Coaxial Audio Cables: Uses, Specs and the Digital Standard
Quick answer / TL;DR: Coaxial audio cables are 75-ohm shielded RCA cables carrying the S/PDIF digital audio stream – 2-channel PCM or a compressed surround bitstream. They run 10 m and beyond where optical is at its limit, seat more securely, and are the receiver's standard digital input alongside the optical port.
Coaxial audio cables are the workhorse digital interconnect of the home theater room: a 75-ohm shielded coax with RCA plugs carrying the S/PDIF stream between TV, receiver, player and DAC. They sit next to the optical TOSLINK port on every receiver, and they win more rooms than the fiber does.
This guide covers the uses, the one spec that separates a digital coax from an analog one, and the lengths where the cable stops being a question.
The Uses, in the Order They Show Up
| Use | Source | Destination | Why coax |
|---|
| TV audio to receiver | TV digital coax out | Receiver coax in | The run is long, the rack is clean |
| Cable box to receiver | STB coax out | Receiver coax in | The STB's digital out, one cable |
| Player to DAC | CD/SACD transport | Standalone DAC | The secure seat, bit-perfect |
| PC to receiver | USB DAC coax out | Receiver coax in | The optical port is taken |
| Console via TV | TV coax out | Receiver coax in | The TV's aggregated feed |
The pattern: coax is chosen when the run is longer than the fiber's comfort zone, when the connector seat matters more than the EMI immunity, or when the optical port is already committed to another source. Most rooms end up with both – coax to the cable box, optical to the TV, the two feeds sharing one receiver.
The Digital Coax Spec
75 ohms, shielded, RCA-terminated
The S/PDIF coax standard is 75-ohm impedance, a continuous shield (braid plus foil on the good cables), and full RCA terminations at both ends. The signal is a 0.5-volt square wave, and the impedance match is what keeps the bits clean: a 75-ohm cable into a 75-ohm input reflects almost nothing, and the stream arrives as it left.
The analog trap
The same RCA plug also carries analog stereo and composite video – the physical connector is shared, the electrical job is not. A digital coax cable is a shielded 75-ohm line; a cheap unshielded audio pair is not, and it will pass the signal at a meter and drop bits at five. The spec line that matters is the shield and the impedance, not the plug.
Lengths and the Practical Ceiling
1.5 m and 3 m cover the furniture-scale runs – receiver to the shelf, TV to the console. 5 m is the number where the optical fiber starts to feel its limit and the coax is still comfortable. 10 m is the routine ceiling for a good shield, and 15 m the stretch run that works when the shield is continuous and both RCA seats are full. Beyond 15 m, the path changes – the signal is repeated or the source moves – not the cable getting longer.
- 1.5-3 m: furniture runs, the default
- 5 m: the room-scale run where optical starts to strain
- 10 m: the across-the-room standard
- 15 m: the stretch run, shield quality is the spec
Choosing and Checking
- The jacket or spec says 75-ohm or digital audio – not just RCA
- Continuous shield: braid plus foil, intact terminations
- RCA plugs that seat fully – the friction fit is the failure point
- The source and destination both on the digital coax setting, not the analog stereo
- A test tone before the real session – the receiver's digital input is the thing being verified
Coaxial audio cables are stocked as 75-ohm shielded S/PDIF interconnects at 1.5 m to 15 m; the catalog lists the shield construction per part number.
Real-World Applications
The media wall: the 10 m run from the TV's digital out to the receiver on the opposite wall, the fiber at its limit and the coax in its element. The rack: the transport to the DAC on the same shelf, 1.5 m, the secure seat the fiber's shutter cannot match. The legacy receiver: both digital ins in service – coax to the cable box, optical to the TV, the room's two sources on one machine.
Related reading: The single-cable guide: the audio coax cable, specs and comparison — audio-coax-cable
Related reading: The PC side: the computer audio cable, all forms — computer-audio-cable
Frequently Asked Questions
What are coaxial audio cables used for?
Carrying the S/PDIF digital audio stream – 2-channel PCM or a compressed surround bitstream – between TV, receiver, cable box, player and DAC. They are the copper digital interconnect of the home theater room, the standard alternative to the optical TOSLINK cable, and they win the longer runs and the more secure connector seats.
Are coaxial audio cables the same as regular RCA cables?
The plug is the same, the cable is not. A digital coax must be a 75-ohm shielded line; a thin unshielded RCA audio pair shares the connector but not the electrical job, and it drops bits on the longer runs. Check the spec for 75-ohm or digital audio before trusting the RCA plug.
How long can a coaxial audio cable run?
10 m is the comfortable number for a good 75-ohm shielded coax, 15 m the routine stretch run. Beyond that, the path changes rather than the cable growing – the signal is repeated or the source moves. Furniture runs are 1.5-3 m, room-scale runs 5 m, across-the-room 10 m.
Coaxial or optical for digital audio?
They carry identical S/PDIF data. Optical is immune to ground loops and EMI because light carries no metal path; coax reaches farther and seats more securely. Short clean run with grounding quirks – optical. Long run or a connector that keeps missing its seat – coax. Most rooms end up using both.
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