a way to take a triggered sweep with REW, meaning to play the excitation signal from a CD, or something like that, and grab the acoustic signal with a mic, then analyze in REW AS IF you had sent the signal into the SUT conventionally? Also, has anyone tried out the new beta build that incorporates frequency dependent windowing? There is a recent thread on this topic, and JohnM posts a link to a beta version with this type of windowing as an option. It is this very type of windowing (in other programs) that makes it so easy to acquire useable phase data in a highly reflective environment, like an automotive interior. I have the version on my laptop at work, but haven't tried it yet. If it works like I think it will, this will make acquiring phase data in the HF like in Jtalden's car example totally do-able! Edit: the beta version referred to is REW v5.12 beta 13, (I think, when I boot it up it says v5.13) and it offers a psychoacoustic smoothing option that incorporates frequency dependent window to achieve the smoothing. At least that's my understanding. And I was able to compare some measurements (in the HF Region, in a car) taken with SysTune and windowed using SysTune's TFC, compared against REW's psychoacoustic smoothing option, and YES, it compares very favorably, and phase IS readable with psychoacoustic smoothing engaged. More tests to come. Will try to post pics of the comparisons in the other thread (the one called "feature request: frequency dependent windowing")


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## subterFUSE (May 10, 2014)

jtalden said:


> I have seen the HF XO problem in a car application. I only looked at one car application for subterFUSE found HERE. I also was not able to use REW with the phase tracking process to align the MR-TW due to all the reflections. I was able to do it for the SW-MW XO where the wavelengths are much larger.


That's definitely an old set of measurements because it was before I redesigned my car stereo system.
Almost none of the original equipment is remaining.


I'll try to post some new measurements soon to see if maybe I have gotten any better at measuring, or if the phase will be any easier to read.


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## jtalden (Mar 12, 2009)

I would be interested to look at your new measurements. 

My vague memory of that thread was just that I was not able to use this method because the reflections were too numerous and too strong to clearly see the phase. I just attributed that to the car environment rather than any problem with the measurements. I did not carefully reread or review the data there to see if my recollection was correct.


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## subterFUSE (May 10, 2014)

jtalden said:


> I would be interested to look at your new measurements.
> 
> My vague memory of that thread was just that I was not able to use this method because the reflections were too numerous and too strong to clearly see the phase. I just attributed that to the car environment rather than any problem with the measurements. I did not carefully reread or review the data there to see if my recollection was correct.



I will post some new measurements as soon as I get some free time to mess with the car. Hopefully tomorrow morning.

I've really been trying to come up with a method for measuring that will work well for this.
I've tried mic on axis. Facing up. 45 degrees. I've got a cross spectrum labs calibration.

It sounds like the windowing can help with reflections. I haven't really jumped into that aspect yet, however.


Sent from my iPhone using Tapatalk


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## subterFUSE (May 10, 2014)

Took some measurements today of the Right horn and Right midbass drivers.

Posted the MDAT here: Right Side


I'll be interested to see if we can determine anything about the phase and proper timing?


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## Niick (Jan 2, 2015)

subterFUSE said:


> Took some measurements today of the Right horn and Right midbass drivers. Posted the MDAT here: Right Side I'll be interested to see if we can determine anything about the phase and proper timing?


 subterFUSE, could you possibly send me the .wav files of those IRs. I can import IRs into SysTune and tell you what I see regarding phase, timing, etc.


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## subterFUSE (May 10, 2014)

Gennelle51187 said:


> subterFUSE, could you possibly send me the .wav files of those IRs. I can import IRs into SysTune and tell you what I see regarding phase, timing, etc.


I'm happy to do that, although I recently pulled out my horns and midbass and replaced them.

It might be better to upload some more recent measurements with the current equipment. I'll try to post something soon.


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## Niick (Jan 2, 2015)

Awesome


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## subterFUSE (May 10, 2014)

I'm trying to upload my MDAT here, but it says something about a token is missing. ??


Edit: I have tried 4 different browsers, nothing works. Just says can't upload files because a security token is missing.


