# Issue with timing reference loop back and XMC-1 sub time alignment



## etc6849

I've been trying to use a timing reference, but keep getting a frequency response plot that looks altered. I initially had lots more interference until I disconnected my amp from the XLR connection, but after figuring that part out, the freq plot looks decent, but is skewed only when using a timing reference loop back.

Timing Reference Output:
HDMI 5 (XMC-1 via ASIO4ALL); HDMI 5 = left rear speaker of my 5.2 system.

Timing Reference Input:
Presonus AudioBox Input 2 from XMC-1 RCA preout for left rear speaker (disconnected amp for left rear due to some interference I was getting initially).

ECM8000 non-calibrated mic on Input 1 of Presonus AudioBox

I plot the attached when doing this measurement, but what is strange is low end is elevated when using the loopback!?! I checked "set loopback as timing reference" under analysis and set the timing references as noted above.

I did all this because the normal method I was using (UMIK-1 calibrated USB mic and ASIO4ALL HDMI out), was showing that my subs were not time aligned to my speakers. The excess group delay plot showed about a 12 ms difference! I am using the Emotiva XMC-1 Dirac full version, and a lot users report time aligned issues with subs. This loop back method is confirming my subs (HDMI 4) are out of alignment from my left speaker (HDMI 1). Getting a 10.4 ms difference.

If you are curious, here are some measurements and system details (UMIK-1 calibrated USB mic and ASIO4ALL HDMI out for these files):
https://drive.google.com/folderview?id=0B1J0a4OV_WGLS2lYYl85N1BRNkE&usp=drive_web

Pics:
https://drive.google.com/folderview?id=0B1J0a4OV_WGLREI3eDVXd0xBM2s&usp=drive_web

BONUS QUESTION:
How to fix the sub delay and still use Dirac on the XMC-1 since I cannot adjust distance settings!?! I thought about buying a miniDSP and adding a 50 millisecond delay to the subs, then rerunning Dirac, then doing the loop back reference measurement again and then lowering the 50 millisecond delay. 

I've also thought about bumping up the phase on each of my two subs (they are matched and wired in a mono configuration to a single sub output), rerunning Dirac, then decreasing the phase knob on each sub after doing the loop back measurement.


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## jtalden

Possibly you are expecting that ideally the peak of the SW IR should be closely aligned with the Peak of the Mains IR? That is a common misconception.

My understanding that it is ideal to have the phase of the SW and Mains track closely with each other throughout the XO range, maybe 50-150 Hz. I think this is the common ideal target that results in the closest working relationship of the drivers, I would expect that this is the target for a DL setup. In that case the peak of the SW IR will lag the peak of the Mains by several ms.

There are other commonly used alignments that provide almost equally smooth SPL reinforcement. One of those provides much closer alignment of the 2 IR peaks. There is little likelihood that that any of the good alignment will sound significantly better, but many can apparently hear a noticeable difference and thus may prefer one to another.

From the charts above, the XO SW timing alignment looks very good. There is no suggestion that there is a error in the timing. It is likely that the Dirac setup properly did it's job and I would not be surprised if it was ideally timed. That said, It is impossible to tell for sure with the charts above and it is always comforting to confirm it. 

I can do this for you given just 4 simple measurements using either mic and no loopback is needed. This method is a difficult to easily explain so I may not be able to clearly explain the process to you. The advantage is that it is the easiest for you measure and get quick confirmation that the timing is correct or what adjustment is needed to do so.

You may well prefer to work through the process using the loopback setup and I can help with that also. It may be more of a process, but it is a more conventional one and may be easier to understand. The results will be the same. 

Below is my short thoughts to your questions in case they are helpful for your process.



etc6849 said:


> I've been trying to use a timing reference, but keep getting a frequency response plot that looks altered. I initially had lots more interference until I disconnected my amp from the XLR connection, but after figuring that part out, the freq plot looks decent, but is skewed only when using a timing reference loop back.


See below.



> Timing Reference Output:
> HDMI 5 (XMC-1 via ASIO4ALL); HDMI 5 = left rear speaker of my 5.2 system.
> 
> Timing Reference Input:
> Presonus AudioBox Input 2 from XMC-1 RCA preout for left rear speaker (disconnected amp for left rear due to some interference I was getting initially).
> 
> ECM8000 non-calibrated mic on Input 1 of Presonus AudioBox


I think that is a good loopback setup.



> I plot the attached when doing this measurement, but what is strange is low end is elevated when using the loopback!?! I checked "set loopback as timing reference" under analysis and set the timing references as noted above.


Not sure, but suspect the problem here is that the XMC-1 mode may be the issue. If using surround mode, mono mode, etc the redirected SW output will be adjusted for the several active main channels resulting in higher level for the SWs than for the single measured main. This is no problem for this type of timing analysis. The amplitude does not impact the phase. 



> BONUS QUESTION:


There is a very good chance that all is well so let's hold on this.


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## jtalden

I should have mentioned that to confirm timing via the phase tracking method:

It is necessary to measure FL, SWs, FL+SWs using only channel #1. You should not measure using the LFE, channel #4. That way the XO filters are applied properly for FL channel and the timing and levels will also be correct. The right channel (#2) is then done similarly and so forth for any other channels you want to confirm.


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## etc6849

jtalden said:


> Possibly you are expecting that ideally the peak of the SW IR should be closely aligned with the Peak of the Mains IR? That is a common misconception.


Yes I was!



jtalden said:


> My understanding that it is ideal to have the phase of the SW and Mains track closely with each other throughout the XO range, maybe 50-150 Hz. I think this is the common ideal target that results in the closest working relationship of the drivers, I would expect that this is the target for a DL setup. In that case the peak of the SW IR will lag the peak of the Mains by several ms.
> 
> There are other commonly used alignments that provide almost equally smooth SPL reinforcement. One of those provides much closer alignment of the 2 IR peaks. There is little likelihood that that any of the good alignment will sound significantly better, but many can apparently hear a noticeable difference and thus may prefer one to another.
> 
> From the charts above, the XO SW timing alignment looks very good. There is no suggestion that there is a error in the timing. It is likely that the Dirac setup properly did it's job and I would not be surprised if it was ideally timed. That said, It is impossible to tell for sure with the charts above and it is always comforting to confirm it.
> 
> I can do this for you given just 4 simple measurements using either mic and no loopback is needed. This method is a difficult to easily explain so I may not be able to clearly explain the process to you. The advantage is that it is the easiest for you measure and get quick confirmation that the timing is correct or what adjustment is needed to do so.
> 
> You may well prefer to work through the process using the loopback setup and I can help with that also. It may be more of a process, but it is a more conventional one and may be easier to understand. The results will be the same.


I would like to try using the loopback cable, but I don't mind seeing which plots you would look at for the no loopback setup as I already have a REW for the no loopback measurements here: https://drive.google.com/folderview?id=0B1J0a4OV_WGLS2lYYl85N1BRNkE&usp=drive_web



jtalden said:


> Not sure, but suspect the problem here is that the XMC-1 mode may be the issue. If using stereo mode, mono mode, etc the redirected SW output will be adjusted for the several active main channels resulting in higher level for the SWs than for the single measured main. This is no problem for this type of timing analysis. The amplitude does not impact the phase.


The plots in my original post were just of "HDMI 1" where HDMI 1 is crossed to the subs at 80Hz. HDMI 1 corresponds to the front left channel.




jtalden said:


> There is a very good chance that all is well so let's hold on this.


This is great news! I was only concerned as someone on the AVS forum suggested an issue wrt to sub timing after looking at my excess group delay plot. I read over the REW manual, and it also suggests using EGD plots to check time alignment, so then I became worried that Dirac was doing something wrong.

On my google drive, there is an REW file I made using the UMIK usb mic (no loop back measurement using ASIO HDMI outputs), and it has measurements like this for the left speaker:

























These measurements look very good, and as you suggest seem to indicate Dirac is picking a sub timing that results in the smoothest possible sub transition wrt to amplitude. In the XMC-1 the 80Hz crossover is limited to 12dB slope for the speakers, but you can select a 24dB or a 12dB slope for the sub. Currently I have a 24dB slope for the subs, which luckily gave the pretty results above on my google drive. I did try changing this to 12dB slope for the sub low pass filter and inverting the phase on the sub. It gets rid of one phase shift in the plot, but causes dips in the amplitude, although the excess group delay plot shows a much lower timing difference. I put it back like I had it originally for now as you suggest, and will hold off on randomly changing things.


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## etc6849

See next post.


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## etc6849

Here is the file for the left channel. Contains nine measurements, all use Dirac. HDMI 1 channel only for all (had to turn off subs or amp to get different measurements). Subs are share common signal from XMC-1 Sub1 output. 

For this file, I used the calibrated UMIK-1 USB mic and ASIO4ALL HDMI 1 channel out.

File size is 21MB. File is here: https://drive.google.com/open?id=0B1J0a4OV_WGLdXZ5UzkzN1RuR3M

Or you can view all measurement files here: https://drive.google.com/open?id=0B1J0a4OV_WGLS2lYYl85N1BRNkE

In chronological order: 
The first three are with -24dB/octave low pass, no phase adjustments to the subs.
Second set of three use -12dB/octave low pass, no phase adjustments to the subs.
Last three measurements use -12dB/octave low pass, 180 degree phase switch switched for both subs.

EDIT: Thought it might be worth while to add a tenth measurement of HDMI 1 with no crossover, just the loudspeaker. New version of file is on google drive at the old link.



jtalden said:


> I should have mentioned that to confirm timing via the phase tracking method:
> 
> It is necessary to measure FL, SWs, FL+SWs using only channel #1. You should not measure using the LFE, channel #4. That way the XO filters are applied properly for FL channel and the timing and levels will also be correct. The right channel (#2) is then done similarly and so forth for any other channels you want to confirm.


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## jtalden

etc6849 said:


> Here is the file for the left channel. Contains nine measurements, all use Dirac. HDMI 1 channel only for all (had to turn off subs or amp to get different measurements). Subs are share common signal from XMC-1 Sub1 output.


This was the correct process for this particular analysis.



> For this file, I used the calibrated UMIK-1 USB mic and ASIO4ALL HDMI 1 channel out.


Good, this will work.



> Or you can view all measurement files here:


Since this is an analysis of the of the REW files and the measurements must be manipulated the charts are no help. The file you linked includes what is needed.



> In chronological order:
> The first three are with -24dB/octave low pass, no phase adjustments to the subs.
> Second set of three use -12dB/octave low pass, no phase adjustments to the subs.
> Last three measurements use -12dB/octave low pass, 180 degree phase switch switched for both subs.


This needs clarification. We need to analyze the condition that was used for the DL setup. Was that the first 3 measurements?

Moving an LFE filter to different settings should not impact the results, but it appears it did at first glance. So, maybe this pre-pro really change the SW to mains XO filter slopes as you suggested? That is not an option in the 3 pre-pros I have experience with. I can understand if this is indeed an option. I have just not run across it before. We just need to decide the setting to use and then run the DL setup and confirm the timing.

I will analyze the first 3 measurements on the left channel in case they were done with the correct settings. If you advise this is not the preferred settings then we can try again.


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## etc6849

Thanks for your help!

The Emotiva XMC-1 is a strange beast.

