Optimizing subwoofers and integration with mains: multi sub optimizer - Page 21 - AVS Forum | Home Theater Discussions And Reviews
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post #601 of 777 Old 05-28-2017, 07:34 PM
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Was the diagram you included suggesting that I have a sub on the floor, some kind of spacer and then another next to the ceiling? I could certainly do that in the front - with the help of some of my strong friends. I will ask Mark about that.
Yep, exactly. In fact, I may try it myself.
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post #602 of 777 Old 05-28-2017, 11:31 PM
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Don't fall for "concepts" that look "cool". You can't cheat physics. Everything depends on source location and listener location. Stacking subs isn't per se a good idea (other than the manufacturer making more money). In fact it's a pretty bad idea to cluster all sources around a single location.

DBA can work tremendously well. It provides active absorption that can't be had even with a ton of room treatments. The next best approach is MSO. But, you need to be willing to learn, do a lot of measurements and do them in a methodical manner.

In order to get a basic understanding of the different approaches play around with the "Room Sim" in REW. Attached are a couple of often recommended configurations and DBA.
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post #603 of 777 Old 05-29-2017, 05:32 AM
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Originally Posted by markus767 View Post
Don't fall for "concepts" that look "cool". You can't cheat physics. Everything depends on source location and listener location. Stacking subs isn't per se a good idea (other than the manufacturer making more money). In fact it's a pretty bad idea to cluster all sources around a single location.

DBA can work tremendously well. It provides active absorption that can't be had even with a ton of room treatments. The next best approach is MSO. But, you need to be willing to learn, do a lot of measurements and do them in a methodical manner.

In order to get a basic understanding of the different approaches play around with the "Room Sim" in REW. Attached are a couple of often recommended configurations and DBA.
Let me see if I have this correct: So IF Mark Seaton (sub designer) said it made sense acoustically (he has yet to say that that I am aware of) and BossoBass (sub designer) said it makes sense acoustically (I did read the BossoBass articles) then they are wrong and you are right.

And NEITHER said to cluster ALL sources around a single location. Maybe you should read the comments on the Bosso Bass site.

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post #604 of 777 Old 05-29-2017, 06:23 AM
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Originally Posted by audioguy View Post
Let me see if I have this correct: So IF Mark Seaton (sub designer) said it made sense acoustically (he has yet to say that that I am aware of) and BossoBass (sub designer) said it makes sense acoustically (I did read the BossoBass articles) then they are wrong and you are right.
No. There are certainly situations where stacking subs will improve the response compared to a single sub (see http://bossobass.com). At the same time there are most likely other potential subwoofer locations that would improve the response even more. MSO can help you explore this.

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post #605 of 777 Old 05-29-2017, 07:06 AM
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No. There are certainly situations where stacking subs will improve the response compared to a single sub (see http://bossobass.com). At the same time there are most likely other potential subwoofer locations that would improve the response even more. MSO can help you explore this.
Maybe I was not clear on something. I want the best bass possible with some limitations:

(1) I can't/won't move my front subs. They are in the front corners. I like them there (cosmetic reasons) and so does my wife (she can't see them). I could add "spacers" if that will do anything substantive to get me where I want to go. I do, however, have lsome flexibility on the rear subs. They can go virtually anywhere along the back wall (except for blocking a door). And "some" flexibility along the side wall. And I can replace them with 4 more F18's - and that I KNOW will at least add headroom AND provide the same sonic signature that I have in the front subs. and

(2) To the extent that optimizing all/most of the seats compromises the performance at the MLP, I am not interested. I have NO non-audiophile friends who care about any of this stuff, and the audiophile friends I do have want the same thing I want: the best possible performance at the MLP

My personal "opinion" is that I will continue to struggle in getting what I want until such time as I replace the rear subs.

I am willing it to give MSO a go to the extent it will provide me what I want - and the limitations I have now articulated (hopefully clearly). Based upon the response I got from the author, it seems as though it won't but I am still willing to try it - at least once I understand it's objectives. As I have stated more than once, what I am looking for clearly is more than just uniform bass FR - as I can get that very easily.

The search continues.

