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Author Topic: SMAART help  (Read 29829 times)

Phillip_Graham

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Re: SMAART help
« Reply #20 on: April 28, 2010, 09:29:14 am »

Evan Kirkendall wrote on Tue, 27 April 2010 17:20

You want your phase trace to look similar to the pink trace in this shot:

http://i39.photobucket.com/albums/e194/HarfordSound/sublowdelay.png

Measurements were made 10' away from the cab in the ground plane. The pink trace is the combined sub and low of the system once they've been aligned.



Evan


Adam,

Not to confuse you further, but Evan's posted way of doing this and what Mac is describing are not using the phase information in the same way, though the end result is the same.  The difference is why Mac's phase traces will not be flat near the XO point, but Evan's phase traces will be.

Mac is instructing you to pick a fixed reference delay time in Smaart (by using AutoSM/Delay Finder) and then adjust the top delay till the slope of the sub phase and the top phase are the same in the crossover region.

Evan's way is manually adjusting the reference delay till you have zero apparent group delay at the desired XO point.  You do this for each of the boxes, and then subtract the adjusted reference delay times from each other to find out the relative delay difference between the boxes.

In the specific example Evan posted, Evan appears to have done:
1. Adjust the SMAART reference delay time for the sub (i.e. Blue) trace until it looks like the blue trace on the screen.  Typically starting with an AutoSM and then adding additional delay.
2. Shoot the top trace (i.e. Orange) using the current (i.e. Blue) reference delay time.

The next step would then be:
3. Adjust the Smaart reference delay until the Orange curve lays on top of the Blue curve.
4. Compare the reference delay of the Blue curve to the Orange, and apply the necessary differential delay to the appropriate box.  Usually that is the top box, but not always.

The final result of this, using the original Blue reference delay time, is the pink curve displayed.

Both this method and Mac's method achieve the same final result (i.e. phase alignment at the XO).  Mac's method is easier to explain, but can be more difficult to perform.

I personally find the method Evan shows easier to do in difficult acoustic environments, and that is the method I teach new users first.  Also, in a class setting, the method Evan is doing allows me to expound a deeper conceptual understanding of what is really going on.

Since I taught Evan this method, he can expound on whether he felt that it helped give him a deeper understanding of what the phase trace is really saying.
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Adam Schaible

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Re: SMAART help
« Reply #21 on: April 28, 2010, 10:33:59 am »

Ok... I am following this I think - however, the blue and orange lines seem to have opposite(ish) slopes... shouldn't they be similar?
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Tim McCulloch

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Re: SMAART help
« Reply #22 on: April 28, 2010, 11:16:58 am »

No.  You are interested in the phase AT THE POINT OF ACOUSTIC CROSSOVER.  What the phase does above or below (beyond an octave from that point) is mostly irrelevant (unless it affects yet another acoustic crossover).

Re-read Phill's post.  Using delay within SMAART to flatten the phase trace in the frequency range of interest is manipulating the *display* to make it easier to line up.  It's not how flat the trace is but how well the traces from 2 adjacent pass-bands overlay.

Harry teaches both methods in his class, and folks usually grok 1 method first and then slowly figure out the other.  Don't freak out if you don't "get it" the first time.  Keep practicing, making bad measurements, etc until you get it.  It will happen.

Have fun, good luck.

Tim Mc
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Adam Schaible

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Re: SMAART help
« Reply #23 on: April 28, 2010, 11:25:43 am »

Well, I might be more confused now than prior to re-reading Phillip's post.  I really don't see the orange laying on the blue at all?  I understand that everything above 200-250hz is not relevant in this situation and I do understand the method -- you're just adding the delay to SMAART rather than your DSP until it lines up, and then transferring that delay to the DSP -- or am I off base?  My problem is I seem to be interpreting the measurement graph incorrectly.  When I look between 63hz and 125hz the orange line (tops) has a negative slope and the blue line has a positive slop (subs).  I thought that would indicate a polarity issue - but clearly the magnitude trace shows pretty good summation.

And thanks again Tim et all.
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Mac Kerr

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Re: SMAART help
« Reply #24 on: April 28, 2010, 11:33:29 am »

Adam Schaible wrote on Wed, 28 April 2010 11:25

Well, I might be more confused now than prior to re-reading Phillip's post.  I really don't see the orange laying on the blue at all?  I understand that everything above 200-250hz is not relevant in this situation and I do understand the method -- you're just adding the delay to SMAART rather than your DSP until it lines up, and then transferring that delay to the DSP -- or am I off base?  My problem is I seem to be interpreting the measurement graph incorrectly.  When I look between 63hz and 125hz the orange line (tops) has a negative slope and the blue line has a positive slop (subs).  I thought that would indicate a polarity issue - but clearly the magnitude trace shows pretty good summation.

