MODELING

Acoustic Models for Calculating Coverage

An example of our modeling software

Computers running acoustic models are the best way to determine the coverage of your sirens. There is a wide number of acoustic models that range from simple spreadsheets to complex computational models. However, all models share some basic principles. There are also several different software packages that can be used to compute your coverage contours.

Acoustic Principles

There are several basic acoustic principles that govern all sound propagation. We’ve put some of the most crucial elements together into the short document shown below. Click on it to download the paper.

The front cover of our Propagation Primer

Some of the core acoustic propagation topics are provided below, with more details on the links.

  • Spherical Spreading – The loss of acoustical energy as the sound spreads out from the source.
  • Atmospheric Absorption – The absorption of acoustical energy by the air between the source and the receiver.
  • Ground Reflections – Sounds we hear come directly from the source, and are reflected off of the ground.
  • Diffraction – The ‘bending’ of sound around obstructions.
  • Refraction – The ‘bending’ of sound due to gradients in temperature and/or wind.

Propagation Algorithms

Different acoustic models handle the basic acoustic principles differently, with some providing more detail than others. The following is a list of some of the current models in increasing levels of complexity. Click on each model to learn more about it.

  • Outdoor Sound Propagation Model (OSPM) – This is included because it has been used in the past for some siren system design. No information is available about the inner workings of this model.
  • CONCAWE – An older, largely heuristic model developed to calculate industrial noise generated by petroleum and petrochemical complexes.
  • ISO 9613 – An international algorithm for propagating industrial noise. Uses some simplistic formulas and table look-ups, and generally assumes down-wind propagation. It is designed to be conservative for industrial noise, meaning that it tends to over-predict the received sound level.
  • Nord2000 – A modern propagation algorithm that includes a more complex propagation system. This model includes many real-world conditions, such as atmospheric turbulence, and includes more complex definitions of barriers. 
  • Computational Models – New and updated models are always being investigated. However, they often have shockingly complex data input requirements.

Software Packages

Acoustic Analytics has developed our own custom build software that uses a simple map interface and ISO 9613 as the propagation algorithm, and was specifically designed to rapidly develop and display siren contours. There are also several commercial software packages for computing the noise from a wide range of sources. Most, unfortunately, have steep learning curves and tend to be expensive.

  • SoundPLAN – This is a software package designed for computing the noise of a large number of sources spread out over a wide area. With this software the user can select the propagation algorithm to use. It includes CONCAWE, ISO 9613, Nord2000, plus many others. While it is well suited to do full siren system calculations, it is complex and cumbersome, making quick what-if calculations difficult.
  • CadnaA – This is a similar software package to SoundPlan. These software packages are used in Europe to compute city-wide noise footprints, and come with an equal level of complexity.

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