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Author Topic: Smaart subwoofer alignment  (Read 3152 times)

Michael Storey

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Smaart subwoofer alignment
« on: January 08, 2017, 08:38:42 pm »

I'm currently researching the process of time aligning subwoofers to mains using Smaart, and came across the video linked bellow. I'm curious what those of you well versed in the subject think about his method, particularly his choice to not "delay locate". I assume he is referring to the process of delaying the reference signal to the mic signal? Please correct me if I'm wrong.

https://www.youtube.com/watch?v=j6Z_sIDrs8A&t=11s
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Ivan Beaver

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Re: Smaart subwoofer alignment
« Reply #1 on: January 08, 2017, 09:15:17 pm »

I'm currently researching the process of time aligning subwoofers to mains using Smaart, and came across the video linked bellow. I'm curious what those of you well versed in the subject think about his method, particularly his choice to not "delay locate". I assume he is referring to the process of delaying the reference signal to the mic signal? Please correct me if I'm wrong.

https://www.youtube.com/watch?v=j6Z_sIDrs8A&t=11s
I did not watch in detail the whole video, but he is NOT delaying the reference to the mic.

He is playing with the delay between the full range signal and sub.

HOWEVER I find it REALLY strange that he is not "taking the time of flight" into account.

It will make the phase response MUCH MUCH easier to look at.

It will remove all the phase wraps he is seeing and be MUCH flatter-at least in the area of interest.

There are much easier ways to see this alignment.

His basic idea appears to be correct (again I didn't watch the whole thing), regarding get the phase traces to overlap. 

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Mark Wilkinson

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Re: Smaart subwoofer alignment
« Reply #2 on: January 09, 2017, 10:21:45 am »

Echoing what Ivan said, and just adding as to why delay locating makes it much easier to get more accurate results....

There is a lot more phase difference in slight misalignment between steep traces, than there is in flatter traces. 
IOW, his method looks easier because it is easier.....it requires less precise alignment than using flatter traces.


Also, we want to make sure we align to the fewest wraps possible...I don't know if his method makes this possible.
Kinda doubt it, but need to think it through..

It all really begs, why NOT use delay finder? 
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Mac Kerr

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Re: Smaart subwoofer alignment
« Reply #3 on: January 09, 2017, 01:07:46 pm »

It all really begs, why NOT use delay finder?

Because delay finder uses the peak of the highest frequency it can read, which may be well above the frequency of interest. Using the phase slope to set the time offset can be done at whatever frequency you want to use. The "phase wrap" can be eliminated by selecting phase unwrap in the menu.

The fallacy of all methods of sub to mains alignment is that unless the 2 systems are located very near each other the alignment only applies to a limited area.

Mac
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Mark Wilkinson

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Re: Smaart subwoofer alignment
« Reply #4 on: January 09, 2017, 02:39:04 pm »

Because delay finder uses the peak of the highest frequency it can read, which may be well above the frequency of interest. Using the phase slope to set the time offset can be done at whatever frequency you want to use. The "phase wrap" can be eliminated by selecting phase unwrap in the menu.

The fallacy of all methods of sub to mains alignment is that unless the 2 systems are located very near each other the alignment only applies to a limited area.

Mac

Yes, familiar with those points.  I just find it easiest to work with as clean a phase screen as possible and getting to traces as flat as possible, for aligning overlay. IMHO, starting with delay finder's time/distance on the main(s) helps that.....gives me a intuitive base for ballpark sub timing with just a few back of envelope calculations. And most importantly, let's me know if measurements are passing the smell test  ;D

I've been meaning to ask you...in a previous thread somewhere, I had wished Smaart had the ability to target a user select frequency for determining delay. 
IIRC, you suggested to put a single freq sine wave in the pink for smaart to lock on.
I tried it and found if the sine wave had greater or even competing magnitude, smaart wouldn't find delay at all.
If I lowered the sine magnitude down below the pink, smaart would find delay, but at exactly the same time as if no sine... still using highest peak.

So I hit the manual, and read that smaart can't use repeating waveforms for transfers....?

Maybe I misunderstood your suggestion or remembering it wrong...
Any redirection ?   

Thx.  mark
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Ivan Beaver

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Re: Smaart subwoofer alignment
« Reply #5 on: January 09, 2017, 07:05:55 pm »


The fallacy of all methods of sub to mains alignment is that unless the 2 systems are located very near each other the alignment only applies to a limited area.

Mac
Yeah.

I have done some designs/installs that violate EVERY rule in regards to top/sub alignment.