According to Emotiva's engineers (links below), the crossover slope for the sub (e.g. low pass) is user changeable from -12dB/octave or -24dB/octave. The high pass slope is always set to -12dB/octave no matter what (well unless it is disabled of course). Also, Dirac does not use the crossover when EQ'ing. The crossover is set AFTER Dirac (I know this is backwards from every processor I've owned, but it is what Emotiva's engineers state in the thread below).

http://emotivalounge.proboards.com/post/728764/thread
http://emotivalounge.proboards.com/post/728893/thread

EDIT: 
And some other really good points from KeithL on how they designed Dirac and bass management:
http://emotivalounge.proboards.com/post/744469/thread

"Just to clarify something - Dirac doesn't "handle" crossovers at all.

Dirac Live treats each channel as if it's full range, and corrects it as such (although it may not apply corrections above or below the frequencies which it considers to be the functional limits of the speaker, it doesn't block any frequencies form reaching the speaker). Dirac DOES NOT KNOW OR CARE what the crossovers in the XMC-1 are set to. The crossovers in the XMC-1 then act independently of Dirac Live to do bass management.

There also seems to be some serious misunderstanding about what a crossover does (in the quoted post).

You CANNOT "tell the XMC-1 not to play the test tone over the front speakers"; what you can do is to instruct the XMC-1 to apply an electrical filter that will alter the level of those test tones based on frequency.

For example, you can set the XMC-1 to apply a 24 dB/octave high-pass filter at 100 Hz.
If you do this, then the XMC-1 will leave all frequencies well above 100 Hz alone, apply a cut based on frequency that works out to -3 dB 100 Hz, -27 dB cut at 50 Hz, and approximately -50 dB at 25 Hz.
This is how a 24 dB/octave filter is SUPPOSED to work, and how they all do.

However, there's nothing to prevent the filters created by Dirac Live from applying additional boost or cut at some frequencies.
Likewise, if you're using the manual PEQs in the Speaker Presets instead, there's nothing to prevent them from making additional changes to the frequency response.
And, finally, these changes are applied to the frequency response of the speaker as it already is in your room.

As an extreme example, let's assume that your room and speaker (as a combination) have a nasty resonance that results in a 27 dB peak at 50 Hz.
If you add the response of our 100 Hz 24 dB/octave filter in the crossover to that in-room frequency response, the net result will be that the response will be 0 dB at 50 Hz (the peak in the room will cancel out the action of the crossover at 50 Hz).
This is, again, the way it is supposed to work.

If you want the crossover to cut in more suddenly, and do a more thorough job of blocking sound below its cutoff frequency, then you need a SHARPER FILTER.
Unfortunately, the sharper a filter you use, the more processing power it requires, and the more likely it is to produce audible unpleasant side effects.
For this reason, very few vendors offer filters sharper than the 24 dB/octave ones we use."



jtalden said:


> Moving an LFE filter to different settings should not impact the results, but it appears it did at first glance. So, maybe this pre-pro really change the SW to mains XO filter slopes as you suggested? That is not an option in the 3 pre-pros I have experience with. I can understand if this is indeed an option. I have just not run across it before. We just need to decide the setting to use and then run the DL setup and confirm the timing.
> 
> I will analyze the first 3 measurements on the left channel in case they were done with the correct settings. If you advise this is not the preferred settings then we can try again.


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## jtalden

I reviewed the 3 sets of timings:
The first set (3 measurements) is a good alignment as seen by good SPL support in the XO range. The phase timing is good with a crossing phase situation near the XO frequency. From a sound quality perspective it is fine to use this setting and be assured that this is a good alignment.

The second set is poor as easily seen by the SPL sag through the XO range.

The third set is also good as is easily seen by good SPL support in the XO range. In this case the phase does not cross, but due to a slight timing error they track a little separated.

If we want to nitpick there is a more ideal setting in terms of optimizing phase tracking if that is our objective. The sound difference is not likely to be significantly better than the first or third series however. There is a little more SPL support through the XO if that is desired, but that may not be needed to achieve your target house curve.

The optimized timing is based on setup 3 (the third series) but with the SW delay reduced by 2ms. That is, the SWs polarity should be set to -180° and their delay reduced by 2ms. This may not be possible as you indicated the SWs distance setting cannot be adjusted after the DL setup is conducted? If the distance can be changed just increase the SWs distance setting by 2 feet. If not then just use the first or third settings as they are considered good by providing a reasonably flat SPL response. If it meets your desired house curve then either one should work great. 

Selected charts below to illustrate: 

SPL Support; Series 1,2,3 vs Optimized








Phase Tracking; Series 3 Current








Phase Tracking; Series 3 Optimized


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## etc6849

Thanks for taking a look! How did you do the optimized timing plot? Is this an iterative process where you modify the subwoofer plot so that phase better matches the phase plot for the left speaker with sub turned off (e.g. reduce by 5 ms, then 4 ms, etc...) ?

Do you think I can trick Dirac by adding a miniDSP with an extra delay (maybe 30 milliseconds), and then that way I have 30 milliseconds to remove if needed to better optimize?

I'm a little confused on why 180 degrees setting on the subs works so well to be honest! In theory, this can't subtract from the DSP delay in the sub right? I do have phase knobs also on my subs, but was under the impression that these will never reduce time delay, but can add to the delay.

EDIT: I really think #3 sounds a tad more natural than before. Can't tell if this is a placebo effect though. Of course #1 was the best system I've ever heard and I lived with it for many months now which makes it really hard to beat.



jtalden said:


> The optimized timing is based on setup 3 (the third series) but with the SW delay reduced by 2ms. That is, the SWs polarity should be set to -180° and their delay reduced by 2ms. This may not be possible as you indicated the SWs distance setting cannot be adjusted after the DL setup is conducted?


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## etc6849

This is the excess group delay measurement Markus on the AVSforum showed me. Pretty interesting to compare trial 1, 3 and no crossover at all (front left only):


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## jtalden

etc6849 said:


> How did you do the optimized timing plot? Is this an iterative process where you modify the subwoofer plot so that phase better matches the phase plot for the left speaker with sub turned off (e.g. reduce by 5 ms, then 4 ms, etc...) ?


Basically yes. 
> Find the 'Current real' SW IR position relative to the FL IR position. Since loopback was not used that is not originally known. I have method to do that accurately using the step response chart, but is difficult to explain the process. Now that 2 forms of loopback are available in REW this complicated method is not needed. Just create measurements using loopback.
> Offset (shift) the SW IR (as you suspected) to find the best phase tracking. That may require inverting the SWs polarity to get the best overlay as it did in this case. It just depends on the XO filters being applied and the driver responses. There is no 'correct' SW polarity. It is just the one that provides the best phase tracking. 
> Use 'Trace Arithmatic' FL + Shifted SWs to see the resulting response of the new alignment.



> Do you think I can trick Dirac by adding a miniDSP with an extra delay (maybe 30 milliseconds), and then that way I have 30 milliseconds to remove if needed to better optimize?


I am suggesting that settings 1 or 3 is just fine. A 2ms (2 foot) shift from ideal for settings 3 is not likely to make a practical difference. I would not complicate the system with additional boxes. I would think there is a way to change the delay/distance in the current setup, but if not, then just use it as is. Adding a box to the SW output would allow additional delay, but you need less SW delay so you really would need to increase the delay in all the main channels instead - sounds complicated.



> I'm a little confused on why 180 degrees setting on the subs works so well to be honest! In theory, this can't subtract from the DSP delay in the sub right? I do have phase knobs also on my subs, but was under the impression that these will never reduce time delay, but can add to the delay.


You are correct.
The 180º polarity setting just flips the polarity without changing the timing/delay. A variable phase control on a SW just increase the delay around the XO freq and that may help in some cases. It will probably be counterproductive for settings 3 as you need reduced delay. Settings #1 is pretty close to the correct timing for that crossing phase style of timing. I don't think the phase control will help much there, but if I recall the situation correctly, I think it is directionally correct. The phase tracking chart may then look marginally better, but I would expect no noticeable change to the sound quality. It would take a lot of work to find out for sure.



> EDIT: I really think #3 sounds a tad more natural than before. Can't tell if this is a placebo effect though. Of course #1 was the best system I've ever heard and I lived with it for many months now which makes it really hard to beat.


:smile:

Either is very good technically. You may have preference to which sounds a little better to you so use the one you prefer.


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## jtalden

etc6849 said:


> This is the excess group delay measurement Markus on the AVSforum showed me. Pretty interesting to compare trial 1, 3 and no crossover at all (front left only):


Yes, the excess delay is increased a little with settings #1 vs #3. Excess delay is another (less sensitive) way to try to determine the if there is an issue with timing. The phase tracking chart is much more helpful for me. The excess phase chart does not identify that settings #1 is a good setup although that can be inferred from the SPL chart without looking at phase.


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## etc6849

The idea is to add a box to give extra delay, run dirac, then have delay "padding" I can reduce to get the plot the way I want (versus right now where I can't reduce delay at all). Hopefully this would trick Dirac into doing what I want. 

There really isn't a way to modify Dirac's delay settings, that's a big drawback to the XMC-1. Also, Dirac was added to the XMC-1 after it came out, and there is some limitation on the DSP they used, so Emotiva can never modify the XMC-1 to apply the crossover before Dirac. Dirac on the XMC-1 is fantastic for the price though. It blows away my Marantz AV8801 and I hear no hiss at my MLP.

Still, looking at how effective Dirac is, makes me really want to do the crossover outside the XMC-1 so Dirac would be applied to fix the entire crossover region (by setting the XMC-1 main speakers to large). I could even do the filter using the same miniDSP box being used to "pad" the delay. Not sure if it's worth the hassle though. My setup sounds truly fantastic the way it is, and it's not worth adding a second box just to fix that last phase shift.

If I could live with the extra 1% distortion from my main speakers below 80Hz, I'd do away with the crossover altogether which had the best looking phase plot, but I swear I hear inter-modulation distortion, especially on tracks with bass strings.

Thanks for your help. I learned a neat trick from you, and I greatly appreciate it!



jtalden said:


> I would think there is a way to change the delay/distance in the current setup, but if not, then just use it as is. Adding a box to the SW output would allow additional delay, but you need less SW delay so you really would need to increase the delay in all the main channels instead - sounds complicated.


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## jtalden

I am surprised you can't change the speaker distances either before or after the DL setup. That sounds like a real limitation to me. Fortunately for you, there are 2 settings that provide good XO timing results even without that capability. Possibly the owners can lobby Emotiva to update the firmware to provide that option. I suspect that has probably been tried, but I had to say it anyway. It represent a significant oversight on their part in my opinion.

I would not expect the distortion to be impacted by either setting. Are you sure there were not other factors involved impacting the distortion results? All sorts of things impact the distortion level more than 1% from run to run in the low frequencies so it is easy for these effects to creep into the results. A minor phase shift between drivers is not a major factor so far as I have experienced.

I just looked at your distortion results. They look very good. Even the relatively poor series 2 setting only measure 2.4% at 68Hz where there is a small peak. The small improvement in series 1, 3 is more related the small increase in SPL at that frequency rather than a reduction of the measured distortion level. You may want to measure the noise floor level just before and after each distortion measurement and see if there is a peak at that freq range. If so then that is more the issue than the timing is. Note also that there are several other minor distortion peaks at other higher frequencies as well. These also may be related to noise floor limitations. Just thoughts FYI...


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## etc6849

I've never measured the noise floor of my room, this is a great idea! In the file named "NOISE FLOOR TEST FRONT LEFT UMIK-1" there are some distortion measurements with several trials. I used the UMIK-1 USB mic and HDMI 1 channel. I turned the XMC-1 volume all the way down, then placed it on mute.

