SoundPLAN indoor noise modeling


The Indoor calculations are based on the VDI 3760 but extend the standard with transmission through openings, screening and a more flexible room geometry.

This diffraction factor is characterised by the relationship between the direct way and the real way between source and receiver:




find the shortest (existing) path between source & receiver


calculate the resulting extra path length


calculate the reduction of energy density:


  c1 = 3, c3 = 40

  m = extra path length

  λ(i) = wavelength

SoundPLAN’s Indoor Factory Noise Propagation Module helps you:

bullet Identify where there are risks from noise at work;
bullet Determine the most economical way to control the noise producing those risks;
bullet Ensure the legal limits on noise exposure are not exceeded.

SoundPLAN can accurately model any size and shape room to show noise levels from all sources. The results allow you to determine locations where workers need hearing protection, to optimize sensible noise reduction measures like absorbers and screens in rooms with work places, or to properly locate sirens or speakers so they can be heard where needed, etc.

Noise breakout from room to room

Scattered sound could appear from all quarters by reflections or scattering objects, therefore it doesn‘t make sense to calculate the diffraction factor from single paths – the more practical method is to use the relation between the opening (green) and the total area (green+red).




calculate the size of both the open surface and the total area


calculate the reduction of energy density by taking the ratio between the open area and the total area



The presented calculation method was tested in two ways:

bullet comparison with available test series
bullet comparison with other calculation methods

The model created by Braunstein + Berndt proved to be in relatively good agreement with measured data, it is better than models that calculate the  noise level in the door opening and then start from there with a new source and it is better than most particle models.

An example with a factory building

The next few pictures are from a step by step improvement of the noise situation inside and the subsequent noise levels that the surrounding community is subjected to


A cross-section through the factory

A cross-sectional noise map in the factory with the roof removed and the walls semi transparent gives the viewer a much better understanding where the noise problems are in the factory.


The raw noise map

This is the factory building before improvements were made.

Entering some walls inside

The industrial building is an integral part of the industry and indoor noise models. Full height and half height walls can be inserted inside the factory, the calculation core will take care of the rest.

As the shell is part of both the indoor and the outdoor industrial model, it is easy to define the factory once in SoundPLAN, then do the simulation indoors and calculate the noise on the inner walls and  then calculate the transmission from the inside to the outside and lastly into the environment.

Walls inside can be assigned with absorption coefficients in octaves or third octaves.

The noise map with some partitions

The noise map after some quiet zones were established with partitions.


Designing the improvements

With extra absorption material on the ceiling the noise situation can be improved further, lets try.

The indoor model with extra absorption on the ceiling

The improved noise model with partitions and extra absorption material on the ceiling.

The difference map shows the improvement

The best way to show the improvement is to make a difference map between the raw first look and the final design with partitions and extra absorptive material.


The outside model

Now we can see how much of the noise will be getting out of the factory and into the community. We see that the biggest problem is the big entry door that is open often.


The Sound Propagation Curve

An acoustic account of the room itself with all absorption and the partition in place can be obtained with the SAK curve. A theoretical source is placed into one corner of the room and a path of receivers is entered. The further the receivers are away from the start of the SAK, the bigger the spacing of the receivers. The free field decay is presented along with the simulated decay.

It is apparent that the reflective nature of the factory hall will increase the noise levels in the near and middle distances but the partition then creates some areas where the noise levels are less than the free field conditions would allow.


Copyright 2014 SoundPLAN international LLC, Shelton, WA 98584, USA