Trying to align and Eq 4 subwoofers with REW, Umik1 and Minidsp 2by 4 HD. Is this output what I should expect?

warek

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Hi all

Thanks for the forum. I have 4 identical 18 inch sealed subwoofers with Hypex DS8 plate amps. The room 5.3*4.5 metres with 2.7 metres ceiling. This room is used for watching movies and the subs have been individually measured, moved around, remeasured and then taken a combined measurement. The subs are basically close to 4 corners of the room. I probably do not need 4 subwoofers in this room but they came from a different house and a much larger movie room that was lacking bass. I have not tried only EQ 1-2 subwoofers.

I am trying to achieve more bass below 30 hz.. The subs designer has modelled the subs as one sub can produce 120dB of output about 25Hz and at 20-15hz and below it can still produce 110dB

I have tried time aligning the subs in REW and have tried them in all combination over the last few 3-4 months. Eg 1234, 4321, 3241, 3421. Time alignment gives me a better aligned response with lower bass and removes some dips than simply playing all 4 subs together. It gives me delays on some subs and suggest invert polarity on 1 or 2 subs depending on which order I start with. My concern is that when I then try and Eq the aligned response and import into the file into minidsp 2*4hd and measure the actual response is not close to the predicted response. I also find that when I enter the time delay and inverse polarity from the aligned response into the minidsp that the actual response is worse than if I leave the delays all blank and ignore the suggested inverse.

I get a reasonable result if I try and have a 2db room/house curve and a target level around 81 hz. If I try and add a larger 3,4,5,6 db house curve the actual results are much more ragged.
4 subs non aligned and aligned sum.jpg
actual Eq results.jpg


I think I am making progress, and this is the best results I have so far. I am now listening to a few action movies with good bass soundtracks.
Is this the kind of result that I would expect? These are non smoothed results. In the image of the actual results Sweep 9 config 1 has a low shelf at 35 hz with 4 db gain and a Q of 1.0 entered on the input side of the MInidsp 2by4HD. Sweep 6 has a 20 HZ peak filter 5 db gain entered into the minidsp input side.
One thing I am finding hard to follow is that I have a 105 db output at 42 HZ before EQ and EQ is applying 15 Db cut to this peak. I have tried to manually reduce the amount of cut at this frequency but without great success in actual results

I have not spend much time adjusting subs with mains but have mains crossover set at 100 hz, and the subs are running full range. The mains are two way speakers with 8 inch bass driver
I do not have any experience trying to phase align the subwoofers using impulse overlays and have not looked at this feature. is this an important thing I should do?

Thanks for any suggestions?
Have a good day
Kevin
 

warek

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Thanks, I have watched this video several times. Either I am missing something or is my result to be expected?
 

JStewart

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My concern is that when I then try and Eq the aligned response and import into the file into minidsp 2*4hd and measure the actual response is not close to the predicted response.

You'll need to overcome this first. With REW, the measured will be identical to predicted.
 

hemiutut

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Thanks, I have watched this video several times. Either I am missing something or is my result to be expected?
Are the 4 18" subwoofers placed in the best possible locations? I say this because between 15-20 Hz they should give more gain. You can always try another filter at 18 Hz with +8-9 dB for those frequencies. 4 18" subs is a lot, but for the rest I see a very coherent frequency response, normal with 4 well-optimized subwoofers
 

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Hi all
I do not have any experience trying to phase align the subwoofers using impulse overlays and have not looked at this feature. is this an important thing I should do?

Thanks for any suggestions?
Have a good day
Kevin

I am just an amteur, but with my 2 subs it appears that phase aligned them was the most important part to get them play well together and @jtalden gave me so much help. Many info here among others:


 
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warek

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Thanks for the links, I have made some progress and found more success with not using REW time alignment menu , instead I followed the you tube video home theatre gamer minidsp part 2 to set delays and phase. I then used REW to eq and produce file for export into the dsp.
latest results.jpg
 

warek

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Thanks for the replies and for looking at my posts. I will be on an extended holiday and will not be able to do any more with REW and Minidsp until October. Hope to get some more tips at that time and learn some more about REW
 

jtalden

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Hi warek,
Regarding your PM:
I'm not sure if I can help much. A full remote setup is not possible. The chosen room placement of the 4 SWs and the LP has a large impact on how smooth the raw SPL will be. The SPL roll-off below 30 Hz and the peak at 40 Hz in your first chart is due to these positioning choices. A random placement of SWs can be helpful in many cases. Most of us have little or no opportunity to move SWs and LP around though. The first chart shows it currently requires a lot of EQ to reach a typical house curve, but you achieved reasonably good results in the second chart. The post 7 chart is much better if you can accept the roll-off below 30 Hz.

