Ground Loops and EMF shielding
Thanks guys. I did some googling and found that the arrows point to the end where the shielding is not connected. This is intentional to remedy any ground loop noise that may occur when a grounded sub and grounded AVR compete for ground on the electrical circuit. With the shield/ground disconnected within this cable, the loop and consequential hum or noise is reduced/eliminated. I understood that the LFE signal is still caried through the core of this cable to the sub and circuit is completed through the ground instead of the shield wrapped around the core of the cord.
I hate excess wires, so I'll try a single short RCA and see if I get any ground loop noise or not.
I am not sure where you found the information abou the shielding, but in order to have a circuit you need two wires. In a typical co-axial cable the center wire is one wire and the outer braided sheath is the second wire. You are only going to obtain shielding if you have two separate wires besides the outer braided sheath and most RCA cables don't.
Now shielding and ground loop itself needs to be explained. There are two different problems that are really not related.
Ground loop is a condition where an unintended connection to ground is made through an interfering electrical conductor. Generally ground loop connection exists when an electrical system is connected through more than one way to the electrical ground.
When two or more devices are connected to a common ground through different paths, a ground loop occurs. Currents flow through these multiple paths and develop voltages which can cause damage, noise or 50Hz/60Hz hum in audio or video equipment. To prevent ground loops, all signal grounds need to go to one common point and when two grounding points cannot be avoided, one side must isolate the signal and grounds from the other.
The bottom line is that a perfect "quiet" ground does not exist. The basics of all noise problems on the grounding system boils down to what is objectionable current. With the exception of hospital systems, the definition is vague at best. The standard electrical grounding system throughout the building isn't designed to have current constantly flowing through it--and yet it does, you cannot stop it. The reason a ground will not and never be perfectly noise free is that the grounding electrode conductor is nothing more than a long wire from point A to point B. And the longer the wire the more noise it will pick up.
Electromagnetic shielding is the process of limiting the penetration of electromagnetic fields into a space, by blocking them with a barrier made of conductive material. Typically it is applied to enclosures, separating electrical devices from the 'outside world', and to cables, separating wires from the environment the cable runs through. Electromagnetic shielding used to block radio frequency electromagnetic radiation is also known as RF shielding.
The shielding can reduce the coupling of radio waves, electromagnetic fields and electrostatic fields, though not static or low-frequency magnetic fields. (A conductive enclosure used to block electrostatic fields is also known as a Faraday cage.) The amount of reduction depends very much upon the material used, its thickness, the size of the shielded volume and the frequency of the fields of interest and the size, shape and orientation of apertures in a shield to an incident electromagnetic field.
Shielding is entirely differnet and caused by the braodcast of EMF (Electro Magnetic Field). This occurs anytime electicity goes through a wire. As with an electromagent the amopunt of EMF depends on the number of turns times the current. Because of the electrical skin effect a coaxial type wire, where each conducter has a common center, tends to minimize the effective EMF. Having said that, even cheap RCA cables are basically coax and the current at prepro level is so low that very little EMF is emmitted anyway. One example is a shielded cable, which has electromagnetic shielding in the form of a wire mesh surrounding an inner core conductor. The shielding impedes the escape of any signal from the core conductor, and also signals from being added to the core conductor. Some cables have two separate concentric screens, one connected at both ends, the other at one end only, to maximize shielding of both electromagnetic and electrostatic fields.
So what is the bottom line. A ground loop could exist and cause a hum type noise problem, but shielding does not solve any ground loop problems. Putting an arrow on the cable makes you think it is more expensive and better and helps you justify paying 10 to 20 times as much for the same cable length. But that is about all.
JMHO
MidCow2
