How to use a compressor/limiter for PA speaker protection.

Discussion in 'Recording/Live Sound' started by hector, Jun 23, 2017.

  1. hector

    hector Member

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    I'd like to use my compressor/limiter to protect my PA speakers from hard volume spikes. Also, my power amp is rated higher than my speakers too (more than 2X the power). I understand how to use it as channel inserts, but I don't have enough compressors for all the channels being used. I am using an Allen Heath mix wizard 3 board. I thought about putting the compressor on the main outs, just before the power amp. Is this not a good idea, to put the compressor on the entire mix?

    I'm thinking of maybe a brickwall setting for the mains, and still use a different compressor for a few channel inserts to smooth vocals out.

    I currently have a dbx 2 channel and a behringer autocom 2 channel.
     
  2. gigsup

    gigsup Supporting Member

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    If no one is at the console, or if different people are doing mixes for different bands, it can't hurt for safety reasons.
    But the trade off is your entire sound is now the sound of the compressor you use, probably a $199 compressor.
    So, you need to ask yourself if that is the best sounding, nicest piece of gear you own. (It isn't).

    If you are really "brick walling it" at ∞:1, the entire mix is subject to the sound of the compressor limiting the program material.
    Worst case scenario, the mix becomes the cliché, no attack, 'whoommp, whoommp' pumping sound that EDM groups are now emulating in their music.

    I own a Mix Wizard in a rack with EQ's, compressors, effects, CD player, I've had it for years and it sounds great, it's gathering dust now because the digital boards are easier and lighter. But I never strapped a stereo compressor across the mix. I would use the compressors on the channels that needed them. If you're worried about hitting the speakers too hard, you can turn down the input attenuators on your amps. That won't correct for console or channel clipping, but it will reduce the signal being amplified by the amp and delivered to your speakers.
     
  3. hector

    hector Member

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    Thanks.
    Across the entire mix probably isn't the best solution.
    I mostly use this setup for band practice. CD player, vocals, and synths in the mixer.
    I will most likely use inserts on the vocals and synth.
    The vocals could use some smoothing out, and some of the preset synth patches can deliver a real blow to your speakers, when previewing them.
    So, it will be more of a limiter on the synth channel.
    I will probably let the CD/MP3 player run wide open, since it's pre-mixed already, and usually somewhat leveled out.
     
  4. tshall

    tshall Member

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    +1 on power amp attenuation, if you can trust no one will mess with the knobs. If not, perhaps a smaller power amp, paired with judicious channel-specific compression/limiting, would be a cost effective solution to protect the speakers while preserving the sound quality of the mix?

    (Or get a digital board and have compression/limiting on every channel.)
     
  5. walterw

    walterw Gold Supporting Member

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    why would anything at band practice be remotely loud enough to need compressor protection?

    for live use, make sure that if you're insert comping vocals that the monitor auxes are not affected by the compression.

    if you did want to comp the entire mix as protection (i never would) be sure to set it as a brick wall limiter, tweaked so the threshold is just above normal levels so it never hits while normal playing but only if something goes wrong.
     
  6. zenmindbeginner

    zenmindbeginner Silver Supporting Member

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    I use a brick wall limiter set so my main bus doesn't ever go into the red... protects my speakers and power amp from "fader creep"... when the party gets hot and the dancing is at it's most intense... I always find myself pushing my system just a tiny bit more... without the limiter, my speakers would need replacing more frequently.

    Most power amps have built in clipping whenever the levels get too hot... that clipping is usually pretty ugly sounding... I'd rather hear my limiter clip than my power amp... I'd also rather hear my limiter do the clipping than a farty sounding failed surround or a blown tweeter.
     
  7. walterw

    walterw Gold Supporting Member

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    the problem is that the more you push the signal into the limiter, the more compressed it is; there's less difference between loud and quiet moments like between kick drum hits, meaning the sound is continuously loud the whole time.

    this gives the speakers less time to cool off between peaks, so you can end up still blowing up your stuff.

    (that is to say you've reduced the peak levels with the limiter, but now the average level is still higher, and that can kill drivers too.)
     
  8. zenmindbeginner

    zenmindbeginner Silver Supporting Member

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    My fader creep during the height of the energy on the floor is just throwing a few extra dbs into the limiter... it's just set so it barely triggers but is there to catch crazy transients above a certain level... just a sort of insurance for my system... protects my power amp too. I'm a DJ, so I'm bobbing my head and grooving while I am searching my database... not the same situation as a "sound man" who might not be sidetracked with searching a database, feeling the atmosphere or riding a certain energy wave on the floor.

    It's actually the cheapo DBX Peak Stop-Plus built into my graphic EQ... no attack or release controls but only a threshold. The built-n attack is slow enough and the release is fast enough to stay punchy sounding without turning into a spongey mess as long as it's only lightly touching on the highest transients.

    Good points though, your post is 100% correct.
     
  9. walterw

    walterw Gold Supporting Member

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    seems reasonable then.

    my warning would just be a general one for folks out there, just because you've got a "limiter" on your stuff doesn't mean you can't still blow it up.
     
  10. griggsterr

    griggsterr Supporting Member

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    Trying to idiot proof a system (which is what it sounds like you are trying to do) is always a slippery slope.
    I almost always set hard limiters on either my LR mains system mix or the subs or maybe both.
    But then it's me there running the console.
    Also for Me, I don't care if the party is hot etc. I'm not going to push anything into any danger zones. Does something occasionally hit a peak and get into the red zone. Sure. It depends on how I'm running the system that night. If I have my subs on an aux then I will insert a limiter there to limit the dynamic range of the subs. Which will also protect the speaker and add life to it. The 2 things that you are likely to blow up are the sub, or the HF driver. other than fader and eq there isn't much you can do to protect them. The sub can be protected by the limiter.
     

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