We suggest giving the following a shot:
- Curtains: Curtains do wonders when it comes to absorbing subwoofer frequencies. Plus, it helps sound quality as well - you don't get the nasty reflective noise bouncing off your windows.
- Rugs: Like curtains, rugs can absorb noise from bouncing all around your room and helps with general noise absorption.
- Night Mode: If you've got a night mode on your sub, we suggest making good use of it. The night mode usually doesn't degrade sound - it usually just makes the listening "sweet spot" more constrained with less intensity.
- Dampening Wall Materials: Other materials like egg cartons, blankets, and professionally manufactured paneling can definitely help take some of the vibrations from going next door.
Got a recommendation to help Sam be less of a bass-head to his neighbors? Let him know in the comments!