Diagnosis
The soundbar is likely set to a dialogue-enhancing mode, or the bass module (if you have one) isn't connected or powered. Without a module, bass is limited by the small drivers.
How to Fix It
Check your sound mode. Press the “Music” button on the remote to cycle through modes. Avoid “Dialogue” mode for music and movies. Use “Music” or “Movie.” In the Bose Music app, go to Settings > Audio > Bass and adjust the level.
If That Didn't Work
If you own a Bose bass module, check its connection. The module's status light should be solid white. If it's off or flashing, re-pair it via the Bose Music app under Settings > Speaker & TV > Manage Bass Module.
Heads Up
The AdaptiQ calibration is sensitive. If the setup microphone was placed on a soft surface like a couch cushion, it calibrated for that, robbing your room of bass. Re-run AdaptiQ with the mic on a rigid stand at ear height.