Fourier Acoustics

Chapter 3

The Inverse Problem: Planar Nearfield Acoustical Holography

3.1 Introduction

Acoustical holography, the predecessor of NAH, appeared in the mid 1960s.¹ Acoustical holography, however, is only an approximation to the inverse problem of reconstructing sound fields. This inverse problem backtracks the pressure field in space and time towards the sources. Only source details greater that the acoustic wavelength can be retrieved in this procedure. Nearfield acoustical holography, which appeared in 1980,² provides a rigorous solution, however, to the inversion resulting in an almost unlimited resolution in the reconstruction. When evanescent waves are present (such as plate vibrator sources which contain subsonic waves), an essential requirement ...