A subwoofer that hums, or that sounds soft and slow no matter where the crossover is set, usually gets blamed on the amplifier or the room. The cable is rarely the first suspect, which is exactly why it is often the last thing fixed. A line-level low-frequency run is short and narrow in bandwidth, so it fails quietly: a little hum here, a little loss of grip there. The fix starts with impedance and shield design, not with a more expensive amplifier.
Quick answer: Specify a 75 ohm coaxial cable for subwoofer runs and use the shield as the signal return. RG-6 with a copper braid plus foil shield is the safe default up to roughly 10 m; RG-59 is acceptable on patch leads under 3 m but has higher loss and thinner shielding. For runs beyond 15 m, move to RG-11 or to shielded twisted pair with a balun at each end. Never route unbalanced coax beside mains cable.
Coaxial Cable for Subwoofer: Why 75 Ohm Matters for Bass
What a subwoofer coax run actually carries
A powered subwoofer takes a line-level signal, typically under 200 Hz and often below 2 V RMS, from an AV receiver, a preamplifier, or a DSP. The bandwidth is narrow and the voltage is small, so a poor cable almost never produces obvious distortion. It shows up instead as hum, as a buzz that rises with gain, or as a loose bottom end that no crossover setting repairs.
The parameters that decide the result are the same as in any 75 ohm coaxial line: characteristic impedance, shield coverage, and the resistance of the return path. A room-scale LFE run is short compared with a video run, so attenuation is seldom the limiting factor. Interference pickup and ground reference are.
Why 75 ohm impedance is a system value, not a marketing label
Characteristic impedance comes from geometry: the diameter of the center conductor, the dielectric constant of the insulation, and the spacing to the shield. 75 ohm is the nominal value used across unbalanced video and digital audio interfaces, including composite video, S/PDIF coaxial, and the LFE output on consumer AV gear. A cable described as 75 ohm is not equally 75 ohm at every frequency, which is why an impedance figure without a frequency range tells a buyer very little.
Mismatch matters most where the run is long and the signal is wideband. A subwoofer channel is neither, so a modest mismatch will not audibly change the low end. What does change the result is the shield, and what follows from it: where the return current actually flows.
Shielding, hum, and the return path
Hum in a subwoofer run is nearly always a shield problem rather than a conductor problem. A foil layer bonded to a braid gives high coverage at radio frequencies and keeps the assembly thin; a dense braid is more flexible and survives repeated handling in a rack. The cheapest assemblies use a sparse spiral shield that passes a bench test and then picks up noise once a rack is filled with switching supplies, LED drivers, and a wireless router.
Ground loops deserve their own paragraph. When the subwoofer and the receiver sit on different circuits, the shield carries a small current at mains frequency. A ground-loop isolator or a transformer-coupled input solves that; a heavier cable does not. Diagnose the loop before replacing hardware.
Keep the run away from mains cable and from the back panel of a large display, and keep it as short as the room layout allows. Where a long run is unavoidable, shielded twisted pair with a balun at each end usually behaves better than stretching a single coax for the same budget.
Which coaxial cable should you use for a subwoofer run?
Match the cable to distance and environment, not to the price on the label. The table below is the selection matrix we use when a customer asks for an LFE assembly without giving a length.
| Cable | Nominal impedance | Center conductor | Shield | Sensible line-level run |
|---|---|---|---|---|
| RG-59 | 75 ohm | Stranded or solid, about 0.6 mm | Braid, frequently sparse | Up to 3 m; patch leads |
| RG-6 | 75 ohm | Solid copper, about 1.0 mm | Foil plus braid with drain wire | 3-10 m; the general default |
| RG-11 | 75 ohm | Solid copper, about 1.6 mm | Foil plus dense braid | 10-25 m in-wall |
| Shielded twisted pair plus balun | 100 ohm pair, matched at both ends | Two insulated conductors | Overall foil or braid | 15-50 m with transformers |
| Thin audio-grade RCA lead | Not specified by maker | Small stranded | Spiral, low coverage | Under 1 m; avoid in racks |
Two rules sit behind that table. First, larger center conductors lower series resistance and loss, which is why RG-6 and RG-11 travel further than RG-59. Second, shield construction decides noise performance, and it is the specification most often left off a quotation. If the buyer only names a connector type, quote the shield and the conductor material alongside it.
Does cable length really change subwoofer sound?
