Direct answer
For the Sonos Sub (Gen 3), source balance, mono/accessibility, cable/earbud contact, pairing and driver hardware should be separated. First, swap ears/channels and test another source.
What this covers
- Sonos Sub (Gen 3) (Sub Gen 3)
- Sonos product; Wi-Fi/Ethernet, Bluetooth, voice, home-theater and line-in capabilities vary.
- The specific fault this record addresses: plays from only one side or channel
What it does not cover
- ×The same symptom on a different Sonos product line, which has its own record and its own cited source
- ×An on-screen error code whose meaning has not been checked against this exact model's manual
- ×Live electrical, gas, sealed-system, internal battery-cell or structural repair — a technician boundary, not a self-service step
Differential
What actually causes this, and how to tell them apart
These are ordered by how often each one is the answer, not by how easy it is to try. The point of the middle column is that two causes producing the same headline symptom rarely produce the same detail — that detail is what tells you which one you have before you change anything.
- 1
The balance control has been moved
What separates it One side is quiet on every accessory and every app, not just this one.
How to confirm Both iOS and Android have an audio balance slider in accessibility settings that is easy to move by accident and affects everything. Check it before assuming hardware.
- 2
Channel assignment or a surround setting is wrong
What separates it One channel silent on a soundbar or a grouped speaker set.
How to confirm Check the channel or stereo-pair assignment in the app, and test with a known stereo source. A speaker assigned as a surround or a pair member will deliberately play only part of the content.
- 3
The source is sending stereo rather than surround
What separates it Rear or surround speakers silent on some content while the front stage plays normally.
How to confirm Surround speakers only carry content that exists in the surround channels. A stereo source genuinely has nothing to send them, and many broadcasts and apps are stereo despite the system being capable of more.
- 4
A speaker has dropped off the network rather than gone silent
What separates it One speaker missing from the group entirely rather than playing quietly.
How to confirm A speaker that has lost its network connection disappears rather than playing wrongly. See disconnects and multiroom.
- 5
Room calibration has been run with the speakers in different positions
What separates it One side consistently quieter after the speakers were moved.
How to confirm Calibration sets per-speaker levels for where they were at the time. Re-running it after any move restores the intended balance.
Before you touch a setting
Record this first — changing settings destroys the evidence
Every item below stops existing the moment a reset, re-pair or settings change is made. Written down first, they are what separates the causes above; recovered afterwards, they are guesswork.
- Whether the same physical side is always affected, or whether it swaps.
- Whether the problem persists with a different source device and a different app.
- Whether the accessibility balance slider is centred.
- Whether the silent side is completely silent or just quiet and muffled.
Check the audio balance slider in the phone's accessibility settings
ReversibleIt affects every accessory and every app, is easy to move by accident, and is free to rule out.
Test with a different source and a known stereo track
ReversibleSome recordings and some app settings genuinely play to one channel.
Check the channel or stereo-pair assignment in the app
ReversibleA speaker assigned as a surround or as one half of a pair will play only part of the content by design.
Test with content known to be in surround, not stereo
ReversibleSurround speakers carry only what exists in the surround channels, and a stereo source genuinely has nothing to send them.
Confirm every speaker is still present in the app
ReversibleA speaker that has dropped off the network disappears rather than playing quietly, which is a different problem.
Re-run room calibration if any speaker has been moved
ReversibleCalibration sets per-speaker levels for the positions they were in at the time.
Model-specific
What is true of this model and not of its siblings
Generic advice for the product line fails here. Each item below is a property of this specific model family that changes which of the steps above apply to you.
- Model scope
- Sub Gen 3. Sonos product; Wi-Fi/Ethernet, Bluetooth, voice, home-theater and line-in capabilities vary.
- Type — wireless subwoofer (mains-powered)
- A mains-powered wireless subwoofer that bonds to a Sonos soundbar or speaker pair over WiFi to add deep bass. It has no battery and no standalone function — it only works bonded to another Sonos product in the app.
- Bonding
- 'No bass / Sub not working' is usually the bonding: confirm the Sub is added to the same room as the soundbar in the Sonos app and is on WiFi. It must be assigned to a soundbar/speaker to do anything.
- Placement & level
- Sub bass is adjustable in the app; a Sub in a corner sounds boomier. If bass seems wrong, run/adjust the level and Trueplay tuning rather than assuming a fault.
- Symptom boundary
- This record covers Sonos Sub (Gen 3) when it plays from only one side or channel. A different symptom on the same hardware, or this symptom on a different Sonos product line, has its own record with its own causes and its own cited source.
Stop boundary
When this stops being a self-service repair
Continuing past any one of these costs more than the repair saves — in safety, in warranty, or in evidence a technician needs.
- !Do not push anything into an earbud's sound outlet to clear it — use the manufacturer's cleaning method, since a punctured mesh cannot be repaired.
Evidence ledger
Sources behind this answer
Visible sources support the visible claims. Home Product Support records the publisher, the fact used and the review date; community reports can suggest an issue but do not become a published fact on their own.
Where the manufacturer's article stops. Sonos publishes this as "Low audio from surround speakers when listening to music". Sonos' article on one channel or side playing quietly or not at all in a home-theater set. Probed 2026-08-21: title-verified. What that article does not carry is the model boundary — it is written for a product line, and Sub Gen 3 is the scope applied here. Where a control label, terminal, indicator pattern or reset sequence differs on your unit, the manual for that exact model is the authority, not this page and not the article.
Exact questions
Common follow-ups
My Sonos Sub isn't producing any bass.+
The Sub only works when bonded to a Sonos soundbar or speaker pair, so first confirm in the Sonos app that it is added to the same room and shows connected. It also needs power and WiFi. If it is bonded and still silent, adjust the Sub level in the app (it may be turned down), check placement (corners boom, open floor is flatter), and re-run Trueplay. A Sub that will not bond at all is usually a WiFi/network issue.
My rear surround speakers are silent.+
Test with content you know is actually in surround rather than stereo. Surround speakers only reproduce what exists in the surround channels, and a great deal of broadcast and streaming content is stereo — so silent rears are frequently the source having nothing to send them rather than any fault in the speakers.
One side of my soundbar went quiet after I moved things around.+
Re-run the room calibration. It sets the level for each speaker based on where they were standing when you ran it, so moving a speaker — or the soundbar itself — leaves those levels tuned for positions that no longer exist.
Does this answer apply to every Sonos model?+
No. It is scoped to Sub Gen 3. Sonos product; Wi-Fi/Ethernet, Bluetooth, voice, home-theater and line-in capabilities vary.
What should I record before troubleshooting one side or one earbud?+
Record the complete model identifier, exact message or indicator, software/firmware where visible, the operating stage and what still works.
Why is a factory reset not the first step?+
A reset can erase accounts, networks, maps, schedules or preferences without distinguishing one side, one earbud. The ordered checks preserve that evidence.
When should I stop and use qualified service?+
Stop for heat, swelling, liquid or exposed wiring.
Answer for the exact device and software version shown above.