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1947-48 Theatre Catalog, 6th Edition, Page 264 (250)

1947-48 Theatre Catalog, 6th Edition
1947-48 Theatre Catalog
1947-48 Theatre Catalog, 6th Edition, Page 264
Page 264

1947-48 Theatre Catalog, 6th Edition, Page 264

wave. The dissipation of this energy is referred to as absorption.

A sound wave once started in the theatre will continue to travel around the room until it is completely absorbed. Practically all of this absorption results from the contact of the wave With the walls, ceiling, floor, seats, patrons, or other obstructions. The distance traveled within the room is so short, friction within the air accounts for so little it can be ignored. How long the sound exists and travels depends upon the amount of energy that is extracted from it with each contact.

In the case of hard, dense surfaces, such as plaster walls, 3 per cent or less of the energy is absorbed at each contact. The wave travels at approximately 1,120 feet a second, so it is readily seen that hundreds of contacts are required to absorb that wave. In the meantime, the wave is bouncing around from wall to wall, floor to ceiling; and as it travels back and forth throughout the room, the ear hears it as one prolonged sound. A souni wave is reflected from a hard, impenetrable surface just as a light wave is reheated from a mirror. In fact, a hard wall is a more efficient reflector of sound than are most mirrors of light.

A certain amount of reflection is desirable. A once or twice-redected wave will reinforce the original wave. It is this reinforcement that gives liveness to indoor sound. In establishing a desirable reverberation time, adequate absorption is placed in the room to kill quickly all but these wanted once or twice-reflected waves.

The absorption capacities of all common building materials and of practically all theatre furnishings are known,

THE ACOUSTICAL TILE along the side walls of the auditorium of the Senatobia Theatre, Senatobia, Mississippi, is Acousti-Celotex, but on the ceiling is plain interior finish tile. A certain amount of sound reflection is desirable. A once- or twice-reflected wave will reinforce the original

consequently it is relatively simple to calculate, by established formula, the amount of absorption necessary in each house.

If absorption alone were the only problem involved in setting up good acoustical conditions, an array of mattresses, bed blankets and old burlap bags could probably do a fairly good job. However, these would hardly enhance the appearance of the theatre, and the cleaning bills would be a mite high.

In selecting acoustical materials, the theatre owner must take into consideration a number of factors in addition to absorption coefficients, or capacities. Will the acoustical effect be permanent? Can the material be decorated and redecorated as necessary? Are maintenance costs excessive? Can the material be readily cleaned?

Acoustical materials depend largely upon their porosity for their soundabsorbing ability. Such a material will absorb sound so long as a sound wave can enter the porous body of the material. It is obvious that the wave must have access through the surface. If the surface is closed tightly with a film of paint or clogged with dirt, then, of course, the porous back or body is no longer effective. The sound is reflected from the closed surface just as readily as it is from the surface of a hard material.

The first acoustical material that could be painted with ordinary paints in an ordinary mannerewith brush or spraye and as often as necessary without loss of efficiency, was the familiar AcoustiCelotex, introduced more than twenty years ago. This material established the basic principle for all paintable acous tical materials. It has a hard, smooth surface through which perforations are. drilled. These mechanically made openings permit the sound waves to reach the absorbing back, and are of such size that painting with ordinary mixtures or methods does not close them up.

Like any wall or ceiling surface, when Acousti-Celotex is finished with an oil base paint or other washable finish, it can be cleaned by any method suitable to that finish.


Time has conclusively proved that there are no satisfactory substitutes for a fully paintable acoustical material. In the early days of talking pictures, many exhibitors attempted to correct acoustical conditions in their houses by using ordinary fibre building board, which in its natural, unpainted finish did have a high degree of sound absorption, as compared with plaster walls and tin ceilings. Where enough of this material could be installed, it did add enough absorption to effect some improvement.

Eventually, this material became soiled and dirty. When it was painted, these houses were back to their original conditions. The only available relief then was to install a bona tide acoustical material over the old interior finish.

While some types of materials, which depend upon their natural surface porosity for their absorption, can be painted within narrow limits, with certain types of paint properly applied (provided the pores are not filled with dirt particles), in most instances much, if not all of the absorption is lost when paint is applied.

About the only safe way to clean these

wave. It is this reinforcement that gives liveness to indoor sound. In establishing a desirable reverberation time. adequate absorption is placed in the room to kill quickly all but these wanted once- or twice-reflected waves. The maintenance costs on Acousti-Celotex are considered to be low.

1947-48 Theatre Catalog, 6th Edition, Page 264