Regarding SW Phase:
We want a smooth SPL response to match our chosen house curve. We can just adjust SW delays to account for the difference in distances of each SW to the LP. This works to time align the direct sound phase of SWs. However, aligning the phase of multiple SWs is often not the best setting for favorable raw SPL. A smoother raw SPL is often possible when the phase is not closely aligned. That opens the possibility of finding a combination of delays and/or polarity reversal of one or more SWs to achieve a smoother response. Doing this manually with 4 SWs can be a very time-consuming effort in REW. There is a freeware program called Multi-Sub Optimizer (MSO) that can do this automatically. If MSO greatly improves the raw response, it is helpful in reducing the amount of EQ needed. Less EQ is better in several ways, but I don't know how much practical difference it makes if the final SPL response is similar after EQ.

Any remote help with SW delay/polarity setting needs to be based on accurately timed REW measurements of each SW after the final SW/LP positions are chosen. If you are not using MSO, I can take a look at the 4 measurements to see if I can find a better delay/polarity setting for RAW SPL than you have found.

Once the SW group EQ is finalized, the timing of the SWs to the main speakers can be confirmed using the REW alignment tool. If you have a processor with an automated XO setup routine that often works fine. If you like I can confirm the reasonableness of the result if given the needed measurements. If you need to do this manually, I can help with that as well.

Are you confident yet in using the acoustic timing feature in REW? That is a prerequisite. If so, you may want to start with more information about your setup/equipment and post the .mdat of the 4 raw timed SW measurements with any questions or concerns you have.
 
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warek

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Hi All

I think I am getting closer. I have uploaded a zip file of front, left and right and centre speaker REW sweeps with acoustic timing reference. I have also sweep each of the 4 subs, 18 inch sealed identical units.

Subs are connected to 1 mono output of AVR, All Eq is off and processing is set to through. I was not sure of what frequency range to use for the REW sub sweeps, but chose 15 to 150, although I have sweeps of 15-200 I did not include these to reduce file size.

This is currently a 5.1 home cinema system, but will become a 7.1 with 4 overhead Atmos speakers in the future.

I made previous sweeps experimenting with sub and mains crossover and have set current speakers XO at 100 HZ
I have time aligned the 4 sub results and then EQ in REW and loaded the file into minidsp and tested results. I am not sure if this is as good in terms of distortion, waterfall, spectrograph, decays. I have attached two previous results Config 2 and Config 4, that I did with manual delays and without using ATR. I am not sure if there is much to choose between but welcome any feedback and the latest sub result

Would appreciate any feedback on my result and realise that this is only the start and will align subs with the mains and centre once I get some feedback on sub alignment in case there is more work I need to do with the subs alignment.

Thanks for any looking and any feedback.

Have a good day

Kevin
 

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jtalden

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I was not able to find any better raw timing than you have found for the 4 SWs. Good Job. Next is to EQ the 4 subs and you already provided 3 options. We don't need to look at all 3 as they are pretty similar so just pick the one you prefer.

The next step is to determine the timing between the SWgroup and the mains. You can just run AVR automated setup routine if you have one. Then measure L, R, C channels. If the SPL response in the XO range is smooth the job is done. If it looks poor we can confirm if better timing is possible.

To do it manually or to confirm a poor result the following measurements are needed:

Setup:
  • Choose the XO frequency and activate it in the AVR (main speakers set to small)
  • Mic at LP
  • All SWs active and preferred EQ active.
  • REW Acoustic timing active
  • Sweep full-range for all 4 measurements (10-20k Hz for example)
Measurements:
  1. L (alone)
  2. R (alone)
  3. C (alone)
  4. SWgroup (alone)
Only these 4 measurements are needed.
 

hemiutut

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Hi warek
Do you have any open thread where your room can be see?
Does it have acoustic treatment?

written with translator

Greetings
 

warek

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I was not able to find any better raw timing than you have found for the 4 SWs. Good Job. Next is to EQ the 4 subs and you already provided 3 options. We don't need to look at all 3 as they are pretty similar so just pick the one you prefer.

