How to correct phase problem with 2 subs?

Discussion in 'Speakers' started by Steve Morgan, Jul 8, 2003.

  1. Steve Morgan

    Steve Morgan Second Unit

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    Steve
    I have a PB2 and a Von Schweikert S/3 sub connected to the sub out on a Lex MC-8. I'm eq'ing them with a BFD. I am having phase problems I believe in the upper frequencies from say 80 to 160hz. I am using the crossover in the pre/pro and have disabled them in both subs. The crossover on the Lex is set to 70hz for the front L/R. If you look at the post in the speaker forum you can see the numbers. My subs are corner loaded on the same wall as the front but about 15 feet from them. The fronts are 11 feet from the meter and the subs are about 14 feet from the meter when taking readings. I have added an extra second in the distance settings to account for the BFD. What is the corect way to set the phase so the fronts and the subs are not fighting each other?
    Thanks,
    Steve
     
  2. Edward J M

    Edward J M Cinematographer

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    Steve, I'm not sure the phase of the sub will much help problems from 80 to 160 Hz since your sub crossover is set to 70 Hz. The low pass filter rate for most pre/pros is 24 dB/octave and I can't see the subs having much influence in the 80-160 Hz region.

    In any event, to get the most from the PB2+ and the S/3, try setting the PB2+ phase control to 180 degrees. I know it seems unconventional, but my 20-39 PC+ and my PB2+ both show the smoothest transition to the mains when their phase controls are set at 180 degrees. If I set them at 0 degrees, it creates a pronounced dip at the sub crossover frequency.

    Failing good results from that, first set the S/3 phase control to 0 degrees. Then bring on the PB2+ and have a helper slowly go from 0 through 180 on the phase dial on a few sine wave test tones (say 30, 40, 50, 60 Hz) playing through both subs, and see what exact phase control setting on the PB2+ gives you the highest SPL readings. There should be an obvious sweet spot on the PB2+ phase dial where the SPL jumps up a few dB and it reinforces with the S/3. That will be the most "in-phase" setting for both subs. Good luck.

    Regards,

    Ed
     

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