Setting subwoofer delay

[ppataki]

I know this topic has been discussed before but I would like to provide a new approach (or ask if that makes any sense at all)

I have tried different methods to set sub delay but all of them resulted in a different delay figures.....no consistency whatsoever
Using acoustic timing reference in REW (two different kinds), using Excess Group Delay curve, using the Wavelet Spectrogram - ended up with totally different results and none of them sounded good

An alternative I am trying now is this:
Copying the front channels to the sub then turning off any crossover then start to delay the fronts by an increment of 0.3ms (or 0.1ms) and in the meantime checking the RTA curve in real-time

My assumption is that when the RTA frequency curve looks the best (=highest SPL in the low register) that is where the drivers are aligned

Is that a correct assumption? I would appreciate any comments
Many thanks

 

[spalmgre]

I have also tried several different ways to align my woofer to mids in my 3-way speakers. I even used the Audiolence trial version that shows the delay between drivers. The result was close to the REW method but not the same. Also tried to use the step response and iterate delay values.

So my experience is the same that you can not find consistency. You get close but not the same delay.
I assume that this is because the low frequencies rise slowly. This makes it difficult to judge where to measure on the time scale that the signal is rising or at its peak whatever your approach is. So when many factors change between measurements even at the same session. So you get different values for the delay.

Your idea to use the RTA might work. If it does then you should find a minimum if you invert the driver. But why turn of all crossovers as they do ad some phase shift and/or delay to the signal when in normal use.

One other approach that I also tried is that when aligning why not use just frequencies that are in the crossover region. One would think that this is where the timing between drivers does matter.
Maybe the RTA approach does solve this matter as you can study the change on the curve and see where changes are occurring.

 

[ernestcarl]

But why turn of all crossovers as they do ad some phase shift and/or delay to the signal when in normal use.

Yeah, turning off all xo will alter the phase resulting in a different optimal delay when you finally turn them on. There is also REW’s “alignment tool” to auto generate a predicted summation so no need for RTA while fiddling with the delays.

 

[spalmgre]

"auto generate a predicted summation" I did take a look at this but did not understand how it can work if the woofer/subwoofer driver's timing is not measured accurately. And even if you measure it right but the right value keeps swinging around you end up with something that can be right or not so right.

MMM (moving microphone measurement) also use RTA to find an integrated value of what is close to the truth. So I would at least try to measure with RTA.

 

[ppataki]

In the meantime I tried the RTA method with the crossover turned on
It seems to be working, the only thing is to be able to decide which curve is the 'best'
I found three of them, now analyzing further which to nominate as the 'best'

I am using a mixed phase crossover btw

 

[spalmgre]

Upload some pictures so we can see and learn. Maybe somebody can give some thoughts on what's right and what's not.

 

[ernestcarl]

Upload some pictures so we can see and learn. Maybe somebody can give some thoughts on what's right and what's not.

I have a simple snapshot here: https://www.audiosciencereview.com/forum/index.php?threads/two-double-dip-regions.17460/post-582657

I did take a look at this but did not understand how it can work if the woofer/subwoofer driver's timing is not measured accurately.

You have to use an acoustic time reference to know your speakers' and sub's accurate phase relative to a certain timing reference point. You can use either left or right speaker as your timing reference for either speaker and/or sub.

REW's alignment tool is not going to do the legwork of determining optimal placement, delays, sub EQ & xo filters, and volume level calibration settings. You will have to determine that yourself. What it does do is create a summed response prediction based on two separate timed measurements you've already taken prior. It's really quick and easy to test for yourself. It is not fool-proof and you will still have to check if the prediction is accurate afterwards. In many cases, it might just be able to save you a ton of time rather than experimenting with incremental sweeps one by one. Accurate phase data is what's important here...

 

[ppataki]

It's been a while since I created this thread and since that time I (hope) I have learned a lot so just wanted to share my experience on this subject:

The current method I am using is the acoustic timing reference method with REW but not exactly the same way that was described here in various threads
Since I only use DIY subwoofers (and all the other speakers in all my systems are also DIY) they are not bandwidth limited with a factory built-in LPF, meaning that they can emit their full bandwidth when connected to the system.
So I use 0 - 20 000 Hz bandwidth when measuring the acoustic timing reference and I use 128k sweep length
Then using the Info button I check the System Delay value and I enter all of them in this Excel sheet that I have created and it will give me the necessary time delay values that I enter in Jriver accordingly

I usually use my front Left speaker as the reference and align all others to that one

This method is providing me with pretty consistent results, however I need to add that since I am using a UMIK-1 USB microphone it often has a clock drift so I usually make 3-5 measurements per speaker just to make sure I get consistent System Delay values.

This is the order of things when I configure a system with one or more subs:
- determining the best position of the sub in the room using REW measurements (if there are multiple possible positions available at all....)
- volume matching all speakers with REW's SPL alignment tool
- delay matching using the above mentioned method
- setting the crossover (I always use linear phase crossover, mostly at 80Hz and 24dB/octave slope so it has zero impact on the phase curves)

Any comments are welcome

 

[spalmgre]

This method is providing me with pretty consistent results, however I need to add that since I am using a UMIK-1 USB microphone it often has a clock drift so I usually make 3-5 measurements per speaker just to make sure I get consistent System Delay values.

