Incident Angle Correction Algorithm for Impulse Noise Injury Assessment

Abstract

Objectives We developed an empirical algorithm to account for the effect of the change in the A-weighted sound exposure level (SELA) as a result of the change in angle of incidence (AoI) of the impulse noise on the prediction of hearing loss. The product is the upgraded software tool, Auditory 4.5 that incorporates the incident angle correction algorithm. Methods The SELA calculated from free-field pressure data is used as the dose metric that was corrected for AoI. The angle-dependent eardrum pressure was measured by performing shock tube tests with the Acoustical Testing Fixture varied over a wide range of orientation angles. The yaw angle was varied from 0 to 360° and the pitch angle from -60° to +90° in 15° steps. The algorithm was constructed by calculating a correction factor, ΔSELA for any given AoI at the ear relative to the SELA at normal incidence. The ΔSELA values were applied to correct the dose values to predict injury for all AoI. Results A three-dimensional contour of ΔSELA as a function of the AoI was produced. The largest ΔSELA was 9.81 dB at pitch = -15° and yaw = 255°. ΔSELA values compared well against available benchmark data. Conclusions A new capability has been incorporated in Auditory 4.5 to predict the effects of AoI on impulse noise injury.