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## jtalden (Mar 12, 2009)

I had a strange unrelated error message once when my file was too large. I don't remember if it was the same as your error message or not.
You may want to try to zip the file or break it into 2 parts and see if that works.


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## Niick (Jan 2, 2015)

Hmmm......Maybe it would be possible to email me the files at [email protected], as long as they are .wav files, we're good.


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## subterFUSE (May 10, 2014)

Trying again.

Just took some more measurements, but then deleted the ones that are not needed any longer.


This shows my 4 primary drivers, plus the subwoofer. I used IR to time align the main speakers, and then I linked the left/right pairs and adjusted the time alignment some more by viewing the phase plots.

The fronts are crossed over at 230Hz.



Lastly, I measured the subwoofer with zero delay. Then I viewed the phase plots between the subs and the midbass, which are crossed over about 60Hz. I used Filtered Impulse Response @ 63Hz to align the subs and the midbass. The result was that I needed 5.9ms of delay on the sub, quite a lot more than I had been using previously.


Just did a brief test listen, and I think the subwoofer sounds very transparent and is not localizable in the trunk anymore. Nice, solid impact coming from kick drums in the front of the soundstage.


Still can't attach my MDAT. It's only 17MB, so it should not be too large to post. I'll stick it in Dropbox and link it here.



Edit: Dropbox Link Time Alignment by IR and Phase


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## 3ll3d00d (Jun 6, 2006)

you're trying to precisely align your mains but where is the mic? is it precisely aligned between them?

Can you explain what those 6 measurements are exactly? I'm not sure what a WB is for example.


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## Niick (Jan 2, 2015)

3ll3d00d said:


> you're trying to precisely align your mains but where is the mic? is it precisely aligned between them? Can you explain what those 6 measurements are exactly? I'm not sure what a WB is for example.


 this is a little different than the norm. These measurements are from a car. The mic should be (subterFUSE, am I correct here?) in the drivers listening/head position.


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## subterFUSE (May 10, 2014)

3ll3d00d said:


> you're trying to precisely align your mains but where is the mic? is it precisely aligned between them?
> 
> Can you explain what those 6 measurements are exactly? I'm not sure what a WB is for example.



Microphone at listening position, in driver's seat. Approximately at center of where my head would be.


WB = Wideband driver

I don't have tweeters. I'm running a pair of wideband drivers in the A pillars, and then a pair of 10" midbass on the kick panels. 2 subwoofers in the trunk.


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## Niick (Jan 2, 2015)

subterFUSE, I'm excited that you were able to post a link to the measurements!  nice! I'm always very intrigued to take a look at as many different kinds of acoustic "scenarios" as I can. Can't wait to take a look. (I'm off work today and tomorrow). So hopefully Friday I'll get a chance.


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## jtalden (Mar 12, 2009)

The timing of the MR/TW XO is ideal.
The timing of the SW/MR XO is not good for either SW delay option provided.


The SW/MR timing can be improved by:
> Invert the polarity of the SW
> Set the SW delay to 2ms.


That would put the phase tracking near ideal.


To confirm the Left channel timing yourself take 4 measurements:
SW
L MR
L TW
SW + L MR + L TW


Overlay each channels 4 SPL traces. If SPL support is good through the 2 XO ranges then the timing is good.


Then do the same to confirm the Right channel.


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## jtalden (Mar 12, 2009)

Below is how the SPL overlay chart should look for the left channel when the timing is correct.


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## JohnM (Apr 11, 2006)

Your measurement files will be much smaller if you select the "Allow 96PPO log spacing" option in the Analysis preferences and only measure subs to a few hundred Hz rather than 20 kHz.


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## Niick (Jan 2, 2015)

SubterFUSE, I'm taking a look at your data in SysTune right now........thanks again for these


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## Niick (Jan 2, 2015)

SubterFUSE, 

I imported all measurements (6 of them correct?) into SysTune. Let me know if you'd like any targets made, anything at all. Delay analysis....anything.....


