Index of content:
Volume 122, Issue 5, November 2007
- NOISE: ITS EFFECTS AND CONTROL 
Acoustical, sensory, and psychological research data and procedures for their use in predicting effects of environmental noises122(2007); http://dx.doi.org/10.1121/1.2782748View Description Hide Description
A demonstration field-research study reveals that aircraft noisemeasured at two one-story houses is less attenuated from measured outdoor levels than is street traffic noise, and, found in other studies, less than railway noise. Comparable differences are found between these noises from the application of basic acoustical formulas for quantifying attenuations that occur on site of one- and two-story houses. Reasonably consistent with those findings are results from attitude surveys showing that daily exposure levels of aircraft must be less than levels of street traffic noise, and less than levels of railway noise to be perceived as an equal cause of annoyance and related adverse effects. However, USA government guidelines recommend that equal exposure levels of noisemeasured outdoors from vehicles of transportation should be considered as being equally annoying. Changes in present USA noise-measurement procedures and noise-control guidelines are proposed that provide more accurate predictions of annoyance, related adverse effects, and criteria for setting “tolerable” limits of noise exposure in residential areas. Key acoustical and psycho-acoustical principles and data pertaining to predicting correlations between dosages of environmental noises and its effects on people and land noise zoning in residential communities are examined.
122(2007); http://dx.doi.org/10.1121/1.2783122View Description Hide Description
This paper presents a theoretical and experimental study of noise control in enclosures using a T-shaped acoustic resonator array. A general model with multiple resonators is developed to predict the acoustic performance of small resonators placed in an acoustic enclosure. Analytical solutions for the sound pressure inside the enclosure and the volume velocity source strength out of the resonator aperture are derived when a single resonator is installed, which provides insight into the physics of acoustic interaction between the enclosure and the resonator. Based on the understanding of the coupling between the individual resonators and enclosure modes, both targeted and nontargeted, a sequential design methodology is proposed for noise control in the enclosure using an array of acoustic resonators. Design examples are given to illustrate the control performance at a specific or at several resonance peaks within a frequency band of interest. Experiments are conducted to systematically validate the theory and the design method. The agreement between the theoretical and experimental results shows that, with the help of the presented theory and design methodology, either single or multiple resonance peaks of the enclosure can be successfully controlled using an optimally located acoustic resonator array.
122(2007); http://dx.doi.org/10.1121/1.2785041View Description Hide Description
Rubber has traditionally been used for underwater sound absorption. Porous metal is a relatively lightweight material and also has higher strength than rubber. However, exactly how porous metals can be used as effective underwater sound absorbers remains unclear. This paper shows how to use porous metal absorbers so that they work well under water, even under fairly constrained conditions. A method of nondimensional analysis is proposed that allows identification of vital characteristics. This means that such characteristics can be varied and the absorbers themselves filled with different types of viscous fluids. Such analysis suggests that the sound absorption coefficient of porous metals does not always increase when there are either increases in porosity or decreases in average pore size. The same method of analysis can show how, by choice of the right characteristics to choose a suitable viscous fluid, a porous metal absorber can be built that takes up little space but still effectively absorbs underwater sounds at low frequencies.
122(2007); http://dx.doi.org/10.1121/1.2766777View Description Hide Description
Applied acoustics is becoming an important field for civil infrastructure and environmental assessment, and road maintenance or rehabilitation strategies. In this research has developed a GPS-based measurement techniques and apparatus on a test vehicle, for monitoring the acoustical properties of different road pavement surfaces with a reference tire. A field test on PA-12 Spanish porous pavement found in Ciudad Real is developed. The test procedure, a modification based upon the close-proximity method (CPX), relies on the use of three standard microphones situated very close to the tire/road contact patch. This procedure allows the simultaneous measurement of the sound emission synchronized to a GPS receiver, which permits tracking of the position of the sound emission. Geo-referenced sound spectra for every during individual passes of the test vehicle are analyzed to determine the tire/road noise emissions from tire/PA-12 pavement interaction. Noise levels of around , with a variability of approximately , are found at a reference vehicle speed of . The frequency spectrum analysis over the test section shows noticeable differences for frequencies above , where the tire/road noise generation mechanisms are dominated by air pumping.
122(2007); http://dx.doi.org/10.1121/1.2785809View Description Hide Description
Environmental noise is a growing and well recognized health problem. However, in many cases people are exposed not to a single noise source—for example, road, railway, or aircraft noise—but to a combination of noise exposures and there is only limited knowledge of the effects on health of exposure to combined noise sources. A socio-acoustic survey among 1953 persons aged 18–75 years was conducted in residential areas exposed to railway and road traffic noise with sound levels ranging from in a municipality east of Gothenburg, Sweden. The objectives were to assess various adverse health effects, including annoyance, and to elucidate the impact of exposure to single and combined noise sources. In areas exposed to both railway and road traffic, the proportion annoyed by the total traffic sound environment (total annoyance) was significantly higher than in areas with one dominant noise source (rail or road traffic) with the same total sound exposure . This interaction effect was significant from and increased gradually with higher sound levels. Effects of the total sound exposure should be considered in risk assessments and in noise mitigation activities.