Delay help please |
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DMorison
Old Croc Joined: 14 March 2007 Location: Aberdeen Status: Offline Points: 1647 |
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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
Registered User Joined: 12 May 2020 Status: Offline Points: 161 |
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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
Registered User Joined: 24 February 2016 Status: Offline Points: 11 |
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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
Old Croc Joined: 03 January 2012 Location: Europe Status: Offline Points: 7199 |
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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. |
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Earplugs Are For Wimps!
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studio45
Old Croc Joined: 16 October 2007 Location: United Kingdom Status: Offline Points: 3863 |
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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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Studio45 - Repairs & Building Commotion Soundsystem -Mobile PA
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JonB67
Young Croc Joined: 22 April 2016 Location: UK Status: Offline Points: 1376 |
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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. |
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DMorison
Old Croc Joined: 14 March 2007 Location: Aberdeen Status: Offline Points: 1647 |
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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
Registered User Joined: 12 May 2020 Status: Offline Points: 161 |
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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 Edited by Sonic the hedge - 17 September 2020 at 5:54am |
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