The first 3-6 chronologically are how the room would be during normal listening. For 7-9 I unplugged everything that was feasible to unplug while leaving on the amps, subs and XMC-1. Also did some RTA captures after doing sweeps 7-9.
https://drive.google.com/drive/folders/0B1J0a4OV_WGLS2lYYl85N1BRNkE

Seems there are some noise spurs in the mid-range region. Could be my UMIK-1 USB mic or could just be a little pink noise from my amps that I left on. I'll have to run a similar test next week when my calibrated EMM-6 comes from Cross-Spectrum. I'll also remember to do a test with the amps off (duh).

The distortion difference is when using only the front left speaker which will go below 20Hz on its own (e.g. with no crossover). This low frequency distortion is a little higher when not using the two subs, presumably since the subs are of very good quality and have larger drivers, and there is a better modal coupling of dual subs to the room versus just the front left speaker. However, the front left speaker by itself is very impressive. This plot of just the front left was plot 10 in the CROSSOVER TEST file.



jtalden said:


> I would not expect the distortion to be impacted by either setting. Are you sure there were not other factors involved impacting the distortion results? All sorts of things impact the distortion level more than 1% from run to run in the low frequencies so it is easy for these effects to creep into the results. A minor phase shift between drivers is not a major factor so far as I have experienced.
> 
> I just looked at your distortion results. They look very good. Even the relatively poor series 2 setting only measure 2.4% at 68Hz where there is a small peak. The small improvement in series 1, 3 is more related the small increase in SPL at that frequency rather than a reduction of the measured distortion level. You may want to measure the noise floor level just before and after each distortion measurement and see if there is a peak at that freq range. If so then that is more the issue than the timing is. Note also that there are several other minor distortion peaks at other higher frequencies as well. These also may be related to noise floor limitations. Just thoughts FYI...


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## etc6849

I hope you are doing well.

I ended up buying the Dirac software and now do all processing on my PC (movies and music are on my server). This lets me use the distance settings in the XMC-1 to fine tune the subs.

To get rid of the distortion, I found that tri-amping and removing the passive crossovers helps a bunch (and sounds better too). I added two Ashly XR1001's.

However, now I am revisiting sub delay setting (since passive crossovers being removed made my EGD plot less than 2ms from 20-20000Hz for just the left channel and no sub and now the sub doesn't match). I made a spreadsheet that calculates a distance that yields an expected degree for the subs.

For 80Hz, this gives: C7 = degree difference = main left degree at xo - dual subs degree at xo.

(1/80Hz)*(C7/360)*(13503.9 inches/s) = expected distance needed to change distance setting in XMC-1.

I think I duplicated your method:
0. Turn off all processing/EQ.
1. Set crossover in AVP/AVR.
2. Measure left speaker with subs off (acoustic timing ref is right speaker)
3. Measure subs with left speaker amp(s) off (acoustic timing ref is right speaker)
4. Note degrees crossover frequency from step 2 and 3. Also set level of sub to be similar at crossover frequency to freq resp plot of step 2.
5. Calculate the needed distance to move the sub distance setting in AVP/AVR.
6. Set new distance = old value + calculated value.
7. Measure things and see if it works.

This seems to work well, but the impulse is off from 0 by about 9ms and the EGD plot shows a 12ms timing difference below 60Hz which makes me think I need to go 360 degrees from 4' 7 feet , but then the phase slope is opposite of the left speaker at ~18' 7" (4' 7" + 360 deg @80Hz).

I'm tempted to use 18 feet 7 inches even though this shows an impulse that is -2ms versus +9ms for 4 feet 7 inches. It sucks the phases increase and decrease in opposite directions at 80hz though? I know though that the impulse plot is not reliable for setting subs from the REW manual...

EDIT: I think the smart thing to do is since when I plot both left and right with no crossover, phase is not linear and smooth at 80Hz (presumably due to the room). Would be smarter to just use a crossover point where the sub and both front speakers have linear and smooth phase.




jtalden said:


> I am surprised you can't change the speaker distances either before or after the DL setup. That sounds like a real limitation to me. Fortunately for you, there are 2 settings that provide good XO timing results even without that capability. Possibly the owners can lobby Emotiva to update the firmware to provide that option. I suspect that has probably been tried, but I had to say it anyway. It represent a significant oversight on their part in my opinion.
> 
> I would not expect the distortion to be impacted by either setting. Are you sure there were not other factors involved impacting the distortion results? All sorts of things impact the distortion level more than 1% from run to run in the low frequencies so it is easy for these effects to creep into the results. A minor phase shift between drivers is not a major factor so far as I have experienced.
> 
> I just looked at your distortion results. They look very good. Even the relatively poor series 2 setting only measure 2.4% at 68Hz where there is a small peak. The small improvement in series 1, 3 is more related the small increase in SPL at that frequency rather than a reduction of the measured distortion level. You may want to measure the noise floor level just before and after each distortion measurement and see if there is a peak at that freq range. If so then that is more the issue than the timing is. Note also that there are several other minor distortion peaks at other higher frequencies as well. These also may be related to noise floor limitations. Just thoughts FYI...


----------



## jtalden

If I follow correctly:
> The 3-way mains are now tri-amped using the Ashly boxes for the XO's. All is found well with this this change.
> The XMC-1 is providing an 80 Hz XO (mains to SW's). The unit can now also provide delay timing, i.e., speaker distance settings for the mains and SW's.
> A miniDSP Dirac box follows the XMC-1 and will provide EQ for the system. [This is an optional place for timing adjustments.]

You are looking now to set/confirm the proper XMC-1 distance settings prior to running the Dirac EQ.

This sounds like a reasonable approach to me.

I can help in confirming the distance settings. If you need any Dirac EQ help, others will need to provide that assistance.

So, concerning distance settings:
I don't really follow the logic for distance settings in Post 17. I'm also not comfortable trying to use EGD as a measure for that purpose. It may work just fine, but I no experience with that method so I have no good feel as to the its accuracy or repeatability. The phase tracking approach I use is likely to be a little more sensitive and thus at least as reliable however. So, If you want me to check your work I can do that. I will provide some charts with a brief explanation. If a distance adjustment is advised the needed change will be detailed.

Minimizing the needed measurements for a full analysis, I would need:
*Setup*
> Mic Centered at the LP
> Record and provide me the distance settings in the XMC-1 for these measurements.
> Set the XMC-1 desired 80Hz XO on using the chosen slope.
> MiniDSP Dirac box on, but no EQ, delays, or other active settings, i.e., set as a bypass mode.
> Engage either loopback timing or acoustic timing in REW (depends on USB or XLR mic type).
*Measure*
> SW's only
> FL main only
> FR main only
> CC main only (if desired)

From that mdat file of 4 measurements I will be able to calculate the SPL and phase responses of the 3 channels (SW's + FL, SW's + FR, and SW's + CC) using REW 'Trace Arithmetic' functions. I will also be able to shift the timing if needed to confirm the delay setting needed for optimal phase tracking. 

Other Comments:
Phase and GD are related so either is usable for timing adjustments. EGD provides a cleaner trace than GD so that is why it works better. I assume you are just looking for a smooth transition from mains to SW's in the EGD trace. That should work pretty well given a relatively smooth trace. If there are room modes in the XO range that can make it more difficult. Using phase instead, the 'frequency dependent window' controls in REW help a lot in smoothing the phase curve so adjusting the timing is probably easier in that situation.
Using that method requires IR shifting and REW trace settings, so it is not quickly explained. Some idea of the process (a bit outdated now) is shown here.


----------



## etc6849

EDIT: I'm thinking about a Yamaha SP2060 so as to align the mid-range and high range horns to the woofers at the MLP. I'm thinking I can still use REW to find the PEQ settings and time alignment, and that I'd just copy these over. If you'd like, please take a look at my tweeter and midrange in the REW below. Is time alignment worth exploring for the MF and HF drivers? I have a dip at 5kHz that was not present before. Might be 5" or so difference at the front of the speaker.

I will be using the PC version of the Dirac software. It shows up as a sound device to windows, but is really a virtual soundcard that binds to an actual soundcard output: http://www.dirac.com/online-store/

So signal chain is PC->XMC-1->Ashly XR1001 analog active xo->3 amps.

Might order a Yamaha SP2060, so PC->XMC-1->Yamaha SP2060 digital active xo-> 3 amps.


I ended up loading PEQ filters into the XMC-1 since REW lets me export them for the XMC-1. This was used to flatten out the curves (Ashley XR1001 is an analog active crossover). When I did this, I'm pretty sure my THD went up, but I'm assuming IMD will not be impacted.

Here is the link to the file. First measurement description has current XMC-1 distances I'm using (via the method I attempted to describe, which appears to be the same as you were doing in your other post except instead of inverting polarity, I attempt to offset phase at the crossover point by using the distance equation I posted previously). 

This first measurement was my stab at the settings after many attempts, but the EGD plot is not as pretty as before when you did an awesome job last year.

I think adding the shelves and amps up front and removing the cinder blocks that helf up my center speaker has impacted room response. There is now a room mode at 70Hz for the subs I'm guessing.

File: https://drive.google.com/open?id=0B1J0a4OV_WGLUFdCZzJ6cXFsOG8

It will be interesting to see if you can come up with a better timing as I tried to learn from your posts from before and spent hours on this so far. I'm sure you will find something better though as this if my first time using these features in REW.

Thanks again for your other posts and wisdom.



jtalden said:


> If I follow correctly:
> > A miniDSP Dirac box follows the XMC-1 and will provide EQ for the system. [This is an optional place for timing adjustments.]
> 
> You are looking now to set/confirm the proper XMC-1 distance settings prior to running the Dirac EQ.
> 
> This sounds like a reasonable approach to me.
> 
> I can help in confirming the distance settings. If you need any Dirac EQ help, others will need to provide that assistance.
> 
> So, concerning distance settings:
> I don't really follow the logic for distance settings in Post 17. I'm also not comfortable trying to use EGD as a measure for that purpose. It may work just fine, but I no experience with that method so I have no good feel as to the its accuracy or repeatability. The phase tracking approach I use is likely to be a little more sensitive and thus at least as reliable however. So, If you want me to check your work I can do that. I will provide some charts with a brief explanation. If a distance adjustment is advised the needed change will be detailed.
> 
> Minimizing the needed measurements for a full analysis, I would need:
> *Setup*
> > Mic Centered at the LP
> > Record and provide me the distance settings in the XMC-1 for these measurements.
> > Set the XMC-1 desired 80Hz XO on using the chosen slope.
> > MiniDSP Dirac box on, but no EQ, delays, or other active settings, i.e., set as a bypass mode.
> > Engage either loopback timing or acoustic timing in REW (depends on USB or XLR mic type).
> *Measure*
> > SW's only
> > FL main only
> > FR main only
> > CC main only (if desired)
> 
> From that mdat file of 4 measurements I will be able to calculate the SPL and phase responses of the 3 channels (SW's + FL, SW's + FR, and SW's + CC) using REW 'Trace Arithmetic' functions. I will also be able to shift the timing if needed to confirm the delay setting needed for optimal phase tracking.
> 
> Other Comments:
> Phase and GD are related so either is usable for timing adjustments. EGD provides a cleaner trace than GD so that is why it works better. I assume you are just looking for a smooth transition from mains to SW's in the EGD trace. That should work pretty well given a relatively smooth trace. If there are room modes in the XO range that can make it more difficult. Using phase instead, the 'frequency dependent window' controls in REW help a lot in smoothing the phase curve so adjusting the timing is probably easier in that situation.
> Using that method requires IR shifting and REW trace settings, so it is not quickly explained. Some idea of the process (a bit outdated now) is shown here.


