Perspective of the sound quality approach applied to noise control in earth moving machines

The paper describes two experiments aimed at evaluating the feasibility and potential of the "sound quality" approach in improving the design of noise reduction treatments for Earth-Moving Machines (EMMs). In both experiments, binaural noise recordings taken in EMMs operating at stationary idle conditions have been used and subsequent laboratory listening tests have been carried out. In the first experiment, the recordings taken in three EMMs at different engine speeds were considered and presented by headphones to 35 naive subjects using the paired comparison method. In the second experiment, one of the previous recordings has been modified to get six sound stimuli, all having equal overall unweighted Leq levels but with different spectral shapes. The results confirm that subjective preference for a sound stimulus is influenced both by the overall sound energy and by its distribution in the frequency domain. Thus, sound energy-oriented parameters turn out to be not sufficient to characterise the auditory perception in EMMs. To investigate this aspect deeply, a principal component analysis has been performed on the sound stimuli. The results show that the most important factors which explain the subjective preference include the 400-5000 Hz frequency range and low engine order harmonics. In addition, loudness and PSIL appear to be promising for assistance with choosing suitable noise treatments more related to auditory perception.