Time alignment/delay questions. (1 Viewer)

[John H]

Guy,
I have tried using your phase alignment technique several months ago when you first made this information available.
I just attempted to align my L main and Center channel speakers again.
At both times I can not get the SPL meters needle flucuation to vary. I am moving the meter slowly in ½" increments up to 1' on each side of center.
I have the meter in the fast responce C weighted positions.
I can get the meter to vary several dBs between swings when measuring the alignment my Mains and moving the meter. They are positioned for maximum needle swing.
I am using bipolar Mains and a Monopolar center.
My processor has a calibration microphone. I have used it to calibrate speaker distance several times in the past and preset. It sets them the same as measuring with a tape.
I would like to get a finer alignment between my Center and Mains.
John
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[Guy Kuo]

John, as I understand your note, you can get the SPL meter to show reinforcement/cancellation when you check the left and right mains, but cannot get it to work when checking left main and center. This basically boils down to the signals from the left and center speakers for some reason not being identical when they arrive at the SPL meter. Things to look at....
1. Speaker position or timing delay being off in the processor setup. This would dramatically push the acoustic central plane left or right, possibly several feet.
2. Mismatch of acoustic response between the left and center speakers. The test works because identical noise signals are fed to the channels under examination. If the speakers or the acoustic environments for them are poorly matched, the actual sound arriving from the two are not similar enough for cancellation and reinforcement to occur. You see this as a smaller deflection on the meter. For example on my own system the mains give a 6 dB swing up/down as they are similar in acoustic response. In comparison, my left/center deflection is only 3 to 4 dB. The acoustics of the left and center speakers simply aren't identical in my case so the sound from the two speakers simply don't match each other as well. Hence, smaller deflection.
I think I'd start by getting closer to the left and center speaker, say about five feet, and moving the SPL meter to see if you can detect the acoustic center at a shorter distance. If you can't find one, they something really is very different about the sound coming from the two speakers. If you do find the acoustic center (maximal SPL meter swing) then slow move further away and see if you can trace it out to the listening distance.
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Guy Kuo
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