Practical Ranges of Loudness Levels of Various Types of Environmental Noise, Including Traffic Noise, Aircraft Noise, and Industrial Noise

In environmental noise control one commonly employs the A-weighted sound level as an approximate measure of the effect of noise on people. A measure that is more closely related to direct human perception of noise is the loudness level. At constant A-weighted sound level, the loudness level of a noise signal varies considerably with the shape of the frequency spectrum of the noise signal. In particular the bandwidth of the spectrum has a large effect on the loudness level, due to the effect of critical bands in the human hearing system. The low-frequency content of the spectrum also has an effect on the loudness level. In this note the relation between loudness level and A-weighted sound level is analyzed for various environmental noise spectra, including spectra of traffic noise, aircraft noise, and industrial noise. From loudness levels calculated for these environmental noise spectra, diagrams are constructed that show the relation between loudness level, A-weighted sound level, and shape of the spectrum. The diagrams show that the upper limits of the loudness level for broadband environmental noise spectra are about 20 to 40 phon higher than the lower limits for narrowband spectra, which correspond to the loudness levels of pure tones. The diagrams are useful for assessing limitations and potential improvements of environmental noise control methods and policy based on A-weighted sound levels

Urban background noise mapping: the multiple-reflection correction term

Mapping of road traffic noise in urban areas according to standardized engineering calculation methods systematically results in an underestimation of noise levels at areas shielded from direct exposure to noise, such as inner yards. In most engineering methods, road traffic lanes are represented by point sources and noise levels are computed utilizing point-to-point propagation paths. For a better prediction of noise levels in shielded urban areas, an extension of engineering methods by an attenuation term Acan has been proposed, including multiple reflections of the urban environment both in the source and in the receiver area. The present work has two main contributions for the ease of computing A(can). Firstly, it is shown by numerical calculations that A(can) may be divided into independent source and receiver environment terms, A(s) and A(r). Based on an equivalent free field analogy, the distance dependence of these terms may moreover be expressed analytically. Secondly, an analytical expression is proposed to compute A(s) and A(r) for 3D configurations from using 2D configurations only. The expression includes dependence of the street width-to-height ratio, the difference in building heights and the percentage of facade openings in the horizontal plane. For the expression to be valid, the source should be separated from the receiver environment by at least four times the street width

Application of the Lattice Boltzmann method in acoustics

In this paper, practical aspects of the lattice Boltzmann method for fluid flow are explored and application to sound propagation is investigated. This work was performed within the framework of the European ITEA project MACH, which aims at optimizing scientific calculations on various parallel platforms. For fluid flow, our attention was drawn to the lattice Boltzmann method because of its advantages over other methods: the method is suitable for parallel computation, and it can be applied easily to systems with complex boundaries, such as porous media. We first developed simple 2D and 3D lattice Boltzmann codes for fluid flow in a lid-driven cavity. We explored possibilities to run it on the GPU of a personal computer, and we investigated GPU speedup factors. Next we developed a lattice Boltzmann code for simulation of sound waves. Various acoustic phenomena were investigated with this code, such as geometrical spreading of sound waves generated by a point source, reflection of sound waves by a rigid surface, and diffraction of sound waves by a noise barrier. Reflection of sound waves by a porous medium was also explored, and a comparison was made with theoretical solutions. Finally, the possibility to simulate sound propagation in an atmosphere with wind and temperature gradients was considered

Urban background noise mapping: the general model

Surveys show that inhabitants of dwellings exposed to high noise levels benefit from having access to a quiet side. However, current practice in noise prediction often underestimates the noise levels at a shielded facade. Multiple reflections between facades in street canyons and inner yards are commonly neglected and facades are approximated as perfectly flat surfaces yielding only specular reflection. In addition, sources at distances much larger than normally taken into account in noise maps might still contribute significantly. Since one of the main reasons for this is computational burden, an efficient engineering model for the diffraction of the sound over the roof tops is proposed, which considers multiple reflections, variation in building height, canyon width, facade roughness and different roof shapes. The model is fitted on an extensive set of full-wave numerical calculations of canyon-to-canyon sound propagation with configurations matching the distribution of streets and building geometries in a typical historically grown European city. This model allows calculating the background noise in the shielded areas of a city, which could then efficiently be used to improve existing noise mapping calculations. The model was validated by comparison to long-term measurements at 9 building facades whereof 3 were at inner yards in the city of Ghent, Belgium. At shielded facades, a strong improvement in prediction accuracy is obtained

On the improved point-to-point calculations for noise mapping in shielded urban areas

Noise mapping of urban areas according to standardized engineering calculation methods systematically results in an underestimation of noise levels at areas shielded from direct exposure to noise, such as inner yards. In these methods, road traffic lanes are represented by point sources and noise levels are computed utilizing point-to-point propagation paths. For a better prediction of noise levels in shielded urban areas, the attenuation terms describing these propagation paths are extended by terms including geometrical aspects of the urban environment both in the source and in the receiver area. In the present work, it has been studied to what extent these terms may be treated as being independent of the source-receiver distance. Also, the validity of treating the propagation path in a 2D plane rather than in 3D is investigated. Results obtained from a wave-based acoustic propagation model have been used for this assessment

Job polarization: an historical perspective

© The Author 2018. This paper uses historical labour market data for Belgium for the period 1846-2011 to illustrate how the employment impacts of the ongoing Digital Revolution after 1980 compare to those of the Second Industrial Revolution before 1980. Our analyses show that the period 1846-1947 was characterized by economy-wide skill-upgrading due to an increase in the demand for skilled relative to unskilled workers because of skill-biased technological change (SBTC). The period 1947-81 is characterized by particularly high labour market turbulence, in part due to a gradual switch from economywide skill-upgrading to job polarization. Consequently, the impact of the ongoing Digital Revolution on labour markets after 1980 is not uniquely characterized by exceptionally high labour market turbulence but by the nature of changes in the composition of jobs, namely a process of job polarization. To explain job polarization, the paper discusses the hypothesis of Routine-Biased Technological Change (RBTC) that has recently emerged in the academic literature.status: publishe