Best way to set phase on 2 corner loaded subs?

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

  1. Steve Morgan

    Steve Morgan Second Unit

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    I have a PB2 and a Von Schweikert S/3 sub. I have eq'd them with the BFD but am having trouble with the front L/R fighting the subs in the 100hz to 160hz area. Here are the reading I get after giving an -18db. cut centered at 40hz with a 1/3 octave bandwidth. This is in 2 channel mode on the Lex MC-8 with the tones that I downloaded from snapbug playing on a Panny RP-91 at -25 on the Lex volume scale.
    HZ SPL
    16 73.5
    20 82
    22 80
    25 79.5
    28 80
    31.5 82
    36 84
    40 86
    45 87.5
    46 87.5
    50 86.5
    56 81.5
    63 77
    71 73
    80 72
    89 69
    100 68.5
    111 57
    125 73
    142.5 54
    160 71.5
    These were taken with the phase set at 180 for both subs. The subs are about 13 feet from the mains and 14 feet from the listening position. They are on the same wall. The room is about 7500 x3. Wayne P has helped me with the numbers but suggested it might be a phase problem. As you see I can use help. These numbers are for the PB2.
    Thanks,
    Steve
     
  2. Greg Bright

    Greg Bright Second Unit

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    Are you eq-ing the subs together (coupled) on the BFD or individually? Also what are your mains, and are you running them large or small? You state how far the subs are from the listening position. How far are your mains from the listening position? How far the subs are from the mains is only partially relevant.

    Greg
     
  3. Steve Morgan

    Steve Morgan Second Unit

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    I am eq'ing them individually and the mains are set to small. I am 11.5 feet from the mains and am using the crossover in the Lex set at 70hz. The mains are Von Schweikert VR3.5's as is the rest of the 7.1 system.
    Steve
     
  4. Kevin C Brown

    Kevin C Brown Producer

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    Have you tried setting the phase of each sub to the mains individually, *then* powering both to see what happens?

    And then you can also compare the phase to each as well.

    The dip might not actually be due to phase. Might be a room interaction. What are the crossover frequencies you're using on the MC-8? 160 Hz is probably too high for a phase problem.

    Good article here that talks about multiple subs and freq response in a real room:

    http://www.harman.com/wp/index.jsp?articleId=1003
     
  5. Lewis Besze

    Lewis Besze Producer

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    If you set the lowpass at 70hz,then with the typical slope [24db/oct],it should be down anyhow,and your mains should "pick up the tab".Phase issues usually happens close to the crossover frequency.This could be an issue between your mains and your room,like Kevin said.
     
  6. Greg Bright

    Greg Bright Second Unit

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    Steve,
    The distance differences between you, your mains, and your subs would not, IMO, justify a 180 degree phase shift, maybe 60-90 degrees or so. Some of the dip in that 100-160 Hz region may be due to "floor bounce", a cancellation that affects almost all speakers.

    As an aside, I am using a corner sub and two large powered towers. I tried putting the sub on one BFD channel and the subs in the towers on the other. What a can of worms to adjust properly. I finally set the volumes on all three subs to approximately the same level then coupled all of them. The BFD (and essentially any equalizer) can only provide smooth frequency response at the ONE location where you measure the output. This approach has netted outstanding results with much less effort.
     

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