I forgot to mention Litz wire (which you mentioned in your email). The arrangement of the strands in Litz wire is different than in normal stranded wire (and the strands are individually insulated). The arrangement causes each strand to wind its way to the inside of the bundle and then to the outside and then back again, multiple times along the length of the bundle. This helps to reduce the proximity effect which the conductors have on each other. This still breaks down above 1MHz or so: http://en.wikipedia.org/wiki/Litz_wire Sean On Sun, Mar 24, 2013 at 10:21 AM, Sean Breheny wrote: > Hi Justin, > > This link gives a table which lists the frequency at which the AC > resistance begins to increase above the DC resistance due to skin > effect (they call it maximum frequency for 100% skin depth): > > http://www.powerstream.com/Wire_Size.htm > > It looks like anything smaller than 20 AWG wire would have AC > resistance=3DDC resistance up to at least 20kHz. This would mean that > cables for typical audio do not have any resistance change due to skin > effect. > > However, a coil is different. When you place several conductors close > to each other, the skin effect ends up happening across the entire > bundle - albeit to a lesser degree than if they were all one solid > wire. This is often called "proximity effect". I don't have any data > on this but I suspect that this would come into play even at audio > frequencies for many coils. There is also some amount of eddy current > induced in the wire itself when you have a multi-layer coil and this > would make the AC resistance higher than the DC resistance. I don't > have data to show whether this is likely to happen at audio > frequencies. > > A much bigger effect, however, is core loss (for iron or ferrite > cores). This definitely causes a difference between AC and DC > resistance at audio frequencies. > > Sean > > > On Sun, Mar 24, 2013 at 10:05 AM, Justin Richards > wrote: >>> >>> This is quite significant - even just the skin effect alone has a >>> profound effect - it is quite common for an inductor to have a real >>> part of its impedance which is 2 or 3 times the DC resistance within >>> its operating frequency range. >>> >> >> I had always considered skin effect at audio frequencies to be >> imaginary and only existed in the minds of the marketers of speaker >> cables. Along with oxygen free and polarity concious cable which is >> a hoot considering the AC nature of audio. >> >> However, wiki seems to indicate that skin effect is very real at audio >> freq. For domestic application where the power is lowish and the runs >> are shortish the effect would be minimal. >> >> Looks like cat5 could make reasonable litz wire. >> -- >> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .