Refer to my post, dated 09-18-2022 at 09:32am (Indiana time)
This one?
@holmz -
Maxwell's equations weren't wrong, but: there's much more involved*, when we're dealing with retaining a plethora of frequencies/voices (instrumental and vocal), ambient/room information (height, width, depth) and placement of the afore mentioned voices, within that space. (iow: much more sensitive info, than what's contained in DC or AC).
The electrical signal has no idea about the placement of musicians in a room.
And the plethora of frequencies are all <20 kHz, which is not like MHz or GHz, where transmission line theory is used.
The author in the link you provided below says so.
Even those involved in manufacturing PC boards for more the more sensitive RF systems, take into account the variables involved when choosing materials, as signal speed is dependent on their dielectric constants and possible frequencies to be encountered.
Ok we can talk about dielectric constants.
We've engaged in this conversation before, so: I suspect your queries to be more argumentative, than inquisitive. Hence: this post is more for those extant, that are genuinely interested in the Physics of what's what with our wires.
If I'm wrong: my apologies!
"But what part of a stereo systems is like a transmission line?"