Evaluation of sound quality of wheel loaders using a human subject for binaural recording

Abstract

The sound quality of four different models of wheel loaders was evaluated using twenty-eight experienced male operators as subjects. Using these human subjects, sounds were recorded binaurally and played back through headphones. Tachometer recordings were also made from the engines and transmissions in order to trace the origins of amplitude peaks in the signals. There were two sessions (viz. lift and transportation) for each wheel loader. Altogether, there were eight sessions for all four wheel loaders. Tachometer signals indicated that peaks were dominated mainly by pinion and drop box for the transport sounds, whereas the peaks of hydraulic orders (i.e., between 250 and 1000 Hz) were dominant for the lift sounds. The dominant peaks were damped by either 3 or 6 dB, thus creating new modified sounds. Both original and modified sounds were then played randomly and separately for all sessions using a paired comparisons method. The results showed that the pinion and drop box were causing annoyance for the transportation sounds, while the hydraulic orders were causing annoyance for the lift sounds. The results also revealed that damping the tonal components created by the drop box reduced the annoyance response more significantly than damping the tonal components made by the pinion. This indicates that the tonal components in higher frequencies were more annoying than the tonal components in lower frequencies. In the final part of the study, multivariate analysis was applied in order to model annoyance of noises from the four different models of wheel loaders for both sessions (i.e., lift and transportation) on the basis of the sound quality descriptors. Annoyance prediction models for all sessions were developed based on the articulation index and a newly developed descriptor, viz. tonal ratio. The new descriptor identifies the tonal components by comparing the sound pressure level of each 1/3-octave band of the peaks between 125 and 3150 Hz with the two 1/3-octave-band levels adjacent to it.