One of the problems with in-wall speakers is how they are affected by the properties of wall interior and surface construction. One solution that Atlantic Technology has come up with is an in-wall speaker design in which the speakers are in sealed enclosures. This design results in minimizing the effects of the actual properties of the walls in the resultant sound reproduced by the in-wall speakers.
In this photo, the in-wall sealed enclosure speakers are on the left, and traditional, unsealed in-wall speakers are pictured on the right.