----------



## Joe Bloggs

The conversation here has gone over my head, but I don't see the graph I would use so I would mention it here:

Why not just run a full range measurement of your system then look at the Spectrogram: :laugh2:

A perfect impulse has a horizontal line as its spectrogram. You can tick the "Plot the peak energy curve" option to show the timing clearly.
[1st image]

When I first recorded my system it looked like this (also a synthetic impulse to illustrate more clearly):
[2nd image]

Two problems. Firstly a too-steep crossover was introducing excess group delay centered on the crossover frequency; secondly the sub was lagging the mains.

After lowering the crossover slope and delaying the mains, I got a measurement like this: (crossover frequency 70Hz)
[3rd image]

Finally, my sub has a +/- phase switch rather than phase knob (I wouldn't know what a knob does...) to set the right phase, I simply flicked the switch while playing tones around 70Hz and chose the position that gave louder tones (indicating reinforcement rather than cancellation).

Hope that helps :smile:


----------



## jtalden

Thanks for the data. It’s clearly labeled and just what is required.

> Some steps were taken in REW to properly adjust the data for the following SPL and phase tracking charts. The Right and Left phase closely tracks each other and both traces cross the Subs phase trace at 80 Hz. This is a very good 'alternate' setting. Your setup process worked very well. This timing is in my opinion the second best choice. It provides some reduction in overall phase rotation (reduced total GD) and still provides excellent SPL reinforcement. My system sounds very good using this type of alignment. The phase crossing condition is not the 'ideal' case however as it is considered more correct to have the phase of the Subs track closely to the phase of the mains rather than sharply crossing at the XO frequency. 

















The following is the adjustment needed to provide a closer phase tracking.
> Invert the Subs polarity
> Change the Subs delay by +6.5 ms

The resulting SPL and Phase tracking is shown below. The XO range SPL is slightly better away form the XO point as a result of the phase tracking is much closer.

















Below is an overlay of the Left SPL Initial (red) Vs Adjusted (yellow). The impact on SPL is minor as expected.









Either alignment is a good one. 

Other Comments:
> The phase tracking would be even closer when the acoustic XO filter slopes are more similar. It appears the HPF slope chosen was 24 dB/octave and the LPF was 48 dB/octave. A change of the HPF to 48 dB/octave would make the phase tracking even closer. The practical impact of that 'improvement' is insignificant so this is mentioned only for general interest to readers. [If you change it now the timing would need to be adjusted again so it is not advised.]

> If your mains XO's are at 250 and 5k Hz then the dips in the SPL may be related to timing error at those XO points. A speaker management box instead of the Ashly would allow the timing to be adjusted at those XO as well. Again this is just info. You could try inverting the polarity of the MR (or both the MR and TW) to see if the dips are improved even using the Ashly.

> Dirac does an amazing job of EQ. The flat house curve you set is likely to sound too bright however. Most everyone prefers some HF roll-off at the LP to account for the measuring distance related roll-off that is normal when the speaker is designed as flat at 1m. Don't hesitate to adjust to a house curve that you prefer in your situation.


----------



## etc6849

Wow. Awesome job! I should have experimented by swapping polarity. I don't know how you did that so fast. I guess it would only take me a few hours next time around (versus a few days reading and learning, plus developing the steps and then seeing your other post that did the same thing). I am glad to hear I am getting better at this.

The Ashly XR1001 is very limited, and unfortunately has the slope set internally. If you are talking about the subs/LF slopes, I'm not sure why one slope is 48dB/octave for the sub's high pass, other than I accidentally must have applied a 24dB slope when I exported PEQ settings from REW for the LFE channel, and this is getting added to the XMC-1's filter for the sub crossover (which I thought was 24dB, but could be 12dB internally).

The response knob just lets you adjust for dips at the xo and does not adjust the actual crossover slope (had to read the directions as this cost me a few hours too).

I still am confused on the 5kHz dip (have the Ashly HF xo set to a little below 4kHz), and it makes since that it is the Ashly because the dip was not there when I did fools tri-amping with the Ashly limiting what went to each amp, but still using the passive crossovers. Needless to say, I am not going back to passive as it sounds clearer even without Dirac. I did have to add a 4.5 ohm and 6 ohm wire wound resistor in series with the MF and HF driver (to bring total impedance to about 10 ohms for each driver). This was because the hiss from my now oversize amps was pretty loud even with the Ashly turned off. let me know if you think this was a bad idea or not. I used "non-inductive" wire wound resistors from Vishay/Mills Division.

I like the idea of inverting the mid-range polarity, thanks! I will try that when I get home tonight for sure.

The curve is flat since I quickly used REW to export filters into my AV processor (XMC-1). I usually use the default Dirac curve, and agree it sounds better having a slightly downward sloping house curve. I think when I get a digital active crossover I will copy the slope of the Dirac curve, and will likely still use Dirac on my PC too. The software based version is the best Dirac Live version I've tried (thinking you commented on my Dirac Live post back in August); I'm thinking this is because of the power a CPU has versus a DSP in a consumer grade processor.



jtalden said:


> Other Comments:
> > The phase tracking would be even closer when the acoustic XO filter slopes are more similar. It appears the HPF slope chosen was 24 dB/octave and the LPF was 48 dB/octave. A change of the HPF to 48 dB/octave would make the phase tracking even closer. The practical impact of that 'improvement' is insignificant so this is mentioned only for general interest to readers. [If you change it now the timing would need to be adjusted again so it is not advised.]
> 
> > If your mains XO's are at 250 and 5k Hz then the dips in the SPL may be related to timing error at those XO points. A speaker management box instead of the Ashly would allow the timing to be adjusted at those XO as well. Again this is just info. You could try inverting the polarity of the MR (or both the MR and TW) to see if the dips are improved even using the Ashly.
> 
> > Dirac does an amazing job of EQ. The flat house curve you set is likely to sound too bright however. Most everyone prefers some HF roll-off at the LP to account for the measuring distance related roll-off that is normal when the speaker is designed as flat at 1m. Don't hesitate to adjust to a house curve that you prefer in your situation.


----------



## jtalden

etc6849 said:


> If you are talking about the subs/LF slopes...


Sorry for my confusion, Yes I was referring to the HPF on the 80 Hz XO. I was mistakenly remembering that you indicated you had 2 choices 24 and 48 dB/octave for the HPF of the XO - just another short term mental lapse. I know that would be unusual. Choices of 12 and 24 dB/octave on the *HPF* would make more sense. Looking back, you mentioned 12 and 24 dB/octave for the *LPF*. I would expect that to be unusual also. In the end, you have whatever is offered in the XCM-1and, since I am confused on what those choices are, let's just stick to the principle involved. 

As stated, the objective is to have the acoustic HPF and LPF slopes to have similar roll-off rates. That provides the opportunity for the closest phase tracking across the entire XO range. Looking at the SPL roll-off rates, the HPF is a much shallower slope than the LPF. That is why the phase tracking still crosses each other a little rather than following more closely on top of each other. You may, or may not, have any control of either of the XO filters slopes offered in XMC-1. If you do have choices, just choose the setting that best matches the roll-off slopes.



> I still am confused on the 5kHz dip (have the Ashly HF xo set to a little below 4kHz), and it makes since that it is the Ashly because the dip was not there when I did fools tri-amping with the Ashly limiting what went to each amp, but still using the passive crossovers. Needless to say, I am not going back to passive as it sounds clearer even without Dirac. I did have to add a 4.5 ohm and 6 ohm wire wound resistor in series with the MF and HF driver (to bring total impedance to about 10 ohms for each driver). This was because the hiss from my now oversize amps was pretty loud even with the Ashly turned off. let me know if you think this was a bad idea or not. I used "non-inductive" wire wound resistors from Vishay/Mills Division.


I can't help much with what you did with the 3-way mains. You are moving in the right direction however. Active DSP is the best answer as it provides the controls needed for fine tuning. Not much further can be done with the current Ashly unit other than trying inverting the polarity of the drivers to confirm which polarity provides the smoothest SPL through the XO range. Don't change the polarity of the woofers unless you also change the polarity of the Subs unless you are starting over with setting up the timing. 



> I like the idea of inverting the mid-range polarity, thanks! I will try that when I get home tonight for sure.


Just use which ever setting provides the best SPL support. The phase rotation of the midrange unit 250 Hz - 4 kHz appears to be much greater than normal. I am not sure why that is. Possibly this is a horn unit. The only way to really improve the timing further than choosing polarity is by using a DSP speaker management box. That way proper timing can be set.

I forgot to mention in all this that it may be necessary to rerun Dirac after any timing changes are made. Dirac applied EQ in the XO ranges as well as across the rest of the range. SPL changes due to timing changes may or may not have enough of an impact to warrant another Dirac setup.


----------



## etc6849

Ok, I wanted to ensure I could copy what you did this time. Very clever. What I did is to invert the sub plot (settings under impulse response plot).

Then I put in -.1ms for t=0 offset and clicked apply a while counting and stopped when the phase slope matched well. I snapped the windows as shown in the attached screenshot.

What made you invert the sub in the first place though? Do you just try +.1 ms and -.1 ms without inverting and see that it doesn't look as nice?











jtalden said:


> Below is an overlay of the Left SPL Initial (red) Vs Adjusted (yellow). The impact on SPL is minor as expected.
> 
> View attachment 135466
> 
> 
> Either alignment is a good one.


----------



## etc6849

It is a horn loaded mid-range and a horn loaded tweeter with regular woofers. In the spur of the moment decision today I ordered a Yamaha SP2060. Was a good chunk of change even at $400 off the street price/MAP. Based on how much of my middle class income I've spent on audio, it is a drop in the bucket though. I spent a lot of hours battling the Ashley XR1001; the numbers on the dial are impossible to get exact. Mainly due to the 500Hz and 3.9kHz frequencies I want, but the dial itself is very touchy.

I greatly appreciate your help, and think you have developed some neat methods that I should be able to post some nice plots for you in the near future (all thanks to you of course).

Needless to say, I'm going to browse most of your old posts here when I get some time.



jtalden said:


> The phase rotation of the midrange unit 250 Hz - 4 kHz appears to be much greater than normal. I am not sure why that is. Possibly this is a horn unit. The only way to really improve the timing further than choosing polarity is by using a DSP speaker management box. That way proper timing can be set.


----------



## etc6849

Imitation is the ultimate form of flattery... Knowing this, I tried your method without inverting sub too. I did math like you taught me in REW (really like this method of yours as I had previously calculated an angle difference at the xo point, then measured the actual setup after adjusting distance).

Not sure if this makes physical sense to set my sub from 20' 3" to 7' 10" when I know there is probably a 12ms delay inside the sub, but option 3 below? Would this option be more desirable in that the summed plot has a nice evenly sloped phase with very little bumps or horizontal areas (after unwrapping phase about the crossover point)? 

What is strange is I'm pretty sure my sub has ~12ms delay, so perhaps this is really not enough distance... hmm?

