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Author Topic: Phase align subs to mains  (Read 21898 times)

JoeyCurran

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Phase align subs to mains
« on: February 28, 2014, 02:00:03 pm »

Hi Folks,

I'm hoping someone may help me learn to use Smaart to align  subs to mains systems.

As I understand it, we can’t time align a subwoofer to the mains, as subwoofers are stretched over time per frequency. So we cannot use the Impulse Response function in Smaart 6 to accomplish this. However, when attempting to measure with Impulse Response, the arrival times of the mains and subs at the mix position, I ran into some issues I hope someone can help me understand.

Measuring the arrival time of the mains at the mix position seemed to be very easy. I simply set a level, chose the IR Analysis page, started the Signal Generator using pink noise, and started the IR Analysis. The resulting trace was an easily discernible trace showing arrival time and positive polarity. I utilized the following settings in IR analysis: Type – Linear IR, FFT – 64k, TC (ms) – 1365, Avg – 4.

I then attempted to measure the subs arrival at the mix, with the same settings and method, but failed miserably. I tried increasing the FFT size and averages with no success. The trace that resulted was a nearly flat line, with no way to determine polarity or arrival time.

I hope someone who sees this post will know why I was unsuccessful in my first attempt. I must say I am not completely surprised at the result, as the more I attempt to come to terms with this very powerful tool the more I realize how little I know regarding its use.

Best Regards,
Joey

edited for spelling
« Last Edit: February 28, 2014, 03:57:04 pm by JoeyCurran »
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JoeyCurran

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Phase align subs to mains post
« Reply #1 on: February 28, 2014, 02:25:26 pm »

Hi Folks,

I'm hoping someone may help me learn to use Smaart to align  subs to mains systems.

As I understand it, we can’t time align a subwoofer to the mains, as subwoofers are stretched over time per frequency. So we cannot use the Impulse Response function in Smaart 6 to accomplish this. However, when attempting to measure with Impulse Response, the arrival times of the mains and subs at the mix position, I ran into some issues I hope someone can help me understand.

Measuring the arrival time of the mains at the mix position seemed to be very easy. I simply set a level, chose the IR Analysis page, started the Signal Generator using pink noise, and started the IR Analysis. The resulting trace was an easily discernible trace showing arrival time and positive polarity. I utilized the following settings in IR analysis: Type – Linear IR, FFT – 64k, TC (ms) – 1365, Avg – 4.

I then attempted to measure the subs arrival at the mix, with the same settings and method, but failed miserably. I tried increasing the FFT size and averages with no success. The trace that resulted was a nearly flat line, with no way to determine polarity or arrival time.

I hope someone who sees this post will know why I was unsuccessful in my first attempt. I must say I am not completely surprised at the result, as the more I attempt to come to terms with this very powerful tool the more I realize how little I know regarding its use.

Best Regards,
Joey

edited for spelling
« Last Edit: February 28, 2014, 03:58:00 pm by JoeyCurran »
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Art Welter

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Re: Phase align subs to mains post
« Reply #2 on: February 28, 2014, 03:41:16 pm »

Hi Folks,

I'm hoping someone may help me learn to use Smaart to align  subs to mains systems.

As I understand it, we can’t time align a subwoofer to the mains, as subwoofers are stretched over time per frequency.
Joey,

This thread explains the procedures:

http://www.rationalacoustics.com/forums/showthread.php?5137-How-to-measure-Sub-with-Fullrange

It also helps to know where you are "starting from", testing your system outside with the subs next to the mains with the mic on the ground equidistant between the two at about 2 meters (and away from big objects by 10 meters or so) will make it much more easy to see when the phase traces line up.
Then when you move indoors you can have a more educated guess as where to start with delay times- roughly a millisecond per foot of physical offset between subs and tops in relation to the listening/measurement position from your outdoor figures. If your mains are always stacked on your subs, the delay will not need to be changed regardless of the venue.

One "gotcha" that messes up alignment is you can over delay the tops by one wavelength and  still phase align the subs, but if your crossover is around 100 Hz the subs would then end up lagging by around 10 ms, they can measure flat, but sound "slow". That said, the output of a ported top cabinet lags the main output by 180 degrees at Fb (box tuning) so depending on the acoustical crossover point in relation to Fb, things can be interesting to figure out...

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JoeyCurran

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Re: Phase align subs to mains post
« Reply #3 on: February 28, 2014, 04:07:09 pm »

Hi Art,

Thanks for your reply. Thanks for the link, I'll check that out straight away. The system is installed and is not available to take outdoors.



One "gotcha" that messes up alignment is you can over delay the tops by one wavelength and  still phase align the subs, but if your crossover is around 100 Hz the subs would then end up lagging by around 10 ms, they can measure flat, but sound "slow". That said, the output of a ported top cabinet lags the main output by 180 degrees at Fb (box tuning) so depending on the acoustical crossover point in relation to Fb, things can be interesting to figure out...

