Suchergebnisse

3.6.4 Further factors and limitations3.7 Transport noise; 3.7.1 Road; 3.7.2 Rail; 3.7.3 Air; 3.8 Summary; Section 4: Noise control at source; 4.1 Introduction; 4.2 Choosing which source to control; 4.3 Control of noise by design or choice of process; 4.4 Isolating structure-borne vibration; 4.5 Enclosures; 4.6 Frequency dependence of noise reduction; 4.7 Summary; Section 5: Control between source and receiver; 5.1 Introduction; 5.2 Active noise control; Feedback and feedforward; 5.3 Indirect sound paths; 5.4 Absorption and absorbing materials; 5.4.1 Porous absorbers; 5.4.2 Panel absorbers.

2.4.5 The directional influence of winds2.4.6 Identifying atmospheric stability; 2.4.7 The atmospheric boundary layer; 2.4.8 Calculating wind speed; 2.4.9 Estimating depth; 2.5 The main air pollutants; 2.5.1 Sulfur; 2.5.2 Nitrogen compounds; 2.5.3 Carbon compounds; 2.5.4 Atmospheric aerosol; 2.5.5 Summary of pollutants; 2.6 Effects of air pollutants; 2.6.1 Human health effects; 2.6.2 Effects on vegetation; 2.6.3 Effects on animals; 2.6.4 Effects on materials; 2.7 Acid deposition; Causes of acidity; 2.8 Climate change; 2.8.1 Greenhouse gases; 2.8.2 Further causes and effects.

The acoustical performances of regular arrays of cylindrical elements, with their axes aligned and parallel to a ground plane, have been investigated through predictions and laboratory experiments. Semi-analytical predictions based on multiple scattering theory and numerical simulations based on a boundary element formulation have been made. Measurements have been made in an anechoic chamber using arrays of (a) cylindrical acoustically-rigid scatterers (PVC pipes) and (b) thin elastic shells. Insertion loss (IL) spectra due to the arrays have been measured without and with ground planes for several receiver heights. Data and predictions have been compared. The minima in the excess attenuation spectrum i.e., attenuation maxima due to the ground alone resulting from destructive interference between direct and ground-reflected sound waves, tend to have an adverse influence on the band gaps (BG) related to a periodic array in the free field when these two effects coincide. On the other hand, the presence of rigid ground may result in an IL for an array near the ground similar to or, in the case of the first BG, greater than that resulting from a double array, equivalent to the original array plus its ground plane mirror image, in the free field. © 2011 Acoustical Society of America. ; This work was supported by the UK Engineering and Physical Sciences Research Council (Grant Nos. EP/E063136/1 and EP/E062806/1) and by MEC (Spanish Government) and FEDER funds, under Grant No. MAT2009-09438. Authors are also grateful to reviewers for their valuable comments. ; Krynkin, A.; Umnova, O.; Sánchez Pérez, JV.; Chong, AYB.; Taherzadeh, S.; Attenborough, K. (2011). Acoustic insertion loss due to two dimensional periodic arrays ofcircular cylinders parallel to a nearby surface. Journal of the Acoustical Society of America. 130(6):3736-3745. https://doi.org/10.1121/1.3655880 ; S ; 3736 ; 3745 ; 130 ; 6