Sound Absorbing Layers: A Simple Prediction Model for Calculating Absorption and the Effect on Sound Transmission

The acoustical performance of a sound absorbing layer or facing added to a wall or ceiling can be of interest not only in terms of sound absorption but also because the transmision loss is increased.The work presented here started at The Norwegian Institute of Technology (NTH) and results from renewed interest in glass covered spaces. in particular glam covered "streets".The requirement for heat insulation in the facades of the buildinp in such "streers" '5 then reduced, but because of possible noise build up some additional acoustical treatment is normally required.A model for computing the sound absorption as well as the sound insulation of a combination of lightweight panels and porous insulation materials was then in demand.Owing to the complex nature of the problem any single model is not able to cover all practical cases with the desired accuracy.It is believed.however.that the model presented here gives estimates suitable for design purposes in a wide range of cases.The model evaluates the absorption and the transmission characteristics of multiple layers including limp panels.limp perforated panels.mineral wool type absorbents and air spaces.It is based on four-pole theory using partly theoretical.partly empirical data for the impedance of the variotu layers.