Reduction of Knocking Sound Annoyance Through Engine Sound Order Simulation

The objectives of this study were to mitigate the annoyance caused by engine noise identify the underlying factors contributing to knocking noise during engine vehicle acceleration, and explore methods for its reduction. A time-frequency analysis was employed to examine the characteristics of knocking sound, revealing a peak frequency between 1 and 5 kHz at the onset of acceleration, which was identified as the knocking sound. Given the proximity of the frequencies in the low-order components at the onset of acceleration, it was hypothesized that annoyance arises from the simultaneous occurrence of low-frequency humming or fluctuations alongside the knocking sound. To address this, stimulus sounds were generated by isolating the order components and knocking sound during acceleration. A sound synthesis method, called the Sinusoidal Model, was used to generate the stimulus sounds with high and low-order components. The knocking sound was isolated by applying a 1 kHz high-pass filter to the acceleration sound. Subsequently, the isolated order components were combined with the knocking sound to create the stimulus. Auditory evaluations were conducted using these stimulus sounds, and the results were analyzed in conjunction with psychoacoustic indices such as loudness and roughness.