So.. it turns out Dad wasn't actually intentionally cranking the bass while I was playing games on the weekend with a friend…
The subwoofer's integrated plate amplifier was slowly getting louder in recent months. By tonight, the volume knob had no effect at all, max gain, shaking the bedroom door at gentle music volume.
I'm used to amps dying by getting weaker or stopping, such as the amp that was in this sub previously. This is the first time I've had one be "NO, I will not go quietly into that dark night."
(Maybe the amp is easily fixable, and if not at least it's replaceable within the subwoofer. Yay for standards and serviceability!)