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Author Topic: PA system makes loud noise like a gunshot  (Read 17475 times)

Brian Wombaugh

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PA system makes loud noise like a gunshot
« on: July 13, 2011, 09:18:44 pm »

All of a sudden we have started getting a loud "bang" through our system at church.  It does not happen often or with any kind of irregularity.  There has not been any new equipment added to the system over the last year.  This problem has just surfaced out of nowhere.  It is loud and sounds almost like a gunshot.  We have a Soundtech 1250T powered mixer running through 2 Peavey PR12n's and a set of 12" Yamaha monitors.  Any ideas would be greatly appreciated.  I am beggining to wonder if it could be a problem in the mixer such as a short of some sort.  I have tried using a temporary 3 to 2 adapter plug to take the ground out thinking that may be an issue - but the problem is still there.  Thanks for any help !
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Rick Perry

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Re: PA system makes loud noise like a gunshot
« Reply #1 on: July 15, 2011, 05:32:46 am »

All of a sudden we have started getting a loud "bang" through our system at church.  It does not happen often or with any kind of irregularity.  There has not been any new equipment added to the system over the last year.  This problem has just surfaced out of nowhere.  It is loud and sounds almost like a gunshot.  We have a Soundtech 1250T powered mixer running through 2 Peavey PR12n's and a set of 12" Yamaha monitors.  Any ideas would be greatly appreciated.  I am beggining to wonder if it could be a problem in the mixer such as a short of some sort.  I have tried using a temporary 3 to 2 adapter plug to take the ground out thinking that may be an issue - but the problem is still there.  Thanks for any help !

I would disconnect any channels to the mixer and connect an ipod for testing. If you are powered up and you temporarily lose a signal from say, the acoustic guitar, you can get this same sound. Also try running a drop cord and plugging the board into a different outlet.  If you do not get the sound anymore, try plugging in one thing at a time until the sound comes back. If you've ever had someone connected to a DI unplug, you will know what I am talking about.
Good Luck
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Karl Winkler

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Re: PA system makes loud noise like a gunshot
« Reply #2 on: July 15, 2011, 12:05:42 pm »

Off the top of my head it sounds to me like static discharge through a high impedance input that has a lot of gain on it. Something maybe like an acoustic guitar with a piezo pickup or similar, or a condenser microphone.

Where are you located? Here in the SW, we have had an extremely dry summer. I remember in my early days in the studio in Tucson when I was a student, we kept a spray bottle of soapy water to mist around the kick drum pedal so that the buildup of static from the pedal would not "crack" through the microphone and onto the recording.

It may be a pain in the butt to use the process of elimination with something unpredictable like this, but I would suggest disconnecting one input at a time, letting the system run, and waiting until you get the pop again (or not). It may take you all day depending on the frequency of the pops.

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Brian Ehlers

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Re: PA system makes loud noise like a gunshot
« Reply #3 on: July 15, 2011, 02:08:01 pm »

The good news is that, since you're using a powered mixer, your challenge lies in simple determining if the problem is inside the mixer or coming from one of the mics, cables, or pieces of equipment feeding the mixer.

The bad news is that, if the problem seldom occurs, it can take a long time to track it down.  The next time it occurs during a service, take notes on your configuration.  What position were all the faders at?  What channels were muted?  Etc.  Then spend a few hours at church by yourself trying to recreate the problem.

I agree that static discharge is a likly candidate.  Maybe you'll notice that someone touched their microphone just before the bang.  Another possibility is a bad connection in a connector, cable, or microphone on a channel which is using phantom power.  Phantom power puts +48V on both legs of the balanced signal.  If one leg opens up momentarily, it creates a differential voltage much larger than the typical mic signal, resulting in a bang.
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Karl Winkler

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Re: PA system makes loud noise like a gunshot
« Reply #4 on: July 15, 2011, 02:57:48 pm »

Another possibility is a bad connection in a connector, cable, or microphone on a channel which is using phantom power.  Phantom power puts +48V on both legs of the balanced signal.  If one leg opens up momentarily, it creates a differential voltage much larger than the typical mic signal, resulting in a bang.

