software maintenance

Indoor Noise Calculations

Indoor Factory Noise calculations are fully integrated into the SoundPLAN suite of programs. Indoor noise levels, along with transmission loss spectra, can be used to predict noise that will be transmitted into the environment. The outside aspect of noise propagation is part of the module Industrial Noise. For Indoor Factory Noise, the noise levels in the factory are defined as a sound pressure spectrum inside the building. If these data are not available, the module offers facilities to calculate the spectra 1 meter in front of the inside walls. The Indoor Factory Noise Module not only offers simulations as feedstock for the environmental calculations, but also generates noise maps inside the factory and assess the acoustical quality of the room using a Sound Decay Curve.

The screenshot below shows a factory building with point, line and area sources. The absorption coefficients on the inside walls are defined over frequency.

The acoustical properties of the buildings are set for the different purposes in different sections. Use the General tab to enter data for the height of the building and the absorption for reflections outside. These settings are the equivalent to the definitions of normal buildings.

Use Sources to define the walls, roofs, windows, doors and other inserted items. See Industry Noise for details. Use "Indoor Noise" for the data entry described here. Like the Source section, each object of the factory building has sub-objects (walls, roof, windows...) listed in explorer style to the right. Pulling open a new box in the window on the left side inserts a new absorption area in the wall.

Define the absorption of the inner walls for the entire wall or for sections of the wall. If a material mix exists within the area, set the percentage in the table and select the material from the library. Continue until the wall is completely defined.

The Indoor Factory Module is based on the German VDI 3760 standard. The model is a hybrid between a mirror source model and a Sabine type diffuse scatter model. The advantage of this combination is that the amount of input data required is limited and the calculation is relatively fast. The properties of the reflections on the outside walls are defined in the section, Absorption area. The scatter part is defined under General.

The mean room height may be different from the building height. The most important settings are the Scattering objects. The density is defined as the sum of all surfaces aside from the outer walls, divided by 4 times the volume of the room (the formula q=S/(4*V)). The density of the scattering objects leads to the average distance a wave travels between reflections. With each reflection, sound is absorbed. As the objects are not clearly defined in their location, only one - the average absorption coefficient for all objects in the room, is required.

There is no limit on the number of industrial buildings in a single calculation for environmental noise calculations. For indoor simulations, however, only one building can be loaded at a time. Therefore, it is wise to place each industrial building in its own Geo-File.

The following screenshot shows the indoor noise model integrated into the outdoor noise model. For environmental noise calculations, the simulation indoors produces the noise levels on the inside facades. With the additional transmission information, SoundPLAN calculates the noise emitted into the environment.

The next screenshot shows a noise map inside a factory building. The hatched part shows area sources and the purple lines are line sources. The calculation was made on a grid based system and then contoured in the graphics.

Noise maps in a factory are usually made to determine the zones where noise protection gear must be worn. Single receiver calculations provide more insight into which of the sources are responsible for excessive noise, and how many dB each source had at the receiver. The results can be formatted in extensive calculation result sheets in the SoundPLAN Documentation. SAK curves are the best tool to assess the acoustical quality of the room. Traditionally, the acoustics in a room are described with the reverberation time. This figure does not give hints as to which frequency band is used or where the problems are in the room. SAK provides the reverberation information plus more. A virtual source is placed in a corner of the room where the most dominant source will be located. From that source, SoundPLAN automatically places receivers along a line to the user defined end position of the SAK line. The Documentation clearly shows how noise decays from the source to the end of the SAK line. The decay is presented as the average decay over frequency allowing a much more detailed response in preparing the room for additional absorption in certain frequencies.

Last modification: 15 June 2005