# Measuring Speaker Distances/Delays



## GGA (Oct 31, 2006)

I thought I had read that REW could measure the time delay between the onset of the signal and its arrival at the mic, thereby giving an indirect measurement of speaker distance, but I can't seem to find out where it is in the program. Did I imagine this?

I understand that the time delay will include the latency of all the devices in the chain. I think that is ok since I am really interested only in the differences in the time delays.

I want to measure how far away each speaker in my 7.1 setup is from the listening position so I can put the values in my surround processor. Since the chain before for each speaker is not necessarily identical because of external boxes such as crossovers and equalizers, I want to measure the time delay of the chain and not the simple physical distance.

I assume for my subwoofers with 80Hz crossovers that I will not be able to measure their delay because of the long wavelengths and will have to make a best guess.

Thanks!
George


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## JohnM (Apr 11, 2006)

To do this you need to make a loopback connection on the channel you are not using for measurement (e.g. left channel if you are measuring with the right) and in the REW Analysis preferences tell it you have done this by ticking the box "Use Loopback as Timing Reference". If you look at the Info box (Info button in the toolbar) for measurements made after you have done that you will see a System Delay figure that shows the time and the corresponding distance.


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## Jonas_h (Jan 7, 2009)

I know this is an old thread, but I have a follow up question.

The point about long wavelengths and distance-calculation for subs makes sense. But does this mean, that all phase traces etc is not usable below a certain frequency? How would you actually measure the subs distance with REW?


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## JohnM (Apr 11, 2006)

Jonas_h said:


> But does this mean, that all phase traces etc is not usable below a certain frequency?


No, but phase info requires a time reference to be meaningful (i.e. to remove the effect of time delays), but that is true for all frequencies.



> How would you actually measure the subs distance with REW?


Give the sub as wide a bandwidth signal as it can reproduce and bypass the crossover, the more bandwidth the signal has the better resolved the peak, but for low bandwidth signals modal resonances can shift the peak substantially, giving incorrect delay estimates. A more accurate method would be a tape measure for the physical distance to the sub and direct electrical connection of the signal driving the sub to the soundcard input to accurately measure the delay of the signal feeding the sub.


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