Noise-induced hearing loss associated with earbud use is an increasing trend in modern society. All smartphones are coupled with earbuds that expose the human auditory system to unsafe sound pressures. Acoustic waves enclosed in the ear canal force the tympanic membrane to move 100–1000 times greater than acoustic waves of equal amplitude in open air. Classical acoustics has not fully explained this biophysical phenomenon. Maxwell's kinetic molecular theory was used, in conjunction with Special relativity, to quantify sound pressure exposures in personal listening devices more accurately. A non-linear dependence of sound intensity on speaker excursion is predicted, demonstrating that earbuds sealed in the ear canal can exceed the National Institute for Occupational Safety and Health's ceiling limit of 140 dB. Sound intensities predicted from molecular mass and velocity produce similar results to Beranek's model of acoustic waves in a closed, rigid cylinder and support previous observations of trapped volume insertion gain in personal listening devices. © 2017 The Author(s). Published by S. Hirzel Verlag · EAA. This is an open access article under the terms of the Creative Commons Attribution (CC BY 4.0) license (https://creativecommons.org/licenses/by/4.0/).