The relationship between uncomfortable loudness level and maximum power output in subjects recently fitted with NHS...

It is generally agreed that the maximum output from a hearing aid should not exceed the subject's uncomfortable loudness level (ULL). However, this relationship is not easily defined as electroacoustic data are usually measured in a 2 cc coupler and auditory measurements are usually obtained from supra-aural transducers calibrated in a 6 cc coupler. The aim of the study was to investigate this relationship in 21 adults who were being fitted with a hearing aid for the first time. A probe-tube microphone system was used to measure the sound pressure level of both variables in the ear canal. The measurement of ULL was determined using the method recommended by the British Society of Audiology (1987). The ULL values were around 110 dB SPL (+/-10) when measured in the ear canal. The maximum output of the hearing aid was obtained by correcting the SSPL90 with the subject's own real ear to coupler difference. The results revealed that the real ear saturation response (RESR) of the newly fitted hearing aid was typically 115-120 dB SPL (+/-8). The RESR exceeded the ULL for 19 (90%) subjects on average at five of the seven frequencies and by 12 dB. While further research is needed to determine whether discomfort occurred in real life situations, the implications are that the subject may use the hearing aid at less than optimum settings to prevent loudness discomfort or may ultimately reject the hearing aid altogether.