Sound Propagation Level Calculator

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.
• 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? Check out our other tools

This is an approximate calculation tool and should not replace your own calculations and real-life measurements.

Assumptions

• No significant sound transmission around the barrier sides. The total level around the sides of the barrier must be at least 10dB below that from over the top of the barrier.
• No significant sound transmission through the barrier. The total level through the barrier must be at least 10dB below that from over the top of 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.
• 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 ("Geometrical Divergence")

Sound waves propagate outwards from the source as a sphere and follow the inverse distance law of reduction in level.

A general rule is that the level reduces by 6dB per doubling of distance.

Sound Attenuation due to a Barrier using ISO9613-2 or CNOSSOS-EU

Sound waves are reduced by a barrier depending upon the frequency, with low frequencies being less affected. The greater the path difference, the more effective the barrier is.

The "Apply Limit" checkbox applies the following limit, as per the guidance methodology:

• ISO9613-2: The barrier effect is limited to 20dB for a single barrier and 25dB for two barriers.
• CNOSSOS-EU: The barrier effect is limited to 25dB

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).

Ground Factor Values (ISO9613-2)

• 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.

Ground Factor Values (CNOSSOS-EU)

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.

The attenuating effect is only significant with high frequencies and long distances.

Calculation Method

ISO9613-2 (Worldwide)

• ISO9613-2:2024: The recommended method for calculation. Propagation is downwind or under moderate downward temperature inversion.
• ISO9613-2:1996: The older version of the method.

CNOSSOS-EU:2015 (European Union)

• CNOSSOS-EU:2015 "Favourable conditions": The speed of sound increases with altitude. The sound rays are curved towards the ground due to downward-refraction.
• CNOSSOS-EU:2015 "Homogeneous conditions": The atmosphere has a constant speed of sound at all altitudes. The sound rays are straight.

Note: ISO17534 includes recommendations and test cases for the correct implementation of ISO9613-2 and CNOSSOS-EU.