I have a niche as a wardrobe in my bedroom. The niche is built upon the stairs and has a wooden grille on the wall facing their side (think of it as a window-shutter, I guess it was made to give the clothes new air).
I don't live alone and I can clearly hear anyone in the hallway or in the stairs as they were in my room (and the other way around). I share the room with my girlfriend in the weekends, so I'd like to have some privacy; right now it's kind of not having a door. :)
How can I soundproof my room?
Some additional info:
- the grille has no moving parts and it isn't linked with any duct, I can surely tell because I can see its back from the stairs;
- there is no forced air system for heating or cooling the house;
- the grille dimensions are roughly 85x70 cm (width x height), the room is about 9 square meters;
- a 3 cm thick panel could easily fit over the offset between the grille and the wall the grille is placed upon;
- I don't use any speakers in my bedroom except for a small tv (volume is never loud);
- I don't own the house, so I'm not allowed to make any extreme (= hardly reversible) change.
EDIT: Here are two pictures of the grille, the first one from within the niche in my room, the second one from the stairs my room is next to.