I occasionally hear some audiophoole wax poetic about the benefits of wire made of such exotic materials as silver or oxygen-free copper (OFC) wire. It always bugs me to hear this, and sometimes stimulates my usually suppressed desire to educate the phool with a long-winded lecture. As I get older and wiser, I realize it's a waste of breath because so few people listen. I am quite pleased to see that Audioholics is doing a good job at correcting this myth. Buried in the articles that AH posts on the Audio Principles page are two brief discussions of OFC. I point them out here because they say it better than I can.
From page 3 of
Component Video Cables - The Definitive Guide
3.1 Conductor and Ground
It is important to clarify the reason why OFC copper is used in place of pure, unalloyed copper. Unalloyed copper is an important metal for cables because of its high electrical conductivity. Electrolytic tough-pitch (ETP) copper is an inexpensive industrial copper used for the producing wire, rods and strips. ETP copper has a nominal oxygen content of about 0.04%. Oxygen is almost insoluble in ETP copper and forms interdendritic Cu20 when the copper is cast (Note: interdendritic means located in-between crystal grain boundaries). For most applications the oxygen in ETP copper is an insignificant impurity. However, when ETP copper is heated to a temperature above around 400̊ C (752̊ F) such as when using a high temperature solder in an atmosphere containing hydrogen (found in air), the hydrogen can diffuse into the copper and react with the internally dispersed Cu20 to form steam according to the chemical reaction:
Cu20 + H2 (dissolved in Cu) --> 2Cu + H20 (steam)
The large water molecules formed by the reaction do not diffuse readily in copper and form internal holes, particularly at the grain boundaries, which makes the copper brittle. Brittle copper at solder joints (the area that was heated) will decrease the life of the cable since this area is usually under high stress from supporting the weight of the cable at the connector point. To avoid hydrogen embrittlement caused by Cu20, the oxygen can be reacted with phosphorus to form phosphorus pentoxide (P205), but this is not practical when hand soldering RCA connectors onto a coaxial cable. Another way to avoid hydrogen embrittlement is to eliminate the oxygen from the copper by casting the ETP copper under a controlled non-oxygen reducing atmosphere. The copper produced by this method is called oxygen-free high-conductivity (OFHC) copper (alloy C10200), or oxygen-free copper. OFHC can be heated and soldered in an open environment without becoming brittle at the heat effect zone (solder joint).
Pursuing the Truth: The fact of the matter is that OFHC copper and pure unalloyed copper, both oxidize at around the same rates. Some cable manufacturers use the OFHC as an advertisement that it will not oxidize, or it will oxidize less than other copper conductor materials, but there is no truth to these claims.
The second mention of OFC is from:
Exotic Materials and Cable Construction
Oxygen-Free Copper
Many cables today are advertised as using "oxygen-free copper," copper which has been annealed in an oxygen-free atmosphere. OFC is popular in audio cables, and has begun to make inroads into the video cable market as well.
We all know, of course, that oxygen is bad for things made from copper. Copper oxidizes and turns green and flaky; in so doing, it loses its high conductivity and begins to fall apart. But the amount of oxygen present in conventionally annealed, non-OFC copper is so tiny that it simply isn't a factor in cable quality. We have cut into pieces of Belden coaxial cable 25-years old that have been used in radio transmission applications and found them clean and bright, completely lacking any sign of oxidation. Modern coax is better still, with nitrogen-injected foam dielectrics that keep oxygen entirely away from the center conductor.
As it is with silver, there's nothing wrong with OFC; but electrically speaking, OFC wire is indistinguishable in audio and video applications from ordinary annealed copper wire.
My minor beef: “Modern coax is better still, with nitrogen-injected foam dielectrics that keep oxygen entirely away from the center conductor.” This is not so. Molten plastic injected with nitrogen or any other gas will form bubbles upon cooling. These bubbles contain nitrogen only for a short time because the plastic is quite permeable to most gases. By the time you buy cable with foamed dielectric insulation, the bubbles contain a mix of nitrogen, oxygen and carbon dioxide identical to the air we breathe.
Thanks to the AH editors for posting these tidbits of info. It has cured me of the need to rant and rave
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It is worthwhile to point out that the copper wire industry did not start making OFC wire for the needs of the audio industry! It was first made because the windings of large electrical generators, made from standard copper, would became brittle and fail due to their continuous exposure to high temperature, high g-forces and vibration. Generator windings made from OFC copper last longer. Apparently it is now routine for much, if not all, copper wire to be made under OFC conditions. Because of this, the difference in cost between ETP and OFC copper wire is small.
Now I can go back to work
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