- Thread Starter
- #21
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Manually time-aligning subwoofer(s) to mains - how to
- Thread starter QMuse
- Start date
- Thread Starter
- #23
That looks fine, but I actually need response with XO80 while both, main and sub are playing.
So, you apply XO at 80Hz via AVR to both of them, keep the 2.37m distance for the main and 0.62m for the sub and run 2 sweeps, 40-120Hz and 20-20kHz.
P.S. I don't need measurement for the sub with 1.75 distance
That's exactly what I did. Here, I cleaned it up from the extra measurement.
Measurement 4: Left 2.37 TopSub 0.62 is with the AVR XO @80Hz 40Hz - 120Hz
Measurement 5: Left 2.37 TopSub 0.62 Full is with AVR XO @80Hz 20Hz - 20,000Hz
The null shifted from 100Hz when subwoofer only to about 85Hz when playing both the left speaker and the sub crossed over @80Hz.
Maybe time alignment should be done with Xover engaged but isolated measurements of sub and main
?
ernestcarl
Major Contributor
I tried the time-alignment method using just the "impulse" in REW's overlays window for my 'pseudo' 5.1mch desk setup... and it's pretty straightforward once you get the hang of it.
As suggested, I removed all filters -- *other than for the sub and three 'tone filters' above 1kHz for the surrounds (helps match LSR305s to KH120 fronts).
I had to use a 12dB/oct slope for the speakers since the roll-off looked too steep (target mismatch) if I used the 'normal' 24dB/oct slope. Could be caused by placement and room or something else altogether -- I'm too tired to investigate any further.
As you can see above, the actual crossover is way over 120Hz... not to mention the surrounds miserably fail to even xo properly.
As expected, after switching the sub's phase/delay back from max setting to the default zero or 'no delay', I needed to makes changes to all my delays: the sub had to be inverted to match fronts; also, extra delay had to be added to both the mains and sub to accomodate my late surrounds (much further away).
Impulse for the surrounds looks somewhat more uncontrolled (LSR305 situated right against sidewalls [above head level] with ports plugged). It looks better with the fronts (KH120), but I had to create a vector average since there's a small time difference between left and right and I wanted a clearer picture of just the average.
The step between fronts and surrounds fits nicely, except for the sub which is a little late -- well, kind of expected really.
The phase is confusing, though:
L&R are well aligned to each other, but there's a large gap (~300 degrees) between them and the surrounds & sub. Ironically, while the phase of the sub and surrounds are closer to each other here, the phase of the SL & SR past 1kHz comes apart and cancels quite a bit when playing a mono sweep. With actual music or mch audio tracks, this should not be an issue. And, regardless of the gap, the subwoofer and front mains sum with no noticeable induced cancellation in the FR around the xo region.
Sub's response looks a bit weird right now -- I know, I'll fix it fixe later -- and that huge null at ~70Hz... Yeah, don't worry, it disappears completely when using my desk's 'standing mode'.
Overall delay for all channels is not too bad!
Relevant mdat files are attached if interested.
*BTW, it looks like 512k length is perfectly fine (2M or longer not necessary) if you're just trying to align the impulse.
As suggested, I removed all filters -- *other than for the sub and three 'tone filters' above 1kHz for the surrounds (helps match LSR305s to KH120 fronts).
I had to use a 12dB/oct slope for the speakers since the roll-off looked too steep (target mismatch) if I used the 'normal' 24dB/oct slope. Could be caused by placement and room or something else altogether -- I'm too tired to investigate any further.
As you can see above, the actual crossover is way over 120Hz... not to mention the surrounds miserably fail to even xo properly.
As expected, after switching the sub's phase/delay back from max setting to the default zero or 'no delay', I needed to makes changes to all my delays: the sub had to be inverted to match fronts; also, extra delay had to be added to both the mains and sub to accomodate my late surrounds (much further away).
Impulse for the surrounds looks somewhat more uncontrolled (LSR305 situated right against sidewalls [above head level] with ports plugged). It looks better with the fronts (KH120), but I had to create a vector average since there's a small time difference between left and right and I wanted a clearer picture of just the average.
