The concept of critical level and impulse noise

Abstract

Current noise standards are based on the assumption that predictable relationships exist between noise exposure (presented as either continuous or impulse noise) and hearing loss. These studies were conducted to expand on previous evidence that noise presentation above a critical level may disproportionately damage the cochlea. Chinchillas were exposed to noise conditions in which impact and impulse noise were presented at different peak amplitude levels and in different temporal patterns of presentation. While the amount of total acoustic energy was kept equal within each experiment, significant differences in hearing loss were seen with different peak amplitude levels of noise. Impact noise generated disproportionately greater hearing loss at amplitude levels above 119 dB peak SPL; impulse noise caused greater permanent threshold shift at 150 dB peak SPL than at 135 dB. The results suggest that a critical level of noise exposure may exist, partially dependent on the rate of noise presentation.