REW Alignment tool - Guides or Manual?

jtalden

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One point - would the timing not sound better if they were in phase at crossover and if the crossover is set low do we need to worry about the EQ being flat up to 180 or just up to a point just above the Xover?
The sound quality is primarily the result of a smooth SPL response. Phase irregularity is much less important. Phase is a very helpful indicator of why the SPL is behaving as it does. Phase analysis assists in helping to choose the XO frequency and timing that supports a smooth SPL using a minimal amount of EQ. We expect that EQ will be needed in most all cases to optimize the SPL smoothness up to the transition frequency; about 200Hz for small rooms.
I have limited choices really in my room:-

1. Stack the two subs in the position of sub 1 which gives me a 6db increase in headroom. Dirac loves the position of Sub1 and seems to give a fairly flat response on its own down very low. I can bump up the curve at low frequencies and it allows the adjustments to the curve. Loads of output! You only have to time one sub position.

2. Use Sub1 and Sub2 in their different locations see diagram below. Sub 1 is located exact middle of my right hand wall pointing in to the room. Sub2 is located to the left rear of my sofa. See attached Room Sim. This spreads the bass more in the room but it seems at the expense of some cancellation and SPL. Dirac struggles with the Sub2 trace with big dips at about 25hz and it can't be eliminated by tweaking that curve.

1. Based on the technical results only which option is best?
Use the option that best meets the objective stated above: Provides a smooth SPL with minimal EQ up to 200 Hz. The 40 Hz XO with the the distributed SW locations does not look as promising as the earlier options if I recall correctly. Dirac may still successfully EQ it however.
2. The simulation indicates gains could be made by inverting Sub2 - is that worth exploring? I presume a new Dirac run would be needed after Sub2 is set as inverted. I measured the output at 40hz sine but it did not seem to increase when it was inverted.
I would not think that would be an improvement on the options already found. The SWs would be out of phase over most of their range.
3. Would you still personally go for a 80hz Xover with the two subs and the JBLs? From what you say 40hz seems to be Ok?
40 Hz is okay if Dirac can successfully EQ it. I personally would not use the 40 Hz XO. I think a 60, 80 or 100 Hz XO would be more appropriate. Are the Dirac predictions of Post-14 realized in actual REW measurements or was there a problem?
4. Would stacking two subs in Sub 1 position + adding a third in Sub2 position be worthwhile?
There is likely nothing significant to be gained with a 3rd SW given where it can be located.
Could you kindly please explain the procedure for EQing the two subs and calculating the filters in REW if I want to try this manually. There is a Storm format output option so the .txt EQ filter files can be exported from REW and imported into the Storm by individual sub/speaker but I am not sure whether I would need to create one filter per sub or combine them in REW somehow and put the same filter on both.............. and if so how?!
I may be missing the concerns you are having. My take on this setup is that Dirac BM successfully mitigated a major L vs R phase issue that cannot be corrected using standard PEQ filters. Thus Dirac is the logical choice to use. I would tend to follow its recommended settings or maybe also try 60 or 80 Hz XO as well as the 100 Hz XO to see which one results in the best REW measurements. If the measurements look good and there is still a sound quality issue, I suggest that adjustments to the house curve in Dirac would be the first thing to try. The Post-14 Dirac settings do not call for any of the normal house curve rolloff for the higher frequencies, but it looks like you can easily adjust it as needed to suit your preference.
 

lexicon

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The sound quality is primarily the result of a smooth SPL response. Phase irregularity is much less important. Phase is a very helpful indicator of why the SPL is behaving as it does. Phase analysis assists in helping to choose the XO frequency and timing that supports a smooth SPL using a minimal amount of EQ. We expect that EQ will be needed in most all cases to optimize the SPL smoothness up to the transition frequency; about 200Hz for small rooms.

Use the option that best meets the objective stated above: Provides a smooth SPL with minimal EQ up to 200 Hz. The 40 Hz XO with the the distributed SW locations does not look as promising as the earlier options if I recall correctly. Dirac may still successfully EQ it however.

I would not think that would be an improvement on the options already found. The SWs would be out of phase over most of their range.

