Recommendations of sound absorption areas for everyday architectural spaces

In the Architectural Institute of Japan, an acoustic standard and its design guideline of sound absorption are currently being established to ensure basic sound environment for a variety of everyday rooms, referring to DIN 18041. In the new standard, reasonable recommendations of the amounts of absorption will be incorporated with the indicator of equivalent absorption area per floor area. This indicator is a dimensionless quantity and corresponds to the sum of absorption coefficients of floor and ceiling if not taking the absorption of walls into account. Everyday rooms are subdivided into four types according to their absorption needs, which are determined by the loudness of generated noise and the need of quietness or speech transmission. Considering the balance of noise reduction and reverberation suppression, the recommended values of the indicator are formulated for thefour room types as a function of average ceiling height. Specifically, as the ceiling height increases, noise reduction is strengthened while allowing the increase in reverberation to some extent. In addition, the recommended values are set to increase by 25% for the four room types, which corresponds to a 20% decrease in reverberation time and a 1 dB reduction of noise level.