Good point about an intermittent connection and possible phantom power discharge. I agree that's probably equally if not more likely than static discharge in this case.
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Brian Wombaugh

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Re: PA system makes loud noise like a gunshot
« Reply #5 on: July 16, 2011, 06:10:35 am »

I am pretty sure that the phantom power was turned off.  We only have one microphone that requires phantom and it is used infrequently.  When it is not being used I usually shut the phantom power off.  One interesting note that I see from these post.  I said that we had not added anything "new" to the system recently - Well that is not entirely true.  There has been an acoustic guitar player who wanted to be ran through the house system as well as still being able to run through his personal amp.  I noticed that he is using a Whirlwind IMP2 DI box that splits the signal from his guitar.  One cable goes to his amp and the XLR cable coming out plugs into one of the mic inputs of the main system on stage.  The last time this sound occured, it was before the church service started.  He was not playing his instrument.  In fact, no one was playing anything or using any of the equipment.  I have since went back and wiggled every connetion on the board, every piece of equipment, every cable and every plug.  I have not been able to reproduce the sound myself.  Could there be some sort of issue with the acoustic guitar of the DI box since this is the only thing about the system that has changed at all since the problem began ?  If so, what should I do to troubleshoot ?   Thanks for all the help !   Brian
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Marty McCann

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Re: PA system makes loud noise like a gunshot
« Reply #6 on: July 19, 2011, 03:30:16 pm »

I am pretty sure that the phantom power was turned off.  We only have one microphone that requires phantom and it is used infrequently.  When it is not being used I usually shut the phantom power off.  One interesting note that I see from these post.  I said that we had not added anything "new" to the system recently - Well that is not entirely true.  There has been an acoustic guitar player who wanted to be ran through the house system as well as still being able to run through his personal amp.  I noticed that he is using a Whirlwind IMP2 DI box that splits the signal from his guitar.  One cable goes to his amp and the XLR cable coming out plugs into one of the mic inputs of the main system on stage.  The last time this sound occured, it was before the church service started.  He was not playing his instrument.  In fact, no one was playing anything or using any of the equipment.  I have since went back and wiggled every connetion on the board, every piece of equipment, every cable and every plug.  I have not been able to reproduce the sound myself.  Could there be some sort of issue with the acoustic guitar of the DI box since this is the only thing about the system that has changed at all since the problem began ?  If so, what should I do to troubleshoot ?   Thanks for all the help !   Brian

Is it possible that perhaps the acoustic guitar player may have plugged from the DI to his amp while you had his channel up in the mix?  As it is near impossible to put the 1/4 inch phone plug into the 1/4 phone jack without having the tip touch the ground and this could be the source of your bang.
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Rob Truesdell

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Re: PA system makes loud noise like a gunshot
« Reply #7 on: July 20, 2011, 11:55:03 am »

How about any wireless systems?
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Dave Manini

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Re: PA system makes loud noise like a gunshot
« Reply #8 on: July 22, 2011, 02:31:40 pm »

How about any wireless systems?

Agreed.  If you have anything that's wireless hooked into the system if anyone turns on something electrical like a ceiling fixture or item in a nearby room on the same circuit it could be intercepted. Mute out all wireless devices and see if the problem dissappears, OR run the system with no activity in the building. some wireless systems are better isolated than others.
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Mac Kerr

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« Reply #9 on: July 22, 2011, 06:37:43 pm »

Agreed.

Please go to your profile and change the "Name" field to your real full name as required by the posting rules clearly displayed in the header at the top of the section, and in the Site Rules and Suggestions in the Forum Announcements section.

Mac
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« Reply #9 on: July 22, 2011, 06:37:43 pm »


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