Study of the Performance of Acoustic Barriers for Indiana Toll Roads

Abstract

Prepared in cooperation with the Indiana Department of Transportation and Federal Highway Administration. AbstractThe purpose of this study was to optimize the geometry and the acoustic properties of sound barriers for traffic noise applications. The approach consisted of developing and validating boundary element predictive models, which were subsequently exercised in order to refine the barrier characteristic and determine optimized configurations.The simple geometry of a circular disk was chosen to validate the boundary element model in the first part of this work. Experiments were performed in an anechoic chamber to validate the numerical model. Complex barrier geometries were then investigated to study the effects of geometry on sound barrier performance. Boundary element models were used to quantify the accuracy of existing, approximate diffraction-based models. Diffraction-based models have been widely applied in noise control engineering applications owing to their relative ease of use. Recent research suggests that multi-path diffraction components should be summed on a phase-coherent basis instead of on an energy basis. The accuracy of a phase-coherent diffraction model has been verified against the boundary element solution and the limitations of the diffraction model are discussed for both the case of infinite length barriers and barriers of finite length. A new barrier performance metric, based on the sound power propagating within the shadow zone was also investigated. It was found that variation of barrier geometry while maintaining the surface area constant did not yield any meaningful difference in the sound power propagating within the shadow zone.The performance of straight-edge barriers with various top geometries and sound absorptive treatments was then investigated. Experiments were performed using a finite size barrier in an anechoic chamber to verify the boundary element model. Good agreement was obtained between the results from the numerical model and the experimental data. The most important finding was that absorptive treatment applied to the top of a barrier was more effective at reducing sound levels in the shadow zone than a simple increase of barrier height. The use of the boundary element method to calculate the new barrier sound power performance metric is also discussed in connection with the complex geometry. It is shown that the propagating sound power calculated on a recovery plane in the barrier shadow zone provides a more effective performance measure than insertion loss when comparing the performance of different barrier designs. 17.

Investigation of Novel Acoustic Barrier Concepts Phase I: Concept Development and Preliminary Evaluation

“…The details of this procedure were described at length in a previous report [1]. The time domain impulse response function can be calculated from the frequency domain transfer function measured between the loudspeaker input and each of the microphone outputs.…”

“…The report of the first part of this study [1] includes a summary of a number of research articles discussing: 1) analytical methods; 2) empirical models; and 3) experimental investigations related to noise barriers. In this section, the emphasis is on literature pertaining to the performance of sound absorptive treatments on the barriers.…”

“…In a previous research project [1] conducted at the Ray. W. Herrick Laboratories at Purdue University, it was found that addition of sound absorptive material along a barrier edge could enhance the barrier's performance.…”

Investigation of noise barriers enhancement efficiency for attenuation of low frequency traffic noise

“…[19,20]) or boundary element methods are used (eg. [21,22]). On the other hand, for solving complex acoustics tasks, finite element method (FEM) is widely used.…”