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The acoustical criteria to be applied for design and assessment of subway stations have been well defined by Environmental Noise Control Act of Turkey, since 2005. In the architectural design phase, the material and geometrical attributes are adjusted to fit related criteria mostly by application of ray tracing simulations. Reverberation time and sound pressure levels are two major indicators. The basic limitation of ray tracing is that the method is more valid as the sound field is closer to a diffuse field. Subway stations, on the other hand, are longitudinal volumes and depending upon the source location the sound is not always evenly distributed. This problem appears when subsequent field tests are compared to the simulation results. For this reason, in this research an alternative method is searched, namely, diffusion equation modelling (DEM), in order to better estimate the acoustical parameters in such disproportion-ate rooms. Diffusion coefficient in DEM takes its form from mean free path, so the mesh sizes are not even high for mid to high frequencies to be applied in a finite element medium, which is one basic advantage of this model. This new method is previously searched for its reliability in long rooms as well as in rooms with some sound absorptive surfaces. Two cases of İstanbul Metropolitan subway lines are selected, namely, station BAG and station USK, to comparatively evaluate ray tracing and DEM solutions. The results indicate that ray-tracing simulations underestimate the sound attenuation in the case stations and results in higher reverberation times in comparison to DEM solution. Sound pressure level distributions provide a similar pattern of decay, while in ray-tracing the levels are still higher as the receiver is moved away from the source. DEM results are found to be more coherent with field test results, and computationally more efficient than ray-tracing. There is still a variation for specific receiver positions in between field and DEM results. The reasons of deviations per receiver positions need to be further investigated. In the optimization of acoustical material application in subway stations, which is highly important for economic purposes, DEM can be used as a reliable and practical method.
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