Sound Propagation Level Calculator (Version 3.6) - MAS Environmental Ltd 2021 - www.masenv.co.uk
This interactive diagram is an approximate calculation tool for combining sound level reduction due to propagation over a distance, insertion of a barrier, ground effect and air absorption.
If you find this useful, you might want to check out our dBmap.net Noise Mapping Tool.
How to use
- Choose between "Single Frequency" for tonal sources and "Multi Spectrum" for broadband sources.
- Edit sound levels and distances (in metres) or click and drag the items in the diagram to modify their position.
- Move the barrier/building top to change its position, click the body to toggle on/off.
- Click "Wall+" to add a reflective surface behind the source/receiver (facade level).
- In "Single Frequency" mode click "Show calculation breakdown" to see the effect of the attenuation factors listed below.
- You can bookmark or link directly to the results by clicking "Link to this calculation" under Options.
- Need to calculate with multiple sources? Use our original noise source calculator
This Interactive Sound Propagation Level Calculator is an approximate calculation tool and should not replace your own calculations and real life measurements.
- No transmission of sound around the barrier - therefore, the combined transmission of sound around the sides of the barrier must be at least 10dB below the level of sound transmission above the barrier.
- No transmission of sound through the barrier - therefore, the total transmission of sound through the barrier must be at least 10dB below the level of sound transmission above the barrier.
- There are no reflections from the barrier. In reality when dealing with short distances and many reflective surfaces the "canyon effect" may occur with repeating reflections.
- There are no affecting weather conditions, such as wind or temperature inversion, as these will affect the propagation path of a noise source and diffraction around the barrier.
- The noise source behaves as a point source and is far-field, where inherent directivity is minimal.
- Walls used in the model are considered to be perfectly reflecting and at 1 metre distance (facade level).
- Conditions are free-field and there is no reverberant field.
Sound Attenuation due to Propagation (aka "Geometrical Divergence")
Sound waves propagate as a sphere and follow the "inverse square law" of level reduction.
A general rule is that the level reduces by 6dB per doubling of distance.
Sound Attenuation due to a Barrier using ISO9613-2:1996 (up to 1000m)
Sound waves are reduced by a barrier depending upon the frequency of the sound waves with lower frequencies less affected. The greater the path difference, the more effective the barrier is.
A general rule is that a single barrier at eye level with a source and receiver will reduce the level by approx 5dB.
ISO 9613-2 only considers up to two screens. In the case of more than this, choose the two that are most effective and ignore all others.
The guidance also states that barrier attenuation is limited to 20dB for a single barrier and 25dB for two barriers. Toggle this with the "Apply limit" checkbox.
Ground Effect (reflection and absorption) using ISO9613-2:1996
Sound waves are reflected or absorbed by the ground depending upon the frequency of the sound wave and how porous the ground is (indicated by the "Ground Factor" value G).
- For "Hard Ground" G = 0. Hard ground reflects sound waves. Examples include roads and paved areas.
- For "Soft Ground" G = 1. Soft ground is porous and absorbs sound waves. Examples include grass, trees and other vegetation.
- For "Mixed Ground" use a value for G between 0 and 1 that represents the fraction of the ground that is soft.
Barrier insertion cancels ground effects. ISO17534-3:2015 has a recommendation that ground reflections are not removed by a barrier.
Air Absorption using ISO9613-1:1993
As sound waves travel through the air a small portion of the energy is converted into heat depending upon the atmospheric temperature and humidity, however the amount is only significant with high frequencies and long distances.
Find out more
More information about the calculations used in the tool can be found in the guide for our dBmap.net noise mapping tool under "Parameters in detail".