Finding optimal geometries for noise barrier tops using scaled experiments

Abstract

Scaled acoustic laboratory experiments are used to develop a methodology for obtaining the acoustic characteristics of different barrier top designs and for identifying geometries that may have advantages over the traditional thin vertical screen. The idea is to use a short impulsive spherical sound pulse possessing a broad frequency spectrum. If the duration of the pulse is sufficiently short, the entire primary signal, which travels by the shortest direct route diffracting at the top of the barrier, arrives at the receiver much earlier than any secondary signals reflected from the surroundings. Secondary signals may therefore be ignored and only the information from the primary signal can be analyzed. When the typical frequency band of the sound pulse is about an order of magnitude higher than typical traffic noise spectra, then scaled acoustic modeling using the same scaling factor for lengths and distances is possible. The results of such experiments are reported here for barriers with six different geometries. Using spectral analysis, insertion losses as functions of frequency were calculated for different source-receiver positions and barrier tops. The results were then rescaled for full-size traffic barriers and, using a typical traffic noise spectrum, single number ratings of barrier performance were obtained.

Insertion Loss Spectrums Behind Straight Noise Barriers: Scaled Experiments

“…The results obtained were rescaled to traffic barriers and for the typical traffic noise spectrum the single number insertion loss ratings were calculated for different source-receiver positions and the directivity diagrams derived. The methodology developed was successfully used for barriers with different top geometries, including T-, L-shape, jagged, etc., "unpublished" [2].…”

“…Details of the experimental set-up and methods are similar to that used in [2] and only brief description is given below. Custom build 3-electrode spark discharger was used as a sound International Conference on Sustainable Energy and Environmental Engineering (SEEE 2015) source.…”

“…Recently a comprehensive experimental study with different barrier tops (T-, L-shape, jagged regular and random, etc.) was conducted in "unpublished" [2]. We do not repeat this material and only results related to the straight tops, which are not included in [2], are reported below.…”

Calculation of Noise Barrier Insertion Loss Based on Varied Vehicle Frequencies

“…The theoretical value of diffraction is defined as (Equation (10) (10) where N is the Fresnel number, 170…”

“…Current research on noise barriers primarily focuses on noise calculation [8,9], the effects of barrier shapes [10,11], and the design of barriers [12][13][14][15]. As one of the important aspects, prediction of the insertion loss by the noise barrier has been attracting the attention of scholars, and both mathematical and experimental approaches have been developed.…”