A model of the occlusion effect with bone-conducted stimulation

TLDR

An acoustical model using simplified ear anatomy was designed to predict the ear‑canal sound‑pressure occlusion effect in humans. The model’s predictions were validated by comparing them to perceptual judgments and ear‑canal pressure measurements obtained with foam earplugs of varying depth and a circumaural earmuff, and by testing occlusion effects with supra‑aural and insert earphones. The model accurately predicted measured occlusion effects, showing that all occlusion positions produce noticeable effects, that forehead bone‑conduction yields perceptual occlusion close to ear‑canal data in 0.3–2 kHz, while mastoid stimulation differs by ~10 dB below 1 kHz, and that insert earphones generate larger low‑frequency occlusion than supra‑aural earphones.

Abstract

An acoustical model using simplified ear anatomy was designed to predict the ear-canal sound pressure occlusion effect in humans. These predictions were compared perceptually as well as with ear-canal sound pressure occlusion effect measurements using a foam earplug with shallow insertion, a foam earplug with deep insertion into the bony part of the ear canal, and a circumaural earmuff. There was good resemblance between model predictions and ear-canal sound pressure measurements. It was also found that all occlusion positions, even deep ear-canal occlusion, produced noticeable occlusion effects. With the bone-conduction transducer at the forehead, the perceived occlusion effect was close to that obtained from ear-canal sound pressure data in the 0.3 to 2 kHz frequency range; when the stimulation was at the mastoid the difference between the perceived and measured ear-canal sound pressure occlusion effect was around 10 dB at frequencies below 1 kHz. Further, the occlusion effect was obtained in two clinical settings: with supra-aural earphones (TDH39), and insert earphones (CIR22). Although both transducers produced occlusion effects, insert earphones produced a greater effect than surpa-aural earphones at the low frequencies.