The Acoustics of Instant Ear Tips and Their Implications for Hearing-Aid Fitting

Today, approximately 70 to 80% of hearing aid fittings are made with silicone instant ear tips rather than custom earmolds. Nevertheless, little is known about the impact of instant ear tips on the acoustic coupling between the hearing aid receiver and the individual ear canal, even though it can have a major impact on the overall sound of the hearing aids. This study aimed to investigate the acoustic properties of different instant ear tip types and their across-subject variability, the within-subject reliability of those properties, and the influence of the users’ level of experience with ear-tip insertion on the acoustics. Furthermore, subjective ratings of occlusion produced by the ear tips were considered. DESIGN: Five types of instant ear tips (Open, Tulip, Round [2-vent], Round [1-vent], Double Domes) provided by the hearing aid manufacturer Widex were considered in this study. Probe-microphone measurements were performed at the eardrums of 30 participants (60 ears). In the first experiment, the real ear occluded insertion gain and the vent effect (VE) were measured, and the listeners rated the subjective occlusion experienced with each ear tip. In the second experiment, the same measurements were repeated six times per participant. The within-subject variability of the acoustic ear tip properties was investigated as well as the impact of the degree of users’ experience with ear tip insertion on the resulting real ear measurements. RESULTS: All tested ear tips were, on average, acoustically transparent up to 1 kHz except Double Domes, which were only transparent up to 600 Hz. Distinct VE profiles were found for each ear tip type, but a large across-subject variability was observed for both real ear occluded insertion gain and VE. However, the within-subject reliability was high. The measured VE was highly correlated with the perceived occlusion. Finally, no significant effect of the level of experience in ear tip insertion on the acoustic properties of the ear tips was found, but the within-subject variability was larger in the less experienced group. CONCLUSIONS: These results suggest that the acoustic properties of instant ear tips and their coupling to the individual ear canal impact the resulting hearing aid fitting and should be considered by the hearing care professionals and reflected in the fitting software. The high within-subject reliability indicates that the ear tip acoustics remain stable for the individual in daily use. Finally, real ear measurements should be considered an essential part of the hearing aid fitting process in clinical practice to ensure an optimal fit for the individual hearing aid user.