Buzzing in mains and feedback

Dennis Fieger

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model 16 mixer
Greetings All, in our PA system we use a model 16 board, Behringer Eurolive B205 monitors, and 2 ea Bose Array speaker/woofer units.We try to be careful with mains and monitor placement but we occasionally will get sudden feedback, sometimes at mid show an after a flawless previous set, it just suddenly occurs without any adjustments. We've also had the mysterious "Buzz" occur in the mains and monitors. This past weekend we isolated it to the channel for our drums input on the board. After changing out the cable and then moving the drum input to an alternate channel input we were able to resolve it. But at our gig the night before everything worked perfectly. We are considering moving to in ear monitors to resolve any potential feedback loops being generated between monitors and mics. We've heard tilting our array units slightly "out" may help with potential feedback as well. We know power source quality at venues can be questionable, we've used ground lifts in the past but with limited success. I'll be the first to admit my knowledge of our board is limited but I know enough to get by but could use some coaching. The Gremlins are creeping in and we would appreciate any helpful suggestions you might have regarding set up techniques or online resources. Thanks to all in advance.

 
You've asked 3 previous questions where several experienced forum members have replied with detailed answers. You have never followed up to let us know how our suggestions have worked out for you. Neither have you replied with a single "thank you" post. Now you're asking for some very high level advice with difficult issues that will require interaction with you. But you don't interact.
 
You are right, and I am sorry for not at least posting a thank you in the past. I should not have ignored the fact that when someone replies it means they have taken time out of their day to read, consider, reflect on experience, and then construct a reply that hopefully will me resolve or at least get close to a resolution to the problem I'm encountering and seeking help with. It may appear as so, but it's never been my intention to ignore the above, but I see that I have, and for that I offer a sincere apology to all who have invested time in the past attempting help. I will be more responsible in the future.
 
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Apology accepted! That took a lot of humility. Let it not be mention it again.

Your post mentions 2 distinct issues: Buzz (noise in the audio) and feedback.

Starting with the buzz issue, there are several aspects that I've dealt with in professional life when it comes to that. Most of the situations I've worked in are permanent facilities; however some of the principles can be applied to portable installs.

1. Balanced signal paths. If possible, use DI/isolation boxes to convert any unbalanced signals to balanced. One advantage is that most DI boxes have a "ground lift" switch that can make a difference (which you mentioned). Also, floating the shield at the source can help too. I used to have a set of directional cables with the shield floating at one end to reduce ground loops.

2. Power conditioning: There are power strips with extensive filtering built-in. Those can be a real help keeping stuff out of your audio. Most likely the light dimmers are on the same circuit as your audio gear and that can wreak havoc on audio systems. There are also transformers that are basically 1:1 and don't alter the voltage but act as a filter when plugged inline.

3. Instrument shielding: In the case of guitars, you'll want to shield the cavities and back/scratch plates.

4. Wireless transmission: Sometimes, eliminating a cable with a wireless system can help with buzzing issues. Bear in mind that depending upon the technology used and the frequencies employed, a wireless system can also add noise. If you have noisy wireless inputs, try replacing with a cable to see if there is any difference and work from there.

5. Ground lifting: This one is tricky. Removing the ground connection from the entire system can be dangerous in case of something going bad (like a power supply). But maybe you can choose your ground instead. In the studio, we disconnected the "Edison" power ground connection on all the equipment and instead ran a piece of #10 stranded to the chassis of each piece of gear, and ran those wires (soldered them onto) to a "000" length of welding cable that I personally connected to the street side of the water main in the building foundation. You may be able to find a good ground connection in the club and run a thick cable to that and then float the grounds on each piece of gear. Those ground lift plugs have a tab to connect a wire to, and that wire can go to your "star ground" that you attached to a water pipe. For the console and recorders you can try a computer type UPS and see what that does.

One of the problems is that when you're setting up for a show you don't have time to waste on troubleshooting. But, if time permits, connect the inputs to the console 1 x 1 and observe the results. There might be one thing that is causing the system wide issue.

Some of your gear plugs into the wall. Other things have a wall wort. Those things that run on DC from the wall wort don't have the same ground reference. So, it's possible to have micro current flow on the ground paths. It gets complicated but those isolation techniques can help break those loops.
 
mjk, there is a lot to consider in your response, much of it is a bit over my head but I intend to review these suggestions with my bandmates to see which ones we can address. We'll be addressing some of the obvious potential contributors this week, ie mains placement and positioning as related to our mic line. in ear monitors vs hot spot, cable condition and type used for each application, etc. We know we get it right some/most of the time as we do not encounter these issues. It's that occasional episode in the middle of a show that sends us off the rails into a panic mode trying to find a resolution so the show can go on. Thanks for your input and patience.
 
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"5. Ground lifting:"

I've always loved (sarcasm intended :) ) dealing with ground loops.
 
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It's that occasional episode in the middle of a show that sends us off the rails into a panic mode trying to find a resolution so the show can go on.
That is very frustrating Dennis. That kind of pressure can make it very difficult to work under.
 
What do you call a cow with no legs?


Ground beef.


That's my grounding joke for the year.
 
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Someone posted this useful link on Behringer World

 
Update: In ear monitors have been purchased to eliminate potential feedback loops there. Evaluated where unbalanced conditions existed and purchased new cables to correct. Have done some channel EQ training and trouble shooting with our sound crew. 1st show with IEM"S is tonight, wish us luck. I'll let you know how it goes. 🤞
 
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