A comparison of two methods for estimating sound pressure level at the tympanic membrane at high frequencies for hearing aids.

Abstract

For hearing aid fittings, it is important to know the delivered sound pressure level (SPL) at the tympanic membrane (TM) over a wide frequency range. Because it is infeasible to measure the SPL at the TM clinically, an indirect estimation based on measurements away from the TM is often used in practice. Furthermore, it is highly desirable that such a method does not require a clinician to use extra accessories to perform extra calibration in a clinic. Two such methods were proposed in the past. One used a set of empirically derived correction factors to estimate the SPL at the TM (Recker et al. (2009), the other used a lumped-element model to estimate the SPL at the TM [LoPresti et al. (2009)]. In this study, both methods were evaluated using actual hearing aid prototypes. An ITC hearing aid was built for each of ten participants. For each participant, the SPL in the ear canal was measured using a hearing aid microphone. The SPL at the TM was estimated using each method separately. The results were compared with the measured SPL at the TM. The relative strength and weakness of each method were discussed with the implications for clinical applications.