You are talking about such things as in-wall and in-ceiling speakers right? They work well, but there are a lot of variables to contend with. One is that you have to deal with the studs and any insulating material in the wall section (between the two studs). Plus, there are cross brace studs in there too, and the sound can leak around the edges where they are nailed in. All the studs near the woofer will rattle with low frequencies. If you are putting it in the ceiling, you have a lot of dust that will settle into the woofer's backside that could work its way into the voice coil space.