Weird Studio Monitor Problem

[Jonasson]

After purchasing everything I needed for a small studio, I moved it to an office building and set it up. I was surprised to hear a radio station clearly audible in my studio monitors (Event TNR-8s) with nothing plugged in. The monitors are only plugged into the outlet, and I'm getting some hum and a radio station.

I did a few Web searches to try to figure out the problem and read a couple of nice articles on grounding and electrostatic interference (here (http://www.epanorama.net/documents/groundloop/index.html) and here (http://members.ozemail.com.au/~tabbler/GndRule/GndM02.html)). Unfortunately, I don't have the sophistication to make the jump from the possible theoretical causes to the potential solutions, especially since I don't own or control the building (limited electrician work may be a possibility).

Does anyone know of anything I can try that won't involve major construction? I've already tried the following:
1. Unhooking all audio and power cables that could interact with the speakers (no audio cables were hooked up to the speakers - still heard the interference).
2. Switching outlets (varying levels of audible interference).
3. Moving the speakers around in the room (no real change - except that it gets louder when I touch the back of the speakers).

Notes:
1. The company that owns the building recently replaced a bunch of lights on my floor with flourescent lights.
2. I don't have any sophisticated equipment for checking the grounding in my outlets, but I did plug in a UPS that will usually let me know if there is no grounding.
3. I'm not aware of any radio stations in the immediate area.
4. I think I'm hearing AM.

Ideas? Anything will be appreciated.

[WillyT]

You're probably sitting real close to a radio studio. Short of building a Faraday cage around your studio you won't be able to keep the microwaves out.

But first check all your other gear with headphones. If it is in other gear you're sunk. If its only getting in the monitors they may just be bad...


I have had the unfortunate experience of trying to do live sound in a theatre next to a radio studio. I could get the interference very low in the sound system(all but inaudible if you stuck your ear to the speakers) but a lot of guitarists had horrible problems with a TOP NAME BRAND amp that just would not work. (terrible 120hz hum and overheating) We had to warn all the groups not to use that particular style amp.

Your problem isn't a ground loop as it exists with NOTHING connected to the monitors except power. (thus only one ground thru the mains) It could be electrostatic (capacitor coupled) from the mains. Or it could be radio (RFI) aka electromagnetic, (the second site uses this term loosely when they are actually talking magnetic coupling) thru any wire acting as an antenna.

I hope you got a bad set of monitors. (Gee I never thought I'd ever say anything like that)

[Jonasson]

Thanks, Willy. I'll check the area for radio stations (I guess I could just listen until they say their call letters). Now I wish I hadn't signed a contract. They usually don't let you rent a place without one, though.

My only question about the radio station theory is why it would also cause hum on the speakers.

[michaelhoddy]

If you've got hum as well, you've likely got a grounding issue in your building power or in the speakers themselves. Sounds like there's an earth groung lifted somewhere.

[lord toranaga]

Hello,

Same problem, same speakers. I live right next to a giant cross that is also a radio antenae. I have a friend that is an electrician. He came over to my house(rented). He discoverd that the main electric box is not grounded to earth, just water. Next he discoverd that all the various household installations(cable, phone, direct tv) are grounded to the improperly grounded main electric.

His Solution, for my house, is to install proper ground rod. And to uninstall all unused coax cable.

This is to take place on monday. I will post results.

Peace & Love, Lord Toranaga.

[WillyT]

3. Moving the speakers around in the room (no real change - except that it gets louder when I touch the back of the speakers).
So yes of course it could be a grounding problem so check that out too. (Thanks Michael) You may need to hire an actuall electrician (I'm an industrial electrician in my day job) to check for proper building electrical grounds.

If the landlord can't or won't fix ground problems that could be an out. Actually I'm surprised you didn't check out the power before signing, but then I'm an electrician.

If the grounds are ok this could be a senario.
Actual RF in an amplifier output stage may exceed the the ability of a class A-B amp to switch off on the alternating cycles. Thus power goes straight thru the output transistors. Pulls the power supply down till it ripples 120Hz (Full wave bridge)

result:
Hum in the speakers, some rectified RF->audio and a very hot amp.

So yes if you hear the audio its probably AM. Tho if the RF gets clipped FM audio may come through also.

But please check the other equipment. If everything else is clean you will only have to deal with the monitors. Maybe call Event to see if they have an easy solution.


Anywhere I setup my system I check power with a Wiggy. This checks that the ground can actually carry some current and trips GFI's. Of course if I trip a GFI, I usually can't get 50A 220V from that source.:D

[djui5]

How about ramming a long steel rod into the ground outside of the building and running a cable from the rod into your studio and using that as a ground buss?

[Jonasson]

Great suggestions. Thanks, all. Willy, I'll admit to being naive. Yes, you should always check the power before signing a lease. I was in a rush, and I overlooked it. It won't happen again!

Anyway, I do know a very skilled, professional electrician, and I'll consult with him. I'm sure the owner would be more than happy to have me do some power work on the building (since it will come out of my pocket).

I'll try some of the suggestions in the other posts as well. Once again, thanks. Lord Toranaga, let me know how it goes.

[Dan Shay]

Hi all.

I am an assistant engineer at a radio station, so I thought I might be of some help.

You don't have to be right next to a radio studio to have this problem.

Studios now use transmitters, or studio to transmitter links (STLs) to send their signal from their station to their tower. These are powerful, but very directed signals, and if you are in their path, most likely you could fall victim to radio freq. interference, or induction.

Here's the good news. The FCC and all radio stations have on file maps of the exact global positions and directions of STLs, so you can do your homework pre lease signing and avoid a hot spot. Radio stations are required to have this information in their Public File, which they are required to keep open to the public during their operating hours.

Otherwise, you could also just have moved into a spot that is close to an actual transmitter. Short of building that Faraday cage, or metal window screen stapled to the inside of your building, you'd be SOL.