We were on Deck 7 Midship of the Fantasy. I was really impressed with how well the doors muffle sound. Maybe at most I could hear if someone was talking *right next* to our door, or the ship announcements (the ones not being piped in to the rooms) very faintly.
What I couldn't get used to, were the footsteps of children running, running, running -- all day, all night. It must be how the inner structure of the ship is built or something, that carries the echoes. I could hear them running on the floors above and below us as well. When my two year old toddled from one of our adjoining staterooms to the other, it sounded like a pack of dinosaurs! I was really tired of those footsteps by the end of the trip, to tell you the truth.
We've only been on the one cruise so far, so I don't know if I'd have had a different experience on a different deck/section of the ship.