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Delay help please

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DMorison View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DMorison Quote  Post ReplyReply Direct Link To This Post Posted: 15 September 2020 at 1:21pm
Originally posted by Darkstar Darkstar wrote:

Originally posted by Earplug Earplug wrote:

"You will need a microphone you can trust for the measurement."

With the above method, you don't actually need a microphone! Just a decent signal generator.   Smile


How are you going to find out if you're canceling?

With your ears!

Seriously, anyone that can't hear the cancellation when this method is properly applied does not belong in charge of any kind of sound system.

No, it's not as good as a proper measurement mic/dual channel FFT analyzer like Smaart, Systune etc, but the whole point is to get at least in a credible ballpark without that investment.
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Sonic the hedge View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Sonic the hedge Quote  Post ReplyReply Direct Link To This Post Posted: 15 September 2020 at 4:15pm
Originally posted by DMorison DMorison wrote:

Originally posted by Darkstar Darkstar wrote:

Originally posted by Earplug Earplug wrote:

"You will need a microphone you can trust for the measurement."

With the above method, you don't actually need a microphone! Just a decent signal generator.   Smile


How are you going to find out if you're canceling?

With your ears!

Seriously, anyone that can't hear the cancellation when this method is properly applied does not belong in charge of any kind of sound system.

No, it's not as good as a proper measurement mic/dual channel FFT analyzer like Smaart, Systune etc, but the whole point is to get at least in a credible ballpark without that investment.

I would agree WRT to phase setting but as I described previous it's a little harder to find the correct delay using only your ears and a test tone, due to the width of the cancellation band.

A dB meter phone app is perfectly adequate for this task and also free, no investment required.


Edited by Sonic the hedge - 17 September 2020 at 4:18am
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Semtek_soundsystem View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Semtek_soundsystem Quote  Post ReplyReply Direct Link To This Post Posted: 15 September 2020 at 4:22pm
Thank you very much for the replies, from what I gather this means I could create an audio file which is a narrow band sinewave  at the crossover frequency, and if it is pulses instead of a continuous sine I should be able to time align and phase align at the very first peak? So would hear no sound whatsoever when time aligned correctly, other wise I'd hear the sine by the amount of incorrect delay, see that makes sense to me, please let me know if I'm way off? Thanks again for taking time to reply
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Earplug View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Earplug Quote  Post ReplyReply Direct Link To This Post Posted: 15 September 2020 at 6:13pm
Originally posted by Semtek_soundsystem Semtek_soundsystem wrote:

Thank you very much for the replies, from what I gather this means I could create an audio file which is a narrow band sinewave  at the crossover frequency, and if it is pulses instead of a continuous sine I should be able to time align and phase align at the very first peak? So would hear no sound whatsoever when time aligned correctly, other wise I'd hear the sine by the amount of incorrect delay, see that makes sense to me, please let me know if I'm way off? Thanks again for taking time to reply



Use a swept sine wave up and down around your xover point.

If say, you're crossing at 100Hz, use 90Hz - 110Hz, etc.

Then set the delay for maximum cancelation.



Earplugs Are For Wimps!
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studio45 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 15 September 2020 at 6:15pm
Nah that's overcomplicating things, plus it probably wouldn't work very well as the pulse rate would be tied to a very specific frequency, and you don't know what the real acoustic crossover point between your cabs is until you get the rig set up, the gains and EQ all set, and measure it with a mic. 
If you want to be sure you've hit the first peak, once you know the real acoustic crossover freq., you can wind the delay back and forward in increments of the time for 1 cycle at that frequency, and see if it sounds/measures better or worse.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JonB67 Quote  Post ReplyReply Direct Link To This Post Posted: 15 September 2020 at 8:52pm
Ok, slightly different track,  first one is a 'how to" link for using room eq wizard and second one is a thread with lots of info in the next few pages, several links and ideas, including using warbles instead of sine waves. Hope they're helpful and interesting for you.  

https://forum.speakerplans.com/time-alignment-using-rew-and-cheap-mic_topic102425.html


