The Architectural Institute of Japan is currently establishing an acoustic standard and its design guidelines of sound absorption to ensure a basic sound environment for a variety of architectural spaces. Based on the framework in Part 1, this part presents the recommended criteria and the design procedures for general rooms classified into four types according to the need of absorption. For each room type, the minimum requirements are specified by “equivalent floor absorption coefficient,” which means the equivalent absorption area per floor area. The criteria are given as functions of ceiling height, incorporating with a balance parameter for noise reduction and reverberation suppression. Through a quantitative consideration of the tradeoff between reverberation time and noise level, the appropriate value of the parameter is finally determined. As a practical design procedure, if the required equivalent floor absorption coefficient is somewhat smaller than 1, it is sufficient to consider only installing an absorbing material on the ceiling and then to determine its coverage rate. If the required coefficient is greater than 1, the installation of absorbing materials should be carefully considered not only on the ceiling but also on the floor and the walls.
Sakuma et al. (Wed,) studied this question.