Acoustic model for evaluation of rooms with absorbent ceilings

A room with absorbent ceiling treatment will behave acoustically quite differently from a reverberant room. The non-uniform distribution of absorption will alter the behaviour of the sound field compared to the assumption in the classical diffuse field theory. As a consequence, several room acoustic parameters are needed for a relevant evaluation that relates to the subjective perception of the sound environment. The rooms with ceiling treatment comprises a large group and many work places like schools, offices, etc. are equipped with this type of acoustic treatment. From engineering point of view there is a need of methods for estimation of relevant acoustic parameters in order to secure an efficient acoustic design. This paper presents a model for estimating room acoustic parameters, in rooms with ceiling treatment. Calculated parameters are reverberation time T20, speech clarity C50 and sound strength G. A method for quantification of the sound scattering effect of interior objects like furniture is outlined and incorporated in the model for estimating the room acoustic parameters. Theoretical considerations behind the model as well as measurement results in a classroom and conference room like configuration will be presented.