Individual variability in equal-loudness contours of high-level narrow-band impulse noise

Individual differences associated with equal-loudness contours for one-third-octave-bandwidth impulses, the centre frequencies bf which varied from 1 to 8 kHz, have been determined. The psychophysical method of adjustment has been used. The measurements were performed at 74, 79, 84, 89 and 94 phons. A group of 10 male and 10 female subjects with normal hearing took part in the experiment. The findings did not show gender differences. However, large inter- and intra-individual differences were obtained in the levels of loudness of impulses of different centre frequencies. Differences of over 20 dB Sound Exposure Level (SEL: the integral of the instantaneous squared pressure over a reference duration of one second) were found between the most sensitive and the least sensitive subject at some centre frequencies. In half the subjects, sensitivity varied over a frequency range of only one octave by more than 10 dB SEL. It is concluded that energy concentration within narrow frequency bands with impact or impulse noise can interact with considerable individual differences in outer- and middle-ear transfer functions. In all probability, this interaction accounts for much of the marked individual variability associated with the auditory effects of impact and impulse noise.