Running performance, output power and styling aside, mechanical noise is also an important factor for determining the merchandise value of a motorcycle. However, the evaluation of mechanical noise has conventionally relied on human judgment and thus posed problems with respect to the uniformity, consistency and reproducibility of evaluation results. We therefore attempted to develop a method of quantitatively expressing the intensity of mechanical noise.
Two principal aspects of mechanical noise are discussed in this paper. One was the “rattling noise” that is periodically generated when a motorcycle is idling at a constant engine speed. The other was the “whistling noise” that is generated when the engine speed varies, for example, when the engine is raced. Instead of evaluating the level (i.e., sound pressure) of the motorcycle's overall noise that includes exhaust noise, we used as evaluation values the ratios of rattling and whistling noise levels to the overall noise level.
This method produced evaluation results that more closely reflected human perceptions. Further, we made this evaluation hardware system as simple as possible for easier on-site use.