Subwoofer humming or buzzing: how to fix it
A steady low hum or buzz from a subwoofer — the kind that's there even with nothing playing and doesn't change when you turn the volume down — is almost never a broken sub. It's an electrical problem called a ground loop: two connected devices reaching earth by slightly different paths, and the difference leaks in as 60 Hz mains hum.
The good news is that ground loops are cheap and quick to fix once you've confirmed that's what you have. Work through the steps in order — most subwoofer hum is solved by the first three.
Diagnose and fix, in order
Confirm it's electrical, not the audio
Turn the volume all the way down and pause all audio. If the hum is still there and doesn't change with volume, it's a ground loop or power issue (this guide). If instead it's a buzz that gets louder with volume or only appears with certain content, that's a signal/cable problem — jump to the cable step.
Unplug the signal cable from the subwoofer
Leave the sub powered on but pull the RCA/LFE interconnect out of its input. If the hum stops, the noise is entering through the signal path — a classic ground loop between your sub and receiver. If the hum continues with only the power cord connected, the loop is elsewhere (or, rarely, it's the sub's own transformer — see escalation).
Put the sub and source on the same outlet
Plug the subwoofer and your receiver/amplifier (and ideally the whole system) into the same wall outlet or a single power strip. Sharing one ground point is the single most effective fix and resolves the majority of ground-loop hums for free. Avoid running the sub off a different circuit across the room.
Disconnect the TV's coax/cable line
If your system connects to cable TV or an antenna, temporarily unscrew the coax cable feeding the TV or receiver and listen. Cable/coax is the most common ground-loop path in a home theatre — if the hum vanishes, that's your culprit. Fix it permanently with an inexpensive coax (75-ohm) ground-loop isolator on that line.
Add a ground-loop isolator on the sub line
If same-outlet power doesn't fully cure it, fit a cheap inline RCA ground-loop isolator on the subwoofer's signal cable between the receiver and the sub. It breaks the loop while passing the audio. This is the proper fix — do not lift the sub's mains earth pin with a 3-to-2 'cheater' plug; it silences hum but defeats the safety ground.
Check the cable and its routing
A cheap, damaged, or unshielded RCA cable — or one run alongside mains power leads — picks up buzz. Reseat both ends, try a different quality subwoofer cable, and route the signal cable away from and across (not parallel to) power cords.
Rule out a mechanical rattle
If it's a physical buzz or rattle that tracks specific bass notes rather than a constant electrical hum, it's vibration, not a ground loop. Check for loose driver or grille screws, a port resonating, the cabinet touching a wall, and objects in the room rattling. Decouple the sub from the floor with isolation feet or a pad.
Frequently asked questions
Why is my subwoofer humming?
A constant hum that's present with no audio playing and doesn't change with volume is almost always a ground loop — an electrical difference between the sub and the device feeding it, leaking in as mains hum. It's not a fault in the subwoofer. Putting both units on the same outlet, checking the TV's coax line, and fitting a ground-loop isolator fixes the large majority of cases.
Why does my subwoofer hum even when nothing is playing?
Because the hum isn't coming from the audio signal — it's mains-borne. A ground loop injects 60 Hz (or 50 Hz) hum through the ground connection regardless of what's playing, which is exactly why it's there in silence and doesn't rise with volume. That behaviour is the telltale sign you have a ground loop rather than a bad cable or a blown driver.
How do I stop ground-loop hum on a subwoofer?
In order: plug the sub and the source into the same outlet; disconnect the TV's coax/cable line to test (add a coax ground-loop isolator if that's the cause); and fit an inline RCA ground-loop isolator on the subwoofer's signal cable. Don't use a 3-to-2 cheater plug to lift the mains earth — it works but removes a safety ground.
Is a humming subwoofer dangerous?
The hum itself is harmless — it's annoying, not a hazard. The one thing to avoid is 'fixing' it by defeating the mains earth (lifting the ground pin), which removes an important safety protection. Use a ground-loop isolator instead, which cures the hum without compromising the ground.
What's the difference between subwoofer humming and buzzing?
A steady hum that's independent of volume is electrical — a ground loop. A buzz or rattle that changes with volume or appears only on certain bass notes is usually mechanical (a loose part, port, or object vibrating) or a cable/connection fault. The volume test tells them apart: constant regardless of volume points to ground loop; changes with volume points to signal or mechanical.