Room acoustic planning

Acoustic calculation

An acoustic calculation using the Sabine equation is recommended for making an initial assessment of the acoustic situation of a room and the necessary optimisation. This allows for calculation of the reverberation time in rooms. The equation was developed by the American physicist Wallace Sabine (1868 – 1919) and is as follows:


Reverberation time = 0.163 x room volume / absorption surface area


The calculation depends significantly on the accuracy of the absorption coefficients and absorption surface areas. It can therefore always only provide a first estimate. It is especially suitable for simple, rectangular rooms, as more complex floor plans may distort the results.


The equation is used for the acoustic calculation for new construction projects as well as for subsequent optimisation. It can provide information on the number of absorbers that are necessary, but not on their optimum placement: this requires acoustic simulation.

Acoustic simulation

An acoustic simulation enables the precise planning of room acoustics. It is suitable for new construction projects as well as the subsequent optimisation of existing rooms.


For this purpose, a 3D model of the room is initially created, and each surface is stored with the corresponding absorption coefficient. In the next step, the sound propagation from different assumed sources of the sound is simulated. The result of the simulation is obtained by means of the geometric room acoustics, which takes account of the sound propagation in the room with the corresponding absorptions, reflections and scattering. In addition to the reverberation time, the speech intelligibility can be determined and purposely improved in the acoustic simulation.


An acoustic simulation provides information on the number of acoustic products that should be used and where they should ideally be placed. The result is presented in graphs and 3D displays using a heat map.


“Auralisation” is a procedure for creating audio samples of the room before and after its acoustic optimisation. It is thus possible to directly compare the acoustic conditions.

Acoustic measurement

Acoustic measurement, in combination with acoustic calculation or acoustic simulation, is the most precise form of acoustic planning. There are several aspects in which measurement is one step ahead of calculation alone.


In acoustic calculation or simulation, small items of furniture, such as plants, the contents of shelves, desk paraphernalia, among other things, cannot be considered, as the volume of data would otherwise be too large. The types of materials or wall structures that were used, especially in older buildings, are often not known. Moreover, if materials are not installed correctly, they do not achieve the standard assumed absorption coefficients. As all of these factors influence an acoustic measurement, this is the most realistic representation of the actual situation.


In order to achieve as accurate as possible a picture of the acoustic situation in a room, the source of the sound (e.g. loudspeaker) and the receiver (e.g. microphone) are repeatedly placed at different locations. For the final result, all measurement positions are taken into account together, and also irregularities in individual areas. Besides reverberation time, speech intelligibility can also be measured in an acoustic measurement. A long-term test can also be used to measure the average sound level.


In addition to simple acoustic measurement using a starting clapper and a hand-held recorder, XAL also provides professional, standard-compliant testing using a dodecahedron loudspeaker (spherical loudspeaker), signal generator and sound level meter.