Multi-Reference Scan-Based Nearfield Acoustical Holography
Multi-reference, scan-based Nearfield Acoustical Holography (NAH) is a useful measurement tool that can be applied when an insufficient number of microphones are available to make measurements on a complete hologram surface simultaneously. The scan-based procedure can be used to construct a complete hologram by joining together sub-holograms captured using a relatively small, roving scan array and a fixed reference array. For the procedure to be successful, the source levels must remain stationary for the time taken to record the complete hologram: that is unlikely to be the case in practice, however. Usually, the reference signal levels measured during each scan differ from each other with the result that spatial noise is added to the hologram. A non-stationarity compensation procedure that is based on the acoustical transfer functions between the sources and both the reference and scanning, field microphones are invariable is introduced. Numerical and experimental results show well the availability of the introduced procedures to suppress the spatially distributed noise and to get better sound fields partially separated.
Seung-Seok Lee, Joon Hyun Lee, Ik Keun Park, Sung-Jin Song, Man Yong Choi
H. S. Kwon "Multi-Reference Scan-Based Nearfield Acoustical Holography", Key Engineering Materials, Vols. 321-323, pp. 1249-1252, 2006