Reflections on Noise Modelling

Reflections on Noise Modelling

Constructing a noise barrier or enclosure can be a significant investment. BKL works alongside owners and project managers to help them decide how to most efficiently allocate their resources—and meet regulatory requirements.

To assess noise propagation outdoors, the BKL team usually turns to ISO 9613-2, the industry standard method for predicting how sound travels outside. This general calculation accounts for atmospheric absorption, ground absorption, terrain contours and simple reflections between source and receiver. Often, the ISO standard is the best choice for noise modelling and, when implemented in BKL’s Cadna/A software, it provides graphics that are informative and accessible to an audience that includes laypeople and public stakeholders.

Sometimes a project demands a more sophisticated noise modelling software, one that considers the complex way that noise reflects in partial enclosures or particularly reverberant spaces. In these cases, BKL turns to Olive Tree Labs Terrain, whose algorithms incorporate the latest research in outdoor noise propagation.

OTL Terrain enabled us to model more complex sound reflections, something that’s not always possible with ISO 9613. This gave us added confidence that the proposed enclosures would be effective.

“One benefit of Terrain is that it can predict all the possible paths that noise can take from source to receiver,” says Mark Bliss, BKL partner and senior consultant. “This ability to analyze sound reflections makes Terrain a very useful tool in creating 3-D noise models for rooftop unit enclosures, loading bays or other outdoor spaces that present complicated sound reflections.”

On one commercial project, BKL assessed a proposed rooftop heat pump for a shopping centre with several residences nearby. BKL looked at two possible locations for the heat pump and, with Terrain, modelled three mitigation options for each proposed location.

For a recent residential project, BKL was retained to predict how noise from four separate rooftop units would affect residents on the same property. Because the project featured both low- and high-rise buildings, BKL used Terrain to model two-, three- and four-sided enclosures, some with partial cantilever roofs.

“In both cases,” says Bliss, “OTL Terrain enabled us to model more complex sound reflections, something that’s not always possible with ISO 9613. This gave us added confidence that the proposed enclosures would be effective.”

In one case study, Terrain predicted the ineffectiveness of a proposal to use a billboard to reduce noise emitted by rooftop chillers. While the billboard would’ve mitigated noise travelling in a direct path between the chillers and an apartment, it didn’t account for noise reflecting off the roof and sides of the building. Terrain offered a more precise prediction, and once the final barriers were installed, the measured noise levels matched those predicted in the model. The results of this case study are supported by current research showing that Terrain’s results can be more accurate than ISO 9613-2.

BKL assesses each noise prediction project and carefully determines which method will create the most appropriate model, whether in Cadna/A, Terrain or even in other software, like Odeon. BKL has the experience and technological aplomb to navigate complicated noise modelling scenarios and help its clients choose noise mitigation solutions that are both effective and practical.

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