davedotco said:
There is no electrical reason for balanced (or unbalanced) to be shielded, they work fine either way.
Shielding a cable is to prevent random electrical fields from getting onto the signal and causing noise, in electrically noisy environments thay may be of some benefit. Think of the output of a typical microphone, similar in level to the output of a mm phono cartridge being sent through 30ft of cable across the studio floor, very different environment to a home hi-fi.
Many hi-fi cables use a co-axial construction, single centre conducter for the signal and a screen which also carries the 'return' signal. Given that this is an alternating current music signal, it is hard to see how this construction can keep noise out of the signal return.
I am afraid Dave is wide of the mark here.
Although the two conductors in a screened cable do form a circuit, it is better to think of the screen as being stationary and the centre conductor swinging positive and negative relative to this stationary point. The screen is called 'ground' for a reason, in many systems it is actually connected to the earth lead in the plug, and then on to a ground rod at the nearest transformer.
Thinking of the screen in the cable as a stationary ground now makes sense as to its function - it forms an eathed Faraday cage around the signal lead, protecting it from stray EM fields that would introduce noise. Unscreened cable will work as a low level interconnect, but anything except the shortest run will pick up mains and hum.