Purpose Mumbling as opposed to clear speech is a typical male characteristic in speech and can be the consequence of a small jaw opening. Whereas behavioral reasons have often been offered to explain sex-specific differences with respect to clear speech, the purpose of this study is to investigate a potential anatomical reason for smaller jaw openings in male than in female speakers. Method Articulatory data from 2 data sets (American English and German) were analyzed with respect to jaw opening in low vowels during speech. Particular focus was placed on sex-specific differences, also incorporating potential interactions with different accent conditions in 1 of the data sets. In addition, a modeling study compared the articulatory consequences of similar jaw-opening settings in a typical male and a typical female articulatory model. Results Greater jaw openings were found for the female speakers, in particular in the accented condition, where jaw opening was found to be larger. In line with this finding, the modeling study showed that similar jaw-opening settings in male and female speakers led to differences in pharyngeal constriction, resulting in complete radico-pharyngeal closure in the male model. Conclusion The empirical and modeling findings suggest a possible physiological component in sex-specific differences in speech clarity for low vowels.