Time alignment setting with 2 subs in different locations?

Discussion in 'Archived Threads 2001-2004' started by Steve Morgan, Feb 11, 2002.

  1. Steve Morgan

    Steve Morgan Second Unit

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    I have a Paradigm Servo 15a and a new Von Schweikert S/3. My Ref 30 has the distance in feet from listening position for the subs.The servo is 3 feet away and the Von Schweikert is about 11 feet away.What should I set the distance at? They are connected with a Y out of the pre/pro ther is only 1 sub out on the Ref 30.I am in the process of connecting my BFd and learning how to run the ETF software so This will probably effect the subs.

    Also where would you set the phase on each? The servo has no phase control I will have to do it from the Ref 30 the Von Schweikert has a phase control 0 or 180. appreciate thoughts on this.

    Thanks,

    Steve
     
  2. Kevin C Brown

    Kevin C Brown Producer

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    Steve- I think you are kind of stuck.

    Without a variable phase control on at least 1 of the subs, I think you will only be able to get it *somewhat* right. (Unless you have *some* flexibility in placement of either sub.)

    Ideally, I would say set the B&K distance for 1/2 way in between the 2 subs, and then adjust each subs phase knob until you get them in phase with each other, *and* in phase with the mains.

    I have found that using a discrete test tone disc with an SPL meter the best way to do phase adjustements. (RTA/EFT software will work too, of course.)

    You need to measure the output of all of the following below, through, and above your chosen crossover point:

    1) mains by themselves

    2) each sub by alone

    3) 1 sub with the mains

    4) the other sub with the mains

    5) both subs with the mains

    The outputs should be as follows for loudness to get the phase somewhat correct:

    5 louder than 3 and 4. 3 and 4 should be about the same loudness. And 3 and 4 should both each be louder than either 1 or 2.

    If that makes sense!

    The whole point is to have both subs in phase with each other, *and* with the mains. All "in phase" means is that you're getting constructive interference at your measuring point.
     
  3. JonathanB

    JonathanB Auditioning

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    Time alignment isn't that huge of an issue with the distances you are dealing with, but one thing I have done in 2 lfe sub systems is set the rear lfe sub at a lower crossover point than the front lfe sub.
     
  4. Kevin C Brown

    Kevin C Brown Producer

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    Unless I am calculating wrong... [​IMG]
    A 3 ft difference in sub placement is the equivalent of the wavelength from a 367 Hz signal. So, if I cut that in 1/2, that means that for a 183 Hz signal where that 3 ft is *not* accounted for either by a phase knob somewhere, or the distance setting in a pre/pro, you will get (ideally) 100% destructive interference.
    (1/2 a wavelength difference in distance between 2 sources will cancel them.)
    If you think more about it, there may also be problems at multiples, and even fractions of that wavelength.
    But you'd have to judge any difference in sound for your room yourself I reckon.
     

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