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Author Topic: Am I on the right track here? (time alignment)  (Read 7933 times)

Bennett Prescott

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Re: Am I on the right track here? (time alignment)
« Reply #10 on: April 05, 2011, 03:59:41 am »

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.

That technique works, of course, but the problem with it is... what is the crossover frequency?

This is a lot easier to do if you have made the phase slope of your tops and subs equal for an octave or so around what you want to be the crossover point. This usually means adding a few orders of XO to the sub LPF, or subtracting a few from the top HPF. My preference is to subtract from the tops HPF, which usually means a 2nd order filter. I find anything more than 4th order sounds like dog shit, which really means you're dealing with 6th-8th order acoustically if you're crossing near the tuning frequency of the box or the natural rolloff of a driver.
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luis Markson

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Re: Am I on the right track here? (time alignment)
« Reply #11 on: April 05, 2011, 04:07:40 am »

That technique works, of course, but the problem with it is... what is the crossover frequency?

This is a lot easier to do if you have made the phase slope of your tops and subs equal for an octave or so around what you want to be the crossover point. This usually means adding a few orders of XO to the sub LPF, or subtracting a few from the top HPF. My preference is to subtract from the tops HPF, which usually means a 2nd order filter. I find anything more than 4th order sounds like dog shit, which really means you're dealing with 6th-8th order acoustically if you're crossing near the tuning frequency of the box or the natural rolloff of a driver.

Rather than hassle you for a beginners lesson on XO, so I can understand your above post, could you refer me to a good resource on XO fundamentals...
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Marsellus Fariss

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Re: Am I on the right track here? (time alignment)
« Reply #12 on: April 05, 2011, 04:09:48 am »

In the case of a system like a Mackie S410s with S408 pole mounted on top, is there anything to be gain 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 tis area?

Doubtful. If they picked a distance to allign the two they'd be wrong in a lot of other user scenarios. But having the tops right over the subs is a good scenario. Things will be pretty close depending on your distance to the rig but you can experiment with your DSP. I find it a great lesson in physics if you can delay the rig to a rather loud backline in real time and hear how it pops together while the shows going on.
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Marsellus Fariss
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luis Markson

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Re: Am I on the right track here? (time alignment)
« Reply #13 on: April 05, 2011, 04:16:33 am »

Post deleted because it was unnecessary waffle
« Last Edit: April 05, 2011, 04:23:09 am by luis Markson »
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Marsellus Fariss

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Re: Am I on the right track here? (time alignment)
« Reply #14 on: April 05, 2011, 04:38:57 am »

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.

Yea, thanks for correcting me on that. Your right.

Even though things get cloudy in the realm of time arrivals often enough if you get close with the math you'll hear a noticeable improvement under the right conditions. I think the more the backline volume effects your mix (like a small venue) the more you'll hear the difference. A few times I've forgotten to reset my delay to backline from the night before and have done it mid show and went WOW! Make sure your DSP or console can do this w/o audio dropouts though. 
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Marsellus Fariss
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Russel Murton

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Re: Am I on the right track here? (time alignment)
« Reply #15 on: April 05, 2011, 11:18:29 am »

Yea, thanks for correcting me on that. Your right.

Even though things get cloudy in the realm of time arrivals often enough if you get close with the math you'll hear a noticeable improvement under the right conditions. I think the more the backline volume effects your mix (like a small venue) the more you'll hear the difference. A few times I've forgotten to reset my delay to backline from the night before and have done it mid show and went WOW! Make sure your DSP or console can do this w/o audio dropouts though.

I played with time aligning my QSC KW rig to the backline but I came into problems with the bleed from the monitors near the front of the crowd, also whilst the rest of the band's definition increased in clarity, the vocals started to cancel with the monitor bleed. Then when I had a band which didn't have a drumkit and lots of line level the cancellations between the monitors and the FOH were even more startling, resulting in it sounding a little off timing wise.

In the end I now time align the subs to the tops and leave the tops at 0msec as the vocal clarity is my main concern. I'd rather use a Radial Phazer 4 channel rack to align the guitars, bass DI and snare bottom than worry about aligning to the backline. It might be worth it in a very big room or outdoors, but when you are in a norrow room the side reflections mess with things a lot.
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Bennett Prescott

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Re: Am I on the right track here? (time alignment)
« Reply #16 on: April 05, 2011, 03:02:10 pm »

Rather than hassle you for a beginners lesson on XO, so I can understand your above post, could you refer me to a good resource on XO fundamentals...
Luis,

Here is a fantastic resource, math heavy but if you're good at that (I am not) it can help you a lot. This guy is the L in the Linkwitz-Riley crossover filter set.

http://www.linkwitzlab.com/crossovers.htm
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Scott Middleton

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Re: Am I on the right track here? (time alignment)
« Reply #17 on: April 06, 2011, 08:12:51 pm »

I played with time aligning my QSC KW rig to the backline but I came into problems with the bleed from the monitors near the front of the crowd, also whilst the rest of the band's definition increased in clarity, the vocals started to cancel with the monitor bleed.

Try flipping the polarity on the wedges.  I had to do this the other day for a gig.
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Todd Huffines

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Re: Am I on the right track here? (time alignment)
« Reply #18 on: April 07, 2011, 09:53:16 pm »

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.

   I thought that sound traveled at 1130 or so feet per second.  That speed is constant.  Humidity has an affect on the thickness of the medium "air" which has a big deal with how far the sound carries from the source.  Since sound will not travel in a vacuum then the thicker the air the better sound moves. 

This thread has struck me as one of the most interesting for me.  When there is plenty of stage bleed, I am gathering that a little delay will help.  I am going to play with my dr260 on this.  Should be easy to do at the next soundcheck.   I am loving this!
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Rob Spence

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Re: Am I on the right track here? (time alignment)
« Reply #19 on: April 08, 2011, 12:51:50 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.

   I thought that sound traveled at 1130 or so feet per second.  That speed is constant.  Humidity has an affect on the thickness of the medium "air" which has a big deal with how far the sound carries from the source.  Since sound will not travel in a vacuum then the thicker the air the better sound moves. 

This thread has struck me as one of the most interesting for me.  When there is plenty of stage bleed, I am gathering that a little delay will help.  I am going to play with my dr260 on this.  Should be easy to do at the next soundcheck.   I am loving this!
Sound travels at different speeds through air at differing humidities and temperatures.
In dry air at 20 C (68 F), the speed of sound is 343.2 metres per second (1,126 ft/s).
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Re: Am I on the right track here? (time alignment)
« Reply #19 on: April 08, 2011, 12:51:50 am »


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