40 Hz is okay if Dirac can successfully EQ it. I personally would not use the 40 Hz XO. I think a 60, 80 or 100 Hz XO would be more appropriate. Are the Dirac predictions of Post-14 realized in actual REW measurements or was there a problem?

There is likely nothing significant to be gained with a 3rd SW given where it can be located.

I may be missing the concerns you are having. My take on this setup is that Dirac BM successfully mitigated a major L vs R phase issue that cannot be corrected using standard PEQ filters. Thus Dirac is the logical choice to use. I would tend to follow its recommended settings or maybe also try 60 or 80 Hz XO as well as the 100 Hz XO to see which one results in the best REW measurements. If the measurements look good and there is still a sound quality issue, I suggest that adjustments to the house curve in Dirac would be the first thing to try. The Post-14 Dirac settings do not call for any of the normal house curve rolloff for the higher frequencies, but it looks like you can easily adjust it as needed to suit your preference.
Thank you again. My original perception with the second sub post Dirac was that the timing seemed less focused than with one (or 2 stacked) but I will persevere with it and try the other higher Xovers. But yes it looks like the subs stacked in one single location may be the way to go.

I also agree that based upon your results using Dirac EQ with Bass Control seems the best option.

Kind regards

Jon
 

Test4echo

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Wow, trying to wrap my brain around this.

Anthem MRX 520 using Arc Genesis. Arc Calibration run, crossovers set to 100hz. SW 120hz
Paradigm Studio Ref V1's L+R
SVS PB 3000 in sealed mode.

ARC Set my SW at 12Feet

From what I have read so far, does what I did here seem right?

31776
 

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jtalden

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Yes, that is basically the correct timing using those measurements, but... The issue is that the SW measurement indicates that the L channel acoustic timing reference was not activated. Without acoustic timing active, we have no idea of the current timing of the SW. It was active for the L and R main measurements.

[As an aside, it is also better to sweep full-range for all measurements so we can consider the overall SPL level trend when adjusting the XO. That makes it easier to adjust the SW gain to best support the following EQ step.]
 

Test4echo

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Perfect! Thanks for input!

I did actually unhook my Mains when I did the SW sweep. I also noticed I had no Accoustic timing chirp, but didnt figure out how I was supposed to get a chirp from the
L Speaker and run the sweep for the SW without the L Speaker playing the sweep as well....Just learning...

I will run Full Freq sweep next time I can.

Thanks!
 

lexicon

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The sound quality is primarily the result of a smooth SPL response. Phase irregularity is much less important. Phase is a very helpful indicator of why the SPL is behaving as it does. Phase analysis assists in helping to choose the XO frequency and timing that supports a smooth SPL using a minimal amount of EQ. We expect that EQ will be needed in most all cases to optimize the SPL smoothness up to the transition frequency; about 200Hz for small rooms.

Use the option that best meets the objective stated above: Provides a smooth SPL with minimal EQ up to 200 Hz. The 40 Hz XO with the the distributed SW locations does not look as promising as the earlier options if I recall correctly. Dirac may still successfully EQ it however.

I would not think that would be an improvement on the options already found. The SWs would be out of phase over most of their range.

40 Hz is okay if Dirac can successfully EQ it. I personally would not use the 40 Hz XO. I think a 60, 80 or 100 Hz XO would be more appropriate. Are the Dirac predictions of Post-14 realized in actual REW measurements or was there a problem?

There is likely nothing significant to be gained with a 3rd SW given where it can be located.

I may be missing the concerns you are having. My take on this setup is that Dirac BM successfully mitigated a major L vs R phase issue that cannot be corrected using standard PEQ filters. Thus Dirac is the logical choice to use. I would tend to follow its recommended settings or maybe also try 60 or 80 Hz XO as well as the 100 Hz XO to see which one results in the best REW measurements. If the measurements look good and there is still a sound quality issue, I suggest that adjustments to the house curve in Dirac would be the first thing to try. The Post-14 Dirac settings do not call for any of the normal house curve rolloff for the higher frequencies, but it looks like you can easily adjust it as needed to suit your preference.
1. 40hz V 60hz Xover after Dirac Bass Control (both subs + both mains)
2. 1 sub stacked V 2 subs in separate locations after Dirac Bass Control (both subs + both mains)

40hz Xover sounds noticeably grippier/tighter to me.