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DMorison View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DMorison Quote  Post ReplyReply Direct Link To This Post Posted: 16 September 2020 at 1:19pm
Originally posted by Semtek_soundsystem Semtek_soundsystem wrote:

Thank you very much for the replies, from what I gather this means I could create an audio file which is a narrow band sinewave  at the crossover frequency, and if it is pulses instead of a continuous sine I should be able to time align and phase align at the very first peak? So would hear no sound whatsoever when time aligned correctly, other wise I'd hear the sine by the amount of incorrect delay, see that makes sense to me, please let me know if I'm way off? Thanks again for taking time to reply

I'm not sure that would work, as you'd be trying to hear very short portions of a cycle which may not even be audible.

As I said earlier but I'll emphasize again, this is only a technique for getting in the ballpark.

If you want absolute time alignment done properly, you're into software & a mic.

I'm not as up to date on the various phone apps as Sonic is suggesting; if they're up to it all well & good.
Otherwise even a 30 quid Behringer mic & free SW like REW will still be better than doing it by ear.

Cheers, 
David
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Sonic the hedge View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Sonic the hedge Quote  Post ReplyReply Direct Link To This Post Posted: 16 September 2020 at 6:37pm
Originally posted by Darkstar Darkstar wrote:

Originally posted by Semtek_soundsystem Semtek_soundsystem wrote:

Thanks darkster, but although it would be phase aligned at crossover it could be poorly time aligned still, it just doesn't make sense in my head.  Imagine these arrows are up and down cycles of a sinewave <><><><><><>
As long as any of those positive or negative cycles are allinged it will cause phase cancellation, but they may not be the same  positive or negative peak so will not be time aligned correctly,? 

As Sonic said that is correct, you will be time and phase aligned at crossover frequency but it won't guarantee full band phase alignment (unless you have a linear system).

That was my point.

You also have to keep in mind that any changes in the EQ or output level will alter the crossover point and everything that goes with it.

I agree with all of that - any band EQ (e.g. LMS output EQ) and level for each band must be set before testing and aligning phase. Remember too, that limiters on LMS outputs or amplifier inputs, are also gain controls, so may impact phase if triggered! 

Full range EQ/limiting isn't a problem, because phase shift due to that will be equal/consistent around any particular frequency/x-over point.

Another key point is that real world speakers almost never have linear phase response. There is always some sort of tilt, curve, or pattern, so it's nigh impossible, to match phase, over full bands, between two or more bands. 

IMHO, the most important goal, is to eliminate any big step in phase response. This can be achieved, by adjusting phase of one band, so it joins up with the phase of the adjoining band, at the crossover frequency, or thereabouts. This can be done easily, using just a test tone and dB meter.

FFT analysis does allow smoother matching, because you can compare phase plots for each band and find a region where the slopes are more or less quite similar. By centering the phase alignment point on that region, you get a closer phase match over a wider band. 

You may then choose to move crossover point to suit the phase match frequency, but obviously there are other considerations e.g. power, sensitivity and dispersion etc. 

Another possibility, adjust crossover slopes to suit - steep rolloff when phase match region is narrow, shallow rolloff when a wider phase match region has been found.

TLDR: tone method gives good result and is easy. FFT analysis, can give better result, but it's much, much, more complex! IMHO not just about cost  - not everyone, has the time, or inclination, to spend days researching and twiddling! 

Worth also to remember, that phase adjustment, is essentially in reality, just a frequency dependent delay. So the delay added, by phase adjustment, applies to the whole band. But amount of delay added, by LMS, for particular phase angle setting, is based on x-over frequency, at bottom of band. 

So whatever setup method is used, you have to start at the bottom. Set phase for each band in turn, taking into account phase shift(s) already applied to proceeding band(s), either by measurement, or by calculation. 

That's how I understand it anyhow...as always DYOR, there are many considerations, sometimes conflicting, so ultimately there are no right answers, only viewpoints, IMO Tongue



Edited by Sonic the hedge - 17 September 2020 at 5:54am
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