I do not remember if I mentioned this here, but you do not have calibration data for the phase in your microphone calibration file. Here is a video on how to add this to your calibration file. The video starts where this is explained.

 

[ppataki]

I do not remember if I mentioned this here, but you do not have calibration data for the phase in your microphone calibration file. Here is a video on how to add this to your calibration file. The video starts where this is explained.

Thank you, I will definitely give this a try!

 

[ernestcarl]

you do not have calibration data for the phase in your microphone calibration file

That information is not at all necessary according to Dennis Sbragion, etc. I believe @JohnPM agrees with this as well.

The UMIK-1 calibration txt file itself is bandwidth limited by default, however, and so I arbitrarily extended the end limits.

 

[ppataki]

That information is not at all necessary according to Dennis Sbragion, etc. I believe @JohnPM agrees with this as well.

@ernestcarl @spalmgre
Do we know if the above has any impact on the measurements?
Like would it help at all with for example the acoustic timing measures?

 

[ernestcarl]

@ernestcarl @spalmgre
Do we know if the above has any impact on the measurements?
Like would it help at all with for example the acoustic timing measures?

I think there's minimal impact or improvement -- if you could even call it that:

 

[ppataki]

I think there's minimal impact or improvement -- if you could even call it that:

View attachment 386474 View attachment 386475

Yeah, close to none

On that matter of the clock drift: do you guys experience the same? Like measuring for example the time delay with acoustic timing reference and having to repeat it several times to get a relatively consistent result with UMIK-1?
Or is it just me screwing up something?
Would using a UMIK-2 help? I understand it has its own clock instead of using the system clock

 

[ernestcarl]

On that matter of the clock drift: do you guys experience the same?

Pretty much, yes. I take repeat measurements and discard "off" looking IRs. I also try to make sure the computer is not running anything else in the background. Although it's annoying, not nearly enough to make me buy a UMIK-2, yet.

 

[levimax]

If you are using a UMIK-1 it is not accurate enough for timing measurements like this due to USB bus issues. You will never know what is correct and what is wrong. A UMIK-2 or an analog Mic using loopback is the best way to get timing measurements. See link to developer of REW showing the issue https://www.avnirvana.com/threads/acoustic-phase-measurements.13300/#post-99941

 

[ppataki]

If you are using a UMIK-1 it is not accurate enough for timing measurements like this due to USB bus issues. You will never know what is correct and what is wrong. A UMIK-2 or an analog Mic using loopback is the best way to get timing measurements. See link to developer of REW showing the issue https://www.avnirvana.com/threads/acoustic-phase-measurements.13300/#post-99941

Thank you, that helps!
Apparently it's time to upgrade to UMIK-2!

 

[levimax]

Thank you, that helps!
Apparently it's time to upgrade to UMIK-2!

The other way to go, and always a good sanity check no matter the method, is to use a tape measure. If you know what the delays are for your subwoofer (for instance SVS subs have 6 ms delay due to their built in DSP) and anything else in your chain a tape measure can be quick, easy, and very accurate. The reality is you probably need a UMIK-2 or similar to figure out the other delays. In my case I spent a long time measuring and buying a new MIC and after it was all said and done using the 6 ms SVS delay (confirmed by measurements) combined with physical measurements I came up with the exact same answer as using all acoustic measurements.

 

[DVDdoug]

I' NOT a room-correction expert...

- setting the crossover (I always use linear phase crossover, mostly at 80Hz and 24dB/octave slope so it has zero impact on the phase curves)

Phase differences will ONLY be an issue in the narrow band around 80Hz where the regular woofer and sub are working together (where the soundwaves might be partially or completely out-of-phase relative to each other).

Assuming there is no "different DSP processing" to the high-pass or low-pass signal paths, and assuming neither one is inverted relative to the other, the ONLY phase-timing issues will be from difference in distance between the sub and the main speaker to your listening position.

The wavelength at 80Hz is 14 feet. So a half-wavelength is 7 feet and if the sub or main speaker is 7 feet closer than the other, you'll have a 180 degree phase-shift (at 80Hz) and the soundwaves will cancel. That's the worse case. (At 1.5 wavelengths you'll get 540 degrees and cancelation.) It wouldn't be unusual to have the main & sub 7-feet apart but a 7 foot difference would be unusual at home.

And since sound travels about 1 foot per ms, 7 feet is about 7 ms of time difference. (If you delay the nearest speaker by 7ms they will be back in- phase at 80Hz).

 

[ppataki]

The other way to go, and always a good sanity check no matter the method, is to use a tape measure. If you know what the delays are for your subwoofer (for instance SVS subs have 6 ms delay due to their built in DSP) and anything else in your chain a tape measure can be quick, easy, and very accurate. The reality is you probably need a UMIK-2 or similar to figure out the other delays. In my case I spent a long time measuring and buying a new MIC and after it was all said and done using the 6 ms SVS delay (confirmed by measurements) combined with physical measurements I came up with the exact same answer as using all acoustic measurements.

Yes, I forgot to mention but I also use a laser to help with the delay measurements (to filter out the garbage)