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derrickdj1

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Not much going on with new stuff in this section of the forum.  I thought that I would share a calibration dilemma with the group.  I ran MCACC the other day a got this graph. 

 

Not enough info:

4 front subs = SW 1

4 rear subs = SW 2

Calibration sets the Front speakers to Large until changed.  So, I run MCACC a second time with the Front(Mains) speakers set to small.   All 8 subs are on in these two graphs!  All graphs 1/12 smoothing unless noted.

 

FR post MCACC.png

FR run 2 mains plus subs MCACC.png

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Ok, 16 views and nobody is taking a stab at this.

 

First, define the problem: The graph is screwed up, lol.......  There is a phase issues somewhere, SW 1, SW2 or the Mains.

 

Next, what approach to the problem to use:

  • Use all like subs, lol?
  • switch to Auddysee, chuckle, chuckle:D
  • ask for help:ph34r:
  • more resolution to the graph and less smoothing to see what is going on;)

 

Now, I will say that all of the subs are at 0 phase except one in the rear of the room.

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Yea derrick I was one of those 16 views.....lol lol

This is the type of technical stuff that is above me.... When I look at your graphs I have no clue what I'm looking  at....

I've just started to enter in this HT stuff and the only "calibration" I've done is what my Pioneer can do. 

Even when I set up my JBL's my audio buddy came over and got them set-up for me. I was talking to him about my new Pioneer and he's going to come over and help me get my system dialed in and give a education on sll this HT stuff.

My HT system sound good to me but I know it can sound better....

Good luck....hopefully someone will be able to help ya out....

 

MKP :-)

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I always said that this forum should be more educational and try to do a bit now and then.  First we want a flat frequency response.  This is what MCACC, Auddysee, etc. try to accomplish.  Most calibration programs are fine for two subs.  A flat FR means that all the sounds are being reproduced as correctly as possible and nothing is hot or cold, no elevated or greatly decreased frequencies.  Not the graphs below: http://www.eartechmusic.co/flat-frequency-response-dont-forget-phase/

 

For now just the yellow and blue lines.  This what everyone is shooting for with sub setup and integration.

FIG1_FreqRes_InPhase-300x214.png

FIG2_FreqRes_OutPhase-300x214.png

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In the first post the, graph one shows a 25 db drop starting around 35 Hz with the mains set to large but, when I set the mains to small, the drop is gone but, a nasty dip comes in at 35 hz up to 200 Hz.

 

We know it is a phase problem since this occurred after changing the mains to small.  Below are two more graphs, subs only and mains only XO at 80.  No major problem except when they are combined. (red lines)

 

The blue line is the ambient room noise.  HVAC is on.

FR Subs only.png

FR Mains.png

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Ok, it's a phase issue.  even in the graphs below the FR looks good but, why worry about phase.

 

Phase issues rob the accuracy, depth, sound stage and presence.  It will cover up detail and can make the bass muddy.  Out of phase will decrease the Oomph in the tactile response for HT or the chest slam that some music lovers like.

 

So, it looks like I'm royally screwed with my FR.:(  The yellow line is the graph in phase. http://www.eartechmusic.com/flat-frequency-response-dont-forget-phase/

FIG1_FreqRes_InPhase-300x214.png

FIG2_FreqRes_OutPhase-300x214.png

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I really recommend using the "room sim" within REW.  When you're below the Schroeder frequency of the room, the exact geometry of the room, the position of the loudspeakers, subwoofers, and your listening/microphone position makes all the difference in the world...

 

REW Room Sim screen shot.GIF

 

Once you find where the 1/4 wavelength nulls are--using the above room sim--relative to your listening/microphone position, you can pick out subwoofer and loudspeaker phase issues.  Typically phase corrections are done one subwoofer or loudspeaker at a time, recording phase/delays to the listening position vs. frequency, then a few calculations to zero the phase (or at least result in multiples of 360 degrees--otherwise known as "phase alignment" instead of "time alignment".

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Chris, I normally don't have problems with room modes with subs spread around the room.  I switched my rear Mini Marty's with my LLT's which is where the nasty response came into play.  I wanted to keep this thread simple and illustrate a couple of points only since we don't see enough FR /phase issues on this subwoofer forum.

 

 

 

Four quick and easy things to do after autocalibration:

Do these 4 things one at and time and keep best result

  1. Change Mains from Large to small/ck FR

  2. Change XO up or down by no more than 20 Hz, Ex 60 Hz or 100 Hz for an 80 Hz XO, ck/FR

  3. Change sub/s phase/ck FR(this is almost never need if done correctly earlier)

  4. Change sub distance(never change more than 7 ft. or a 180 degree phase shift occurs)

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Ok, time for a quick recap.

 

Problem: Phase issues

 

Four quick and easy things to do after autocalibration:

Do these 4 things one at and time and keep best result

  1. Change Mains from Large to small/ck FR

  2. Change XO up or down by no more than 20 Hz, Ex 60 Hz or 100 Hz for an 80 Hz XO, ck/FR

  3. Change sub/s phase/ck FR(this is almost never need if done correctly earlier)

  4. Change sub distance(never change more than 7 ft. or a 180 degree phase shift occurs)

The Mains were changed and did not solve the problem.  The XO was changed and did not solve the problem.  The phase was rechecked on all the subs and correct.  This is easy to verify with an spl meter.  With the addition of each sub the FR should get better or the spl should go up

 

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2 hours ago, derrickdj1 said:

We know it is a phase problem since this occurred after changing the mains to small. 

