Investigation of additional insertion loss from t-profile and absorptive noise barriers

This paper presents the findings into a study of the relative performance of custom-design noise walls of different heights, with and without T-profile noise wall tops of various dimensions. The study was undertaken at a test facility using noise walls of heights 2.4 m and 3.5 m, with T-profile widths of 600 and 1200 mm. The testing was undertaken using measurement positions of varying height behind the wall, with a loudspeaker used to generate an MLS-type signal. The impulse response was stored for post-processing and calculation of the spectral insertion losses was carried out for each test. Additionally, the influence of absorptive treatment on the T-profile was tested. These results were compared to the untreated T-profile, the standard noise wall and a standard noise wall with an absorptive capping but without a T-profile. The reduction achieved with the T-shaped profile is quantified in terms of both an additional spectral insertion loss relative to the base wall as well as the equivalent reduction in noise wall height that can be obtained while maintaining performance by using the modified top. The performance of the different noise wall configurations is also compared to the theoretical and tested performance of other modified noise wall types. Finally, the practical application of the tested insertion loss results to predicted noise levels is discussed.