Volume 118, Issue 3, September 2005
Index of content:
- AEROACOUSTICS, ATMOSPHERIC SOUND 
118(2005); http://dx.doi.org/10.1121/1.1992707View Description Hide Description
Infrasonic windscreens, designed for service at frequencies below , were fabricated from a variety of materials having a low acoustic impedance, and tested against four specifications (the first three in a small wind tunnel): (1) wind-generated noise reduction (“insertion loss”) at a free-stream wind speed of , (2) transmission of low-frequency sound from a known source (subwoofer), (3) spectrum of sound generated from trailing vortices (aeolian tones), and (4) water absorption (to determine suitability for all-weather service). The operating principle is based on the high penetrating capability of infrasound through solid barriers. Windscreen materials included three woods (pine, cedar, and balsa), closed-cell polyurethane foam, and Space Shuttle tile material. The windscreen inside diameter ranged from , and wall thickness from . A windscreen made of closed-cell polyurethane foam revealed a wind noise reduction of from , transmission coefficient near unity from , and spectral peaks beyond due to vortex-generated sound. Following a description of past methods, the principle of operation, and the experimental method, experimental data are presented for a variety of windscreens.