I am fairly certain I have heard this effect!!!
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Martyn ferrit Rowe

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Doug Fowler

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Re: Phase align subs to mains
« Reply #5 on: February 28, 2014, 06:47:13 pm »

Hi Folks,

I'm hoping someone may help me learn to use Smaart to align  subs to mains systems.

As I understand it, we can’t time align a subwoofer to the mains, as subwoofers are stretched over time per frequency. So we cannot use the Impulse Response function in Smaart 6 to accomplish this. However, when attempting to measure with Impulse Response, the arrival times of the mains and subs at the mix position, I ran into some issues I hope someone can help me understand.

Measuring the arrival time of the mains at the mix position seemed to be very easy. I simply set a level, chose the IR Analysis page, started the Signal Generator using pink noise, and started the IR Analysis. The resulting trace was an easily discernible trace showing arrival time and positive polarity. I utilized the following settings in IR analysis: Type – Linear IR, FFT – 64k, TC (ms) – 1365, Avg – 4.

I then attempted to measure the subs arrival at the mix, with the same settings and method, but failed miserably. I tried increasing the FFT size and averages with no success. The trace that resulted was a nearly flat line, with no way to determine polarity or arrival time.

I hope someone who sees this post will know why I was unsuccessful in my first attempt. I must say I am not completely surprised at the result, as the more I attempt to come to terms with this very powerful tool the more I realize how little I know regarding its use.

Best Regards,
Joey

edited for spelling

The energy from the sub is so spread out in time it's very difficult to see what's actually going on in IR.   Because it's so spread out, there is much "less amplitude" than in the HF, where everything is pretty much (but not exactly) arriving at the same time.

Smaart 6 was not very good at locking onto LF arrival times IIRC.  It seems to be quite a bit better now.

One of the other things you're dealing with here is the LPF on the subs.  The crossover will cause the peak energy of the sub to be later than if it were a full range signal.  You can verify this easily with electronic measurements.  Measure through a crossover, put the delay finder on "auto", and start to lower the frequency on a LPF.  You'll see the peak really start to move as you get near the sub region.

This is precisely where many have (wrongly) rolled up the LPF over 1 KHz, gotten their "delay time", and called the job done.  Clever, but totally wrong.
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JoeyCurran

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Re: Phase align subs to mains
« Reply #6 on: March 01, 2014, 04:57:22 am »

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JoeyCurran

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Re: Phase align subs to mains
« Reply #7 on: March 01, 2014, 05:02:53 am »

The energy from the sub is so spread out in time it's very difficult to see what's actually going on in IR.   Because it's so spread out, there is much "less amplitude" than in the HF, where everything is pretty much (but not exactly) arriving at the same time.

Smaart 6 was not very good at locking onto LF arrival times IIRC.  It seems to be quite a bit better now.

One of the other things you're dealing with here is the LPF on the subs.  The crossover will cause the peak energy of the sub to be later than if it were a full range signal.  You can verify this easily with electronic measurements.  Measure through a crossover, put the delay finder on "auto", and start to lower the frequency on a LPF.  You'll see the peak really start to move as you get near the sub region.

This is precisely where many have (wrongly) rolled up the LPF over 1 KHz, gotten their "delay time", and called the job done.  Clever, but totally wrong.

Hi Doug,

Thanks for explaining that. So in order to get in the ballpark with setting a delay for the subs to mains, would I be better off measuring propagation to the listening area of each system separately, then adjusting the time from one or the other through electronic delay? After I'm in the ballpark, then I can fine tune Phase and slope?

Cheers,
Joey
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JoeyCurran

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Re: Phase align subs to mains
« Reply #8 on: March 01, 2014, 05:39:44 am »

Hi Folks,

Which would be more appropriate for measuring phase and slope between these pass bands? Noise/sine/program? Sine wave at the crossover freq in the processor? Or pink noise in the octave 63-125hz, covering the crossover area? Sub heavy music?

Cheers,
Joey
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JoeyCurran

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Re: Phase align subs to mains post
« Reply #9 on: March 01, 2014, 06:07:01 am »

Hi Folks,

Thanks for the great info. I was tying to find delay/propagation times for the different sub-systems I was measuring, hence the use of Impulse Response. I understand now why this is an inappropriate approach, as the energy from the sub is so spread out in time it's very difficult to see what's actually going on in IR. Thanks again for your help.

Which would be more appropriate for measuring phase and slope between these pass bands? Noise/sine/program? Sine wave at the crossover freq in the processor? Or pink noise in the octave 63-125hz, covering the crossover area? Sub heavy music?

Cheers,
Joey
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