But that does not keep them from sounding great and everybody loving it.

It all depends on freq capabilities of the mains (how low do they go) and overall positioning.

There are a lot of "it depends" when it comes to alignments.

It is VERY GOOD to understand the "proper ways" and know how to do it, so you can better understand the tradeoffs you have to make and whether they are worth it or not.

Just "willie nillie" ignoring the "rules" is NOT an excuse and often leads to poor results.
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Tim McCulloch

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Re: Smaart subwoofer alignment
« Reply #6 on: January 10, 2017, 04:29:19 pm »

Yeah.

I have done some designs/installs that violate EVERY rule in regards to top/sub alignment.

But that does not keep them from sounding great and everybody loving it.

It all depends on freq capabilities of the mains (how low do they go) and overall positioning.

There are a lot of "it depends" when it comes to alignments.

It is VERY GOOD to understand the "proper ways" and know how to do it, so you can better understand the tradeoffs you have to make and whether they are worth it or not.

Just "willie nillie" ignoring the "rules" is NOT an excuse and often leads to poor results.

Herein lies The Truth.

Not everything we did in The Days Before Measurement was wrong but it was almost always the result of a blind compromise.  We could hear things working (or not) but we weren't really sure *why*.

Today we can over-measure something and turn a situation with no clear best outcome into paralysis by analysis.  Having some experiential basis for making the adult-in-the-room decision about what alignment & optimization compromises to make is much more important than making yet another measurement and hoping to find The Solution.
« Last Edit: January 10, 2017, 04:35:24 pm by Tim McCulloch »
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Ivan Beaver

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Re: Smaart subwoofer alignment
« Reply #7 on: January 10, 2017, 08:41:52 pm »



Not everything we did in The Days Before Measurement was wrong but it was almost always the result of a blind compromise.  We could hear things working (or not) but we weren't really sure *why*.


When I started actually LEARNING about "how audio things worked", it was like a whole bunch of light bulbs getting turned on.

I started learning WHY all of the "things I had experienced" actually happened.

NOW I could start to put some actual science/math etc to my sonic experiences.

This now makes it MUCH EASIER to "guess" about a lot of things-by understanding the basics behind it.

I was EXHAUSTED after the first day of my first Synaudcon class.  It was like "explosions" all day with experiences and reason coming together.

But one without the other leaves a bit of a "hole" in the whole "understanding experience".

Many people often talk about things as if they understand, but have never experienced, so they don't know the "topic at hand" and tend to "blow up" what is actually going on.
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Mark Wilkinson

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Re: Smaart subwoofer alignment
« Reply #8 on: January 11, 2017, 01:30:21 pm »

Yep to all said...  ears, experienced from so many situations, rule.
I think we do have to admit though, that making measurements, along with DSP control, are impacting nearly every area of audio setup and SQ, from the largest arrays all the way down to home theater.
IMHO, making good measurements is mattering more and more...

I like to think of good measurements as needing two wings to fly. 
One wing being practical application; as in why measure to begin with, exactly what to measure, and what can really be done with the measurements.
Second wing being technical proficiency; how to make the measurement, how to isolate and know what's actually being measured,.. and how to achieve as much accuracy and repeat-ability as possible.

I really think it takes both for measurements to make better sound. There's of course many additional points to each of the "wings", but I'm sure you get the drift...experience and practicality on one side, technical ability and consistency on the other.......

I do enjoy measurements and know I can be a bit of a measurement junkie sometimes... I do apologize if this comes off overbearing...

Please realize I recognize my experience level is at best a few % of each of you who has posted in this thread.... ( what I'd give to apprentice to any of you....=)

Also please realize,  IMO measurements are often very valuable for learning audio fundamentals,..... having no immediate goal to set up a system or make better sound. 
And I do believe in trying to routinely achieve the best accuracy and repeat-ability we can....you know, whether it 'matters' or not...
Thx for listening....Mark
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Tim McCulloch

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Re: Smaart subwoofer alignment
« Reply #9 on: January 12, 2017, 02:56:31 am »

Yep to all said...  ears, experienced from so many situations, rule.
I think we do have to admit though, that making measurements, along with DSP control, are impacting nearly every area of audio setup and SQ, from the largest arrays all the way down to home theater.
IMHO, making good measurements is mattering more and more...

I like to think of good measurements as needing two wings to fly. 
One wing being practical application; as in why measure to begin with, exactly what to measure, and what can really be done with the measurements.
Second wing being technical proficiency; how to make the measurement, how to isolate and know what's actually being measured,.. and how to achieve as much accuracy and repeat-ability as possible.