There is a boost applied to the (sealed port) JBLs from 40-100 which makes them more punchy.

Seems that DBC has done as billed and that 40hz with separately located subs wins out. The big room dip between 110hz and 140hz has been reduced in width presuamably helped by the subs being separate.


40 v 60 mains Xover.PNG


40hz v 60hz Xovers with subs in separate locations

2 subs stacked v separate at 40 hz Xover.PNG


40hz Xover Stacked subs (Red) in one location v 40hz Xover with subs in separate locations
 
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Test4echo

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Quick Question for Everyone,

Pardon my newbness....How do I use the Accoustic time alignment for my SW when I have unplugged my Mains for the SW sweep?

I don't want my L or R playing the sweep at the same time as the SW correct? So, how does that work?

Edit...figured it out.
 
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jtalden

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Seems that DBC has done as billed and that 40hz with separately located subs wins out. The big room dip between 110hz and 140hz has been reduced in width presuamably helped by the subs being separate.
:T
 

lexicon

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Do you know anything about reading the impulse graphs?
If I take REW readings of both subs on their own with a TR, then average them together using Trace Arithmetic in ALL SPL and then change the tab to impulse and select the average trace, will it give me the combined impulse response of both subs?
 

jtalden

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Yes, that will provide the average when needed.

Normally we just sum them instead of averaging them with Trace Arithmetic to show the combined SPL level we will get if we just measured them together. That is what the alignment tool does using the 'Aligned copy'.

There will be a 6 dB offset between the average SPL and the summed SPL, so another way to get an average of 2 SW when its needed is to take the alignment tool 'Aligned copy' result and reduce its SPL level by 6 dB.
 

lexicon

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Ok many thanks - so with the attached what am I looking for to get great timing? What makes this better or worse?!


Average Impulse.PNG
 

jtalden

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Better or worse sound quality is primarily a function of the SPL chart. The other charts can be helpful in understanding more subtle issues. This particular chart is not helpful for me.

??, I think I missed the context of the question in Post-84 though. Are you referring to comments made elsewhere concerning using the impulse to aid time alignment? It can be helpful when used as an overlay chart in the '%' mode to confirm that the chosen delay timing between 2 drivers doesn't stray too far from from each other.
 

lexicon

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Better or worse sound quality is primarily a function of the SPL chart. The other charts can be helpful in understanding more subtle issues. This particular chart is not helpful for me.

??, I think I missed the context of the question in Post-84 though. Are you referring to comments made elsewhere concerning using the impulse to aid time alignment? It can be helpful when used as an overlay chart in the '%' mode to confirm that the chosen delay timing between 2 drivers doesn't stray too far from from each other.
From what I understand from this - https://www.soundoctor.com/whitepapers/subs.htm as regards sub/sat and sub/sub integration, getting the impulse timing correct is vital.

I (and many others) have been following the advice in this white paper as regards ports and timings and it seems to make a massive difference to achieving tight bass and a clean clear soundfield.

If you were to purchase a JL Audio sub in the UK, the distributor will come out and adjust the calculated delays arrived at by Dirac in accordance with these guidelines. From my experience this offers a big improvement.

The problem is that these changes often do not result in a flat SPL chart at below Xover frequencies.

So, whether or not one considers that there may be something in this hypothesis, I am trying to understand what a great looking impulse graph should look like to assist me in explaining what I am hearing.
 
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jtalden

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We can't look at an impulse chart and say much of anything important regarding sound quality. We definitely cannot confirm if the XO timing is favorable. The impulse measurement contains all the information needed to create the other charts. That is why it is emphasized as most important. It is the other charts; SPL, phase, GD, RT60, waterfall and spectrogram that allow us to view more helpful information contained within the impulse response data. The combination of these charts is the better indicator of favorable sound quality.

The linked paper has a lot of helpful general background information about XO timing issues. It also then provides a lot misleading information. I may have missed something in my scan, but did not find a reliable method of measuring and analyzing data to verify favorable XO timing. That is what we are providing with the REW alignment tool. This was possible to do in REW and other programs previously. The new tool just makes it easier for DIY hobbyist to do. It is still difficult for the casual user. It takes a dedicated effort to feel comfortable using it. Automated setup programs in AVRs or other software programs are common and normally provide favorable XO timing result along with XO frequency, EQ and gain settings as well. I assume many of the reported negative results with these programs are as a result of difficulties dealing with particular room issues. The room setup often makes it very difficult to decide which timing setting should be used. Some of the automated programs may not be as robust as others when dealing with these issues.

