Theatre Catalog (1946-47)

An Acousti-Decorative Use for Filerglas An Artistic Sound-Proofing for Ceilings Uses Fiberglas Blankets, Cords, Fabrics In numerous applications, Fiberglas in the wool-like forms used for thermal insulation has been employed for the control of sound as well as heat. During the war, it was installed as acoustical insulation in the control rooms of Navy ships, in aircraft, in bomber assembly plants, dynamometer rooms, sound stacks, and motor test stands. It was also employed to deaden sound in chambers used for the testing of communications equipment at Harvard University’s Electro-Acoustic Laboratories and at the New York Navy Yard. Harvard’s chamber is a huge, windowless, concrete box the size of a four-story house, half buried in the ground. The thick walls enclose 72,000 cubic feet of the most anechoic (without echo) space on earth, for the sound waves that would otherwise be reflected from the walls, floors, or ceilings are absorbed by 20,000 Fiberglas wedges, 8 inches square at the base and 4 feet long, set to project in close array from all the interior surfaces of the chamber. FIBERGLAS IN SOUND-PROOFING These and other war uses of Fiberglas as an acoustical material laid the basis for its use to control sound in commercial and private aircraft, in auditoriums, theatres, restaurants, offices, motion pic FIGURE 1—A 2 by 4-inch fire-resistive-treated Wood anchor rail (notched as shown in detail in Figuze 6) is attached to the long sides of the room with its bottom surface at least 12 inches below the existing ceiling. (The virtual dead-air space between the final decorative fabric and the ceiling itself helps in the insulation 232 ture, radio and television studios, factories and other types of commercial or industrial structures. The Role of Fiberglas Over-all sound control may require not only coatrol of air-borne sound within an enclosed space, but exclusion of sound from the space, and the minimizing of sound at its source. The minimizing of sound at its source is not a function of Fiberglas sound-control materials except as Fiberglas may be used as lining for ducts or plenum chambers in air conditioning equipment, and the like to quiet machinery noise where such quieting can be accomplished by absorption of airborne sound. Except in aircraft applications, the exclusion of outside sound is a function of Fiberglas sound contro] materials to only a limited degree. In building construction of all types, exclusion of sound depends primarily upon the ability of walls, floors and ceilings to resist vibration. This, in turn, depends chiefly upon their weight and rigidity. Efficient sound exclusion can be obtained only by great weight in single construction, or by the use of double construction. In double wall construction, the efficiency depends partly upon weight and rigidity, and to a large extent upon the degree of structural isolation between the two walls. Even a single nail driven through both sides of a dousle wall greatiy reduces efficiency by conducting vibration across the air space. This also applies to floors and ceilings. the volume of an enclosed space, and the reflecting or absorbing power of the surfaces, determines the length of time a sound originating within the space will be prolonged, the amount of sound overlapping, and, as a result, the hearing conditions within the space. The more reflective the surfaces, the longer a sound will reverberate; the more absorptive the surfaces, ‘the shorter the time of reverberation. The chief function of Fiberglas sound control materials in buildings of all types is the control of sound originating within an enclosed space, by absorbing the air-borne sound waves and preventing that prolongation and overlapping which results in a confused jumble. Properties of the Materials Use of Fiberglas sound control materials by the armed forces was based primarily upon their acoustical efficiency, but was also influenced to a large degree by their incombustibility, their non-moisture absorptive and rotproof characteristics, and their light weight. Light weight may be of minor prope-ties of the system.) Fiberglas cord is then stretched across the room on nails inserted on 12-inch centers on top of the anchor rails. All wood or other normally combustible material should be especially treated with chemicals to make it fire-resisting, further to protect the inherent fire-proof advantage of Fiberglas. THEATRE CATALOG 1946-47