# Cell Phone Interference With Wireless Microphone Signal



## JimP0771 (Apr 13, 2020)

Hi All

I am a technical director for a non-profit youth theater in my local area. I have never been to school for lighting or sound and have no degree in either field matter of fact I have a BS in Hotel Management. I have been doing sound for this theater group for years and have my own 24 channel sound board, powered speakers and wireless microphones and all the cables and things that go with them to be able to do sound for the shows. Every time we do a show we ask the audience to shut off there cell phones so they do not interfere with wireless microphones. Is this true though? Does a cell phone signal really interfere with the wireless signal of a wireless microphone? 

Just something I have been wondering for years 

Thanks


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## MNicolai (Apr 13, 2020)

Generally not unless you're setting a phone directly next to the wireless receivers or other audio equipment. The "GSM buzz" can go buzzz bzzz bzzzzr, but it's pretty rare these days unless you're negligent about it. If you hear this kind of noise, you're either using older equipment that isn't as protected from it and/or your sound op or SM has put their phone directly on the mixer.

As for interference from the general audience, this is unlikely to ever be a problem unless you're using 2.4GHz based mic's, which you absolutely shouldn't be for theater. Think about all the music festivals where there are 10,000 people in the crowd with their phones on, texting, taking calls, sending Snapchats and Tik Tok's. You don't hear cell phone interference during a Billy Joel concert.


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## JimP0771 (Apr 13, 2020)

MNicolai said:


> Generally not unless you're setting a phone directly next to the wireless receivers or other audio equipment. The "GSM buzz" can go buzzz bzzz bzzzzr, but it's pretty rare these days unless you're negligent about it. If you hear this kind of noise, you're either using older equipment that isn't as protected from it and/or your sound op or SM has put their phone directly on the mixer.
> 
> As for interference from the general audience, this is unlikely to ever be a problem unless you're using 2.4GHz based mic's, which you absolutely shouldn't be for theater. Think about all the music festivals where there are 10,000 people in the crowd with their phones on, texting, taking calls, sending Snapchats and Tik Tok's. You don't hear cell phone interference during a Billy Joel concert.




Thanks for the answer on that. You knew I never took the moment to think about those big concerts where people are texting and snap-chatting it all makes sense 

Thanks


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## Ben Stiegler (Apr 14, 2020)

well ... maybe its not quite that cut and dried. Billy Joel's team has the budget and ability to deploy a tuned, directional distributed diversity antenna system covering the stage, to equip him with dual/backup transmitters, and to use top-end gear like Axcient where a remote audio engineer can command the transmitter to change freqs on the fly if interference is detected. I'm guessing Jim is operating with somewhat more limited technology.

Jim - how many receivers? What brand/model? What band? Are you using each receiver with its separate antennae, or do you have a central antenna system feeding all receivers? Some pix and a floor plan or drawing of where you place antennae and receivers relative to the stage would be helpful. also - your zip code - so we can cross-reference existing DTV and EMS svcs that may have priority in your area.

As more cellular and wireless devices start operating in the low 600Mhz (613Mhz plus) band, the potential for intermodulation distortion in existing wireless receivers increases greatly. So ... I do support asking the audience to shut 'em down ... and its accepted practice (to make that request) at regional rep houses here in NorCal. PM me if you want to work thru your frequencies, etc.


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## TimMc (Apr 14, 2020)

It's always a good idea to have the audience shut down their phones even if it's not for technical reasons.

Pretty much the entire 600mHz band is no longer available for Part 15 (unlicensed) use. Anyone with wireless mics that use 602mHz - 698mHz need to retire those units. They will potentially interfere with the licensed service users of these reassigned freqs which, if someone complains, will result in an FCC investigation, fines and confiscation of the offending transmitters.

The sound @MNicolai is talking about is what we called "GSM noise" and invariably happened with the VP of Nothing Important was delivering his 237 power point slide presentation, and he set his cell phone on the lectern next to the mic cable or it was in the breast pocket of his jacket, near the mic. GSM noise is an RF signal that is part of the phone's administrative connections to tower facilities - polling, RF level setting, keep-alive, etc. If you go back 10 year or so and look at the lectern mics offered Audio-Technica (as an example), they made a point of marketing mics that used filters to avoid this noise - it was that prevalent. The GSM noise was picked up by the mic element wiring or the cable to the mic; it was NOT AN INTERMODULATION PRODUCT FROM OTHER WIRELESS devices.


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## MNicolai (Apr 14, 2020)

Ben Stiegler said:


> its accepted practice (to make that request) at regional rep houses here in NorCal.



Accepted practice may be true and it's very reasonable to request cell phones to be turned off, but there's very little technical basis for those requests.


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## JimP0771 (Apr 14, 2020)

Ben Stiegler said:


> well ... maybe its not quite that cut and dried. Billy Joel's team has the budget and ability to deploy a tuned, directional distributed diversity antenna system covering the stage, to equip him with dual/backup transmitters, and to use top-end gear like Axcient where a remote audio engineer can command the transmitter to change freqs on the fly if interference is detected. I'm guessing Jim is operating with somewhat more limited technology.
> 
> Jim - how many receivers? What brand/model? What band? Are you using each receiver with its separate antennae, or do you have a central antenna system feeding all receivers? Some pix and a floor plan or drawing of where you place antennae and receivers relative to the stage would be helpful. also - your zip code - so we can cross-reference existing DTV and EMS svcs that may have priority in your area.
> 
> As more cellular and wireless devices start operating in the low 600Mhz (613Mhz plus) band, the potential for intermodulation distortion in existing wireless receivers increases greatly. So ... I do support asking the audience to shut 'em down ... and its accepted practice (to make that request) at regional rep houses here in NorCal. PM me if you want to work thru your frequencies, etc.




