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I have a set of Logitech 5.1 speakers where each speaker and the source plug into the subwoofer. I'm using a Griffin Firewave with output from my MacBook Pro, and output from my custom-built desktop with a switch in the middle (built it myself out of an old Belkin A/B parallel switch)).

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Recently, I've noticed that I can hear a local Punjabi radio station being picked up by my speakers, and the volume of this interference increases as I increase the volume of the speakers. I'm fairly sure that this radio station is at the low-end of the FM spectrum, below 90MHz (or it may be at the high end, above 105MHz, my memory isn't infallible). It gets quite annoying as I can't put my audio very loud without the interference.

I've tried to put a ferrite core on the input cable just before the 3.5mm jacks plug into the subwoofer. I don't know if putting the same core around all three of the cables (green, black, orange) would negate the effects, but I'm assuming not. There has been no change.

Is there any reason why this would be happening? I'm assuming the interference is coming somewhere between the FireWave and the subwoofer, because the noise gets amplified with volume increases. If anybody has any suggestions, I'd be grateful!

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Our church Hammond organ informs audience sometimes by message from heaven... eh airport "ready for takeoff". –  Aki Oct 11 '11 at 7:25

2 Answers 2

up vote 3 down vote accepted

It's probably your cables picking up the signal from a transmitter that is close to your home. Usually this is caused by folded cables (Like when you neatly tie them together). If you have folded cables or lots of cables tied together, try if unfolding them or seperating the speaker cable from the rest helps.

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Is it better to loop them than fold them? I couldn't live without my organization; better the interference than cables all over. –  squircle Jan 16 '11 at 1:38
    
@squircle best thing is to get a cable thats the right size and doesn't need folding or looping. The longer the cable, the more potential of being an antenna and thus more potential interference. Also, I always leave my speaker cables outside of the main cable bundle. –  BloodPhilia Jan 16 '11 at 1:41
    
@squircle oh and have tried looping the cables around the ferrite core... not just sticking them through it... –  BloodPhilia Jan 16 '11 at 1:46
    
I'll try and let you know how it works out! :) –  squircle Jan 16 '11 at 1:51
    
I looped the cables instead of folding them and the sounds completely went away; no ferrite core required. Thanks for the suggestion! –  squircle Jan 19 '11 at 3:36

Whoa, trippy dude!

I assume that your audio cable (comp -> amp) is acting like an antenna. It seems surprising that it picks up only one station instead of a few at the same time, that is very selective. Drastically changing the shape or length of the cable should wreck your "antenna" ;)

I would build a low pass RC filter with a cutoff around 1 MHz. For example: R = 160 ohms, C = 1 nF according to an online filter calculator. Or you could buy a filter I guess. It may be sold as a noise suppressor, they are used in car audio installation. Install it at the receiving end of the problem cable.

You could instead wrap the cable in tinfoil, and ground it to the (metal?) computer chassis.

If all else fails, just do what the voices tell you to do. YMMV.

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Thanks for the suggestion, I'll do this if BloodPhilia's solution doesn't work. –  squircle Jan 16 '11 at 1:51

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