Nearfield Acoustic Holography Experiments on Variously Correlated Compound Sources

Experiments were performed to determine guidelines for the placement of multiple reference microphones for NAH measurements on weakly correlated source regions. It was found that multiple references are not required to image the same source, and thus the number of references should approximate the expected number of source regions. It was also found that reference microphones should be placed as close to the source as possible, but should be sufficiently separated from each other that they provide independent information. Characteristics of measured data also suggest that it may be possible under certain conditions to carry out NAH-type reconstructions without using reference microphones at all, by sampling a pressure field in blocks and shifting phases to minimize discontinuity