Nightmare buzz scenario in powered speaker installation

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rockstudio
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Nightmare buzz scenario in powered speaker installation

Post by rockstudio » Tue Jun 26, 2012 1:54 pm

Hey folks, Here is another "buzz" topic. This one is perplexing to me and so I am reaching out to you for input.

Here is a drawing of the plan.

Setup: 3 powered Behringer (be ringin') speakers spread about 120' throughout a restaurant / bar.

Problem: terrible hf buzz.

The buzz is worse when:
1. one specific lighting dimmer is dimmed.
2. any extension cord is plugged into the primary outlet, so two speakers are on one outlet, primary outlet feeds the third.
3. one touches an input cable to the volume / source controller.

I wanted to run all three speakers from one outlet, however the buzz got so bad when I tried to run ac from the outlet closest to spkr a to the other two.

This configuration has the minimal amount of buzz so far. I know you think I'm a noob for using behringer in an installation, but I assure you my client was adamant about using them, as they were familiar and use them in their other restaurants. I have a feeling the buzz would not be an issue if they were using a speaker with better circuitry.

The Volume / Source device is a unit that I make that I haven't had a problem with to date. It uses an Edcor TX to sum an unbalanced RCA stereo input to mono balanced output in an aluminum Hammond box. I have adjusted the ground scheme while troubleshooting this install, and nothing makes it better.

I'm using the cheap balanced Gepco install cable from Redco, which I can replace with star quad if need be. I'm not able to charge for labor any further to fix the problem, so I'm trying to knock this out in as short a time possible.

What should I DO???

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Randyman...
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Post by Randyman... » Tue Jun 26, 2012 7:34 pm

I'm assuming you've already tried the standard "Lift Pin 1" on the speakers' XLR's?

Do you still get a buzz with only (1) speaker connected to your Source Selector?

This would seem to be a grounding issue between connected speakers since your source unit(s) are galvanically isolated from the speakers via a transformer.

The fact that touching one of the RCA Inputs (likely touching the RCA shield, correct?) on your galvanically isolated Source Selector makes the hum worse seems a bit odd - and might indicate other faulty grounding issues in the facility. Have you checked that all outlets are wired and grounded properly?

That's all I got. Sounds like a job for one of the electricians around here! :P

:cool:
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goose134
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Post by goose134 » Tue Jun 26, 2012 8:22 pm

I'm with Randy. It sounds like it could be a grounding issue.

1. Check the polarity of the outlet you're plugging into.
2. Try the ground lift Randy suggested.
3. Make sure the dimmer isn't controlling ANY CFL lamps.


If you have an opportunity to see if the outlet is on the same circuit as the dimmer, do so. Dimmers and CFL's, even the right combination tend to generate a lot of electrical noise. When used in the wrong combination, they are catastrophic, world ending, machines. I tried it on a lark in my house and actually got the breaker connection humming audibly.
I make a living as an electrician, not recording in the basement.

rockstudio
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Post by rockstudio » Thu Jun 28, 2012 8:10 am

Thank you for your input, I'll try your suggestions. The outlets are on a different power feed and panel completely, separate from the lights. Maybe the electricians connected to two panels accidentally in some way. There are no CFLs in the place, just incandescent lamps.

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Snarl 12/8
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Post by Snarl 12/8 » Thu Jun 28, 2012 1:01 pm

This is a restaurant? There's lots of other stuff in a restaurant (or house, or whatever) that can induce EMF in stuff. Stove hoods, fridges, any thing with a motor, basically. Is all that stuff on a different circuit?
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Post by The Scum » Thu Jun 28, 2012 3:43 pm

Try unplugging the audio lines to the speakers, so they're just plugged into the wall AC, no audio cabling.

Do they buzz in that configuration? If so, it's either dirt in the AC power, or something coming through the air (RFI, EMI).

If they don't buzz, reconnect the audio lines one at a time, and listen as you go. Is there a connection that suddenly makes things worse?
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rockstudio
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Post by rockstudio » Thu Jun 28, 2012 4:29 pm

the speakers are on two dedicated circuits, not sharing with any motorized things. I will try the other steps also, it's a 45 min. drive to this place, so I can't run down and try one thing at a time! I have to have a whole checklist ready to go! thank you all so much for your suggestions.

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Snarl 12/8
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Post by Snarl 12/8 » Thu Jun 28, 2012 8:18 pm

Also, don't assume your cables are good either. Could be an effed ground in a cable. Stranger things have happened. If it's a pain in the ass to get to the location, it is possible to be systematic about these things. Unplug everything, try the speakers individually, then individually on the most minimal source possible. Then together. If a problem crops up, does it move with the speaker if you move the speaker to a different cable, etc., etc. Eliminate variables one at a time until you get your answer. And RFI/EMF can fly through the air too and through walls. So, having a speaker that's near (or, whose improperly (or maybe even properly) shielded and grounded cable is near) a source can cause problems.
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gullfo
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Post by gullfo » Wed Jul 11, 2012 8:00 pm

also, dimmers (of the electronic kind) tend to generate a lot of noise and ground loops can also result in very dirty signal lines and depending on what else is cross the power lines, induce noise there. fluorescent lights are also prone to causing a lot of noise due to ballasts etc.

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EMI, RFI, dimmers...

Post by Rosy » Thu Aug 09, 2012 9:42 pm

I think Scum is on the right track. I work in wireless networking where we see a lot of RFI and EMI related interference causing the innerwebs to slow and halt. RFI can be horrible, but EMI can be worse. Subsequently a restaurant might be the worst place in the world for EMI. If you still haven't found the problem and this has become critical then look for some of the following in your area:

Try turning off ALL the microwaves, and this might not be possible, but unplug the refrigerators and freezers. Before you go that far though, does the level of noise increase with the dimmers in your diagram? Does it go away when the dimmer is all the way up? I know a guy that kept buying different wireless routers and realized his desk lamp was the issue. I know I'm talking internet here, but the source problems are similar....so are the offending frequencies, I suppose. If it's the microwaves, refrigerators or other electromechanical then you may have to move the speakers. Just a thought: One walkie talkie, or cordless phone can knock out wireless for 1/2 a Wal-Mart Supercenter but a microwave can knock out the whole store (Not that this translates directly to audio sources, but I know dimmers and power crossed or run with audio cables can wreak havoc. I once had a customer with a computer monitor that "shaked" so bad we had to put a lead box over her workstation. The source was EMI from florescent lights 15ft and two brick walls away. Her monitor refresh rate was 60Hz as which equals the 60Hz that accompanies anything 120v.

RFI: unplug ALL cordless phones, both receivers and bases. If it's the phones have them replaced with corded phones or phones using a different bandwidth (Change 900Hz to 2.4KHz, change 2.4KHz to 5KHz), Anything with a wireless connect could be suspect.

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