Near field acoustic holography with double layer array processing

Near field acoustic holography (NAH) is an experimental technique for analysing sound fields near sources. A simulation study has been carried out, and this paper examines and compares i) classical planar NAH based on spatial transforms (single layer NAH), ii) a similar technique based on measurements in two parallel planes (double layer NAH), and iii) a method that avoids spatial transforms and thus leakage by using statistical considerations (SONAH). The source is a point driven panel that generates a complicated sound field. The influence of reflections and background noise from other sources is examined. The results indicate improved accuracy in localisation and characterisation of a sound source with double layer array processing in the presence of sources from the 'wrong' side of the measurement array. An investigation of the influence of transducer mismatch errors on the global accuracy of the NAH calculations shows that NAH with single and double layer arrays are affected in a similar manner.