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Splitting the Main Out Signal?

Discussion in 'Live Sound [BG]' started by petro_bass, Jan 4, 2013.

  1. petro_bass

    petro_bass

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    We haven't played a larger venue that doesn't have house sound, so I'm trying to fill the room with what we have,
    so this question arose.
    We would like to run our 4 JRX125s as mains, pairing them on each side for stereo sound. Typically we only use 2.

    Will splitting the signal with a y-cable from the board to the power amps effect signal or cause issues?
    Ex: L output to split both "L inputs" on amps. R output split to both "R inputs" on amps.
  2. testing1two

    testing1two Gold Supporting Member

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    What kind of amps are you using? A typical power amp has a parallel output on each channel so you can daisy chain.
  3. petro_bass

    petro_bass

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    That was my initial thought but I was told the cabinets only have a single combo speakon input on them.

    EDIT: After looking they have a speakon and a 1/4 "parallel in/out" but they are rated at 4ohm, chaining them would drop to 2ohm. The Crown can't pull 2ohm.

    The amps are a QSC 2450 and a Crown XLS802. Since they are not identical amps, my thought is to run a left and right to each one to make sure the signal is equal to each side.
  4. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

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    If your amps don't have a pass-through, yes, you can use Y-cables to split the signal from the board to the amps.
  5. testing1two

    testing1two Gold Supporting Member

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    Your QSC has XLR and 1/4" inputs wired in parallel. Therefore you can come out of your mixer via XLR to the XLR inputs of the QSC and then use 1/4" TRS to XLR cables from the QSC to the Crown.
  6. petro_bass

    petro_bass

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    The manual doesn't state anything about using both sets of outputs simultaneously. If they are wired in parallel that would drop our load to 2 ohm.
    I know the particular amp is capable of the load in stereo, I'd prefer to avoid the strain on the equipment if possible since its going to be an 8 or 9 hour show.

    I'm not sure if I'm following this correctly, but the other thing the manual says to switch to bridge mono, and engage the parallel switch.

    Use the #2 input as a signal pass? This seems odd to use an input and not an output for this.

    http://http://media.qscaudio.com/pdfs/manuals/RMX_User_Manual.pdf
  7. testing1two

    testing1two Gold Supporting Member

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    The 1/4" and XLR input jacks for each channel of the QSC amp are wired in parallel (see page 15 of the manual). This is not to be confused with the speaker outputs being connected to multiple speakers in parallel, thus lowering the overall output impedance.

    Basically, think of the XLR and 1/4" jacks as an input and a passive slave output or splitter. It doesn't matter which one you use as the input, the other will function as a slave output which can be connected to the input of another amp.
  8. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

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    He's talking about inputs, not outputs. So run the output of your board to one input of the amp. Then run another XLR or TRS cable from the other input of that amp to the input of the other amp.
  9. walterw

    walterw Supportive Fender Gold Supporting Member

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    right! the only "output" on a power amp goes to speakers and nothing else! use the XLR inputs to go into the amp, and use the 1/4" inputs to jump from one amp to another, so you don't need XLR turnarounds or anything.

    anyway, are you going to be spreading these pairs of top boxes out and splaying them so that they aren't hitting the same area at the same time? because you don't want to double up tops hitting the same "zone" or you get weird comb filtering.

    now you could get clever here and do a "dual PA" thing;

    have one of each pair going to different sides of an amp, and send them different things from the board; if one left-right pair was doing all the instruments and the other left-right pair was just doing the vocals, there would be no phase weirdness from having them side-by-side.

    it could actually work really well.

    the other issue is that if you have 4 top boxes cranking out, but no subs to balance the overall sound, it could be loud but thin-sounding.
  10. petro_bass

    petro_bass

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    Thanks for the clarification. I was unsure about the parallel input portion.
    Looking at the Crown manual, when running in bridge mono mode, it only allows for one output to be utilized, and is only able to run at an 8ohm load. So it looks like the amp passthru option won't work.

    Unfortunately we don't have access to subs at this time, but the cabinets use a built in crossover to direct the bottom 15 as a dedicated low and the other 15 and horn to function as a standard cabinet.

    The two pa thing is a possible idea.
    The cabinets have a projection angle of 90 degrees essentially covering 180 degrees, so it would be hard not to have any overlap in the room without early reflections since the room is rectangular. Why would 2 pair be any different then 1 pair when dealing with cancellations?
  11. gearhead1972

    gearhead1972

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    I don't get why you would want to run the crown in bridged mono when your trying to run 4 4ohm speakers. Like the guys above said, run your L and R outputs of your mixer xlr to xlr into the xlr inputs of the QSC then run trs to xlr cables from the QSC's 1/4" input to the Crown's xlr inputs. as I am looking at the manual for the QSC if your model is in fact the RMX 2400 then that amp can run in 2 ohm stereo. So run your 1/4 speaker wires from amps to 1st set of mains then speakon from speaker to speaker, or vise versa if you already have long speakons, but them being expensive I am thinking you dont. Edit I read yout JBL's have the NL-4 speakon, they are not combo jacks with a 1/4" jack in the center.
    Also if you can get your hands on a electronic crossover, you could use that as your splitter and run two cabs as bass and two as highs. You can get somewhat decent crossovers for under 2 bills http://www.parts-express.com/pe/showdetl.cfm?partnumber=246-105
  12. Hactar

    Hactar

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    As gearhead1972 said above, there's no sense in running bridge.
    With 4 4ohm speakers, you can run 1 speaker per amp channel.

    Main L & R via XLR to QSC, and then TRS-XLR cables from the QSC to the Crown.

    That said, running 4 JRX125s is probably not the best decision, although I understand that that's all you've got.
    However, you could probably beat 4 JRX125s with two subs and two strong tops, properly driven.
    2x15 cabs tend to be both muddy sound and difficult to transport/deal with on stage, because they are too big to be raised off the floor.
  13. petro_bass

    petro_bass

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    Sorry, I was under the assumption that the parallel inputs were between channels 1 and 2 and not the two on the same channel as if it were running one input per the 2 outputs like in bridge mono... in that case I would only have one input passing on the signal to the crown...
    The stage at the venue is large and about 4-1/2 feet tall, so no height issues this time.

    I understand what Gearhead is saying, that I can use parallel in stereo.

    The equipment is a combo of two previous bands, like I said we never needed to run two sets of mains before. We are working on getting new equipment for the future. JBL PRX618S-XLF subs paired with Yamaha DSR112s are whats on the shopping list, just keep the others for backup.
  14. walterw

    walterw Supportive Fender Gold Supporting Member

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    whoa, stop!

    it sounds like you're still confusing the line-level amp inputs with the speaker-level outputs! you need clarity on this before doing anything or you're gonna blow something up!

    one pair means one speaker on each side of the stage, each covering its own section.

    two pairs means side-by-side speakers on each side, which is where the issues start.

    the dual PA idea (say, instruments in the outside pair of speakers, vocals in the inside pair) lets those side-by-side speakers do different things from each other, so you don't have the comb-filtering problem.

    you'd still be better off with just 2 tops and some subs.

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