Investigating how predictions of reverberation time can be affected by incorrect absorption coefficient assumptions

The methods of predicting reverberation time for any given space rely on the correct choice of absorption coefficients for the room’s surfaces. For many materials the absorption coefficient can be found in literature, taken from measurements carried out using an impedance tube or a reverberation chamber. For other materials finding the absorption coefficient may not be possible, either because the material has not been measured before, or because the construction of the material is different from that found in literature. In this scenario an acoustic consultant will have to choose the closest material they can find, based on what it’s made of, its thickness, its construction, and its positioning. This introduces a degree of error to the acoustic modelling process which may have an impact on the predicted reverberation time, as well as subsequent predictions such as speech intelligibility. This paper examines the variance in reverberation time predictions caused by the use of incorrect absorption coefficients, and compares the results to measurements taken in accordance with ISO 3382-2:2008. This paper also investigates if the use of an acoustic impedance “gun” (by Microflown) is suitable for use in measuring the in-situ absorption coefficients of every surface of a room, to be used in the prediction of reverberation time using acoustic modelling software. If the acoustic impedance of materials can be measured in-situ the calculated absorption coefficient is likely to be more suitable for use in determining the reverberation time of the space, as opposed to using assumed values of absorption taken from literature