The next step is to determine the timing between the SWgroup and the mains. You can just run AVR automated setup routine if you have one. Then measure L, R, C channels. If the SPL response in the XO range is smooth the job is done. If it looks poor we can confirm if better timing is possible.

To do it manually or to confirm a poor result the following measurements are needed:

Setup:
  • Choose the XO frequency and activate it in the AVR (main speakers set to small)
  • Mic at LP
  • All SWs active and preferred EQ active.
  • REW Acoustic timing active
  • Sweep full-range for all 4 measurements (10-20k Hz for example)
Measurements:
  1. L (alone)
  2. R (alone)
  3. C (alone)
  4. SWgroup (alone)
Only these 4 measurements are needed.

Thanks jtalden

A question re levels, Before I started the subwoofer sweeps, I ran each sub individually and set its output to give a level of 75 db Slow C weighed at the LP. Is this too high considering I have 4 18 subs in a room that is 5.3m * 4m *2.7 M High. when I aligned and Eq subwoofers I finished with a subwoofer curve after EQ 10 db lope from 95 DB at 40hz finishing at 86 Db at crossover point of 100 hz, confirmed by entering into the minidsp and doing several sweeps. The individual Sweeps from the Right and left mains have a level of 66 db at 100 hz and averaging about 75 db from 500 hz to 4K HZ. Nearly a 20 db difference in output at the crossover frequency.

I have read a few things that suggest the subwoofers EQ response should finish at about 75 db at the crossover point for mains alignment. Do you agree with this level? If true rather that EQ all of my sub output and waste that power, am I best to reduce all sub power levels to 65-70 DB and remeasure and produce new sub EQ finished at around 75 db. I do find that when I have all subs on at current level on most movies I will reduce the AVR level for subs from 0 to -4 -5 DB, unless it is a major action movie, rather than just turn off 2 out of the 4 subs as I believe they work better as a group to smooth the response. With my AVR output level at -25 I can hit bass peaks of 101 Db on action movies at the LP. Movies such as the opening scene from the Greatest Showman.

Turn down my subs or should I rerun the sweeps for Left and Right mains at a higher level?

Lastly I have been watching a video from Home theatre gamer on Youtube about using the REW time alignment window to align the Eq sub output with the front Lft and Right speakers as a pair and he used align phase slopes at cursor, to get the delay. What do you think of this method and his using both mains at the same time. He then continues to adjust centre with subwoofers at crossover point using same method ?

Thanks very much for your earlier advice

Have a good day
Kevin







in that case I have options to turn down all su
 

warek

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Hi warek
Do you have any open thread where your room can be see?
Does it have acoustic treatment?

written with translator

Greetings
Hi

I do not have a plan on line, but is is a rectangular room about 5.3 m *4.0 M with ceiling about 2.7M

Currently it has not acoustic treatment except carpet, curtains and furniture.

Thanks for your interest
 

jtalden

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A question re levels...

I have been watching a video from Home theatre gamer on Youtube about using the REW time alignment ...

Regarding SW levels:
The first step, to align the 4 SW into a group, we can start using any reasonable SPL level. Your target of 75 dB for each SW is fine. This step is independent of mains integration. We are only looking at the SW interactions. We can look at all variables available to achieve a favorable SWgroup response including SW locations, LP locations, room treatment, individual SW levels (they don't need to be at the same level), individual SW polarity, and timing. I only looked at the timing and polarity portion of this process. As I hinted the current SW locations are likely to be the primary reason for the problematic 20-50 Hz region. The similarity in the raw SPL responses is not helpful. There are likely different SW locations that would result in more dissimilar SPL responses and that would be helpful in smoothing the overall raw SWgroup. While location changes may be advantageous, your EQed results are reasonably good using the current locations.

Regarding manual WSgroup to mains levels and timing:
The SWgroup and mains SPL levels should be adjusted to fall along the house curve. A common target for the house curve setting is 75 dB. This also can be done within REW by just be offsetting the SPL levels of measurements as needed. It works just as well to determine the timing and provides the correct predicted results. The final levels still need to be adjusted accordingly at either before the 4 measurements requested here or after the timing is correction is established. There is no impact on the final result either way. The REW calculated IR (SPL, phase, GD, Step, etc.) will be identical with final confirmation measurements. So, if you already have the SWgroup measured with EQ and XO active and the mains include the XO also we can just offset the levels in REW as needed to your house curve.

