DETERMINATION OF THE DIRECTIVITY OF A PLANAR NOISE SOURCE BY MEANS OFNEARFIELD ACOUSTICAL-HOLOGRAPHY .3. MEASUREMENTS OF HOMOGENEOUS, PROFILED AND COMPOSITE PANELS
Ma. Rowell et Dj. Oldham, DETERMINATION OF THE DIRECTIVITY OF A PLANAR NOISE SOURCE BY MEANS OFNEARFIELD ACOUSTICAL-HOLOGRAPHY .3. MEASUREMENTS OF HOMOGENEOUS, PROFILED AND COMPOSITE PANELS, Journal of sound and vibration, 189(3), 1996, pp. 369-398
In two companion papers, a method has been presented for determining t
he directivity of a planar noise source by using the technique of Near
field Acoustical Holography [1, 2]. In this paper, a practical NAH mea
suring system based upon a single scanning microphone is described. Th
e system is employed to measure the directivity of a number of planar
noise sources consisting of panels excited on one side by a reverberan
t sound field. The noise sources include profiled panels which are str
ucturally orthotropic and for which it has been suggested there should
be two critical frequencies. Evidence for the existence of two critic
al frequencies for quasi-sinusoidally profiled panels is presented wit
hin, from the observed directivity pattern. Similar evidence for the e
xistence of two critical frequencies for trapezoidally corrugated pane
ls was not observed. This is believed to be due to the sharp bends in
the profile of such panels acting as localized reflecting boundaries.
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