Just a reminder, RLC characteristics are important transmission line measurements (you sure aren't going to measure 75 ohms across a cable with an ohmmeter). The question is, are audio interconnects considered 'transmission lines' in the EM sense?
I'll quote Bill Whitlock in his transmission line article (that you can find on google pretty easily) since he does a very good job of setting up what a transmission line is http://digitalcontentproducer.com/ma...ion_lines_why/
|What is a transmission line, anyway? There are broad definitions, such as "the conductive connections between system elements which carry signal power" (ANSI/IEEE Std 100-1977 Dictionary of Electrical and Electronic Terms, page 739), under which every cable becomes a transmission line. Most engineers, myself included, would narrow the definition considerably. The following is the most concise, accurate and simple definition I have encountered: "A transmission line consists of an arrangement of electrical conductors by means of which electromagnetic energy is conveyed, over distances comparable with the wavelength of the electromagnetic waves, from one place to another. Transmission lines differ from simple electrical networks in that their inductance, capacitance, and resistance are not lumped but are distributed over distances such that the time required for electrical energy to travel from one part to another has to be taken into account. A uniform transmission line has what is called a `characteristic impedance'. This is the impedance that would be measured at the end of such a line if it were infinitely long. The importance of this characteristic impedance lies in the fact that if any length of line is terminated in an impedance of this value, then all the energy flowing along the line is absorbed at the termination and none is reflected back along the line." (Radiotron Designer's Handbook, F. Langford-Smith, Amalgamated Wireless Valve Company, Sydney, 1953, pages 890-891.)
The second definition is what is important to us. Is an audio cable a transmission line in that sense?
For that purpose, I'll point you to another very well written (read easy to understand) article on transmission line effects and why they exist: http://www.allaboutcircuits.com/vol_2/chpt_14/1.html
Transmission line effects arise from the fact that signals propagate through a line at close to the speed of light. For short lines, this is for all intents and purpose, instantaneous. For longer lines, a wave does not propagate to the end instantaneously. As electrons start to 'move,' you get an electric field forming between the two conductors due to an imbalance of charge. This contributes to the capacitance of a line. Once current starts to flow, you get the formation of a magnetic field and hence your line has inductance. What you get is kind of like the phenomenon you get at a stop light turned green where not all the cars move at once and you have a delay between when the first car starts moving and when the last car finally gets going.
The key points to glean from the last link (if you read through all the succesive chapters) is that in order for transmission line effects to become significant, the wavelength of signal you are transmitting is typically on the order of 10% the total length of the line you are transmitting it through. What does this mean? A signal at 10-20kHz would have to travel on a line that is miles long in order for effects to become significant (keep in mind the speed of light, and the distance of the cable.)
Now what about a coaxial cable? They're so short. What's up with that? In this case, coaxial cables typically handle video signals comprised of frequencies in the millions of hertz. This means the wavelength of a signal at that frequency is significantly smaller than that of a signal in the audio frequency range and the cable does not have be as long in order for wave propagation times to become significant.
The question is, are these differences significant enough to hear at audio frequencies?
edit: The same reasoning applies to power cables. Assuming a cable is well shielded, transmission line effects should be negligible as well. You've got an incredibly short cable carrying what is a very low frequency (60 hertz) signal. Resistance is almost zero for a cable run of that length and ample conductor gauge. What else can a high end power cable improve on?