If the noise source has inherent directivity this is often not correctly modelled.The accuracy is always going to be limited to the details of the model, which will never quite match the real world conditions perfectly. How accurate are sound level calculations and noise mapping? Our sound propagation calculator and our sound modelling tool calculates sound levels using the methods set out in this document. The method predicts the equivalent continuous A-weighted sound pressure level (as described in ISO 1996) under meteorological conditions. It is a international standard that describes a method for calculating the attenuation of sound during propagation outdoors in order to predict the levels of environmental noise at a distance from a variety of sources. Use our sound propagation calculator or our sound modelling tool to calculate these values for yourself. Temperature inversion, where the temperature varies considerably at different heights, can also bend sound paths over long distances.It is usually necessary to consider downwind conditions to minimise these affects. Wind speed and direction can considerably affect sound levels.This is energy lost by friction in the atmosphere and considers the temperature and humidity of the air and the frequency of the sound.To understand ground absorption better, check out the section in the noise mapping tool guide.This depends on the softness of the surface and the frequency of the sound.Absorption from the ground and reflecting surfaces.This is sometimes called the “façade level”. A perfect reflection will increase the level by 3dB.The extent of this depends upon the qualities of the surface and the frequency of the sound. This is frequency dependent and is mostly based on path difference (the difference between the direct path and diffracted path).Screening and diffraction around screens.This is a relatively straightforward physical phenomena as mentioned above.There are many aspects to consider when modelling sound level both regarding the laws of physics and environmental effects on the sound. Use our sound propagation calculator to calculate this for yourself. So the reduction from 1m to 2m distance is the same as from 100m to 200m distance. This is easily understood as a reduction in 6dB per double of distance. Sound energy propagates outwards in a sphere and therefore reduces in energy based on the “inverse square law”. How to calculate sound level at a distance? How does distance affect sound? To understand this better check out our decibel calculator, which provides the formulae to convert the decibel values back to the linear scale and performs calculations such as addition. Sound levels (decibels) are logarithmic so they do not scale the same as other units of measurement. How to combine noise levels? What is different about a sound level calculation?
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