...how would you isolate the general characteristics directly due to shielding, or lack thereof?
Tholt - I agree with you that the best way to know this would be to have two cables of identical design, except one shielded and the other unshielded. An even better experiment would be to have several pairs of cables of varying designs, each pair consisting of a shielded and an unshielded version. That would be a good way to determine if "openness" were a typical characteristic of unshielded cables.
Having said that, I arrived at this (admittedly tentative) conclusion through a different route: I owned a number of unshielded cables. Other than the fact that they were all unshielded, the cables varied in design (copper/silver, stranded/solid core, single wire/multiple runs, different terminations, etc.). Because the absence of shielding was the only design feature they all seemed to have in common, I was inclined to conclude that their common characteristic of "openness" was attributable to the absence of shielding. But I recognize that this conclusion could easily be wrong.
I tend to think of "openness" as correlating with upper treble extension. For a line level interface, what would maximize upper treble extension (or at least minimize any degradation of it) would be low cable capacitance...
Al - In light of this, are there any generalizations about the typical effects of shielding on cable capacitance? Does shielding diminish capacitance?
And I should add that, while the characteristic of "openness" is partly a matter of high frequency extension, I feel like there's more to it. I don't exactly know how to describe what the "more to it" is, except to say that the sound of "openness" is also a matter of PRaT and imaging. I wish I could be more precise about it - I recognize that "openness" is a metaphor, and a rather vague one at that.
Bryon