Episode 19: I'll Take The Gold-free Extra Oxygen Cable Please

Overview:

Tackling two types of common cables you'll find: Speaker cable and HDMI cables. HDMI they obsess over gold plating; Speaker cable they obsess over OFC. Which is worth the extra money?

Warning: Hardcore audiophiles may be upset by the contents of this episode.

Pre-show Acknowledgements [01:10 - 05:01]

We're always grateful when people take inspiration from the show and write posts or podcast about things we've discussed during the show.

In response to Episode 16 One Man's Hopes and Dreams of an RF Buble Dave Liggat wrote an article called IPv6: An Unreachable Wall that expanded on just how far our the IPv6 'wall' actually is. Thanks to Dave - it was a great read and thanks for doing all the maths for me!

We also really appreciate iTunes reviews and a recent review in the German store from Flavor Dynamics made comment regarding the Outtro music being from a 1980s elevator. Okay, so I laughed when I read that but seriously I've written about The MOD Tracker Scene previously that discusses how I came across that song and the corrections are: it was a 1990s song and is highly unlikely that it was ever played in an elevator. ;)

Oxygen-Free Copper (OFC) [05:02 - 19:06]

OFC cables are typically found in audio applications for stereo systems for connecting the amplifier to the speakers themselves. The configuration of these cables is often referred to as "Figure 8" which is a play on the appearance of the cables cross-section that looks like the number 8. The examples we consider specifically are this OFC Cable and contrasted with a Standard Cable. Making Oxygen-Free Copper perhaps not surprisingly requires an environment with an inert-gas during production that is, well, Oxygen-free.

Technically speaking though it's still valid to count copper as being Oxygen-free even if there are 10ppm or less of Oxygen contained in it. The truth is that OFC copper only presents a 1% improvement in resistance over standard copper and the whist OFC cables are associated with greater reliability this has nothing to do with the OFC nature of the copper but rather the general construction of the cables.

OFC cables use high core counts to acheive the same Cross-Sectional Area (CSA) of equivalent cables and due to Skin Effect this often results in lower effective AC resistance and better performance in that regard only. Claims of improvements to noise performance with OFC over standard copper are unfounded.

Gold Plating Connectors [19:06 - 34:50]

Primary reasons for gold-plating connectors come back to a desire to improve the contact resistance and corrosion-resistance. There's an excellent article called the Golden Rules (PDF) which is from an connector vendor discussing all of the advantages of Gold plating for connectors.

The problem is that all metals will erode with every connection/disconnection cycle of the plug and the socket. How much they degrade (how much is scraped off) will vary based on the hardness of the metal in question. In 1812 a German geologist and mineralogist Friedrich Mohs developed a scale of hardness that is still used today although it has been refined further it at least illustrates the point.

Any plating used will eventually erode as the harder of the two surfaces gouges/scrapes off the other surface with the HDMIstandard for example requiring a 10,000 total connect/disconnect cycles for compliant connectors. Ultimately contact resistance improvements are minimal but measureable but the cost of adding gold to a connector is often over-assumed by consumers. A gold-plated connector of a HDMI cable will have less than 0.1 grams of gold worth less than $5 USD and yet such cables sell for anywhere between $10 USD to $50 USD more than a standard HDMI cable.

Real-world Consumer Applications [34:50 - 45:55]

Ultimately resistance is the enemy with speakers as the more resistance there is between the amplifier and the speaker the less total power is delivered to the speakers. Given a typical household cable run of 10m for a typical 25W bookshelf speaker, comparing the two cables mentioned previously we end up with a total reduction in power output of only 0.3dB of volume. Given that 3dB is half the power output, this is essentially barely measurable by a sound pressure level meter and would be barely noticable by the human ear at normal volume levels.

Regarding HDMI there are both 5V and a I2C(aka IIC) bus on a standard HDMI cable and given the typical length of a HDMI cable is about 5m we can conclude that in order to drop below the minimum "Digital True" voltage a cable of extremely high resistance would need to be used. Looked at another way, given that both gold and non-gold plated cables exist and yet both work, the gold plating does nothing to improve the quality/reliability of the signal transfer for HDMI.

Summary of What Makes a Good Cable [45:55 - 55:42]

Good speaker cables don't need to be flexible or made using OFC in order to perform well. Save the money spent on cables and spend it on a better amplifier and speakers. Good HDMI cables are well shielded. On balance neither gold-plating nor OFC is worth the additional money spent for essentially all consumer applications.

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