Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 610 - AVS Forum | Home Theater Discussions And Reviews
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Old 03-28-2016, 03:22 PM
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Originally Posted by markus767 View Post
Works for me. Add 2ms to 10 then add 1 and 10 and you'll get the same response as 14.
Yes, you are indeed correct. If have noticed an anomaly in the Controls panel for the Impulse measurement screen. Initially, the panel looks like this:



Note that the "T=0 offset (Distance)" is expressed in inches. Thinking that adding 24 inches to the offset is the same as adding 2ms, I entered 24 in the box and clicked apply. Now look at the panel:



It has applied 24 foot offset, not a 24 inch offset. Not sure why it would switch from inches to feet, but I didn't catch this in the first go-around, which is why I couldn't get the results to match up. Do you consider this a reportable bug, or am I just doing it wrong?

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Old 03-28-2016, 03:37 PM
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Originally Posted by 3ll3d00d View Post
Attachment 1344682

obviously they sum nicely as they are so this is probably a curiosity but it might be interesting to see (hear) what happens if you were to reverse the front pair and then ran through the whole shebang from scratch. Mind you if you were to do that then might as well take MSO for a spin and see what that comes up with. Alternatively just kick back
Very interesting. And the scientific part of my brain wants to go through this exercise. And, of course, there is that little voice that says, "Leave well enough alone, Jerry".

By the "whole shebang", I suspect you mean these steps:

1. Using either the on-sub polarity switch, or the software switch in the 2x4, reverse polarity for two front subs (either approach preferred?) Run REW sub measurements (Dirac in bypass) to observe phase relationships.
2. Generate combined response for all four subs and check the test tone level for the Dirac calibration. I suspect the level will have changed.
3. Assuming the combined sub response needs to be adjusted, re-do the gain-matching until the sub output is once again in-line for Dirac.
4. Run a fresh Dirac Live calibration.
5. Run the REW measurements again to observe results (especially the group delay with minimum phase).
6. Pick the configuration that produces the best results.
7. Post results here for others to observe and opine.

Did I forget any important steps? Sounds like another full-day project in the works...


Edit: BTW, I seem to recall consistently getting an "out of phase" warning for the sub channel when running Audyssey XT32, which saw the front and rear pairs independently. Since the wiring was correct, and the polarity switches were in the correct positions, I simply ignored the warning and was pleased with the results. This was before I ever looked at a Group Delay or Minimum Phase plot, or even knew what they were used for.
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Old 03-28-2016, 04:02 PM
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Where's the <popcorn> emoji when you need it!

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Old 03-28-2016, 08:05 PM
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I would like to thank AustinJerry for the guides that he has produced for REW and MiniDSP as they have helped me greatly in my recent journey.

Like others who have posted here, I have struggled with the IR stuff, so I greatly appreciate AustinJerry taking the time to also document this and also the others who are working with him demystify this.

I have also had a quick look at MSO, however my efforts failed. When revisiting AndyC's site, I re-read (yes I did read it at the beginning, but did not comprehend the specific issue I am about to comment on) the section on issues with HDMI. If I have understood it correctly, it seems that at times there can be issues arise with a measurement and this is evidenced by a sound being emitted by the timing reference speaker after the measurement. I have encountered this on a number of occasions. Based on AndyC's comments, any such measurements should be binned and re-done. I suspect that this may be the cause of my poor MSO results and will revisit this when I get a chance.

I have raised this issue here, as if I have understood it correctly, it is a point that we all need to be aware of and would be prudent to include comment in any guide that is being developed.
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Old 03-28-2016, 09:25 PM
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Originally Posted by mR_Mo View Post
Should I try and add about 10 ms to the subs? Is that correct?
1. Take a REW measurement of the center without the sub with bass management and Dirac on (call this measurement 1) Note: all measurements should include a timing reference.
2. Take a measurement of the combined sub signal with center off (call this measurement 2)
3. Take a measurement of center+subs with bass management and Dirac on (call this measurement 3)
4. Open measurement 2 in the Impulse tab, open the Controls panel, and add 10ms and click Apply.
5. Open the All SPL tab.
6. In the Controls panel, in the Trace Arithmetic section, define A=measurement 1, and B=measurement 2.
7. Open the drop-down and select A+B and click Generate. You now have a new measurement on the display which represents center+subs with the 10ms adjustment applied.
8. Click on measurement 3 so it is displayed along with the A+B measurement.
9. Compare measurement 3 with A+B. Does A+B show improvement? If yes, experiment with other offsets (e.g. 9ms or 11ms), following the same procedure.
10. Stick with the offset that provides the best result.

