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speaker phasing convention for PA

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  • speaker phasing convention for PA

    Hi

    I'm making up some speaker cables for PA use and am wondering if I there is a phasing convention for this - if it's just random then I would think there are out of phase systems all over the place....

    Thanks

  • #2
    Bob,

    AFAIK, the polarity 'convention' is to wire speaker cabinets so that a positive voltage applied to the + input terminal causes forward (i.e., away from the magnet structure) cone/diaphragm motion.

    Ray

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    • #3
      thank yoy Ray

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      • #4
        I think it's mostly about speakers in the same enclosure or cabs that are very close together.
        Even though on stage the PA cabs are pretty far apart and the distructive interference from phase relationships are not so critical, I'd still try to keep all the speakers firing in the same phase anyhow Bob.
        ******************

        Anyway.. how is the premier "SURF BAND of the Rockies" doing these days?
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        Last edited by Bruce / Mission Amps; 10-20-2006, 05:25 PM.
        Bruce

        Mission Amps
        Denver, CO. 80022
        www.missionamps.com
        303-955-2412

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        • #5
          Every speaker I've ever seen is marked with a (+) and (-), so just stick with that and you'll be OK.

          It would be possible to describe everything scientifically, but it would make no sense; it would be without meaning, as if you described a Beethoven symphony as a variation of wave pressure. Albert Einstein


          http://coneyislandguitars.com
          www.soundcloud.com/davidravenmoon

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          • #6
            Just a little monkey wrench: older JBL speaker models (they started transitioning in the 90's) were marked such that positive voltage on the red terminal pulled the cone back instead of pushing it out. The factory-made box wiring accounted for this so at the input terminals things were right.

            The grisly details are here:

            http://www.jblpro.com/tech-library/J...eN1V12C_v5.pdf

            JBL (and many others) often also purposely wire the HF driver backwards in a cab - as it turns out that corrects (mostly) for the physical placement of the driver at the back of a horn causing sound to arrive at the mouth out-of-phase with the woofs.

            Oh - and just when you thought you could trust at least ONE thing to be standard - older QSC MX-series amps are wired so on the 1/4" inputs the RING is positive and the TIP is negative. Even says so on the graphic near the inputs...

            Add to this the mass confusion over whether pin-2 or pin-3 is hot on the XLR inputs of older equipment and you get plenty of chances for phase problems.

            From what I have seen of factory-wired speaker cables from people like Rapco and Horizon the white wire would usually be used for positive in a black/white pair.
            Last edited by Mark Black; 10-20-2006, 06:34 PM. Reason: Added thought

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            • #7
              So many thoughts here.

              First cables are cables. 1/4" for example should be wired tip to tip and sleeve to sleeve. It is irrelevant what they did inside the cab when wiring cables. And Speakons or any other connectors would be the same. Wire pin to pin and the cable is proper. It doesn't matter which color goes where, all you need do is wire both ends of the cable the same.

              JBL exceptions aside, I can think of no reason to do anything but + to + makes cones move forward as Ray says, when wiring cabs.

              The reason QSC amps are wired with the inverting input is that the amp itself has a new phase inversion. They wire the input "backwards" so that when it comes out the amp, it will be correct.

              Wiring the high freq driver in recerse polarity is not to time align the driver with the woofer, it is to correct for the phase shift of the crossover. If you look at a lot of speakers where the HF driver ap-pears to be wired hot to +, you will find that at the crossover, the red wire is actually ground and the black wire is hot. So it is visually comfortable to wire the HF red to + and black to -, but the reality is the reverse, which is good for fixing the Xover phase delay. If you time align the drivers, you still need to invert the HF driver wires. Two separate issue.
              Education is what you're left with after you have forgotten what you have learned.

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              • #8
                So many thoughts here.

                First cables are cables. 1/4" for example should be wired tip to tip and sleeve to sleeve. It is irrelevant what they did inside the cab when wiring cables. And Speakons or any other connectors would be the same. Wire pin to pin and the cable is proper. It doesn't matter which color goes where, all you need do is wire both ends of the cable the same.

                Agreed.

                JBL exceptions aside, I can think of no reason to do anything but + to + makes cones move forward as Ray says, when wiring cabs.
                Also agreed - just wanted to call attention to the JBL weirdness.

                The reason QSC amps are wired with the inverting input is that the amp itself has a new phase inversion. They wire the input "backwards" so that when it comes out the amp, it will be correct.

                Well - I'm not so sure (QSC's take on it found here): http://www.qsc.com/support/technical...faq.htm#pafaq6

                Wiring the high freq driver in recerse polarity is not to time align the driver with the woofer, it is to correct for the phase shift of the crossover. If you look at a lot of speakers where the HF driver ap-pears to be wired hot to +, you will find that at the crossover, the red wire is actually ground and the black wire is hot. So it is visually comfortable to wire the HF red to + and black to -, but the reality is the reverse, which is good for fixing the Xover phase delay. If you time align the drivers, you still need to invert the HF driver wires. Two separate issue.

                I'm sure you are right about the phase shift, although I think both that and the distance offset are factors. I think it just works out kind of happily that way at the usual crossover frequencies and horn lengths. We once looked at a biamped JBL SR4733X with an Audio Controls IASYS tool and the IASYS recommended reversing the polarity to the horn as well based on measurement...

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                • #9
                  Well, JBL does a lot of things weird. Just pray that JBL and Bose never work together on something. I think in general that the phase shifting from caps and inductors in the Xover are much greater than phase shifts from time alignment errors. So for example a woofer and a mid that are in phase will sound better if their VCs are aligned, but they were still in phase either way. Put another way, at audio freqs the wavelengths are such that the several inches of misalignment is nowhere near 180 degrees, or even 90.

                  QSC - fair enough. As a QSC service center and working with a sound company that had me seeing many of them, my impression has always been that since they use flying rails, AND wanted grounded collectors instead of the more common grounded emitters, it esentially reverses the polarity iof the output. Rather than change anything, they felt it better to offer a rationale for the reverse connection. On the other hand it could well be a genuine concern. I just have not encountered said mystery problems. And I think my original assertion was not stated very well. mea culpa.
                  Education is what you're left with after you have forgotten what you have learned.

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