Originally Posted by 100db
Hello AVS Members,
This is my first post here but I can say that I have visited here on a number of occasions and always found this forum quite informative, which is why I would like to raise a question here.
How do uni directional subwoofer cables actually work?
I have done some research and the only viable explanation is the ground loop theory. This means that the ground shield of the coaxial cable is not connected at the subwoofer end to reduce the chances of hum as a result of "hearing" the amp at the other end.
So I dug out a spare coaxial RCA cable that I had with a screw off plug so I could take a look inside. I could see that the inner core was connected to the inner part of the connector and the woven copper shield was connected to the outer part of the plug (as expected)... So I decided to test out this theory and I cut the part connected to the outer woven copper shield to the outer part of the plug and tested it out on my subwoofer (again a cheaper spare sub as I don't want to risk blowing up some good stuff!)... However, the result was an extremely loud hum! Which is exactly the opposite to what this theory prescribes.
Have I misunderstood something? Which part exactly is meant to be left disconnected to create a uni directional subwoofer cable?
This thread has already derailed, but to answer your question, YES there are actually audio cables that one might consider "directional." It has nothing at all to do with the cable being better in one direction than another, I am not at all referring to snake-oil BS that has arrows printed on it because somebody thinks the electrons "flow better" in one direction.
What you likely are asking about are cables with the shielding lifted at one end, which is not an uncommon practice for professional installations. You can't do this with coaxial cable, as you discovered, because the shield is your neutral return. If you lift the shield at one end, then you break the circuit and get no sound (and also get a whole lot of noise as a result.).
Instead, this is usually done with twisted-pair audio cabling which has a separate shield. One of the conductors is your positive signal, the other conductor is the neutral return(ground). Then around that you have usually a foil shield(and often a drain wire too). In any case, in many cases an installer will only terminate the shield at the source end, so any noise induced on the shield will go back to the source and not on to the next piece of equipment in the chain. If you were to turn that cable around, then all the noise moves forward in the system, not backwards, so to speak.
Obviously is you were to terminate the shield on both ends, then there's nothing at all directional about the cable and it doesn't matter.