Audio
L-Acoustics KS28 Subwoofer troubleshooting
The L-Acoustics KS28 Subwoofer problems live-event techs bring to Ask Roadie most (also called KS-28, KS28). Pick your symptom, or describe your own in plain words, and get the likeliest fix first, with the manual page when there is one.
Common KS28 Subwoofer errors & problems
What techs run into most, and what's usually behind it. The step-by-step fix for your exact unit is in Ask Roadie.
- Step-by-step fixGet the fix →
Buzzing or rattling coming from the cabinet
Likely cause: A mechanical rattle is either loose hardware or a damaged voice coil/cone; testing the driver out of the box isolates it definitively.
- Step-by-step fixGet the fix →
Cardioid sub array gives no rear rejection
Likely cause: Cardioid cancellation depends on the reversed box getting the correct delayed/polarity-shaped preset; layout and preset must agree or the rear null collapses.
- Step-by-step fixGet the fix →
Keeping KS28 systems current — firmware
Likely cause: Firmware updates ship inside LA Network Manager and include safety fixes; a mandatory-minimum floor plus matched versions across the rig prevents faults and mismatch problems.
- Step-by-step fixGet the fix →
KS28/LA12X not showing up or dropping out in LA Network Manager
Likely cause: Amps are addressed and monitored over L-Net; a cabling, IP, or firmware-mismatch fault breaks discovery even though audio hardware is fine.
- Step-by-step fixGet the fix →
LA12X display blinks "Unit service required" or shows an SMPS/varistor/hardware error
Likely cause: These messages indicate power-supply or logic faults inside the amplified controller that are not field-serviceable and can escalate to damage.
- Step-by-step fixGet the fix →
LF sounds compressed / distorted at high SPL, L-Drive or limiter LEDs active
Likely cause: L-DRIVE limits before mechanical/thermal damage; more boxes share the load, so each works within its excursion limit and stays clean.
- Step-by-step fixGet the fix →
No output from the sub / LA12X shows "Short-circuit on ch #" and the channel mutes
Likely cause: A voice-coil or cabling short pulls excessive current; the LA12X output stage self-protects by muting.
- Step-by-step fixGet the fix →
Sub is quiet / LA12X shows "Under impedance on ch #" and attenuates the channel
Likely cause: The LA12X protects itself by attenuating when the measured load impedance is below spec, which happens with over-paralleling or a shorted transducer.
- Step-by-step fixGet the fix →
Sub level drops or cuts out after running loud for a long time (thermal)
Likely cause: The amp monitors per-channel output-stage temperature and stages attenuate/mute/shutdown to protect itself and the transducers.
- Step-by-step fixGet the fix →
Subs and mains do not couple well / hole or cancellation around the crossover
Likely cause: The wrong preset puts the sub crossover in the wrong place, causing overlap or a gap with the mains; matching preset to hand-off frequency restores flat coupling.
Not on the list? Describe it your way, or paste the error code off the display. Ask Roadie works the problem with you until it's fixed or you have a clear next move.
How Ask Roadie helps with the KS28 Subwoofer
- 1. Pick the L-Acoustics KS28 Subwoofer. It's already in the list.
- 2. Describe what you're seeing. In your own words, or the error code off the screen.
- 3. Get the likeliest fix first. Steps in order, the manual page when there is one, and a note when other techs have confirmed it.
- 4. Still broken? Tap 👎 and it keeps going from where you left off.
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