The step between fronts and surrounds fits nicely, except for the sub which is a little late -- well, kind of expected really.
The phase is confusing, though:
L&R are well aligned to each other, but there's a large gap (~300 degrees) between them and the surrounds & sub. Ironically, while the phase of the sub and surrounds are closer to each other here, the phase of the SL & SR past 1kHz comes apart and cancels quite a bit when playing a mono sweep. With actual music or mch audio tracks, this should not be an issue. And, regardless of the gap, the subwoofer and front mains sum with no noticeable induced cancellation in the FR around the xo region.
Sub's response looks a bit weird right now -- I know, I'll fix it fixe later -- and that huge null at ~70Hz... Yeah, don't worry, it disappears completely when using my desk's 'standing mode'.
Overall delay for all channels is not too bad!
Relevant mdat files are attached if interested.
*BTW, it looks like 512k length is perfectly fine (2M or longer not necessary) if you're just trying to align the impulse.
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ernestcarl
Major Contributor
Ah... I forgot to apply FDW! It seems to clear up the weird gap seen in the phase response:
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- Thread Starter
- #27
That's exactly what I did. Here, I cleaned it up from the extra measurement.
Measurement 4: Left 2.37 TopSub 0.62 is with the AVR XO @80Hz 40Hz - 120Hz
Measurement 5: Left 2.37 TopSub 0.62 Full is with AVR XO @80Hz 20Hz - 20,000Hz
The null shifted from 100Hz when subwoofer only to about 85Hz when playing both the left speaker and the sub crossed over @80Hz.
Maybe time alignment should be done with Xover engaged but isolated measurements of sub and main
Nope, null didn't shift at all. Everything looks fine, phase is smooth, no peak in GD and sub and main response summed nicely.
Here's the initial response of your sub (gree) and main (blue) when they were both set to 2.37 distance combined with your measurement 5 (red).
As you can see green and blue responses summed as they should around 80Hz but the null around 80Hz existed in both, sub and main's response, so it stayed there.
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Very cool, thank you again!
BTW, I went ahead and did the extra credit exercise -- I tried to align my other sub BSub to the TopSub (which is already aligned with the Left speaker). I came up with a distance of 3.75 where both subs showed a match in the Step overlays
mdat file is attached also if you are interested.
Below is a chart with a full frequency sweep where Front Left speaker, TopSub, and BSub are playing, crossed over at 80Hz
I am still worried about the nasty dip between 70hz and 100Hz, but I will continue to search for a better spot for my 2nd sub to help there...
- Thread Starter
- #29
Well done! It looks like you did a good job on aligning 2nd sub and overally response. onsidering it's non-EQed, is looking very decent to me. IMO you shouldn't be much concerned with that dip around 85Hz as it is quite narrow. It will stay there no matter where you put your subs. Besides, in pretty much every room you'll get at least one such dip.
Can you now apply EQ of FR instructing Audyssey not to interfere with the timing/distances of the speakers?
P.S. Before doing EQ I suggest increasing level of your subs for app 6dB.
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- Thread Starter
- #30
Ok, let me explain in more detail how I came to this +6dB for the sub figure, in the light of new alignement tool in REW that @ernestcarl mentioned in his post in the other thread.
You activate Alignment tool under All SPL tab via Control icon. @_Bass I am here using your v3 measurement which you made after aligning Top sub with mains.
Upper graph shows Left and Top sub FR with black line showing predicted summed response. As we can see dip is still expected there, and measurement confirmed it.
Lower graph shows phase Left and Top sub phase response and predicted summed response. Nothing to do here as those 2 are already time-aligned so their phase responses are close to ecah other.
But when I increase the gain of the sub for 6dB here is what I'm getting:
Well, that 6dB increase in Top sub gain nicely lineariesed the summed FR so that dip around 85Hz is practically gone. I suggest you try it and post your measurement.
You activate Alignment tool under All SPL tab via Control icon. @_Bass I am here using your v3 measurement which you made after aligning Top sub with mains.
Upper graph shows Left and Top sub FR with black line showing predicted summed response. As we can see dip is still expected there, and measurement confirmed it.
