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Why is this phase changing ?

mamba76

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Hi all. I been trying to align the phase of my car's sub to the rest of the system which is timed up and Im happy with. Iv attached my REW measurements.
What I find strange is that I am measuring just the sub and playing about with the crossovers etc. If I take one measurement, change nothing and take another one Yes its exactly the same, as you would expect. But if I change the DSP to delay the sub say, 5ms, the phase of the sub changes ?? change to 10ms the phase changes again as shown.


My question is Why ?
Nothing has changed in the car, no other DSP settings have changed, same crossover types and cut offs etc, nothing changed except the DSP's output delay.
Shouldn't you expect the phase shape to be identical wether you changed the delay to 5ms or 5 DAYS! ?

The only thing I can think of is the absolute delay from mic to PC but how could this change the room response ?

I should say Iv timed up the rear 8 inch midbass to the front with this method and intial thoughs are the sound is incredible. I use bessel filters between the two and have never had such acurate bass reproduction.

The idea was to match the unwrapped wrapped phase of a speaker to the unwrapped wrapped phase of the rest of the system, AS CLOSELY AS POSSIBLE, in the range most concerned, given the tools that I have. Im my case several filter types (dozens of combinations), variable xover points and delays.

Thanks

The orange trace is the rest of the system I am trying to match the sub to, each of the other traces are the sub with increased delay by 5ms. Is it possible to upload a REW file here ?
subphases.png
 
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JohnPM

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If I take one measurement, change nothing and take another one Yes its exactly the same, as you would expect. But if I change the DSP to delay the sub say, 5ms, the phase of the sub changes ?? change to 10ms the phase changes again as shown.


My question is Why ?
If you are using a loopback as a timing reference the DSP delay means the sub signal has shifted relative to that loopback, so the phase will change correspondingly (e.g. 5 ms is 180 degrees at 100 Hz).
 
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mamba76

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If you are using a loopback as a timing reference the DSP delay means the sub signal has shifted relative to that loopback, so the phase will change correspondingly (e.g. 5 ms is 180 degrees at 100 Hz).
Ah I see, thank you. It could only be something between the mic and the software but still nice to know. Is there a better way / process to match the phase of the sub to the rest of the system ? Im only concerned with 40 - 70 Hz region. The problem you explained was not a evident when doing the same to midbass / mids. This might actually require me to do some maths for once tho )
 
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mamba76

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That is a super useful tool, never realised REW had it!
Cheers
 
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mamba76

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I must say Im really getting results now, after 7 years I feel Im really starting to master this software. Enough respect to John!
 
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