On 12 ears of 10 children with bilateral hearing loss, the hearing threshold SPL levels at 500, 1000, 2000 and 4000 Hz were measured either by a hearing SPL meter or a conventional audiometer. Further the output SPL levels of hearing aids of 10 children were determined while giving 60 dB input at frequencies within speech range.
Thus obtained output SPL levels of hearing aids were compared with the hearing threshold SPL levels for the individual subjects and the differences between them were evaluated. The results were as follows:
1) In cases with moderate hearing loss, the output SPL levels of hearing aids ranged over 20 dB below their hearing threshold SPL levels. In cases with severe hearing loss, the output SPL levels of hearing aids were scattered more and deviated from the hearing threshold SPL levels much greater than in cases with moderate hearing loss. The woking gain of hearing aids in everyday use was found insufficient for hearing loss of all cases in this study.
2) Five children out of 10 subjects used, for 6 months, thier own hearing aids with gain increased. In the 6 months, increase in the gain of hearing aids was found to improve their auditory acuity, though gain of hearing aids could be at most 11 dB above the hearing threshold SPL levels and could not exceed them by 20 dB.