I really think it takes both for measurements to make better sound. There's of course many additional points to each of the "wings", but I'm sure you get the drift...experience and practicality on one side, technical ability and consistency on the other.......

I do enjoy measurements and know I can be a bit of a measurement junkie sometimes... I do apologize if this comes off overbearing...

Please realize I recognize my experience level is at best a few % of each of you who has posted in this thread.... ( what I'd give to apprentice to any of you....=)

Also please realize,  IMO measurements are often very valuable for learning audio fundamentals,..... having no immediate goal to set up a system or make better sound. 
And I do believe in trying to routinely achieve the best accuracy and repeat-ability we can....you know, whether it 'matters' or not...
Thx for listening....Mark

Don't get me wrong, Mark.  I'm not denigrating measurement, I'm actually heavily invested in it.

Rational Acoustics and AFMG do a great job providing training to use Smaart and Systune (respectively).  What they can't do in 20 hours is give the operator the experience of:  making bad measurements, measuring for the wrong thing, or making measurements without a clear idea of why a particular measurement is being made.

Measurement does not exist for its own sake - it's there as a visual aid to system alignment and optimization.  Effectively using measurement requires the operator to have some foundational knowledge of those things or the operator is just making pretty pictures on the laptop screen.

Finally that gets us to *where* in the venue do we align the major parts?  You can pick any seat (or sometimes a small block of seats), put the measurement mic in that spot and align away.  There is good reason to do this:  at least a few people can experience a fully aligned listening position and if you align for where the artist's manager, spouse or band VIP guests congregate you'll be more likely to keep your FOH mixerperson gig.

Aligning to one spot is just that, one spot.  You can't align for 3 or 7 or 28 places, what you can try to do is minimize the differences.  In the end, there is still one physical place in the venue where things come together in time.  Over thinking the impossible distracts from applying our principles of alignment and optimization to the things that *are* possible.
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Ivan Beaver

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Re: Smaart subwoofer alignment
« Reply #10 on: January 12, 2017, 07:52:10 am »


Rational Acoustics and AFMG do a great job providing training to use Smaart and Systune (respectively).  What they can't do in 20 hours is give the operator the experience of:  making bad measurements, measuring for the wrong thing, or making measurements without a clear idea of why a particular measurement is being made.


Aligning to one spot is just that, one spot.  You can't align for 3 or 7 or 28 places, what you can try to do is minimize the differences.  In the end, there is still one physical place in the venue where things come together in time.  Over thinking the impossible distracts from applying our principles of alignment and optimization to the things that *are* possible.
One of the hardest things for people to get their head wrapped around is "IS this a good measurement?"

Either in position or parameter settings on the computer.  If not-WHY?

I ALWAYS question my self when I see something I don't expect-WHAT is causing it?  Is it the measurement position or the actual device being measured.

As the saying goes "If you don't know the answer BEFORE you start to measure-how do you know you are getting a good measurement?"

One of the things that REALLY REALLY started to help me understand what was going on in a sound system in multiple seats was using multiple mics.

I built my own rig (back when we could only input 1 mic at a time into a measurement system) that allowed me to calibrate my mics and to easily switch between them (without having to plug and unplug each one).

I would spread the mics (8) around the room.  That was I could see what was happening at different seats when I adjusted different parts of the system, without having to get up and move the mic around.

It allowed me to get much more information much faster and get a better overall result.

One of the things that many people miss is how much one part of the sound system affects other parts that aren't anywhere near the coverage pattern.  Being able to see it is a REAL eye opener.

And it leads to looking for better tools to use that don't interfere as much.
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Mark Wilkinson

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Re: Smaart subwoofer alignment
« Reply #11 on: January 12, 2017, 10:46:08 am »

Thank you Tim, 'Copy' to all you say....

I think a mistake I make in responding to measurement questions, is taking for granted that folks understand common limitations , and reply as if their only question is about best technique. (limitations such as being able to align to only one place unless subs are adjacent to mains)

I mean, I barely even try to align subs to mains indoors in the small rooms I see...I'm almost always far more concerned with how the subs interact with the room and stage.
Placement and cutting out modal boosts with eq get most my attention.  If any tuning time is left, I might try to align, but most often I just wing it with a ball park guess based off known 'stacked' timing.
And in fairness to the video that started this thread, he was talking about inside.......and doing more than I usually do !

