Richardson's handbook of projection (1930)

1080 HANDBOOK OF PROJECTION FOR dolly trucks, then the stage floor should be marked to show the exact location of each truck. In addition to painted floor markings it is well to provide suitable means for anchoring the truck in exactly correct position. One simple method is to screw two stout eye-bolts into the side of the truck timber near the floor, one a few inches above the other, at two corners of each truck. Then place the truck in exactly correct position and, having provided a suitable substantial bolt to drop through the eye-bolts, bore holes in the stage floor so that the bolts will drop through them, and thus not only compel the correct placing of the trucks, but insure them against being moved out of position until the bolts have been raised. MANAGER'S INSPECTION.— In theatres where it is necessary to move the horns to accommodate tableau or vaudeville, it will be well that the manager appear on the stage and inspect the horns occasionally. Stage crews are not, it grieves me to say, always quite as careful as they might be about such things, and unfortunately the "aw that's good enough" won't work well with horn location, unless it be applied only to horns in exactly the right position. Fig. 401 is a diagram of an auditorium fifty feet wide by eighty deep, drawn to scale. A B is a screen sixteen feet wide. D C is the center of two horns. Solid black lines J J represent the acoustic axis of either horn when they are set with their openings parallel to the screen surface. Solid lines E E and F F represent the outline of the sound beams when the horns are thus set. These sound beams each include approximately a forty degree angle. Broken lines I I represent the acoustic angle of the