Noise calculations are done both to survey existing noise levels and for planning purposes. The location of calculation points should be carefully selected, using the same rules and principals on all projects using the same calculation method. In many cases the selection of calculation points will lead to large effects to the sound pressure level. Especially this will account for the height of the calculation point above ground level.

It is recommended that calculation points are selected 2m above ground level for calculation of free field values. Free field areas are outdoor areas such as parks and recreation areas which are not influenced by sound reflection from vertical surfaces.

For the calculation of sound pressure levels in front of building facades, it is recommended that each floor of the building are calculated separately. The height of the calculation point should be selected as corresponding to 2/3 up on window. If the windows of a floor have different heights, basis should be windows of living rooms.

If just one floor is to be calculated, the floor which is most influenced by noise in the building should be selected.

The figure shows the selected height of the calculation point for a house with two floors. On the first floor, the height is determined by the height of the living room window, while the other windows are ignored.

The calculation point for a building is to be located a=1m (see figure) out from the facade. In connection with the planning of detailed noise alleviation measures on a housing facade, it is recommended to calculate a value for each room (in the middle of the part of the facade constituted by the relevant room). For other planning it will generally be sufficient to calculate one value per building or flat. If the building has several noise exposed facades, all or only the most noise exposed facade are calculated. For most purposes it is common to select one calculation point in the middle of the facade, and not at the corner. Calculation points in front of a facade make the basis for calculating the indoor sound pressure level. An example of selected horizontal placement of calculation point is shown in the figure below.

A: One calculation point for each room
B: One calculation point in the middle of the facade

Display of calculation points is defined in an AutoCAD BLOCK named _TS_MOT. To change the display, it is possible to update the definition of this BLOCK:

Create one or more objects around origo, which you want to represent calculation points.
block
Set “Name” to “_TS_MOT”
“Select objects”
Choose all objects to be used as the new representation for calculation points.
“OK”
A message will show: “_TS_MOT is already defined…”.
“Yes”

If you want to change this permanently, you can make an AutoCAD template drawing with this BLOCK definition. When you create new drawings later and select this template, your calculation points will display accordingly.