The use of loudness discomfort levels for selecting the maximum output of hearing AIDS

Most hearing aid selection procedures assume that MPO should not exceed the user's loudness discomfort level (LDL). As LDL varies which frequency it is logical that it be measured at several frequencies and that the prescribed MPO curve should vary across frequencies. However, because of loudness summation it is possible that when MPO is selected from narrow band (frequency specific) LDLs it may be too high for listening to broad band signals. This was investigated by measuring LDLs, for 6 normal hearing and 6 hearing-impaired subjects, using pure-tone, one-third octave band noise, octave band noise and pink noise stimuli. The SSPL₉₀ of 5 hearing aids was measured with sweep pure tone and pink noise inputs and the differences were compared with the differences in LDLs for narrow and broad band stimuli. The differences in LDLs varied across subjects and for some subjects MPO selected from narrow band LDLs would be too high for listening to intense broad band signals. Some (not all) subjects showed a systematic increase in LDLs across sessions and this 'practice effect' may be a problem in the clinical use of LDL for MPO selection.