# Understanding delay



## phazewolf (Feb 5, 2012)

Well I have all my speakers setup and a nice avr but there is something I need help with and that is understanding how delay aka distance works. Now if I am reading it right if my mains are 10 feet away and I set there distance to 10 feet that will add about 10ms of delay to when they fire however if that is true speaker that are closer to me would fire sooner then speakers that are not at close and that don't sound correct to me.

Would you not want the speakers that are greater distance away to fire first so all the sound gets there at the same time? Please help me understand what I am missing here.


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## SAC (Dec 3, 2009)

Your understanding is skewed a bit, but you are on the right track..

As sound travels at ~1.13 ft/ms, by setting the delay in terms of distance you are setting the time value for the signal delay corresponding to the various sources. 

And yes, the sources spaced further away are delayed less than the nearer sources, such that the goal is that the signal from each all arrive simultaneously at the designated spot from which you determined the distance.

But the way the unit is set up, it translates your settings relative to the listening positions and does not literally delay each source by the same literal 'value' you input. Thus, to keep this simple - and simplifying the velocity of sound to be 1ft/ms - if you have speakers spaced 10 feet away and another at 6 feet, the closer speaker would be delayed 4ms (or 10ms-6ms) in order to have its signal arrive simultaneously with the further speakers.


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## phazewolf (Feb 5, 2012)

OK so the mains are 10' when I set then too ten feet and the back speakers to 7' your saying the rears will be delayed more then the mains because they are closer correct? I ask because the pro amp I have for the subs has delay in ms and also feet and the way it looks the lower the amount in feet the lower the delay.


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## SAC (Dec 3, 2009)

phazewolf said:


> OK so the mains are 10' when I set then too ten feet and the back speakers to 7' your saying the rears will be delayed more then the mains because they are closer correct? I ask because the pro amp I have for the subs has delay in ms and also feet and the way it looks the lower the amount in feet the lower the delay.


NO. The furthest speakers are not delayed at all. The rear speakers are not delayed "more" than the mains. The mains being farthest away are not delayed at all. And the rear speakers, being closest have their signal delayed relative to the mains located farthest away.

The signal to the speakers set closer are delayed to be equal to the time required for the furthest speaker signals to arrive.

I would suggest using REW and the impulse or ETC response to precisely determine the time value of the signal offset required for each source if you have a precision delay unit incorporated in an amp (such as the Crowns).. Simply using the receiver settings to the nearest foot is not very precise.


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## phazewolf (Feb 5, 2012)

Ok that is kind of what I thought. It is really hard to find info on how delay works and I really like too understand how things work. I may take a 4 channel scope and hook it up and play with the delay and see how it offsets as I adjust things.


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## SAC (Dec 3, 2009)

A "4 channel scope" will not display signal arrival in the time domain sufficient to effect the adjustments necessary!

There is a reason I stated a _time _domain based tool such as REW.


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## phazewolf (Feb 5, 2012)

Well I am getting a Mic and the power supply soon so I guess it will wait until I get that setup and go from there. I just thought a scope would work sense I have used it to work on electronics for years and had it handy. Thanks for the help.


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## SteveHi (Nov 19, 2009)

One can certainly use an oscilloscope to measure time delay. You can connect four probes to four separate signal paths, choosing the farthest one (physically located) to trigger the 'scope. The use of specific-frequency test tones, 200 Hz for example, is helpful in establishing a consistent trigger for a solid display. This technique can be used (with proper calibration) to determine picoseconds of delay differences. Any inherent errors in the 'scope probe setup will be on the order of nanoseconds, and will be irrelevant to the overall measurement. This error comes from the physical length of the connections from the 'scope to the speakers, 10 feet ~ 10 nanoseconds, 30 feet ~ 30 nanoseconds, etc.


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