Sound absorption and reflection from ceilings in open offices

Abstract

Sound attenuation between work areas in open offices depends on barrier height and the sound-absorbing properties of the ceiling. Two methods for evaluating the sound-absorption ceilings are available: ASTM E1111, which gives a rating called the articulation class (AC), and ASTM C423, which gives sound-absorption average (SAA). Measurements of six ceiling systems made in accordance with ASTM E1111 and ASTM C423 provide a link between AC and SAA. Manufacturers often do not provide both ratings for their products, and it is useful to be able to use either rating system. SAA and measured AC for a 1.5-m-high screen are related by AC=102×SAA+91.4. SAA and calculated values of AC for a 1.8-m-high screen are related by AC=118 SAA+93. In the absence of E1111 test data, C423 SAA values can be used to select ceiling systems. The commonly recommended minimum SAA of 0.9 corresponds to an AC of 180 when the screen height is 1.5 m and to an AC of 200 when the screen height is 1.8 m. An approximate conversion from absorption coefficients to reflection coefficients agrees well with earlier work.