I'm confused about how small audio signals are immune to interference. Headphone wires seems twisted but are they also differential signals?
As far as I know differential/balanced signals are carried by two wires and they are mirrored as shown here: https://upload.wikimedia.org/wikipedia/commons/thumb/e/e7/DiffSignaling.png/1200px-DiffSignaling.png
So the common mode noise is rejected.
But in headphone case the little headphone which goes to our ear is not a differential amplifier hence it is just an impedance. It DOES NOT subtract two incoming signals.
I accept my ignorance on the issue but couldn't find a clear explanation about this.
Lets say you have a smartphone or laptop and you plug your headphone to the device, what kind of signal is that audio signal passes through the vibrating earphones? And how come the wires reject the noise? Can this be shown with a simplistic circuit model?
I would be extremely glad if someone can reply these two point confuses me:
Premise: In below diagrams grounds are meant as analog signal grounds there is no earth involved. Imagine the circuits are in space to neglect confusion.
Sorry for the above quick hand drawn diagrams.
I. represents the original question. As you see the phone's headphone driver circuit has a GND which is connected to the one terminal of the headphone coil. So some say "no way to tell which, if any, of the lines is grounded". But there is ground. All phone circuit's analog ground is tied to the one terminal of the headphone. (?)
This is regarding diagram II above.
in A and B why B cannot reject the common mode noise? Isn't B similar to the headphone scenario in I ?