In an effort to validate previous theoretical studies of phonation onset [Z. Zhang, J. Acoust. Soc. Am. (2009); J. Acoust. Soc. Am. (2010)], the dependence of phonation threshold pressure and phonation onset frequency on vocal fold stiffness and geometry was experimentally investigated in a two‐layer physical model of the vocal folds. The biomechanical parameters of interest include the medial surface thickness, vocal fold depths of the body and cover layer, and the body layer stiffness. Clinically, changes in these parameters may occur either due to laryngeal muscle activation, vocal pathology, or aging. To isolate the effects of individual parameters, experiments were conducted so that only one variable was varied at a time. Experiments show that phonation threshold pressure increased with increasing body‐layer stiffness, increasing medial surface thickness, and decreasing cover layer depth, which was consistent with numerical predictions. Increasing body‐layer stiffness also helped to maintain small gl...