Can someone explain to me, in engineering terms, how, if an interconnect is truly directional, it doesn't screw up half of the waveform?
I can't, but Mike Vansevers can. Mike is an electrical engineer.

Good question. It would seem that 1) if a cable is directional and 2) the signal is AC then 3) the cable is going to act like a rectifier. Who wants that going on between the pre and amp with a cable? I never understood that? If you get a good answer please let me know.
I am not a very technical person, but it seems that the signal would be going in a "circle" to complete the circuit, one way through the (+) lead and the other way through the (-) lead. If this is correct then the cable is "directional", perhaps due to the grounding scheme (@ one end only) and/or if one pays attention to which direction the wire is "drawn" during the manufacturing process, then this pattern (or draw direction) would preferably be reversed on the (+ & -) leads in order that the signal "goes with the flow".
Unless there is some form of circuitry inserted into the interconnect, the notion that wire has "directionality" is mostly a myth. When wire receives an electrical signal, the voltage flows from positive to negative, and the propogation time is fairly constant. It is theoretically possible that, over time in wires with crystalline structures, there could some degree of alignment, but this would still not impair the ability of electrons to flow in the "correct" direction. Our high-end audio hobby has, particularly in recent years, seen the development of a lot of "mumbo jumbo", and "directionality" of wire falls into that category.
Someone once told me that cables don't start out directional, but they become directional after they have been used for awhile because the conductors get used to the current travelling in a certain direction (which is also why they are supposed to sound better after being broken in). You can reverse the direction by simply turning the cable around and breaking it in again. It is similar in concept to magnetizing a nail by rubbing a magnet along it many times in the same direction. To make things simpler on the customer, some cable companies put a little directional arrow on the jackets so that you always use it in the same direction. Plus they use it as a marketing tool, because it makes their cable look more "high-tech". Networked cables have their little boxes placed at an optimum point in the cable for a certain direction, so networked cables are more truely directional than other cables.

While i am not an expert on anything, i play one in my mind : )

Having gotten that out of the way, some cables use what is called a "telescoping ground" scheme. This means that you have the normal + & - wire to complete the circuit but you also have a third wire / braid / shield that is only connected at one end to ground. The grounded end typically connects to the source and the "floating" / unconnected side is attached to the load. This is not a new approach and has been shown to reduce RFI, magnetic field induced distortion, etc... at the expense of slightly altering the cables electrical characteristics ( increased capacitance ).

As to the "crystal structure" forming in a certain direction, etc... I have NO idea about the "technicalese" end of this. All i can tell you is that i can tell a very noticeable difference in interconnects before and after burning them on my Mobie. Evidently, others can too.

I just sent some cables back to one of my buddies in Ohio. He had 5 sets of reasonably priced interconnects that he thought were completely unusable i.e. hard, bright, grainy, glaring, etc.... He disliked them so much that he was going to remove the high quality RCA's and literally throw the wiring out. I talked him into sending them to me for "burning" and then giving them another chance. I just shipped them back to him and he now has them installed in two different systems. He could not believe the difference that it made and finds them completely different in terms of their new sonic signature. Much more relaxed, transparent and smooth.

By the way, the above mentioned cables were "directional" as marked on the jacket and sold by the manufacturer. I checked the cable geometry while they were here and they were making use of the "telescoping shield" design. Sean
I like Sean's possible explanation ... grounding only at one end. Seems plausible. However the concept of ANY directional cables in audio because of "crystal grain", winding of strands etc etc seems like total nonsense to me since they're all AC signals. I have always tried "directional" cables in both orientations and never heard the slightest bit of difference, so my ears tend to agree that it's nonsense.
Sean has it about right... that's called a "drain wire" in
most places...

You'd want to know which end is which in that case. Thus

Anyone who claims the metal wire or the plastic insulation
is "directional" is, uh, questionable.

In all cases the signal is AC and reverses direction on
each and every cycle, so there is no "direction" to the
signal - think of it as pulling on the rope that makes
up a clothesline with pulleys! Back and forth...

I was once told by a 30 years old cable manufacturer/designer, directionality a more of a marketing phenomenon than practical.
Ben Duncan in HFNRR found bulk wire to be directional and presented his measurements and findings......
Bob, in what issue is that ? Do they have a website ? Sean
August 2001 as I recall.....Nice of old Ben to measure what we have been hearing for years wasn't it? Ben has a website as I recall and imagine it is reprinted there, but haven't checked....Can't find the issue, but think it was titled something like "diode effects in wire".....
If anybody knows where the article by Ben Duncan mentioned above (post by Rcrump) is online (if it is) or in print please post it here. I cannot find it anywhere.
Make that August 2000, not 2001.....

There is an article by Ben Duncan in the August 2000 (re: polarity)and another in the Sept 2000 (re: cable directionality) issues of Hi-Fi News and Record Review. If anyone wants any info from these please email me (as long as I don't infringe the original copyright...!!!)

Happy New Year to all, regards, Richard.