A study of earmould modification effects on the frequency response of body worn hearing aids

Abstract

A study was made of the influence of different receivers and the effects of variation of ear mould sound bore diameter, length and parallel vents on the frequency response of body worn hearing aids. In order to obtain real ear estimates of the magnitude of the effects, these measurements were made using a modified Zwislocki (IRPIDB-100) ear simulator. The results indicate that while there may be little value in varying the length of the sound bore, diameter variation could be very helpful in the control of the high frequency response of a hearing aid. A wider diameter of the sound bore results in an improved high frequency response, whereas poorer high frequency response is associated with narrower diameters of the sound bore. Parallel venting of ear moulds results in a reduction in the low frequency response of a hearing aid. The length and the diameter of the vent determine the amount of the low frequency cut in the response. The shorter length and the wider diameter of the vent result in a greater amount of low frequency reduction. The effects of parallel venting of ear moulds are independent of the frequency response of the receiver. The study was made using the receivers commonly used with the body worn hearing aids in India. The data of the ear mould modification effects may prove useful in predicting the effects of such work in a clinical situation. However, no subjective assessment of ear mould modification effects were made in this study.

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