Sound Quality Evaluation of Noise Emitted from Brush Cutters

Engine-driven brush cutters generate noise with the high sound pressure level. Although such noise should be firstly attenuated as a countermeasure, the sound quality design may also be one of the valid approaches for brush cutter noise. Perceived quality of noise generated by brush cutters, which were driven at various engine speeds, were measured using SD method. Stimuli induced impressions of muddy, rough, noisy, unpleasant, etc. We found the difference in perceived fluctuation strength between two-cycle engine sounds and four-cycle engine sounds. Furthermore, correlation analysis between rating results and metrics indicated that perceived quality of them were generally affected by loudness. In the next step, therefore, we employed stimuli with identical value of loudness. Results of SD experiments revealed that two-cycle engine sounds were significantly rated as being more fluctuating and unpleasant than four-cycle engine sounds in various engine speeds. Furthermore, rating results of unpleasantness were significantly correlated with those of perceived fluctuation strength under wide range of engine speeds. It was supposed that perceived fluctuation strength was created by impulsive waveform of stimuli, which were caused by incomplete combustion of fuel in the engine. Therefore, suppression of such acoustic characteristic may produce the improvement of sound quality.