"Acoustical" parameters

Few of the "acoustical" parameters used to describe the visco-inertial and thermal behviors of acoustical porous materials are directly measurable.
The open porosity, the static air flow resistivity and the high frequency limit of the dynamic tortuosity can be directly measured. The devices used in these cases are borrowed from science fields related to other porous materials (such as rocks) or are adapted from these other porous materials to acoustical ones (which have usually very large permeability and porosity compared to rocks).

The major part of the "Acoustical" parameters are estimated via indirect measurements, numerical computations or curve fiting techniques.

• the open porosity,
• the static air flow resistivity,
• the high frequency limit of the dynamic tortuosity,
• the viscous characteristic length,
• the thermal characteristic length,
• the static thermal permeability,

"Visco-elastical" parameters

Most of the experimental methods used to characterize "visco-elastical" parameters (Young's moduli, loss factors and Poisson's ratios) are adaptations of techniques used for polymers or metal [Ashby.Book,Corsaro.Book,Hilyard.Book]. Modifications of existing devices are usually due to account for the interaction between the two phases of an acoustical porous material or to account for specific ranges of values for these acoustical porous materials. Young's moduli and loss factors of acoustical materials range from approximately $10^{0}$ to $10^{9}$ N.m$^{-2}$ and from $10^{-2}$ to 1 respectively.

• a complex Young's modulus,
• a Poisson's ratio.