Can anyone give me a sure fire way to phase a sub with the rest of the main speakers?

Discussion in 'Speakers & Subwoofers' started by Greg Carl, Apr 28, 2003.

  1. Greg Carl

    Greg Carl Auditioning

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    I've set up all of my main speakers and got the phasing dialed in perfect between them all. Thanks to Guy Kuo and his great method of phasing speakers, one can not only hear the improvement but one can see it on a SPL meter.

    My problem is that I cannot get the subs set dialed in and verified with a SPL meter. no matter where I place them, no matter what time delay I use, no matter what crossover I use, no matter what phase setting I use, I cannot SEE a difference on the SPL meter between one phase setting and another. I use the Phase Filtered Pink Noise and left front tones on the Avia disk. Guy says in one of the past posts that I should expect to see about a six db swing between in and out of phase. I'd be happy with a two db swing, at least then I'd know it was setup correctly.

    Does anyone have any suggestions, perhaps another sure-fire, verifyable method?

    Greg
     
  2. Justin Ward

    Justin Ward Supporting Actor

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    Is your phase setting variable between 0 and 180 degrees or are only 2 options availible? If the latter is true, maybe they are both out of phase by about 90 degrees which means they both sound about the same. You might want to try relocating the sub and see if you get the same results.
     
  3. PaulT

    PaulT Supporting Actor

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    You could confirm the same thing as Justin's post by moving the position you are measuring the SPL levels from, that way you wouldn't have to drag the subs around.
     
  4. Greg Carl

    Greg Carl Auditioning

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    Justin,PaulT

    Thanks for your response.

    I have two SvS subs(16-46's) and their little black box that has a variable adjustment(0-180). I've used the black box and only one sub at a time and tried to get the expected response but that does not work. I've tried moving the sub many times to correct just the problem you mention but that does not work either. I've reset my delays for the sub 1/10 th foot at a time to correct just such a problem but that does not work either.

    I can hook up both subs at the same time through the black box(one is direct the other is phase adjustable), play the phase filtered pink noise and adjust the phase knob and the SPL give an obvious swing between in and out of phase, so I know the phase knob works when I'm trying to phase two speakers with the same output.

    It appears the when I play the phase filtered pink noise that there is no frequency match between the main and the sub at a given crossover frequency. It's like the corssover is at 80HZ and the subs produce everything below 80 and the mains produce everything above. It's like there is no overlap but I know this can't be true. I always assumed that in order for the SPL meter to show in and out of phase difference the two speakers must have like frequency output somewhere in the audio spectrum.?????

    Thanks,
    Greg
     
  5. Dave Milne

    Dave Milne Supporting Actor

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    I'm not sure I know what "phase-filtered pink noise" is... but the "pink noise" part is likely your problem. The phase relationship between sub and mains changes with frequency. If you play pink noise (many frequencies), you are probably getting such a mis-mash of readings that they sum to about the same average SPL. I would try to use a single frequency --the crossover frequency (or a narrow warble tone at or near the crossover frequency) --and see what happens.

    You don't see this problem when comparing the two subs because they have the same phase response throughout their output region.

    Are you planning to have the subs in the same location (stacked, side-by-side) or in different parts of the room? The latter will add a dimension of complexity to your setup. Room modes have a huge influence on bass response: expect peaks and valleys 12dB or more. You may want to measure the frequency response of the system (with all speakers and subs active) from the listening position throughout the entire bass range (20-200Hz). You'll likely need to do a bunch of experimenting with placement and/or phase setting to get optimally flat response.

    Good Luck!
     
  6. Greg Carl

    Greg Carl Auditioning

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    Dave,

    I used a tone generator program to feed the system various tones in the bass range and this worked fine. Now there is no doubt that it is correct.

    I had no idea this would be so time consuming but I feel it was worth the effort.

    Thanks to all who replied..

    Greg
     
  7. Ronnie Ferrell

    Ronnie Ferrell Second Unit

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    I know you have fixed your problem, but I thought I would toss this out. When using test tones at the x-over frequency to set the sub phase, I have found it helpful to do the following. I can detect a drop-out or a suck-out of bass more easily than a hump. So when you set your subs phase, reverse the speaker wire polarity of your mains. Hook the + speaker wire to the - of the speaker terminal and the - speaker wire to the + of the speaker terminal on both your mains. Then have someone adjust the phase control on the sub while you sit in the listening position. When you detect the suck-out or drop-out in the tone, you have found the correct setting for the sub to be in phase with the mains. Set your mains speaker cables back to + to + and - to - and your done! [​IMG]

    Ronnie
     
  8. Greg Carl

    Greg Carl Auditioning

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    Ronnie,

    Doing what you describe is the affecively the same thing as using the phase tests in Avia. The greatest difference between in and out of phase, or the largest swing on the meter, is the location of correct phase. Great idea! I think I'll try that.

    Thanks,
    Greg
     
  9. Jeremy Anderson

    Jeremy Anderson Screenwriter

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    I ran Avia's bass frequency sweeps for each channel and paid attention to the SPL meter when it reached 80Hz (my crossover point). If you're getting cancellation due to phase, you should see a dip on the SPL meter as the transition across the crossover range takes place. For me, this dip was largest around 63Hz. Basically, the setting that isn't cancelling out frequencies is the right one.
     
  10. Dave Milne

    Dave Milne Supporting Actor

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    One caution Jeremy... As Justin pointed out, there's always the possibility that your sub and mains are 90 out at the crossover frequency. If you only have a 0/180 switch, there won't be any change with either setting. Here is where you need to perform a frequency response measurement ---or trust your ears --to pick the setting that gives the flattest response.

    Likewise, with a continuously variable phase control, you may wish to adjust the control away from optimum at the crossover frequency to give the flattest overall response.
     
  11. RichardHOS

    RichardHOS Second Unit

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    Dave is correct. Unfortunately, analog phase adjustments are frequency dependant on their absolute phase shift. The best you can do is attempt to set coherent phase at the crossover point. The phase incoherence between widely separated frequencies will be, hopefully, not that disturbing.
     

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