calculation of effective (density,Rho and bulk modulus, K) for absorbing materials.

vickyeight

We are doing a test on absorption characteristics of sound materials. in this we are trying to derive the acoustic and non acoustic parameters of the absorbers. However we are stuck with the efffective Rho and effective K.
What does effective Rho and efffective K mean here? Does it mean their values change with frequency? If yes, are the variations large or very low?