NPL Acoustics: Calculation of absorption of sound by the atmosphere
ISO 9613 Part 1 describes the calculation method for absorption of sound by the atmosphere. For pure-tones the standard specifies the attenuation coefficient as a function of frequency, temperature, humidity and pressure.
The calculator presented here computes the attenuation coefficient according to ISO 9613-1, given those four variables. This model assumes uniform meteorological conditions. The reference ambient atmospheric pressure, is that of the International Standard Atmosphere at mean sea level (101.325 kPa). The reference air temperature is 20 °C.
You can verify the calculator using some validation data taken from Table 1 of ISO 9613-1, and calculate attenuation due to atmospheric absorption at a distance.
According to ISO 9613-1 the accuracy of the calculated pure-tone attenuation coefficients for atmospheric absorption is estimated using the following table:
|Accuracy (%)||Molecular concentration of water vapour (%)||Temperature (°C)||Atmospheric pressure (kPa)||Frequency-to-pressure ratio (Hz/Pa)|
|±10||0.05 to 5||-20 to +50||200||0.0004|
|±20||0.005 to 0.05 and > 5||-20 to +50||200||0.0004|
|±50||< 0.005||> -73||200||0.0004|
For more details and advice on applying this to wide-band sources please refer to ISO 9613-1.
Any comments or suggestions about this model please contact Richard Jackett.