Impedance boundary condition in Acoustical problems

[Davide]

Hello,

I'm starting using Agros2d for acoustical FEM simulations and I'd like to use it to simulate the behaviour of some circular lined ducts from FCR.

The lined ducts are the SC ones decribed here:

http://www.fcr.it/sites/default/files/prodotti/schede-tecniche/02-sc_0.pdf

I'm going to modelize the transmission loss of the silencers using the impedance boundary condition to simulate the behaviour of the rock wool inside them (which is used as sound absorbent material).

The producer of the rock wool makes available the real and the imaginary perts of both the normalized superficial impedance 

Z = Re Z + i Im Z 

and of the normalized characteristic acoustic impedance 

Zc = Re Zc + i Im Zc

Having Zc and the complex propagation constant g (g = Re g + i Im g) we have that 

Z = (Re Zc + i Im Zc)*[coth(Re g + i Im g)*l]

My question is:

the software asks me for a single number impedance Z0 in Pa*s/m, and I'm confused about what to put inside it, since I just have impedance values as dimensionless complex numbers.

Thanks in advance for your help,

Davide