Sound Intensity Visualization with a Rigid Spherical Microphone Array in a Vehicle Cabin

• Main Authors: Takashima, Kazuhiro, Nakagawa, Hiroshi, Williams, Earl G
• Format: Report
• Language: English
• ISSN: 0148-7191; 2688-3627
• DOI: 10.4271/2009-01-2176

Measurement of the sound intensity vector distribution is a useful way to identify noise sources in a vehicle especially at low frequencies. Due to the effect of standing waves, it is difficult to identify the source location from the sound pressure measurement at the driver's ear position. Direct measurements, such as scanning the entire vehicle cabin with a three-dimensional sound intensity probe is very time consuming, and is not able to track temporal and spatial changes in the sources. In this paper, an approach is presented that provides a prediction of the vector sound intensity field throughout a volume exterior to a rigid spherical measurement array consisting of flush mounted microphones. The theory is called spherical near-field acoustic holography (Sp-NAH) based on spherical harmonic expansions of the measured sound pressure field with the radial variation of the near-field pressure obtained using the Green's function with vanishing normal derivative at the rigid sphere surface. Measurement results showing volumetric sound intensity vector reconstructions in a vehicle cabin are presented. The measurement equipment was used in previous demonstrations to visualize the acoustic field using a spherical beamforming (Sp-BF) technique superimposed on pictures from on-board cameras. Comparison between Sp-NAH and Sp-BF is also presented and discussed in this paper. In this study, sound intensity reconstructions using Sp-NAH are successful in locating and quantifying sources, demonstrating the usefulness of this technique in an enclosed space such as a vehicle cabin, an aircraft cabin, a small room, etc.