REW plot after actual changes using your methods yields results similar to those predicted: https://drive.google.com/open?id=0B1J0a4OV_WGLVS1jWVloTXVHWm8 

Amazing how you can represent a system with just frequency and phase. I guess the results are slightly off, so does that mean it is not a perfectly linear system? So that linear systems class I took in college is this useful...!?!

(or maybe control systems can't remember which it's been so long)

























*Real versus predicted:*
















*Left+Sub as measured with new settings:*











jtalden said:


> Below is an overlay of the Left SPL Initial (red) Vs Adjusted (yellow). The impact on SPL is minor as expected.
> 
> View attachment 135466
> 
> 
> Either alignment is a good one.


----------



## jtalden

etc6849 said:


> Then I put in -.1ms for t=0 offset and clicked apply a while counting and stopped when the phase slope matched well. I snapped the windows as shown in the attached screenshot.


That works. I did that for a time. It's a good way to start. I find that method hard to keep track of though even with taking notes. My limited counting and concentration skills make it difficult to follow how many steps were taken adding and subtracting a bunch of 1 ms steps. Worse yet is with the higher frequency XO's when we are dealing with various small fractional ms steps to find the alignment timing. 

As to direction for the shift (+/-), I have enough experience to recognize the direction needed just by inspection of the phase traces. It just takes some practice.

Here is the hint: If we load another copy of the Subs measurement so we have 2 versions of the same sub measurement, we can identify the 2nd as the copy and move that one without trying to keep track of the distances. It does not matter the increments used the directions of each shift or how may steps it takes to find the best alignment. When we've found the best alignment use the REW Control-Shift-Right Button tool to measure the distance between the original sub IR position and the sub-copy IR position. That the delay shift needed.

This time I just estimate that it would take sub inversion and about XX ms sub delay to align them and then found I needed another 1 ms adjustment and it happened to fall just right - no fractional shift needed. I still measured the offset to be sure I remembered the 2 steps I took correctly.



> What made you invert the sub in the first place though? Do you just try +.1 ms and -.1 ms without inverting and see that it doesn't look as nice?


it was pretty clear by inspection that 1/2 wavelength sub delay with sub inversion was likely to be best. I still tried a 1 wavelength shift just to be sure. This sounds like it was easy, but I still get confused and often have to start over so it helps me to stay in practice. I've spent about 6 hr on this thread since Post 17. Most of this is in just struggling with my poor typing and editing skills. That doesn't seem to improve as easily at the timing analysis skills. :frown:


----------



## jtalden

Nice purchase. That Yamaha looks like a really nice box!



etc6849 said:


> I tried your method without inverting sub too. I did math like you taught me in REW (really like this method of yours as I had previously calculated an angle difference at the xo point, then measured the actual setup after adjusting distance).


I am not sure what math you refer to. If it is the offset needed for a 1/2 or 1 wavelength shift after one of the good alignments has been found then that just puts us in the correct area. It does not result in a finely tuned alignment. A small adjustment is still needed for those want to optimize. The sound quality difference is probably trivial however.



> Not sure if this makes physical sense to set my sub from 20' 3" to 7' 10" when I know there is probably a 12ms delay inside the sub, but option 3 below? Would this option be more desirable in that the summed plot has a nice evenly sloped phase with very little bumps or horizontal areas (after unwrapping phase about the crossover point)?


12 ms in the Sub? This sounds wrong. I have seen it mentioned that ~1 ms is more typical. You could check it out easy enough if it is a concern and the specs aren't available. Place any mic ~0.5" from the VC cap on the driver so there is ~0 ms time of flight. Rig up an all analog measuring system (soundcard out > Sub > Mic > Soundcard in). Any cheap $1 mic that plugs into a PC soundcard will work fine. No calibration is necessary. Use loopback timing and take a measurement sweep 40-60 Hz. The IR offset from 0dB is a close estimate of Sub DSP delay. I haven't tried this, but it should work. We can just trust that our objective is to align the relative positions of the drivers though. The absolute values of the various delays in the system are inconsequential for a music system - Trust the measurements.



> Amazing how you can represent a system with just frequency and phase. I guess the results are slightly off, so does that mean it is not a perfectly linear system?


The IR provides all. 

The phase tracking results are a little off? I see that in the first chart. They shouldn't be off. My guess is that possibly the window control reference point was not properly zeroed for one of the 2 drivers. REW is inconsistent in how the reference position impacts the phase. Most times it has no impact, but for some small IR shifts zero is shifted and the phase trace is impacted. I have no idea how to predict when or why and have been meaning to try understand that better. The behavior may make sense for some uses, but for timing of XO's it means each IR shift needs to be to have the reference point reset to 0 ms to be safe in reading the phase chart. This is true even if the window popup indicates 0.0 ms as smaller decimals do not show up. The dotted line on the IR chart is a good indicator of where REW has zero located. I always either zero each shift or insure the dotted line is still at zero after any shift before looking at phase relationship between drivers. If that is not the reason for the discrepancy then there was another mistake made. That's easy to do!


----------



## etc6849

jtalden said:


> Nice purchase. That Yamaha looks like a really nice box!
> I am not sure what math you refer to.


Just speaking of the math that REW is doing like inverting phase, shifting the impulse, etc... bad wording on my part.



jtalden said:


> 12 ms in the Sub? This sounds wrong. I have seen it mentioned that ~1 ms is more typical. You could check it out easy enough if it is a concern and the specs aren't available. Place any mic ~0.5" from the VC cap on the driver so there is ~0 ms time of flight. Rig up an all analog measuring system (soundcard out > Sub > Mic > Soundcard in). Any cheap $1 mic that plugs into a PC soundcard will work fine. No calibration is necessary. Use loopback timing and take a measurement sweep 40-60 Hz. The IR offset from 0dB is a close estimate of Sub DSP delay. I haven't tried this, but it should work. We can just trust that our objective is to align the relative positions of the drivers though. The absolute values of the various delays in the system are inconsequential for a music system - Trust the measurements.


I can attempt this using a signal generator with trigger and digital oscilloscope, mic and preamp to determine actual delay of the sub, after removing the sub from my system (since I do not want to also include any delay the XMC-1 could be adding).



jtalden said:


> The IR provides all.


Thanks! I remember this now and it makes complete sense. I am forgetting simple things like this after taking linear systems 17 years ago 



jtalden said:


> The phase tracking results are a little off? My guess is that possibly the window control reference point was not properly zeroed for one of the 2 drivers.


Thanks! I will start by zeroing the impulse for now on like you do. So if I use right as the acoustic reference and then measure right wrt to the acoustic reference, the red reference line on the impulse plot should be at 0? It is often times off by about ~200us to the left of zero. Why can't REW perform some calibration and subtract this 200us error? Wouldn't that make things easier?

I also forgot to account for rounding to the nearest 1 inch, pretty stupid of me. .1ms is 1.35039 inches, and the XMC-1 just lets you are adjust distance by 1" increments. Doh! I bet this is why the results aren't the same. You are a world class expert at this stuff! I'm sure the digital crossover I ordered will have better distance adjustments and the zeroing you do will become a common practice for me so I really appreciate you elaborating on it. Eventually after I get better at this stuff, I will move to mono 1x4 digital xo's. I would then hook the left xo's sub output to the left input of each of my two subs, and do the same for the right (since my subs internally sum the L and R XLR's).

I also plan to follow these Rane guidelines for how to rewire my XLR cables so as to reduce shield induced noise (since all my Emotiva amps are fully balanced/purely differential end to end and has a signal ground on pin 1 that is NOT tied to the chasis ground with no metal locking tab either that would normally ground to the metal shell of the XLR connector): http://www.rane.com/note151.html [EDIT: fixed link]


----------



## jtalden

etc6849 said:


> Thanks! I will start by zeroing the impulse for now on like you do. So if I use right as the acoustic reference and then measure right wrt to the acoustic reference, the red reference line on the impulse plot should be at 0? It is often times off by about ~200us to the left of zero. Why can't REW perform some calibration and subtract this 200us error? Wouldn't that make things easier?


There may be some confusion. There are 2 different subjects regarding 'setting zero'.

1. Setting *IR offset *to remove total measuring system delays:
Using loopback there is an IR offset from 0 ms. For the loopback cable method it can be large (think 10-100ms) and for a acoustic loopback like this it's normally smaller (think 0-2ms). It depends on the particular setup. When analyzing the relative delay between drivers as we are doing here, it is required to move both measurements near to 0 ms so the phase rotation is minimized and thus the phase traces are easier to read. This is critical for HF XO, but in this case of a 0.2 ms offset on a 80Hz XO the shift is not big enough to cause a problem reading the chart in the 20-200 Hz range. I still always make the shift to 0 ms for consistency. It's just good practice and is critical if we also look at the higher frequencies and want to see total phase rotation. Both drivers must be shifted the same amount or the relative timing between them is changed. After this type of shift to set the IR's of the 2 drivers near 0 ms the following still applies.

2. Setting the 'Window Ref Time' in the 'IR Window Control' popup:
After any IR shift (large or small) when doing relative driver delay analysis it is necessary to open the 'IR window control' popup and confirm/set the 'Window Ref Time' to 0.000 ms. If one or the other drivers 'Windows Ref Time' is not exactly at 0.000 ms there may be an impact on its phase trace. Revisit my comments in my last post for more detail on this.


----------



## etc6849

Thanks! Yes, there was confusion. Here are the results. I think I told you in a PM that I ended up getting a Xilica XD4080 (4 way active crossover) for my three way left and right fronts crossed to subs. This thing is awesome!

REW file for pre-dirac using only 6 PEQ's: https://drive.google.com/open?id=0B1J0a4OV_WGLeTZGTGZyTEdKaGM

Post Dirac REW file was done after bypassing all PEQ's (I only listen to music and movies via Dirac Live on my PC): https://drive.google.com/open?id=0B1J0a4OV_WGLY2hMSV9YNDNwRmc

Some pictures are attached for the front right after Dirac was applied. Makes for some really nice plots if I just leave the mic in one spot for all nine measurements. Normally one shouldn't do this, but my room is very well treated, and I really like how the house curve sounds now (+/-2.5dB even with the downward slope included with no smoothing applied whatsoever).



jtalden said:


> There may be some confusion. There are 2 different subjects regarding 'setting zero'.
> 
> 1. Setting *IR offset *to remove total measuring system delays:
> Using loopback there is an IR offset from 0 ms. For the loopback cable method it can be large (think 10-100ms) and for a acoustic loopback like this it's normally smaller (think 0-2ms). It depends on the particular setup. When analyzing the relative delay between drivers as we are doing here, it is required to move both measurements near to 0 ms so the phase rotation is minimized and thus the phase traces are easier to read. This is critical for HF XO, but in this case of a 0.2 ms offset on a 80Hz XO the shift is not big enough to cause a problem reading the chart in the 20-200 Hz range. I still always make the shift to 0 ms for consistency. It's just good practice and is critical if we also look at the higher frequencies and want to see total phase rotation. Both drivers must be shifted the same amount or the relative timing between them is changed. After this type of shift to set the IR's of the 2 drivers near 0 ms the following still applies.
> 
> 2. Setting the 'Window Ref Time' in the 'IR Window Control' popup:
> After any IR shift (large or small) when doing relative driver delay analysis it is necessary to open the 'IR window control' popup and confirm/set the 'Window Ref Time' to 0.000 ms. If one or the other drivers 'Windows Ref Time' is not exactly at 0.000 ms there may be an impact on its phase trace. Revisit my comments in my last post for more detail on this.


