Improved Equivalent Source Method Applied to Sound Source Identification on a Vehicle

For measurements on a vehicle, Near-field Acoustical Holography methods like Equivalent Source Method can be applied to sound source identification at relatively low frequencies. However, at a large distance and high frequency, NAH loses its ability to provide good resolution. The objective of this study is to maintain good medium-to-high frequencies resolution by introducing an improved Equivalent Source Method. Similar to the Equivalent Source Method, it can build a functional model between the elementary equivalent sources and measured pressure. Then a quadratic residual function can be obtained by the optimization method. Using the regularized least squares solution of ESM as the initial solution. Similar to the wideband acoustical holography, the threshold filtering method also can be introduced. Eventually, the equivalent source strengths can be evaluated by calculating the iterative approximate solution. Based on the equivalent source strengths, it then can reconstruct the surface field at arbitrary position. Because of the introduction of the steepest descend and threshold filtering method, IESM can identify the main sources much more accurately. Both the simulations and experiments have shown that the sources are correctly detected and separated by the IESM at medium-to-high frequencies.