Room acoustic modelling of textile materials hung freely in space: from the reverberation chamber to ancient churches

The aim of this study is to investigate how sound absorbing materials like curtains should be modelled in geometrical acoustic (GA) software when hung freely in space. The use of these tools is widespread today. Whatever the scope of the simulation, dealing with textile materials can be particularly challenging as they both absorb and transmit sound, and absorption is dependent on distance of the walls. Therefore, care must be taken to enter properly validated data. Absorption coefficients found in the literature are measured with samples close to wall, and are not suitable when materials are hung freely. The effects of material placement on both absorption and transmission coefficients were therefore investigated using scaled-down physical models of a reverberant chamber and a church. Subsequently, GA models of both spaces were used to demonstrate that simulated results are reliable assuming that absorption and transmission coefficients are correctly determined.