Sub woofer output challenge

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This topic contains 4 replies, has 4 voices, and was last updated by Profile photo of Brian Brian 3 weeks, 6 days ago.

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  • #120784
    Profile photo of JayEm
    JayEm
    Participant

    We would like to connect up our subwoofer but exclude certain inputs from it (We particularly have challenges with acoustic guitar feedback). We have outputs (mtx & aux) available and could route what we need to one of them but cannot work out how to link our main FoH fader to also control its level. Sadly, outputs cannot be ganged together like inputs can, or that would do it perfectly! The best we can come up with is to put the sub fader at the extreme right, next to the main fader, and manually move them both together.

    Any better ideas?

    #120786
    Profile photo of Tobi
    Tobi
    Participant

    Use a DCA.

    Best Regards,
    Tobias

    #120789
    Profile photo of Teresabutler
    Teresabutler
    Participant

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    #120803
    Profile photo of Brian
    Brian
    Participant

    As Tobi said, you can set up a DCA with the Main speaker output and the sub output in it. Then use the DCA fader/mute to control your “speaker system” as a whole.

    Now there are lots of ways to set up this sub output. One of the easiest is probably to run “subs on an aux” where you set an aux up and only feed the inputs into it that you want being outputted to the sub. This makes it easy to not put things like vocals and your acoustic guitar in this output. Then that aux output gets sent directly to your subs.

    That being said, I have a couple of questions and suggestions for your acoustic guitar. Is the guitar feeding back from the subs, or a nearby monitor wedge? It’s more likely it’s feeding back from a monitor wedge, but it certainly could be feeding back from a sub. If it’s feeding back from a monitor wedge, using “subs on an aux” isn’t going to help because the low end will still be coming through the monitor even if it’s not coming through the sub. Simply using a high pass filter on the acoustic guitar that is set high enough to prevent a lot of low end energy from hitting ALL of the outputs (subs and monitor sends) is usually the first way to prevent feedback. I realize that the high pass filter will not prevent ALL low end from hitting the output, but it should definitely help prevent feedback.

    On the other hand, if the guitar is really feeding back from the subs, in addition to using the high pass filter, another option is to move the guitar player to a location where the sub energy is less pronounced. Obviously moving the player farther way from the sub will help but if you are running subs on both sides of the stage, you might be surprised at how the comb filtering could be affecting the position where the guitar player currently is. They might currently be in a “power alley” where the sub energy is higher than normal and simply moving the guitar player a couple of feet one direction or another might put them in a cancelation lobe where the sub energy is less than normal which will obviously help.

    Here is an example of the comb filtering that happens when you separate your subs….. The image is skewed to show the affects in the audience seating area, but the same affect is happening on stage too.
    Sub Comb Filtering

    #120808
    Profile photo of Brian
    Brian
    Participant

    Obviously that image didn’t work. Let me try again…..

    This is from Merlijin van Veen’s site. (https://www.merlijnvanveen.nl/en/study-hall/169-displacement-is-key)

    You can see how this affects the stage area too (the portion of the image behind the speakers – located towards the top of the image).
    PS – in this image, the green is actually the “power alley” where sub energy is higher and the red is the “power valley” where the sub energy is less. The picture itself doesn’t really matter, just the concepts it is trying to convey.

    null

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