Determination of preference-equivalent levels for fan noise and their prediction by indices based on specific loudness patterns.

Abstract

In a previous study by the authors, two indices were identified as appropriate descriptors for perceptual dimensions of fan noise. The index Nlow describes the amount of low-frequency loudness relative to the overall loudness. The index Nratio represents the ratio between the amount of loudness resulting from mid-frequency content and that from high frequencies. The aim of this study is to quantify how variations in these two indices affect subjects' preferences and loudness judgments. In listening experiments, fan noise signals were adjusted separately to equal loudness and equal preference compared to a common reference sound by varying their level in an adaptive procedure. The fan noises used in the listening tests consisted of 11 typical signals from three major groups of fan sounds from the earlier study and 18 signals that were parametrically varied in terms of the two indices. Reductions in A-weighted sound pressure level of up to 15 dB were necessary to make unpleasant fan sounds equally preferred as the fixed reference sound. A regression model based on the index Nratio explains 81% of the variation in the evaluation data with a root-mean-squared error of 2.53 dB.