Lower graph shows phase Left and Top sub phase response and predicted summed response. Nothing to do here as those 2 are already time-aligned so their phase responses are close to ecah other.
But when I increase the gain of the sub for 6dB here is what I'm getting:
Well, that 6dB increase in Top sub gain nicely lineariesed the summed FR so that dip around 85Hz is practically gone. I suggest you try it and post your measurement.
- Thread Starter
- #32
I took a more thorough look at your Balc sub alignement and here are my thoughts.
Here's the step response of your left main, Top sub and Balc sub:
Everything looks pretty good here, but let's not forget time alignement is about getting the phase of the speaker as close as possible. Here's the phase response graph:
Here it seems that Bsub would have done better if it's phase is closer to the phase of Left main and TopSub around 80Hz.
Now if we move Bsub response for 2.5ms ahead here is what we get:
I suggest you re-measure BSub with this value, together with Left main and Topsub, all 3 relative to the right main acting as timing reference.
Besides that, BSub is also showing strange dip around 100Hz and it looks way low with it's level.
P.S. as BSub response needs to be pushed 2.5ms ahead you should increase it's distance settings by 2,5*0,343=0,86 meters.
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Noted your last post, @QMuse, but let me share some more... I looked for improved positioning of BalcSub and here is what I managed to get.
1. Both subs now sum really nice at MLP. I am practically +- 7-10db between 20Hz and 20Hz. BalcSub now is very flat for the most part.
2. I measured the three seats of my couch and they look decent and similar, except the dip around 85Hz on my Left seat. I am OK with that. This is still Subs only measurements.
3. Now when I tried to measure the subs and my mains crossed at 80Hz weird notches appeared. Especially with my Left speaker measurement... And I do not understand why. They are aligned and all...
As for gain on both subs, I have them set at the same level, and since they are identical that should be fine. Perhaps because TopSub is closer it is louder... they are gain matched though.
Attaching mdat with measurements if interested.
1. Both subs now sum really nice at MLP. I am practically +- 7-10db between 20Hz and 20Hz. BalcSub now is very flat for the most part.
2. I measured the three seats of my couch and they look decent and similar, except the dip around 85Hz on my Left seat. I am OK with that. This is still Subs only measurements.
3. Now when I tried to measure the subs and my mains crossed at 80Hz weird notches appeared. Especially with my Left speaker measurement... And I do not understand why. They are aligned and all...
As for gain on both subs, I have them set at the same level, and since they are identical that should be fine. Perhaps because TopSub is closer it is louder... they are gain matched though.
Attaching mdat with measurements if interested.
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- Thread Starter
- #34
Well, level aligning sub(s) to your mains is even more important than time aligning them, but as it is out of scope of this thread I won't go into it. All I can tell you is that I strongly advise you to use REW alignement tool to do it the way I have shown in my post here, as I don't know of any better way.
Setting subs at same level (gain) will only work if they are equally distanced from your LP and I don't think it is the case with your room. And even if they are there is no guarantee that that level is matched to the level of your mains around XO area.
Let me work through that tomorrow.
Meanwhile, I tried running Audyssey as I wanted to see what I will get and if it will be close to my manually found distances and alignment.
Well, I think the results are... interesting
1. Frequency response is neither bad nor what I would consider satisfactory
I thought the perhaps Audyssey is looking for a linear combined response of both subs and speakers, so I measured that.. but it did not produce what I hoped for
2. Let's look at Phase
- L speaker is definitely not in phase with R speaker
- L speaker seems to be matching the phase of my BalcSub (2nd sub)
- the phase of TopSub (sub1) is matching the phase of the combined sub response. I wonder if Audyssey simply takes the phase of the 1st sub and just uses that for both
3. Examining the Step response results are sort of confirmed
- Step of TopSub is perfectly matched to combined sub response
- Step of BalcSub (sub2) is not matching anything
- Step of Left speaker does not match anything
I did try to overwrite the Audyssey distances with the ones we found manually with REW. Needless to say, Frequency Response and time alignment were out of wack.
Attaching the mdat file if people want to play with the data. My measurements have detailed comments.
