Today's in-wall speakers are far more sophisticated than those in the old days. Gone are the days of simply cutting a hole in between a few studs and slapping some drivers into your drywall.
Most of today's top-performing in-wall speakers come with a sound box, or "back box" that is specifically tuned to get the best audio performance (specifically bass) out of the empty space between studs. Gone is the unknown open volume in the wall and in its place is a more predictable box that can get speaker performance from an in-wall speaker that is much more on par with a traditional loudspeaker.
All the speakers below have sound boxes, click for full reviews.