"ESDU 72002 gives a method of estimating the near field sound pressure levels due to high velocity jet noise from a single stationary conical nozzle. From a comparison with measured data@ the accuracy of the estimated levels is expected to be within 5 dB@ i.e. between approximately 60 per cent and 170 per cent of the actual r.m.s. pressure. Under reheat conditions@ however@ the discrepancy could be wider. At low jet velocities@ where sources of noise other than pure jet mixing noise can be significant@ the method underestimates the apparent jet noise. The noise levels predicted by the method described here are free field values but do not apply to the field within a conical surface emanating from the jet nozzle perimeter and expanding at a semi-angle of approximately 15 degrees relative to the jet axis@ since this region contains the turbulent mixing region of the jet. The data are not applicable to the case of ""shock cell noise""@ a phenomenon that can occur when a jet nozzle is operating in an over-choked condition. See also ESDU 99006 and ESDUpacs A9906@ B9906 and C9906 for programs that provide a near-field noise database and a method of extrapolating outside it or interpolating within it."