A double-blind cross-over study of a non-linear hearing aid

New hearing aids are usually introduced after clinical trials. These are mostly based on subjects reports, in which it is possible that the subject's judgment of the acoustic performance might be influenced by the awareness that it is a new hearing aid which is being investigated. To examine the benefit of a new non-linear amplification circuit, a double-blind cross-over study was conducted. Two 'new' hearing aids were developed; they were identical in external appearance and differed only in that one involved ordinary linear amplification while the other employed compressive amplification (the K-amp circuit). Forty-five experienced users with sensorineural hearing loss, aged 60-80 years, used each of the aids for ten weeks, in balanced order. The subjects' need for hearing aid ranged from listening to radio and television to extensive use in all kinds of demanding listening situations. The results, using a structured questionnaire concerning real-life settings, speech reception tests and subject preferences for a particular hearing aid, showed little difference between the two hearing aids. Twenty-three subjects selected the non-linear amplification circuit, 20 subjects preferred the linear hearing aid and two chose to return to their previous aid. No consistent differences between those preferring the linear circuit and those preferring compression were found. It can be concluded that this compression amplification circuit is not significantly preferred to the traditional linear hearing aid.