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Need to set delay on subs or everything?

klettermann

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I'm getting my feet wet with MSO and Minidsp Studio for a 2.2 audio system. I'm pretty amazed at what MSO can do. MSO generated delay times for the respective subs that i plugged into the MiniDSP. Using them resulted in an astonishing improvement in low end FR. One sub is in front corner while the other is about 2\3 back against the opposite wall. Speakers are large Magnepans about 4ft back from the front wall, so one of them sits a couple feet in front of the corner sub.

Here's the question: Do i also need to delay the mains since they aren't equidistant from MLP vs the corner sub? I'll try it at some point but if like to know if this world be the preferred practice. Comment welcome! Thanks and cheers,
 
Basicaly an easy thing: The sound source furthest away from the listening spot needs no delay, the one nearest the most.
As you can't accelerate the sound reproduction, you delay it. In your case the Magnepan's theoretically would need a little delay.
Anyway, you got to measure this with some kind of app.
I check the distances with a laser distance meter and found my room correction the be spot on to a fraction of an inch. If something goes wrong, usually the phase of a speaker is 180° off and polarity must be changed.
 
Thanks, very helpful. I just ordered a laser ruler, wanted one anyway. Anyway, makes sense. MSO specified sub delays of 0.08ms and 8.3ms. Why the 0.08ms for the far sub 2 have no idea, but went with it. The result is below, showing the effect of increasing delay on sub 1. Blue is both subs EQ'd by MSO. The other stuff is increasing delay on sub 1. The sweet spot was 8.5ms. I'm thinking that the same exercise with the mains might be worthwhile. Cheers,

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Once you have run MSO and uploaded filters and delays into the MiniDSP, you have now created a single "virtual" sub that is the combination of your 2 subs. There is now a single "virtual" distance to this "virtual" sub that may or may not be intuitively related to the actual measured distances from your seat to the subs or the main speakers. So yes, you would and should verify that this virtual sub distance aligns well with the mains, focusing on the cross over region (typically near 80Hz).

If using an AVR, you would typically use the "Sub distance tweak" procedure (google it) to modify the subwoofer distance setting to minimize the cancellation of the combined sub+mains signal in the cross over region. A more sophisticated approach is to look at the group delay plots of the combined sub+mains sweeps in REW, click on generate minimum phase, and inspect the "Excess Group Delay" plot and look for delays between the single virtual subs (in 50-100Hz range) compared to the mains in the 100-300Hz range. Search for Excess Group Delay in the REW manual and there is an excellent write up (it may take a few read throughs to really understand what it is doing).

For example in the plot below of Front Left Speaker+subs, you can see that the Excess Group Delay is at 13ms on the y axis, and the main speakers are at around 3ms delay, so in this case I would add 10ms delay to the main speakers to bring them into proper time alignment.


1734669686218.png
 
Once you have run MSO and uploaded filters and delays into the MiniDSP, you have now created a single "virtual" sub that is the combination of your 2 subs. There is now a single "virtual" distance to this "virtual" sub that may or may not be intuitively related to the actual measured distances from your seat to the subs or the main speakers. So yes, you would and should verify that this virtual sub distance aligns well with the mains, focusing on the cross over region (typically near 80Hz).

If using an AVR, you would typically use the "Sub distance tweak" procedure (google it) to modify the subwoofer distance setting to minimize the cancellation of the combined sub+mains signal in the cross over region. A more sophisticated approach is to look at the group delay plots of the combined sub+mains sweeps in REW, click on generate minimum phase, and inspect the "Excess Group Delay" plot and look for delays between the single virtual subs (in 50-100Hz range) compared to the mains in the 100-300Hz range. Search for Excess Group Delay in the REW manual and there is an excellent write up (it may take a few read throughs to really understand what it is doing).

For example in the plot below of Front Left Speaker+subs, you can see that the Excess Group Delay is at 13ms on the y axis, and the main speakers are at around 3ms delay, so in this case I would add 10ms delay to the main speakers to bring them into proper time alignment.


View attachment 415176

Thanks very much for that. I'm trying to absorb it all, takes several readings as you indicate! Anyway, I took a crack at GD per below, same scale as yours. If I'm getting it right then I'd delay the main by about 20ms? Seems like lot but I really have no idea. And of course your scan is lot cleaner than mine, something else to work on. Comments welcome, thanks again and cheers,
1734724109518.jpeg
 
I'd say it's closer to 15ms of delay (it looks to be about 20ms - 5ms - there is excess group delay in the main speakers as well) - so you just need to add about 14 to 15ft of distance to your subwoofer setting.

BTW I've just posted a new MSO tutorial video onto Youtube that you might want to have a look at.

 
I'd say it's closer to 15ms of delay (it looks to be about 20ms - 5ms - there is excess group delay in the main speakers as well) - so you just need to add about 14 to 15ft of distance to your subwoofer setting.

