Uncertainty in acoustic metrics due to spatial variations of the non-diffuse sound field measured in a variable acoustics classroom

Abstract

Acoustic metrics are commonly expressed as single numbers in classroom acoustical designs, often neglecting the physical quantity's uncertainty due to the non-diffuse sound field in the seating area. A database of measured monaural and binaural room impulse responses (RIR) was previously gathered from a fully furnished mock-up classroom. Different wall and ceiling absorption configurations were used to alter the mid-frequency reverberation times (RT) in five scenarios between 0.4 and 1.1 s. The middle three RT scenarios were additionally created from two different material configurations. For each material configuration (eight in total), two furniture orientations were utilized. RIRs were measured at 9 to 10 receiver positions for each material/furniture configuration to document the spatial variation in the resulting sound field. Diffuseness has been calculated for each receiver position utilizing the measured RIRs by following Hanyu's (2013) method using normalized decay-canceled impulse responses. Variations in diffuseness and in the assorted acoustic metrics calculated from the measured RIRs are investigated across different receiver positions. These acoustic metrics, pertinent to classroom acoustical designs, include RT, speech transmission index, clarity, and interaural cross-correlation. Means to quantify uncertainty in these metrics due to spatial variation in the non-diffuse sound field will be discussed.