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How to hook up new JBL subs?

Discussion in 'Live Sound [BG]' started by slap-a-da-bass, Aug 12, 2012.


  1. slap-a-da-bass

    slap-a-da-bass

    Sep 28, 2009
    I ordered a pair of JBL PRX618s-xlf subs last week, & they'll be here tomorrow. I understand how my board works, and I'v been giging & running sound for us for a year or so now, so I'm not a complete newb.

    Here's my thoughts. We are a five piece, two guitars, bass, drums, vocals, and we always run in mono. I'm thinking of taking the sum mono out of the board, into the 1st sub, link to the 2nd sub. Now engage the x-over on the 2nd sub, up to my powered RCF are 312, and lastly come back to the last top. This would be one continuous chain, and seems like it will work, I don't know that it's ideal though.

    I did have a question about the JBL subs, they have a L & R input, and the specs say 2 x 500w for the amps. I'm wondering if I only use the L or R input, & I only getting 1/2 the power? Should I be splitting the signal going into the subs? or will the sub use both amps when it only see's one signal?
     
  2. modulusman

    modulusman Banned

    Jan 18, 2004
    montana
    It would be easier to help you if we knew what your mixer and any outboard gear is. You will still be getting full power no matter what input you use.
     
  3. uhdinator

    uhdinator

    Apr 20, 2010
    Maine
  4. Floyd Eye

    Floyd Eye Banned

    Feb 21, 2010
    St. Louis
    Aux 'em.
     
  5. slap-a-da-bass

    slap-a-da-bass

    Sep 28, 2009
    I read in the manual that the inputs are summed, but I didn't see anything how the internal amps are used. I've read on forums, from people that are using them, that there seems to be more output when the L & R inputs are used. Someone stated +6db.

    My board for my next gig is a Peavey 16FX, but after that I'll be using a Presouns StudioLive 16.4.2.
     
  6. modulusman

    modulusman Banned

    Jan 18, 2004
    montana
    Not sure why you would wan't to run in mono with those boards. I own both of them I would run stereo or as Floyd Eye mentioned use an aux send. If you are not doing aux subs then uhdinator post is the way to go.
     
  7. Hactar

    Hactar

    Sep 25, 2011
    Boulder, CO
    You should either go with uhdinator's suggestion or Floyd Eye's suggestion.
    Chaining left to left and right to right is probably more traditional, and works fine.

    Running the subs of an aux buss gives you more control and generally keeps some mud out of the subs.

    And it will be full power with just one input.
     
  8. gearhead1972

    gearhead1972

    Feb 21, 2012
    Kent NY
    Kind of makes sense, the manual states 2x500 and dual voice coil driver, so These might help
     
  9. modulusman

    modulusman Banned

    Jan 18, 2004
    montana
    That doesn't make any sense at all. No special cables are needed.
     
  10. Makes sense to me. If you sum two identical signals you get one signal that is 6dB hotter than either.

    The two amps/dual voice coil setup doesn't have anything to do with it. Don't worry about that.
     
  11. uhdinator

    uhdinator

    Apr 20, 2010
    Maine
    Going into the sub L/R is louder yes, and summing 2 identical signals = +6 db more gain.

    If you're only running 1 input yes the level is lower.
    So you turn up the input sensitivity a little....solved.

    sending one signal to a spiltter to get it into the L/R is defeating yourself. Each side of the split will be lower in level than using a single signal to a single input. That is not the way to do it. Your gaining nothing except a lighter wallet and more un-needed cables.
     
  12. Stumbo

    Stumbo Wherever you go, there you are. Supporting Member Commercial User

    Feb 11, 2008
    the Cali Intergalctic Mind Space
    Song Surgeon slow downer software- full 4 hour demo
    Also be concerned about stage placement. Here's a TB thread with some graphs displaying optimal placement (spoiler-it's not one per side).

    Since you purchased dual voice coil subs, maybe one will do. The +6db is a big difference; maybe enough that you can return one.
     
  13. The dual voice coil thing is a red herring. You don't need to worry about it, how that thing works internally is completely transparent to the user. Just think of it as a sub with a built in two input mixer. Which is what it is.
     
  14. Stumbo

    Stumbo Wherever you go, there you are. Supporting Member Commercial User

    Feb 11, 2008
    the Cali Intergalctic Mind Space
    Song Surgeon slow downer software- full 4 hour demo
    Dual voice coil means it accepts two power outputs for maximum output.

    It could be used for a home theater setup where the power amps dual outputs are run through the subs/xover and then out to the mains.

    It does matter. :)
     
  15. Internal to the enclosure is a two channel class D power amp and a dual voice coil driver. The engineers at JBL/Crown decided that this was the most robust/cost effective/best sounding solution to the engineering problem at hand.

    From the perspective of the end user it is a black box. Doesn't matter.
     
  16. uhdinator

    uhdinator

    Apr 20, 2010
    Maine
    the XLR output does not power other things. It just passes line level thru it.

    The 2 power amps are for the dual voice coils.
     
  17. Hactar

    Hactar

    Sep 25, 2011
    Boulder, CO
    I think that it needs to be made clear that the sub having dual voice coils and two power amps has nothing to do with how the sub needs to be fed signal. The two power amps do not take their signals from the right/left inputs respectively, but rather both power amps receive the same signal, a signal from the summing of the right and left inputs.

    One good way to set up this rig would be to crossfire the subs at center stage, feed one from an aux buss, and daisy chain the other one. Ideally, you'd have separate HPFs on the tops, but it's not crucial.
     
  18. gearhead1972

    gearhead1972

    Feb 21, 2012
    Kent NY

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