
246 Structural Acoustics: Deterministic and Random Phenomena
© 2011 by Taylor and Francis Group, LLC
Thus, it is found that, by measurement of G(P, P, ω) and several trans-
formations, a set of cross spectra that produced this eld can be obtained.
Butler
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has demonstrated the soundness of using autospectra (or intensity)
to obtain the coefcients in the expansion and then using these coefcients
to compute the far eld directivity pattern. By using a spherical wave
expansion to obtain the eld from three point sources with nine hydro-
phone measurements, he obtains excellent results. (Butler does not use the
Green’s function expansion ...