Cinematographic annual : 1930 (1930)

332 CINEMATOGRAPHIC ANNUAL the acoustic design of sound stages. In the early stages of talking pictures, it was felt that the sound-proofing of the stage was about the only factor which required consideration. It is, to be sure, an important factor, although no more important than the problems of stage and set reverberation. Experience and measurements have indicated approximately the following: (1) If the stage has an insulation value of 50 db at 512 d. v., which means that a tone of this frequency will be reduced 50 db when it is transmitted through the stage, it will provide tolerable insulation for a single stage. If two or more stages of this type adjoin each other it may be necessary to shut down in one stage while recording in another. (2) If the stage has an insulation value of 60 db at 512 d. v., it will be found to be fairly satisfactory under usual conditions. Outside noises such as the racing of a motor or the passing of a heavy truck, will be adequately insulated. In general, it will be possible to record in adjacent stages, except when there are very loud sounds in one stage, such as a large orchestra or very loud shouting. (3) If the stage has an insulation value of 70 db at 512 d. v., it will be entirely satisfactory for all types of recordings which are now made in the studios. There will be no interference between adjacent stages, and it will not be necessary to stop recording in one stage while recording in another. Two methods are in general use for the insulation of sound : (1) the use of heavy rigid walls and partitions; and (2), the use of multiple layers separated by air spaces. In the heavy rigid type of partition the insulation value is proportional to the logarithm of the mass of the wall per square foot of wall area. The insulation values provided by rigid walls, varying in