If the mains are still to be manually EQed they are often set to fall a little above the house curve so most of the EQ filters will mostly be cutting the mains peaks rather than boosting the sags. I normally have them setup with an Initial EQ so all 4 measurements are just adjusted to fall on house curve.

Like the referenced video, I also normally set SWgroup timing to match with the L+R pair because it is easier to find a favorable compromise timing as often the L and R differ significantly in their most favorable timing with the SWgroup. This is done using the measurements suggested here by first vector averaging the L, R together into L+Raverage prior to using the alignment tool. The result is the same as measuring the L+R and reducing the level by 6 dB. The advantage is that there is a minimum of measurements, and we can also use the alignment tool to see the resulting impact of the chosen timing in the L, R channels individually as well as together.

There are now several good REW alignment tool videos using slightly different process steps that can be followed for good results. I've seen 2 or three of them but chose to use the process I developed.

PS: I must emphasize that the SWgroup and mains measurement needs to include the impact of the AVR XO so the SWgroup needs to measured using either L or R channel with that main speaker disconnected. Using the LFE channel will provide erroneous timing.
 

warek

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Hi Jtalden

Following your suggestion that sub positions may be a limitation. I looked at previous output of sub 4 and decided it was not contributing much, so I am moving 1 and 4 around in hope I can get more bass in 15-30 hz region and less at peak 40-50 hz. At this stage results are a WIP but time alignment has fallen apart and actual results are not close to predicted. The ATR is inconsistent on multiple sweeps of same sub.
I have given up for the day.

Will work on it tomorrow and do a manual sub alignment as well.

Regards

Kevin
 

jtalden

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Use the impulse overlay chart to determine if ATR is working correctly. Repeated measurements of the same SW should fall on top of each other. The delays reported in the SW measurement notes may vary so they are not the best indicator of SW timing repeatability.
If the overlay chart shows variation post the mdat here so I can see the problem.
 

warek

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Use the impulse overlay chart to determine if ATR is working correctly. Repeated measurements of the same SW should fall on top of each other. The delays reported in the SW measurement notes may vary so they are not the best indicator of SW timing repeatability.
If the overlay chart shows variation post the mdat here so I can see the problem.
Hi Jtalden

I have moves some subs around and now have sub 1 and 4 at front of room under TV between main left and main right with centre speaker between the two subs. Sub 2 is on next furthest away on side wall and sub 3 is on rear wall closest to main listening position..

I have tried the time alignment feature starting with 4 with 1 then adding 2 and finally adding sub 3. I have attached individual results of each sub all subs and one example of a config after I entered the delays and polarity into the minidsp, swept that and then used that output for the EQ and saved that result into the minidsp as Config 1

I have a sweep of the main left and main right. I tried a few examples of combining the config 1 with the main left and right, but have a large dip at the 100 hz crossover point I have used for mains and for the individual sub sweeps. I did not save any of these as not being useful

Question, before I try mains and subs alignment should I now make multiple sweeps of mains at different XO frequencies and do I need to sweep the 4 subs again at each new XO and then realign re eq, or can I just run config 1 with different XO and save each one under a new name eg config 1 XO 80, config 1 XO, config 1 XO 110 etc

If possible I would appreciate if you could check my results of the individual subs combined under time alignment before I go any further? I have uploaded the latest file

Thanks for taking the time to check this for me

Regards

Kevin
 

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jtalden

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SW thoughts:
Well, I was expecting different SW locations to improve the sag below 50 Hz and reduce or shift the large boost at 40 Hz. The new positions chosen were no particular help, however. You can try moving the LP to see if that is a major improvement. Stacking 2 of the SWs may help if this is a floor to ceiling mode issue. At some point though we all just decide to stop experimenting and accept the best setup we found. Your EQed responses look pretty favorable unless you want to shake the room. With 4 large SWs there shouldn't be an issue with EQ boosting that 20 Hz range quite a bit. Although, one off the wall thought is that if these are custom ported SWs then maybe the ports have been tuned to 40 Hz. This could easily explain the boost there and the sag below. If so, just sealing the ports may then help a lot to reduce that peak and improve the low end. We do not want to apply EQ boost below the tuning frequency of ported SWs.

