Left Channel Popping

[trswen05]

I am the "technical director" at my high school but I am also a student. The school refuses to spend any money it doesn't have to, so they will not hire an experienced technical director to teach. The theater teacher also doesn't know enough about tech to run it himself and leaves it to me to learn and teach to the other students. Therefore, I have self taught most of what I know, and still do not know a lot about sound. About three or four months ago we noticed that our left main speaker was making random popping noises. We haven't found anything that triggers it. Speaking or playing music through it doesn't worsen it. It happens when it pleases. The sound it makes sounds like someone is tapping on a mic or something of that equivalence. Also, we have an Auto Mic feature in our auditorium. There is a dial on the stage that turns on our amps and we can hook a cd player into certain outlets on our stage that allows us to use the sound system without having to turn on the sound board. The popping also occurs when the auto mic dial is turned on. Therefore, I doubt it has anything to do with the sound board itself because the board isn't on half of the time the popping occurs. I have no idea what I need to check with the sound system to try and fix this issue. I was researching and thought maybe it could be clipping, but the sound board doesn't have to be on for it to happen so it wouldn't be a problem with the equalizers. I think something is wrong with either the speaker itself of the amps, because the popping occurs both with the sound board on, but also when just the auto mic feature is on. Info- Board- Allen Heath GL2800 Amps- Crown CTS 3000 and CTS 600 Main Speakers- A stack of two EV XS 212 with 7 EV XLD 281 underneath For the left channel we have one amp (CTS 3000) that reads- CH.1 Top Left High Frequency CH.2 Top Left Full Range. The one under that (CTS 600) reads- CH.1 Bottom Left High Frequency CH.2 Bottom Left Full Range. And the last one that (CTS 3000) includes the left channel- CH.1 Left Sub CH.2 Right Sub. The rest of the amps (CTS 600's) are for the right speaker and our dressing rooms/orchestra pit/etc. I thought of maybe turning off either the amp that controls the top or bottom speakers in the stack to see if it stops the random popping, maybe narrowing it down to it being half of the speakers or that amp. Marshall Audio was the company that installed our sound system, and will not give keys to the cabinet for safety issues. They have been out here once to try and fix it. They opened the cabinet and found that one of the amp power cords was not completely inserted so they assumed that was the issue. The popping is still happening and they haven't been out to figure out the problem since then. Is there anything that I can try to myself to figure out what the issue is? Could one of our speakers be blown? Any advice would be greatly appreciated! Thanks Note: Since I am self taught, any type of testing that you suggest, please provide a description of how to do the test as I may not know how to do so.

 

[wolf825]

It doesn't sound like a blown speaker--you would hear nothing with a blown speaker. The type of random common popping you describe is often an electrical issue...a common grounding interference or something somewhere in common with another electrical device, HVAC or thing that is somehow in common with the power--like an air handler, or some auditorium / merc vapor lighting or something else that may 'cycle' or charge/discharge etc... Without seeing this issue firsthand based on your description--that is my best guess... It could be in your signal processor or your amp or the signal cabling in between or the power that feeds any of those.. I say this since you seem to have eliminated the FOH console and outboard and other input signal systems since those do not need to be on to get this issue to occur.. It would be helpful if you can be in front of or staring at your DSP processor and amp racks when this popping occurs... At the very least..when it pops you should SEE some indication on the amps and/or DSP processor to hep you identify or narrow it down.. If you can SEE some things light up when the pops occur--that can be a starting point to trace from.

I can give you step by step ways to work backwards to try and narrow it down to a piece of equipment or a power issue...but ideally if you can't get in to the racks then you won't be able to do anything to really narrow down.. I could write you a book on how to step check this to narrow it down...but ideally you should have someone locally with you help you troubleshoot. If Marshall Sound the installers won't help you troubleshoot etc--then call a couple of other companies and find one of their competitors who would be happy to help you diagnose...