----------



## jtalden

The SPL looks great and that is the primary contributor to sound quality. 

*Pre-DL:*
The higher XO's appear to be improved to some extent, but... Given the new DSP box it appears that significant improvement in phase tracking is possible if you so desire. See the chart below. The apparent phase rotation of the TW, MR, W and SW's is sketched in and labeled. In the XO areas it appears the phase tracking could be improved in all 3 XO's areas. It is impossible to be sure that this apparent condition really represents the actual condition however. Individual driver measurements would be needed to confirm the actual situation.









*Post-DL:*
It appears DL greatly smoothed the SPL and also had some phase improvement in 2 of the XO's as well. There still seems to be a phase issue with the W-MR XO (not shown). There is a limitation as to what DL can do in correcting phase. Its effect appears to be able to improve the on-axis phase response. That effect will also impact the off-axis phase, but does not work to correct it. The off-axis phase, and thus SPL, will still be less than ideal as it is dependent of the actual timing of the drivers. 

It is thus better to clean up the phase tracking Pre-DL rather than relying on DL. That will significantly improve the off-axis phase/SPL response. If you want me to confirm the XO timings please provide 'timing referenced' measurements (left or right channel) of each driver (TW, MR, W, SW's) with the mic at the LP. There is no need for both channels so just 4 measurements.


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## etc6849

Clearly this is an art to this that will take me many years to master!

Here is the REW file for the drivers. I did left and right both, so you can take your pick  I do want to here what the best possible phase coherence sounds like and plan to AB yours versus mine.

https://drive.google.com/open?id=0B1J0a4OV_WGLcFpmMHVJTmQyLUU




jtalden said:


> The SPL looks great and that is the primary contributor to sound quality.
> 
> *Pre-DL:*
> The higher XO's appear to be improved to some extent, but... Given the new DSP box it appears that significant improvement in phase tracking is possible if you so desire. See the chart below. The apparent phase rotation of the TW, MR, W and SW's is sketched in and labeled. In the XO areas it appears the phase tracking could be improved in all 3 XO's areas. It is impossible to be sure that this apparent condition really represents the actual condition however. Individual driver measurements would be needed to confirm the actual situation.
> 
> View attachment 135858
> 
> 
> *Post-DL:*
> It appears DL greatly smoothed the SPL and also had some phase improvement in 2 of the XO's as well. There still seems to be a phase issue with the W-MR XO (not shown). There is a limitation as to what DL can do in correcting phase. Its effect appears to be able to improve the on-axis phase response. That effect will also impact the off-axis phase, but does not work to correct it. The off-axis phase, and thus SPL, will still be less than ideal as it is dependent of the actual timing of the drivers.
> 
> It is thus better to clean up the phase tracking Pre-DL rather than relying on DL. That will significantly improve the off-axis phase/SPL response. If you want me to confirm the XO timings please provide 'timing referenced' measurements (left or right channel) of each driver (TW, MR, W, SW's) with the mic at the LP. There is no need for both channels so just 4 measurements.


----------



## jtalden

I have just started to look at the file. The Woofer section (74-700 Hz) has a large phase transition at about 250 Hz. This is not related to an XO as I was hoping it was. I am now wondering about the cause of this. Is the Woofer driver in a type of horn or transition line box? Is this a ceiling bounce or possibly a rear wall bounce. How close is the LP to the back wall? Can you provide some info on this section? This 250 Hz phase shift may limit the phase control that I was hoping to achieve. I would like to understand the situation better. If a picture will help explain the situation please provide one. Thanks.


----------



## etc6849

I took the driver measurements with the mic pointed upward at the MLP (just as I would when I run Dirac).

Here are some older pics (speakers in same place, but shelves for amps were added and the center was removed when I tri-amp the main speakers):
https://drive.google.com/open?id=0B1J0a4OV_WGLREI3eDVXd0xBM2s










Room dimensions:
https://drive.google.com/open?id=0B1J0a4OV_WGLczBnZmdOMW5MbXM

I am happy to move the speakers. I could swap their location with the subs that are pictured, what do you think? I will experiment some to see if I can fix the room mode for you. It has always been there.



jtalden said:


> I have just started to look at the file. The Woofer section (74-700 Hz) has a large phase transition at about 250 Hz. This is not related to an XO as I was hoping it was. I am now wondering about the cause of this. Is the Woofer driver in a type of horn or transition line box? Is this a ceiling bounce or possibly a rear wall bounce. How close is the LP to the back wall? Can you provide some info on this section? This 250 Hz phase shift may limit the phase control that I was hoping to achieve. I would like to understand the situation better. If a picture will help explain the situation please provide one. Thanks.


----------



## jtalden

Thanks. Impressive speakers!
That woofer range is bass reflex. I just found a review in Stereophile that states all 3 drivers are working together covering the same frequency and range. That unfortunately does not help with my understanding of what is going on at 250 Hz in your room.

If I were to investigate, I would:
[with; acoustic timing disabled, 15-1200 Hz sweep]
1. Left main, mic at LP.
2. Left main, mic on axis with the middle woofer and about 1 m away from it.
3. Left main, Chair aside, mic at LP [listening chair moved away from the LP].
4. Left main, chair aside, mic ~24" left from LP
5. Left main, chair aside, mic ~24" right from LP
6. Left main, chair aside, mic ~12" up from LP
7. Left main, chair aside, mic ~12" down from LP
8. Left main, mic at LP, Plug the ports temporarily with foam or rags or..., anything that would restrict most of the air flow but not harm the finish. A tight seal is not needed.

This is a completely optional experiment. I am not sure that it will help identify a better path forward, but it might. Do any part of it that appeals to you. 

I will now get back to the data you already provided and suggest improve timing. There will be only some relatively minor changes to what you now have applied.


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## jtalden

Okay...
I have finished the timing analysis. The following are the changes to the current delay settings in the Xilica. I chose the TW as the reference timing so its delay does not change. 
TW = 0 ms (Ref)
MR = -0.060 ms (Also reverse the polarity of this driver)
W = +0.800 ms
SW's = +0.100 ms

The net SPL impact (a minor improvement around 3500 Hz) can be seen below:








The XO range SPL reinforcement is shown below:








The net impact on overall phase rotation is shown below:








The impact on the step response is shown below:
















The overall SPL is not significantly impacted. The phase rotation now follows a more conventional track and thus the step response also looks more conventional for a well timed 4 way system. The 250 Hz room effect is not addressed in these changes.


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## jtalden

Phase tracking charts for the revised delay settings are shown below:
[Note that in creating these charts I find a small error as to the SW's delay adjustment. I am now unsure whether the +1.000 ms shift stated above is correct or if 0.000 ms is correct (no shift). I will need to confirm by running through the analysis again. This difference is very small for a 75 Hz XO so either way the phase tracking will be very close. The main concern is if there were any other errors made. It easy to do. I will advise.]


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## jtalden

The correct change to the SW's delay is 0 ms (no change). That results in the phase tracking shown above. The overall phase tracking comparison looks only slightly different as a results of the minor change from Post-37. No other charts were significantly impacted.


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## etc6849

You are the phase whisperer! I will apply these now and hopefully post some pics before and after I run Dirac. It is getting late here though (I'm on EST)! Good thing I saw these wonderful posts of yours before I moved anything.

I would like to explore the 240Hz room issue in a few weeks, but I really hate to mess with the work you've done here as it's outside of my ability to recreate this. At least I had pondered about reversing phase on the mid-range! I can't believe how much better they track, you are absolutely right looking at the plot; incredible.

TW = 0 ms (Ref)
MR = -0.060 ms (Also reverse the polarity of this driver)
W = +0.800 ms
SW's = +0.000 ms



jtalden said:


> View attachment 135930


----------



## etc6849

Wow! All is well with these settings, but I am going to guess you forgot to mention also invert the tweeter (in addition to the mid-range)? I had to invert the tweeter also to get the pretty plot below.

In addition, your xo points were off (the one's i was using were 80, 500, 3.8kHz)? I'm going to assume you intent was to leave crossover points the same? If I bump the woofer to 700Hz, distortion goes to 1% at 90dB?

TW = 0 ms (Ref Also inverted)
MR = -0.060 ms (Also reverse the polarity of this driver)
W = +0.800 ms
SW's = +0.000 ms

Left speaker (work of art):








Versus Left speaker original (not bad for first try  ):











jtalden said:


> Okay...
> I have finished the timing analysis. The following are the changes to the current delay settings in the Xilica. I chose the TW as the reference timing so its delay does not change.
> TW = 0 ms (Ref)
> MR = -0.060 ms (Also reverse the polarity of this driver)
> W = +0.800 ms
> SW's = +0.000 ms
> 
> The net SPL impact (a minor improvement around 3500 Hz) can be seen below:
> View attachment 135890
> 
> 
> The XO range SPL reinforcement is shown below:
> View attachment 135898
> 
> 
> The net impact on overall phase rotation is shown below:
> View attachment 135906
> 
> 
> The impact on the step response is shown below:
> View attachment 135914
> 
> 
> View attachment 135922
> 
> 
> The overall SPL is not significantly impacted. The phase rotation now follows a more conventional track and thus the step response also looks more conventional for a well timed 4 way system. The 250 Hz room effect is not addressed in these changes.


----------



## jtalden

Yes, XO points the same. I was just referring to the approximate acoustic XO freqs as shown on the driver and overall SPL chart. The effective acoustic XO points often differ from the electrical settings. I was just too lazy to look up the exact electrical settings again.

Reverse the polarity of the TW from the way it was when your measurements were made?? That should not have been necessary based on the data file you sent. The TW driver IR should look like the chart shown below. Are you sure you did not change the TW polarity after you posted that data file? Maybe I accidental inverted it during my initial setup manipulation of the IR locations. I did not go back that far when I double checked the timing changes. I will start from the original data and run through the entire process again tomorrow to triple check everything again.


----------



## etc6849

Strange. I also left original timings and offset them as you stated.

For example, I added .8ms to the woofer, subtracted from the existing MR setting, etc... If I don't invert the tweeter I get a nasty dip at 5khz. I think it sounds really good, no time to play with dirac tonight though. Really blends well and sounds like imaging is better.



jtalden said:


> Yes, XO points the same. I was just referring to the approximate acoustic XO freqs as shown on the driver and overall SPL chart. The effective acoustic XO points often differ from the electrical settings. I was just too lazy to look up the exact electrical settings again
> Reverse the polarity of the TW from the way it was when your measurements were made?? That should not have been necessary based on the data file you sent. The TW driver IR should look like the chart shown below. Are you sure you did not change the TW polarity after you posted that data file? Maybe I accidental inverted it during my initial setup manipulation of the IR locations. I did not go back that far when I double checked the timing changes. I will start from the original data and run through the entire process again tomorrow to triple check everything again.
> 
> View attachment 135978


----------



## jtalden

You followed the instructions correctly. I reviewed my work again and found no issue, but there is still a difference between our results.

Your measurement, the first chart in Post-41, does appear to be the correct relative polarity between the drivers. It is impossible to be sure how accurate the timing is just by casual inspection however. 

I did note that polarity of the TW in that chart is definitely Negative. It flattens out at -180°. That is reversed from convention and my intent. It does properly merge with the MR so that suggest it is reversed from my intent as well. Everything else also appears to also be reversed, so far as I can tell with a casual look. It's possible that reversing the polarity of all the drivers (SW's, W, MR, TW) will result in my intended target response.

