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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?"
http://www.aca.gov.au/publications/info/cbradio.ht m
Done. Now we can close this topic.
There are quite a few issues to look into. The top two would be to:
.. and for much more reasons than just the interferance, and ..
.. it may be a (semi)common problem.
a) get someone in (professionally) to test the grounding
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
Robert Anton Wilson
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
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.
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
If your power cables and your speaker cables are running parallel some times it turns your speaker cables into radio antennas. You can solve this either by
a) Moving your power and speaker cables further apart.
b) If they have to cross put them at a 90 degree angle to each other. This minimizes the effect.
This happened to me while I was doing sound back in High school and wireded me out until the band instructor told me about this. Same thing happened first night in the dorms in college, I thought it was my neighbors radio for the first two nights. (:
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.
Mea navis aericumbens anguillis abundat
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.
Liquor
Sanity is a highly overrated commodity.
As previous posters have said, electronic equipment should not emit radition, nor accept radiation. In most western countries, this is part of law.
You're wrong on with regards to the accept radiation.
From an FCC Declaration of Conformity:
Pursuant to Part 15 of the FCC rules. Operation is subject to the following two conditions:
(1) This device may not cause harmfull interference and
(2) This device must accept any interference that may cause undesirable operation.