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- Forssén, Jens, 1968, et al.
(författare)
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Statistics of A-weighted road traffic noise levels in shielded urban areas
- 2006
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Ingår i: Acta Acustica united with Acustica. - 1610-1928 .- 1861-9959. ; 92:6, s. 998-1008
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Tidskriftsartikel (refereegranskat)abstract
- In the context of community noise and its negative effects, the noise descriptors used are usually long-term equivalent levels and, sometimes, maximum levels. An improved description could be achieved by including the time variations of the noise. Here, the time variations of A-weighted road traffic noise levels have been studied. Of special interest are situations with a shielded courtyard. For numerical results, a ray model has been used for calculating the sound propagation, and the traffic has been modelled as a Poisson process. With this model the statistics of A-weighted levels have been investigated for different situations with varying traffic flows. Results from an in-situ measurement have been compared with those from the numerical model, showing acceptable agreement. It is shown both by numerical modelling and measurements that the time variations in noise level are smaller in a courtyard than in a corresponding directly exposed situation. One of the additional conclusions is that the noise reduction of the maximum level can be significantly higher than that of the equivalent level.
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- Forssén, Jens, 1968, et al.
(författare)
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Statistics of road traffic noise in shielded urban areas: an initial study of A-weighted levels
- 2006
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Ingår i: 6th European Conference on Noise Control: Advanced Solutions for Noise Control, EURONOISE 2006; Tampere; Finland; 30 May 2006 through 1 June 2006.
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Konferensbidrag (refereegranskat)abstract
- In the context of community noise and its negative effects, the noise descriptors used are usually long-term equivalent levels and, sometimes, maximum levels. An improved description could be achieved by including the time variations of the noise. Here, the time variations of A-weighted road traffic noise levels have been studied. Of special interest are situations with a shielded courtyard. For numerical results, a ray-tracing model has been used for calculating the sound propagation, and the traffic has been modelled as a Poisson process. A numerical study has been performed, where the statistics of A-weighted levels have been investigated for different situations with varying traffic flows. Also, results from an in-situ measurement have been compared with those from the numerical model, showing acceptable agreement. It is shown both by numerical modelling and measurements that the time variations in noise level are smaller in a courtyard than in a corresponding directly exposed situation. An additional conclusion is that the noise reduction of the maximum level can be significantly higher than that of the equivalent level.
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- Hornikx, Maarten, 1980, et al.
(författare)
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A scale model study of parallel urban canyons
- 2008
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Ingår i: Acta Acustica united with Acustica. - 1610-1928 .- 1861-9959. ; 94:2, s. 265-281
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Tidskriftsartikel (refereegranskat)abstract
- Shielded urban areas are of importance regarding urban citizens’ annoyance and adverse health effects related to road traffic noise. This work extends the existing knowledge of sound propagation to such areas by a scale model study, rather than by model calculations. The scale model study was executed for two parallel urban canyons at a 1 to 40 scale, with a point source located in one canyon. Cases with acoustically hard façades and absorption and diffusion façade treatments were in vestigated. To correct for excess air attenuation of the measurements, a wavelet-based method has been applied. The measurement results in the shielded canyon show that, in contrast to the directly exposed street canyon, the levels and the decay times are quite constant over the length of the canyon. The energy-time curve in the shielded canyon is characterized by a rise time, which can be related to the sound pressure level. The rise times and decays can be explained by separate reflection, diffraction and diffusion processes. A closed courtyard situation enlarges the level difference between acoustically hard façades and applied façade absorption or diffusion treatments at both the directly exposed and shielded side. A comparison between measurements with two different diffusion mechanisms, horizontal and vertical diffusion, reveals that vertical diffusion yields lower levels at the shielded side compared to horizontal diffusion for the investigated situations.
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- Hornikx, Maarten, 1980, et al.
(författare)
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A scale model study of parallel urban street canyons
- 2005
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Ingår i: Proc. 149th MEETING OF THE ACOUSTICAL SOCIETY OF AMERICA, May 2005, Vancouver, Canada. (Only abstract).
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The access to quiet areas in cities is of increasing importance. Recently, the equivalent sources method for a two dimensional situation of parallel urban street canyons has been developed. One canyon represents a busy road, whereas the other is one without traffic; the quiet side. With the model, the transfer function between the two canyons can be calculated, as well as the influence of diffusion, absorption, and atmospheric turbulence on the transfer function. A scale model study of two parallel canyons has now been executed. A scale of 1:40 has been chosen and the maximum length sequence technique has been applied using the MLSSA system. Results of the scale model study have been compared to calculations with the equivalent sources method. The difference between a two-dimensional and a three-dimensional quiet side, between a coherent and an incoherent line source and the influence of absorption and diffusion has been investigated. The scale model study also gives insight in the evolution of the sound field in the time domain. [Work supported by the Swedish Foundation for Strategic Environmental Research (MISTRA).]
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