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post #606 of 777 Old 05-29-2017, 07:10 AM
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Cleaned up the tail end of this thread. The take away is those seeking help need to be open to new ideas and other points of view (and appreciative for the help). Those providing help and alternative points of view shouldn't become defensive, if the person seeking the advice, doesn't take the advice.

If the bickering continues, all parties will be banned from posting in this thread.

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post #607 of 777 Old 05-29-2017, 07:31 AM
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Originally Posted by audioguy View Post
Maybe I was not clear on something. I want the best bass possible with some limitations:

(1) I can't/won't move my front subs. They are in the front corners. I like them there (cosmetic reasons) and so does my wife (she can't see them). I could add "spacers" if that will do anything substantive to get me where I want to go. I do, however, have lsome flexibility on the rear subs. They can go virtually anywhere along the back wall (except for blocking a door). And "some" flexibility along the side wall. And I can replace them with 4 more F18's - and that I KNOW will at least add headroom AND provide the same sonic signature that I have in the front subs. and

(2) To the extent that optimizing all/most of the seats compromises the performance at the MLP, I am not interested. I have NO non-audiophile friends who care about any of this stuff, and the audiophile friends I do have want the same thing I want: the best possible performance at the MLP

My personal "opinion" is that I will continue to struggle in getting what I want until such time as I replace the rear subs.

I am willing it to give MSO a go to the extent it will provide me what I want - and the limitations I have now articulated (hopefully clearly). Based upon the response I got from the author, it seems as though it won't but I am still willing to try it - at least once I understand it's objectives. As I have stated more than once, what I am looking for clearly is more than just uniform bass FR - as I can get that very easily.

The search continues.
Flat frequency response equals perfect time domain behavior IF the response is minimum phase. This is physics. No way around it. So if equally flat frequency responses sound different then you're either attributing the differences to the wrong frequency range (might be the crossover region to the satellites) or filters/sources were added that create time domain issues (look at the time domain and not just the frequency response). Another possibility is always faulty measurements.
And, always do multiple measurements within the listening area. Humans have two ears several inches apart. We also tend to move during listening. So at least cover a space of 1.5' when optimizing a single seat.

Regarding the use of MSO: http://andyc.diy-audio-engineering.org/mso/html/
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post #608 of 777 Old 05-29-2017, 09:46 AM
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Flat frequency response equals perfect time domain behavior IF the response is minimum phase. This is physics. No way around it. So if equally flat frequency responses sound different then you're either attributing the differences to the wrong frequency range (might be the crossover region to the satellites) or filters/sources were added that create time domain issues (look at the time domain and not just the frequency response). Another possibility is always faulty measurements.
And, always do multiple measurements within the listening area. Humans have two ears several inches apart. We also tend to move during listening. So at least cover a space of 1.5' when optimizing a single seat.

Regarding the use of MSO: http://andyc.diy-audio-engineering.org/mso/html/
You may be making assumptions about what I am and am not measuring. I AM measuring more than 1.5 feet - a good bit more; I add no filters after Dirac; Dirac deals with frequency, time AND phase.

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post #609 of 777 Old 05-29-2017, 10:27 AM
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I wasn't talking about Dirac Live. In case you need help with MSO, feel free to ask questions.
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post #610 of 777 Old 05-30-2017, 12:10 AM
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When I came across MSO I had a two channel DSP amp with four 18" Subwoofers in my room. I am still amazed by the theoretical concept and the quality of user friendly design of the software. To top it all the author provides it for free and gives free support. Come on, what more can you ask for?

As the first results measure great I invested in some more DSP, amplifier and driver channels. Only the weather has gotten so great in Germany that priorites shifted to BBQ, but quite soon I will be back with more measurements.
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post #611 of 777 Old 05-30-2017, 06:25 AM
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Hello AndyC,

Thank you for developing MSO. It is especially useful for integrating a helper sub to a main sub.

(A minor bug: Optimizing is ignoring the user defined max Q value in Parametric EQ, eg. DCX2496 has max Q of 10. Optimizing always using default of 25.) Please ignore. Forgot to rerun optimising after changing parameter.