And thanks again Tim et all.


The orange trace doesn't line up because it is the pre adjustment trace. The pink trace is after adjustment. I still think my way is simpler (I think I learned it from 606, but I could be wrong). Remember that you are looking for the difference between the 2 delay times. The time you end up with in Smaart is not the delay time for the tops.

Mac
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Adam Schaible

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Re: SMAART help
« Reply #25 on: April 28, 2010, 11:37:37 am »

Ok, that makes more sense now.

I agree, that method is simpler -- I understand you're looking for the difference between the initial Auto SM delay and the new delay to get them to lay on top of each other.

However, mine looked similar - but my reaction was to invert the polarity of my subs because that made the lines roughly 2.25ms apart.  I would have had to delay quite a bit more without the polarity reversed.

So, how do I know if I should reverse polarity, or add more delay?
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Bennett Prescott

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Re: SMAART help
« Reply #26 on: April 28, 2010, 11:53:57 am »

Adam Schaible wrote on Wed, 28 April 2010 11:37

So, how do I know if I should reverse polarity, or add more delay?

Heh... first, do this about a thousand times with different systems set up different ways in different locations.

Seriously, it's not just one or the other. If inverting polarity allows you to get your desired phase alignment with less delay, then do that. Just don't get into any arguments about absolute polarity with anyone, I wouldn't win one of those either...
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Rich Grisier

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Re: SMAART help
« Reply #27 on: April 28, 2010, 12:01:16 pm »

Adam Schaible wrote on Tue, 27 April 2010 13:28

My goal is to phase align my tops and subs, but before that I need to time align them.


Here's a simple method I've used to time align a top:

1. System is on, but volume is off.
2. Send a sine wave into the FOH board with the frequency set to the top/sub crossover frequency.  The signal generator in Room EQ Wizard can do this.
3. Reverse the phase on the signal going to the sub.  I use a speaker cable with a banana connector flipped over at the amp end.
4. Set up a flat mic (dbx rta mic) in front of the system.
5. With the pfl ON and fader down on the rta mic, bring the sine wave volume up so you can hear it.
6. While monitoring the rta mic level, adjust the delay time of the tops.  The level seen by the mic should start to drop as you increase the delay time.  The level will reach a low point and then start to come back up.  At that point there is too much delay.  The delay is properly set when the level is at its lowest point.

Of course this doesn't help you with SMAART at all, but it does achieve your goal.
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Adam Schaible

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Re: SMAART help
« Reply #28 on: April 28, 2010, 12:03:08 pm »

Ok, thanks Bennett..

One more question -- is there any difference between time and phase alignment?  It may be a fairly obvious question, as I really don't see how one could adjust time alignment without affecting phase and vice versa.

Also - would the measurements change if the source volume changes?  When doing my subs, if I got them too loud my furnace/etc would resonate so I turned the signal generator down some.  For the tops, I bumped it up a bit.

I think I have it close now.
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Adam Schaible

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Re: SMAART help
« Reply #29 on: April 28, 2010, 12:05:12 pm »

Rich Grisier wrote on Wed, 28 April 2010 11:01

Adam Schaible wrote on Tue, 27 April 2010 13:28

My goal is to phase align my tops and subs, but before that I need to time align them.


Here's a simple method I've used to time align a top:

1. System is on, but volume is off.
2. Send a sine wave into the FOH board with the frequency set to the top/sub crossover frequency.  The signal generator in Room EQ Wizard can do this.
3. Reverse the phase on the signal going to the sub.  I use a speaker cable with a banana connector flipped over at the amp end.
4. Set up a flat mic (dbx rta mic) in front of the system.
5. With the pfl ON and fader down on the rta mic, bring the sine wave volume up so you can hear it.
6. While monitoring the rta mic level, adjust the delay time of the tops.  The level seen by the mic should start to drop as you increase the delay time.  The level will reach a low point and then start to come back up.  At that point there is too much delay.  The delay is properly set when the level is at its lowest point.

Of course this doesn't help you with SMAART at all, but it does achieve your goal.



That's how I did it initially but I think with a sine wave you can be 360 degree's out (or 180 + polarity reversal of course) and still have perfect summation, but not have achieved your goal.  Am I off base here?
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