Motion Picture Herald (May-Jun 1946)

or concrete, depending on the local cost of these materials. Fundamentally, there is a choice of flat or sloping roof. Sloping roofs reduce the heights of walls and snow loading. Parapets may be omitted if roof slopes exceed 20°, but gutters for drainage are necessary. For roof slopes greater than 20°, as in the hipped frame, the visibility of the finished roofing must be considered, and an attractive material be used. The interior ceiling treatment varies according to roof type. A suspended plaque treatment may be used except for the arched interior (E). Ventilating ducts and cove lighting are readily provided in all cases, except the arched interior^ where sloping furred walls become necessary. The arched interior is not acoustically favorable. For steel construction, there is a choice of riveted or welded trusses and frames. A typical welded knee and column base is illustrated for a steel rigid frame, which shows the simplicity of detail in welding. Structure is a function of plan and section. The walls may be parallel or tapered in plan, but parallel walls are objectionable acoustically, especially for narrow theatres, while tapered walls raise the important cost issue of varying spans. Economy in trussed roofs is obtained only in repetition of identical trusses, and severe cost penalties result with varying spans. A great virtue of the riffid frame designs is that, with identical knee details, varying spans and column heights can be provided by changing the infifling lengths of members. This is illustrated in perspective of the gabled rigid frame (C). The insurance ratings for various materials and assemblies should be carefully investigated with the fire underwriters, since the possible cumulative savings in premium costs may be quite important. ?kEfABMCAl\OU Standardization possibilities for the small theatre naturally depend on a standardized auditorium plan for varying capacities and a high demand for identical units. The steel rigid frame (C), as previously described, can be economically shop fabricated, with minimum field connection. The tendency in roof material would be to use rigid panels of minimum volume and of size permitting easy transit and handling. Pre-built wall panels must have required fire rating, rigidity and successful joint treatment. ACOUSTICS In treating a small 400-seat theatre acoustically, we must consider four fundamental properties of the structure: 1. The relative proportion of length, width and ceiling height. 2. The reverberation time or the time tequired for sound to die away. STRUCTURAL FORMS fSEE TEXT* 3. The elimination of standing waves and interference patterns. 4. The tonal characteristics of the house. Each of these four considerations has been taken into account in the auditorium provisions discussed in this presentation. SHAPE OF THE AUDITORIUM In the Business Section plan, intended for a long and narrow lot, it was found advisable to provide for the proper number of seats by an overlapping design, making At left: Type E: Arched Frame. use of a balcony in reducing the total length of the auditorium. This has the good effect of bringing the ratio of length to width close to a value of 2 to 1. This value should never be greatly exceeded. Although the ceiling is high enough to clear all projection lines {see cross-section on page 21), it is nevertheless low enough to hold the cubical volume per seat somewhere between 110 and 140. In a house of this size, and having upholstered seats with upholstered backs, no BEHER THEATRES, JUNE 1, 1946 23