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Crossover Gain During Gain Structure Setup

Kyle AbelKyle Abel Posts: 16
edited April 2007 in PA General Discussion
Great product, great forum, great people. TONS of info! But I still am confused on one specific part of the gain structure setup - when/how to set gain levels on the crossover.

I received recommended crossover specs and speaker tunings from DBX that included crossover gain settings of -5dB on the highs and -2dB on the lows. With those settings, the output meters on the DRPA are naturally lower than the input meter.

I read on the old forum that during the gain structure setup process the crossover gain should be set so the DRPA output meters on each section (HI, LOW) match the DRPA input meter. I didn't see this in the DRPA manual though.

So, my question is...

When I'm going through the gain structure setup process, do I leave the crossover gain settings at the recommended settings, then adjust the amp input to just below clipping? Or do I adjust the crossover gain on each section (HI, LOW) so the output meters matches the input meter, then adjust the amp input meter to just below clipping?

Thanks in advance!


PS - Here's my setup
(1) DRPA (from 2 years ago, doesn't include my speaker or amp settings)
(2) JBL JRX125 mains
(2) JBL JRX118S subs
(1) QSC PLX1804 powering the mains
(1) QSC RMS2450 powering the subs


  • It gets a bit tricky here because there two competing requirements. First of all is the gain structure where the aim is to get the maximum S/N ratio out of the system by maximising the levels. Secondly, and in some ways more importantly is to get the correct levels of all the different speakers in the system to give a seamless crossing between drivers.

    It may be such that only one amplifier (read pair of channels) in the system (for a pink noise source anyway) will be close to clipping. It's related to driver efficiency.

    There is no functional reason you could not leave all crossover gains at 0db and adjust the relative levels of each amp to get the correct levels for each set of drivers *but* you would then have to mark the volume controls in whatever position they end up in so you don't have to reset the levels each time the system is assembled. This may or may not be easier for your application.
  • GadgetGadget Posts: 4,915
    Hi Kyle...
    I wish I knew who or what thread that is because its VERY misleading and I'd like to cut it out... Here's the deal.. don't believe EVERYTHING you read! Ok, first off there is no absolute way to do this...I know thats NOT what you want to hear but...

    If you can get the amps to peak then yes that would work fine. REMEMBER THIS ....NO CLIPPING EVER in the DRPA! Thats the ultimate sin! and will cause horrible noise a that will wreck your speakers...

    As jakobsladderz points out the goal is S/N but the thing is if you set the input level to the DRPA less than clipping but at or more than unity you can leave the crossover gains at -0- and not have any signal degradation..and if you can, then you'll have plenty of makeup gain if needed.

  • Kyle AbelKyle Abel Posts: 16
    Jakob & Gadget - thanks for the input! I guess as long as I correctly set the amps' input attenuators, the output LEDs don't really matter?

    Gadget, I found the article I was referencing. It's in the old forum, Small Venue section. On 10/30/2005, Jon Wilder writes:
    4) Turn up the main mix fader up to the point where the input meters on the DRPA are JUST going into clip.

    5) Set the high band output gain on the crossover section of the DRPA to 0dB. The high band should now be clipping exactly like the input meters are showing.

    6) Turn up the low band output gain until it also clips just like the input and high band meters(the low band needs some gain since there are far less frequencies in the low band, resulting in much less musical energy in this band)

    Perhaps I read this out of context - I don't know.

    Thanks again!
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