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Comment by Greg Cameron on March 20, 2014 at 11:15am

Just make sure if you're using local power from different sources along the course for your powered boxes or amps for stationary speakers that have have plenty of balanced line level isolation transformers to avoid ground loop noise. If you use a wireless distribution system instead of hardwired, it's a non-issue of course...

Comment by Paul Tringuk on March 20, 2014 at 7:23am
I usually use several powered 12"2 way boxes on stands at the starting line generator powered and then just move it to the finish line while the race is in progress
Comment by Mike Siegel on March 20, 2014 at 3:21am

I am looking for information on providing sound systems for 5k type foot races thru city streets. Most of the reinforcement is needed near the start area and possibly the finish line.

Comment by David on May 13, 2012 at 7:18pm

Hey everybody, I've been pondering M/S theory and thought I'ld throw this thought out and see what people think: Drastic changes in mixing the M/S channels definitely change the effective pattern of the mic, but would you agree that minor balances change the projection of the mics onto the stereo field of the mix more-so than the actual pickup width? I've only used M/S a handful of times but this idea seems to fit my experiences. 

Comment by Tony Tartaglia on February 13, 2012 at 4:15am

Aall great comments, Don has the best one. Your problem sounds like a bad cable making a shoeted connection on your front nine in a wall unit or breakout box. As a professional audio engineer I have come to the point where I will NOT purchase any premade cables at all. I prefer to build all of my XLR and 1/4" balanced cables with Canare quad star and real Neutrix connectors. This way I can eliminate 99% of all noise issues. My speaker cables are also overkill by using the next size than the book calls for. Once the cables meet my standards the ony thing in my systems that can cause problems is the outboard gear itself. (easy to diagnose) As Don said any premade cables from a big store are (for the most part) very poorly made, conductors touching, too much insulation stripped off,etc. They are meant for beginners, not for professionals.

 

Comment by Don Lanier on February 12, 2012 at 1:24pm

Nice explanation David, One more small thing, dont assume ANY cable thats bought from a Guitar center etc is right, you can have a connector thats got a marginal connection explaining why when you ramp things up its starts getting worse, your going to have to LOOK at each one, and be sure you dont have a Pices of Older Outboard gear thats using 1/4 connections in the middle of the rack thats using XLR connections....Variables all have to be varified....

Comment by Donovan Drake on February 11, 2012 at 4:12pm
You should double check the type of connectors used in the floor boxes. I had a problem like this once when I built a monitor amp rack. If you use the all metal switchcraft TS connectors then be aware that the (-) is wired to the chassis. This caused a lot of problems when I had a whole rack of amps with their (-) leg wired together. While I didn't wire any of the xlr inputs ground to the chassis, I imagine that if I had it would have cause a very similar situation to this one.

Just check the wiring and if the XLR ground is wired to the chassis undo it. Also if it's wired with the all metal switchcraft jacks then use the plastic neutrik trs jacks or NL4s.
Comment by David on February 11, 2012 at 3:50pm

Ooops - one addendum, XLR inputs and monitor outputs can interfere if run in parallel in the same conduit or near a cheap Di or 1/4". But that is a noise floor issue and not a serious electrical problem.

Comment by David on February 11, 2012 at 3:48pm

FOH and stage should always share the same ground but that doesn't explain his problems. If they were on different grounds he would probably get a humming as current flowed through the shields of the XLRs between the console and the amps. The monitor outputs and XLR inputs of a system should NEVER be able to interfere with each other. My best guess is that someone didn't terminate the connections at a panel properly. The connections on both XLRs and monitor drives should be completely physically isolated from everything all the way from the output of the console/amp to the input of the microphone/microphone. With amp outputs there is no such thing as "ground," the output voltage is the difference between the - and the + terminals. For example you can't wire + to the speakers and just ground the black wires - bad stuff could happen. With XLRs, the "ground" pin is really a drain for the shield, or a ground reference for phantom power. The shield/pin 1 should never touch the chassis of any panels or the shell of any connectors between the console and whatever it's plugged in to. It should be wired exactly like pin 2 and 3 all the way from the console to the microphone/Di/whatever.

An electrician can verify that the grounding of the stage & FOH is done correctly, but in this case it really seems like bad wiring on the XLRs & monitor outputs. The two most important things in the power design of a sound system is having a common isolated ground for all things audio related on stage and in FOH, and having all audio related plugs fed from their own subpanel(s). Having there own subpanel is usually enough to keep those stupid wall dimmers or cheap motion sensors from causing noise or pops. Good grounding can be tricky and requires planning and careful/firm communication with the electric contractor, it requires special types of subpanels that have an isolated ground bus. The outlet plugs are grounded separately from the conduits and j-boxes to prevent any accidental grounding to metal studs or stuff like that. As the system gets larger you'll need things like surge suppressors and isolation transformers, but those are usually secondary concerns in smaller installs.

Don is right, be methodical and check everything. Start at the console and trace every wire from end to end to ensure proper termination. If the problem is affecting multiple inputs then it's probably a systematic error and you'll find a batch of bad terminations.

Comment by Don Lanier on February 11, 2012 at 1:34pm

You could be experiencing a GROUND DIFFERENTIAL issue especially if you have Metal conduit going to floor boxes with Mixer/Eqs, FOH being on one Ground, and the amps, Stage and Backline being on another, or different LEGS/Phase of the House power. I would consult a Pro Electrician who understands these issues, and I would reinvestigate ALL the Interconnects, Speaker, Line, AC and be sure there all correctly wired in Phase, Polarity etc...ya it will take time but starting at A and working to Z is far easier then jumping into the middle and nevr knowing whats been checked, use some sort of marker to verify youve checked that cabling, dont assume ANY cable is wired correctly.

 

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