Effects of ear canal temperature gradients on altitude-related resonance shifts and hearing aid output.

Understanding how altitude influences hearing aid performance is increasingly important as more users are exposed to high-altitude environments. A previous computational model predicted substantial output reductions near the first-resonance region but assumed that ear canal temperature followed ambient temperature, potentially overestimating resonance-related effects. The present study incorporated an ear canal temperature-gradient sensitivity model and evaluated its effects on predicted hearing aid output and speech audibility at sea level (0 m) and 4572 m using two representative hearing-loss profiles fitted with the National Acoustic Laboratories-Non-Linear Version 2 prescription. Across all temperature-gradient conditions, peak attenuation was reduced to less than 3 dB, compared with approximately 5.7 dB in the original uniform-temperature model, and decreased further to approximately 1.8-1.9 dB under the strongest thermal-regulation condition. A finer-resolution 18-band American National Standards Institute-style Speech Intelligibility Index analysis showed only small between-model differences, with maximum absolute differences at 4572 m of approximately 0.011 for the N3 audiogram and 0.002 for the N6 audiogram. These findings suggest that incorporating the temperature-gradient model substantially reduces predicted altitude-related resonance effects without producing a correspondingly large change in predicted speech audibility.