Acoustic characterisation of chair absorption and simple methods for predicting occupied states

The current knowledge of the sound absorption characteristics of chairs is insufficient for a comprehensive understanding, as the sound absorption ranges of chairs and auditors are limited and obtained using several different measurement techniques. In this study, the absorption characteristics of chairs occupied by realistic scale-model auditors are systematically investigated based on the ISO 354 standard method, considering the available maximum variations in the amount of sound absorption, structure of chairs, and clothing worn by auditors. A series of 1/15-scale reverberation room measurements are performed to investigate the effects of the seat position, underpass and backrest heights, and amount of clothing on the sound absorption coefficients for both unoccupied and occupied chairs. In addition, using a wide range of measured data, simple and practical prediction models are proposed to determine the sound absorption coefficients of occupied chairs based on the unoccupied state for both known and unknown auditor characteristics. The validity of the prediction models is evaluated through comparison with the measured results in full- and reduced-scale reverberation rooms, and the comparison results confirm that the predicted absorption coefficients of occupied chairs are in good agreement with the measured values. The application range for the proposed models should be limited to P/A = 1.34 m^-1, which is approximately 20 chairs in a general reverberation room.