The RGxx cable numbering system is ancient and obsolete.
Audio and EMI/RFI expert Jim Brown writes:
RG-numbers have not been a spec for half a century. They are a generic descriptor, telling us Radio Frequency Characteristic Impedance and approximate outside diameter, and nothing more. Rather, we should be specifying (or talking about) a particular part number from a particular manufacturer. My last print copy of Belden's catalog is probably 15 years old. It lists fifty two RG59 cables, sixty four RG6s, eighteen RG8s, and thirty two RG11s.
Contemporary MIL specs use a very different numbering system.
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While some cables that meet the RG6 spec are suitable for audio there are other that are only suitable for cable TV signals.
Stick with major cable manufactures like Belden, Canare and Mogami.
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Note that many excellent, suitable bulk cables, cost less than $2.00 per foot.