This is a rough draft of what will be added to the REW Guide, subject to feedback, of course. The Guide update will contain screen shots as examples of each step, of course.

I'm very close to my "Ah hah!" moment....
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Old 03-28-2016, 09:29 PM
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Originally Posted by mcb61 View Post
I would like to thank AustinJerry for the guides that he has produced for REW and MiniDSP as they have helped me greatly in my recent journey.

Like others who have posted here, I have struggled with the IR stuff, so I greatly appreciate AustinJerry taking the time to also document this and also the others who are working with him demystify this.

I have also had a quick look at MSO, however my efforts failed. When revisiting AndyC's site, I re-read (yes I did read it at the beginning, but did not comprehend the specific issue I am about to comment on) the section on issues with HDMI. If I have understood it correctly, it seems that at times there can be issues arise with a measurement and this is evidenced by a sound being emitted by the timing reference speaker after the measurement. I have encountered this on a number of occasions. Based on AndyC's comments, any such measurements should be binned and re-done. I suspect that this may be the cause of my poor MSO results and will revisit this when I get a chance.

I have raised this issue here, as if I have understood it correctly, it is a point that we all need to be aware of and would be prudent to include comment in any guide that is being developed.
Thank you for the kind words. I have not experienced the issue you have described, but I'll be on the lookout. I too need to go back and re-read AndyC's MSO thread. I think I will be closer to being able to follow it this time.
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Old 03-28-2016, 11:03 PM
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Originally Posted by AustinJerry View Post
Very interesting. And the scientific part of my brain wants to go through this exercise. And, of course, there is that little voice that says, "Leave well enough alone, Jerry".

By the "whole shebang", I suspect you mean these steps:

1. Using either the on-sub polarity switch, or the software switch in the 2x4, reverse polarity for two front subs (either approach preferred?) Run REW sub measurements (Dirac in bypass) to observe phase relationships.
2. Generate combined response for all four subs and check the test tone level for the Dirac calibration. I suspect the level will have changed.
3. Assuming the combined sub response needs to be adjusted, re-do the gain-matching until the sub output is once again in-line for Dirac.
4. Run a fresh Dirac Live calibration.
5. Run the REW measurements again to observe results (especially the group delay with minimum phase).
6. Pick the configuration that produces the best results.
7. Post results here for others to observe and opine.

Did I forget any important steps? Sounds like another full-day project in the works...


Edit: BTW, I seem to recall consistently getting an "out of phase" warning for the sub channel when running Audyssey XT32, which saw the front and rear pairs independently. Since the wiring was correct, and the polarity switches were in the correct positions, I simply ignored the warning and was pleased with the results. This was before I ever looked at a Group Delay or Minimum Phase plot, or even knew what they were used for.
Sounds reasonable. I don't think it matters which way you reverse polarity. As to the method, i would go measure each sub with no dirac but with BM observing the ir and phase alignment. Compare to your existing graphs for reference. I don't see why the gain would need to change but no harm checking. I would then move onto dirac.

FWIW In my example i shifted the distance for the subs to align the initial rise of the impulse to the peak of the main channels. Of course dirac may move this again so there might be some iteration involved and you might need to accept Dirac's position on this rather than your own as you might end up fighting with it.
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Old 03-29-2016, 01:27 AM
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Originally Posted by AustinJerry View Post
Thank you for the kind words. I have not experienced the issue you have described, but I'll be on the lookout. I too need to go back and re-read AndyC's MSO thread. I think I will be closer to being able to follow it this time.
A quick clarfication re the HDMI issue. The comments are located at http://andyc.diy-audio-engineering.o...ring.html#hdmi, last paragraph, rather than the MSO thread.
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Old 03-29-2016, 03:17 AM
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Originally Posted by andyc56 View Post
I don't mean to be a killjoy, but when looking at the excess group delay plots, a low-frequency plateau at an elevated level from the high-frequency excess group delay may indicate a time alignment issue, but it does not necessarily indicate that.

For example, take a 4th-order Linkwitz-Riley crossover connected to perfect and time-aligned low- and high-frequency drivers. The frequency response of a perfect acoustic summation of the low-pass and high-pass outputs will be a second-order all-pass filter. An all-pass filter has a flat magnitude response, but a phase response that varies with frequency. Since its magnitude response is constant over all frequency, its minimum-phase group delay is zero. Therefore, its group delay and excess group delay are one and the same.

