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Atmospheric absorption implementation verification

Presentation

This section proposes a validation of the implementation of atmospheric absorption in the numerical codes (SPPS, TCR, MD) within I-Simpa, according to ISO 9613-1, mainly in terms of reverberation time.

• SPPS

• TCR

• MD

Geometry

• Quasi cubic room (5m x 4m x 3m)

• Uniform wall diffuse reflection (100%)

• 10% uniform surface absorption

• Single source at the room center (100dB per each frequency band)

• Punctual receiver at location (1,1,1)

• Atmospheric conditions: Temperature: 20°C; Humidity:50%

References

ISO 9613-1:1993, Acoustics – Attenuation of sound during propagation outdoors – Part 1: Calculation of the absorption of sound by the atmosphere http://www.iso.org/iso/catalogue_detail.htm?csnumber=17426

Files and data

Files/data are located in the following folder:

<I-Simpa installation folder>\doc\validation\atmospheric_absorption

• Validation_atmospheric_absorption.proj: I-Simpa project file

• Validation_atmospheric_absorption.xlsx: Results file

• Atmospheric_absorption_geometry.png: Geometry image file

Results

What is expected?

• a decrease of sound level and reverberation time when increasing the frequency du ti the increase of atmospheric absorption coefficient with the Frequency

• an agreement between the TCR (Classical theory of reverberation) and the SPPS/MD codes, since the room is choosen to be as closed as possible with the hypothesis of diffuse sound field.

Results

The numerical simulations (see figures below) show a very good behavior of the SPPS/MD codes when considering the effect of atmospheric absorption on the reverberation time (RT30) and the sound level (SL). In terms of sound level, the deviation between simulations is around 2 dB, for higher frequencies, and are due to the inherent implementation and hypothesis of each model.