Originally Posted by Gerben Van Duyl
The optimal screen size (horizontal image) is Seat Distance / 1.2. Meaning that if you sit 10 feet away from the screen, the screen should be 8.33' wide. This is because this is exactly 45 degrees to the Left and Right edge of the screen, which is also where the speakers should be, behind an acoustic transparent screen. All per THX cinema specs. Of course your room needs to be dark without any reflective surfaces or objects.
Using this formula, I would need an 180 in. diagonal screen! Not going to happen for me.