AC Power Cords: The Last Six Feet – Do They Really Matter?
With some accessory AC power cords now costing as much as thousands of dollars, it’s no surprise that audiophiles are asking how the last six feet of wire – the cable from the wall to their system — can possibly make an audible sonic difference when the power it delivers might be coming through as much as hundreds of miles of other wire to get to that wall. It’s a good question, and most of the companies that make those accessory cables still haven’t come up with a good answer.
In fact, though, the answer is quite simple: The current that our audio electronics run on isn’t the AC that comes out of the wall; it’s positive and negative DC made internally, out of that AC, by the power supply section of each of our components.
Light bulbs, toasters, other home appliances, and the AC motors used in some of our LP turntables and CD or DVD players do use AC as it’s delivered by the power company. The electronic components of our audio systems, however, take the power from the wall and change it — from AC to DC of whatever voltage and polarity may be required for the specific task at hand.
The AC current coming from the power plant alternates (changes direction from positive to negative current flow and back) 50 or 60 times a second, depending on which country we live in. That frequency, plus whatever other frequencies and irregular current surges or reductions may be imposed onto the AC power as “noise” (EMI and RFI) or the effects of other uses of power along the way to our homes is what comes out of the wall.
The DC created by the power supplies in our equipment, though, is, at least theoretically, at zero frequency – either continuously positive or continuously negative, varying, if at all, only in voltage and relative current availability. The process of creating it (rectification) cancels-out and eliminates most or even all of the accumulated effects of travel from the generating plant to our homes. To the extent that its effect is canceled-out in the rectification process, even the most extreme distance from the power plant or the most extreme level of induced power line noise becomes irrelevant, and the only thing that really matters is what happens in just that last six feet of wire.
To understand why this is true, it’s important to know that every current-carrying wire (the wires of an AC power cord, for example) creates and, for as long as current flows through it, maintains an electromagnetic field around it that has no dimensions other than its point of origin, and extends to infinity, diminishing in field strength or intensity in accordance with the Inverse Square Law.
Normally, the Inverse Square Law for fields is stated as: “The intensity of a field declines as the inverse square of the increase in distance from its source”. This means that the field intensity at any two units of distance (two feet, two meters, or two miles) from the field’s point of origin (the wire, in this case) will be just one quarter of its intensity at one same unit of distance. What’s easy to overlook, though, is that the same thing also applies in the opposite direction: The intensity of any field at any one unit of distance from its point of origin will be FOUR TIMES GREATER than at two units of distance, and it will continue quadrupling every time the distance is halved.
What this means is that the effects of fields get very much stronger the closer you get to the field’s point of origin and very much less as you get farther away. This is important because every time a field collapses, it induces current flow in every grounded conductor within its limits, and with all fields extending to infinity, every conductor in the universe is within its limits!
That’s the principle behind radio and television: a collapsing field from a transmitting antenna induces current flow in a receiving antenna and, voila, you’ve got music or the evening news! And the thing that makes it important to our audio systems is that before the AC to power your system gets rectified into DC, the alternating current in your wall and in your power cord is changing direction (in the US) 120 times every second (60 positive phases plus 60 negative phases) and that every time it changes direction, the electromagnetic field surrounding it collapses, inducing out-of-phase current flow in every grounded conductor (all of your components and other cables and power cords) within range.
What’s The Range?
So…what’s the range? On the one hand, out to forever, but, on the other hand, because of the squared-rate-of-decline-with-distance, only a few feet. And the very greatest effect (the greatest induced current-flow in other conductors) will be to the wiring and electronics closest to it – in short, your own system.
That’s the most important reason why AC power cords need to be shielded – not to protect the incoming AC current from distant external interference getting INTO the power, but to protect the system against damaging electromagnetic interference getting OUT of the cable and into your system! (Again, the last six feet)
What We Do That’s Different
Every reputable accessory AC power cord is shielded – including the high performance AC power cords from RSX. RSX goes much further, though.
Minimize Capacitive Discharge Effects: Every RSX AC Power Cord is designed to minimize capacitive discharge effects, (a phenomenon first discovered by RSX’s Designer, Roger Skoff, more than twenty years ago), which can result in clearly audible signal cancellations or even the creation of out-of-phase artifacts at or near the “zero” line of each change of signal polarity.
Demand Coupled™ Design: Another RSX exclusive feature (and reason why that last six feet is so important) is “Demand Coupled Design”. This does something no other cable brand is known to do, and, recognizing a basic fact of the incoming AC power, integrates it with the power demand curve of each component under power to produce faster signal rise-times, less hangover, greater definition and clarity, and cleaner, “punchier” dynamics.
So, does the last six feet really matter? RSX strongly thinks it does and you can prove it for yourself. Audition RSX cables in your home for 60-days risk-free. Hear the music…not the cables.