The parameters such as lower noise levels, quietness, etc. of a vehicle has no longer remained the only driving features since the passenger car buyers are greatly influenced by the perception of the sound. In a scenario like this, the sound quality becomes of great importance especially for smaller diesel powertrains as they are more annoying than their gasoline counterparts. The idling noise is critical as its noise creates the first impression of the vehicle on the buyer. The Indian passenger car market is dominated by diesel cars equipped with smaller engines less than 2 liter capacity.
Present work describes the methodology to formulate the equation for annoyance/pleasantness for the diesel powertrains used in Indian passenger cars. The index, Sound Annoyance Rating (SAR) developed through this work is significant for powertrain level target setting and benchmarking purposes.
The sound data is recorded at powertrain level in hemi anechoic chamber at idling condition for 16 different powertrains with the capacity ranging from 1 lit-2 lit. Subjective evaluation is carried by combination of two jury evaluation techniques i.e., paired comparison method and percentage rated scale. About 80 subjects were involved in the evaluation of 16 powertrains. Analytical accuracy is improved by eliminating the outliers statistically. Psychoacoustic index (Loudness, Sharpness, Fluctuation Strength, Roughness, Articulation Index, etc) were calculated which forms the objective data. Analyses involves the identification of correlating metrics and further use multiple regression analysis where jury ratings are input as dependent variables and relevant sound quality metrics as independent variables to develop SAR index.
The annoyance correlates with loudness, roughness, sharpness& fluctuation strength significantly. SAR is utilized to improve the sound quality of the test engine by modification of pilot injection strategy.