Spatial sampling criteria for nearfield measurements made on cylindrical surfaces

The spatial sampling criteria were established for nearfield sound measurements, made on a cylindrical surface enclosing the sources, that enable the farfield of those sources to be calculated faithfully from the nearfield data. Examples are given of the criteria applied to both omnidirectional and directional sources: their nearfield and calculated farfield. In general the common practice of using half wave length samples circumferentially is shown to be adequate for omnidirectional fields (narrow spatial bandwidths) but not adequate for the broad circumferential spatial bandwidth fields encountered with directional sources. The appropriate sampling criteria may be deduced from equations described.