Some Considerations Regarding the Use of Perceived Noise in Vehicle Acoustics

Loudness of sounds is often assumed to be an adequate indicator of the unwantedness, for general noise control purposes, of sounds. Experiments have shown, however, that for many sounds there are differences between some physical aspects of sound, and judgements of Loudness (soft/loud) compared to judgements of Noisiness (acceptable/unacceptable), which is sometimes called Perceived Noise or Perceived Noise Level, depending on the units used. Internal sound pressure level of two sets of vehicles, commercial and passenger cars, are used to calculate the acoustic parameters: Loudness in sones, according to Stevens and Noisiness in noys according to Kryter. The calculations are similar, but Kryter's Equal Noisiness Contours emphasize the high frequencies. We look for the degree of linear correlation of these acoustic parameters, applying to the experimental data least squares curve fittings. In addition we establish a ranking for both parameters using a specific set of vehicles. We use propagation of errors in the mathematical expressions regarding the acoustic parameters to discuss the divergencies in the ranking order, using a specific category of vehicles. We comment and discuss the results obtained, taking into consideration the overall values, their band contributions, the traditional acoustic parameters used in vehicle acoustics and subjective considerations found in the literature.