Here is a plot of the excess group delay of such an all-pass filter that results from a 4th-order Linkwitz-Riley crossover at 80 Hz. It has a low-frequency plateau of about 5.6 msec, which could lead one to believe that the sub is 6.3 feet behind the main speakers, but this is not true. It's the classic group delay response of the combined outputs of a 4th-order Linkwitz-Riley crossover at 80 Hz with time-aligned drivers.

[...]
True but the amount of time delay through the filter still is not constant for all frequencies. So if we can reduce such delay while maintaining a good frequency response then why not do it?

For anybody trying to get his head around this, here's a good read: http://www.linkwitzlab.com/frontiers.htm#F
And of course the crossover primer by Rane: http://www.rane.com/pdf/ranenotes/Li...ers_Primer.pdf

Markus

"In science, contrary evidence causes one to question a theory. In religion, contrary evidence causes one to question the evidence." - Floyd Toole

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Old 03-29-2016, 05:36 AM
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I am getting ready for my "the whole shebang" project this morning. I think that there will be a key decision point, at which I will be able to assess whether changing the front sub polarity shows promise.

I will start by setting Dirac to bypass and running REW measurements of the uncorrected sub responses. I will then reverse polarity on the front subs and take the same set of uncorrected response measurements. I am thinking that this will provide an early indication as to whether proceeding will be worthwhile, and provides an easy fall-back position to get things back to exactly how they were with a minimum of effort.

Expect a progress report soon.
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Old 03-29-2016, 06:18 AM
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Newbe on the REW software and measurements.

This measurement is done with the setup i have at the moment. I guess i have to place some basstraps.

Measured on 80dB on a 7.2 setup on all channels.
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Old 03-29-2016, 06:53 AM
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Originally Posted by wackid View Post
Newbe on the REW software and measurements.

This measurement is done with the setup i have at the moment. I guess i have to place some basstraps.

Measured on 80dB on a 7.2 setup on all channels.
If you want some feedback, we need more information:

- Are you using room correction?
- What make/model AVR and sub(s)?
- How many subs?
- What are the room dimensions?
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Old 03-29-2016, 06:59 AM
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Originally Posted by AustinJerry View Post
If you want some feedback, we need more information:

- Are you using room correction?
- What make/model AVR and sub(s)?
- How many subs?
- What are the room dimensions?
Okay that sounds logic.

It's an Onkyo tx-nr709
With a KEF Htb2 and a Klipsch SW115R subwoofer.
I has the Audessey XT calibration.

My room dimensions are 4.5 meter (15ft)by 7 meter (22ft).

It's an L space house the MLP is not enclosed in two walls. Just one.
But the speakers are in the dimensions I gave.
It looks like I have a lot of "echo" in the waterfall. But the thing is. It doesn't real sound like a bathroom or something.

Last edited by wackid; 03-29-2016 at 07:05 AM.
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Old 03-29-2016, 08:01 AM
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Originally Posted by wackid View Post
Okay that sounds logic.

It's an Onkyo tx-nr709
With a KEF Htb2 and a Klipsch SW115R subwoofer.
I has the Audessey XT calibration.

My room dimensions are 4.5 meter (15ft)by 7 meter (22ft).

It's an L space house the MLP is not enclosed in two walls. Just one.
But the speakers are in the dimensions I gave.
It looks like I have a lot of "echo" in the waterfall. But the thing is. It doesn't real sound like a bathroom or something.
You have several areas for improvement. The frequency response has some 20dB swings, which are pretty severe. The waterfall demonstrates pretty bad bass ringing (areas where ridges start at the top and extend all the way to the bottom). The two issues are somewhat related. You are at the beginning of a lengthy journey for improvement, if that is your objective. It is the same journey that most of us have travelled, so you are not alone. Milestones along the road are:

- Experimenting to find the best spot for the sub, based on REW measurements.
- Adding additional subs (critical--one sub just can't do a very good job).
- Considering upgrading to an Audyssey XT32 AVR, which has better bass correction technology (meaning a move away from Onkyo, since Onkyo has dropped Audyssey)
- Adding bass traps in the right spots.

