Severe noise

[Tommy077]

I have a problem at a venue that I had done the electrical work for last year that I am hoping to find some help with. The problem is severe noise (buzz, hum, and even radio station interference) in different sound systems that people use there. I can say that my church had an event there at the beginning of Dec. last year and we had no problems, but I was there the other day and heard it with a group that was setting up for an event.

My setup included a Behringer EURORACK 1202 mixer with a Crown amp and Yamaha speakers. We ran 2 Shure wireless mics and 1 wired mic with an Ipod input also. The sound was crystal clear.

The group that was setting up the other day had a digital mixer/D.J. station (not sure of the brand) using monster cables and surge suppressor. He had a portable rig that he flew speakers and lights from for the show. The speakers were a pair of Behringer powered speakers. When he turned on the sound, he first had a slight buzz (even with the sound turned all the way down). Then he stated getting radio stations (one on one speaker and another one on the other speaker). We tried running the speaker power through a Furman power condition as well as an FM trap and could not get it to go away. We turned everything off and back on and got rid of the radio stations, but the buzz was still there.

I am pretty sure that the metal beams that are in the building are not grounded or bonded to the electrical system. I am wondering if I were to ground and bond them, would that be all I need to do, or is there going to be something else that I will need to install on the electrical system to clear up this issue. The owner of the place is wanting to get something done about this as soon as possible since several people are always in and out of there on a regular basis and they are complaining.

Any and all help would be appreciated.

 

[Morpheus]

I'd look at the audio cables before I look at power... are all the runs clean? (away from power as much as possible), are there any bad connections? Radio stations indicate a bad shield on audio, not power... start swapping out cables until you find a/the bad one...

Also, if you have a cable tester, that might help and save some time.




Oh, and you should only worry about the grounding if it's a 'clean' 60-cycle hum

 

[Tommy077]

I had someone else tell me to look at the cables as well. The issue seems to happen to many different people as well as the one regular that I was there with that one day. Now I can say that the person I was there with that day had the speakers as lights on the same rig with both power and audio signal cables running along the same path and within inches of each other.

The grounding does make sense and it would also explain why the event I ran sound for had no issues. I can also say that this other person has a Bose setup that has had no issues like this other setup he had when I was there.

Thanks for that quick reply!

 

[BillESC]

Start with a multi-meter and read neutral to ground on any of the outlets that were used. Is there any voltage present?

Are the cables being used all balanced or are some unbalanced? Long unbalanced cables act as antenna and can pick up radio stations, planes and emergency broadcasts.

 

[Kally123]

I'd look at the audio cables before I look at power... are all the runs clean? (away from power as much as possible), are there any bad connections? Radio stations indicate a bad shield on audio, not power... start swapping out cables until you find a/the bad one...

Also, if you have a cable tester, that might help and save some time.




Oh, and you should only worry about the grounding if it's a 'clean' 60-cycle hum

I agree with everything, except the very last statement. We have just completed a full upgrade of the sound system at my venue. This included having a 100% dedicated power supply and ground for just the sound system.

That detail was the first thing installed and after that 90% of our troubles with interferance and 60 hum went away. Now I realize that this may seem weird or even counter intuitive, however, we had trouble with Radio station, TV, and even Fire department interferance before the new power source was installed and after our only issues were with the tired and old equipment not sounding so good.

The last 10% of our interferance issues went away with the installation of our 18 new Lectrosonics wirelless microphones, now we hear only what we want to hear and nothing more.

Not sure how much being right next to a Radio/Tv station and only a block away from the Fire house has to do with it but I am sure it probably does not help.

Now I am definately not a certified electrition and I am only trying to share my personal experience with the upgrade of the system that I work with. But i do know that when I used to live by the theater I had to lift all the grounds in my house to keep from hearing the radio station in my walls. And to that I could only say; Weird, Very Weird!

 

[FMEng]

About 98% of the time, RF interference is the result of poorly designed equipment that happens to land in a location with a significant amount of RF energy from a nearby source. Chances are the source was an AM broadcast station.

Poorly shielded cables can contribute to the problem. But even with the best cables, once the RF signal is on the shield, it has to have a place to go. On a badly designed piece of gear, the current from the shield gets shunted onto skinny little traces on the PC board, right next to high gain op-amps. Neil Muncy calls it "the pin 1 problem," and has written extensively about it. Many otherwise excellent manufacturers commit this sin because they can save a few $ and still sell the product, because the problem only shows up in some locations.

There are tricks to resolve pin 1 problems. Transformers, toroid core donuts, proper bonding and shielding can all help. Don't jump to the conclusion that you have to rewire half the building because one portable system had a problem.

I can probably take any collection of equipment and hook it up in any venue, in such a way to produce bad noises.

Also, don't buy into Monster Cables. They are no better or worse than any other decent cable, but they sure cost a lot more.

 

[DuckJordan]

i would bet its the DJ mixer, i have found the cheaper the mixer the less quality you should hope for. the 60 hum could be a ground issue but picking up a radio station is from an unshielded device. so unless this venue is right next to an AM or FM transmitter you should have no problems with your equipment if its properly shielded.

 

[SHARYNF]

How is the ground set up, is it a dedicated green wire all the way back to the service panel OR is the conduit being used?

Sharyn

 

[TimmyP1955]

Make sure that all the lines are balanced.

Make sure that pin 1 is not connected to the case of the connector (this connection should be made only by the equipment, never by the cabling).

Check for neutral/ground, hot/ground, and hot/neutral reversal in all building wiring, extension cords, and equipment power cables.

If all else fails, try lifting the shields at the receiving end.

 

[museav]

The owner of the place is wanting to get something done about this as soon as possible since several people are always in and out of there on a regular basis and they are complaining.

Am I correct in understanding that what you are saying is that there is no permanent system but that some people bringing in their own portable systems have difficulty with hum, buzz and RF pickup while others do not?

Do the hum and buzz problems seem to be directly related to using a particular receptacle or to using two different receptacles for power, e.g. one for the mixer and a different receptacle for the amps. In that case there could be a ground loop issue or even a bad ground. Otherwise, since the problem does not affect everyone then it sounds like the problem may be in the portable systems and that you should be the ones complaining.