The objective of this paper was to determine an acoustic parameter describing quality changes in crackers as a function of water activity (a_w). The scope of the study comprised the analysis of acoustic descriptors, which could be applied to describe losses of crispness owing to water sorption by crackers. It was found that the increasing water activity significantly influenced a change in the quality of crackers manifested by the gradual fading of the acoustic emission. The number of acoustic events and the crispness index decreased with the increasing water activity in crackers, however, as for a_w in the range from 0.2 to 0.4, those changes were not statistically significant. The number of events and the crispness index can be used to determine changes in the quality of crackers. With a_w reaching a level of about 0.5, losses in the crispness were produced, and it was evidenced by the critical water activity determined using a Fermi equation.