I have listed the recommendations in order of priority (IMO).
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Old 03-29-2016, 08:23 AM
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Originally Posted by AustinJerry View Post
You have several areas for improvement. The frequency response has some 20dB swings, which are pretty severe. The waterfall demonstrates pretty bad bass ringing (areas where ridges start at the top and extend all the way to the bottom). The two issues are somewhat related. You are at the beginning of a lengthy journey for improvement, if that is your objective. It is the same journey that most of us have travelled, so you are not alone. Milestones along the road are:

- Experimenting to find the best spot for the sub, based on REW measurements.
- Adding additional subs (critical--one sub just can't do a very good job).
- Considering upgrading to an Audyssey XT32 AVR, which has better bass correction technology (meaning a move away from Onkyo, since Onkyo has dropped Audyssey)
- Adding bass traps in the right spots.

I have listed the recommendations in order of priority (IMO).
Thanks for the detailed advice.
So you don't think I have to start immediately with acoustics treatments, like basstraps and so on?

What the receiver concerns. I have set my mind on the new Onkyo RZ3100. Yes also without Audyssey.
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Old 03-29-2016, 08:34 AM
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Originally Posted by wackid View Post
What the receiver concerns. I have set my mind on the new Onkyo RZ3100. Yes also without Audyssey.
Any AVR without proper EQ capabilities is a waste of money.

Markus

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Old 03-29-2016, 09:06 AM
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OK, I have finished the first stage of the "whole shebang" project and am at a decision point, seeking input. The measurements posted below were taken with Dirac in bypass and with bass management on.

First, a comparison of the impulse responses:

Compare front and rear sub pairs normal polarity, Dirac on (from Matt's post yesterday)



Compare front and rear sub pairs normal polarity, Dirac in bypass (some difference, but still clearly displaying a polarity issue, so Dirac is not the cause):



Now, Compare front and rear sub pairs with front pair reversed polarity (not sure why the screen shot is smaller) Notice that the impulse response matches now (as expected).



And finally, compare Center+all four subs, normal polarity vs. two front subs with reversed polarity. Clearly not improved!



However, on the good news front, the non-minimum phase shown at 125Hz when the front subs have normal polarity has completely disappeared when the polarity is reversed.




I need to decide now whether to proceed with a fresh Dirac calibration to see how Dirac handles a 15dB dip at 41Hz. On a side note, the combined sub level as measured in DLCT is now 3dB higher (measuring at -9 on the test tone level scale, as opposed to the target level of -12). I prefer not to re-adjust the subs' gain matching, because that would make reverting to the previous calibration much more difficult.

So, the opinion I am asking for is:

A. Proceed with the Dirac calibration, leaving sub levels 3dB high, or
B. Abandon the exercise, because things look worse with the polarity reversed.
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Old 03-29-2016, 09:09 AM
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Originally Posted by wackid View Post
Thanks for the detailed advice.
So you don't think I have to start immediately with acoustics treatments, like basstraps and so on?

What the receiver concerns. I have set my mind on the new Onkyo RZ3100. Yes also without Audyssey.
+1 on Markus' comment. Bad choice for new AVR. Onkyo has abandoned Audyssey to save money, leaving you as the consumer in a much worse place. Move on. Or consider replacing Audyssey with Dirac Live using the MiniDSP 88A (~$1,000) and keeping your present AVR.

And my original order of importance still stands.
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Old 03-29-2016, 09:20 AM
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Originally Posted by markus767 View Post
True but the amount of time delay through the filter still is not constant for all frequencies. So if we can reduce such delay while maintaining a good frequency response then why not do it?
The key word here is "if". The point I was making was that equalizing the delays of mains and subs according to the excess group delay plot may work, but will not necessarily work, and may make things worse. I got the impression (maybe wrongly) that Jerry was thinking of writing up a procedure to do just this. So far, Jerry's procedures have been such that you can perform them and almost certainly get the desired result if the procedure is performed correctly. But a delay equalization procedure such as this has no such guarantee. If people performed this procedure and didn't get the desired result, it could cause a lot of confusion and extra work. Maybe it's best to say that you can give this technique a try, but there are no guarantees.
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Old 03-29-2016, 09:29 AM
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@3ll3d00d , @markus767

Where are my advisors?

So, the opinion I am asking for is:

A. Proceed with the Dirac calibration, leaving sub levels 3dB high, or
B. Abandon the exercise, because things look worse with the polarity reversed.
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Old 03-29-2016, 10:08 AM
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Originally Posted by andyc56 View Post
The key word here is "if". The point I was making was that equalizing the delays of mains and subs according to the excess group delay plot may work, but will not necessarily work, and may make things worse. I got the impression (maybe wrongly) that Jerry was thinking of writing up a procedure to do just this. So far, Jerry's procedures have been such that you can perform them and almost certainly get the desired result if the procedure is performed correctly. But a delay equalization procedure such as this has no such guarantee. If people performed this procedure and didn't get the desired result, it could cause a lot of confusion and extra work. Maybe it's best to say that you can give this technique a try, but there are no guarantees.
I agree.