Ivan, I really concur with the multiple mic learning experience.  I had the opportunity to build a fairy large audio room (11,000 cu ft) and spend several years measuring it with bunches of speaker/sub placements.  (I still remember the joy in learning what corner stacked labhorns could do hehe.) I set up multiple mics, and used both pink and sine waves.  Pink variations were of course large, but the sines blew my mind...could not believe the variations even foot by foot.  Ultimately, apart from the fore mentioned attention to speaker/sub placement and cutting room modes with eq, the real gains came from acoustic treatment.  Taming early reflections, getting an even RT60, and a few other acoustic techniques made for a great sounding room. 
Never could get smaart to work for aligning inside haha....had to go outdoors to learn how to do it!

On the reality of being not able to align to more than one place when subs and mains are separated...

I've found very good alignment with speakers right on the sub, but with subs on the ground and speakers on a stick 14ft in air, alignment of course loosens up moving away from 'aligned to' location.
OK, that's just the way it works..critical xover region will suffer some as you move around.

But what I'm thinking is why not at least minimize the critical  region of xover overlap...more than typical....
Why not run as steep a x-over as possible between the subs and mains? 
I'm toying with 96db right now @100Hz , and it's kinda cool how bass sounds like it stays with the main despite moving the main around.  This is inside, so no real telling till I get outside....and there's also the added delay issue from steeper xover to contend with....so a lot of dunnos still ..
   
Any experience here? Pitfalls beyond delay?
thx

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Ivan Beaver

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Re: Smaart subwoofer alignment
« Reply #12 on: January 12, 2017, 12:14:28 pm »


But what I'm thinking is why not at least minimize the critical  region of xover overlap...more than typical....
Why not run as steep a x-over as possible between the subs and mains? 
I'm toying with 96db right now @100Hz , and it's kinda cool how bass sounds like it stays with the main despite moving the main around.  This is inside, so no real telling till I get outside....and there's also the added delay issue from steeper xover to contend with....so a lot of dunnos still ..
   
Any experience here? Pitfalls beyond delay?
thx
One of he reason for not using high order filters is the ringing that happens with really steep slopes.

I try to stay at 24dB/oct or less.

The best "sounding" filter is a simple 1 pole/6dB/octave.  But often it does not provide enough protection for louder systems that push drivers.

If the drivers are not going to be pushed, then shallower slope filters are better.
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Mark Wilkinson

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Re: Smaart subwoofer alignment
« Reply #13 on: January 12, 2017, 03:11:29 pm »

One of he reason for not using high order filters is the ringing that happens with really steep slopes.

I try to stay at 24dB/oct or less.

The best "sounding" filter is a simple 1 pole/6dB/octave.  But often it does not provide enough protection for louder systems that push drivers.

If the drivers are not going to be pushed, then shallower slope filters are better.

Aah ringing...yes.  Gosh, I've been doing tons of research on this. 
And I get the power handling issue with low slope, thx

I've found what you say about steep filters is very well documented for normal minimum phase filters.
And some of the better explanations  show that ringing is the term used for the phase distortion that occurs with steep recursive filters......that freq response can be fine, but time response gets real sucky. 

Linear phase filters seem to be another animal though. ( I should have said the 96dB xover attempt is linear phase).
I read debate as to whether linear phase pre-ringing is audible.....

So far, I can't hear any pre-ringing...but who knows how well I hear ?  :)
I can measure a very small amount of pre-ringing, but it really appears inconsequential.

Below is an impulse plot of a main high passed with 96dB at 100Hz.  You'll see a wee bit of pre and post ringing.

Right below it for comparison, is an impulse of an x-32's I/O that was used as the soundcard for the main's measurement, so the impulse of the soundcard is part of the impulse of the main.  The x-32's AD/DA conversion is nearly as ringy as the speaker !

I'm just not seeing speaker ringing worth paying attention to ??
Are there better ways to identify ringing?

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Charlie Hughes

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Re: Smaart subwoofer alignment
« Reply #14 on: March 04, 2017, 09:48:36 am »

Aligning to one spot is just that, one spot.  You can't align for 3 or 7 or 28 places, what you can try to do is minimize the differences.  In the end, there is still one physical place in the venue where things come together in time.  Over thinking the impossible distracts from applying our principles of alignment and optimization to the things that *are* possible.

