The current study examines the propagation of sound in street canyons with geometrically reflecting surfaces. An image source method is a popular numerical model to estimate the propagation of sound energy in a street canyon. This numerical model calculates the total sound energy received at a field point by summing the contributions from individual image sources incoherently. The discrete image source model is generalized by replacing rows of point sources with their respective line sources. An integral formulation is derived, which can be evaluated exactly to give a simple analytical solution. The expression permits rapid computations of the sound energy due to a point source placed in a street canyon. The transient sound energy at a receiver point is also examined. It has been demonstrated that the transient sound energy can be expressed in terms of a standard exponential integral. The Schroeder integration method is then used to calculate the reverberation times, which allow a straightforward assessment of the acoustic environment in street canyons. Indoor and outdoor experiments were conducted to validate the proposed integral formulation. The analytical formulas were also compared with numerical results based on the standard image source method and with published experimental data.

The speech intelligibility in long enclosures is primarily affected by two factors: The reverberation time and the signal to noise ratio. To predict the speech intelligibility, previous studies were mainly focused on predicting either the sound field or the reverberation time in long enclosures. In these predictions, the sound sources were usually assumed to be a monopole source. However, it is well known that many noise sources have distinct directional characteristics. For example, noise radiated from railway vehicles and from ventilating fans is best modeled as a dipole source. This paper presents a numerical model to predict the sound field due to a dipole source in a long enclosure. The numerical model is validated by field measurements. The experimental dipole source was built by using a pair of identical loudspeakers placed at a close distance to each other that generate sound at equal amplitude but opposite in phase. Measurements are conducted at two test sites. Tolerable agreement between numerical predictions and experimental data is obtained.

The current study was devoted to investigate the propagation of noise along a town street where building façades and road surfaces form a street canyon. An energy based approach was used to estimate reverberation times and the sound pressure levels due to a point source located along the town street. An image source method was developed to compute sound energy in this semienclosed space. However, the image source model can be simplified leading to the numerical solutions expressed in an integral formulation. The absorption coefficients of the boundary surfaces and the air absorption factor can be included in the present analysis. The integral can further be evaluated analytically with the sound pressure levels expressed in a closed form solution. Both outdoor full scale measurements and indoor scale model experiments were conducted and compared with the computed results. The numerical results due to the proposed formula not only agree well with the experimental measurements but were also in accord with the published data.