Fifty new hearing aid users were summoned to individual follow-up about one year after they had completed their hearing aid fitting. About 30% of the hearing impaired seldom used their hearing aid (< 1 h/day). The hearing aid was mainly used in conversation between two, conversation in groups, listening to TV/radio, etc. The hearing impaired who had a steep hearing loss used the aid to a lesser extent. There is a strong need of follow-up visits. Reliability of the subject's own judgement was good.
This study included 10 subjects with sensorineural hearing loss. They had not previously used hearing aids. The hearing aid fitting with "behind-the-ear' aids was based on the NAL method. Judging the sounds in their ordinary home environment, three sound situations (programmes) were selected, permitting the subjects to listen to one programme with speech, another with music and a third with "background noise'. For the group as a whole, significant differences were found between the sound quality judgements with and without the hearing aid. When the judgements of the programmes with background noise were excluded in the analysis, there were significant differences over time in the group as a whole on the scales for clarity and total impression.
Nine normal-hearing subjects listened to speech and music in a hearing aid, either through a vented earmould or a closed earmould. The complex frequency responses of the two systems were made equal by compensating the aid and closed mould combination with a digital filter. The subjects rated the perceived sound quality of the systems on seven perceptual scales and a scale for overall impression. The results of the ratings support the hypothesis that there is no difference in perceived sound quality between vented and closed earmoulds that are equalized in frequency response, provided that the perceived loudness is the same in both cases.
In order to select hearing aids with a highly predictable real ear gain, in situ gain and compliance through the individual ear mould were measured on 8 normal-hearing subjects. The latter were chosen in order to reduce gain variation caused by various pathological conditions of the ear. All behind-the-ear aids commonly used in Sweden and one in-the-ear aid were studied. One sample of each hearing aid type was tested and the subjects had identical ear moulds. Hence, the variables were hearing aid type and subject. The study showed wide intra-subject coupler-related real ear gain variation (30 dB). Most of the aids showed a distinct correlation between coupler-related overall gain, and mould compliance. Some of the aids gave more uniform real ear gain, i.e. low interaction between subject and frequency-dependent gain. These results are elucidated by measuring the aid's acoustic output impedance.
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