With the growing number of hearing aid users and the increasing frequency of travel to or through high altitudes, it is important to understand how altitude affects hearing aid output. This study employed computational simulations to examine how altitude influences the output sound pressure level (SPL) of hearing aids. Simulations were conducted at four altitudes: 0, 2743, 4572, and 10 668 m. The input level was fixed at 60 dB SPL, and gain and compression ratios were prescribed using the National Acoustic Laboratories Nonlinear version 2 formula for four representative hearing loss profiles. The model incorporated the outer ear transfer function and atmospheric absorption, assuming an open-closed tube (2.5 cm long, 7 mm in diameter). Three conditions were simulated: (1) SPLs incorporating altitude-dependent effects without gain, (2) SPLs with prescribed gain, and (3) SPLs with gain under constant temperature. Results showed that both SPLs and resonant frequencies decreased with altitude. Gain application increased overall output levels but preserved altitude-related trends. When temperature was held constant, SPLs continued to decline with altitude, but resonant frequencies remained unchanged. These findings suggest that hearing aid prescription formulas should include altitude-related correction factors, with careful consideration of temperature effects.
Donghyeon Yun (Sun,) studied this question.