Qu-PAC Interference Problem?

[molliganParticipant]

Dear all,

We have been using the Qu-PAC at our church for the past few months and have really enjoyed the experience. Our current setup is quite simple: a few wired microphone, guitar, and Roland V-drums. We have an airport express for wireless control and will play audio through ST3 input using Airplay for intro and outro music. This past Sunday we had a very strange occurrence. During the middle of the sermon a clear signal came across the PA that sounded like an aberrant analog radio signal. Our wireless router is obviously password protected, so the AV team cannot figure out how this happened. It sounds like analog radio signal interference, but that would obviously not make much sense given our complete lack of wireless microphones and the Qu-PAC being a digital console. I have provided a clip of the recording below. Other than someone jumping onto our wireless airplay (weird, but plausible I guess), does anyone else have any explanation on how this could technically happen?

Here is the recorded audio interference

Kindest,
JM

[AndreasModerator]

Well, I doubt this is some sort of interference. Hijacking your AirPlay seems to be the most plausible explanation. Are you sure there isn’t any open wireless access left?

[molliganParticipant]

Our airport express is set up to be hidden and is also password protected. Other than that, we don’t even own any wireless gear. It was just very strange, but perhaps someone jumped on the Airplay. Just throwing it out there to see if there were any other technical explanations. Thanks

[PEJParticipant]

I have seen, actually heard, a radio station come in on a wired mic input. It was balanced xlr over very old install cable. I assume the shielding had broken down. We bypassed it with new cable and it cleared up. In another case of interference someone had used unshielded telephone wiring to build a mic cable.
Check the quality of the cable on ST3?

[Anonymous]

My Guess is interfernce over an XLR…?

This past weekend I had a laptop bag with an old Samsung phone inside the bag put on top of a lectern mic line and I collected 3G network interference.
Its a good live sound mic cable however.
it took a little while to track down as in the middle of a show and we were running 5 Laptops with 2 QU mixers with cell phones on wifi around us…
I couldnt see the bag from FOH.

So you need to check your mic leads is my guess 😐

[AndreasModerator]

Hmm ok, if AirPlay can safely be ruled out I agree to check cables. If we assume RF interference, this can only be some AM station. Since the signal fades out quickly, I doubt the origin is a stationary transmitter but probably some stronger CB radio from a car or truck driving by.
I’d try to walk around with a mobile CB transmitter near your equipment.

[dpdanParticipant]

it is unarguably a trucker with a very illegally equipped CB radio. The fact that it fades out proves the fact that when he “keyed” his mic he was right in front of the church and was driving past and away. There is nothing you can do about this, apart from praying that he never drives by again and if he does, I highly suggest getting a dedicated church member to sit outside during the service to monitor the sound and watch for a trucker to drive by. Take a picture of every truck that goes by and make sure to get the license plate number ON THE FRONT OF THE TRACTOR, (not the trailer) and report him to the local police department.

I used to get the same thing through my living room stereo every once in a while and it was always a big truck going by. These massively boosted CB radios are very illegal, but that doesn’t stop truckers from buying and using them.
The Apple router is most likely the weak device in the system that is allowing this to “get into” the sound system. The signal is literally blasting the analog portion of the 3.5mm output.

Was ST3 turned up when this came through?

[Anonymous]

Was ST3 turned up when this came through?

Yes good question!

[DoctorGParticipant]

It was certainly a CB transmitter, probably an illegal one. It was probably a very unusual moment – a truck with an illegal CB radio passing by during a service — and may never happen again.

The only thing I might suggest is to be sure you have a good system ground connection. Be sure all your XLR and other signal cables are in good working order. You’ll probably need a cable tester to check them if there is any doubt, but you might get by with a simple ohmmeter.

For more ideas check out these links:
RFI Interference in AV equipment
CB Radio Interference

[molliganParticipant]

Hey guys,

Thanks for your help. The input on ST3 was indeed turned up, as we typically control the volume output through the iPhone. Also, ST1 is on a ducker with the vocal mic channel so that when the pastor speaks it will limit the background music, but I guess the CB radio was just blasted the input. It came through quite loud. The cable from the airport router to ST1 (sorry, my mistake) was just a cheap 3.5mm to mono TS splitter from amazon. It is probably not shileded, but it is new. This sounds like it is the most likely explanation. You guys are great!

[dpdanParticipant]

I think DoctorG mentinoned something very valuable when he said,,,,,,,
“it may never happen again”.

[Author]

Posts