https://youtu.be/ASzI-DAHDFE?si=3bH-feSPz4HdpPXEI built the above. Both for in wall & in ceiling.
But wait! I cheated, I built 12”x12”x6” boxes… for the recommended 0.5 cubic foot volume for sealed boxes. So, these wouldn’t actually fit in a 3 1/2” stud wall.
The in ceiling… above was attic & in wall back side is attic too… since listening room is ‘Great Room’ with raised ceilings.
Pretty cheap & sound good too. About the same price as GR X-on set… built a couple of those too. GRs are better.
In wall speakers off the shelf can be dirt cheap & junk or very expensive.
I was surprised what a difference quality surrounds make… I’d thought surrounds as simply producing the ‘hint’ of sound to produce the surround effect. Yeah, I was wrong.