The geometry of a cable matters more than most folks realize, and less than cable manufacturers want you to believe.
Stan and I spent a good chunk of the early 1970s wiring up prototype circuits with whatever cable we could scrounge. Back then, nobody in our little corner of high-end audio was agonizing over whether their RCA interconnects used coaxial construction or shielded twisted pair. We just grabbed some decent coax, soldered on the connectors, and got back to listening. It took years of building and measuring before I truly appreciated how cable geometry affects the signal riding inside it.
Coaxial cable is elegant in its simplicity. You have a center conductor surrounded by a dielectric, wrapped in a shield that doubles as your return path. The geometry gives you a consistent characteristic impedance and excellent rejection of external interference. For single-ended RCA connections, coax is a natural fit because the signal and return paths are concentric, keeping the electromagnetic field neatly contained. This is why most well-designed RCA interconnects are fundamentally coaxial in nature, even when they dress it up with fancy braiding on the outside.
Twisted pair, on the other hand, was designed for balanced signal transmission where both conductors carry equal and opposite signals. The twist cancels out electromagnetic interference picked up along the run. In a balanced XLR connection, twisted pair is ideal because the differential receiver at the far end rejects any noise common to both conductors. But in a single-ended RCA application, you lose that common-mode rejection advantage because there is no differential receiver. The twist becomes mostly cosmetic. You are essentially running an unbalanced signal through a balanced cable topology, and the benefits of the geometry largely evaporate.
That said, a shielded twisted pair used as an RCA interconnect is not necessarily worse than coax. It simply is not leveraging its main advantage. The shield still provides noise rejection, and the cable can sound perfectly fine if the conductors and dielectric are quality materials. What actually matters more than the twist-versus-coax debate is conductor purity, dielectric constant, shield coverage, and connector quality. I have heard superb-sounding cables in both configurations and terrible ones in both as well.
The honest truth is that cable geometry is one variable among many, and probably not the one that should keep you up at night.
If you are shopping for RCA interconnects, listen to a few candidates from trusted manufacturers like Audioquest and Kimber in your own system and trust what you hear. A well-made coaxial interconnect and a well-made shielded twisted pair will both get the job done. The differences between good and bad cables have far more to do with materials and construction quality than whether somebody twisted the conductors or kept them concentric.
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