The Use of Wideband Acoustical Holography for Noise Source Visualization

Regularization is an important step in the acoustic holography process, since it can help mitigate problems associated with evanescent waves, the ill-posed nature of the problem, etc. and there is no single regularization method that is best for all problems. Recently, a new monopole-based equivalent source procedure referred to as wideband holography was developed by Hald (J. Hald,"Wideband Acoustical Holography", INTER-NOISE 2014) as part of which regularization procedures were proposed to optimize the solution in the case of an under-determined system. By using this method it is possible to balance the model accuracy and the sparsity of the system: i.e., the procedure allows the systematic reduction of number of the equivalent sources in the model. In the present work, experiments were conducted by using a loudspeaker cabinet and an eighteen channel irregular array placed in front of the loudspeaker. The equivalent source distribution consisted of an array of monopoles placed behind the reconstruction surface. It was found that wideband holography gives accurate noise source location predictions, and allows efficient and accurate acoustic field reconstruction results compared to other methods.