You mentioned the material regarding vented vs ported speakers in the link. The comments there are particularly misleading. It is highlighting vented differences and embellishing them as major negative effects. I suggest a more balanced analyses would serve us better. There is no clear superiority for either of them. The suggested issues with polarity and normal phase rotation are also misleading and worth noting. These subjects can be relatively easily tested by those who want to confirm their impact for themselves.
 

lexicon

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We can't look at an impulse chart and say much of anything important regarding sound quality. We definitely cannot confirm if the XO timing is favorable. The impulse measurement contains all the information needed to create the other charts. That is why it is emphasized as most important. It is the other charts; SPL, phase, GD, RT60, waterfall and spectrogram that allow us to view more helpful information contained within the impulse response data. The combination of these charts is the better indicator of favorable sound quality.

The linked paper has a lot of helpful general background information about XO timing issues. It also then provides a lot misleading information. I may have missed something in my scan, but did not find a reliable method of measuring and analyzing data to verify favorable XO timing. That is what we are providing with the REW alignment tool. This was possible to do in REW and other programs previously. The new tool just makes it easier for DIY hobbyist to do. It is still difficult for the casual user. It takes a dedicated effort to feel comfortable using it. Automated setup programs in AVRs or other software programs are common and normally provide favorable XO timing result along with XO frequency, EQ and gain settings as well. I assume many of the reported negative results with these programs are as a result of difficulties dealing with particular room issues. The room setup often makes it very difficult to decide which timing setting should be used. Some of the automated programs may not be as robust as others when dealing with these issues.

You mentioned the material regarding vented vs ported speakers in the link. The comments there are particularly misleading. It is highlighting vented differences and embellishing them as major negative effects. I suggest a more balanced analyses would serve us better. There is no clear superiority for either of them. The suggested issues with polarity and normal phase rotation are also misleading and worth noting. These subjects can be relatively easily tested by those who want to confirm their impact for themselves.
Thank you again for your help with this.

Ok - so I am reading that we cannot rely on the impulse graphs to tell us anything useful here so duly discounted.

" Automated setup programs in AVRs or other software programs are common and normally provide favorable XO timing result along with XO frequency, EQ and gain settings as well. I assume many of the reported negative results with these programs are as a result of difficulties dealing with particular room issues. The room setup often makes it very difficult to decide which timing setting should be used. Some of the automated programs may not be as robust as others when dealing with these issues."

This is the crux of the matter here I agree. We are relying on these automated programs to provide optimal results that translate into the best possible listening experience but we cannot IMHO assume that they are always making the right choices.

Let me try this from another angle.

Attached are some new measurements of the two subs taken exactly from my listening postion. The first measurement of Sub1 is "at base" as the delay on that is 0ms. Crossovers set at highest possible 200hz no EQ.

I have then measured Sub2 first at 2ms delay and then at 16ms delay. (Interestingly on my latest calibration attempt Dirac set it at just 1.08ms!)

Then I averaged the responses using your Trace Arithmetic A+B/2 and compared them.

The 16ms delay average is showing a load more bass up to the Xover frequency that would then (afterwards) be set for the mains at 40hz. Sure, it may not be as level overall and there is a dip at 56 that isn't on the 2ms average but that's above the Xover frequency. The mains may be able to help with that? Overall it's not looking too bad?

I'll leave you to look at the phase graphs..... :cool:

On the basis that this delay between the two subs could be "fixed" and then Dirac be run on top of this to bring the mains in to the equation and EQ the rest, I am wondering whether fixing the 16ms delay between Sub1 & Sub 2 would be the better place to start?
 

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jtalden

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Ok - so I am reading that we cannot rely on the impulse graphs to tell us anything useful here so duly discounted.
Not from the chart you posted...
Based on the overlay impulse chart the difference in timing between the 2 SWs is approximately 3.5 ms. Based on the overlay phase chart the difference in timing between the 2 SWs is approximately 5 ms when using a heavy FDW to see the direct sound.
Attached are some new measurements of the two subs taken exactly from my listening postion. The first measurement of Sub1 is "at base" as the delay on that is 0ms. Crossovers set at highest possible 200hz no EQ.

