Just noticeable differences of loudness and sharpness for earth moving machines

Recent research on the improvement of the noise climate at the operator station of construction machines during real working conditions showed that loudness and sharpness are the parameters best correlated to the annoyance sensation. In order to verify the efficacy of some noise control solutions in improving the operator comfort conditions, it is necessary to detect the minimum differences in these metrics which are subjectively perceived: the just noticeable differences. The subjective listening tests were performed following the classical Method of Limits on a jury of subjects tested one at a time. The subjects were asked to detect the just noticeable differences for both loudness and sharpness sensations, the step size of the stimulus being 0.3 sone and 0.02 acum, respectively. The test was repeated at three different signal presentation levels. Results show that the just noticeable difference in loudness becomes greater as the overall sound pressure level of the signal increases. On the contrary, the just noticeable difference in sharpness has very small variations with the overall level. Focusing on the highest presentation level, 75% of subjects perceives a different sensation when sounds have a loudness difference of at least 0.8 sone and a sharpness difference of 0.04 acum