Qu-16 active subwoofer integration

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This topic contains 13 replies, has 7 voices, and was last updated by Profile photo of BBEgo BBEgo 4 years, 1 month ago.

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  • #62604
    Profile photo of BBEgo
    BBEgo
    Participant

    Hi all.
    Here’s my rig:
    Qu-16
    2 JBL MRX515 mains
    JBL PRX818XLFW active Sub
    Carvin DCML3800 Power Amp driving the mains
    Crown XTi1000 driving 2 monitors

    Been using mix 4 to send lows to the sub. It works well enough, but I haven’t figured out how to slave the mix 4 level to Master L/R. So I have to turn them down one at a time.

    It was explained in another thread from months ago, but I tried the steps and ultimately failed to make it work.

    I can’t just tap off the L/R line because I’m using the master EQ on that channel as a HPF of sorts. This keeps the mains from being pummeled by kick drum, synth, and bass guitar.

    Can someone help?
    Thanks!

    #62610
    Profile photo of airickess
    airickess
    Participant

    All channels you want to send to Mix 4 (your subwoofer feed) should be sent POST FADE and at UNITY gain. Assign both the Mix 4 Master fader and the L/R Master Fader to a DCA. Then, on the custom layer, assign that DCA to a fader and you have level control of the entire PA with a single fader.
    You can also assign the entire band to another DCA and use that to control their level. This is handy when you have folks speaking in-between band sets as it allows you to mute the entire band without affecting the PA level.

    #62613
    Profile photo of WaihekeSoundie
    WaihekeSoundie
    Participant

    You could take the Aux fed sub approach as above or alternatively and simpler, route L&R main outs through the crossover in the sub and out into your poweramps driving the mains.
    My experience of the Aux fed approach is that you do really need external crossovers for the tops and subs and match their slopes to make it sound nice.

    #62614
    Profile photo of BBEgo
    BBEgo
    Participant

    Thank you!
    The Airickess approach is what I was hoping for. Thanks for the input!

    #62621
    Profile photo of [XAP]Bob
    [XAP]Bob
    Participant

    Just be aware that the ‘main’ fader no longer does what you think…

    Given that your subs have a dedicated crossover – why not use that rather than bodging a ham fisted hpf with the peq?

    #62630
    Profile photo of BBEgo
    BBEgo
    Participant

    So Bob, you’re saying send the L/R stereo out to the 2 sub inputs and then let the active sub out send back the signal with the lows filtered out?
    Will a stereo mix be maintained? I only have a single sub.

    I don’t understand why they didn’t include a dedicated subwoofer out on this unit.

    #62633
    Profile photo of debzdoodle
    debzdoodle
    Participant

    Although it is a single sub, it has 2 channel input so yes – stereo will be maintained.

    #62634
    Profile photo of Mike C
    Mike C
    Participant

    If you loop the main L R outs into the sub and then take the subs L R outs to your amp
    for the mains the mains will be in stereo. You will want to turn on the high pass switch just above the subs link outputs. The stereo inputs are summed to mono for the subwoofer but will pass the stereo signal through.

    If you go with the sub on an aux method I would suggest getting a real crossover to put in line between the boards L R outputs and the power amp for the mains, even a good analog crossover would be fine. Set it for somewhere around 90hz for a start.

    #62636
    Profile photo of Andreas
    Andreas
    Moderator

    sigh, taken from The JBL PRX818XLFW Manual, Page 17:

    HI-PASS Button – This push button determines whether the signal coming out of the THRU connector is unaltered (FULL RANGE) or has a high-pass filter (HI PASS) applied to it. By default, the speaker is in a FULL RANGE mode.
    If HI PASS is selected, an 80Hz 24dB/Octave high-pass filter is applied to the signal coming out of the THRU connector. Engaging the highpass filter allows for a smooth transition between the subwoofer and full-range speaker that is connected to the output connector. This button must be pressed and held for 2 seconds to switch between options.

    #62637
    Profile photo of BBEgo
    BBEgo
    Participant

    Well, this method does seem considerably less complicated. Hard to argue with that!
    Gonna need a few more cables for this method. I bought 2 short XLR patch cables specifically to run L/R straight to the Power Amp, but for this configuration I’ll need 4 longer XLR.
    Makes good sense though. Thanks!

    Sent from my HTC 10 using Tapatalk

    #62638
    Profile photo of BBEgo
    BBEgo
    Participant

    I appreciate the assistance, but was the sigh really necessary?
    Not everyone is as proficient or experienced as the pro guys.

    Sent from my HTC 10 using Tapatalk

    #62640
    Profile photo of Andreas
    Andreas
    Moderator

    Please do not take my “sigh” personal, its just that I’m too often find answers rather quickly in the available documentation which I check for personal interest without ever having hands on the device. The “sigh” is for my failure suppressing some personal force to post a link to the manual then… 😉

    #62646
    Profile photo of [XAP]Bob
    [XAP]Bob
    Participant

    Those two short cables can still be used – just pop the power amp near the sub…
    You’ll need two cables to the sub (i.e. your speaker cables are probably long now), but you should be close enough to a stage box (analogue or digital) to wrangle those easily enough.

    It is technically a much nicer solution than trying to fudge it on the desk.
    It might be nice to be able to allocate ‘mix1’ as a ‘sub output with proper crossover from LR’ but I suspect that most places have either:
    – An active sub like this which has it’s own crossover
    – A full speaker processing facility

    #62650
    Profile photo of BBEgo
    BBEgo
    Participant

    This rig is solely for my band, where house sound is not provided.

    The existing configuration has a really nice sound (the QU16 is an amazing board), but I am looking forward to hearing a properly crossed solution.

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