# Subwoofer in Phase test?



## johngalt47 (Oct 10, 2008)

I don't know how to test to see if my sub is exactly in phase with my mains. The sub amp is an O-Audio 500 watt so I can adjust the phase as necessary.

I want an objective test because, even though I don't think it is exactly in phase now, I don't know if I can tell when it is exactly in phase.


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## Anthony (Oct 5, 2006)

What kind of test equipment do you have? I guess you could do a sweep measurement through the system with REW and vary the phase. It will null at the crossover point when they are out of phase and flatten out (or even peak a little) when they are in phase.

The ear test I used to do was to purposefully flip the polarity of the mains, play a tone at the crossover frequency, and then adjust the phase until the sound was the lowest level (perfectly out of phase). Then flip the mains back and they will be back in phase. Obviously there's some subjective slop in that method, but it works.

I'm sure there are other methods or variations thereof -- hopefully other members can share what they do.


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## SAC (Dec 3, 2009)

The meaningful test is for signal alignment using the impulse and Envelope Time Curve (ETC) response which provide the means to both determine the existing signal offset in time as well as to identify when they have been successfully aligned with respect to time.

The most direct way to measure that is not with phase but with eh impulse response or (preferably) the ETC response. The impulse response will also verify that they are both equal in polarity with the cone moving forward with the initial application of stimulus.

Measure each source with the mic at precisely the same listening position.

The degree of offset in time will tell you how much delay needs to be adjusted - or potentially, how much they need to be physically repositioned to physically achieve signal alignment (assuming that 1ms offset =~1.13ft).


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## gdstupak (Jul 13, 2010)

I've always used an outboard eq for my subs.
While playing CD test tones of the crossover frequencies, if I moved the sub eq slider up and the spl also went up, then they are in phase. If I moved the sub eq slider up and the spl went down, then they are out of phase.


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## CdnTiger (Feb 16, 2007)

SAC said:


> The meaningful test is for signal alignment using the impulse and Envelope Time Curve (ETC) response which provide the means to both determine the existing signal offset in time as well as to identify when they have been successfully aligned with respect to time.
> 
> The most direct way to measure that is not with phase but with eh impulse response or (preferably) the ETC response. The impulse response will also verify that they are both equal in polarity with the cone moving forward with the initial application of stimulus.
> 
> ...


I had to read that over a couple times to wrap my head around it. :nerd: So if one measures a difference of, say, 2 ms between the subwoofer and main speakers, how does one convert that to an appropriate phase delay on the subwoofer? Just curious for when I have to play with these things myself.


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