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Using REW to set delays - timing reference vs x-over null

Oilman

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Jan 18, 2022
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What is the recommended practice to set home theater channel distances (delays)?

I have used two different methods:

1. Invert sub polarity, use REW to play sine wave at crossover frequency, adjust sub volume and phase knob to produce greatest cancellation (lowest level) with left speaker using REW SPL meter. Return sub to 0 degrees. Then, using REW acoustic timing reference sweeps, with left speaker as timing reference, check all other speakers distance/delay. Adjust distances to minimize delay from left speaker referenc.

OR

2. Repeat null adjustment for left speaker as per above. Then repeat this with all other speakers, except instead of using phase knob on sub, adjust distances in processor menu to find distances that produce nulls for each speaker at crossover frequency (using REW sine wave generator and SPL meter again). Use distance that best nulls level at crossover frequency with sub polarity inverted. And then obviously, return sub back to 0 degees.

My preference is to perform #2 over #1, because i’ve found time/phase alignment with sub is critically important to blending mains with subs. However by performing the #2 procedure, and then checking the acoustic timing reference using process described in #1, the #1 process would suggest most of my channels are not time aligned. So for example, my center channel shows it is 60”/4.25ms delayed.

I suppose this comes down to time alignment being different for high frequencies (which I think REW is really measuring with the acoustic timing reference function) vs bass frequency at the crossover region. But which would you say is more important to getting right in home theater? How are you all setting main/sub phase/time alignment?
 

dasdoing

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May 20, 2020
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not a full reply, but keep in mind that you get a phase match every 360 degrees, so 2 drivers can be in phase while one is actualy delayed. I personaly look at excess group delay first to get the timing in the same ballpark. than I look at cancelations while trying finer steps in delays.
 
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