ABSTRACT
Knowledge of ear impression compounds, as well as earmold materials, is important
to provide quality-hearing solutions to hearing-impaired people using BTE hearing
aids. This article offers a chemist's and a rheologist's review of earmold materials.
The sound attenuation properties of silicones, acrylates, and polyurethane foams have
been measured using a novel Acoustic Test Fixture (ATF). The authors conclude that
of these three polymeric materials, compliant viscoelastic polyurethane foam provides
the best current earmold material solution for hearing-impaired individuals. It overcomes
the fundamental limitations of shrinkage and mechanical compatibility to the dynamic
ear canal. Also, compliant foam provides an ultra soft modulus at body temperature
and superior energy dissipation capability in the audible acoustic range of frequencies.
KEYWORDS
Earmold materials - impression compounds - silicone - acrylates - polyvinylchloride
- viscoelastic foam - polyurethane foam - rheology - acoustic test fixture - foam
earmolds - otoplastics
