In article , Ralph D.
writes

I need a cable (ideally about 20ft), stereo 3.5mm male/male, highly shielded
to connect my audio source to a transmitter across a room. This cable passes
many sources of interference, so the shielding is critical.

Off-the-wall suggestion: run them through a length of copper pipe or
through that flexible metal conduit used in electrical installations?

You'd probably want to earth (ground) just one end to be sure a ground
current didn't flow, causing interference.

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