Heavy curtains and rugs are a good call—soft surfaces absorb vibrations pretty well. I've had decent luck with bookshelves loaded with books or dense furniture against shared walls too.
Insulation definitely helps, but honestly, I've found that heavy furniture or bookshelves don't do much for bass frequencies. Those vibrations travel through the structure itself—floors, joists, studs—so surface treatments only go so far. If you're serious about cutting bass noise, you'd need to decouple the walls or ceilings with resilient channels or isolation clips. It's a bit more involved (and pricier), but it's the only thing that's noticeably cut down bass rumble in my old place.
You're right about decoupling being the gold standard for bass frequencies—no argument there. But honestly, in a lot of homes I've worked on, resilient channels and isolation clips aren't always practical, especially if you're renting or don't have the budget or permission to open walls and ceilings. I've seen clients get pretty frustrated once they realize what's actually involved in installing those solutions.
From experience, insulation alone (even the fancy "soundproof" kind) doesn't really stop bass—it's more effective at muffling higher-pitched sounds like voices or footsteps. But heavy furniture and loaded bookshelves still do help somewhat. Sure, they're not gonna eliminate deep bass vibrations completely, but they can dampen resonance and reduce the overall echo effect, making the sound less intrusive. I've noticed that sometimes just softening or diffusing sound can make it seem less irritating, even if the actual decibel reduction isn't huge.
Another thing that helps surprisingly well is sealing air gaps around outlets, switches, and baseboards. Bass travels structurally, yeah, but small air leaks can amplify sound transmission too. I've had clients swear their noise issues improved noticeably just by sealing those simple gaps with acoustical caulk.
Bottom line from my perspective: decoupling is ideal if you can swing it, but don't completely dismiss simpler methods. Even small improvements can make a difference in comfort when major renovations aren't an option...
