RCA Cable Length: The Unbalanced Distance Question
Quick answer / TL;DR: Short answer: keep RCA line-level runs under about 3 metres where possible, and treat 5 metres as the practical limit for most consumer equipment. Subwoofer runs tolerate more length because the signal is low frequency, so 10 metres with a well-shielded cable is usually fine. Beyond that, use a balanced connection or move the equipment. If hum appears after lengthening, suspect a ground loop rather than the cable.
Same plug, three builds: the ring contact is what wears first.An RCA connection is unbalanced: one conductor carries the signal and the shield carries the return. That arrangement works well over short distances and degrades predictably as the cable lengthens.
Two mechanisms act together. Capacitance per metre accumulates and rolls off high frequencies depending on the source impedance, and the longer cable picks up more interference because there is no common-mode rejection.
What Length Does
The figures below assume typical cable capacitance of about 100 pF per metre and a source impedance in the low kilohms.
| Length | Capacitance | Effect | Suitability |
|---|
| 1 m | about 100 pF | none | any use | 3 m | about 300 pF | negligible | fine | 5 m | about 500 pF | slight roll-off with high impedance sources | acceptable | 10 m | about 1 nF | audible with some sources | only for low-frequency signals | 20 m | about 2 nF | measurable, hum likely | not recommended |
The source impedance is the other half of the filter. A low-impedance output drives capacitance comfortably, while a high-impedance one does not, which is why the same cable behaves differently on two devices.
Subwoofer Runs Are Different
A subwoofer carries only low frequencies, so the high-frequency roll-off caused by capacitance is irrelevant. The limiting factor becomes interference and ground loops.
- Use a shielded cable designed for the purpose rather than a thin audio lead
- Keep the run away from mains cable where the route allows
- A ground loop isolator resolves hum that appears when both devices are earthed
- Long runs are acceptable if the shielding is adequate
- Check the subwoofer's input sensitivity before choosing level
Real-World Applications
Turntable to amplifier
Phono signals are low level and the cable capacitance forms part of the cartridge load, so this run must be short. Extending it changes the frequency response in a way that is measurable.
Subwoofer across a room
A 10 metre shielded run is usually fine because the signal is low frequency. The risk is hum rather than high-frequency loss.
Second zone from an amplifier
Long runs to another room are better served by a balanced connection or by a wireless link. An RCA run of 15 metres invites both hum and roll-off.
Where a long RCA cable is defensible
A powered subwoofer with good shielding, kept away from mains wiring. In that specific case the electrical objections are largely removed.
Related reading: Extending an RCA connection — blogs/news/rca-extension-cable
Related reading: Choosing RCA cable by construction — blogs/news/rca-cable-guide
Standards and Verification
The RCA connector is dimensioned in IEC 60130-8. Line-level audio conventions place output around 1 to 2 volts into an input impedance of 10 kilohms or more, and the interaction between cable capacitance and source impedance sets the roll-off.
Verify by comparing a short cable with the long one on the same material. A loss of high-frequency detail or a rise in hum identifies the cable length as the cause rather than the equipment.
Measure capacitance if the specification matters. A meter with a capacitance range gives a figure that can be compared with the source impedance to estimate where the roll-off begins.
Do not coil excess cable tightly against a power supply. The coil concentrates the coupling, and the resulting hum is often attributed to the equipment rather than to the installation.
Frequently Asked Questions
How long can an RCA cable be?
About 3 metres for critical listening, with 5 metres as a practical limit for consumer equipment. Subwoofer runs can be longer because the signal is low frequency.
Does a longer RCA cable reduce bass?
No. Capacitance affects high frequencies. Bass loss is more likely to be a level or impedance issue.
Why does a long RCA cable hum?
Interference pickup and ground loops. The unbalanced format has no common-mode rejection, so length increases susceptibility.
Is a subwoofer cable different from a normal RCA cable?
It is usually better shielded. The electrical requirement is otherwise similar, and the low frequency content makes capacitance less critical.
Can I use a long RCA cable for a turntable?
No. Phono signals are low level and capacitance-sensitive, and the cable forms part of the cartridge load.
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