The OP focused on inductance due to 40 meters of 18 g wire while only looking at the upper limit of the audio frequency range. My main point (which I didn't say directly) was he ended up ignoring the forest for the trees.
I appreciate your response. However, it is quite frustrating to ask a specific question and have it shot down because of reasons not relevant to the question. I did not ask a general question and needed to be reminded that these effects are negligible and I should look elsewhere. I asked a specific question because I am interested in a 40m length of AWG18 wire at 22kHz. If you take a 40m length of cable at 18kHz (which most people CAN hear) you will STILL find the inductive reactance to be greater than the resistance.
Using
https://www.eeweb.com/toolbox/parallel-wire-inductance/ for 22kHz:
R = 0.85 Ohms
XL = 2.25 Ohms
For 18kHz:
XL = 1.84 Ohms
I do not want to debate the merits of my question - I just want to understand:
1) Did I perform my inductance calculation correctly given these parameters?
2) If my calculations were correct and inductance is significantly larger than resistance for these parameters, why do people focus on wire thickness as inductance actually only gets worse the thicker the wire.
You also mention:
Straight speaker wire lacks an inductor coil, therefore the inductive reactance is insignificantly low, and the OP's original premise is wrong.
Which again is making assumptions about what I am trying to understand. You are very wrong if you believe two straight parallel conductors have no or insignificant inductive reactance. I just calculated it for you above - that is not a coil, it is just two parallel conductors. And it is greater than the resistance by a factor of more than 2. Whether it is relevant in an audio system is a separate question.
I never said capacitance is not an issue. In fact, I have previously calculated it using C = (pi * epsilon * l) / arcosh(d/(2a)), which gives 13.7pF thus it changes the impedance from 2.25 to 2.25012) and its effect is truly negligible (by a factor of approximately 10000 compared to inductance).
And lastly:
In my opinion, the OP is trolling and should be ignored. I'm sorry I didn't realize this sooner.
That is extremely rude. You have no basis for such a remark. You must be a millennial, with no manners.
The first link is probabally the most important link to show why the transmission line model does not work in audio frequencies. The bolded part should answer your question.
My understanding is that this article is mostly about wave propagation - something very important in transmission line design due to the extended lengths of the cables. In audio environments this is negligible because at 22kHz a quarter wavelength of light is 3.4km, which is way longer than typical cable runs - hence the reflection property of electromagnetic waves can be ignored.
There are much more aspects of transmission line analysis that are relevant to audio speaker cables. The fact that you have two conductors with opposing currents in parallel carrying low frequency currents are all the same. Therefore the inductance and capacitance analysis, including skin effect and proximity effect are all similar. That said, due to the shorter lengths these attributes are of course much more benign.
My intent with this post is to calculate just how benign it is, and not just take it on word of mouth.