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Author Topic: LR-24 360 phase shift?  (Read 6458 times)

Daniel Mock

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LR-24 360 phase shift?
« on: March 27, 2015, 08:02:50 pm »

So I figured that if I measure the horn paths I could easily calculate delay for system time alignment, but I just read an article saying I need to account for the 360degree phase shift cause by LR-24.
How do I do this?

My system is 4-way:
SUB: BW HP 30hz, LR-24 LP 127hz, 50"hornLength
LOW: LR-24 HP 127hz, LR-24 LP 440hz, 30" hornLength
MID:LR-24 HP 440hz, LR-24 LP 5.5khz 10" hornLength
HI: LR-24 HP 5.5khz, off, 8" hornLength

What polarity setting and delay do I need
to properly time align system when using LR-24?
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John Roberts {JR}

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Re: LR-24 360 phase shift?
« Reply #1 on: March 27, 2015, 08:32:15 pm »

What does the article say to do?  ;D

Phase shift and time delay are different things.

A 4 pole Linkwitz-Riley exhibits 180' of phase lead, in one output and 180' of phase lag in the other. !80'+180'=360'=0'

The L-R alignment are both -6dB at tuning so they combine, in phase to 0dB, or unity.

Any delay you add should be to compensate for path length transit time differences, not the crossover.

JR
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Daniel Mock

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Re: LR-24 360 phase shift?
« Reply #2 on: March 28, 2015, 04:28:32 am »

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Ivan Beaver

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Re: LR-24 360 phase shift?
« Reply #3 on: March 28, 2015, 11:47:57 am »

So I figured that if I measure the horn paths I could easily calculate delay for system time alignment, but I just read an article saying I need to account for the 360degree phase shift cause by LR-24.
How do I do this?

My system is 4-way:
SUB: BW HP 30hz, LR-24 LP 127hz, 50"hornLength
LOW: LR-24 HP 127hz, LR-24 LP 440hz, 30" hornLength
MID:LR-24 HP 440hz, LR-24 LP 5.5khz 10" hornLength
HI: LR-24 HP 5.5khz, off, 8" hornLength

What polarity setting and delay do I need
to properly time align system when using LR-24?
It is not that simple.

As you change freq-the "delay" (phase shift) of the filter also changes.

This is easily seen on a measurement.

And when you are figuring your "horn length", what is this based on? The actual length of the horn? or a distance to some point in space.

  If the horns do not occupy the same physical space (and that is NOT simply being in the same cabinet) then the distance to a person listening will be different for each horn.

And once you move the position of the person listening-the distance from each horn will change.

You have to figure out "what position is most important" and go from there-and just accept the fact that all the other listening positions will be "off".  No way around it.

The problem is that phase/delay is not something that is an "easy question".

You also need to account for the phase response of each particular driver.

That is why it is SOOOOOO much easier to simply measure and see the phase response than to attempt to "calculate it"-especially when there are "unknowns" in the equation.

You can adjust the delay time in real time-see the results-see the interactions above and below crossover freq and so forth.
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Ivan Beaver
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PHYSICS- NOT FADS!

John Roberts {JR}

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Re: LR-24 360 phase shift?
« Reply #4 on: March 28, 2015, 12:19:01 pm »

Here is the article
http://www.livesoundint.com/archives/2003/july/align/align.php

I just looked at that article and did not see any mention about a L-R crossover alignment.

John did list his email.  ;D ;D ;D (I knew him when he worked at Peavey on Media Matrix)

As Ivan stated there is nothing easy about this...

JR
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Timo Beckman

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Re: LR-24 360 phase shift?
« Reply #5 on: March 29, 2015, 10:38:25 am »

So I figured that if I measure the horn paths I could easily calculate delay for system time alignment, but I just read an article saying I need to account for the 360degree phase shift cause by LR-24.

Measuring the distance between drivers doesn't do the trick. If you apply a low pass filter  on a driver the timing changes. I did a couple of screen recordings where you can see what happens at processor level when a low-pass filter is applied.

https://timobeckmangeluid.wordpress.com/2015/02/28/butterworth-high-and-low-pass-filters-up-to-8th-order-and-back-again/

From about 3min in to the screen recording the fun starts with the low-pass filters and at 5min into the recording i set Smaart to
delay tracking to show what happens.
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Daniel Mock

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Re: LR-24 360 phase shift?
« Reply #6 on: April 03, 2015, 03:17:37 am »

My goal is for full coverage area to be "pretty good". Perfecting a sweet spot only makes other areas worse which isn't good when you're trying to cover a large audience.
I guess you could say I'm seeking the full possible summation from horns/drivers out of the cabs overall.
Most of the time I do this by measuring horn paths to get an estimation of delay then twiddle with the delay unit it sounds the loudest.  But honestly have no idea of what I'm doing is correct at all, especially now considering LR24 phase shift.
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Daniel Mock

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Re: LR-24 360 phase shift?
« Reply #7 on: April 03, 2015, 03:19:45 am »

Are FIR filters void of this phase shift issues?
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Luke Geis

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Re: LR-24 360 phase shift?
« Reply #8 on: May 09, 2015, 07:24:33 pm »

It's linear. So the phase shift is the same at all frequencies. Quick and dirty article. http://www.dspguru.com/dsp/faqs/fir/properties
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Lyle Williams

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Re: LR-24 360 phase shift?
« Reply #9 on: May 10, 2015, 04:13:52 pm »

But FIR boxes still suffer from the bigger issue that all the drivers aren't in the same place and that the patterns they throw change with frequency.

FIR is a fix to the fourth biggest problem in the room.
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ProSoundWeb Community

Re: LR-24 360 phase shift?
« Reply #9 on: May 10, 2015, 04:13:52 pm »


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