Perception of noise from diesel-engine powered vehicles

Abstract

A program was developed to simulate diesel engine sounds to have control over timing and amplitude variations in combustion events. The simulation includes this combustion-related noise, together with a noise floor and families of tones from auxilliary components. Additional shaping filters to control the spectral balance of the sounds are also included. Sound and vibration measurements from ten vehicles powered by diesel engines were taken and combustion event timing and amplitudes were extracted to determine what ranges and types of variations typically occurred. It was found that there were random, deterministic and individual cylinder variations present in one or more of the vehicles. From this analysis, the simulation program was used to generate 199 sounds for a listening test in which 40 subjects participated. Spectral balance, tonalness, and, fluctuations all affected the subjects’ responses and, above certain levels, as they increased so did subjects’ annoyance ratings. Based on the results of this test, modifications to the psychoacoustic annoyance model [Zwicker and Fastl, Psychoacoustics: Facts and Models, 2nd ed. (Springer, New York 1998)] are proposed. These modifications include the incorporation of a term that quantifies how the tonal character of the sound affects annoyance. [Work supported by Isuzu Motor Company.]