DETERMINATION OF THE DIRECTIVITY OF A PLANAR NOISE SOURCE BY MEANS OF NEARFIELD ACOUSTICAL HOLOGRAPHY, PART III: MEASUREMENTS ON HOMOGENEOUS, PROFILED AND COMPOSITE PANELS
✍ Scribed by M.A. Rowell; D.J. Oldham
- Publisher
- Elsevier Science
- Year
- 1996
- Tongue
- English
- Weight
- 754 KB
- Volume
- 189
- Category
- Article
- ISSN
- 0022-460X
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✦ Synopsis
In two companion papers, a method has been presented for determining the directivity of a planar noise source by using the technique of Nearfield Acoustical Holography [1,2]. In this paper, a practical NAH measuring system based upon a single scanning microphone is described. The system is employed to measure the directivity of a number of planar noise sources consisting of panels excited on one side by a reverberant sound field. The noise sources include profiled panels which are structurally orthotropic and for which it has been suggested there should be two critical frequencies. Evidence for the existence of two critical frequencies for quasi-sinusoidally profiled panels is presented within, from the observed directivity pattern. Similar evidence for the existence of two critical frequencies for trapezoidally corrugated panels was not observed. This is believed to be due to the sharp bends in the profile of such panels acting as localized reflecting boundaries.