Please add sentence to MSO web page Optimizing Strategies: in "Optimizing Subs only" section. To optimize subs only, Choose Config, Create New Sub-only Configuration.
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post #612 of 777 Old 05-30-2017, 07:12 AM
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Please add sentence to MSO web page Optimizing Strategies: in "Optimizing Subs only" section. To optimize subs only, Choose Config, Create New Sub-only Configuration.
Yeah, I also needed quite some time to find that.
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post #613 of 777 Old 05-30-2017, 09:09 AM
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Please add sentence to MSO web page Optimizing Strategies: in "Optimizing Subs only" section. To optimize subs only, Choose Config, Create New Sub-only Configuration.
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Yeah, I also needed quite some time to find that.
Thanks for the bug report guys. I've added some information to the documentation.

Edit: I've also updated the .CHM help file, which you can download and copy to the program directory if you want the latest in offline format. I don't make a new installer when I update only the help, as the help gets updated pretty often.

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post #614 of 777 Old 06-04-2017, 03:16 AM
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Cut vs. boost? Ran a quick comparison where in case 1 only EQ cuts were allowed and in case 2 only boost was allowed. Don't the resulting filter curves look very much alike
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post #615 of 777 Old 06-04-2017, 05:23 AM
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Had a little play with MSO to try and get rid of a null between 70-90hz. Like most things the more times you use it, the more obvious things become.

I have four subs across the front of my room running off two channels. So I have to just treat them as two subs. Although I'm not overly concerned with everyone else on the couch I thought why not let's just copy the tutorial and used the same weighting structure and took readings from 3 position of the two separate subs. Ran the program and whilst it all looks good on paper what I don't get is the dip in my response between 70 and 90hz corrected as it predicts at MLP.

When it starts optimising I notice it puts in the starting point on all three positions from which it has already adjusted gains and delays I assume. This is where I got excited as it had already removed the dip.

Just wondered if there is anything to be done or is it just not able to correct. I stupidly cleaned up my desktop so I don't have the pictures to use as examples, but I still have the REW files at least so could start from scratch if I need to get to a certain point for you guys to help.

Here's the normal response at MLP with 110hz LPF.



and here's the MSO prediction with no LPF in place:



One thing I wanted to double check when taking the initial readings in REW, with regards to the acoustic timing reference I left all the options on default. Is that correct? Also with Inukes do I need to adjust the values in any way?

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post #616 of 777 Old 06-04-2017, 08:25 AM
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When it starts optimising I notice it puts in the starting point on all three positions from which it has already adjusted gains and delays I assume. This is where I got excited as it had already removed the dip.
I'm not sure what you mean by "the starting point" here. When you create a sub-only configuration and use the Optimization Options dialog to set the options, you specify a reference level for the MLP in the Method tab of this dialog. In the Criteria tab, you specify a start and stop frequency. The optimizer tries to force (among other things) the average, in dB, of the MLP SPL over the optimization frequency range specified in the Criteria tab to be the value specified in the Method tab. If a big positive peak is taken out, this reduces the average, so the gain must be increased to keep the average the same. But many other things are also going on at the same time.

If this isn't what you're referring to, you'll need to be more specific in your question.

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Just wondered if there is anything to be done or is it just not able to correct.
Sometimes just running the optimization for a longer time can help. It may appear that the optimizer is "stuck" after a few minutes, but often by just waiting it may come up with something better. Or, you might try changing to the other optimization method in the Method tab of the Optimization Options dialog.

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One thing I wanted to double check when taking the initial readings in REW, with regards to the acoustic timing reference I left all the options on default. Is that correct?
Are you referring to the Analysis tab of the REW Preferences dialog? If so, it looks like you've disabled smoothing, which is good. Using the defaults for the other options there should be good also.

