Boxing ceiling speakers is a common question that is asked about a few different scenarios. First, they don't have to be boxed to be effective. In a few cases, though, I would look at boxing them or consider adding a fire hood. The first situation is there is nothing behind them. If you are installing and you have an attic with nothing there, you will lose sound out the back. Another situation is that you have a lot of crap around the speaker, and you want to protect it from debris or destructive elements. Finally, if you have a room, like a bedroom, right above the speaker, you may want to limit the noise above the speaker.