I have then measured Sub2 first at 2ms delay and then at 16ms delay. (Interestingly on my latest calibration attempt Dirac set it at just 1.08ms!)

Then I averaged the responses using your Trace Arithmetic A+B/2 and compared them.

The 16ms delay average is showing a load more bass up to the Xover frequency that would then (afterwards) be set for the mains at 40hz. Sure, it may not be as level overall and there is a dip at 56 that isn't on the 2ms average but that's above the Xover frequency. The mains may be able to help with that? Overall it's not looking too bad?
16 ms is likely to work just fine. There is good SPL support and the phase tracks very closely without a FDW. The tradeoff to other timing options is the larger 10 dB peak at 40 Hz that will require more EQ to match a typical house curve. There is also a little additional group delay across the SW range. Neither of these is likely to be a significant issue.
The option in the 3.5-5.0 ms range will better match the direct sound timing and provide closer direct sound phase tracking and thus a little less group delay. The EQ would be a little less aggressive.
On the basis that this delay between the two subs could be "fixed" and then Dirac be run on top of this to bring the mains in to the equation and EQ the rest, I am wondering whether fixing the 16ms delay between Sub1 & Sub 2 would be the better place to start?
There are tradeoff to each setting. Some setups do not have a clear setting that works best for measurements. This is one of those. The tradeoff here are; direct sound phase tracking vs LP phase tracking, EQ favorability and group delay. Fortunately these settings appear to be reasonable candidates.

We backed up and are now only discussing the SW integration and not the integration of the mains. The bottom line is still to either select the SW delay setting that seems best to you or evaluate 2 or 3 of them. Dirac may handle one of them better when it sets delay time for the SWs XO and applies EQ. The overall SPL of the FL and FR channels with Dirac applied is still the best overall measurement indicator of sound quality. There is no way to forecast which setting you will prefer. you may want to listen to options and pick the one that sounds best to you.

SPL Comparison:
31934


Impulse Comparison:
31938
 

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lexicon

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Many thanks - very interesting indeed.

I have tried adjusting the sub delays post dirac using my old favourite delay between sub1 and mains and maintaining a 16ms delay beween sub 1 and 2. To my ears the bass sounds much "tighter" and the soundfield clearer but of course the ideal target flat SPL graph is a thing of the past as I have effectively made it FUBAR by messing with things after Dirac.

The problem I have is that I can find no way to fix my own preferred delays between the two subs because Dirac just overides anything you set when it does its thing.

The next thing to try I think is a Minidsp HD that will allow me to EQ and delay the subs and then present them to Dirac as a fait be complit on one channel. All :cool: Dirac then has to do is set the delay correctly between that one channel and the mains before it tidies the rest of the EQ.

I've ordered the Minidsp HD so I will see what I can do with that! Could take me some time to check all those delays as each Dirac calibration can take a while to do. Would be great to be able to end up with a really grippy bass + a relatively flat SPL at my MLP for sure.
 
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The next thing to try I think is a Minidsp HD that will allow me to EQ and delay the subs and then present them to Dirac as a fait be complit on one channel. All :cool: Dirac then has to do is set the delay correctly between that one channel and the mains before it tidies the rest of the EQ.
This is what I must do because the AVR does not support Dirac Live Bass Management (or whatever its name is today :)).
I first first set each subwoofer SPL at MLP to the same value and check that the combined SPL of the sub channel is within a couple of dB of a main channel so Dirac doesn't set large trim differences.
Then used REW alignment tool to find relative delays to enter to MiniDSP.
Then, because my AVR does NOT support changing any delays, added 5ms delay to each MiniDSP output channel. (in case a delay decrease was required post Dirac)
Ran Dirac
Measured Dirac's results with REW and used REW alignment tool to check mains/subwoofer alignment only to find that Dirac had hit the delay spot on. YMMV
 

