# Subwoofer timing set by YPAO



## Fredrik74 (Mar 8, 2015)

Hey all! I am a new user to REW and I am trying to check the distance settings made by YPAO on Yamaha RX-V677 reciver on my subwoofer, just to make sure it is correct and to learn a few things in the process.

I am using REW with HDMI and UMIK-1. So I did three measurements, Left with sub off, sub with left disconnected and both combined. But I am not sure I understand how this works, it looks as the sub is aligned correctly by looking at the graphs but when checking with impulse graphs I don't know.

Some more info on my setup, YAPO issues a phase warning om my main left and right speaker and I have checked the wiring and it is correct. Crossover is set at 80Hz and all speakers are set as small. The distances set by YPAO is spot on for my mains set to 3.05 meters and for my sub YPAO has added about 0.8 meters to actual distance so it is 2.4 meters. My main speakers are the Infinity Reference mkII model 61 and the sub is a QLN Sub 12. The sub is EQed with a miniDSP 2x4 and YPAO is run withe the miniDSP 2x4 attached and EQ filters in place.

So my question is simply, does it all look good? I am attaching a file with the three measurements for all of you to have a look at.


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## littlejohn74 (Feb 11, 2014)

The "Distance" label on AVRs is misleading. It should really be Delay and measured in ms.
In your case, the additional 0.8m "distance" is due to the processing done by the minidsp.
As for the phase warning, do you have the latest firmware? I recall some issues with the early firmware rev for the 77 series.


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## Fredrik74 (Mar 8, 2015)

Yes, I have the latest firmware, version 1.50.


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## jtalden (Mar 12, 2009)

Fredrik74,
I analyzed your measurements to check the timing.

I first needed to find the current IR timing. REW did not align the SW IR at the correct timing relative to the L main. This is expected as REW 'loopback timing' was not possible using a USB mic. I shifted the SW Impulse -18ms (more delayed) and found the true current timing. This placed the initial rise of the SW IR right at 0ms. The L was already placed there by REW. A + B math confirmed my estimate of the timing was correct. That is, my calculated L Main + SW result was identical to your measured Left result. 

Below is the current timing as you measured. Note that there is only a small amount of SPL support in the XO range. This is indicative an approximate 90° phase tracking error. In fairness YPAO did a reasonable job for an automated system. It aligned the 2 IRs closely in time. Had the acoustic slopes followed the target LR-24 shape, the timing would have been spot on. Speakers in rooms rarely match the target shape exactly and thus the phase tracking can often be a little off.








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I then adjusted the SW IR position to find the delay that provided the closest phase tracking and thus the most SPL support across the XO range ~35-120Hz. A SW delay reduction of +5ms was found to provide the best tracking and thus best SPL support through the XO range. See Results below. 








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*Notes:*
> The mains polarity is fine as it is. The initial IR moves negative a small amount. That normally indicates the driver is wired with negative polarity. There are a couple of things that can impact this though. [I have seen horns with a phase rotation at the very top of freq range for instance. That will result in this effect.] Anyway, the relative phase of the mains and SW is correct. You should not invert either the mains or the SW.

> You may find that the Right main may track best at slightly different timing. It should not be more than a 1 or maybe 2ms however. If so just compromise between the 2 values. Some asymmetrical room setups can be difficult with differing room modes in this range.

> To make this 5ms SW delay reduction for best tracking you can just *increase* the SW distance in the AVR by 1.77m (5.8ft) from its current setting. 

jaPost 1 Final.mdat


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## DomeTrust (Mar 4, 2015)

Hello, I am also a new user of REW and have looked at the file and like to learn more about this so I have a question about how you came to the solution that the SW was 18ms of?


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## jtalden (Mar 12, 2009)

To be clear, the 18ms is the amount of the original error between the REW relative IR timing and real timing when the measurements were taken. I will assume you understand that and also why REW placed them wrong in this case. Note that, in my file I renamed the 3 original measurements to 'Left Main' and 'SW Current' and 'Left Current' just to help keep them straight in my mind.

1. There is only one time alignment that will align the 2 IR such that A + B math (SW Current + Left Main) results in the same response as the 'Left Current' measurement.

