Reducing Intereference in Your Speakers?

PolicyWonk asks: "I just bought a new stereo, a Sony CMT-EP707, into which I intend to plug my laptop when watching DVDs, and my iPod when listening to music. When I first turned the stereo on I was horrified to hear interference from a local radio station, as well as a general hum emanating from the speakers. The hum and the radio emissions are audible even when the stereo's volume is set to 'min' and irrespective of what setting the stereo is on (i.e. Tuner, CD, or MD), or what input is (or isn't) plugged into the stereo. (I have tried my laptop, iPod, and no input). That means that during a quiet pause in a movie, or the intro to a song, this background noise is clearly audible. No amount of moving the speakers around the room, or plugging the stereo into different grounded outlets seems to fix the problem. I've checked my outlets, and they appear to have a ground connection, but I live on the fifth story of a circa 1900 apartment building in Manhattan, so it's anyone's guess what happens to the wires once they are in the walls. Anyone have any good solutions for reducing or eliminating interference from nearby radio sources?"

Comments

RFI chokes

[Kizzle]

A fairly cheap method of reducing radio/TV signal interference involves just the opposite of "grounding". Go to your local Radio Shack store and get a bag full of "RFI chokes". They have several different shapes and sizes. They snap together and are supposed to be placed over wires and interconnect cables in order to prevent RF currents from flowing along the outside of the wires. You don't have to disconnect anything to install them. Just place them over the cables and snap them closed.

Re:RFI chokes

[waytoomuchcoffee]

Actually, RFI chokes are just magnets that clamp over a wire. A better solution (one I have done successfully) is to buy that magnet tape stuff -- it has sticky stuff on one side, and is made to fasten things to metal. The stuff is much cheaper, and you just wind it around the wire you want to protect. Put some duct tape over it so it won't come loose and you are good to go.

Re:RFI chokes

[Wakko Warner]

Yeah, duct tape will look great wrapped all over the wires on my new G4.

Not all of us build our computer desks out of sawhorses and discarded dining-room doors.

- A.P.

Re:RFI chokes

[Liquor]

RFI chokes are NOT simple magnets (nor are they permanently magnetized like a magnet).

What they are is a ferrite core that makes a complete closed loop around the cable. Radio frequencies currents can't go through the middle - it blocks high frequencies. (If you want to get technical, the radio frequency current induces a magnetic field in the choke, and the change in magnetic field induces a voltage that exactly opposes the current.)

While strip magnets are made from a similar material, you simply cannot make it as effective as a proper choke.

On the other hand, the original question mentions hum - presumably AC 60Hz - and a choke will have negligible effect on a frequency that low.

Re:RFI chokes

[jrwillis]

"If you are going to prioritize style over substance..."

He already said he was using an Apple. No need to be redundant. :)

How-To

[the eric conspiracy]

http://www.aca.gov.au/publications/info/cbradio.ht m

Done. Now we can close this topic.

To quote google

[anthony_dipierro]

"Did you mean: Interference"

Urg!

[McCarrum]

There are quite a few issues to look into. The top two would be to:

a) get someone in (professionally) to test the grounding .. and for much more reasons than just the interferance, and ..

b) try turning off hotspot applicances, like microwaves, the fridge, air conditioners -- and then try it. More sensative equipment may pick up what less sensative equipment will not.

Oh, and a final though, do a google search on your sterio equipment in case there are others who have found this problem .. it may be a (semi)common problem.

Change the length of cable

[isorox]

We sometimes pick up Radio 5 on the external mike of one of our cameras - We plug a different lead in of a different length, and it just works

Interestingly it only seems to happen in theatres

My Sony player does this too

[Cyclone66]

My mini sound system does this too. You're going to need to buy a better system.. The mini's just aren't built for enthusiasts. They aren't built to last either. My system is 3 years old and the volume control randomly increases or decreases the volume when I turn the knob...

Grounded Outlets

[Anonymous Coward]

You know you can buy a ground tester at a hardware store, right?

I don't know but your landlord might be legally required to supply you with grouned electrical outlets.

Ground Loop Isolator

[Gormless]

I had the same problem while trying to play DVD audio from my PC to my home stereo.

I bought an "Audio System Ground Loop Isolator" (# 270-054A) from Radio Shack for $20CDN... problem solved.

Here is a link to some info on the problem and possible solutions.

Powerlines

[droyad]

Could try filtering the power outlet. I've heard of the powerlines picking up a signal and transfering to the speakers via the AC electricity stream

RFI

[Detritus]

It is common for the unshielded speaker wires on audio systems to behave as antennas. The received signals are coupled into the final amplifier stage of the device that is driving the speakers, where they are detected and converted into audio frequency signals that you can hear, sort of like an old crystal radio.

The ARRL has a web page with some information on the subject.

You might ask the engineer at the local radio station for suggestions. Even though it is not the radio station's fault, he may be willing to offer some assistance. Local amateur radio clubs can also be sources of people who are willing to help.

Ask the support department of the manufacturer of your audio device for assistance. They may have technical bulletins on how to solve the problem.

If you are asking people for help, be nice, not confrontational. Remember that it is your audio equipment, not the radio station, that is at fault. Consumer electronic equipment manufacturers could avoid most of these problems by adding less than a dollars worth of parts to their equipment. Most do not, reasoning that it is cheaper to deal with some complaints of susceptibility to RF interference than to prevent the problem.

Re:I have a similiar problem.

[Jonny 290]

hehe.

you just complained about a Koss audio product.

Dear eMachines,

Did you know your computers are crap?

Sincerely,
Customer

Re:I have a similiar problem.

[Glytch]

Gee. I humbly apologize for not being able to afford top-of-the-line speakers. Does that make you feel superior?

Dick.