Comparison of reverberation times and average absorption coefficients in classrooms, based on in situ measurements versus calculated from material databases as during design

Reverberation time (RT) is an acoustic descriptor used widely by acousticians for characterizing indoor acoustic environments, as specified in standards such as ANSI S12.60 “Acoustical Performance Criteria, Design Requirements, and Guidelines for Schools”. It is often calculated in the design phase for simple spaces by applying equations like Sabine’s or Eyring’s, requiring information on room dimensions and the surface areas and acoustic absorption coefficients across frequency of room materials. In this project, measured RTs from a recent survey of over 200 K-12 classrooms are compared against the RTs predicted across speech frequency octave bands using Sabine’s and Eyring’s equations. Agreement between predicted and measured values varies based on the octave band and material selection. The working group currently revising ANSI S12.60 is considering providing guidance on the desired average absorption coefficient in classrooms, rather than reverberation time, so this study also compares the average absorption coefficients for the classrooms. The coefficients are back-calculated from the measured RTs using Sabine’s and Eyring’s equations, and compared against those calculated from surface dimensions and commonly available material absorption coefficients.