PA help

[phillytomcat]

I was singing this past weekend at my church choir. We have a 24 channel mackie onyx board, several mics for band and vocals , including two wireless ones, monitors, speakers, and of course the amp.
I don't know what in the chain of all of this caused this noise. In the middle of our set and intermittently, there was a loud machine -gun- like static, like rapid pulses of the stuff, coming from the pa. The electrical system is very old , so I suspect it cannot handle our newfangled equipment. Just a theory though . What could be causing this?

[yearlongyeti]

Did the sound man leave a mobile phone beside the desk and it kept ringing? I've had that before. Makes a noise very similar to what you are describing

[phillytomcat]

no, but there was a laptop next to it. We do it all the time. It doesn't happen in that case.
The sound engineer did mention that the choir director puts the wireless mic too close to the speakers.

[Z3NO]

Contrary to popular belief it's not usually the mixer or the sound engineer's phone that causes the interference (which it sounds like it was)... but the microphones (wireless ones in particular), or more rarely the speakers themselves (unlikely on a balanced PA). Chances are someone in the band had their phone on silent.

If it was the electrical circuit you would have heard a permanent hum or buzz rather than an occasional one.
A wireless mic too close to a speaker causes feedback, not the type of noise you described.

[mikemc]

Did you by any chance record these pulses, and do they correspond to the ordinal values of letters in the ancient Aramaic alphabet?



Seems like there wired and wireless mics-- could one or more of the mic cords been bad?

[phillytomcat]

Possibly I was thinking that just this evening.

[evaodland]

That is definitely cell phone interference...you can't have a cell phone within 20 feet of a condenser mic or the cables attached to them. podium/lecturn mics are omni condensors (the skinny black sticks) these are particularly sensitive to cell phones.

Cell phones have to be OFF not just on vibrate they check in with their network every few minutes.. If you have a bunch of people singing in front of mics you can bet one of them has a cell phone on.

[blakbeltjonez]

it's RF interference.... if you can't change the wireless frequencies to avoid the alleged cell phone interference, then lose the two wireless mics for the evening. some days you just can't win..... it could also be some other radio device(s) in the are stepping on your mic frequencies. this is not uncommon in RF-dense areas that have hospitals, TV stations, police/fire, etc...

[dancerchris]

If it truly is the cell phone causing RF interference, reproduce it by purposely calling a nearby phone. (of course do this during a rehearsal/test time). If you can reproduce it mute each of the sources on the mixer board until you identify the bad mike. Most likely it is a poorly or improperly shielded wire. If there is a bad ground just moving the bad wire will cause the static. Also check for worn out batteries in acoustic guitar pickups. When those 9 volts go bad they can make a similar noise. (Just happened at our worship service).

Unless your power is very low < 110v or very high > 130v I wouldn't worry too much about source issues. While appliances, flourescent lights, dimmers, etc can cause some noises I don't think this is your prop, and filtering power properly is very expensive.

[re.mark]

Could it have been wireless lapel mic's rubbing on clothing??
Or loose cable connections in any of the cables