Reply To: How to hookup subwoofers to QU 24?

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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 🙂