Motion Picture Herald (Mar-Apr 1939)

How the Auditorium Size^ Shape and Surface Forms Affect Acoustics By C. C. POTWIN and BEN SCHLANSER [This is the second and concluding installment of a condensation made by the authors expressly for Better Theatres, of their paper, " Co-Ordinating Acoustics and Architecture in the Design of the Motion Picture Theatres," which they presented before the Fall 1938 convention of the Society of Motion Picture Engineers. The original paper was published in the February issue of the SMPE Journal. — The Editor.] the study presented in Figure 1, was made to determine which one of five possible auditorium designs having the same seating capacity would prove most efficient for both vision and hearing, keeping in mind that economy in construction and architectural appearance are also important guiding factors. A seating capacity of 900 was selected for this study because this capacity has been found to answer the needs of the average motion picture theatre, and because a large proportion of the theatres now being erected have approximately this capacity. It is interesting to note in the five theatre designs shown that the areas enclosed by the auditoriums vary from 108,450 to 134,100 cubic feet. Furthermore, the required screen width varies from a minimum of I63/2 feet to a maximum of 22 feet due to the increases in maximum viewing distance. Such variations in design are not justified ivhen fhe seating capacity is the same in all cases. Ceiling heights have been kept down to a minimum in all five designs. The seating arrangement is the same in each case ; i.e., two aisles separating three banks of seats, the middle bank being fourteen seats wide, and the side banks against the walls being seven seats wide. This particular horizontal arrangement was selected because it is the most efficient plan for capacities of approximately 900 seats. It requires the least amount of aisles and thereby reduces at the beginning the total volume for all of the auditoriums here dealt with. The following is a table giving the characteristics of the five designs shown in Figure 1 : Max. Cu. Ft. of Viewing Screen Vol. per Seat Distance Width Design A 151 104' 20' Design B 148 119' 22' Design C 130 150' 20' Design D 136J4 89' 16'6" Design E 120J^ 89' 16'6" In the design types A, B and D shown in Figure 1, the orchestra floor slopes approximate those which have been commonly used in past practice. These slopes ordinarily do not allow a sufficiently unobstructed vision of the screen. Increasing the slope to correct this condition would result in a slight increase in the total volume whereas the volume is already excessive ; however, vision could also be improved in these designs by the use of a stagger system of seating, which would effect a slight reduction in the total volume. This reduction would benefit design D primarily. But ■ •KT C «M.WC (1 Aim ffi 1 ■ 1 , 1 h— ■ » 1 •9 a ID U 1 1 10 u 10 r le 1 Figure 2. — Volume of 100 theatres seating 800 to 1,000. designs A and B would still have an excessive volume. Effect of Regular Seating Plan In designs C and E, the staggered system of seating has been used for the lower seating areas. A non-staggered plan could also be used in these designs. This would result in a floor slope which would pitch downward toward the screen approximately one foot more, and upward in the front half of the floor to a point about level with the floor behind the seats farthest from the screen. The volume added to designs C and E due to using this non-staggered plan would raise the total volume only a negligible amount. Volume of Auditorium The designs shown here have varj'ing horizontal ratios. In designs D and E, the depth is a little more than half again as much as the width (1:1.65), while in design B the auditorium is twice as deep as it is wide (1:2). Although all of these ratios between width and depth are suited to good acoustical conditions, coming within the acoustical limits heretofore recommended, it is particularly significant from this study that the proper vertical solution of a design (ceiling heights) not only has much to do with getting a good auditorium shape, but in most cases is what really tells you just how big an enclosure (cubic footage) your auditorium ought to be. The data given in Figure 2, afford us CROSS SECTION LONGITUDIUAL SECTION Figure I. — Longitudinal sections for five cubage values per seat. Figure 3. — Theatre forms showing surfaces for reflection control. [36] BETTER THEATRES: March 4, 1939