That's counterintuitive.  In order to have a phase issue, both sources have to play frequencies out of phase with each other thus canceling each other out.  When you switch to small the mains are not playing frequencies that the subs are, so phase issues should go away.  I understand that the crossover isn't a brick wall and there's some overlap between mains and sub but the problem should get better when switching to small if phase is the problem.

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Just now, CECAA850 said:

That's counterintuitive.  In order to have a phase issue, both sources have to play frequencies out of phase with each other thus canceling each other out.  When you switch to small the mains are not playing frequencies that the subs are, so phase issues should go away.  I understand that the crossover isn't a brick wall and there's some overlap between mains and sub but the problem should get better when switching to small if phase is the problem.

You are correct and in most cases the response gets' better.  The LLT subs present an unusual problem in the rear of the room which is what I am thinking is the problem.  Two things, there design and location.  First, they were design to get down stair and could be no wider than X inches.  Second, the driver and the port are 90 degrees from each other.  This interaction along with the other subs in the rear cause a phase error that autocalibration can't correct.

 

So, now we go back to the list and the only thing that was not done-DISTANCE of the speakers(Mains), SW1 or SW 2. 

 

The goal of posting this topic was to keep the solution simple without loosing people. There are more complex ways to get the solution but, are not necessary after considering the data presented.

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Changing the phase on a sub or a group of the subs does not work.  This may be possible with a variable phase control which the I Nuke amps don't have.

 

Solution:-Distance

Earlier it was stated, never change the distance by  more than 7 ms or this would result in a 180 degree shift.  Now, there are three distances to work with, Mains, SW1 and SW2.  Let's go back to the original graph.

FR mains plus subs phase corrected.png

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2 minutes ago, derrickdj1 said:

This may be possible with a variable phase control which the I Nuke amps don't have.

Yes, variable phase control is similar to distance setting.  It's not identical but can produce similar results.  That's a nice thing about most sub plate amps.

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The graph abnormality is wide occurring   near the XO.  This tells us that the distance needs to be shorten for one of the three, Mains, SW1 or SW2.  Now we have a simple problem, solve for X or the offending variable, Mains, SW1 or SW 2.  This can be done by doing a quick FR and cutting off one of the three at a time.  In this case, SW2 was X.

 

The driver and port are 90 degrees from each other.  I shorten the SW2 group of subs 4 ms or 4 ft.  Four milliseconds is about 90 degress.  Next, I ran a FR: this time with no smoothing to prove a point.  For subwoofer integration most of the time a resolution of 1/12 is all that is needed.  Other may disagree with this point but, this should be all that is needed and the vast majority of problems can be fixed with 1/12 smoothing.

 

This is a good FR for a vented system down to around 12 Hz, +/-5.  Later I will tweak the response to +/- 3.  REW or Omnimic have a phase function that can be used.  Having these things and not knowing how to use them is no good.  The goal was to walk thru this subwoofer integration problem and have a process to use.

 

The phase relationship can be easily tested by: Phase issues rob the accuracy, depth, sound stage and presence.  It will cover up detail and can make the bass muddy.  Out of phase will decrease the Oomph in the tactile response for HT or the chest slam that some music lovers like.

 

All this can be done without measurements!  As stated earlier, the goal was to keep this simple.

 

 

10.02.216 FR no smoothing.png

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4 minutes ago, derrickdj1 said:

The graph abnormality is wide occurring   near the XO.  This tells us that the distance needs to be shorten for one of the three, Mains, SW1 or SW2.  Now we have a simple problem, solve for X or the offending variable, Mains, SW1 or SW 2.  This can be done by doing a quick FR and cutting off one of the three at a time.  In this case, SW2 was X.

 

The driver and port are 90 degrees from each other.  I shorten the SW2 group of subs 4 ms or 4 ft.  Next, I ran a FR: this time with no smoothing to prove a point.  For subwoofer integration most of the time a resolution of 1/12 is all that is needed.  Other may disagree with this point but, this should be all that is need in and the vast majority of problems can be fixed with 1/12 smoothing.

10.02.216 FR no smoothing.png

That is a huge change in response with a 4foot adjustment!   It almost seems with all those subs the adjustments are magnified.

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22 minutes ago, RoboKlipsch said:

Derrick with MCACC do you find that you have to turn off the HPFs and PEQ shelf adjustments or does it work fine with them on?  

MCACC can work with them on.  This is the first time that I have had to change the distance on a group of subs.  When the LLT's are far from the MLP, the FR has no major peaks or dips.  Remember, when we measure and put distance in the I Nuke, it is a physical distance and not acoustic.  The adjustment is not magnified.  4 ms is not a large amount of time for a correction.  I mentioned the 7 ms rule at the GTG presentation in Oct. but, did not elaborate enough due to time.

 

The key is understanding what might be the cause when you look at your FR graph.  This is need to know where to start looking for a fix.  This FR can deliver reference level tactile response down to 10 Hz.

 

I hope this was fun for some people and simple enough to take a few things from it.

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Rob, you bring up a good point in asking about the filters used.  I never go beyond a three filter max when adjusting the subs.  Filters work on both sides of the target and the more used, the more undesirable IMHO.  With this setup, I am only using two filters on SW1 and one on SW 2.  A good raw FR is possible without using a lot of filters.  Also, the dip that normally occurs at the XO can be eliminated for the most part.

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