Time-evolution of sound levels around a roadside building

Abstract

The time evolution of the sound impact due to single cars driving along a road was evaluated at seven receivers in front of and behind a road-side building. The sound impact was measured in the field and around a scale model of the building in a laboratory. In addition, two calculation methods were applied: a complex numerical finite-difference time-domain model based on the Euler equation and a simple ray-based calculation according to the ISO 9613-2 standard. On the backside of the building where sound waves only arrive by diffraction, the differences between the four methods are disappointingly large. Some of the discrepancies can be explained by diverse assumptions and boundary conditions which go along with the individual methods. However, a major disagreement largely remains an open problem, namely the magnitude of the drop of the sound level in the acoustical shadow of the building. It is fairly strong in the scale-model measurements and the Euler model simulations on the one hand, but rather weak or even not existing in the field measurements and ISO 9613-2 calculations on the other hand.