Change in a) slit resistance and b) slit inertance due to non-linearity for long slits as function of St_b and St_t for several amplitudes at the reference microphone: 10 Pa (△), 15 Pa (□), 17 Pa (⋄), 20 Pa (△), 23 Pa (⋆). In a) quasi-steady potential flow theory (––) and quasi-steady potential flow theory corrected for the effect of quasi-steady viscous boundary layer (- - - -); in b) limit proposed by Ingard and Ising [21] (––).