Modelling of acoustic absorbers

Various empirical models are implemented for getting the characteristic impedance and wavenumber of porous materials such as glass fibre and mineral wool:
1. Delany and Bazley
2. Mechel and Ggrundmann
3. Wilson, simplified relaxation model
These porous absorber models are then used to calculate the surface impedance and absorption coefficient of different absorbents using a transfer matrix approach.
1. effect_of_perforated_sheet_open_area.m Shows how the open area changes the surface impedance and absorption coefficient of some Helmholtz absorbers using a transfer matrix approach.
2. microperforated_absorber.m Calculates the absorption coefficient for a single layer microperforated absorber.
3. slotted_absorber.m calculates absorption coefficient for a Helmholtz absorber that uses slots (slits) rather than round holes.
The formulations for the models are outlined in Acoustic Absorbers and Diffusers by Trevor Cox and Peter D'Antonio