Recently, the quality of engine sound in a passenger car compartment during acceleration has been considered more important for sensory quality, and its improvement method has been under development. An objective evaluation method by psycho-acoustic indexes is effective and necessary for improving the sound quality. In this study, we developed an objective method of evaluating the sound quality during acceleration of a compact sedan with a 4-cylinder gasoline engine.

The result of a subjective evaluation test revealed that the sound quality of a 4-cylinder gasoline engine was expressed by two factors, 'annoying' and 'metallic'. The 'annoying' factor was expressed by psycho-acoustic indexes of booming noise and rumbling noise. The 'metallic' factor was expressed by the metallic sound index (a new psycho-acoustic index) based on another subjective evaluation test. Furthermore, the total engine sound quality for a compact sedan was expressed by these objective factors. As a result, an objective method of evaluating the engine sound quality has been developed. Applying this objective evaluation method to interior sounds of passenger cars with 4-cylinder engine, we found that we could obtain the characteristics of sound quality, which were effective for determining the target of the engine sound quality for a developing car.
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