Hi, I found this on a website:
"A cable becomes a transmission line when it has a length greater than λ/8 at the operating frequency"
I've calculated 1.356 Inches for 10khz signal(but this was airborne audio frequency), and headphone cable is longer than 1/8 of this.
How do you calculate the electrical signal wavelength?
You need the speed signal speed. The speed of sound in air is irrelevant. In this case, the speed of propagation of an electrical signal in an insulated copper wire is typically about 1/2 the speed of light in a vacuum. The speed of light is about 300,000,000 m/s (3*10^8). for a 20 kHz signal, the λ/8 length is (1/2) * 3*10^8 [m/s] / 20*10^3 [1/s] * (1/8) = 0.9375 kilometers
So, like i said, transmission line effects in cables are complete and utter nonsense unless you're trying to use kilometer-length cables.