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Re: attenuation in RF region

Posted by Monk1 on October 9, 2001 at 11:01:51

In Reply to: attenuation in RF region posted by Mart on October 8, 2001 at 22:37:19:

I would agree the skin effect is a factor at the higher frequencies but, the skin penetration at 20 kHz for copper is nearly 0.5 mm. This is more than sufficient strand penetration, even for the skimpiest stranded conductor audiophile speaker cable that I have seen. At 20 kHz, the conductor strand diameter would have to be greater than 1 mm before the skin effect begins. Most sranding in audiophile cables are much finer than that so skin depth should not be an issue.

For high frequency work, there are many different forms of inductance to consider. Self inductance, mutual inductance, internal inductance, partial inductance are only the tip of the iceberg. The dominant form of inductance in a speaker cable is self inductance, which is entirely dependent on path geometry. The resistance due to skin depth is accounted for separately and does NOT replace self inductance, even at radio freqencies. You can easily account for the skin depth resistance in the lumped-circuit model without having to resort to the transmission line model.

On poles and zeros, it may appear on initial inspection that the simple RC "zobel" network would not, by itself, create a pole. However, we're dealing with a complex network with many circuit elements, some of them are parasitic. One would have to consider all variables on a case by case basis because not all speaker cables and loudspeaker crossovers are the same regardless which model is chosen. Use of the "Zobel" directly across the amplifier output should be done with caution. let's not forget that the resistor in the "Zobel", even a low inductance one, turns into an inductor (typically 10 nH or more) at high frequencies. This inductor can resonate with the circuit capacitance to produce... well, more resonances.

BTW, I searched the site and did find the plots and Excel models afterall. Good luck with your experiments.

Monk

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