Hi

Ya my theater group is not doing any shows at this moment and we are actually getting ready for a possible large move from one facility to another. So basically my question was basically was just in general. But we use Audio Technica 2000 and 3000 Series all with there one separate receivers and their own antennas. ( let me clarify a little better here each mic has its own receiver and its own antennas) I never have issues with cellphone interference. Any local theater group or high school school I have gone to that have used had wireless Microphones have asked that you shut off your cell phones. We also like to tell people to do that so no cell phone calls come in and interrupt the performance either.


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## Ben Stiegler (Apr 14, 2020)

JimP0771 said:


> Hi
> 
> Ya my theater group is not doing any shows at this moment and we are actually getting ready for a possible large move from one facility to another. So basically my question was basically was just in general. But we use Audio Technica 2000 and 3000 Series all with there one separate receivers and their own antennas. ( let me clarify a little better here each mic has its own receiver and its own antennas) I never have issues with cellphone interference. Any local theater group or high school school I have gone to that have used had wireless Microphones have asked that you shut off your cell phones. We also like to tell people to do that so no cell phone calls come in and interrupt the performance either.


how many wireless channels do you use? Those separate receivers need to be approx 18" apart to avoid intermod and also inter-antenna interference. I helped one venue that couldn't afford distro ... we had 11 receivers spaced across the front of a mezzanine (non-audience area). cabling nightmare, easy to lose power to one with crew stumbling around in the dark ... and sub-optimal RF soln. If you've got 4 or more channels going ... distro with directional antenna is really the right way to do it.


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## Robert F Jarvis (Apr 14, 2020)

It wasn't the cell phones in house that blanked our wireless mikes out on occasions - the FCC change given the higher 600 and 700 to the cell phone guys got pre-empted here when one carrier got permission to 'test' the new bands! And with a tower right next door to the theater things were getting worse. Since replacing all our wireless mikes at a new (lower) band we haven't had any problems. And, that comment about getting audience to turn off phones is very valid. Standing in the sound booth or upstairs in the lighting booth we get a front seat view as these dam things are surreptitiously pulled from pockets and purses. Why do people bother going to the theater if they want conduct FaceBook session mid scene!


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## donboomer (Apr 15, 2020)

MNicolai said:


> Accepted practice may be true and it's very reasonable to request cell phones to be turned off, but there's very little technical basis for those requests.



True enough when this article was written, but that may not be the case any more. The article is old and does not take into account the pink lightning bolts from T Mobile. While they have been operational in most of the US for years, there were essentially no phones that operated on band 71. Now that there are iPhone 11s, anyone with one on Tmobile is contributing to a rise in your noise floor down to about 550MHz.

Check this out for an easy way to keep TMobile out of your system.


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## BCAP (Apr 29, 2020)

If you were using one of the new digital wireless microphone systems based in the 2.4GHz band, cell phones are seemingly able to severely disrupt those type of microphones in no time flat.


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## Ben Stiegler (Apr 29, 2020)

Indeed - I had the sad task of telling a regional YMCA that the 2.4G digital wireless mics their catalog-flipping (ex)-fitness director bought a ton of were the reason audio was dying during exercise classes. Rip and replace with QLX-D in the 5xx Mhz band, after a spectrum scan - problem solved!


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## BCAP (Apr 29, 2020)

I am sorry to derail the thread here, but I'll be quick - I have similar story - a venue that bought dozen or so 2.4GHz digital mics having numerous problems and asked me for help, after a couple weeks of analysis I was able to demonstrate to them what the issue was and they replaced the entire system with UHF analog in 500MHz band. Rock solid no problems and wow - excellent reception. Recently I had been in the situation to talk to some reps from a well known microphone manufacturer who told me "yeah, those 2.4GHz systems are really basically only if you need 1 or 2 mics". Interesting, the system I replaced in the one venue claimed to enable up to 15 units operating at a time under ideal conditions.


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## TimMc (Apr 29, 2020)

BCAP said:


> I am sorry to derail the thread here, but I'll be quick - I have similar story - a venue that bought dozen or so 2.4GHz digital mics having numerous problems and asked me for help, after a couple weeks of analysis I was able to demonstrate to them what the issue was and they replaced the entire system with UHF analog in 500MHz band. Rock solid no problems and wow - excellent reception. Recently I had been in the situation to talk to some reps from a well known microphone manufacturer who told me "yeah, those 2.4GHz systems are really basically only if you need 1 or 2 mics". *Interesting, the system I replaced in the one venue claimed to enable up to 15 units operating at a time under ideal conditions.*



The conditions are never ideal, I guess. This is the BS that occurs when the marketing folks write the ad copy after spending a mere 30 seconds with the design/engineering dept. It's all about making a "single number specification" into a bigger number than the competitions. Remember when Crown pushed damping factor? Turns out that anything over 25-50 is plenty good, but they got theirs consistently above 400, so Crown was inherently better, right? A 1200W amp is "louder" than a 1000W amp, right? Yeah, a fraction of a dB.

Mark (Samuel Clemmons) Twain said it well: "There are three kids of lies. Lies, damn lies, and statistics." Playing with single number specs is the same basic idea.


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