This paper describes the results of an analytical study of the accuracy and limitations of a technique that permits the mathematical extrapolation of near-field noise data to far-field conditions. The effects of the following variables on predictive accuracy of the far-field pressure were examined:(1) number of near-field microphones;(2) length of source distribution;(3) complexity of near-field and far-field distributions;(4) source-to-microphone distance;and (5) uncertainties in microphone data and imprecision in the location of the near-field microphones. It is shown that the most important parameters describing predictive accuracy are the number of micro phones, the ratio of source length to acoustic wavelength, L/λ, and the error in location of near-field microphones. If microphone measurement and location errors are not included, then far-field pressures can be accurately predicted up to L/λ values of 15 using approximately 50 microphones. For maximum microphone location errors of ±1 cm, only an accuracy of ±2-1/2 dB can be attained with approximately 40 microphones for the highest L/λof. 10., However, this restriction can be lifted to a large degree if more precise measurement techniques are used.
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