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Author Topic: Am I on the right track here? (time alignment)  (Read 7916 times)

Scott Middleton

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Am I on the right track here? (time alignment)
« on: April 04, 2011, 03:46:02 pm »

This is a "bar PA" with (2x) JBL sr4733's hung, and (2x) 1x18 subs (JBL drivers, unknown boxes) ground stacked in the center, stage lip. 

So in trying some experiments the other night (no existing time alignment delay at all), I ballparked the subs being 5-7 feet in front of the mains, and so added 5 ms delay to the subs via the Crown XTI DSP.  This is while the band is playing BTW. 

Great, it sound better the low end is tightened up a bit!  So then I think, well maybe I can tweak it just a bit more by delaying the whole PA back to the drum kit.  Looks like the mains are roughly 10 ft ahead of the where the drum kit is usually set up, so I then add 10 ms to the main out on my 01V(and also the aux output that is driving the subs).  Now it sounds even better.  Drums are clearer and the low end is better still.

Granted, this is all guestimation (non scientific I know), but am I on the right track here?  Are there disadvantages to delaying the PA back to the drumkit?
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Tim Weaver

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Re: Am I on the right track here? (time alignment)
« Reply #1 on: April 04, 2011, 05:16:30 pm »

am I on the right track here? 

Yes


Quote
Are there disadvantages to delaying the PA back to the drumkit?

Not until you get to really big stages where the mains delay wouldn't matter much anyway. 10-15 ms of delay on the mains won't hurt anything.
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Mac Kerr

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Re: Am I on the right track here? (time alignment)
« Reply #2 on: April 04, 2011, 05:24:18 pm »

Not until you get to really big stages where the mains delay wouldn't matter much anyway. 10-15 ms of delay on the mains won't hurt anything.

Unless the band can hear the PA clearly, in which case you have just added 10-15ms of additional delay to the time of flight delay they already hear from the PA, perhaps making it appear to be as much as 30ms behind what they are playing.

Mac
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Bennett Prescott

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Re: Am I on the right track here? (time alignment)
« Reply #3 on: April 04, 2011, 05:50:27 pm »

Scott,

I would also fiddle with that sub->top delay by ear, it is not as simple as physical distance.
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Scott Middleton

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Re: Am I on the right track here? (time alignment)
« Reply #4 on: April 04, 2011, 06:03:58 pm »

Thanks guys. 

Will do Bennett.  I'll have the laptop w/ me next time and I can dial in to the XTI with SA and tweak to taste.
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Marsellus Fariss

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Re: Am I on the right track here? (time alignment)
« Reply #5 on: April 04, 2011, 06:23:08 pm »

I agree with Bennett. I start by sending a sine wave at the crossover frequency through the rig with the phase of the sub (or the tops) inverted then tweak the delay time of the subs back and forth till you get to the point of most cancellation and the apparent volume is at it's lowest point. Then flip the phase back to normal and season to taste by ear.

I also always delay my rig to the back line unless it's going to cause latency problems like those described. Stand on stage yourself and talk in a vocal and see if you can hear any distracting latency. In my room it works out amazingly well. If your doing a show where the muso's are quiet and down stage you can kill the delay if you want.

And also consider that your DSP and console have some small amount of latency on their own. It's probably not enough to cause problems but if you've got other AD/DA in your chain these things can add up. Do a search on this and keep it in mind when programing.

Also I believe the standard feet to milliseconds multiplier is 1.125 milliseconds per foot.


One other thing to keep in mind is that your only time aligning the sources to people who are out front of the rig and the stage. People in other areas will still have arrival time issues. But that's life.   
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Scott Middleton

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Re: Am I on the right track here? (time alignment)
« Reply #6 on: April 04, 2011, 10:06:44 pm »

Unfortunately I can't do the polarity flip trick until I can get in there w/ no patrons.  Its a bar and grill, so this is rare.  I hope to get this done eventually.

I'll keep latency of other gear in mind.

Yep, I was guestimating 1ms = 1ft.

If I can get the "dancefloor" area aligned and sounding good, that's my big concern.  Other areas, not so much.

This is down and dirty for sure.  Any improvement I can get is better than how it sounds now.
« Last Edit: April 04, 2011, 10:15:08 pm by Scott Middleton »
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Brad Weber

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Re: Am I on the right track here? (time alignment)
« Reply #7 on: April 04, 2011, 10:47:02 pm »

If I can get the "dancefloor" area aligned and sounding good, that's my big concern.  Other areas, not so much.
Achieving alignment over an area can be difficult.  For example, on the centerline of the stage the subs may be around 5' in front of the mains but to listeners out to either side of the edge of the mains coverage the subs may be more than 5' ahead ahead of the more distant main but behind the closer main.
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Dan Johnson

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Re: Am I on the right track here? (time alignment)
« Reply #8 on: April 05, 2011, 12:05:59 am »

Also I believe the standard feet to milliseconds multiplier is 1.125 milliseconds per foot.
I think you have this backwards.  It would be 1.125 feet per millisecond which is equivalent to 0.889 milliseconds per foot.

If you want to be really picky, there are other factors that affect the speed of sound such as altitude and temperature but these numbers are good enough for estimating delay times.
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luis Markson

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Re: Am I on the right track here? (time alignment)
« Reply #9 on: April 05, 2011, 03:39:28 am »

In the case of a system like a Mackie S410s with S408 pole mounted on top, is there anything to be gained by experimenting with sub -> top delay?

I am assuming that Mackie would have considered this during manufacture? Or are unpowered speakers at this level often neglected in this area?

How would you go about listening for correct alignment?

I like the sound of using a pure sine wave, flipping the phase of either the top or sub and then listening for maximum cancellation. I am assuming that you would use a tone at the crossover frequency? My understanding of crossover types and their implications is sorely lacking though so I'm guessing there is going to be more to it.



« Last Edit: April 05, 2011, 04:04:04 am by luis Markson »
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ProSoundWeb Community

Re: Am I on the right track here? (time alignment)
« Reply #9 on: April 05, 2011, 03:39:28 am »


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