When specifying a projection screen for a large church auditorium there are a few basic items that need to be considered. The first of these is to make sure the screen is sized properly for the audience. To ensure that everyone in the auditorium is able to read text displayed on the screen, we use the rule of six to determine our screen height. That rule tells us that we take the distance to the least favored viewer (the person in the back corner), and divide by six to obtain the screen height. The width of the screen is then determined by the aspect ratio of the source material. In some cases this aspect ratio will be 4:3, but with HD television becoming prominent in our culture, 16:9 is the recommended aspect ration for the future. So, for a viewer sitting 60 feet from the screen, the ideal size would be 10 feet high (60 divided by 6), and 17.7 feet wide (10 feet * 16/9).
The one item to take into account when determining the size of the screen is the ceiling height and how far from the floor the screen can be placed. In order to determine exactly how far off the floor the screen should be placed a sight line study should be done to make sure that audience members can read what is placed on the screen without having their viewing line obscured by the person seated in front of them. For churches with larger auditoriums it is very likely that ceiling heights are very large and the screen can be placed up high enough to eliminate and obscuring. As a general rule of thumb, screens need to be places higher than 48 inches above the finished floor of the audience seating area. Many times a site line survey will determine that the screen must be placed some where in the range of 48 to 60 inches up from the floor. If the screens will play a prominent role in the service when people are standing, an even higher position will be necessary.
The second item to consider is what type of screen is necessary and desirable for the space. If the aesthetics of the room demand a screen case that will hide the screen and include a closure with a trap door to make the screen disappear into the ceiling, then one that is ceiling recessed is appropriate. If placing a screen on the wall permanently is not an objection, then perhaps a fixed wall-screen is in order. if desired, black fabric treatments for surrounding the screens can be ordered to dress up the installation.
Perhaps one of the most misunderstood criteria when choosing a projection screen for an auditorium is the type of screen surface chosen. Screen surfaces have the ability to direct, or aim, more of the projector's light straight out from the screen, instead of letting it spread out towards the sides of the room. This is referred to as screen "gain". A gain higher than 1.0 means that light would normally go off to the sides of the room gets re-aimed more towards the center. Those siting more directly in line with the screen see a brighter image, at the cost of a narrower viewing angle. Thus, those at the sides of the room will see a dimmer image.
It is critical that the screen, projector and the amount of ambient light in the room be taken into consideration to ensure that the visual display will be capable of achieving the appropriate contrast level. In most visual situations we are attempting to achieve a 10:1 contrast ratio based on the whitest the projector can make the screen and the darkest the screen will be with the projector attempting to create a black image (aka System Black). Ambient light has a very dramatic affect on what many call the "System Black Level". If there is too much ambient lighting striking the screen surface, then an appropriate system black cannot be achieved. Once you have determined that the screen is in an area that is as dark as possible for the auditorium, then you must consider the projector choice and screen gain based on that light level. If the amount of ambient light striking the screen is high (say, 80 lux), then a projector in the 4,000-lumen range might be necessary. It may also be necessary to utilize a high gain screen for this application providing the audience is not too far off the centerline of the screen.
As you can see, there are many different items to consider when choosing a projection screen. These are just a few of those items. In order to ensure that your visual system is designed properly, it is best to consult an audiovisual professional. More information is available from the Da-Lite How of Worship Front Screen Projection Guide, available at http://www.worshipfacilities.com/media/files/HOW_Front_Selection.pdf .