The process for setting the marketability targets and achievement methods for automotive interior quietness (as related to air borne noise above 400Hz, considered the high frequency range) was established. With conventional methods it is difficult to disseminate the relationship between the performance of individual parts and the overall vehicle performance. Without new methods, it is difficult to propose detailed specifications for the optimal sound proof packages.
In order to make it possible to resolve the individual components performance targets, the interior cavity was divided into a number of sections and the acoustic performance of each section is evaluated separately. This is accomplished by evaluating the acoustical energy level of each separate interior panel with the unit power of the exterior speaker excitation.
The applicability of the method was verified by evaluating result against predicted value, using the new method, during actual vehicle operation. The difference between predicted interior cavity sound pressure level (SPL) and that of measured was less than 3dB. In addition, the difference in the level of reduction in interior cavity SPL by countermeasure between predicted and measured was less than 0.5dB. This was judged as acceptable accuracy. This new method is being developed for use within the design process and makes it possible to propose optimized specifications for sound proof package.
