PA issues in a gym

Discussion in 'Location Recording' started by pmolsonmus, Sep 24, 2009.

  1. pmolsonmus

    pmolsonmus Well-Known Member


    They've just completed the first stage of a major renovation at the high school I work at. They installed quite a nice PA system in the new gym (I don't want to discuss what hasn't happened in the fine arts right now!) but I'm having an issue and wonder if anyone can help.

    My first step was to try to contact the sound company but because the project is still unfinished there are all kinds of hoops and protocol that I need to follow and I need an answer sooner then I will get through to them.

    There are a series of Mic inputs and Line inputs on breakout boxes on all 4 walls. We're going to do a quick song for an assembly there so I brought a recorded backing track to run through the house PA mixed with 6 mics and sent it through the balanced line input.

    I first set up the mixer and CD player, checked all cables, played back the CD without any mics connected and a problem appeared. I'm quite sure they've installed some sort of "idiot" limiter on the line in and at irregular intervals I'd lose about 12db or more of the backing track.

    I (as I usually do) assumed something was wrong with my set up or CD. I was coming through a HHB Cd player through the balanced outs so I thought perhaps by going into a mono set-up through the single line out I was creating some sort of weird total phase cancellation because of the English wiring. So I went back to my original track, created a mono mix panned everything hard left on the mixer and voila, same problem.

    I went back later when a volleyball match was about to begin and they had a CD absolutely CRANKED with no problem. ????

    I now think that there may be some limiting device on that line in or the speakers that is creating the signal loss (my levels remain constant) and maybe its not set to the same limit on the line in that they were using. Any suggestions or bypasses that the Live sound folks can think of. I have access to the rack but there are no limiters or anything that I have access to

    Any thoughts? This happened with or without mics plugged in and the backing track is almost (by design) at a static dynamic /db level.


  2. dvdhawk

    dvdhawk Well-Known Member

    Hi Phil,

    I'd think there was a ducker installed to give vocal paging/announcing priority over any other channel - but you say you have the same results without any other mics plugged in anywhere else in the room Puzzling....

    Do you know what mixer / amplifiers they put in?

    Some tests you might want to do:
    Do you know which channel the volleyball CD blasting through?
    Do you get the same volume using that input for your HHB?
    Are you sure there isn't a comp/limiter/ducker hidden behind security covers in a rack somewhere?

  3. pmolsonmus

    pmolsonmus Well-Known Member

    Hey Dave,

    I'm assuming it is some sort of limiter that I can't see or have access to. I do know that there are 4 QSC amps, (didn't get model number) Now I'm wondering if each input is assigned a separate amp and the amps have a builit in limiter. If it is outboard, it may be behind a panel on the rack but it sure isn't accessible regardless.

    My thought was to try the other channel input but because of the set up (4 breakout boxes on 4 walls) The only one that I could use without running a 200 foot cable that 1400 students would walk over was the one I was using.

    I also considered just running the CD player that's used for the house but trying to have the choir sync to speakers mounted in the rafters of a gym without a rehearsal was a little too risky for my taste, and if they had asked me (they didn't) It would have been nice to have a line out on the breakout boxes as well, but....

    The control freak in me wanted to make sure we could monitor near the mics as well. (And yes, the level dropped occurred BEFORE monitors were even in the equation)

    I'm not familiar enough with the "auto limiter" type boxes, but it would seem to make sense that all inputs would be at the same gain, yes???

    The sound company is good and reputable and have done a nice job in all other aspects so I'm sure we'll eventually get to the bottom of it, but???

  4. moonbaby

    moonbaby Mmmmmm Well-Known Member

    Dumb question, but are you POSITIVE that the XLR connection at the breakout box on the wall is really a LINE level connection? You might be hammering a limiter patched to a mic channel...
  5. pmolsonmus

    pmolsonmus Well-Known Member

    Not a dumb question but it is clearly labled LINE IN. Great idea though, they may have screwed up the wiring in the breakout box. I hadn't thought of that!

    In fact, that sounds like a very logical explanation. I didn't try the mic input with a mic directly. Will try that and get back to you.

  6. pmolsonmus

    pmolsonmus Well-Known Member

    Sound company acknowledged a problem and will be in tomorrow to fix it. At least I can breathe easier knowing it wasn't my screw up (at least this time) :D

    Will let you know tomorrow

  7. dvdhawk

    dvdhawk Well-Known Member

    Good news Phil.

    I'd still be interested to know what the sound installer changes to correct the problem. For future reference...
  8. pmolsonmus

    pmolsonmus Well-Known Member

    Just got the word. Because there are 4 breakout boxes (1 on each wall) each with a mic and line input he's got noise gates installed on each input for the open lines that are running to a system that is always on.

    He's changing the threshold and making a longer release to (hopefully) minimize the problem that we had. Will reassess if buzz appears.

    Apparently the recording I created had enough quiet spots to engage the noise gates where the rap they were playing through the house kept the gates open.
    In other words, I too was the victim of the loudness wars even in a live setting!

  9. moonbaby

    moonbaby Mmmmmm Well-Known Member

    Soundperson-less mixing...uuugh! Well, at least you got them to track it down and (hopefully) correct the problem...
    Thanks for the update, Phil !!
  10. As I read my way down the post I was gonna suggest noise gate being too hot. I walked into band practice the other day to see the bass player messing with his new PA and he was complaining about the everything sounding bad. When you would talk into the mic it would take a second for the speaker to kick on. Cause a weird delay type of effect. Soon found out each powered speaker had its noise gate cranked.

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