Mains Thoughts:
It appears the mic was not centered well between the FL and FR. It appears to be about 2 ft off center as there is a 4 ft difference in the impulse overlay. Possibly you still are not getting repeatability using the REW acoustic timing?
55898


I see also that the mains have a similar null to the SWs at around 115-120 Hz Thus moving the XO higher or lower is not likely to help that null. I think a lower XO will not help SPL because the SPL irregularity is very high in the mains at lower frequencies. You are probably better off to stay at 100 Hz.

There is also a lot of early reflections/room interaction in the XO range so there is not a clear best timing in terms of SPL response in the XO range. I did however align the FL and FR to each other and then determine the best SW timing I could find just to see the result. I also lowered the SWs level by 5 dB to look a little better to my idea of a house curve and included the result below:
55899
 

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warek

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SW thoughts:
Well, I was expecting different SW locations to improve the sag below 50 Hz and reduce or shift the large boost at 40 Hz. The new positions chosen were no particular help, however. You can try moving the LP to see if that is a major improvement. Stacking 2 of the SWs may help if this is a floor to ceiling mode issue. At some point though we all just decide to stop experimenting and accept the best setup we found. Your EQed responses look pretty favorable unless you want to shake the room. With 4 large SWs there shouldn't be an issue with EQ boosting that 20 Hz range quite a bit. Although, one off the wall thought is that if these are custom ported SWs then maybe the ports have been tuned to 40 Hz. This could easily explain the boost there and the sag below. If so, just sealing the ports may then help a lot to reduce that peak and improve the low end. We do not want to apply EQ boost below the tuning frequency of ported SWs.

Mains Thoughts:
It appears the mic was not centered well between the FL and FR. It appears to be about 2 ft off center as there is a 4 ft difference in the impulse overlay. Possibly you still are not getting repeatability using the REW acoustic timing?
View attachment 55898

I see also that the mains have a similar null to the SWs at around 115-120 Hz Thus moving the XO higher or lower is not likely to help that null. I think a lower XO will not help SPL because the SPL irregularity is very high in the mains at lower frequencies. You are probably better off to stay at 100 Hz.

There is also a lot of early reflections/room interaction in the XO range so there is not a clear best timing in terms of SPL response in the XO range. I did however align the FL and FR to each other and then determine the best SW timing I could find just to see the result. I also lowered the SWs level by 5 dB to look a little better to my idea of a house curve and included the result below:
View attachment 55899
Hi Jtalden

Thanks for your efforts, I am learning from you.
I will stop asking you questions soon, although I do appreciate your patience and knowledge.
Q1 if I want to shake the room is it sensible to go to my AVR processor which has individual sub PEQ with 4 bands and boost the bottom band, assuming it has more headroom than a MINIDSP 2 by 4 HD?
Q2 When you align mains with subs it says invert subs polarity, as I have 4 subs aligned together and 1 is already inverted is the best way to do this just go to AVR and under setup select subwoofer and change phase?

I dont know if you are interested but I have multiple config from before I moved sub 4 and I ran one of them unchanged , with subs in the new position and the old config has a much shallower dip at 117 and at 144 hz compared to my latest alignments Eq and new config, Attached a copy.
Old config 2 compared to latest config.jpg
This is something I intend to try and tweak and see what improvements I can make.


Regards

Kevin
 

jtalden

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DIY JBL 2235H 15" SW x 2
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JVC DLA-X790R
Screen
Da-Lite Da-Snap 39105V - 92"
Q1 if I want to shake the room is it sensible to go to my AVR processor which has individual sub PEQ with 4 bands and boost the bottom band, assuming it has more headroom than a MINIDSP 2 by 4 HD?
I don't know that it matters which box contains the EQ filters. Either one can probably provide more boost than is advisable to use.
I suggest the actual port tune frequency is confirmed before applying boost down low. The actual frequency often can differ significantly from the design target. EQ at or above port tune frequency is fine. I would tend to do more EQ suppression of the higher range rather than significant boosting of the very low range.
Q2 When you align mains with subs it says invert subs polarity, as I have 4 subs aligned together and 1 is already inverted is the best way to do this just go to AVR and under setup select subwoofer and change phase?
That's fine so long as the AVR "phase" switch is really a polarity switch. It probably is if it only on or off.
 
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