What's better, one conductor or two conductors for an RCA interconnect?

I’ll second what @kijanki wrote. I have never encountered RCA connectors used with coaxial cables. I would expect coaxial cables to use BNC connectors, as I think someone else mentioned. The higher end cables, such as those that came from the factory with my Musical Fidelity turntable, are marked with a directional arrow, which I’m assuming points in the direction of the signal. It also denotes, for me, that the shield is only connected at the phono stage, not the turntable. The turntable does not have a three-conductor line plug 🔌 (which is a good thing to me), it uses a wall wart.

The other thing to consider when selecting cables (aside from whether or not it is shielded), is its impedance rating in Ohms. Cables using the same connectors have different impedance ratings for use in either analog or digital applications. I can’t recall the values off the top of my head, but they will each ‘work’ in place of the other, but the energy transfer is not optimal and shouldn’t be considered for permanent installation. The same distinction holds true for XLR connectors; analog applications (I.e. ‘balanced’ connections) cables have impedance ratings which are different than those cables used in digital cables (I.e. AES/EBU connections).

More experienced or knowledgeable members are free to correct or explain further the reasons for the difference I describe.

If you’re purchasing cables, I would avoid coaxial cables using RCA connectors, if you are contemplating making your own, I would buy at least two-conductor shielded cable (I like Mogami), and consider using four conductor cable (twisted pair) together with the best connectors you can find. I have found good prices and fast delivery from B & H Photo, but would probably consider using one of the specialized cable companies mentioned on this forum the next go-round.

Hope this helps

Blue Jeans Cable recommends coaxial cables for subwoofer, stereo audio, digital audio, etc.  They state that, “The most important attributes of a line-level unbalanced audio cable are (1) shielding, and (2) capacitance. Heavy shielding protects audio signals from interference from outside sources. LC-1 Audio Cable uses a heavy double-braid shield, with one bare copper braid laid directly over another for extreme high coverage and high conductivity to ground; this is the identical shield configuration to Canare LV-77S, which tested best in our review of audio cable hum rejection characteristics (LC-1 hadn't been designed yet so wasn't tested at that time). By shrinking the center conductor to 25 AWG and foaming the polyethylene dielectric, we were able to get capacitance down to an extremely low 12.2 pF/ft, much better than LV-77S at 21 pF/ft. Capacitance can be important, particularly in long cable runs, because it contributes to rolloff of higher frequencies.”

https://www.conch-house.com/best-rca-cables-audiophile/

these are assorted RCA cables. All have a positive and a negative. I’m not sure I’ve ever seen a a RCA cable that doesn’t use both.

All the best.

optimize and oldrooney I learned a bit from both of your responses. I have a purely digital system (can't afford analog). My integrated amp has three connection options (no XLR go figure) so for the fun of it, I have my CD player connected via line stage, coaxial, and optical. Switching between the three my 75 year old ears cannot distinguish the difference between optical and coaxial through my system, the analog line stage as you would expect is inferior to both. 

I was under the impression XLR was the best followed by coaxial, optical, and then line.  

@tcotruvo, coaxial cable is also the cable of choice in almost any scientific application. My understanding is it is better for electrostatic noise rejection but there may be circumstances where shielded twisted pair is better for magnetic. I am going off memory here. It depends on the shape of the noise field. Primary reason for not using co-axial is it is difficult to work with and maintain its properties.

I would expect you would have to have pretty long runs before cable capacitance became important. I am sure there are some bad tube products that could have issues.