screen is referring to the ground and noise shield.... in this case, built like a cross hatched screen.
https://en.wikipedia.org/wiki/Coaxial_cable The image the link, it is the ’B’ item that is the ’shield’ or ’ground’.
Both ground AND shield, in this case of a coaxial transmission line design. To reject RF and noise injection into the center conductor, which is the one carrying the intelligence or signal.
That ’signal’ is referenced to the ground/shield, likened to your riding a bike and the bike is referenced to the ground you ride on. (Bike no workee with no ground to ride on)
Something in the given case has to refer to a standard set point, and in this case it is carried by the ground, and acts doubly as a rejection of noise and interference.
Thus the ground can be referred to as a ’shield’, as well.
It, in conjunction with impedance functions..that..is about all we really need to know when applying to RF signals...grab the engineering bibles and apply, all will be fine.
But it is unbelievably inadequate when it comes to dealing with audio signals, which have the widest bandwidth and go from DC to extremely high (low RF) frequencies.
Audio...which is unique and is the probably the most complex of all in the domain of electrical AC signals and propagation. Impedance applies to audio cables about as much as the given relative speed of the moment..of a car --applies to the design of the entire car. It's applicable, minimally, yes... but relative to the whole package? No.
