Attenuation of the input signal by protective and fixing tools for hearing aids and cochlear implants.

Introduction: Hearing aids and cochlear implants are effective rehabilitation methods for hearing impaired patients. It's necessary to protect a microphone from humidity, cold and wind. For this purpose, different clothes and protective tools are used. The aim was to study amount of attenuation of input signal at the hearing aid (HA) or cochlear implant sound processor (SP) microphone by different protective tools or clothes. Material and methods: The acoustic measurements were conducted in the soundproof cabin using artificial head with HA/SP and different protective tools, which can influence on microphone function. Sequential measurements were conducted in following conditions: 1) SP without any protective tools; 2) with protective case (No 1,2,3); 3) with water-resistant case for swimming; 4) SP fixed on the head using elastic bandage; 5) SP covered with a hood; 6) SP covered with a double- layer knit cap; 7) SP covered with a silk shawl in two layers. Probe microphone was integrated in the microphone input of SP and connected with HA verification system. Results: The most significant attenuation was observed in the water-resistant case for swimming. The changes were detected at the most 1/3 octave frequency bands (12 out of 17). The most of them are located at the speech spectrum, which can lead to a significant decrease of speech audibility, intelligibility and quality. Maximum attenuation by water-resistant case is 9.36±0.33 dB at 4000 Hz. The usage of membrane tissue protective cases helps to avoid penetration of sweat, humidity into HA or SP, as well as protects them from a wind noise, showed that they give 7.67±0.18 dB attenuation at 5000 Hz. The most amount of attenuation was demonstrated with a membrane case, which has maximum sweat protection. In contrast, a textile case demonstrated less attenuation. Fixing bandage influences on sound pressure level as well, especially at middle-high frequency region. Different types of head covering clothes lead to a significant signal changing up to 9.24±0.16 dB, primarily on high frequencies, which less influence on speech intelligibility. Results: The results of the study confirm that using different tools to protect HA of SP leads to a significant change of input signal. Conclusions: The acoustic input signal measurements, presented in this paper, could be used in the certi- fication process of new protective tools for HA and SP, which might allow to control their quality and effects. Audiologists also should use real-ear measurements with protective cases during HA verification process in their clinical practice. The information about signal attenuation must be taken into account during HA fitting to make this case acoustically transparent. [ABSTRACT FROM AUTHOR]