BTW I've just posted a new MSO tutorial video onto Youtube that you might want to have a look at it.
Again, thanks much. I ended up going back to the drawing board a little as I wasn't entirely happy with the outcome. The workflow was this:

1. Recheck alignment timing (correct term??) on MSO'd "virtual sub" to see effect. The sub response seemed OK based on previous MSO setup.
Ran a 6x5 matrix of XO combinations to see if there was an optimum XO, i.e., all combinations of subs at 50, 60, 70, 80, 90, 100Hz and mains at 60-100Hz. That totals 30 scans, quite a few, so I did the perimeter of the matix and the midpoints (X's in matrix below). Partial results pointed to the region between 70-90Hz so those were also scanned (o's in matrix).
60 70 80 90 100
50 x x x x x
60 x x x
70 x x x x x
80 x o x o x
90 x o x o x
100 x x x x x

At the end 80/80Hz turned out best. Lots of work to "prove" what everybody already seems to know, but why not? Anyway, I'm now confident in terms of best FR, XS delay, clarity, etc.

2. Ran a series scans that varied the delay on the mains. The best seemed to be ~13ms.

3. Ran Dirac.

Result: Too many scans to post, but Dirac DID improve everything this time. Most importent, it sounds wonderful. Balanced, very clear, well defined
low end, no boominess. Mids and highs balanced too, unfatiguing. Soundstage and imaging are as good as I've heard them on this equipment. I set up a low boost and low cut variants on Dirac for different genres. See below. I'll also watch your new MSO vid. That will probably move me to start the whole thing over again.:facepalm: Thanks again, Happy Holidays and cheers,

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Pop/Rock: Reelin' in the Years Steely Dan), Telegraph Road (Dire Straits), Angels on a Balcony (Blondie).

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Random House/Trance examples

1734970137607.jpeg
 
A few things I have learned the hard way which may help you.

1. A UMIK-1 , due to USB timing issues, while fine for FR measurements, can not do accurate "timing measurements", you need to use either a UMIK-2 or an regular MIC with a 2-channel interface and loop back.

2. Many subs have DSP which will add delay. For instance all recent SVS subs have 6 ms delay. Since any timing measurements inside a room are fraught with potential problems I have had the best luck measuring the DSP delay of the sub using nearfield measurements and then using a tape measure (or in your case you have a laser) to figure out the distance delays and then manually setting the delays. This is also a good sanity check for automatic delays set up by DIRAC or other programs.

3. I used DIRAC for FR of the mains in the past and have good luck. Unfortunately I have not had any luck with the DLBC sub integration, especially setting the sub timings, I keep getting nonsensical results like 125 ms delay when the right answer is more like 6 ms. There are threads on this subject on this site and hopefully some software updates are on the way. For some people with some setups DIRAC does seem to work.

4. Trying to fix GD of the bottom Octave or so with DSP, while making the graphs pretty, has not been audible to me and uses a lot of processing power in some cases adds a lot of extra latency so I have not been bothering.

Good luck, have fun, and keep in mind that accurate in room (as compared to outside or in a Anechoic chamber) acoustic measurements are not as easy as many would lead you to believe.
 
Quick comment: Forget the laser meter and measure with REW. The sub may fool you as to where the sound originates. Additionally, it's a doddle with REW. Just be sure to place your microphone AT YOUR EAR LOCATION!!

10µs is the miniDSP limit, so you might have to compromise a bit selecting the closest 10µs to measured.

That being said, LF are less critical than HF.

You can adjust the toe-in on the Maggies to get them exactly time aligned at the LP.

The miniDSP time alignment doc is tolerable, but a bit dated on the REW version.
 
better to do it in real time with REW sound generator which has many types of generator and octave modes to use and use variable time delay and phase and frequency PEQ with multi mics to check each sub in each area of the room or both mics at same time with some real time interesting results , frequency sweeps are going to be just the same as doing it with pink noise around the room which can take days to a week or more , or just get fancy at it and manage to do it actually in a few hours or maybe not

frequency sweep is just to show wow look at that and how many filters used to cut a few corners or maybe need all of the filters for how many sine wave tones that are generated REW per each sine wave , get it ? every sine wave , behringer FBQ 2496 is cheap , ( daisy chain channel A to channel B gives 40 bands ) which should be more than enough ?
need a mini dsp to get below 20Hz as behringer gear stops around 20Hz , wonder if there is way to modify behringer FBQ 2496 so it can be used down to 1Hz ?
 
BTW I've just posted a new MSO tutorial video onto Youtube that you might want to have a look at.

I just watched. Wow. Nice job, very valuable, but not exactly for beginners. I'll need to rewatch a couple times and then try to follow along your process with my system. That will have to wait though. I need a holiday break from scanning, and my partner does too! But "I'll be back...." Cheers,
 
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