Airflow resistivity

The static airflow resistivity (SAR), often represented by the Greek letter σ (sigma), is a very important parameter for acoustic material modeling. In fact, one of the first acoustic models presented by Delany & Bazley in 1970 [1] was only relying on this parameter. SAR is not only useful for acoustic simulations, it is also an excellent quality control tool, in fact, a lack of consistency in a given fibrous or porous material can also indicate manufacturing malfunction or supplier material variability that could result in the final product being out of specification.

SAR expresses the frictional retardation to a quasi-static flow (here acoustic wave in air at rest) through the pores, i.e. the pressure drop required to force a unit flow through the material. ​ The static airflow resistance expresses the frictional retardation to a quasi-static flow (here acoustic wave in air at rest) through the pores. It is related to static airflow resistivity: σL ​ The static viscous permeability (SVP) is an effective fluid flow surface independent to the saturating fluid. Both properties are related by the dynamic viscosity μ of the fluid: k = μ/σ. ​ Equipment: Static Airflow Resistance Meter Standards: ASTM C 522-03, ISO 9053-2:2020 Method: Electronic system for the measurement of flow resistance [2] Properties: σ – static airflow resistivity (Rayl/m or Pa.s/m²) k – static permeability (m²) L – sample thickness (m)







Direct Method : σ = (Pe x A) / (Q x L)



[1] REF Delany, M. E. et Bazley, E. N. (1970). Acoustical properties of fibrous absorbent materials. Applied Acoustics, volume 3, numéro 2, p. 105-16.

[2] M.R. Stinson and G.A. Daigle, « Electronic system for the measurement of flow resistance » J. Acoust. Soc. Am. 83, 2422-2422 (1988).