Speech interference and transmission on residential balconies with road traffic noise

Theoretical analysis on structure of sound energy field decay of acoustical radiosity model with finite initial excitation

The acoustical radiosity model (ARM) is a typical algorithm in geometrical acoustics to simulate the sound field in a room of ideally diffusely reflecting boundary. Even in such a room, the sound field decay is a complex process, as the relaxation of the sound field observed in simulations has shown. Based on the Laplace transform of the acoustical radiosity equation, this paper gives a set of properties of the ARM. It shows the system has a series of real or complex conjugate L-eigenvalues and corresponding L-eigenfunctions. Under the relaxation condition, the sound energy decay on the room boundary, generated by finite initial excitation, can be expanded as a summation of decay components, which are composed of real and/or complex conjugate decay modes. Each decay mode is a decaying and oscillating L-eigenfunction corresponding to an L-eigenvalue. The real part of the L-eigenvalue is the exponential decay rate, and the image part is the angular frequency of the oscillation. The reverberant sound field inside the room space has a similar decay structure to the boundary. As an example, the decay structure in a sphere is analyzed. The relaxation of the sound field is explained by the geometrical significance of the sound field decay.

Insertion losses of balconies on a building façade and the underlying wave interactions

This study used scale model experiments to investigate the insertion losses of balconies on a building façade in the presence of ground reflections. The experiments measured both A-weighted broad- and narrowband insertion loss spectra. The underlying wave interactions/interferences and their couplings with and without reflections from the balcony ceilings were also examined in detail, and these findings were related to the dimensions and elevations of the balconies. The findings indicate that the ground and ceiling reflections and their interferences with the direct sound play very important roles in shaping the frequency characteristics of the insertion losses. Strong sound attenuation can be attained with a carefully designed geometry and acoustical properties of the balcony and the balcony ceiling.