Markus

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Old 03-29-2016, 10:14 AM
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Originally Posted by AustinJerry View Post
@3ll3d00d , @markus767

Where are my advisors?

So, the opinion I am asking for is:

A. Proceed with the Dirac calibration, leaving sub levels 3dB high, or
B. Abandon the exercise, because things look worse with the polarity reversed.
Are you asking for permission? You don't need to

Markus

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Old 03-29-2016, 10:33 AM
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I went ahead and ran a fresh Dirac calibration. Results:





To me, the blue lines look better, so I will be sticking with my original configuration, without reversing the front sub polarity.

Looks like this exercise is completed, and I can take that well-deserved nap now.
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Old 03-29-2016, 10:59 AM
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Originally Posted by AustinJerry View Post
And finally, compare Center+all four subs, normal polarity vs. two front subs with reversed polarity. Clearly not improved!


FWIW my suggestion was to setup the 4 subs from scratch, with polarity corrected, and then run dirac on top. I didn't mean to just switch polarity. Anyway you're napping now :P so when you awake, can you post the mdat of the measurements?
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Old 03-29-2016, 11:06 AM
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Originally Posted by 3ll3d00d View Post
FWIW my suggestion was to setup the 4 subs from scratch, with polarity corrected, and then run dirac on top. I didn't mean to just switch polarity. Anyway you're napping now :P so when you awake, can you post the mdat of the measurements?
Can you clarify what you mean by setting up all four subs from scratch? I changed polarity and re-ran Dirac.

Are you suggesting I move the subs around to find better placement as well? Other than placing the subs in their spots and adjusting the gain control for the target output, what else is there to alter? Do you want the MDAT of the final measurements with the new Dirac calibration, or the measurements at the beginning of the exercise with Dirac in bypass?
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Old 03-29-2016, 11:10 AM
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The key word here is "if". The point I was making was that equalizing the delays of mains and subs according to the excess group delay plot may work, but will not necessarily work, and may make things worse. I got the impression (maybe wrongly) that Jerry was thinking of writing up a procedure to do just this. So far, Jerry's procedures have been such that you can perform them and almost certainly get the desired result if the procedure is performed correctly. But a delay equalization procedure such as this has no such guarantee. If people performed this procedure and didn't get the desired result, it could cause a lot of confusion and extra work. Maybe it's best to say that you can give this technique a try, but there are no guarantees.
Based on my experiences so far, whatever I write up will be along the lines of "Here is how to do it. Whether it produces the desired results may vary. Make sure to check the results."

So far, I have encountered few silver bullets when it comes to audio configuration.
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Old 03-29-2016, 11:46 AM
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Can you clarify what you mean by setting up all four subs from scratch? I changed polarity and re-ran Dirac.

Are you suggesting I move the subs around to find better placement as well? Other than placing the subs in their spots and adjusting the gain control for the target output, what else is there to alter?
There are thousands of different settings (level, delay, EQ) that could be tested without even relocating speakers or listener. The only practical way to do this is to have a software that can play through all those possible options. That's exactly what Andy's MSO does.

@andyc56 Haven't played with MSO in a while, is it possible to optimize for lowest point to point variance within the listening area?

Markus

"In science, contrary evidence causes one to question a theory. In religion, contrary evidence causes one to question the evidence." - Floyd Toole
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Old 03-29-2016, 12:04 PM
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I too need to go back and re-read AndyC's MSO thread. I think I will be closer to being able to follow it this time.
Oh great...more additions to the guide!
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Old 03-29-2016, 12:15 PM
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@andyc56 Haven't played with MSO in a while, is it possible to optimize for lowest point to point variance within the listening area?
I deliberately did not put that feature in because I am worried about patent infringement with SFM. We spoke about that a while back here.
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Old 03-29-2016, 01:22 PM
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I deliberately did not put that feature in because I am worried about patent infringement with SFM. We spoke about that a while back here.
Have you ever thought about extending MSO so one could capture responses directly in MSO? It could run on miniDSP hardware similar to DLCT. Finally enthusiast would be able to get the most out of their systems. It's really the missing piece to proper speaker/room integration.

Markus

"In science, contrary evidence causes one to question a theory. In religion, contrary evidence causes one to question the evidence." - Floyd Toole
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