ABSTRACT
A computerized system is described for measuring a hearing aid's etymotic frequency characteristic on patients. A small-scale clinical investigation using this equipment showed that rather large differences can be found between a hearing aid's frequency characteristic as measured according to IEC 118 (using a 2 cc coupler) and the etymotic frequency characteristic as measured by probe microphone at the ear drum. The investigation shows that in practice it is difficult to optimize the etymotic frequency characteristic by modifying the hearing aid and the ear mould. Measurements of the etymotic frequency characteristic using several different hearing aids, but with the same ear mould on the same test subject showed only limited variation in the upper limiting frequency.
