View Full Version : Speakers picking up radio signals
12-18-2004, 04:26 PM
My computer speakers appear to be picking up radio signals. It's probably aliens or government mind-control, but there is a very remote chance that it could be either CB or walkie-talkie (it isn't terribly clear, but you can hear muffled, staticy talking followed by a beep, a pause, then a reply of the same--occasionally you can make out "is (name) in there?" and "Roger"). It's becoming a great nuisance. What can I do to block out the signal? And yes, I tried making a little tin foil hat for each speakers, but that didn't seem to do the trick.
12-18-2004, 05:14 PM
You're probably hearing AM radio. I get this on my el-cheapo Altec computer speakers as well.
12-18-2004, 05:16 PM
I should clarify - I don't mean necessarily in the AM band - just the modulation
12-18-2004, 05:24 PM
I think it is not the speakers per se that are picking up the modulation, but the speaker wire. Perhaps you can find some shielded speaker wire to prevent this. Radio Shack?
12-18-2004, 05:25 PM
IIRC this occurs when the wiring in the speakers has the same wavelength as the sounds you pick up, have you tried nested geodesic domes?
12-18-2004, 05:32 PM
I'm going to put my bet on a CB radio transmission coming through. There are a few options you can pursue. The first would be to find some ferrite cores, either cylindrical or donut shaped. If you find donuts, loop the speaker wire through the center several times. If you find the clip-on cylinders, you may need more than one. You can also try grounding the amp, by running a wire from the chassis to a water pipe, metal ductwork, etc. Something else to try would be to make a 4-6" loop of wire (several turns and bound together) right at the speaker terminals.
12-19-2004, 01:24 AM
I tried making a little tin foil hat for each speakers, but that didn't seem to do the trick.
No no no. YOU are supposed to wear the tin foil.
Ok, seriously, there are two types of speakers, those that are powered by an amplifier in the computer, and those that have their own amplifier. The ones that have their own amplifier tend to pick up electrical noise. This can be from radio stations, CB radios, cell phones, TV stations, you name it. What happens is that all of the wires in your speakers (the power wire, the wires carrying the sound, and all of the little circuit traces on the amplifier circuit board, etc) all act as antennas, and the circuitry from the power supply and amplifier act as radio demodulators. All you need for an AM demodulator is something that conducts a bit better in one direction than the other, so it is very easy to accidentally create a circuit which does a great job at radio decoding. The final piece in the puzzle is the fact that the speakers have their own amplifier, so all you need is a very tiny amount of electrical noise to be picked up for it to get amplified into a big noise that you can hear.
So, what can you do about it? You can try moving around your speaker wires and the power cord, since the length and geometry of these wires is part of what determines which frequencies your speakers will pick up. You can try moving your speakers around, but it sounds like you are picking up walkie talkies in which case their location probably isn't going to matter much. You can buy little things called "ferrites" (I think you can get them at radio shack) which will clamp onto the wires and will help to filter off some of the radio signals. Other than that, there's not much you can do, because what you really need is to add some filtering on the amplifier circuitry, which is not something a typical computer user can do.
The other thing to do is see if your sound card can drive un-amplified speakers. Since the amplifier being used is then inside the computer, it is much more shielded and therefore much less likely to pick up noise.
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