.........when you solve Maxwell's equation for propagation in a good conducter, you obtain a decaying wave because some energy is converted into heat. Also, the velocity is very slow and frequency dependet. It is ths slowly propagating wave thats determines the internal current in the conductor and is the basis of skin depth, it also explains why skin depth increases with decreasing frequency. The loss field is at maximum at the surface and decays exponentially into the conductur.
The current is no longer confined to the conductors surface but penetrates into the conductur, it depends on frequency and decays exponentially. Therefore, when you consider the series impedance of the cable, you find it is made of two principal parts.
There is the inductive reactanse due to the magnetic field within the dielectric between the conductors, and this, as you would axpect rises as 6dB/octav. However, the magnetic flux trapped inside the conductor has both resistive and inductive componetns. If the skin depth is such that the current has not fully penetrated all the way to the center of the conductor, then this component of impedance approximates to 3dB/octave.
What happens in practice depends on the actual cable geometry and therefore which aspect of the impedance is dominant. So to conclude, at lower frequency the penetration is deeper while as frequency rises, the internal conductor impedance increases as the current becoms more confined to the surface layer.
Now, going back to loudspeaker cables, ideally you would want them to have just a very low value of resistance with no reactance.
Due to the phenomena described above, that may not always be true. But there lies the art of loudspeaker cable design!
However, in understandig the problem with loudspeaker cables that can impact their percived subjective performance, there is another important factor. Even if cables are completely linear, they still feed loudspeakers system that offer a nonlinear load due to drive unit impedance changing dynamically with cone displacement, suspention nonlinearity and possibly saturations effects in crossover components. As a result, the current entering the loudspekaer is a nonlinear function of the applied voltage. This in turn means that any voltage drop across the cable also has a nonlienar component which must be added to the loudspeaker input voltage.
It is interesting to audition these error signals in real world systems where distortions can be clearly audible
So in sense cables do impact the final sound where this process is responsible for perceived differences in character or coloration....................
Skrevet av AES medlem med utmerkelse for
Major contributions to engineering research in the advancements of audio reproduction.
