Effects of repitition rate and impulsiveness on annoyance due to simulated helicopter rotor noise

Abstract

Annoyance judgments of 82 different simulated helicopter impulsive rotor noise stimuli were obtained in an anechoic chamber to examine effects of repetition rate and impulsiveness. The stimuli were generated by computer from predicted Fourier harmonic structure with amplitude and phase components corrected for effects of the audio reproduction system. Impulse repetition rates covered a range from 10 to 115 Hz; crest factors covered a range from 3.2 to 19.3 dB. Each stimulus was judged at three sound pressure levels by 48 subjects. Judgments were converted from a continuous numerical annoyance scale to a decibel like scale by comparing them to judgments of annoyance of a 115-Hz tone presented over a wide range of sound pressure levels. Increases in annoyance with increases in repetition rate were found which were not predicted by common loudness or annoyance metrics and which were independent of noise level. The ability to predict effects of impulsiveness varied between the noise metrics, and was found to be dependent on noise level. The ability to predict the effects of impulsiveness was not generally improved by any of several proposed “impulsiveness corrections.” Instead, the effects of impulsiveness were found to be systematically related to the frequency content of the stimuli. A modified frequency weighting was developed which offers improved annoyance prediction.