How to hookup subwoofers to QU 24?

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This topic contains 13 replies, has 9 voices, and was last updated by Profile photo of David Haughton David Haughton 5 years ago.

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  • #54204
    Profile photo of DV
    DV
    Participant

    Hi All,

    I have 2 JBL subwoofers (1000w each), and want to hookup with my QU24 mixer for my live band but don’t know the best way to do it.
    If possible, please give me some advices how to set it up.
    Thank you for your help in advance !
    Don

    #54205
    Profile photo of Andreas
    Andreas
    Moderator
    #54206
    Profile photo of Dick Rees
    Dick Rees
    Participant

    To get a complete answer you need to give a complete description of each piece of gear in the chain with brand and model, the type of material you do, your objectives and indoor/outdoor area to be covered.

    Please give coverage in area with all applicable dimensions, not number of people, and specify desired output in dB SPL, not watts.

    For now:

    What model subs?
    What model tops?
    Passive or powered? If passive, what amps?
    Crossover?
    DSP?

    #54218
    Profile photo of dpdan
    dpdan
    Participant

    DV,
    Andreas and Dick have given good advice and good links of threads to read, but here is how I personally use my subs with my Qu24.

    OK first, yes, I have too much time on my hands right now, not really, but my power was off all day because of weather and now it is back on and I am typing all this crap for fun. I love helping people. 🙂 Plus, isn’t AC power a wonderful thing?

    let me begin,,,
    I use mix 10 to feed my power amps for subs. I don’t need MIX 9-10 for any stereo monitors like in-ear systems, so I just use channel 10 to feed my power amps. My amplifiers (QSC PLD 4.5) all have processing built in and I have already set them to my liking,… crossover point, type, frequency, limiting etc. If your subs are powered, then you too will need to make adjustments to the settings available on the rear of your JBL subs to suit you.

    MIX 10 is the right channel of the stereo pair (9-10). Since this is a stereo pair, you will want to make sure that any extreme pan settings that you have made in the stereo L/R mix is not effecting where your subs get sound from. You can set MIX 9-10 so that it has it’s own panning, irrelevant of the pans for the main stereo mix.

    It is almost always best to use the same “feed” for both subs (MONO). I say almost because after 45 years of mixing and discussing audio engineering, it is safer to not say “IT IS ALWAYS BEST”

    Anyway, you must decide (or whoever is operating the QU mixer) to choose what input channels are deserving of being fed to your subs. Typically, these are the instruments that I choose to run through subs….kick drum, floor toms, bass guitar, key bass, and any other keyboards or instruments that are going to be producing nice deep fat sounds, like a keyboard string Pad patch for ballads, and music tracks, break music etc….your choice here.

    Another thing to remember…your graphic EQ for stereo mains still has EQ bands “faders” for frequencies that lie well below what the mains are able to faithfully reproduce. Regardless of whether or not your mains are powered, frequencies that are just below your sub’s top cutoff frequency should be completely rolled off. This will prevent your mains woofers from wasting energy trying to reproduce frequencies that they are just not very good at,,, certainly compared to subs. Commonly today, bands with drums and electronic instruments demand full range sound systems, so subwoofers are a necessary augmentation to your mains. I say that to say this,… I do some jobs for Barbershop quartets and choruses
    where more often than not, subs are just not needed. It is especially nice to have mains for these events that have no problem reproducing frequencies in the sub range (below 80 Hz.) When sub frequencies are needed, then of course it is best to get the subs out of the truck/trailer and set em up. Another side note,,, I personally do not like to hear any frequencies above 80 hertz from subs, especially if they are 18″ components. Just my opinion 🙂

    If your subs are powered, then use a single XLR-XLR cable and connect it to MIX 10 output. Connect the other end of the cable to the input of one of the subs, (pick the one closest to the mixer’s MIX 10 output,… perhaps an AR2412 near the stage?
    Now use another XLR-XLR cable to daisy-chain) OUT of the first sub and into the input of the other sub. Same thing if your subs are not powered, but then you must decide which channels of which amps are going to drive the sub cabinets with enough power and of course the settings of your speaker processor/crossover. I also suggest setting the input gain on the powered subs to full on. If you don’t need a lot of subs, then obviously just raise the MIX 10 master fader to the desired level. Both subs should be producing exactly the same level which is why I suggest setting them both to full gain.

    Much of the time, we end up having to place our sub cabinets on each side of the stage where we stick our smaller main speakers on poles or tripod stands next to them. (Almost always 🙂 our subs are set up this way, but if we can, we should set our subs as close to each other as possible but as I said, most of the time, we don’t have this luxury.

    On the Qu mixer, hit the blue MIX button (right-hand side),,, any channels that you want to be routed to subs, KICK, BASS KEYS etc…raise only those faders to zero DB. Now, when you return to the main mix, as you raise and lower the channels of the KICK, BASS and KEYS, those levels will be automatically raised and lowered according to the main mix faders, hence (POST fader) POST fader = after fader.

    One more thing…, speaking of PRE AND POST FADERS, it is imperative that you set all input channels of 9-10 MIX to be POST fader, not PRE. To do this, first select mix 9-10 (right-hand side blue button) then on the left-hand side of the Qu mixer, hold down the PRE button and tap each SEL (Select) button of every channel to toggle between PRE or POST fader, do this for all the channels so that the green LED is NOT lit. Once you have done this for all 24 channels, you should also set all of the channels on the second layer to “POST” and then raise the faders of effects and/or stereo return inputs like ST-1, ST-2 ST-3 which might be used for outboard effects or CD/MP3 music players. One more note: if you are mixing and feel like the subs and everything sounds great but the kick is just too stinkin fat, instead of altering the EQ of the kick, just go to MIX 9-10 and lower the fader of the kick a tad.

