Analysis of the observed wavenumbers using wavenumber filtering is of great interest in the investigation of how a source of interest is radiating wave energy. An array beam pattern steered in a particular “look direction” (LD) corresponds to a wavenumber filter which will pass the corresponding wavenumber to the LD while attenuating all other wavenumbers. Wavenumber processing for fields in confined spaces is generally known in structural acoustics as modal filtering. The technique of establishing the Cramer–Rao lower bound (CRLB) for a statistical representation of wave front bearing, or the observed wavenumber by an array of sensors. The CRLB is a lower bound by definition, and is used to form a confidence estimate on the bearing error to go along with the bearing estimate itself. The CRLB is essential to produce bearing information, rather than bearing data. There are other physical problems that make large arrays with closely spaced sensors underperform the theoretical CRLB for bearing error.