Feeding subs via Mix 5-6 using LPF, as a substitute crossover

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This topic contains 6 replies, has 6 voices, and was last updated by Profile photo of JD JD 6 years, 9 months ago.

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    Profile photo of gilly

    We have two passive sub woofers that were initially wired from separate amp via crossover fed from main LRv od desk. The crossover went defunkt.
    Just wondering would this work instead of having to install new crossover:

    • Disconnect the sub-woofer amp from the main LR loop and reconnect to stereo Mix 5-6 outputs.
    • Assign just the bass guitar, kick drum and floor tom to Mix 5-6 and balance the levels.
    • Select Mix 5-6 and apply the lowest Q setting (i.e. widest) on one of the PEQ bands to make it a shelving filter.
    • Set threshold at around 105 Hz, thereby making it a LPF cutting everything above this frequency (you could also, or in addition, use the GEQ in fader flip mode and turn down all the faders above 100 Hz).
    • On all the other instrument and voice channels apply the LPF at 105 Hz, thereby reducing the low frequency burden on the full range LR speakers.
    • Route both the LR and Mix 5-6 to DCA1 group and assign DCA1 on one of the faders (suggest fader 24) in the Custom Layer, so that if you need to lower or raise the overall house volume the sub-woofers volume lowers/raises accordingly just as if the subs were fed off the main LR.

    Would this work??

    Profile photo of cornelius78

    In theory it could work, kind of. An improvement on point 5 would be to instead of taking out <105Hz on every channel without useful bass content (I think you mean the HPF here, not LPF) in LR to instead just take out <105Hz on the LR bus as a whole using LR’s own peq\geq, kind of as you described in point4 for mix5-6, but backwards (create a hpf instead of a lpf.) This may knock all the bass out of your recordings if you’re using LR for recordings though.

    However, I am against using the desk as a quasi-XO. Firstly, the eq filters on the peq\geq are nowhere near as steep (nor do they have as many options: eg Bessel, Buttersworth, Linkwitz-Riley) as they are on a proper XO, so although using the Qu as an XO could produce a semi-acceptable result, the result you’d get with a proper XO will almost certainly be better. Nextly, a board reset or botched scene\show recall without the appropriate safes could nix the settings entirely, and end up sending a full range signal to places that shouldn’t get it, which could be bad for your speakers and bad for peoples’ ears. The chance of this happening increases dramatically as you get over-helpful volunteers and\or people controlling things with ipads. Finally, if something happens to your Qu and it needs servicing, (unless you’ve got your scene backed up and you replace it with another Qu in the interim,) you’re going to need another XO anyway.

    I’m all for running aux-fed subs (and I’d be setting mix5\6 as post fader with send levels at unity, essentially making it a subgroup.) I’m also all for using the outputs’ peq\geq to try to deal with room resonances or shape the mix in general etc (if it goes badly you might get some feedback or it might just sound bad, but it won’t destroy your speakers the same way that introducing a full range signal to drivers that can’t handle it will.) Tying the aux+LR levels together through a DCA will make things easier. I just don’t think it’s a good idea to use the mixer as a speaker processor, if it can be avoided.

    Profile photo of Andreas

    You’ll find some additional information in this thread: use equaliser to put low pass filter in place
    As Cornelius wrote: You don’t get a proper Xover right out of the desk (no LPF at all, frequency response never flat).
    If you still want to go that way, why not using a Matrix output instead of all the DCA stuff?

    Profile photo of gilly

    Thanks guys. Yes Cornelius that was a typo,i meant HPF.
    Andreas te using Matrix instead of DCA, we already have the 4 Mtx’s used to drive other supplementary speakers

    Profile photo of GCumbee

    Used crossovers can be had cheap.

    Profile photo of [XAP]Bob

    As an emergency “it’s an hour until Sunday service and no ones open ‘cos it’s Sunday” then yes…

    I’d not want to though…

    Profile photo of JD

    I run everything but the Bass and Kick through the LR mains, and run the Bass and Mains (and a second feed from the Keyboards)
    through a Hi-Fi Bass Cabinet – EA or Accugroove – using 5&6. Simple and Sweet …

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