Several years ago I presented a method that I think can be very useful for aligning subwoofers & full-range loudspeakers while minimizing the variations within a large audience area.  A video of the presentation can be seen at the link below.
https://www.youtube.com/watch?v=yoASUFGPWwg

A PDF of the slide is available on my website.
http://excelsior-audio.com/Publications/AES129_RH_Charlie_Hughes_Subwoofer_Alignment_with_a_Full-Range_System.pdf

Hope this helps.
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Keith Broughton

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Re: Smaart subwoofer alignment
« Reply #15 on: March 04, 2017, 10:05:59 am »

The "phase wrap" can be eliminated by selecting phase unwrap in the menu.


Now there is a tidbit I missed!
I have quite a time trying to phase align as the "wraps" are so dense, I can't get any good data.
Seemed sooooo easy in the class  ::)
Have to set up a test scenario and figure this out.
Are you referring to the "phase smoothing" in the TF tools?
« Last Edit: March 04, 2017, 11:48:02 am by Keith Broughton »
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Doug Fowler

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Re: Smaart subwoofer alignment
« Reply #16 on: March 04, 2017, 05:14:38 pm »

It's not Smaart, but....

When AFMG were working on the alignment tool built into Systune, I was looking at every angle to find an easier path for beginners with Systune. 

One thing I know for sure (probably the only thing :-) is beginners don't realize frequencies are arriving at different times, and that low frequencies are substantially behind, sometimes 25-30 msec at the bottom of a subwoofer's range.  Add in the effect of the low pass filter and it gets confusing, quickly.  Here is what I came up with, and actually presented this in the Renkus-Heinz booth at Infocomm a few years back: 

I don't think you can do this with Smaart but it works with Systune.

Display phase in one window and group delay in the other.  Assuming you're going to delay the subs, capture the LF from the mains with long averaging.   Group delay will be jumpy, and possibly show negative time at some frequencies due to the nature of the calculation, which is very sensitive to noise.   Let it average and when it stabilizes, capture it.  At this point you can use delay finder and use that value to get the phase display looking "normal".

Examine the frequencies at which you are going to align, let's say 80 Hz.   The arrival time(s) around 80 Hz will be quite clear.  Now mute the LF and unmute the subs, and let it average.  Leave the delay offset in place.  Look at 80 Hz area and you will see the arrival time(s) from the subs.  Start adding delay slowly until the subs match the captured LF trace. 

Now inspect the phase values in the phase window, and fine tune from there.  It works, trust me.  What we're doing here is using a somewhat unstable calculation (group delay) to get us close, then fine tuning with phase until the slopes match.  The value of using a group delay window is no phase interpretation is required.  It's dirt simple: frequency is X axis, time is y axis. 

If I ever get a chance I'll post an example.  This is off the top of my head, but I'm pretty sure this is how I did it.
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Mark Wilkinson

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Re: Smaart subwoofer alignment
« Reply #17 on: March 06, 2017, 02:55:25 pm »

Several years ago I presented a method that I think can be very useful for aligning subwoofers & full-range loudspeakers while minimizing the variations within a large audience area.  A video of the presentation can be seen at the link below.
https://www.youtube.com/watch?v=yoASUFGPWwg

A PDF of the slide is available on my website.
http://excelsior-audio.com/Publications/AES129_RH_Charlie_Hughes_Subwoofer_Alignment_with_a_Full-Range_System.pdf

Hope this helps.

Thanks Charlie,

I stumbled onto your youtube video sometime last year when I was going nuts trying to line up impulse peaks on a 3-way main.   
Your video, which i only half understood  :), led me to examine a perfect impulse response using 1/3 oct filters.  And then I saw the need to align first arrivals..........

It still melts my mellon that a single narrow spike (perfect impulse) can contain all the exploded impulse responses shown by filtering.
I'm left thinking that what the perfect impulse really contains, is a single sample of each frequencies "first arrival" or rather single sample of initial propagation. And that the exploded responses are just mathematical extrapolations out into time....
Is this thinking even on the right path?  I find this stuff hard to conceptualize....

I also noticed that the 1/3 octave impulse peaks showed a delay from time zero, that appears to be about a constant 2.8X the period of the filter center.  For example, 1000Hz showed 2.8ms delay, 100Hz 28ms delay, etc.  Does this sound right? What's going on?

Sorry, too many questions...! 
Mark


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Mark Wilkinson

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Re: Smaart subwoofer alignment
« Reply #18 on: March 06, 2017, 03:04:45 pm »

It's not Smaart, but....

When AFMG were working on the alignment tool built into Systune, I was looking at every angle to find an easier path for beginners with Systune. 

