Diagnosis
The subwoofer is active but not receiving the Low-Frequency Effects (LFE) channel. This happens when the soundbar's input mode or TV output format is set to PCM 2.0, which strips out the dedicated '.1' subwoofer channel.
How to Fix It
Change the TV's digital audio output format. In your TV's sound settings, locate 'Digital Sound Out' or 'Audio Format'. Change it from 'PCM' to 'Bitstream' or 'Auto'. This allows the full Dolby Digital signal, including the LFE track, to pass to the soundbar.
If That Didn't Work
The soundbar's 'BASS BLAST' mode may be off. Press the 'BASS BLAST' button on the remote. The soundbar display will briefly show 'BB ON'. This mode enhances low-frequency output to the subwoofer.
Heads Up
Using the 'Standard' or 'Music' sound mode severely reduces bass output. Use the 'Movie' or 'Bass Blast' mode for full-range audio. Cycle modes with the 'SOUND EFFECT' button on the remote.