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## Niick (Jan 2, 2015)

Ok, so first of all, are "right WB and left WB" supposed to have a 0.38 ms delta in their broadband IR arrival times? If so, ok, I'll sum them as is and offer some subwoofer alignment options. I can also get rid of the 0.38ms differential and sum them when timed equally. Let me know what's up


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## Niick (Jan 2, 2015)

This is how those two traces, WB left and WB right, will sum together:

The reason I sum them together, is because, like in the real world it's gonna be BOTH of them that sum get her thru crossover with your subwoofers


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## Niick (Jan 2, 2015)

And this is how they would sum if you lined up the IR's in time:


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## Niick (Jan 2, 2015)

OOOPPSSSS!!!! I'm sorry, was overlooking midbass traces, somehow I thought it was a 2 way........back to the drawing board!! Well now wait, so I'm not going to be summing WB left and right with the sub, but it does cross over to the MB, hmm......ok, let's check it out...... (so much fun!)

Any word on relative levels? Target curve?


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## Niick (Jan 2, 2015)

Again I notice a 0.38ms difference between the midbass IR traces:

(First pic is original)


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## Niick (Jan 2, 2015)

Ok, so the thick traces are the summations of the current data, with IRs positioned in time the way you acquired them: Thick blue- SUM ALL Thick green- SUM MIDBASS L + R Thick red - SUM FULL RANGE L + R Next let's add a little gain to that sub trace, then we'll optimize the midbass to sub timing to get better crossover summation

(Second trace is correct! First trace was with 3.5 ms of delay on the midbass to full range transition, that is, 3.5ms of midbass, and therefore also sub, delay)


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## Niick (Jan 2, 2015)

I hope I'm not boring or annoying anyone with all these posts, what a fun project this is!  So here is the same midbass to sub transition with 15dB added to sub:

Edit: I did a split screen so you could see the delay analysis module on bottom


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## Niick (Jan 2, 2015)

Ok, so you appear to have achieved about a 4th order butterworth ACOUSTIC roll-off......(sub, obviously.....)

So I'll define that as my target, then we'll do a little eq to better align with said target.......are you running graphic? Parametric?.......


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## Niick (Jan 2, 2015)

With a little eq we could probably pull a 4th order Linkwitz- Riley out of that too


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## Niick (Jan 2, 2015)

With al little EQ we could pull an ACOUSTIC LR4 out of the sub to midbass transition........?


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## Niick (Jan 2, 2015)

Heres the sub after 4 parametric filters, I tried a different method of posting pics, are these pics better?

Edit: ! we've reached closing time! more to come.......


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## Niick (Jan 2, 2015)

subterFUSE, I know it might not "seem" correct, but just try this: to really get your midbass' in phase thru crossover with your subs, apply either 13.19ms delay to the midbasses and invert the sub polarity. OR apply 20.10 ms delay to the midbasses and leave the polarity alone, either way you go, same exact (almost) results, see which one sounds better


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## Niick (Jan 2, 2015)

I got to work this morning and decided to take another look at the sub to midbass transition.

using the trace labeled "sub 0ms" and the summed trace of the left and right midbass, I get this if applying 12ms of belay to the sub, which, when looking at 125Hz octave band filtered IR (125Hz is the lowest octave band filter I can select POST acqisition) , it would require 12ms to line up the IR of the sub and Midbass in time.

so again, here is with 12ms of delay and +10dB applied to sub (no EQ this time on sub, exactly as you measured it), and with the sub's polarity inverted:


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## Niick (Jan 2, 2015)

subterFUSE, im a little confused about something....here is the 2 sub traces you provided, but they dont seem to be 5.9ms apart in time?? top graph is zoomed way in


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## subterFUSE (May 10, 2014)

Sorry, I've been out of town for a number of days and not been watching this forum closely.


I took the car to the INAC Finals in Huntsville, and did well. 2nd Place finish in MECA Modified Class, and a 2nD Place finish in IASCA Pro/Am. My IASCA score actually tied the 1st Place score, but I lost out in the tiebreaker.


There are some changes I want to make with the current tune, most specifically there is some bloat in the midbass I need to tame. I think it's a resonance but I'm not exactly sure where yet. My work and activity schedules don't leave me much time to work on the car. I'll try to get around to it again when I can find some time.


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