The formulae used by the calculator have been taken from the following sources:
Trevor J. Cox and Peter D'Antonio. 2009.
Acoustic Absorbers and Diffusers:
Theory, design and application, 2nd Edition. Taylor & Francis.
J. F. Allard and N. Atalla. 2009. Propagation of Sound in Porous Media: Modelling Sound Absorbing Materials, Second Edition. John Wiley & Sons.
J. F. Allard and Y. Champoux. 1992. New empirical equations for sound propagation in rigid frame fibrous materials. J. Acoust. Soc. Am., 91(6), 3346-53.