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Journal of the Acoustical Society of America

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Jun 2010

Volume 127, Issue 6, pp. EL235-3881

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Theory of compact nonporous windscreens for infrasonic measurements

Allan J. Zuckerwar

J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3327-3334 (2010); (8 pages) | Cited 1 time

Online Publication Date: 09 Jun 2010

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The principle of the compact nonporous windscreen is based on the great penetrability of infrasound through matter. The windscreen performance is characterized by the ratio of the sound pressure at an interior microphone, located in the center of a windscreen, to the incident sound pressure in the free field. The frequency dependence of this pressure ratio is derived as a function of the windscreen material and geometric properties. Four different windscreen geometries are considered: a subsurface, box-shaped windscreen, a cylindrical windscreen of infinite length, a cylindrical windscreen of finite length, and a spherical windscreen. Results are presented for windscreens made of closed-cell polyurethane foam and for typical dimensions of each of the above geometries. The cylindrical windscreen of finite length, featuring evanescent radial modes, behaves as a unity-gain, low-pass filter, cutting off sharply at the end of the infrasonic range. The remaining geometries reveal a pass band that extends well into the audio range, terminated by a pronounced peak beyond which the response plummets rapidly.
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43.28.Dm Infrasound and acoustic-gravity waves
43.50.Yw Instrumentation and techniques for noise measurement and analysis

Meteorological influence on sound propagation between adjacent city canyons: A real-life experiment

Timothy Van Renterghem and Dick Botteldooren

J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3335-3346 (2010); (12 pages)

Online Publication Date: 09 Jun 2010

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Sound propagation between a courtyard and an adjacent street canyon, as influenced by a wide range of meteorological conditions, was investigated by means of a real-life experiment in a dense urban setting. During several months, test signals were emitted on a regular base by an outdoor loudspeaker in the courtyard and recorded by wall-mounted microphones in the courtyard and the street canyon. Detailed meteorological observations were made at nearby buildings with sensors at roof level. A thorough quality check of the recorded signals was performed, given the large amount of shielding and the presence of background noise. With increasing wind speed and sound frequency, a strong increase in coherence loss was observed. The wide variety of measured vertical temperature lapses was shown to have no effect given the short propagation distance. With increasing downwind wind speed, refraction into the shielded canyon was observed to a limited degree only. The rather small effect of building-induced refraction of sound by wind could be qualitatively explained by the geometry of the city canyons under study.
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43.28.Fp Outdoor sound propagation through a stationary atmosphere, meteorological factors
43.28.Gq Outdoor sound propagation and scattering in a turbulent atmosphere, and in non-uniform flow fields
43.50.Rq Environmental noise, measurement, analysis, statistical characteristics

Predicting transmission of shaped sonic booms into a residential house structure

Natalia V. Sizov, Kenneth J. Plotkin, and Christopher M. Hobbs

J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3347-3355 (2010); (9 pages) | Cited 1 time

Online Publication Date: 09 Jun 2010

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Human perception of sonic booms is a major impediment to commercial supersonic flight. Shaping, which reduces the audible shock waves of a boom, can make outdoor perception of booms acceptable. Perception of sonic booms experienced indoors is of concern, and it is not yet established whether shaped booms offer benefit to indoor listeners. A better understanding of the transmission of shaped booms into building structures is needed. In the authors’ earlier work the vibration response of house elements subjected to different sonic boom wave shapes was evaluated using a single degree of freedom model. This paper expands that approach with a modal analysis model. The acceleration of building elements and the resulting sound pressure inside a room are computed in the time and frequency domains. Analytical results are compared with experimental data measured by NASA during sonic boom tests conducted at Edwards Air Force Base in 2007. The effects of wave signature parameters on transmission are studied to evaluate the advantages of various kinds of minimized boom shapes.
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43.28.Mw Shock and blast waves, sonic boom
43.55.Rg Sound transmission through walls and through ducts: theory and measurement
43.40.Dx Vibrations of membranes and plates
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