Comments on "A theoretical model of the pressure field arising from asymmetric intraglottal flows applied to a two-mass model of the vocal folds" [J. Acoust. Soc. Am. 130, 389-403 (2011)].

After demonstrating by means of an in vitro model experiment that the flow in the glottis can become asymmetric, Erath et al. [J. Acoust. Soc. Am. 130, 389-403 (2011)] propose a theory to estimate the resulting asymmetry in the lateral hydrodynamic force on the vocal folds. A wall-jet attached to one side of the divergent downstream part of the glottis is considered. The model assumes that the wall is a flat plate and that the jet separates at the glottal exit. They implement this so-called Boundary Layer Estimation of Asymmetric Pressure force model in a lumped two mass model of the vocal folds. This should allow them to study the impact of the asymmetry on voiced sound production. A critical discussion of the merits and shortcomings of the model is provided. It predicts discontinuities in the time dependency of the lateral force. It predicts this force to be independent from the glottal opening, which is not reasonable. An alternative model is proposed, which avoids these problems and predicts that there is a minimum glottal opening below which the wall-jet does not separate from the wall at the glottal exit. This is in agreement with the experimental results provided by Erath et al.