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Beamforming based on measurements with a spherical microphone array is a recognized technique for localization of noise sources. The method is very efficient for getting a quick overview of the positions of the most dominant sources. However, when more detailed information about the radiation from a source is needed, acoustical holography is normally more suitable, because it provides the actual acoustical quantities (pressure, velocity and/or intensity) at positions on or near the source surface, whereas beamforming only gives a directional map of contribution at the array position. Even though spherical arrays are most often used for beamforming they can also be applied for holography purposes. This means that with the same hardware beamforming can be used to identify a noise source, and then the array can be moved closer to the source to get a clearer picture of the radiation by using holography.

The present paper describes a set of array-based methods that can provide both a snapshot overview of problematic areas across the panels of a car cabin and perform efficient analysis of details of a noise problem. The snapshot overview is obtained with Beamforming, while detailed analysis of problematic areas is performed with a small planar single-layer or double-layer array in combination with SONAH holography. Using the SONAH algorithm for patch near-field acoustic holography, all sound field parameters can be estimated directly on the irregularly shaped panel surfaces. All the array measurements can be performed very efficiently by the use of a position measurement system integrated with the array. Panel geometry can also be measured using the position measurement system. The paper gives an overview of the different methods and presents results from a case study.