Comparison of patch acoustic holography methods for confined space

Localization and characterization of noise and vibration sources through measurement of sound fields radiated from vibrating structures plays an important role in vibration diagnostics. Sound pressure field measured in closed distance to the source with a microphone array is then inversely processed with the suitable near-field acoustic holography method to obtain the estimation of sound field very near the identified source surface. Several restrictions apply when measurement is performed in non-anechoic conditions and with the array smaller than the examined source. In these cases patch holography methods with sound field separation technique should be used. The Equivalent Source Method (ESM), Statistically Optimized Near-field Acoustical Holography (SONAH) and iteratively enhanced Fourier transformation based procedure are examples of such methods. In this paper an extensive comparison of these source identification methods has been carried out while other disturbing sources affect the acquired data. Experimental evaluation of the methods has been performed in ideal anechoic conditions and further in disturbing environment. Real measurement data has been obtained with double layer planar rectangular microphone array with MEMS transducers and the results of principal source identification accuracy for all methods have been presented. Some practical aspects of applicability of each method are also discussed.