Motion Picture Herald (Jan-Feb 1939)

average dimensions for the width and length of an irregular basic outline. Establishing the ceiling height in its most practical and best acoustical relationship to the horizontal dimensions is the next element to be considered in fundamental planning. Ceiling height is very important because it affects both the proportions and the structural volume of the auditorium. From an architectural viewpoint, the determination of ceiling height is governed by three factors : ( 1 ) sightline requirements; (2) light projection to the screen; and (3) the general appearance of the auditorium. Acoustical Factors of Height From the acoustical standpoint, two other important factors determine ceiling height. These are ( 1 ) the proper relationship of the ceiling height dimension to the horizontal proportions; and (2) the optimum cubic-foot volume per seat required for a given design. A ceiling height ratio cannot be fixed which will be adaptable to all designs. The best ratio can only be established by a study of the horizontal dimensions and by a preliminary analysis of the cubic-foot volume requirements for the initial control of reverberation time. Study of Theatre Seating 900 The study to follow will show the variations in proportions and structural volume introduced in the planning of a theatre auditorium seating 900 persons, and how they can be minimized. From an acoustical standpoint, the structural volume of an auditorium seating 900 persons should lie between 120 and 130 cubic feet per seat. These limits are determined by (1) the optimum or best time of reverberation at different frequencies for reproduced sound, and (2) the fixed and variable sound absorption required to produce these times of reverberation. Fixed absorption means that absorption provided by theatre chairs, carpeting and interior surfaces of standard furred construction, finished in an ordinary manner. The variable absorption is that quantity normally provided by the audience. Optimum reverberation times are usually based on an audience condition of two-thirds capacity. Auditorium Seating Factor The chairs constitute the major part of the fixed absorption for a theatre initially planned to be acoustically functional in design. To ensure that the variable absorp The Importance of Getting "Technical" BASICALLY, the discussion which begins in adjoining columns, of acoustic factors in theatre ' planning, illustrates the significance of matters "technical" to the business of Showbusiness. Here, as in efforts in other fields, we have technologies being applied to the purpose of getting more for the same money or less money. A way to do that is really what Messrs. Potwin and Schlanger are talking about. As a result of their studies, they contend that acoustics should not be dealt with separately, but in conjunction with the rest of the planning, as a matter bearing upon the design of a theatre quite as fundamentally as vision, projection, traffic, safety and so on. Vision, projection and the other elements of the theatre planning problem are also being restudied. The purpose of all these studies is definitely the same — to get more for the same money or less money. And such matters "technical" are Showbusiness — and any kind of business. • In the course of this discussion, which is to be continued in the March 4th issue, specific application is made of the system of employing angular or broken-up walls or ceilings to control sound. This system was patented by the Bell Telephone Laboratories in 1932. It is understood that for practical application to new or virtually new theatres, this system can be made to function most efficiently when properly co-ordinated with basic outline, cubic foot volume, and "fixed" sound absorption of the auditorium structure. — George Schutz. tion — -that is, the audience — will not effect a major change in the reverberation time, these chairs should be of an efficient upholstered type, such as one having a leathercovered spring bottom and a fully padded mohair or tapestry-covered back. In the 20-inch width, this chair has a sound absorption value equivalent to more than twothirds that of the average person. The use of such a chair has been assumed for the study. Visual Requirements From the standpoint of vision, the proportions and cubic foot volumes of auditoriums vary for three different reasons. These are : 1. The types of seating arrangement used in the horizontal dimension of the auditorium determined by the number of seats and aisles to be arranged across the width of the auditorium. 2. The type of seating arrangement employed in the vertical dimension such as (a) all seats on a single level; (b) a single level with the rear portion of the seating area somewhat elevated, with a cross-over separating the raised portion from the remainder, known as a stadium design; (c) a modified stadium design in which the raised portion of seats is placed high enough to cover the cross-over; and (d) use of upper levels of seating which partially overhang the seating area of the main auditorium floor below. 3. The inclination or inclinations of the floor for the main or orchestra level such as (a) a steep downward inclination toward the screen; (b) a modified downward inclination toward the screen; (c) a modified downward and then upward inclination toward the screen; and (d) only a slight downward and then upward inclination toward the screen. Affect of Floor Slope The degree of the inclination of the floor in all cases is affected by the manner in which the seats are placed behind each other. When these seats are arranged in a staggered fashion so that the center of any seat, is always directly behind the dividing arrhblock of the preceding seat, the amount of inclination of the floor is reduced by almost one-half. Variations in floor inclination design directly affect the height and inclination of the upper level seating portions, the placing of the projection room, and thereby the total height of the auditorium. [With the concluding installment of this paper in the March 4-tk issue of Better Theatres, the authors will present drawings in 'which they have sought to show ivhy acoustical defects are introduced in planning new theatres, and ho<w design may eliminate these defects, thereby also contributing to economy in construction and to creative architecture. — The Editor. 1 PERSONAL SERVICE ON PLANNING PROBLEMS : Inquiries from readers concerning the laying out and construction of theatres are invited. They are answered by mail as promptly as possible. Readers are asked to remember, however, that in some cases questions concerning a general plan may have to be referred to consultants in more than one field (as, for example, acoustics and air-conditioning) , which is likely to require some time. It is further suggested that the problems be presented in the form of specific questions — : this method permits a saving in time and also reduces the chances of misunderstanding. February 4, 193-9 21