Modelling annoyance from combined traffic noises : an experimental study

Annoyance is one of the most studied reactions to noise. Nevertheless, little is known about the effect of the simultaneous occurrence of noise from different sources. Existing models which predict annoyance resulting from combined noise sources are derived from results for single sources and have not yet been validated. The present study empirically investigates actual annoyance as caused from different combinations of road and rail noise in a laboratory experiment. 72 volunteers were exposed to different noise scenarios consisting of combinations of road and rail traffic noise. During noise presentation, test persons had to carry out a task on a personal computer. After each noise scenario, they had to rate their subjective annoyance. A statistical model is derived from the resulting data set, which describes the relationship between noise exposure, task difficulty and annoyance

NAL-NL2 Empirical Adjustments

NAL-NL1, the first procedure from the National Acoustic Laboratories (NAL) for prescribing nonlinear gain, was a purely theoretically derived formula aimed at maximizing speech intelligibility for any input level of speech while keeping the overall loudness of speech at or below normal loudness. The formula was obtained through an optimization process in which speech intelligibility and loudness were predicted from selected models. Using updated models and applying some revisions to the derivation process, a theoretically derived NAL-NL2 formula was obtained in a similar way. Further adjustments, directed by empirical data collected in studies using NAL-NL1 as the baseline response, have been made to the theoretically derived formula. Specifically, empirical data have demonstrated that (a) female hearing aid users prefer lower overall gain than male users; (b) new hearing aid users with more than a mild hearing loss prefer increasingly less gain with increasing degree of hearing loss than experienced hearing aid users, and require up to 2 years to adapt to gain levels selected by experienced hearing aid users; (c) unilaterally and bilaterally fitted hearing aid users prefer overall gain levels that vary less than estimated by the bilateral correction factor; (d) adults prefer lower overall gain than children; and (e) people with severe/profound hearing loss prefer lower compression ratios than predicted when fitted with fast-acting compression. The literature and data leading to these conclusions are summarized and discussed in this article, and the procedure for implementing the adjustments to the theoretically derived NAL-NL2 formula is described