IF you can get to the amp rack--here are a few beginner steps of that 'book' to trace down the issue. Start by working backwards and see what turns up: Doubtful it is a speaker cable--a regular 12guage speaker cable is often the least problematic in the chain of audio equipment. This kind of issue tends to come either from an amp, from a signal/ signal cable or from power. You say it is your left speaker--first of all pops can often be deceiving so make sure it IS your left speaker and only your left and what part of the left and isolate if possible which left speaker is doing this.

Since you list several Ch1/Ch2 sources for the left top to bottom etc--Start off by turn off or mute your main Right speakers just leaving on the left side to test the whole left side--if it keeps on randomly popping, then mute your Left and unmute your Right and see if you get any popping in the Right side. This will tell you if the issue really IS to one side or not, and may be narrowed to a set of amps or signal cables to those amps. If it is only on the left--next narrow it down even more--each one of those HF and Full Range channels--mute each one leaving one on and see if you get the popping. do this for each channel Left HF, Left TOP/BOTTOM FULL RANGE etc etc... and note which DO and which do not pop. This will take a little while to do...and they all may pop or only one may pop...but it may narrow this down to a single amp with a common issue or a channel or a common power..

If it is on the Right as well--do the same as you did for the left--try and narrow it down channel by channel or amp by amp. If you get popping on right and left--try muting and then powering off your DSP and see if you get the issue with the DSP first muted and then turned off. See the pattern of how to trace and check here?

If you get NO POPS with your DSP turned off--your DSP could have an issue or the power feeding it could be problematic and need to be checked by an electrician.. Turn ON the DSP and see if the pops return. IF you get pops while the DSP is muted and turned OFF--the your issue may be power to your amps. Have an electrician come out and hook up a meter and take a diagnostic of your power--he is looking for spikes and instability between usually ground and neutral.. You can't do this...needs to be an electrician...and he may have to run the diagnostic for several hours to record. It would not surprise me or anyone on this forum to find some eager facility guy or electrician hooked up some new building toy or lighting or HVAC system on or near the electrical or ground of your amp rack that is creating this issue...which leaves you to find an electrician to help identify the problem and do some tracing you are not capable to do...


Just a few things to get you started...others may have other suggestions....but your most ideal way to identify, solve and trace this is to have someone with you who has the experience...


-w

 

[mJohnson880]

hmmm, random popping and clicking when a part of the school's sound setup is running... Sounds like your potential problem right there. If you turn the auto mic off and you don't get any nasties whatsoever, you've found your problem. If it isn't the auto mic, start checking connections, but don't just check to see if every thing is plugged in, inspect the connectors themselves. We had an issue when one of our speakers started this super obnoxious hum and wouldn't stop, no matter what. Through trial and error (replace an unknown quality section with one you know to be good. If that doesn't with, replace another section), I traced the problem back to the board. Lo and behold, one of the 1/4 inch trs connectors was damaged. moral of the story: most sound system errors are in the connectors.

 

[Blacksheep0317]

So many places to look..

Im going to pretty much say to agree with Wolf atm, unfortunatly there is no real way to start narrowing things doing without actually hearing the system and the pop. Different issues make different pops. Chances are its going to be some stupid little thing somewhere, but unless you have a bit of an idea what your looking at you may just look right past it.

When it pops is the rest of the mix still coming through? Or do you completely loose all sound from the speaker when it does it? Or is maybe just the Hi/Mid/or Lows that cut out? Are we sure that there isnt actually a disgruntled phantom of the aud running around with a w/l mic tapping away at will? Were there any major changes in or around the aud when the issue started? All useful tidbits to know.

It really sounds like your best bet is to tell the school to pony up and get it fixed. A fancy newfangled system like that..had to be installed by some company that designed and bidded the whole thing to the school. Tell them to call in installers and make them fix it. Chances are they will be able to back track much faster than you. And even better if it was due to their screw up, make it right for nothing.


**Edit**
Alright so I missed that the original firm was already in. Remember people..PARAGRAPHS AND SENTENCES! Reading long things while in a bunk on a moving bus is hard! lol