Phase align subs to mains

J

Joey Curran

Freshman
Mar 19, 2011
7
0
0
Dublin, Ireland
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
 
Re: Phase align subs to mains

Subs should be the last thing that you try to do an alignment on.

Once you have the mids and highs acting nice with each other, move on to the subs. For a quick and dirty alignment, find the delay time in the transfer function window for the band right above the subs, low mids for example. Lets say 60.25 ms. Take a screenshot of the current transfer function window, with the phase viewable. (make sure you don't have the group delay option checked.) Mute that bandpass. Now turn on the subs, and get the delay time for the subs as close to 60.25 ms as possible. DON'T insert the delay in the find delay window, just keep checking the delay to get the subs close to 60.25 ms. Once you get the delay close, switch back to the transfer function window and adjust the sub delay to get the sub/mids phase overlapped. You should be able to see the mids phase trace that you stored earlier.

I'd suggest using music to align subs, not pink noise. I've had better luck with music program.

Sorry if this post doesn't make all the sense in the world, I'm on my phone in a bus.

Cheers
 
Re: Phase align subs to mains

Joey Curran said:
I'm hoping someone may help me learn to use Smaart to align subs to mains systems.
Click to expand...

I think it's worth taking a Smaart class from Rational, that's the best way to learn how to use their tools.

You say 'phase align', so why are you solely looking at an IR? You have to look at the phase response! I don't even bother with impulse response when aligning subs / mains.

You're going to want to do the alignment at the crossover point, where the boxes have significant overlap. There's no sense in aligning the two components where they're only being used individually.

In short, you're just going to take a look at the phase response of each, and add delay until they match at your crossover frequency.

Delay could be added as 'delay', or as a part of your crossover filters. Also note that your EQ filters will affect the phase response as well, so you're best off tuning the box before aligning to your mains.
 
Re: Phase align subs to mains

David Karol said:
I think it's worth taking a Smaart class from Rational, that's the best way to learn how to use their tools.

You say 'phase align', so why are you solely looking at an IR? You have to look at the phase response! I don't even bother with impulse response when aligning subs / mains.

You're going to want to do the alignment at the crossover point, where the boxes have significant overlap. There's no sense in aligning the two components where they're only being used individually.

In short, you're just going to take a look at the phase response of each, and add delay until they match at your crossover frequency.

Delay could be added as 'delay', or as a part of your crossover filters. Also note that your EQ filters will affect the phase response as well, so your best off tuning the box before aligning to your mains.
Click to expand...

And you want to match the phase slope as well, which can get interesting.

Sent from my SCH-I545
 
Re: Phase align subs to mains

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.

Cheers,
Joey
 
Re: Phase align subs to mains

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
 
Re: Phase align subs to mains

Joey Curran said:
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
Click to expand...

Dual FFT with an measurement mic input and a loop through.
 
Re: Phase align subs to mains

The beauty of the FFT in Smaart is that you don't need loud "anything" to get good results in the sub department. Pink noise at a very moderate volume that isn't filtered is a good bet. If you use pink noise that has been altered you are going to affect the outcome. When I am looking at that alignment in terms of phase I only care about where the sub signal overlaps with the next band. This is the relationship is question. If you have the luxury of doing your tests outside in a free field environment if might be a little easier.

Taking the class was the best money I ever invested in myself as an audio engineer.
 
Re: Phase align subs to mains

Joey Curran said:
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?
Click to expand...

Joey, I like to just use pink noise without any weighting or banding, Smaart's built in "random" noise generator is great and I find a 1-2 second time weighting gives me enough stability. You will probably want to adjust your delay time until the phase trace flattens out in your frequency range of interest. Sometimes this is easier, sometimes it is harder. For instance, here is an alignment I did last week in a 2500 cap theater with large balcony. This is only about 80' away from the mains, which are flown, and the subs on the ground. I have a mic up in the balcony, not shown, which makes the alignment even more complicated. This is one case where your ears are your friend, as this is about as bad as it gets measurement wise.

