Level discrepancies feeding FOH w/Qu24

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This topic contains 10 replies, has 8 voices, and was last updated by Profile photo of SteffenR SteffenR 6 years, 7 months ago.

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    Profile photo of Lobosdoc

    Hello all – thanks for reading. My group is currently using a Qu24 fairly exclusively for all our gigs, local or otherwise. When we play a venue with an existing sound system, I feed them our mains, and when we are on our own, the Qu feeds between 2-4 QSC KW153s. Sound with the QSCs I’m always happy with, but I’ve noted this last year, that occasionally, though the levels appear really good on the Qu, the sound systems I’m feeding start clipping, and appear overloaded by way too much signal. I’d say it’s probably 20-30% of the systems I hook up to, but when it happens, it’s frustrating because I have to compensate by dropping the level of the mains going out to them, which adversely affects our in-ear system, as well as our video and audio recordings, which are also fed from the mains channel. Unfortunately, I haven’t had opportunity in these situations to check over the house sound systems – it’s always been in larger fairs or music festivals with no time to chat or experiment much with setup, but it seems like when I question it, I’m always promised that the house sound system is flat, without any post-processing, and that the problem is exclusively on my end. More than anything else, I’d like to understand why it happens – why what appears to be perfect mains levels on the Qu, when fed to a receiving sound system, are way too hot.

    Profile photo of GCumbee

    Initially it sounds as though the offending systems just have a gain structure difference other that what you are accustomed to just feeding your speakers. They could have a processor in front of their amps or the amps themselves set to receive a lower level that you are sending. I would suggest feeding them with a matrix or Alt out so you can keep the rest of your console at where you normally operate it.

    All systems are not created equal. I can’t know what peak levels you are hitting. A properly designed system has to have its gain structure correct or this will occur.

    Hope that helps.

    Profile photo of Oracle/Steve

    I concur with what GCumbee said about using the Matrix. I always feed the house systems with the Matrix even if I’m not using my own system as well. I use the same QSC speakers for high end & KW181 for subs, and have NEVER seen a clip / compression light on the speakers.

    A lot of house systems have been set up by DJs that sometimes are…how to put this delicately…well, not really up to speed on the necessity of proper gain structure. Too often they feature a smiley faced EQ and amps cranked to the max. Indeed, some house systems also feature consumer grade (i.e. Radio Shack) mixers & EQs often running incompatible line levels.

    I had one club that insisted on bring the line level feeds from the board through the board’s pre-amps, rather than line inputs. They insisted that’s what “all the other bands do” and that it should be fine.

    I also recommend getting a true iso box for your house feed sends to make sure you don’t end up with any nasty ground loops.

    Profile photo of [XAP]Bob

    Alt out gives you a final physical pot for level control to their system, otherwise a simple drop of the master fader shouldn’t affect your in ears etc

    Profile photo of Lobosdoc

    Thanks guys for the quick feedback – I really appreciate the tips. I understand that I’m not giving enough information to cover all the possibilities, but for what it’s worth, I never get clipping (or have peak lights on the board or speakers) when I do the sound alone through the QSCs.
    I had considered passing our sound through the alt out, though the last two times I suggested it, the house sound guys talked me into patching the mains to them. I was never really clear on their explanation of why, mostly things like “that’ll give the truest sound”, or vague suggestions that the sound would somehow suffer through the alt out, as it would give a pre-processed sound. I haven’t used alt out to date, though from looking through the Qu manual just now it seems like I could program the alt out to give a clone of the mains, but with an independent pot to control the level going to the house system. I’ll try it next time. I’m familiar with the use of matrixes, as I use our matrixes already for the in-ear systems, and on occasion satellite speaker sets, or else I would have considered that as well.
    Bob – one of the in-ear channels that I let my guys use gives them the mains, post fader, as they asked “to hear what the audience is hearing”, and our video recorder also is patched into the mains on that same matrix. When I drop the master fader, it does reduce the level to both the in-ear channel, as well as the video camera – did I misunderstand you about dropping the master fader not affecting things, or am I missing something? Thanks again.

    Profile photo of MarkPAman

    I agree with everyone else – Alt Out, fed post fade from L+R will be what you need here. Probably worth keeping a pair of TRS Jack to XLR-M adaptor cables with the desk for this.

    You are right, if L+R feeds a matrix, then you don’t want to adjust it.

    Profile photo of [XAP]Bob

    Alt-Out fed from “L+R Post fade” *is* the main output, there isn’t a difference – except that one has an additional analogue level control. The Alt Out is balanced on TRS Jacks.

    Post fade mains into in ears?!

    Profile photo of airickess

    Lobosdoc, giving that musician a post-fader feed of the Mains in his in-ears mix is not the way to do it. You can give him a pre-fader mix of the LR and he will hear the FOH mix just fine. You can then adjust the levels of the Mains mix without affecting his mix level.
    The Video camera feed should also be on a separate mix output. I typically use mix 9-10 for my record feeds. I simply bring up every channel I’m using to Unity (0) for that mix and then the mix will track with my mix at FOH and I can adjust the level of the L-R without affecting the Video record feed.

    Profile photo of Lobosdoc

    Thanks again guys – I’ll reconfigure my mixes and matrixes and see how it goes… I’ve got TRS to XLR adapters – thanks for the suggestion Mark, and I’ll look into a true iso box – thanks Steve. I was worried that I had something configured wrong, or that there was some difference I was unaware of between the Qu and other systems that was predisposing to this, but it sounds like it’s just something I’ll prevent by feeding the house differently. Haven’t been doing this very long (as is probably apparent) but this board has been great to learn on – and I’m always getting compliments on our sound. Appreciate all the suggestions!

    Profile photo of DoctorG

    The suggestion to use the Alt Out is the best solution. Your comment about the “sound guys” wanting the “truest output” and your uncertainty about the Alt Out source on the QU suggests to me that they may be “amateurs” and you are not in a position to give them solid information. Hopefully, the comments thus far will correct the problem.

    That being said, I’ll add one other thought. The QU has its nominal output set at +4 dBu (1.23 volts RMS) with the Mains at 0 dB, but it can reach +22 dBu. This depends, of course, on the levels in the channels feeding the mains – your gain structure. +4dBu is a typical output level for professional systems, but there are mixers out there that can be set for 0 dB on the Mains = 0 dBu, or 0.775 volts RMS. If the “sound guys” use such a mixer and have optimized their system for that level, then your signal would be a little “hot.”

    Use the Alt Out and the problems will be solved on your end.

    Profile photo of SteffenR

    rethink the problem…

    if you will feed the PA with matrix out, then you have an independent house GEQ, PEQ, Compression and level control just for any PA systems you will see in the future

    use the alt out for the IEM Feed (pre fader or post fader does not matter in this case if you leave your main unaffected with processing) and the second matrix for anything else and maybe your video accepts AES ???

    If you have often struggle against the house PA maybe you can use in this case a system controller for adapting the levels and EQ,

    something like the Lake LM44 or the dbx DriveRack PA

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