Requires Adobe Flash plugin
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 (or don't have a Flash plugin), you might want to check out our in-browser sound modelling 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. Click "scale ratio" to reset the diagram for best viewing.
- Move the barrier top to change its position, click the barrier body to toggle on/off.
- Click "wall" to add a reflective surface behind the source/receiver.
- In "Single Frequency" mode click Σ for a breakdown of the calculation steps.
- You can bookmark or link directly to the results by clicking "Link to this calculation?"
- Need to calculate with multiple sources? Use our original noise source calculator
The Interactive Sound 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.
- Conditions are free-field and there is no reverberant field.
- The barrier is perpendicular to the source to receiver path and has no significant depth.
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 - ISO 9613-2:1996 (up to 1000m)
Sound waves are reduced by a barrier depending upon the frequency of the sound wave, lower frequencies are less affected. A general rule is that a barrier at eye level with a source and receiver will reduce the level by approx 5dB. ISO 9613-2:1996 states that barrier attenuation is limited to 20dB for a single barrier
Ground Effect (reflection and absorption) - ISO 9613-2:1996
Sound waves will be 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). Barrier insertion will take precedence over ground effect, the effect is not cumulative.
- 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.
Air Absorption - ISO 9613-1:1993
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.