Confidence in Room Acoustic Design: an Empirical Approach for Classrooms

Abstract

Methods to predict reverberation time range from the simple Sabine or Eyring relation to more elaborate means such as geometric and numerical acoustic modelling. Classrooms often have a very uneven distribution of sound absorption; measured reverberation times can exhibit a much wider range of values between equivalent rooms than prediction methods would generally indicate. The analytical tools can commonly fail to provide what the designer actually needs: a simple and robust method to advise on solutions for sound absorption that can routinely achieve the stated reverberation time criteria. This paper presents an empirical approach to room acoustic design for classrooms with free-hanging absorbent rafts, wall panels and furniture. Statistical analysis of the measured reverberation time in over a hundred rooms is used to determine confidence intervals for design. With this approach, the acoustic designer can not only describe the proposed requirements to the design team, they can also identify with a stated confidence the anticipated compliance rate. Although this empirical approach is based on measurements in school classrooms, it may be also used to predict the reverberation time for other spaces with similar acoustic characteristics.