lexicon

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This is what I must do because the AVR does not support Dirac Live Bass Management (or whatever its name is today :)).
I first first set each subwoofer SPL at MLP to the same value and check that the combined SPL of the sub channel is within a couple of dB of a main channel so Dirac doesn't set large trim differences.
Then used REW alignment tool to find relative delays to enter to MiniDSP.
Then, because my AVR does NOT support changing any delays, added 5ms delay to each MiniDSP output channel. (in case a delay decrease was required post Dirac)
Ran Dirac
Measured Dirac's results with REW and used REW alignment tool to check mains/subwoofer alignment only to find that Dirac had hit the delay spot on. YMMV
Sounds good. But I think if you change any delay post dirac you are likely to find that the work it has done on the EQ is compromised to some degree. I’d take nice tight powerful bass over a perfect flat Eq though to be honest.
 

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Sounds good. But I think if you change any delay post dirac you are likely to find that the work it has done on the EQ is compromised to some degree
Changing the relative sub to sub delay post Dirac would indeed cause a problem but is not what I was referring to. I was referring to sub group to mains alignment.
 

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Hi,

I have been evaluating two configurations
1 - XO 90 Hz - Main Delay 0 - Sub Delay 1.5ms Inverted
2 - XO 90 Hz - Main Delay 3.5ms - Sub Delay 0.0ms

Whilst listening to music I can't distinguish between the two.

Today, I have runs some sweeps with Left+ Right Main and Left+Right Sub.

Questions:
1 - Is running a sweep of Left+ Right Main and Left+Right Sub correct way to evaluate the measured response at the crossover Frequency ?

2 - It would seen I have a null rather than a flat response at my 90Hz Crossover Frequency? Perhaps I have chosen the wrong crossover frequency ?

32120
 

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jtalden

Senior Member
Joined
May 22, 2017
Messages
426
Location
Arizona, USA
My AV System  
Preamp, Processor or Receiver
Marantz AV7705 Pre/Pro
Main Amp
Rotel RMB-1066 6 chnl P-amp x 2
Additional Amp
Behringer DCX2496 x 2
Universal / Blu-ray / CD Player
OPPO BDP-103 Universal Player
Front Speakers
DIY SEAS H1456/H1212 Spkr x 5
Subwoofers
DIY JBL 2235H 15" SW x 2
Video Display Device
JVC DLA-X790R
Screen
Da-Lite Da-Snap 39105V - 92"
I have been evaluating two configurations
1 - XO 90 Hz - Main Delay 0 - Sub Delay 1.5ms Inverted
2 - XO 90 Hz - Main Delay 3.5ms - Sub Delay 0.0ms
Questions:
1 - Is running a sweep of Left+ Right Main and Left+Right Sub correct way to evaluate the measured response at the crossover Frequency ?
Yes, I analyze L+R mains vs SWs in the REW alignment tool. It results in a compromise timing alignment between the L and R channels. I also then look at each channel separately to see how much difference there is between them. We want them to be similar, but the room may have other ideas.
If there is a lot of difference between them, I sometimes raise the XO range to let the SWs provide more of that frequency range to help even out the 2 channels. You are already at 90 Hz and most people do not like to go much higher than that, but it might well be a good tradeoff if the 2 channels are very different.
2 - It would seen I have a null rather than a flat response at my 90Hz Crossover Frequency? Perhaps I have chosen the wrong crossover frequency ?
If you used the alignment tool you would have seen that was going to happen. Was there no other delay setting that looked better for SPL support? If not, it could be a strong room effect and there may be no way to avoid that null without LP or speaker position changes.
 

Harbord

New Member
Joined
May 9, 2020
Messages
5
I performed a quick Crossover Frequency Analysis at 90Hz, 95Hz, 100Hz and 105Hz with REW Alignment Tool. I have decided to keep my Crossover @ 90Hz but applied a sub delay of 3.5ms with NO inversion. Result is 90Hz null is gone.

The graph below shows:
Blue: Both Subs (XO 90Hz No Delay)
Red: Left Main (XO 90Hz No Delay)
Green: Left Main with Both Subs (XO 90Hz with Sub Delay 3.5ms)

32139


Many thanks for all your help. It have been great to have you assistance on my journey.

Many thanks to the REW software development team; being able to measure and visualise my loudspeakers and subwoofers within my room is invaluable.
 
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