Post by RdM on Feb 18, 2021 19:21:00 GMT 12
I recalled earlier discussions on 'skin effect' here, for instance later down this thread (showing Owen's fine room) -
darklantern.proboards.com/thread/1270/work-progress
It reminded me that I had been unconvinced at audio frequencies, so went looking and found a couple of calculators.
www.daycounter.com/Calculators/SkinEffect/Skin-Effect-Calculator.phtml
shows that at 20kHz, skin depth is 20.1 mil (approx 0.51 mm, see www.convertunits.com/from/mils/to/mm ) and that wire gauge such that Rac=Rdc is 18 AWG.
Put in 48kHz and it's 12.9 mils and 22 AWG,
I'll get to the second part in a moment, but along the way I also found this (more attuned to RF, which is where it does become significant)
voltage-disturbance.com/engineering-calculators/skin-effect-calculator/
and a quite technical discussion, the math is way over my head ~
Some Skin Effect Notes
fermi.la.asu.edu/w9cf/skin/index.html
darklantern.proboards.com/thread/1270/work-progress
It reminded me that I had been unconvinced at audio frequencies, so went looking and found a couple of calculators.
www.daycounter.com/Calculators/SkinEffect/Skin-Effect-Calculator.phtml
shows that at 20kHz, skin depth is 20.1 mil (approx 0.51 mm, see www.convertunits.com/from/mils/to/mm ) and that wire gauge such that Rac=Rdc is 18 AWG.
Put in 48kHz and it's 12.9 mils and 22 AWG,
I'll get to the second part in a moment, but along the way I also found this (more attuned to RF, which is where it does become significant)
voltage-disturbance.com/engineering-calculators/skin-effect-calculator/
and a quite technical discussion, the math is way over my head ~
Some Skin Effect Notes
fermi.la.asu.edu/w9cf/skin/index.html
Anyway, the quite prosaic thing that started me wondering about this was, looking through my old stash of wiring, speaker cables, and discovered 3 + 3 + 7m lengths of old DSE (Dick Smith Electronics) cables that I even think I remembered reading about getting oxidised within the plastic, a bad batch perhaps, and wondering if or how they might be compromised.
Copper oxide being a semiconductor, and yet only a thin film, and easily scraped off.
These cables were terrible to try to split apart, even with a sharp craft knife or by starting a split and pulling apart.
Easily veered to expose copper on one side instead of splitting evenly down the middle. Not "TrueRip" !
Yet quite chunky, I estimate about 1.8mm overall conductor thickness diameter.
I've renewed some ends, merely flattening and scraping while rotating to get back to copper - this pic in low light, adjusted.
You can see the green under the insulation, especially on the left.
My question: Do you think the oxide on the cable strands surfaces internally (despite cleaned terminating ends) will affect the audio signal?
I wish to give these to a broke neighbour whose early NZ made Roberts amplifier (70's?) I've replaced one channel output transistors in, and who scored a pair of Kef Carlton III for free on a renovation job (not wanted by new owners, looked too dull and boring for makeover premises!) - and likely will anyway, but just wondered as above - will a very thin surface film of green copper oxide (reaction with the plastic sheath?) internal in the cable conceivably cause any audible anomalies?
Thanks for indulging me! ;=})