Loudness matching of complex tones simulating sounds from electric trucks

With electric powertrains quickly advancing in the heavy vehicle sector, there is an increasing interest in the industry to find a general practice for evaluating tonal sounds. The challenge to set requirements is complex. Tonal sounds span from extremely annoying to pleasant. Established methods for prediction of tonal magnitude typically estimate individual tonal components without considering interrelations between the tones. In this study, the loudness perception of continuous complex tones with increasing number of harmonics as well as non-harmonic tone components, is assessed using pink noise as reference. Frequencies studied cover 350–11 000 Hz. These frequencies typically occur in electrified trucks, hitting the most sensitive area of the human hearing. The results show a statistically significant positive linear relationship between perceived loudness and increasing number of harmonics, even with decreasing level of amplitude (−6 dB/oct). Significant differences are seen between harmonic and non-harmonic tonal signals, when the second partial is detuned. Increasing the number of tonal components increases the perceived loudness linearly. Non-harmonic complex tonal sounds are assessed less loud than the corresponding harmonic sounds. In case of complex tonal sounds, models of loudness estimation need to take the number of tone components and their frequency ratios into account.