Coax cable causing humming in subwoofer

[tonee sanding]

Hi all, I am new to the forum. I have an issues with my subwoofer. It is a KLH E-12db. Let me explain how it is connected to my Yamaha AV receiver. Subwoofer 1 out to subwoofer cable to a coax adapter to then coax in the wall (pre-installed by the home builder) to coax adapter to subwoofer cable to the subwoofer. I have isolated the humming to be coming from the cable in the wall, because it is only when I have the subwoofer connected to the coax cable in the wall that the 60Hz hum can be heard. I know this because I connected the other cables to the subwoofer and the hum is not present.

BTW, I have not had this issue until about 3 weeks ago. It just suddenly started to occur.

I looked online, and I have tried the following:
1. used matching transformers (75 to 300 connected to 300 to 75) before connecting to the coax adapter: the 60Hz hum is gone, but so is all the rest of the low frequencies.
2. tried connecting the coax through a surge protector, but that had no effect.
3. tried to connect a ground wire from the sub woofer coax, but that did not have an effect either.

I saw that there is a suggestion that for using a subwoofer isolation transformer, but I haven't tried that and it is supposed to address ground loop hum, which should occur if you have a cable connected or not. I do not think this would work anyway.

So I am hoping that by writing about my issue here, I can get some more ideas to remove the noise coming from that coax in the walls.

Thanks

 

[rojo]

@tonee sanding: So you say with direct connection AVR -> RCA -> sub, there's no hum; but AVR -> coax -> sub, there is? Is your room carpeted? If so, then just bury RCA cable in the seam between the baseboards and the carpet. If not, you could always go for a wireless transmitter / receiver solution. I couldn't tell you why the problem mysteriously occurred about 3 weeks ago, other than to say it's often the case that things work until they don't. Just pulling a wild guess out of my ass, I'd guess it's got something to do with the way the cable line is grounded outside the house.