Jon Mooney discusses different textures of ceilings, and how it affects sound in that particular setting.
The meaning of "acoustical" eludes ceiling contractors also, where most are sure that it refers to a suspended grid of mineral fiber ceiling tiles: it doesn't. Any Webster's will set you straight on the true meaning (and spelling; only two c's, not in the same place) of the word. Acoustics is "the branch of physics dealing with sound and the qualities of a room, etc., that determine how clearly sounds can be heard in it." Acoustical is "having to do with hearing or acoustics." Therefore, since all materials in a room affect that room's acoustics, all ceilings are acoustical. Each type of ceiling is a different tool in the acoustical consultant's kit that he or she uses to balance and shape the acoustics of the project.