# Need Help Understanding REW Phase Measurement



## Kevin R. Anderson (Feb 16, 2008)

I ran Audyssey MultEQ 32 and it told me the sub phase was reversed. I went ahead and ran the calibration resulting in the purple graph on REW. I then pulled out the sub, reversed the wiring, and re-ran Audyssey. This time I did not get the phase warning and proceeded with the calibration resulting in the green graph (crossover set at 40Hz per Audyssey recommendation).

Obviously big differences in the phase graph but I'm not 100% certain how to interpret it and how an "optimal" phase graph should look. Any general pointers or references to articles that will explain the phase graph displayed in REW?


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## laser188139 (Sep 19, 2009)

I never made much sense of the phase when I measured multiple speakers together; to understand what was happening I had to measure the sub, front left, front right separately and then compare the curves. 

If you are just interested in the phase switch, you can see the direction of the phase at the leading edge of the impulse curve. You can see some impulse curves in this post. You would like to think all the phases are the same if all the speakers start positive or start negative. If they all start negative, this probably means that your soundcard inverts the phase; you can undo this in the Preferences or in the Impulse Controls. 

If you want to compare the absolute phase of multiple speakers, you need to wire the left channel as a loopback so that you have a fixed reference for time zero in all the measures. You can then overlay the phase diagrams and compare them to see how the phases track in the bass region both sides of the crossover, as in this post. 

If you are concerned that Audyssey might have calculated the distance wrong, e.g., if its calculated distance is less than the physical distance, you can try adjusting the distance setting higher or lower and see if the combined frequency curve improves or worsens. Or you can try what I did in the thread containing the above posts, and adjust the distance to make the impulse curves look similar, then verify the result by looking at the combined frequency response. If Audyssey calculated the distance a little longer than the physical sub distance, allowing for the delay time introduced by the sub's amplifier, then the calculated distance is likely correct. 

Have fun,
Bill


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## Kevin R. Anderson (Feb 16, 2008)

Thanks for the informational response, general tips, and links to further information. Looks like I've got some homework to do. I'll try to replicate the tests in your main thread. Experimentation with REW is a good part of the fun of my home theater obsession.


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