[I also noted that the 2nd chart in Post-41 does not agree with the polarity relationship between the MR and TW of the file in Post-33 that I based my analysis on.] 

The best action now is to measure the left channel drivers individual again as done in Post-33 using your current delay settings (as per chart 1 in Post-41). This time also include the total left channel measurement (SW's+W+MR+TW). Be sure REW acoustic timing is activated. I can then confirm it matches the target (given that all polarities are reversed).


----------



## etc6849

I feel like I should know the answer to this, but could the factory speaker wiring be wired such that the woofer is opposite polarity of the MR and TW from the factory?

I did not take the drivers out, and just accessed the crossovers directly by removing the bottom of the speaker, trusting the factory +/- labeling on the crossover circuit boards along with the + markings on the wires themselves.

I am reading up on a way to verify polarity with 100% assurance, but I cannot easily remove the drivers to examine the voice coil or cone movement. I will verify with absolute assurance how things are wired before remeasuring.

I feel like this is the problem and why I had the big 5kHz dip before with the Ashly XR1001. I definitely did not change polarity on both channels or anything so I am very confused here. I suppose the Xilica XD4080 could have an issue where sometimes when it boots polarity is not set correctly? I do turn off the Xilica everynight (wish it had a 12V trigger).

Also, does it matter that the 500Hz and 3.8kHz are FIR crossovers, while the 80Hz crossover is a butterworth? I would assume not since REW is adding things together and this should be math a computer could do very accurately.

I did swing the mic out from the listening position to sit down on 2/5/2017 after taking the last set of driver measurements for you, but I swung it back last night after making your changes. It is definitely within an inch or two of where it was. If there was some room issue interfering with things, this could be the issue?

I like your idea of remeasuring everything. Seems like a reasonable and pragmatic way to proceed as phase looks noticeably better to me (but I'm no expert).

I have been taking the all measurements (including the driver measurements) at the MLP with the mic pointed upward. 

I also ordered some different amps to try (just for fun has nothing to do with what we are doing here). But since the gain structure will change a third time, I would like to wait until the new amps are installed. I will remove the XLR padding I added, but plan to match the levels from the previous file.



jtalden said:


> Your measurement, the first chart in Post-41, does appear to be the correct relative polarity between the drivers. It is impossible to be sure how accurate the timing is just by casual inspection however.


----------



## jtalden

etc6849 said:


> I feel like I should know the answer to this, but could the factory speaker wiring be wired such that the woofer is opposite polarity of the MR and TW from the factory?


Sure, the polarities are chosen to best blend the handoff between the drivers. Whether a driver is connected with a Positive or Negative polarity depends on the relative acoustic XO filter slopes and driver offset to the adjoining driver. 



> I did not take the drivers out, and just accessed the crossovers directly by removing the bottom of the speaker, trusting the factory +/- labeling on the crossover circuit boards along with the + markings on the wires themselves.


I would expect +/- labeling on the XO board and wires to be correct. 



> I am reading up on a way to verify polarity with 100% assurance, but I cannot easily remove the drivers to examine the voice coil or cone movement. I will verify with absolute assurance how things are wired before remeasuring.


The wired polarity really does not matter now. We chose the needed driver polarity as a result of the measurement analysis and reverses it when needed to get the best handoff. None of my recommendations were concerned with the absolute polarity, only if a driver needed to be reversed in order to achieve the best phase tracking. The exception to that is that is that the convention is to have the TW polarity in positive absolute polarity. That is shown by the phase trace leveling out relatively flat near 0° rather than near 180° near the top of its bandpass range. Reversing a driver polarity is dead simple now as the Xilica would allow that to be done by just checking a box; no concern as to how it was actually connected by wiring. 



> I feel like this is the problem and why I had the big 5kHz dip before with the Ashly XR1001. I definitely did not change polarity on both channels or anything so I am very confused here. I suppose the Xilica XD4080 could have an issue where sometimes when it boots polarity is not set correctly? I do turn off the Xilica everynight (wish it had a 12V trigger).


I'm confident the Xilica boots correctly each time. It would be an major issue if it didn't.



> Also, does it matter that the 500Hz and 3.8kHz are FIR crossovers, while the 80Hz crossover is a butterworth? I would assume not since REW is adding things together and this should be math a computer could do very accurately.


It only makes a difference if there is a change. If the Post-33 measurements were taken with the final XO settings then we would be okay. Any change to the XO settings for IIR slope, freq, or a change to FIR linear phase type will impact the analysis and thus possibly driver polarity and/or delay timing.



> I did swing the mic out from the listening position to sit down on 2/5/2017 after taking the last set of driver measurements for you, but I swung it back last night after making your changes. It is definitely within an inch or two of where it was. If there was some room issue interfering with things, this could be the issue?


Exact mic LP location is not a concern. The REW acoustic timing still provides an accurate relative phase relationship between the drivers. The room impact is trivial to this analysis.



> I like your idea of remeasuring everything. Seems like a reasonable and pragmatic way to proceed as phase looks noticeably better to me (but I'm no expert).


Good, I think that will resolve the situation. Hopefully the only recommended change will be to reverse the polarity of all drivers.



> I have been taking the all measurements (including the driver measurements) at the MLP with the mic pointed upward.


No problem. The phase is not impacted by mic orientation. It is the same at 180° and 0°



> I also ordered some different amps to try (just for fun has nothing to do with what we are doing here). But since the gain structure will change a third time, I would like to wait until the new amps are installed. I will remove the XLR padding I added, but plan to match the levels from the previous file.


I will wait for the new data. Just be sure save all the settings and make no changes to the setup after you post the new data.


----------



## etc6849

Yes, that is how I changed polarity last night was with the Xilica XConsole software. My worry was that you have used the left driver data, and I have measured right (or vice-versa), and one of drivers phase is reversed. I had included right and left driver measurements before though, I just looked at them and don't see any large phase deferences between left and right drivers.

The only thing that could be different in Xilica behavior between the two measurements is level being limited in one set of measurements and potentially impacting the results. I'm guessing the limit settings on the TW and MR could probably impact phase. I take the measurements outside the room, so if the limiter settings were too low, I would not know as I can't see the red lights on the front of the Xilica.

I am going to raise the limits just in case. It is confusing as 0dB limit in the software does not line up with the 0dB on the level setting (as far as I know since the red light doesn't come on on the front of the unit). 

I had to change the gains a lot when I added XLR pads (which I did all before doing the last driver measurements), but I overlooked raising the limits when I did that. To make matters worse, I also bumped incoming gain too as the Oppo HA-1 wasn't getting loud enough after adding pads and level matching the drivers. Beginning to think this is the issue and I have wasted a lot of your time regrettably.

Gains right now (will change a lot with new low wattage amps) are below. I only installed XLR pads on the weekend, but only on MR and TW drivers since the spare amps I had were huge (600W+ into ohms), and I wanted to eliminate the hiss caused by the Xilica. 

New amps (some used Benchmark AHB2 amps) have switchable gain for pro versus consumer gear, much quieter at lower wattage, less IMD, etc...

I think one level in REW was higher than the other, so the higher level must have hit the limiters target (or even the compressor on the incoming channel) and that's why we are seeing strange results?



jtalden said:


> The wired polarity really does not matter now. We chose the needed driver polarity as a result of the measurement analysis and reverses it when needed to get the best handoff. None of my recommendations were concerned with the absolute polarity, only if a driver needed to be reversed in order to achieve the best phase tracking. The exception to that is that is that the convention is to have the TW polarity in positive absolute polarity. That is shown by the phase trace leveling out relatively flat near 0° rather than near 180° near the top of its bandpass range. Reversing a driver polarity is dead simple now as the Xilica would allow that to be done by just checking a box; no concern as to how it was actually connected by wiring.


----------



## jtalden

As you noted the driver polarities in the right channel and left channel in the Post-33 data was identical. I initially confirmed that and also confirmed the mic was reasonably centered. [If the XO's settings in the Xilica was identical for left and right channel as it should be, then that confirms the drivers in both channels were wired identically.] 

In that file the SW's timing reference was the right channel per your labeling. I therefore chose the left channel for the analysis as the those drivers timing reference was also the right channel, thus a consistent time reference. The right channel drivers timing reference was the left channel. That means there could be a slight error for SW to W timing since the timing reference channel was different. 

Once one channel is timed correctly the other should use the identical timing. There is no need to repeat the analysis. If the mic was not exactly centered the only impact is that the effective LP is moved from the actual mic position to one that is exactly centered and either slightly forward or back from the actual mic distance. This is trivial impact from a practical perspective. Using only one channel also cut my data analysis time by 50%. 

Driver gain changes do not impact the driver to driver phase relationship. It will impact the apparent acoustic XO frequency as well as the SPL. This is no concern for driver timing analysis. Timing results will be unchanged. After timing is established the driver levels can still be changed if needed to best prepare for the EQ effort.

I saw no indication that limiting was a factor in the SPL chart, but it is always best to be sure. You are measuring at about 85 dB. We normally recommend 75 dB as good level for this type work. That would provide another 10 dB of headroom to your limiter setting to ease your concern. 

Low power and low sensitivity amps on the MR and TW drivers will help with hiss noise. The gain structure of rest of the system is also a major factor.


----------



## etc6849

Thanks for these detailed answers to my questions. I wish there was a step by step textbook on this that explained all the ins and outs. The best I've found on the internet are your posts. I think another beer is in order! Your response was very clear and well thought out. 

One last question that has been bothering me: how would one know if the timing was off by 360 degrees? If this were to occur, could you see phase alignment at the crossover, but having timing off?

I think the answer would be you look at each drivers unwrapped phase in REW and make sure they are in line with one another (this is possible since we are using an acoustic reference for timing)? If so, do you have to pick a common point to unwrap at (e.g. the crossover point between two drivers)?



jtalden said:


> As you noted the driver polarities in the right channel and left channel in the Post-33 data was identical. I initially confirmed that and also confirmed the mic was reasonably centered. [If the XO's settings in the Xilica was identical for left and right channel as it should be, then that confirms the drivers in both channels were wired identically.]
> 
> In that file the SW's timing reference was the right channel per your labeling. I therefore chose the left channel for the analysis as the those drivers timing reference was also the right channel, thus a consistent time reference. The right channel drivers timing reference was the left channel. That means there could be a slight error for SW to W timing since the timing reference channel was different.
> 
> Once one channel is timed correctly the other should use the identical timing. There is no need to repeat the analysis. If the mic was not exactly centered the only impact is that the effective LP is moved from the actual mic position to one that is exactly centered and either slightly forward or back from the actual mic distance. This is trivial impact from a practical perspective. Using only one channel also cut my data analysis time by 50%.
> 
> Driver gain changes do not impact the driver to driver phase relationship. It will impact the apparent acoustic XO frequency as well as the SPL. This is no concern for driver timing analysis. Timing results will be unchanged. After timing is established the driver levels can still be changed if needed to best prepare for the EQ effort.
> 
> I saw no indication that limiting was a factor in the SPL chart, but it is always best to be sure. You are measuring at about 85 dB. We normally recommend 75 dB as good level for this type work. That would provide another 10 dB of headroom to your limiter setting to ease your concern.
> 
> Low power and low sensitivity amps on the MR and TW drivers will help with hiss noise. The gain structure of rest of the system is also a major factor.


----------



## jtalden

Thanks!!



etc6849 said:


> I wish there was a step by step textbook on this that explained all the ins and outs.