Length changes capacitance and series resistance, and neither behaves the way audiophile folklore suggests. Capacitance rolls off high frequencies, and a subwoofer channel has almost none to lose, so a longer cable does not dull the bass. Series resistance only matters when the input impedance it feeds is low; a line-level subwoofer input is typically 10 kohm or higher, so even a 30 m RG-6 run adds negligible loss.
The real limits on length are interference pickup, the ground potential difference between two pieces of equipment, and the physical handling of a stiff cable. Bandwidth is not the constraint. That is a useful point in a quotation discussion, because it moves the conversation from cable length to shield quality and installation practice, where the buyer can actually solve the problem.
Three installations where the cable decision changes the outcome
- Living-room AV rack. A receiver feeds one subwoofer 2 m away through a thin patch lead. Any reasonable shielded coax works, and the priorities are connector grip and strain relief so the assembly survives being pulled out for cleaning.
- Studio control room. A 12 m in-wall run reaches a soffit-mounted subwoofer. Here RG-6 with foil plus braid or RG-11 is the right family, and the cable should be separated from mains runs and from dimmer wiring on the same wall.
- Bar or venue with four subs. One DSP drives multiple subwoofers on separate circuits, which is a textbook ground-loop layout. Star the runs from a single distribution point, use isolators where circuits differ, and keep every assembly the same length so levels stay predictable.
Connectors, adapters, and the last meter
An RCA plug is a compromise connector: the shield leaves the body well before the mating surface, so the final centimetres of an unbalanced run are rarely a clean 75 ohm. Use crimp or compression connectors on RG-6 instead of screw-on types, and keep adapter chains short. A passive Y-splitter feeding two subwoofers changes both the load and the level seen by the source, so use a buffered distribution output when the receiver offers one.
Direction also matters once an active part appears in the chain. A passive adapter is bidirectional, but a line-level transformer or an isolator has a defined primary and secondary, and reversing it lowers level and raises hum.
OEM notes for LFE and line-level assemblies
On a production order, specify shield coverage, conductor material, and connector plating rather than a trade name. Copper braid over a foil layer, an oxygen-free copper center conductor, and gold-flashed contacts over a nickel underplate cover the great majority of LFE and line-level applications. Where an assembly is repeatedly flexed in a rack, a stranded center conductor with a flexible braid outlasts a solid conductor with foil only. Add moulded strain relief and a colour band if one harness handles LFE, left, and right.
Test every assembly for continuity and for shield-to-center shorts before packing, and leave the shield connected at both ends for consumer line-level gear. Lifting the shield at one end is a cure for specific ground-loop cases, not a default build instruction.
For adjacent analog audio work, the same 75 ohm logic carries over to coaxial audio cables, and the matching speaker-side guidance sits in our guide to speaker cable gauge and run length. Most subwoofer boxes and receivers terminate in an RCA jack, so if you are choosing between assemblies, our notes on RCA jack stereo cables complete the picture.
FAQ
1. Does a subwoofer cable have to be 75 ohm?
Yes, for unbalanced consumer runs. The receiver output, the cable, and the subwoofer input are designed around a 75 ohm system, and 75 ohm coaxial cable is what keeps that consistent. A cable of unspecified impedance will still pass low frequencies, but it offers no guaranteed shield geometry, so it is a poor choice in a rack where interference is present.
2. Is RG-6 better than RG-59 for a subwoofer?
For anything beyond a short patch lead, yes. RG-6 has a larger center conductor and lower loss, and it is normally built with a foil layer plus braid, which gives better coverage than the sparse braid typical of RG-59. RG-59 remains fine for a short receiver-to-subwoofer link where the cable is not run near mains wiring.
3. How long can a subwoofer cable be before sound quality drops?
Length is rarely the limiting factor, because the channel carries very little bandwidth and feeds a high impedance input. Practical limits are noise pickup and ground potential differences, which usually appear beyond about 15 m in an untreated installation. RG-11 or shielded twisted pair with baluns is the usual answer for long in-wall runs.
4. Why does my subwoofer hum when nothing is playing?
Most cases are ground loops or a damaged shield. If the hum stops when the cable is unplugged at the receiver, the loop runs through the shield and a ground-loop isolator or transformer-coupled input will fix it. If the hum persists with the cable removed, look at the amplifier and the mains circuit instead.
5. Can I use an ordinary video cable as a subwoofer cable?
If it is a true 75 ohm coaxial cable with a foil or braid shield and RCA ends, it will work electrically for a line-level run. The risk is mechanical and documentary: video patch cables often use thin conductors and low coverage shields, and their connectors are not built for repeated plugging. Use them temporarily, then fit a purpose-built assembly.