Application of the AVL-Annoyance Index for Engine Noise Quality Development

The development of vehicle sound quality is becoming increasingly important in the automotive industry. Traditional noise and vibration engineering methods, which are used to minimize the overall noise level of a vehicle – its engine as the main noise source respectively – are valid for noise quality engineering but require a reliable measurement scale. The degree of success in reducing sound pressure levels is usually measured on the dBA scale. This is a well-established method and allows for setting firm targets and standards for noise control. Despite this importance to noise control engineering the dBA measure can provide only minimal indication of the annoyance of a particular sound.

Traditional methods of jury subjective appraisal have turned out to be time consuming and costly and often also unreliable. This is mainly due to the fact that a noise quality evaluation has to be carried out repeatedly in an industrial development process. Furthermore this appraisal is usually done by experts and does not necessarily reflect the noise quality impression of the majority of customers.

Thus it was clear to AVL, and others, that a reliable way to measure the annoyance of engine and vehicle sounds was required. What was needed was a single number index which could be used in a similar way to the dBA scale. The term "annoyance" was chosen for the new index to ensure that it could be handled like a level: i.e. lower numbers mean better noise quality. Furthermore the method should provide information on the composition of annoying parameters of the noise. It was clear from the very beginning that noise quality or annoyance impression will be a combined effect of several psychoacoustic parameters.