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Also with Inukes do I need to adjust the values in any way?
When entering the PEQ parameters into the iNuke, be sure to use the Q(RBJ) from the MSO filter report, rather than the "plain" Q. This is explained in the Behringer compatibility pages of the documentation. Though I don't have an iNuke myself, I've recently found that you can get better adjustment resolution for PEQ center frequency and Q in the iNuke software by typing in values into the text boxes rather than using the dial controls of the software. For some reason, after you enter the value in the text box, you need to press Enter, or it reverts to its previous value. This technique gives the following resolutions:

Gain resolution: 0.5 dB
Q resolution: 0.01
Center frequency resolution: 0.1 Hz
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post #617 of 777 Old 06-04-2017, 10:58 AM
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Yep, that's true on the Inukes, the dials have very coarse adjustment. You need to type them in and press enter or it doesn't register.

I am pretty sure I did everything correctly, just wondered why I didn't get the results it predicted.
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post #618 of 777 Old 06-04-2017, 11:56 AM
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Yep, that's true on the Inukes, the dials have very coarse adjustment. You need to type them in and press enter or it doesn't register.

I am pretty sure I did everything correctly, just wondered why I didn't get the results it predicted.
I wasn't sure what that REW capture was in your earlier post. From the look of it, I thought it was the "before" condition. Was that actually the "after" condition?

One way to check your filters is to go into the Setup tab of the iNuke software and save the amp configuration to a .arp file using the Save button in the PC Presets box. This is just a text file that you can look at in Notepad or some other text editor. You can then compare the filter data in the .arp file with what MSO provides in the filter report to make sure there are no discrepancies.

If the initial measurements were taken with the amp not set to a flat response, the result will be in error after optimization, as MSO has no way of knowing the properties of the filters used in the initial measurements.

Edit: Also, before the initial measurement, the delays should all be set to zero, and dynamic EQ should be disabled. The filter, gain and delay results of MSO represent how to change the settings from the as-measured condition, so if the gains, delays and filters aren't set to nominal, zero and flat respectively, it's going to be difficult or impossible to figure out the new settings: impossible in the case of non-flat filters before the initial measurement.

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@andyc56 Would it be possible to add a check that any filter change that MSO wants to apply during the automated optimization run doesn't add any excess phase group delay (although it would improve the frequency response smoothness, i.e. reduce the RMS error)?

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Quote:
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I wasn't sure what that REW capture was in your earlier post. From the look of it, I thought it was the "before" condition. Was that actually the "after" condition?

One way to check your filters is to go into the Setup tab of the iNuke software and save the amp configuration to a .arp file using the Save button in the PC Presets box. This is just a text file that you can look at in Notepad or some other text editor. You can then compare the filter data in the .arp file with what MSO provides in the filter report to make sure there are no discrepancies.

If the initial measurements were taken with the amp not set to a flat response, the result will be in error after optimization, as MSO has no way of knowing the properties of the filters used in the initial measurements.

Edit: Also, before the initial measurement, the delays should all be set to zero, and dynamic EQ should be disabled. The filter, gain and delay results of MSO represent how to change the settings from the as-measured condition, so if the gains, delays and filters aren't set to nominal, zero and flat respectively, it's going to be difficult or impossible to figure out the new settings: impossible in the case of non-flat filters before the initial measurement.

Thanks, the first capture is the "before" response at MLP with no filters, delays or anything in place. That's my starting point before a little eq in the inuke and then Dirac. It sounds ok, would obviously like that 70-90 region to be fixed or improved if possible which is why I gave MSO a try.

I'll start from scratch and remeasure everything and then plug them all into MSO and set it all up again and see if I get better results. I'm pretty confident I did everything right 1st time though.
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post #621 of 777 Old 06-04-2017, 02:10 PM
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@andyc56 Would it be possible to add a check that any filter change that MSO wants to apply during the automated optimization run doesn't add any excess phase group delay (although it would improve the frequency response smoothness, i.e. reduce the RMS error)?
Not without completely rewriting the optimization code.

If I understand you correctly, you're thinking of optimization as a successive refinement of a given (single) solution according to some algorithm, something like:

1) Next solution guess = some function of the current solution guess
2) Repeat (1) until done.

