Re: Projector “glass” box type?
Of course a piece of glass in front of the projector needs to let the image through without distortion which is only slightly less complex than something like a camera filter. Schott is one of the traditional suppliers. Here a prefab unit that is engineered for sound isolation but I don’t know how good it is optically. http://www.acousticalsurfaces.com/acoustic_windows/acoustic_windows_recording_studio.htm?d=40
Given that modern consumer projectors are much quieter than cinema projectors a single layer of glass will probably be suffucient.
Another source is http://www.rsem.com/equipment-list.asp?category=porthole%20windows&show=all who has a unit that’s 10″x10″
Yet another is here: http://www.opticalcoatings.com/processes/water.html
Doing a search on projectro port glass will turn up others.
Bottom line is that it’s important to use optical quality glass if you’re doing a quality theater.