I won’t go over what many have said here but in your case you’re probably best attacking the weak spots to start with. It’s very difficult to suggest something without knowing the situation of the room e.g. what the floor and wall materials are and where the people that might get disturbed are. I have made gobo’s before (google acoustic gobo) with glass fibre insulation and a free hanging limp mass, whether that could be scaled up to work treat whole room I don’t know. Adding mass to the floor beneath the loudspeakers might help as well.
edit-> I just re-read your last post properly and see that most room boundaries are concrete which for sound proofing is a good thing. Perhaps try the limp mass approach on the hallway wall.
edit-> I just re-read your last post properly and see that most room boundaries are concrete which for sound proofing is a good thing. Perhaps try the limp mass approach on the hallway wall.