Annoyance penalty of impulsive noise - The effect of impulse onset

Impulsive sound can be perceived more annoying than a steady-state sound having the same A-weighted equivalent sound pressure level, LAeq. The difference in perceived noise annoyance can be compensated by adding a penalty or an adjustment k to LAeq (rating level). Many legislations apply a constant penalty value, such as 5 dB or more, but the validity of this procedure has been questioned. Nordtest method NT ACOU 112 identifies an impulse from the time profile of sound pressure level by using two measures describing the onset of an impulse: level difference (DL) and onset rate (Ron). The purpose of this study was to determine how the annoyance penalty depends on DL (5-40 dB) and Ron (5-800 dB/s) and to compare obtained results to the penalty prediction model of Nordtest method. A psychoacoustic laboratory experiment of 32 participants was conducted. Synthetic and periodic impulsive sounds were studied with two alternative spectra. The sounds were presented at 55 dB LAeq. Steady-state sounds at levels 49-70 dB were used to derive the penalty of impulsive sounds. The observed penalty values ranged between 0 and thorn 8 dB. The penalty values depended somewhat on spectrum. The penalty deviated from zero when DL > 10 dB or Ron > 15 dB/s and increased with increasing DL and Ron. The penalty predicted by Nordtest method usually overestimated the observed penalty when Ron. 200 dB/s. The results are against constant penalty values and they can be used to develop future penalty schemes.