Right now you can lock a mob in a room out of stone, and still hear it through few meters of concrete. Also would be realy cool and creepy if caves had sound reverberation. Right now its not scary at all. Sound physics mod is a good example of it
The Meaning of Life, the Universe, and Everything.
I think this is a good idea because if you lock a dog in a room with walls 3 blocks thick made of pure iron, you definitely will not be hearing it. and the reverb thing sounds cool for caves aswell, its not going to affect gameplay, but sound still is a very important part of a game.