When you build a home theater with an acoustically transparent screen the speakers are placed behind the screen. These speakers can be placed in a wall or an alcove behind the screen.
The left and right screen loudspeakers should be spaced laterally so that they form a triangle with a 45 degree angle to the primary seat. This size screen will visually work best with 2:35 to 2:50 aspect ratio screens. Sitting this close to a 16:9 screen may not be comfortable. The screen loudspeakers should point to a location on the center-line of the theater seating at a distance about two-thirds the length of the room. Screen speaker tweeters should be mounted no more than 15 degrees off the viewer ear height. The speaker can be angled toward the viewer to help with this.
Using a wall as either a baffle wall for your box speaker enclosures or in-wall speakers will add a boost of up to 6 db to the lower frequencies. The wall itself will work best if it is very dead acoustically and does not vibrate. This can be done with multiple layers of drywall, MDF and 2×4 construction. Placing the speaker on a shelf will cause fewer problems than in another box. Equalization to compensate for this baffle step in bass response may be required if the speaker is not designed for this purpose. Allowing access behind the wall can help with future maintenance if it is possible. The increase in sound output from this baffle wall will reduce the strain on your speakers and amplifiers. Mason Super W pads can be used to reduce vibrations from your speakers to the wall.
It is important to cover all wall surfaces behind the screen with sound absorptive material to prevent interference from reflections. THX recommends 1 inch thick Black Coated Insul-SHIELD® for this purpose. Sound absorption material should be used behind the wall as well and the speaker hole should be not much larger than the speaker.
When installing masking material for various screen formats be sure the material does not obstruct the sound when in the most restrictive position.
Finally be sure everything is visually non-reflective behind the screen and black if possible to avoid seeing reflections from behind the screen. Black acoustically transparent fabric can be used for this purpose as well, but it will absorb another 1 db of the high frequencies.