Open Measurements of Edge Diffraction from a Noise Barrier Scale Model

Abstract

Until today, all known simulation methods for the wave phenomenon of edge diffraction are just approximations, based on either Geometrical Acoustics or the numerical solving of the wave equation. Although these methods work fine for simple test scenarios and a certain frequency range, they fail to simulate the effect of diffraction in its whole complexity. This leads to false predictions especially for more complex geometries where the influence of multiple wave diffraction and sound scattering has to be taken into account as well. Consequently, huge effort is currently put into the development of improved simulation methods. Here, a basic need is an all-embracing validation of simulation results, which also includes the comparison with realworld measurements. Unfortunately, there is a lack of such data which is the reason why the Institute of Technical Acoustics (ITA), RWTH Aachen University, Germany, and the Centre for Quantifiable Quality of Service in Communication Systems (Q2S), NTNU Trondheim, Norway, have started an initiative called openMeasurements, which is aimed to be an internet platform for free acoustic measurement data of any kind, together with their respective simulation models (CAD-model, detailed information on sources and receivers, material data) and helpful tools. As initial step, various measurement series of a scaled-down model of a noise barrier were carried out. These series aim to give researches, developers, and common application users, the possibility to thoroughly test their prediction models of edge diffraction. The measurements were carried out in a full anechoic chamber and a turntable was used to rotate the scale-model during the measurements in steps of one degree. The scale-model was constructed with a changeable ground layer in order to massively influence the object's acoustical properties and, thus, create measurement datasets that considerably differ. Here, datasets for five different ground layers were obtained: 3 absorbers, 1 rigid surface and 1 self-constructed skylinediffuser. A skyline diffuser was chosen as it is a well reproducible geometrical pattern, which enables a simulation of sound scattering in two ways: stochastic and deterministic. In this contribution, detailed information on the measurement setup is given and measurement procedures are described thoroughly. Measurement uncertainties are briefly discussed and first comparisons with simulations are presented. All measurements together with geometrical models of the scale-model (with/without diffuser), detailed information on sources and receivers, material data (absorption-and scattering coefficients) and useful Matlab tools are freely available for download (www.openmeasurements.net).

Recent advances in building acoustics: An overview of prediction methods and their applications

“…With the inclusion of edge diffraction, the accuracy of geometrical acoustics methods is increased [46]. A lot of effort has been put into the development of improved simulation methods for the edge diffraction [47].…”

Approaches for Noise Barrier Effectiveness Evaluation Based on In Situ “Insertion Loss” Determination

“…Experimental studies have been based on diverse approaches relating to (i) the assessment of perceived annoyance reduction efficiency of noise barriers [24,25], (ii) the effects of noise barriers on the perception of urban soundscape quality [26], (iii) the measurement of noise attenuation based on scale model experiments [27,28], and (iv) the measurement of the acoustic properties of full-scale barriers. The latter experiments have been the most reported in the literature, and have addressed the analysis of the effectiveness of barriers based on their various acoustic characteristics:…”

Real-Time Auralisation of Outdoor Sound Propagation

“…To conduct a comparison with measurements, a propagation simulation is performed and the resulting geometrical paths are transformed into the IR and TF by means of acoustic modelling after Section 3.4. In the literature, typical canonical situations regarding screening effects and wedge-shaped edge diffraction problems can be found, that predominantly target the acoustic model quality, for example, those by Schröder et al [SSV11]. A more elaborate benchmark that considers a combination of reflection and diffraction on the one hand, and provides supplementary data to enable a high-resolution coherent reproduction is presented by Aspöck et al as the Benchmark for Room Acoustic Simulations (BRAS) and will be used to verify the acoustic modelling of geometrical propagation paths [Asp+20; Bri+21].…”