3D Acoustic Modeling Challenges of Applying the ISO 9613 Calculation Methods to Sound Sources on Building Rooftops

The International Standard ISO 9613 method for attenuation of sound during propagation outdoors provides no guidance on sound sources above rooftops. This poses a challenge for those tasked with modeling impacts from rooftop equipment particularly when using 3D modeling software. Projects requiring acoustic modeling of rooftop equipment oftentimes result in the highest sound level impacts at receptors that are either immediately next to proposed new buildings or at elevated windows that look down upon the new rooftop sound sources. The CadnaA acoustic model has several tools that allow for a variety of methods, which can be used to approximate these situations, but it can be challenging to know which method to employ. Several CadnaA modeling methods that mimic real world scenarios of rooftop equipment are described along with the resulting differences in predicted sound levels.