    OK Dan wrap it up motormouth… 🙂

    So, I didn’t give any advise as to what the high and low cutoff frequency of your subs should be set to…. but that is exactly why Dick asked you to inform us as to the exact brand and models of the gear you are using, and even the type of venues and music involved.

    And one more thing… while I’m at it..
    the kick drum is NOT what everyone came to hear.
    my .04 worth 🙂

    Dan

    #54220
    Profile photo of Andreas
    Andreas
    Moderator

    Any reason not using the Matrix out on Qu24/32? Seems to be much simpler to setup.
    And if there are channels which potentially produce undesired low end, I just turn in the channel HPF.
    Regarding use of GEQ/PEG as a pseudo X-over don’t forget that these only cut -15dB and nothing below 20Hz. Using an external crossover or speaker processor is still somewhat required until A&H adds LPF/HPF functionality to Mix/Mtx as well.

    #54242
    Profile photo of dpdan
    dpdan
    Participant

    A matrix out can indeed be used to drive subs, any output can be used to drive subs,
    but the whole reason to use a dedicated MIX is to have ONLY instruments with significant low end content, not vocal mics and other delicate things that need to stay OUT of the subs. High pass filters should always be used on vocals, hi-hat etc. but those should never go to subs.

    Andreas, if you want just kick drum and bass guitar to go to your subs, how would you expect to route those two sounds to a matrix?

    A Matrix is just a mix of mixes… NOT what you would want to drive subs with.

    #54244
    Profile photo of Andreas
    Andreas
    Moderator

    Since I basically come from x-over driven PA systems I never bothered which channels to route to Subs and which not. Channels like HiHat or overheads just get the HPF engaged and therefore do not produce something relevant which survives the LPF before the subs.
    But I totally understand this may not work for larger PA configurations.

    #54246
    Profile photo of [XAP]Bob
    [XAP]Bob
    Participant

    http://churchtecharts.org/home/2016/1/14/the-pros-and-cons-of-aux-fed-subs-pt-1

    An interesting mini series on the various methods of running subs.

    #54247
    Profile photo of DavidCo
    DavidCo
    Participant

    Putting Qu’s limitations aside, a better tradeoff (IMO) is to instead use a mono group. The feed from any given channel to the sub is now post fader, and either on or off. That goes some way to alleviate the “Constantly Changing Crossover” issue described in the article Bob mentioned, but doesn’t address the issue of the difference in processing or levels in the master channels themselves.

    DC

    #57118
    Profile photo of BBEgo
    BBEgo
    Participant

    This was Extremely helpful, Dan & co.
    Thank you! I learned a lot!
    I was using a version of Dan’s idea, but had gotten frustrated for 2 reasons:

    I had my subwoofer on mix 4, because I didn’t know you could set the stereo mixes to mono, independent of the L/R mix.

    I got frustrated having to constantly adjust the subwoofer mix level because I didn’t know about the “Post Fade” trick.

    Now I can run subs on Mix 10 (for visual simplicity – nearest the L/R fader), and slave the level control to the L/R fader. Brilliant!
    Thanks guys!
    BBEgo

    #57127
    Profile photo of NZdave
    NZdave
    Participant

    I didn’t know you could set the stereo mixes to mono
    Really?
    mmm ok I have looked for that both in QU32 and in the PDF and the block diagram
    Can someone please put me onto where that switch is located?

    Thankyou
    NZdave

    #57131
    Profile photo of dpdan
    dpdan
    Participant

    I am reasonably confident when I say that the stereo mixes CAN NOT be set to mono.

    #57132
    Profile photo of NZdave
    NZdave
    Participant

    Yes for sure.
    I think just a little bit of confusion there. 😐

    #57143
    Profile photo of David Haughton
    David Haughton
    Keymaster

    Hi All, just to confirm, stereo mixes can’t be split (or summed) to mono, but this is already in the LONG list of user feature requests! 😀

    As Dan and DC say a post-fade send to the sub means that the send relationship is tied with the channel fader. You can also select change all Mix sends to post-fade by selecting the Mix e.g 9-10, press the Green ‘Sel’ button in the Master strip, go to ROUTING menu, set Pre-Fade setting to ‘ALL POST’.

    If you only have 1 sub, then it makes sense to use a Mono Mix for this, as all signals will be summed on their way in. If using 2 subs then use a Stereo Mix as Dan has said. Channels do not follow LR pan settings, and these should be kept centre for the paired sub outs to distribute energy evenly. This even applies to linked input channels.

    You could always pan all inputs to one side of the Stereo Mix (to compensate for the -3dB pan law) and just use the corresponding output socket as a Mono output, if you’re already using all of those Mono outs.

    Most active subs these days will have an Low-Pass built-in, this may even be variable and will avoid the need to pull out frequencies from the Sub Out’s GEQ to set a crossover point.

    HPF and LPF Butterworth/Linkwitz Riley filters on outputs have also been suggested previously and are already on the list of feature requests…

    Hope this helps.

    Thanks.
    Harry.

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