Gooders Posted October 22, 2013 Share Posted October 22, 2013 I have some RCF ART310 and ART712 powered speakers and have been using them for several years for AV and Theatre work. Last week I did an annual event and for some reason the speakers picked up a lot of interference from mobile phones. I disconnected the desk and input cables and the sound was defiantly from the speakers.I was at the same venue last year with the speakers in the same position and nothing. I've contacted the RCF service department who has said that basically all powered speakers do this. I would get this if I had paid £200 for them but not £750! Is this a common problem? and apart from moving the speakers has anyone found a cure? At the moment I'm thinking of putting tin foil inside the speaker bags. Link to comment Share on other sites More sharing options...
timsabre Posted October 22, 2013 Share Posted October 22, 2013 Normally only happens with a phone very close to the audio device... i.e. left on top of the speaker or something like that. From a few metres away it should not have any effect. (I hope you are joking about foil, but if not, you would be wasting your time) Link to comment Share on other sites More sharing options...
Gooders Posted October 22, 2013 Author Share Posted October 22, 2013 This is happening when someone was seated near to the speaker and generally about 4 to 5 feet away from the speaker. I'm kinda half joking about the tin foil. But a grounded sheet of metal around the amp should cut this out. It just seems a bit cheap that they don't shield the amp. Link to comment Share on other sites More sharing options...
Brian Posted October 22, 2013 Share Posted October 22, 2013 I disconnected the desk and input cables and the sound was defiantly from the speakers.Just to clarify - does this mean that the only connection to the speakers were the mains leads? Link to comment Share on other sites More sharing options...
Gooders Posted October 22, 2013 Author Share Posted October 22, 2013 "Just to clarify - does this mean that the only connection to the speakers were the mains leads?" Yes, I thought it may have been coming from the desk / cables so disconnected the audio cable and still had the same problem. Link to comment Share on other sites More sharing options...
BigYinUK Posted October 22, 2013 Share Posted October 22, 2013 I've certainly seen this with other amp/speaker devices, guitar, keyboard amps etc where a phone (mine or another band member's) was 3 or 4 foot away. Did you have the volume controls on the speakers set to full? Did it make any difference when the desk was disconnected and the volume controls turned right down? That might make a difference depending on where the RF was being picked up. Link to comment Share on other sites More sharing options...
Gooders Posted October 22, 2013 Author Share Posted October 22, 2013 I've certainly seen this with other amp/speaker devices, guitar, keyboard amps etc where a phone (mine or another band member's) was 3 or 4 foot away. Did you have the volume controls on the speakers set to full? Did it make any difference when the desk was disconnected and the volume controls turned right down? That might make a difference depending on where the RF was being picked up. The speaker volume was set to about a quarter. It didn't make any difference with the volume setting of the desk. Link to comment Share on other sites More sharing options...
Andrew Edwards Posted October 22, 2013 Share Posted October 22, 2013 We have RCF ART500 and 300 powered speakers and have had a variety of interference but not on all of them. We temporarily hosted our local FM radio station and picked up their transmission to the mast which was half the f of their main transmission of 103MHz. We picked it up regardless of any signal cable. Bizarrely, it only affected 2 out of the 5 identical 500s and 1 of the 300s. Initially it looked like precise location was a factor because one was picking up the transmission but one right next to it wasn't. Having signal plugged in boosted the volume by a noticeable amount but a ferrite ring knocked it back down again. We eventually took one down and moved it about. The (very experienced) engineer from the radio station finally concluded that whatever RF shielding inside must be faulty on 2 of them or the components configured very slightly differently. There is a possibility that another 3 of them were affected but because the wall was reinforced with a big sheet of steel for the bracket this could have been shielding it. I really didn't want to take them down and they moved out before it became a serious problem. Thankfully the phone issue is only noticeable when it is absolutely silent and when I say that I mean 'no audience in' silent. iPhones from version 3 to 5 on O2 are the worst offenders. However, the new 5S on 3 is totally silent on all the gear that I have which usually picks up phones. Even Tecpro comms right next to the mic. even in a call. Link to comment Share on other sites More sharing options...
BigYinUK Posted October 22, 2013 Share Posted October 22, 2013 It'd be interesting to see whether the powered speaker's volume control position (rather than the desk) affected how loud the pickup from the phones was. If you turn the volume on the speaker right down and the RF noise picks up just as loud, it would certainly indicate that the amp's shielding was not as good as it could be. However if it did make a difference then maybe it might then help, interference wise, to run the system with the desk level up high and the speaker input volume right down. Not an ideal gain structure maybe, but if it helped? Regards Link to comment Share on other sites More sharing options...
Gooders Posted October 22, 2013 Author Share Posted October 22, 2013 It'd be interesting to see whether the powered speaker's volume control position (rather than the desk) affected how loud the pickup from the phones was. If you turn the volume on the speaker right down and the RF noise picks up just as loud, it would certainly indicate that the amp's shielding was not as good as it could be. However if it did make a difference then maybe it might then help, interference wise, to run the system with the desk level up high and the speaker input volume right down. Not an ideal gain structure maybe, but if it helped? Regards I did try this at the weekend with the volume pot at 0 and it was very loud when I held a phone close to the speaker. I will try it again but further away. Why would they not shield the amp, it's not like mobile phones are a new thing! Link to comment Share on other sites More sharing options...
sam.spoons Posted October 22, 2013 Share Posted October 22, 2013 I suspect it's not as simple as that or why would some speakers be troublesome and others fine even when they are all the same make? Link to comment Share on other sites More sharing options...
laolu Posted October 23, 2013 Share Posted October 23, 2013 I have those problems with VHF (yes, we still use them) radio mics but not on UHF. Technically, the tin foil makes sense, but only if it shields your speaker on all sides (except the front). You would also have to wire it to the front grill and to the ground. And of course leave a whole in the back for convection. Surely, it looks a bit funny, like a big turkey, ready to go into the oven. :P Link to comment Share on other sites More sharing options...
Brian Posted October 23, 2013 Share Posted October 23, 2013 ...a grounded sheet of metal around the amp should cut this out. A question for you all... When is a ground not a ground (hint: when you're dealing with RF) (another hint: what is the wavelength of a mobile phone signal)? Link to comment Share on other sites More sharing options...
alistermorton Posted October 23, 2013 Share Posted October 23, 2013 Mobile phone signal's about 5-10cm isn't it? Can't remember the frequencies off hand, but 2.4GHz network stuff is about 12cm wavelength. Link to comment Share on other sites More sharing options...
Doug Siddons Posted October 23, 2013 Share Posted October 23, 2013 Had this same problem on a gig recently, duo on stage, one was swearing at the audience to turn their mobile phones off, the other pulled hs mobile out of his pocket turned it off problem went. Much riotous applause! Link to comment Share on other sites More sharing options...
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