For almost as long as the war has been going on over whether premium cables actually do anything, there's been a similar war among cable manufacturers and enthusiasts over what kind of metal cables and their connectors should be made of.
Many alternative cable materials have been tried, including aluminum, plated aluminum, plated steel, A.J. Van den Hul's carbon filaments and the carbon elements used in automotive ignition cables. However, copper and silver, in that order, have remained the conductor materials of choice for the overwhelming majority of cables, and a whole folklore has arisen about which is better and why. A number of reasons have been put forward in favor of each, and a number of counter-reasons have been advanced in every case to show why each of those other reasons is inapplicable, inappropriate or irrelevant.
About the only thing people unequivocally agree on is that the purity of the material matters, and that purer is better. And yet, in this article, I'm going to suggest that what we think we know about conductor purity may not really be true, or at least not as we normally think of it.
Because it's the more widely used conductor material, I'll be concentrating more on copper in this article, but not exclusively; there will be plenty of things to say about silver, too.
If you've read the literature, you know that the great number of cable manufacturers claim to use "99.9999%" or ".999999 pure" copper. In either case it's usually referred to as either "six nines" or "6N" copper, but some manufacturers -- undoubtedly trying to "brand" a generic product -- have come up with other names for it, like "Functionally Perfect Copper ("FPC"), or its silver equivalent, "Functionally Perfect Silver" ("FPS"). When I owned XLO, we simply said that the premium copper that we used was "Laboratory Grade."
The reason for XLO's hesitance to hang a specific number of nines on its copper was pretty simple: Although we were ordering and paying hugely for super-high purity copper, there was no way, other than by accepting the manufacturer's assurances, that its purity could actually be verified.
The most commonly used copper for industrial applications is Electro Tough Pitch, or ETP, or to call it by its ASTM/UNS standard, C110. This low-cost copper is required, for standards compliance, to be at least 99.9% (3 nines) pure, and to have an IACS (International Annealed Copper Standard) conductivity of at least 100%, although actual ETP conductivity of 101% is not uncommon. Oxygen is purposely injected into the ETP refining process for the specific purpose of increasing ETP's conductivity.
The next up on the scale of purity standards is C102 "Oxygen Free" or OFHC, for "Oxygen Free High Conductivity." This has a minimum purity of 99.95% (3½ nines?) and its oxygen content is purposely reduced to .001% (from ETP's .002-.004%) to improve its electrical conductivity. Its conductivity remains at 100-101% IACS.
The very best "standards-rated" copper is C101, which is 99.99% (4 nines) pure. Its oxygen content is reduced still further to .0005%, and it may have a conductivity rating as high as 103% IACS. That's it. There is no higher institutionally rated standard.
Given that last statement, you can probably understand my concern when, after purchasing XLO's first batch of "Six Nines" copper for a ton of money, I wanted to have it lab-tested to confirm its claimed purity, but found out that such testing simply wasn't going to be possible.
This was, of course, back in 1991, when XLO was first starting-out, so things may be different now. At the time, though, we contacted every single test lab -- either commercial or university -- that we could find in the entire United States; told them that we wanted to verify the purity of claimed six-nines copper, and were told by most that the purest they could certify was three-nines; by a few that they could go as far as four-nines; by one that it could certify four nines and might be willing to guess at a fifth; and by none at all that they could test for six nines of purity.
How could this be true? Especially when some cable manufacturers are claiming not just six, but seven nines of purity, and at least one (it may be Ortofon, if I recall correctly) regularly claims eight!
For that matter, how pure is actually possible? What does purity really mean? And does it really matter?
The first thing to understand is that, even if super-high purity still can't be commercially verified, even now, that doesn't mean that it's not possible. Most ultra-pure copper today is manufactured by a "continuous casting" process. The best known of those is Ohno Continuous Casting, which was developed and patented by Dr. Ohno, of Japan, possibly as an offshoot of the "Zone Refining" technique developed in the early 1950s by William Gardner Pfann of Bell Laboratories for refining super pure germanium and silicon crystals for use in the manufacture of transistors. Another (possibly apocryphal) story is that the process was developed at the physics labs of a major American university around 1924 for refining tiny amounts of near-atomically pure copper to be used in physics experimentation, and that the experimenters, never imagining any commercial use for such minuscule amounts of metal, never bothered to patent it.
Regardless of its provenance, continuous casting does claim outstanding results, and it's not only possible but common for a manufacturer, having need for super-specialized test equipment not available from any commercial source, to invent and produce his own.
In short, just because nobody else can test it, doesn't mean that they (the manufacturer) can't, and just the need to test initial results and to maintain their product's ongoing quality control would strongly indicate that they need to and probably have.
The other side of that is that, even if it really is that pure, so what? If, as so many so-called "experts" contend, the only thing that really matters about the metal is its conductivity, and resistance is the only conductor bugaboo that the cable manufacturers are trying to eliminate, there are lots of ways to lessen the resistance of any piece of wire: The easiest is simply to cut it shorter; if it's 20% less long, it will have 20% less resistance. Or you could simply go to a larger size (AWG gauge) of wire. Whatever percentage thicker (more metal per length) the wire is will reduce its total resistance per length by the same percentage. Or, all other things, being equal, you could replace the copper with silver, which is known to be slightly more conductive than copper and is IACS rated at 106%.
Even doing that, though, probably wouldn't make a huge difference. The total range of conductivity (or, to put it the other way around, resistivity) between the very cheap ETP copper at the bottom of the scale, the considerably pricier C101 copper above that, and the use of very expensive silver conductors, at the top, is just a maximum of 6 percentage points of IACS rating.
Now, certainly, the IACS standards were set up in 1913, decades before any of the ultra-pure coppers became available, so it's possible that more recently developed materials might be better. But still, so what? To quote Wikipedia's article on oxygen-free copper, "...the resistance of most metallic conductors increases by about 1% for every 3 °C (5 °F) increase in temperature, which means that a small temperature rise would negate any benefit of having better conductors." [Italics mine.] Even if the differences were significant, though, and constant at every temperature, more or less conductivity/resistivity should still just act like a volume control and make for more or less signal flow. It shouldn't explain either the clear and obvious overall sonic differences claimed for premium cables or why silver -- which, as we have seen, is only slightly more conductive than copper -- is believed by many people to sound greatly different.
Obviously, if there are real differences and if they are related to the purity of the conductor materials, as claimed, there must be some aspect of conductor purity other than just conductivity or resistivity that's making the difference.
We'll go into what that (or those) might be next time.