This is how e.g. "steepest descent" (gradient) optimizers work, as a generalization of Newton's method, sometimes called "greedy algorithms". But that type of optimizer often fails on practical problems whose objective function has many local minima (a multi-modal objective function), such as the following:



The failure involves premature convergence at a local minimum, where it then gets "stuck" and can't get out. By contrast, global optimizers need a way to explore the solution space, with potential solutions wandering about like ants on the "surface" (really a hyper-surface in a space having dimension N+1, where N is the number of parameters being varied). In the case of differential evolution used by MSO, this is accomplished by having an inventory of 100 solution guesses. They're initially randomly generated, except for one, which contains the filter parameters from the UI. Then for each guess vector, the objective function value is computed and saved with the solution guess. So at any optimizer pass, there is not one "current solution guess", but 100 of them. On each pass, new guesses are generated for each solution vector by combining existing vectors in various ways. If this newly-generated guess vector at a given position in the collection of 100 vectors has a better objective function value than the current one, the current one gets replaced - otherwise it stays the same. This is done for each of the 100 guess vectors in the current generation (collection of 100 guesses), in order to form the next generation .

So there is not a current solution guess and a next solution guess, but rather a current generation and next generation. The best solution of the 100 is what gets plotted and used. I suppose it might be possible to calculate the excess group delay for each individual guess in the generation, and only replace it if the new guess also has better (or no worse?) excess group delay. There are so many questions, especially about efficiency, but also other algorithm details. What's the criterion? Rate of change of excess group delay (spikes)? Also, in this algorithm, the connection between "the best solution of the current generation" and "the best solution of the next generation" is not necessarily at all direct.

It's an interesting idea, but I really don't intend or want MSO to be my life's work. Quite the contrary in fact. I'm sitting here with 4 partially built subs in my garage, and none in my system, like the proverbial cobbler with no shoes. That's why there haven't been any changes in MSO in a while, and won't until later this summer when I finish the subs and other home projects.
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post #622 of 777 Old 06-04-2017, 02:26 PM
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I suppose it might be possible to calculate the excess group delay for each individual guess in the generation, and only replace it if the new guess also has better (or no worse?) excess group delay.
Exactly. The idea is, lots of excess group delay = bad time behavior = lots of resonances, no excess group delay = minimum phase behavior = perfect active absorption

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post #623 of 777 Old 06-04-2017, 06:11 PM
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Exactly. The idea is, lots of excess group delay = bad time behavior = lots of resonances, no excess group delay = minimum phase behavior = perfect active absorption
It really becomes a multi-objective optimization problem if you want to bring in the excess group delay. Here is an article about multi-objective optimization by Kalyanmoy Deb. I've tried to avoid the multi-objective techniques by RMSing together the errors over frequency over all positions to get a single number. I can do that because of the similar physical meaning of the RMS flatness errors. But when you have disparate quantities you're trying to optimize simultaneously, that's a different issue. In figure 5b of the Deb article and its surrounding text, you see that there is not a single "best" solution for optimizing as with a single objective function, but a collection of solutions on the Pareto-optimal front. In figure 5b, going from point 3 to point 5 makes f1 better and f2 worse. The same thing happens when going from point 5 to point 6. If such a collection on the Pareto-optimal front for flatness error and excess group delay were found, sorting the collection of solutions by increasing flatness error would be equivalent to sorting them by decreasing excess group delay. So it's a family of compromises. On the Pareto-optimal front, one can't improve the excess group delay without making the flatness error worse, and vice versa. Constraints on the errors could filter out many solutions with extreme errors for either of the parameters.

It's an interesting idea, but a huge impact.

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post #624 of 777 Old 06-04-2017, 06:46 PM
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Further to my comments at Optimizing subwoofers and integration with mains: multi sub optimizer, following are some additional details that I had posted elsewhere, which may be of benefit to others.

My room is far from ideal, being non symmetrical, open at one end, glass wall the other and we sit across the room with the couch on the rear wall (about 300mm away).

I am using three subs, two are SVS PC13's, one with a Bash amp the other is a Sledge amp, thus they are not identical. The third sub is a 4 x 12" driver couch kicker which sits behind couch.

Whilst this is still a work in progress, I am very happy with the results to date -from a listening perspective, not just measurements.

MSO has a bit of a learning curve, however I found that the following link helped simply some if it (obviously some of the steps should be disregarded if an 88A is not being used).



