Inverse Vibro-acoustic Techniques for Automotive NVH Development

Abstract

In vehicle NVH, the essential task to reduce the noise and optimize the radiated sound quality is to identify the contributions from sources and paths modified by dissipation and dynamic transfer characteristics. In many cases, the resultant field exists, but the source distribution or the physical properties of transmission elements need to be known. The object of solving the inverse problem is to restore the target source properties from the known field data, thus one can identify either the source properties, which are causes of propagated sound and vibration, or the physical parameters, which are closely related with the transfer characteristics. Here, some practical subjects of such inverse problems are discussed in automotive NVH areas. Among many, two typical categories in application themes are only to be considered, and the underlying principles are shown in a unified approach. First, the source identification or localization using inverse method is considered for the extended source in connection with the use of the near-field acoustical holography, transfer path analysis, and source localization techniques. Brief discussion on each method and their relation is explained. Second, one can apply the inverse approach to the vibro-acoustic field rendering to achieve a desired field given as a relative response distribution of pressure or vibration amplitude. Using the analogy between holographic identification and field rendering, a brief description on the field rendering technique is provided. Application examples for vehicle NVH refinement are demonstrated. In all foregoing examples, difficulties to overcome in practical implementation are discussed. It is thought that a huge opportunity is open for extending the aforementioned concept to many other unrefined automotive NVH problems.