2. I noted that REW aligned the 'Left Main' IR properly at 0ms, but the 'SW Current' was starting approximately 18ms earlier so I shifted its IR the 18ms. This then is the approximate alignment that would result in an ideal acoustic LR-24 XO if the acoustic responses followed the ideal acoustic filter shapes. This is the alignment that I would expect a basic automated setup algorithm (YAPO in this case) to target. [Of course some setup routines may be more sophisticated than others so this was just a first guess to take out the major portion of the timing error from the REW IR placements.

3. To confirm the timing or make a final adjustments so that it matches the true YAPO timing:
> View: Overlays/Step Tab chart
> Uncheck: 'Plot Response Normalized' in the 'Controls' window.
> Check only the 'Left Current' and 'SW Current' responses to see their overlaid SR's. 
> The impact of the 'SW Current' SR is now clearly visible within the SR of 'Left Current' measurement as shown below. I paid particular attention to the overlay from 20ms and above as that portion of the SR's are easier to match because the impact of the TW in 'Left Current' is much smaller than the impact of the SW.










4. The overlay of these 2 appeared to be close to perfect suggesting that this is in fact the correct alignment in this case. No addition shift was made. An (A + B) math operation on the 'SW Current' (as shifted 18ms) and 'Left Main' resulted the same SR as 'Left Current' as shown below. This confirms the shifted IR alignment is now correct for the current timing.










5. The Overlaid SPL's are also basically the same and that also helps to confirm that the correct current timing has been found. Any minor adjustments from this position would be only a small fraction of a millisecond and that is not significant for a SW XO. 

From here, an SW IR adjustment was then made to find a better alignment. The offset needed to achieve that is the change needed to the current timing/distance being used.

I hope this helps.


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## DomeTrust (Mar 4, 2015)

This helped a lot. Thank you for explaining this :TT


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## Fredrik74 (Mar 8, 2015)

jtalden, thank you for you help and explanation. This was very interesting and helpful, good things to know :T

So, I did check my right channel to see how much delay was necessary to align SW with that channel and I came up with about 7ms. So I changed the distance value on the SW setting to 4.75m from the old 2.4m to compensate for the differences in the timing between the SW, left and right channels as a first attempt.

Interestingly there are something weird going on in the Right channel when measuring the combined Right Main and SW as one unit. A dip/null appears in the 50/60Hz region that don't exist if I measure Right Main without the SW or SW without Right Main. Is this a cause of the speaker and SW timing and speaker positions and room reflections at the MLP? Do I have to re-position my speakers to get rid of this dip?

And attached is the result after changing the SW distance.


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## jtalden (Mar 12, 2009)

Fredrik74 said:


> ...Interestingly there are something weird going on in the Right channel when measuring the combined Right Main and SW as one unit. A dip/null appears in the 50/60Hz region that don't exist if I measure Right Main without the SW or SW without Right Main. Is this a cause of the speaker and SW timing and speaker positions and room reflections at the MLP? Do I have to re-position my speakers to get rid of this dip?


 There are 2 issues. They are related to the L and R Mains not the SW.

1. The 2 Mains are running very out of phase throughout that range and the dip results when they operate together with a mono signal. The phase issue in entirely due to the speaker and mic placements in the room. Many of us have issues like this with L+R Mains in mono when we have asymmetrical room setups.

2. Note however that the Mains are operating too strongly below the 80Hz XO point and that is where the problem is occurring. The SW should be enough stronger there that the Mains influence is relatively minor. This raises the question; was the XO really acting on the mains for these measurements? Some AVRs allow the mains to operate full range while the SW is filtered. Those AVRs require the Mains to set to 'small' as well as having the XO activated. I see the original measurements also show strong output well below the intended XO so it was the same situation with both sets of measurements. If the XO was active on the Mains then the best corrective action depends on the capabilities of your particular equipment. Basically, how get the roll-off of the mains to be more aggressive or try moving the XO to a higher frequency where possibly it will look more normal. Be aware that any change to the XO may impact the XO timing significantly so the timing would need to be reevaluated.

I would expect this to be a relatively minor issue as it relates to sound quality however. So, even if left as is, I would not expect it to be noticeable. It all depends on the particular listener however.


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## Fredrik74 (Mar 8, 2015)

jtalden, thanks for answering. 