One thing I know for sure (probably the only thing :-) is beginners don't realize frequencies are arriving at different times, and that low frequencies are substantially behind, sometimes 25-30 msec at the bottom of a subwoofer's range.  Add in the effect of the low pass filter and it gets confusing, quickly.  Here is what I came up with, and actually presented this in the Renkus-Heinz booth at Infocomm a few years back: 

I don't think you can do this with Smaart but it works with Systune.

Display phase in one window and group delay in the other.  Assuming you're going to delay the subs, capture the LF from the mains with long averaging.   Group delay will be jumpy, and possibly show negative time at some frequencies due to the nature of the calculation, which is very sensitive to noise.   Let it average and when it stabilizes, capture it.  At this point you can use delay finder and use that value to get the phase display looking "normal".

Examine the frequencies at which you are going to align, let's say 80 Hz.   The arrival time(s) around 80 Hz will be quite clear.  Now mute the LF and unmute the subs, and let it average.  Leave the delay offset in place.  Look at 80 Hz area and you will see the arrival time(s) from the subs.  Start adding delay slowly until the subs match the captured LF trace. 

Now inspect the phase values in the phase window, and fine tune from there.  It works, trust me.  What we're doing here is using a somewhat unstable calculation (group delay) to get us close, then fine tuning with phase until the slopes match.  The value of using a group delay window is no phase interpretation is required.  It's dirt simple: frequency is X axis, time is y axis. 

If I ever get a chance I'll post an example.  This is off the top of my head, but I'm pretty sure this is how I did it.

Thanks Doug,

If I get what you're saying...the basic idea is to match group delays at crossover frequency for the coarse adjustment...
And that this should get rid of phase wraps...and then allow fine tuning via phase overlay.

Just trying to make sure it sinks in....

Mark

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Merlijn van Veen

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Re: Smaart subwoofer alignment
« Reply #19 on: June 05, 2017, 02:45:08 pm »

Regarding subwoofer placement in small venues. Instead of doing trial and error, reverse the roles.

Put the sub at the actual listening position where you want it to sound good, turn it on and start listening at candidate positions where the sub could end up.

The spot where it sound best or the the way you like, is where you'll put it. It's a matter of simple reciprocity.


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Ivan Beaver

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Re: Smaart subwoofer alignment
« Reply #20 on: June 05, 2017, 05:58:32 pm »

Regarding subwoofer placement in small venues. Instead of doing trial and error, reverse the roles.

Put the sub at the actual listening position where you want it to sound good, turn it on and start listening at candidate positions where the sub could end up.

The spot where it sound best or the the way you like, is where you'll put it. It's a matter of simple reciprocity.


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That is one of the best ways to do sub placement in a home theater.
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A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

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Peter Morris

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Re: Smaart subwoofer alignment
« Reply #21 on: June 14, 2017, 08:27:53 am »

The interesting thing that nobody has discussed is that he uses two different methods to phase align the subs Ė firstly he polarity flips the subs with no delay, then he delays the subs 8ms but without a polarity flip.  In both case the phase traces overlay each other - but itís not the same :-)
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Mark Wilkinson

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Re: Smaart subwoofer alignment
« Reply #22 on: June 14, 2017, 12:51:28 pm »

The interesting thing that nobody has discussed is that he uses two different methods to phase align the subs Ė firstly he polarity flips the subs with no delay, then he delays the subs 8ms but without a polarity flip.  In both case the phase traces overlay each other - but itís not the same :-)

Yes, and pls correct me if I'm wrong.... he's added 180 degrees of phase, a half a wrap, at 63Hz ( 8ms half wave). And relative phase additions to surrounding freqs (ie 360 deg @ 125Hz, 90 @ 31Hz)
Impulse of this phase-rotation-delay method vs a polarity swap will show it loud and clear, IME
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Peter Morris

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Re: Smaart subwoofer alignment
« Reply #23 on: June 14, 2017, 10:59:18 pm »

Yes, and pls correct me if I'm wrong.... he's added 180 degrees of phase, a half a wrap, at 63Hz ( 8ms half wave). And relative phase additions to surrounding freqs (ie 360 deg @ 125Hz, 90 @ 31Hz)
Impulse of this phase-rotation-delay method vs a polarity swap will show it loud and clear, IME

Exactly, what I try to do is ensure that all the separate pass bands have +ve impulses and then align.

I would be very interested in what others think about this polarity flip.

Itís also important to remember that we tend to run the subs with a little extra gain/SPL relative to the mids, so you could say the actual crossover is noticeable higher than the implied electronic crossover point, so it is especially important that the phase traces are aligned above the crossover otherwise you can end up with the subs cancelling some of the low mids.

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