A detailed example of the overall process is long and complicated and there are numerous paths. Even stepping through a detailed example of my preferred method is more than I want to at this time. Maybe I will do that sometime. The practical value of tuning to this level is probably more in the charts than the actual sound quality benefits. There are probably not too many DIY'ers that want to spend excessive time fine tuning the system rather than listening to it.



> One last question that has been bothering me: how would one know if the timing was off by 360 degrees? If this were to occur, could you see phase alignment at the crossover, but having timing off?
> 
> I think the answer would be you look at each drivers unwrapped phase in REW and make sure they are in line with one another (this is possible since we are using an acoustic reference for timing)? If so, do you have to pick a common point to unwrap at (e.g. the crossover point between two drivers)?


It is clear your efforts have been pretty effective so you are getting your own method pinned down. I think the difference on one XO we discussed was probably a simple confusion as to the settings that were active at the time of the measurement. Possibly the wrong file was posted. 

Below are some short thoughts to your questions in case it helps. If you need more clarification, let me know.

1. I avoid using unwrapped phase as I found it easy to get confused due to room modes and strong reflections. Your heavily treated room provides relatively clean phase trace so... Possibly others have good results using unwrapped phase. I just found it problematic for most all work. I haven't really tried it with FDW now available as I am comfortable using wrapped phase charts.

2. Regarding IIR XO filters:
> The initial rise of the 2 Impulses should initially be set to the same time (initial rise, not the peaks). [They also need to be near 0 ms for their phase to be easily read, but only their relative positions are important in to how they actually complement each other.] From there, the minimum offset that provides a crossing at the acoustic XO frequency and the closest phase tracking is the best solution. That solution assures the same arrival time of the XO frequency from both drivers. Moving relative timing further away in either direction from that solution we can find other crossing points that represent the arrival of the sound from the 2 drivers being 1, 2, 3,... cycles delayed from each other. If we invert one Impulse we find other solutions at 1/2, 1-1/2, 2-1/2,... cycles away. Again the closest phase tracking represents the closest timing across the XO range.
> If the 2 *acoustic* filter slopes ideally follow a low-pass/high-pass LR24 XO shape then phase will track directly on top of each other. The same is true for other complementary filter shapes. To the extent that the 2 acoustic XO filters deviates from being complimentary the best solution involves a phase crossing at the XO frequency and the one and shows the minimum diversion above and below the XO point.

3. Regarding FIR linear phase filters:
> If ideal FIR XO's were implemented then the resulting large positive impulse peaks would be aligned at the same time.
> You applied FIR filters to the upper 2 XOs. Note that Post-33 shows a very shallow slope on the HPF of the 770 Hz SO (acoustic XO). There is significant overlap the W to MR as a result. I don't know if this was a limitation of the taps available or ??. It didn't appear to me that this XO was done following the normal best practices for linear phase XO filters. As a result, I see this as a mixed phase XO and a somewhat less attractive option than just targeting an LR-48 IIR response. Regardless, once the XO filters are chosen and in place, there is still one best solution for delay timing and that is what was recommended above.


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## etc6849

Yes, this is a limitation on the number of taps and how they are assigned. So it is beneficial to use LR-48 for LF HP and LF-MR XO both? 

Or would it be worth while to do LF HP as LR-48dB and spread the available taps out between TW and MR channels (this is how the FIR slope is controlled, the Xilica automatically determines the slope after you assign taps to each channel pair). In this scenario, I'd assign most taps to MR so low pass FIR slope closely matched Linkwitz Riley 48dB/octave and use the remaining taps for the TW channels (e.g. left MR/right MR is a channel pair of channels 3&4, channels 5&6 and TWs, etc...). Otherwise, I am essentially wasting taps unless you think I should do a brick wall for MR & TW crossover?



jtalden said:


> 3. Regarding FIR linear phase filters:
> > If ideal FIR XO's were implemented then the resulting large positive impulse peaks would be aligned at the same time.
> > You applied FIR filters to the upper 2 XOs. Note that Post-33 shows a very shallow slope on the HPF of the 770 Hz SO (acoustic XO). There is significant overlap the W to MR as a result. I don't know if this was a limitation of the taps available or ??. It didn't appear to me that this XO was done following the normal best practices for linear phase XO filters. As a result, I see this as a mixed phase XO and a somewhat less attractive option than just targeting an LR-48 IIR response. Regardless, once the XO filters are chosen and in place, there is still one best solution for delay timing and that is what was recommended above.


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## jtalden

I mislead you with that comment. No XO changes are necessary. I only meant that the *acoustic* W/MR XO looked a little less than optimized in how smooth and symmetrical it is. It's not a classic LR24 or LR48. It's common to spend much more time optimizing the acoustic XO than setting the delay timing. The attached chart shows the acoustic XO's for the Post-33 data.

I have limited expertise and no experience setting up linear phase XO's. For guidance there, I urge you read the available how-to guides. I think MiniDSP.com has some guidance and the rePhase thread on diyAudio forum is comprehensive and it contains other authoritative links as well.

I was mostly intending to point out that the roll-off slopes of W/MR linear phase XO is not very conventional. I also suggested that there was extended overlap of the MR in the W-MR XO. On reviewing that thought again, I now see the initial drop of the MR is about 10 dB and very steep. It then levels out significantly before falling normally. I was hinting that some attention to the XO settings may be worthwhile and I speculated the possibly a simple LR24 minimum phase XO there may be an improvement from the current settings. It is possibly not as significant as I was originally thinking. 

The points are:
> The XO design can be optimized as well.
> With proper XO design either minimum phase or linear phase XO's can provide similar results.
> Once you have designed and applied the XO scheme there is a best timing setting for the drivers. 
> Given Post-33 as the XO settings then the delays suggested previously provide very good phase tracking through the XO ranges. There is no significant improvement available in that regard.

Leave the current XO settings, improve the FIR XO setting, or try IIR XO settings to try to achieve a more idealized acoustic XO target if you like. 
Whatever choice you make, I can then help confirm the delay settings you choose.


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## etc6849

Ended up saving taps by using 48dB/Octave butterworth for all filters except MF to HF at 3.8kHz.

Left driver measurements (taken tonight 2/15/2017): NEW LINK: https://drive.google.com/open?id=0B1J0a4OV_WGLczRRc0VYU091czQ

Also dated the file this time as I was confused. I ended up moving my room around many times, but never could avoid the 248Hz issue, so I moved subs and main speakers to maximize imaging, screen and seating. I also lowered my shelves I made so I can fit my center speaker and also see my entire screen.

Here are the time delays (note I left 16ms of padding in case it is needed later when offsetting the delay to match your settings).

Sorry it took so long. I took my room all apart to fit a floor model couch, but found I couldn't fit the couch into my door due to the hallway 



jtalden said:


> I mislead you with that comment. No XO changes are necessary. I only meant that the *acoustic* W/MR XO looked a little less than optimized in how smooth and symmetrical it is. It's not a classic LR24 or LR48. It's common to spend much more time optimizing the acoustic XO than setting the delay timing. The attached chart shows the acoustic XO's for the Post-33 data.


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## jtalden

The best timing solution is as follows:
1. Reverse the current polarity of both the Subs and the LF Drivers
2. Delay changes from the current settings:

TW = 0.00 ms (ref)
MR = +0.07 ms
LF = +0.90 ms
Subs = +1.80 ms
*Data*
> Acoustic XO's:

MR-TW XO (~3400-4250 Hz):
LF-MR XO (~300-1200 Hz): 
Sub-LF XO (~40-160 Hz): 
> Final Charts:


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## etc6849

How does this one look for MR and TW? I ended up inverting TW and MR (incidentally this polarity means TW and MR polarity will NOT be inverted in the Xilica settings). Then I set TW impulse peak to 0ms (and set IR window delay to 0 for TW verifying wrapped TW phase was mostly horizontal) and modified MR as shown (without changing IR window delay for MR).

After that I compared TW and MR impulses to the originals measured in my previous post from last night.



jtalden said:


> With proper XO design either minimum phase or linear phase XO's can provide similar results.


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## etc6849

Just saw this as I was posting my independent test from this morning. Looks like since in mine I had "Inverted TW and MR. Add MR delay of +213us. Decrease TW delay by -146us" that I might be getting this as the different here would be MR +67us or ~70us = .07ms! How about that; I think I finally got the same optimized result on you.

I suspect if I were to continue with MR and LF I would see the need to re-invert MR and TW? I have no idea how you did this so fast!?! I spend two hours this morning just getting the relative offset for TW and MR.

EDIT: I can see how inverting MR and TW like I did doesn't give as constant of a phase slope one octave below 3.8kHz. I still like yours better. It is a work of art!



jtalden said:


> The best timing solution is as follows:
> 1. Reverse the current polarity of both the Subs and the LF Drivers
> 2. Delay changes from the current settings:
> 
> TW = 0.00 ms (ref)
> MR = +0.07 ms
> LF = +0.90 ms
> Subs = +1.80 ms


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## jtalden

We both found the same relative delay and polarity needed for MR-TW XO. Well done! Since all driver polarities are reversed between us, we both have found the same relative driver to driver solution (this assume the delays for the other 2 XO's are also the same). Only the overall polarity of the total system is reversed and there is of no practical consequence to sound quality as to which overall polarity settings you decide use.


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## etc6849

Looks great. Only a small dip in phase around 3.8kHz that wasn't predicted. I think the small dip might be due to the Xilica rounding to the nearest centimeter when I enter the values.

I did end up swapping TW and MR to normal polarity (had them reversed in the Xilica from before), which if I understand correctly had the same impact as swapping Sub and LF polarity.

If this looks good, I'm going to subtract 18ms from each delay and run dirac.

Thanks again!




jtalden said:


> We both found the same relative delay and polarity needed for MR-TW XO. Well done! Since all driver polarities are reversed between us, we both have found the same relative driver to driver solution (this assume the delays for the other 2 XO's are also the same). Only the overall polarity of the total system is reversed and there is of no practical consequence to sound quality as to which overall polarity settings you decide use.


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## etc6849

Here it is with a small additional delay of .032ms added to the TW (so as to not impact the MR-LF crossover.


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## jtalden

Looks Good!


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## etc6849

Thanks! Dirac did an awesome job last night. You had the LF drivers and subs spot on. I know people say you can't hear differences in phase, but it would seem that my ears like phase coherence very much. Tri-amping has taken my system to a new level thanks to you.

One thing I did different this time is I plugged my front speaker's ports with socks prior to providing the driver measurements you used. Really the best my system has ever sounded, thanks so much!

I also quit doing a one point Dirac calibration as things sound better with 9 points for a one chair calibration. https://drive.google.com/open?id=0B1J0a4OV_WGLMFI5NmZ0eTZ0TGs



jtalden said:


> Looks Good!


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## jtalden

The DL SPLs look great.

Just be aware that the needed Subs delay will be significantly different with the LF driver ports plugged The Subs polarity may also need to be reversed to achieve the best phase tracking. The delays of the other drivers will be unchanged.


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## etc6849

You already aligned the left LF driver with the plugged ports (plugged them on 2/13/2017 prior to taking the 2/15 driver measurements), I just forgot to tell you what I did 



jtalden said:


> The DL SPLs look great.
> 
> Just be aware that the needed Subs delay will be significantly different with the LF driver ports plugged The Subs polarity may also need to be reversed to achieve the best phase tracking. The delays of the other drivers will be unchanged.


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## jtalden

Enjoy the music!


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