Human Auditory Models and Sound Quality Evaluation Method for Diesel Noise

Sound Quality (SQ) improvement is recently one of the important issues in diesel engine development. Therefore a new method was developed by the authors about ten years ago to establish objective criteria for SQ assessment. Considering the sensitivity of human hearing to impulsive sounds such as diesel noise, the human auditory mechanism was simulated by introducing temporal masking in the time domain. Furthermore, each of the human auditory organs was simulated by computer codes, providing reasonable analytical explanations of typical human hearing responses to diesel noise. This method finally provides us a good index of sound quality, i.e. an SQ index, of diesel noise that includes high-frequency intermittent offensive sounds caused by impacting excitations of combustion, piston slap, etc.

This paper describes human audibility of sound structures of diesel noise and also human hearing models, which are implemented in SQ evaluation tools by utilizing recent physiological knowledge. A chemical reaction in the hair cells of the cochlea, for example, is a recent physiological knowledge that assists in understanding the hearing process, where the chemical reaction converts vibration of the basilar membrane in the cochlea into the electrical nerve signals leaving the hair cells. These electrical nerve signals are led to the primary auditory cortex in the human brain for final recognition of hearing events. Additionally it describes applications of the SQ method to diesel-noise development in the past decade on test benches as well as vehicles.