Hi Bryon,
My opinion is that the case for shielding is strongest when it comes to unbalanced interconnects, both line level and phono level.
In the case of unbalanced line level interconnects, signal return currents flow in common with extraneous inter-chassis noise currents which will be present to some degree due to ground-loop effects, as explained in this paper. Since the receiving component cannot distinguish between signal and noise that may be present at its input, the voltages corresponding to those extraneous currents in the return conductor must be minimized. That means minimizing the impedance of that connection path, which in turn will be accomplished by a quality shield, but not necessarily by unshielded configurations. And certainly not by a cable configuration in which the return conductor is a simple piece of wire, which will have substantial impedance at high frequencies due to its inductance, and perhaps also higher impedance at low frequencies due to higher resistance.
As explained in the reference, an important factor in all of that is stray capacitance in the power transformer of each component. Which means that the magnitude of this effect will be system-dependent and unpredictable.
Shielding will also, as others have said, reduce noise pickup caused by rfi/emi effects, which is particularly important in the case of unbalanced interfaces due to their poor common mode noise rejection capability, and in the case of phono level interconnects due to the low signal levels that are involved.
That said, it's always been a mystery to me how, in particular, Anti-Cables unbalanced interconnects, which use a coiled piece of wire as the return conductor, apparently perform very well for many users.
All of the foregoing considerations are pretty much inapplicable to balanced interfaces, as you will realize, and so I would expect shielding to be less important for balanced interconnects.
And I would expect it to be unimportant for speaker cables, with the inter-chassis noise current consideration being inapplicable to a passive speaker, and because sensitivity to emi/rfi effects is lessened by the low impedances and relatively high signal levels that are involved. Although I do recall one thread from some time ago in which an rfi problem was resolved by changing the speaker cables.
Best regards, and happy new year!
-- Al
My opinion is that the case for shielding is strongest when it comes to unbalanced interconnects, both line level and phono level.
In the case of unbalanced line level interconnects, signal return currents flow in common with extraneous inter-chassis noise currents which will be present to some degree due to ground-loop effects, as explained in this paper. Since the receiving component cannot distinguish between signal and noise that may be present at its input, the voltages corresponding to those extraneous currents in the return conductor must be minimized. That means minimizing the impedance of that connection path, which in turn will be accomplished by a quality shield, but not necessarily by unshielded configurations. And certainly not by a cable configuration in which the return conductor is a simple piece of wire, which will have substantial impedance at high frequencies due to its inductance, and perhaps also higher impedance at low frequencies due to higher resistance.
As explained in the reference, an important factor in all of that is stray capacitance in the power transformer of each component. Which means that the magnitude of this effect will be system-dependent and unpredictable.
Shielding will also, as others have said, reduce noise pickup caused by rfi/emi effects, which is particularly important in the case of unbalanced interfaces due to their poor common mode noise rejection capability, and in the case of phono level interconnects due to the low signal levels that are involved.
That said, it's always been a mystery to me how, in particular, Anti-Cables unbalanced interconnects, which use a coiled piece of wire as the return conductor, apparently perform very well for many users.
All of the foregoing considerations are pretty much inapplicable to balanced interfaces, as you will realize, and so I would expect shielding to be less important for balanced interconnects.
And I would expect it to be unimportant for speaker cables, with the inter-chassis noise current consideration being inapplicable to a passive speaker, and because sensitivity to emi/rfi effects is lessened by the low impedances and relatively high signal levels that are involved. Although I do recall one thread from some time ago in which an rfi problem was resolved by changing the speaker cables.
Best regards, and happy new year!
-- Al