I'd love to understand better how to time align multiple subs. Using multi-sub optimizer, I have already eq'd four subs to a remarkably flat FR. Part of the optimization includes playing with delays. So they all have different delays.
That said, they are tuned to simply act as one subwoofer. If you went in and tried to individually time align them, it would throw off their summer FR. Will this technique work to time align, or would the IR and phase responses be too muddy?
thanks
That said, they are tuned to simply act as one subwoofer. If you went in and tried to individually time align them, it would throw off their summer FR. Will this technique work to time align, or would the IR and phase responses be too muddy?
thanks
ernestcarl
Major Contributor
I believe our ears aren't nearly as well tuned to group delay anomalies in the bass -- was it Geddess who said it takes 50-100ms for us to even realize a 100Hz tone or something of the kind -- as long as their delays (multiple subs) are reasonably not too far apart from each other you would be generally okay. In the high frequencies, though, it is dead easy to detect even a 0.1ms delay by playing with DSP speaker delays. But I don't think the IR alignment technique is as useful if you are trying to achieve more evenly flat bass frequencies.
I used to have excess group delay of well over 50ms (partly) due to the use of steep filters... couldn't really tell then that the bass sounded wrong or slow to my ears. But I know some people would likely disagree.
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It's true that bass takes longer to register. I think Geddes is too tied to his steady state theory.
But if you have innate delays in your subwoofers, like DSP, a wireless connection, distance, etc., then they are objectively delayed compared to the mains, and I don't see why you wouldn't just fix it if you easily can.
But if you have innate delays in your subwoofers, like DSP, a wireless connection, distance, etc., then they are objectively delayed compared to the mains, and I don't see why you wouldn't just fix it if you easily can.
ernestcarl
Major Contributor
Alignment using the impulse responses or step (as discussed in this thread) can get you quite close within the ballpark — but I agree with Merlijn that the method is flawed with regards sub(s) to mains alignment. See here:
Personally, I wouldn’t be too concerned about the phases between subs not exactly matching each other as long as I get a more even response with the minimum amount of decrease in overall level.
I think it should be easy enough to check whether between all the subs there isn’t too much of a gross difference between any of them in time contributing to an excessive amount of group delay.
Personally, I wouldn’t be too concerned about the phases between subs not exactly matching each other as long as I get a more even response with the minimum amount of decrease in overall level.
I think it should be easy enough to check whether between all the subs there isn’t too much of a gross difference between any of them in time contributing to an excessive amount of group delay.
Hey sorry to resurrect an old thread, but I'm at my wits end trying to get this figured out. I've made some great progress over the last week by researching, but I'm still having trouble figuring out if the how to make the correction and if it's an improvement or not. I'm trying to align my sub (SVS SB 2000) and mains (Genelec 8030s) for a small home studio.
I followed all the steps in the first post exactly by the OP and now have FDW plots of step and SPL/Phase. I've attached some plots, but the phase plots all look very offset from each other. All alignment has been to the L monitor with the mic at my listening position (UMIK-1).
PHASE
SPL
STEP
I watched a JBL video (See below) and the presenter mentioned we should be aligning the INITAL START of the peaks if we have dissimilar frequency response - not aligning the peaks due to cancellation problems that can be caused from that. Does this limited sweep and windowing account for this? I'm concerned because my sub can go to about 15 hz, and my mains only go to about 50 hz.
If anyone could give me a nudge in the right direction this weekend, I would be forever grateful. I'll buy you a virtual beer Cheers!
I followed all the steps in the first post exactly by the OP and now have FDW plots of step and SPL/Phase. I've attached some plots, but the phase plots all look very offset from each other. All alignment has been to the L monitor with the mic at my listening position (UMIK-1).
PHASE
SPL
STEP
I watched a JBL video (See below) and the presenter mentioned we should be aligning the INITAL START of the peaks if we have dissimilar frequency response - not aligning the peaks due to cancellation problems that can be caused from that. Does this limited sweep and windowing account for this? I'm concerned because my sub can go to about 15 hz, and my mains only go to about 50 hz.
If anyone could give me a nudge in the right direction this weekend, I would be forever grateful. I'll buy you a virtual beer Cheers!
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