A couple of other points for anyone considering using MSO

i) I used 5 locations, the three couch positions and also the two mid-points, when taking my measurements
ii) MSO contains options for subs only, or subs and mains. I have used the subs only option.
iii) At Optimisation Options, I used the Best match of MLP to other listening position option, as final correction will be done at the AVR or 88A.
iv) Experiment with differ target levles and also which position is to be used as the MLP, as changing these can can result in different solutions and some look better than others.
v) run MSO for a considerable period of time ( I use 90 mins), as the default is 0.5min and the results after a longer period are normally quite different to the 0.5min result.
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post #625 of 777 Old 06-04-2017, 11:46 PM
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It really becomes a multi-objective optimization problem if you want to bring in the excess group delay. Here is an article about multi-objective optimization by Kalyanmoy Deb. I've tried to avoid the multi-objective techniques by RMSing together the errors over frequency over all positions to get a single number. I can do that because of the similar physical meaning of the RMS flatness errors. But when you have disparate quantities you're trying to optimize simultaneously, that's a different issue. In figure 5b of the Deb article and its surrounding text, you see that there is not a single "best" solution for optimizing as with a single objective function, but a collection of solutions on the Pareto-optimal front. In figure 5b, going from point 3 to point 5 makes f1 better and f2 worse. The same thing happens when going from point 5 to point 6. If such a collection on the Pareto-optimal front for flatness error and excess group delay were found, sorting the collection of solutions by increasing flatness error would be equivalent to sorting them by decreasing excess group delay. So it's a family of compromises. On the Pareto-optimal front, one can't improve the excess group delay without making the flatness error worse, and vice versa. Constraints on the errors could filter out many solutions with extreme errors for either of the parameters.

It's an interesting idea, but a huge impact.
Thanks for all your thoughts on this Andy. Much appreciated. Maybe when you're finished with your subs and start optimizing them we can pick up this discussion?

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post #626 of 777 Old 06-05-2017, 12:23 AM
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It really becomes a multi-objective optimization problem if you want to bring in the excess group delay.
Is it possible to treat it as a multi pass problem instead? e.g. keep a record of the top x candidate solutions (where best is defined in fr terms) and then sort those solutions according to the excess phase criteria.
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post #627 of 777 Old 06-05-2017, 12:49 AM
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I wonder what the final frequency response would look like if MSO would optimize excess group delay response instead of frequency response. This wouldn't require a rewrite of MSO but "just" a replacement of the frequency response with the excess phase group delay response. What are your thoughts on this?
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A am a newbie with minidsp and the multi sub optimizer and need som starting advices.
My system is a Minidsp DDRC88BM and a Minidsp 2x4HD. 7.1 setup. I have got 4 subwoofers connected to the output of the 2x4, and hooked the input to ch3 on the ddrc88.
Have tried to read the manual for the MSO, and the appendix regarding use of the minidsp setup I have.
The question is what settings I should perform on the 2x4 before running the MSO. The routing
I have figured out, but should I adjust distance/delay, adjust level and lowpass frequency on the 4 subs before running MSO?
Any good advices here for a newbie?
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post #629 of 777 Old 06-08-2017, 11:58 AM
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A am a newbie with minidsp and the multi sub optimizer and need som starting advices.
My system is a Minidsp DDRC88BM and a Minidsp 2x4HD. 7.1 setup. I have got 4 subwoofers connected to the output of the 2x4, and hooked the input to ch3 on the ddrc88.
Have tried to read the manual for the MSO, and the appendix regarding use of the minidsp setup I have.
The question is what settings I should perform on the 2x4 before running the MSO. The routing
I have figured out, but should I adjust distance/delay, adjust level and lowpass frequency on the 4 subs before running MSO?
Any good advices here for a newbie?
It's all answered in the MSO manual. Please read it.

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post #630 of 777 Old 06-08-2017, 12:19 PM
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It's all answered in the MSO manual. Please read it.
As I already wrote, I have read it. But still have questions. Can not see your answer helped me a bit. The manual I have got does not answer my questions.
Anybody else who cam help me?
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