Screen Shot 2014-03-03 at 2.01.53 PM.jpg
 
Re: Phase align subs to mains

Bennett Prescott said:
Joey, I like to just use pink noise without any weighting or banding, Smaart's built in "random" noise generator is great and I find a 1-2 second time weighting gives me enough stability. You will probably want to adjust your delay time until the phase trace flattens out in your frequency range of interest. Sometimes this is easier, sometimes it is harder. For instance, here is an alignment I did last week in a 2500 cap theater with large balcony. This is only about 80' away from the mains, which are flown, and the subs on the ground. I have a mic up in the balcony, not shown, which makes the alignment even more complicated. This is one case where your ears are your friend, as this is about as bad as it gets measurement wise.

View attachment 9475
Click to expand...


Something strange going on on the blue trace with the phase, ins't it?

"end of offtopic."
 
Re: Phase align subs to mains

Bennett Prescott said:
Carlos, everything about this measurement is strange. It is, however, a good example of what you might see in a normal sized room when trying to do an alignment. It is not pretty!
Click to expand...

But it does show that you don't need picture perfect from 20hz to 20khz if you are focusing in on 50-200hz

Sent from my DROID RAZR HD
 
Re: Phase align subs to mains

This is of course completely off-topic as such, but I bet that in most cases you can get the alignment as good as it gets by the old method of flipping the phase of the subs and delaying to max cancellation using a sine at the crossover frequency. Can Smaart really improve on that?
 
Re: Phase align subs to mains

Per Søvik said:
This is of course completely off-topic as such, but I bet that in most cases you can get the alignment as good as it gets by the old method of flipping the phase of the subs and delaying to max cancellation using a sine at the crossover frequency. Can Smaart really improve on that?
Click to expand...


Yes. Quite a lot. The old way is just valid for one frequency, Smaart gives you the whole picture for all frequencies :)

And you can adjust it and see what's going on in real-time and find a compromise for any given situation. It's easy to demonstrate, I can give you one if you wish.
 
Re: Phase align subs to mains

Per Søvik said:
This is of course completely off-topic as such, but I bet that in most cases you can get the alignment as good as it gets by the old method of flipping the phase of the subs and delaying to max cancellation using a sine at the crossover frequency. Can Smaart really improve on that?
Click to expand...
That's assuming both are in correct polarity to begin with. I guess you can continually flip the polarity button during this exercise, or better still see it very clearly on the phase trace.

Nevertheless, flipping the polarity after things are aligned and in correct polarity is a good litmus test of whether the you did your job well or not in getting the subs aligned properly with the mains.
 
Re: Phase align subs to mains

Per Søvik said:
This is of course completely off-topic as such, but I bet that in most cases you can get the alignment as good as it gets by the old method of flipping the phase of the subs and delaying to max cancellation using a sine at the crossover frequency. Can Smaart really improve on that?
Click to expand...

You can certainly get a usable alignment, but you definitely cannot get it as good as it gets. You're making a number of compromises that are invisible to you. How do you choose relative timing between the balcony and the floor? Only one of them can be correct. I always use polarity, delay, and changes in the LPF of the sub bandpass to get the mains and subs to align over as wide a bandwidth as possible. You are forced to rely on the limited resolution available to you in the frequency domain. Maximum cancellation happens from 120° to 180°, pegging 180° exactly is pretty hard when that range is only 1/3 of the phase wheel - and there are plenty of other complications in the frequency domain from reflections to screw you up. Not to mention you have no way to tell if you're one or more entire periods off. Personally it seems like a waste of time to me when you can just get it right.
 
Re: Phase align subs to mains

Per Søvik said:
This is of course completely off-topic as such, but I bet that in most cases you can get the alignment as good as it gets by the old method of flipping the phase of the subs and delaying to max cancellation using a sine at the crossover frequency. Can Smaart really improve on that?
Click to expand...