To clarify, about running L Main and R Main at the same time only happens in graph #3, all other measurements is only one main and sw (all speakers are in small mode). And looking at RM without sub (graph #2, in small mode, sub off) there is a dip in the 65Hz region I guess this is the reason why the RM and sub together (graph #2) display a dip there, that dip is not present in the LM and sub graph. And here is how my room is setup if it helps:

Length 5,5m, width 3,6m and height 2,4m. Mains and center is on the long wall (5.5m) with MLP at the opposite wall with surrounds to the sides of my couch. And all is positioned at the shorter side wall. So it is not quite perfect, so only has minimum possibility of where to put the speakers, and sw is now placed beside my couch at 1.9m from the furthest of the shorter walls and 0.85m from the back wall pointing towards the right main speaker. I can move the sw to a couple of other positions if needed.

About my mains operating strongly below the crossover, I have also noted that when checking in REW they do not follow the slope on the low end (when in small mode), Could this be because they are manually EQed in my Yamaha receiver (using manual EQ of YPAO). The process I followed when doing this was to change L & R Main to large and then measure in REW then using EQ view in REW to set my target curve and then manually set filters in Yamaha and re measure and continue tweaking until it followed my target curve to best ability, and the change back to small mode on L & R Main (all five speakers was done in this way). The target curve was a house curve with boosted bass from 80hz to 30 hz with about 8db.

Should one EQ the main speakers flat in the bass area instead so it more easily follow the slope when in small mode or simply just do the EQ with the mains in small mode to follow the slope?


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## jtalden (Mar 12, 2009)

Fredrik74 said:


> jtalden, thanks for answering.
> 
> To clarify, about running L Main and R Main at the same time only happens in graph #3, all other measurements is only one main and sw (all speakers are in small mode). And looking at RM without sub (graph #2, in small mode, sub off) there is a dip in the 65Hz region I guess this is the reason why the RM and sub together (graph #2) display a dip there, that dip is not present in the LM and sub graph.


If you want to see the how dip develops just do (A + B) math on the L and R mains and compare that to the simple average of those 2 speakers. You will see the dip develop in this range because the room is impacting phase differently. It's very a common situation. [I live with this issue in 100-400Hz range. Other than changing the speaker or listening location there is nothing to do. I suppose adding acoustic treatment may help if done correctly, but I am not willing to do that.]



> ...here is how my room is setup if it helps:
> Length 5,5m, width 3,6m and height 2,4m. Mains and center is on the long wall (5.5m) with MLP at the opposite wall with surrounds to the sides of my couch. And all is positioned at the shorter side wall. So it is not quite perfect, so only has minimum possibility of where to put the speakers, and sw is now placed beside my couch at 1.9m from the furthest of the shorter walls and 0.85m from the back wall pointing towards the right main speaker. I can move the sw to a couple of other positions if needed.


I am not skilled at all things acoustical and can't help very much. I would only say that having the LP close to the back wall may be a strong contributor to overly strong bass below 80Hz. The asymmetry is probably the major contributor to the your dip around 65Hz I would not expect moving the SW to help either situation.



> About my mains operating strongly below the crossover, I have also noted that when checking in REW they do not follow the slope on the low end (when in small mode), Could this be because they are manually EQed in my Yamaha receiver (using manual EQ of YPAO). The process I followed when doing this was to change L & R Main to large and then measure in REW then using EQ view in REW to set my target curve and then manually set filters in Yamaha and re measure and continue tweaking until it followed my target curve to best ability, and the change back to small mode on L & R Main (all five speakers was done in this way). The target curve was a house curve with boosted bass from 80hz to 30 hz with about 8db.
> 
> Should one EQ the main speakers flat in the bass area instead so it more easily follow the slope when in small mode or simply just do the EQ with the mains in small mode to follow the slope?


There are probably several ways to do it that can be successful in a given situation. My approach is different from most. I only use the XO'ed measurements. I first determine the best phase tracking as you did without EQ in the XO range and then apply EQ in that range as needed. It is just a judgment call as to whether to apply the overlapping EQ in both the SW and Mains channels through the XO range. Basically I usually use the main filters above the XO and the SW filters below. It all depend greatly on the situation however. I may approach it differently in a different situation. The main objectives being; select XO filters that minimize the use of EQ in the XO range, provide close phase tracking through the XO range, and to approach the house curve using minimal EQ filters.


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## Fredrik74 (Mar 8, 2015)

jtalden, thanks for the help and plenty of good information given. Will redo my speakers EQ and see what it gives me as a result, to bad the Yamaha has no memory to store the old settings so will have to write them down instead . As it is now it is better then it was with YPAO auto setup


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