Copper Purity and BJC HDMI Cables

We are frequently asked about copper purity in our HDMI cables, so have written this short note to address this subject on which there seems to be a great deal of common misunderstanding.

A lot of audio and video cabling in the consumer market is labeled (not always accurately) as "oxygen-free" or OFHC copper. Oxygen-free OFHC copper is governed by an ASTM specification, and involves particular processes for creating the copper bar from which wire is drawn. Because OFHC is so often written about in connection with consumer-market cabling, there is a common misconception that its use is needed, or is particularly desirable, in communications cabling.

In fact, while the purity of copper is important, following the OFHC spec is only one means of attaining high copper purity, and there is no particular benefit to it as against other means of producing what, ultimately, amounts to very little other than standard annealed copper. For this reason, OFHC is almost entirely absent from professional communications cabling--we know, for example, of no SDI coax, anywhere, which is made with OFHC. While there are some specialty applications for which OFHC is superior to other types of copper (having mostly to do with physical, not electrical, properties), its presence in consumer a/v cabling is pretty much just the result of people using it as a marketing hook to make their product sound as though it is better-made than others.

The terminology "oxygen-free" leads many people to suppose that copper which is not so labeled is laden with huge amounts of oxygen, and that this huge amount of oxygen will cause non-OFHC copper to degrade. This is, simply, not so, and the amount of oxygen is ordinary, standard annealed copper wire is extremely small. We have solid-copper core coaxes, made with standard annealed copper, that have been sitting around for 40 years (at home, that is--we don't have anything remotely that old in inventory!)--and if you strip a length of that coax you'll see fresh, bright shiny copper underneath. You may from time to time see speaker wire that has corroded under its jacket, but this is a wholly different problem, generally related to using poor-quality PVC that actually catalyses oxidation in the underlying copper--it has nothing to do with the purity of the copper itself, and OFHC in a poor-quality jacket would deteriorate just as badly.

Our HDMI cables are made using Electrolytic Tough Pitch copper, with a purity of 99.95 percent; this is a higher purity than some grades of OFHC, lower than others. This same ETP copper is used in high-bandwidth SDI cables, 10 Gig Ethernet cables, and a slew of other demanding applications. It's probably worthwhile to note, too, that the 0.05 percent level of impurity should not be interpreted as "oxygen"--it's the sum of all of the impurities in the copper.

We are committed to keeping our Belden bonded-pair HDMI cables--available only at BJC--the best in the world. If OFHC would make them better than they are, we'd use it. But the fact is, as we've set out elsewhere on our site, that high-quality cable manufacture usually has nothing to do with using special materials (except where special applications, such as plenum wiring, call for it) and has everything to do with putting ordinary materials together with tight, consistent dimensions and tolerances. Dimensional control, in particular, is critical to HDMI cable performance, and our bonded-pair construction, done by American workers at Belden plants, offers the best dimensional control and impedance stability available in any HDMI cable on the market.

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