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In Reply to: RE: Skin Effect, IC's ,and Speaker Wire posted by ddanielsmith on June 27, 2007 at 10:49:57
Dan: ""
Help me out here.""With what? :-)
Dan: ""
One argument maybe that the configuration of a speaker wire can help cancel some of the inductance. But configuration can only cancel mutual inductance, not self inductance which I believe is the cause skin effect.""Skin effect is the reaction of a conductive material to a change in current within it. It occurs regardless of the application, be it IC's, or speakers.
Within a coaxial IC, skinning of the sheild is practically nil. Leaving the center, which will react only to it's own current. The best one can get is a 15 nH per foot reduction in self inductance, as you point out. For high impedance loads typical of IC's, the inductance is not the primary source of energy storage, the capacitance is. Contrast this with speaker runs, where the primary storage element is indeed the inductance.
For most wire geometry's, the reduction of inductance caused by skin effect pales in comparison to the actual inductance of the wire geometry, I recall about 17% for a #12 zip...edit: this number is the total internal inductance contribution to the overall inductance...skinning at rf frequencies can only reduce the inductance by this 17%, audio frequencies are far less capable of this reduction.
The equations below presented by cheap jack are correct if you consider the effect via the penetration depth approximation equation. It is an incorrect formula for the actual effect when it comes to practical wire guages and diameters, as it is basically only applicable for infinite planes of conductive material. For wires, it falls apart in the audio regime; bessels are far better when the skin depth is about 1/5th of the wire diameter..edit; the approximation equation is off by roughly a factor of 3 to 5 for wires in the 18 guage range at 10Khz, it gives numbers that are too small depthwise.
An article published in '85 gave a lot of credence to skin effect and audio, however, there were several fatal assumptions used. One being the assumption that an approximation equation was valid waaaaaay outside the realm where it was indeed correct. A second was the substitution of a magnetic wire for copper when an actual test was done...everybody knows a magnetic material has more inductance..
While skin effect is discussed at length in audio forums, much of it is based on erroneous papers and understandings. The truth is so, shall we say, boring?..or, just not sexy?
Just examine the posts a bit down...some claim "bad sound" because of skin effect at larger guages, but yet others claim the opposite..large guages being ok..
Cheers, John
Edits: 06/27/07 06/28/07Follow Ups:
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