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The user creates a model of a community using the toolbar or the Object Editors from the menu. The model can consist of roadways, railways, aircraft flyovers, point sources areas, receivers (homes), barriers, terrain lines, building rows and others.
The CCNM simulation is a two part process. The CNM uses a time step based simulation where all vehicle positions, speeds and modes are updated at incremental time steps. All moving sources are first moved to new positions and their attributes are updated, then the Acoustic algorithms take over. The acoustic algorithms include the following:
The general acoustic model assumes that each source has a reference sound pressure level that is adjusted by independent attenuation terms.
Each source-receiver combination is evaluated at each time step. The reference sound pressure level of the source is computed followed by the attenuation terms. The reference sound pressure level is dependent on the speed and operational mode of the source (automobiles, rail vehicles, aircraft) or may be essentially constant for stationary point sources. The attenuation terms are all dependent on the current position of the source. The diffraction term is dependent on intervening obstacles such as berms, barriers, building rows, terrain lines and other vehicles. The ground effect term is dependent on the type of ground at each receiver, the incident angle and the choice of ground effect algorithm. This process is repeated for all sources in the simulation until the simulation is completed. At that point, sound level results for each receiver are displayed. Results include overall Leq, Lmax and various Lxx metrics and a 'time' history of receiver results during the simulation.