Christir86 Posted August 31, 2016 Share Posted August 31, 2016 We have had an ongoing issue in the school I work at that there is a low rumble noise emmited from the speakers without anything plugged in or playing through the desk. When the desk is completely muted there is nothing coming through, so it doesn't appear to be an issue with the amps. We have a Soundcraft GB4 16 channel desk. I think it might be an issue with the power, as there is a low hiss coming from the desk too. You can just about hear the rumbling noise from the control desk area with the Master faders up, but it's when you push up the volume (with all EQs and gains set to neutral/off) that the rumbling noise gets more noticable and more so on different channels. I even tried unplugging all the cables (a cable that runs downstairs to the amps and splits into 16 XLR connectors for each channel) and still a rumbling noise. Link to comment Share on other sites More sharing options...
paulears Posted August 31, 2016 Share Posted August 31, 2016 any chance of hearing it? Link to comment Share on other sites More sharing options...
Christir86 Posted August 31, 2016 Author Share Posted August 31, 2016 any chance of hearing it? Unfortunately no - I have tried getting recordings but they sound nothing like the actual sound. I have spent most of today troubleshooting with what little knowledge I have - tried switching out power-cables and sockets, attached a small portable speaker to the desk to see if it still came through that (it did but so quiet you had to stand next to it - like a low purr) and then tried testing is using a cable tester (name on it is Behringer CT100) but can't find anything that shows what results I am getting, which is nothing like what others have shown online. It sent a test tone through okay but not sure if anything is wrong inside the installed (NB: walls!) cables. I tried changing some of the frequencies (above the EQ switch) and it seems to reduce some of the noise, but not sure if that's just masking it rather than getting rid of it. I am at a total loss and thinking it would be simpler to get someone in (again, my sound tech skills aren't that high). Link to comment Share on other sites More sharing options...
MarkPAman Posted August 31, 2016 Share Posted August 31, 2016 I am at a total loss and thinking it would be simpler to get someone in. Probably a good plan - where are you? Somebody may offer.......... Link to comment Share on other sites More sharing options...
Stuart91 Posted August 31, 2016 Share Posted August 31, 2016 Is there an induction loop in the room? I have occasionally come across mysterious noises in PA systems that have been introduced by the loop. Sometimes the loop is a standalone system with a mic sitting somewhere random. Link to comment Share on other sites More sharing options...
paulears Posted August 31, 2016 Share Posted August 31, 2016 There's a thing that happens with PSUs from time to time - usually a capacitor problem and it produces a weird low frequency noise that sounds like a motor boat - sort of low level engine puttering? If pulling all the cables out still lets you hear it, could be this? There's a thing that happens with PSUs from time to time - usually a capacitor problem and it produces a weird low frequency noise that sounds like a motor boat - sort of low level engine puttering? If pulling all the cables out still lets you hear it, could be this? Link to comment Share on other sites More sharing options...
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