Q: "I have 2 Monster cables that have an intended signal direction, and an Acoustic Research cable that has a signal path arrow as well. Of all the things about analog cables, this seems to be the most nonsensical. What is the deal exactly? Can it really matter? Could you ever hear the difference if you turned one of those cables around the other way?"
A: It can be as simple as some way the wires are connected to each end. A certain shielding convention, when carried out properly throughout a system, can make a difference. For example, it's not uncommon for telescoping shields to be used in systems using balanced wiring, and often it's the end at the receiving device that has the shield lifted. (We've done a number of Tech Tips on Telescoping Shields in the past so feel free to search those for more background.) Cables may be marked for signal direction accordingly. Of course, if you're using XLR cables the male and female ends are generally going to determine wire direction anyway.
Beyond literal things like the way the wires get connected it gets substantially more controversial. Some people theorize that the direction wire strands are extruded from the big blocks of copper can have an impact on how they conduct electricity, specifically in regard to what is controversially known as "wire resonances." Wire resonances are minute vibrations that occur in wires caused by the magnetic field generated from current flow through them. The current flow causes the wire to resonate, which in turn has an effect on how it is relating to the magnetic fields already present in most environments, which therefore cause minute changes (in terms of certain reinforcements and cancellations) in how complex signals are transmitted down the wire.
For those cynics in the crowd, this stuff isn't as far fetched as it may sound to you. It certainly can be true that magnetic fields generated from current flow can manifest themselves as physical vibrations. This is what is happening with certain devices in your rack seem to buzz or vibrate - that's the magnetic field generated by the transformer triggering a physical vibration. So we're not advocating these wire resonance theories, and they clearly are going to be very minute in line level signals, but you shouldn't discount the concept out of hand.
Proponents of these theories are thoroughly convinced that wire direction can have an effect on sound. From there, assuming you buy in to this so far, you have to get to the next question, which is, how can a manufacturer know which direction is "right" for labeling of the wire? Some claim this can be determined from the extrusion process. Others claim that not only is this not the case, but that since the wire strands are extruded in both directions and then more or less randomly fashioned into a cable the only way to really know is to do listening tests, which is actually what many of the audiophiles are advocating - not that one direction is always "better" than the other, but that they are different, and cables must be empirically tested, preferably in the specific environment where they will be used. Some manufacturers of very high-end (and high dollar) cables claim to have done these listening tests for you (and charge accordingly) before marking cables for direction.
There are people who strongly claim it makes no discernable difference and there are people who claim it can make a significant difference. This is one of those things you're going to have to decide for yourself through experimentation.
