A subwoofer that hums or buzzes when nothing is playing is one of the most common complaints we hear about, and the good news is that it’s rarely a faulty sub. Nine times out of ten it’s a ground loop, and you can usually fix it in a few minutes without buying anything. Here’s how to track it down.
- Plug the subwoofer and your receiver (or TV/soundbar) into the same power strip.
- If you have cable or satellite TV, unplug the coax from the box. If the hum stops, fit a coax ground isolator.
- Still humming? Try an RCA ground loop isolator on the sub cable.
First: what kind of noise is it?
| Sound | Likely cause |
|---|---|
| Steady low hum (a deep “mmmm”) | Ground loop |
| Buzz that changes with lights or appliances | Electrical interference or dimmer switch |
| Hiss with your ear near the driver | Normal amplifier noise |
| Buzz only when bass plays | Rattle or damaged driver (see below) |
| Hum even with the RCA cable unplugged | Fault in the sub’s amplifier |
Step 1: unplug the RCA cable
With the sub powered on, disconnect the signal cable from the sub. If the hum stops, the problem is in the connection to your other equipment (almost certainly a ground loop). If the hum continues with nothing connected, the sub’s amplifier may be faulty; check the warranty.
Step 2: fix the ground loop
A ground loop happens when two devices are earthed through different outlets and also connected by a cable shield. A small current flows around that loop and you hear it as hum at the mains frequency (60 Hz in North America, 50 Hz in Europe and elsewhere).
- Same outlet: plug the sub and receiver into the same power strip or wall socket.
- Cable/satellite TV: the coax often brings in a separate ground. Unplug it to test; if the hum stops, use a coax ground isolator.
- RCA isolator: an inline ground loop isolator between receiver and sub breaks the loop.
- Go wireless: a wireless subwoofer kit removes the cable entirely.
Safety: never use a “cheater” plug or remove the earth pin from a power cable to stop hum. The earth is there to protect you.
Step 3: check the cable and its route
- Try a different, well-shielded RCA cable.
- Keep the sub cable away from power cables, or cross them at right angles.
- Avoid very long runs; see subwoofer cables and wiring.
Step 4: look for interference sources
Dimmer switches, LED drivers, fridges and some phone chargers can inject noise. Turn things off one at a time to find the culprit.
Step 5: rule out rattles
If the noise only appears when bass plays, it’s probably something vibrating, not hum. See how to fix subwoofer rattling, and if you suspect the driver, signs of a blown subwoofer.
FAQs
Is a little hiss normal?
Yes. With your ear right next to the driver, a faint hiss is normal for most powered subs. You shouldn’t hear it from your seat.
Why did the hum start after I added a new device?
The new device has probably created a new ground path, often through an HDMI or coax cable. Plug everything into the same power strip first.
Will a ground loop damage my sub?
No, it’s an annoyance rather than a danger. But a hum that remains with nothing connected may indicate an amplifier fault.