The effect of furniture on room acoustic parameters and its dependence on the sound absorbing properties of the ceiling

Sammanfattning: In ordinary public rooms such as classrooms and offices, the base line of acoustical treatment is an absorbent suspended ceiling. Due to the non-uniform distribution of the absorptive ceiling material, the scattering as well as the absorption properties of furniture will have a significant effect on room acoustic parameters such as reverberation time, speech clarity and sound strength. In particular, the absorption of the sound scattered energy will depend on the absorbing efficiency of the suspended ceiling. This effect is not accounted for in classical diffuse field models such as Sabine’s formula which is the norm for the calculation of reverberation time in existing standards. To evaluate the effect of furniture on room acoustic parameters, measurements were conducted in the reverberant room with varying degrees of furnishing for ceiling configurations ranging from highly reflective to highly absorptive. Using Sabine’s formula and the Statistical Energy Analysis model, this dissertation analyzes the scattering and absorptive effects of furniture on reverberation time, speech clarity and sound strength. The absorbing and scattering effects of furniture have been quantified by the parameter equivalent scattering absorption area. How this parameter is affected by the absorptive capacity of the suspended ceiling has also been investigated. It is concluded that both the absorbing and scattering effects of furniture have a significant effect on room acoustic parameters and must be accounted for. Moreover, comparisons of the equivalent scattering absorption area show that the scattering mechanism of furniture dominates at different frequency ranges depending on the ceiling’s absorptive efficiency. Therefore, a novel method is needed for quantification of the absorbing and scattering effects of furniture and how it depends on the absorbing efficiency of the suspended ceiling. This thesis gives some guidance towards such a method.