How do you know you're not 2 or 3 or 4x through the phase rotation, i.e. 360°, 720°, etc?
 
Re: Phase align subs to mains

Which begs another question....so how do you determine at what frequency the sub and the mains intersect so that you can choose the right frequency sine wave without the aid of an analyzer?
 
Re: Phase align subs to mains

You post confuses me. It is titled Phase align subs, then you state at the beginning how you cannot "find" the subs with the impulse response, then you state you are trying to do just that and failed. Nothing about using the phase trace at all. Is this an attempt to start a discussion on something you already know or perhaps a language barrier?

Indeed everything you stated is correct. It is very difficult to find the subs using the impulse response. For nearly 2 years (2001-2003) before I knew how to read the phase trace I followed the directions Jamie gave in this very old post and successfully aligned my subs every day.

Re: To Jamie ..re Phase response... SIA Support Forum
From: Jamie
E-mail: [email protected] Date: 13 Oct 2000
Time: 13:40:12
Comments
Dave,
Here is a quick way to look at these two types of crossover time alignment (best impulse response vs best crossover response). I have posted a Smaart .rgp file of my data (crossalign.rgp) for those of you playing along at home.
Start with a simple mid-high crossover. Add the same ammount of delay to both drivers (in the case of the data I am posting, I used 50 ms). Start with just the high driver on. Measure the delay, set Smaart's measurement delay, and make a Transfer Function (TF) measurement. The high driver's phase response should look like a smile with the majority of it's range having a relatively flat phase response. (Ref trace A1 in my data) Notice that the phase trace has a downward (read left to right) angle at crossover. This downward angle is mostly due to the crossover filters and is normal/standard in most analog and digital crossovers. This downward angle also indicates that the energy in the crossover range is lagging behind the rest of the driver's energy. (Don't believe me? Add some delay to Smaart's measurement delay setting - you will see that down-angle part of the phase trace level out as the rest of the trace begins to take on a significant up-angle - which indicates leading energy.)
Save the TF trace for your high driver.
NOTE: For the rest of the measurements, DO NOT CHANGE THE SMAART DELAY. We will be looking at phase/timing relationships so we want to keep the same time reference for all of our subsequent measurements.
Now turn off the High driver and turn on the low driver. Vary the delay on the low driver and watch it's effect on the low driver's TF phase reponse. Start by taking away delay (this is why I had you add extra delay to both drivers - its hard to do negative delay) until the low driver's phase response is basically flat with much the same smile shape as the high driver. Adjust the delay as necessary so that the two phase traces cross at crossover while trying to keep as much of the low driver's phase response "flat" (this is shown as trace B1 in my data).
Now combine the two drivers and note what happens at crossover. (this is shown as trace C1 in my data) You should see addition right at crossover but not so much above and below. This makes sense because the phase traces are diverging above and below crossover. In general, the speaker's phase response will be relatively flat over it's pass band.
Now, mute the high driver again, bring up the stored high driver trace, and now add delay to the low driver until it's phase trace OVERLAPS the high driver's phase trace THROUGH CROSSOVER. (This I stored as trace D1). What you have just done is time aligned the two drivers through crossover.

Now when you add both drivers, you will see more addition through crossover, but not as flat a phase trace. (My trace E1)
LISTENING: If your crossover has an input EQ, EQ both alignments to match each other as closely as possible in TF amplitude. Now listen to each alignment.
Keep in mind that the lower in frequency the crossover point, the greater the difference in time between the two alignments.
Hope this helps, -j
Click to expand...

To explain the phase trace on a forum (it's been done) is very difficult. Instead look here....

Understanding Phase - Part 1 - YouTube

and

Understanding Phase - Part 2 - YouTube


Joey Curran said:
Hi Folks,

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

Best Regards,
Joey
Click to expand...
 
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