Air Absorption Coefficient

Professional Installed
1

Hi Modeler support team,

Could you provide me the coefficient data of the air absorption that Modeler has been using. I will need the concrete numeric value on some conditions about temperature and humidity so a formula to find the coefficient would be better than a graph.

Best regards,
KI

2

Hi Kakudo,

unfortunately, I do not have documentation on this, we would need to double-check with Tom Birkle.

In our Matlab tools, air absorption is applied as defined in ISO 9613-1 and I believe this is the same in Modeler. For the ISO stuff, it’s relatively easy for me to make you a table which lists alphas in dB/km e.g. vs. temperature.

But maybe you are already OK by experimenting in Modeler: Just take an omni source in a free field model and place a listener in a large distance (maybe 100m or even a km). Then predict DF frequency response and note the attenuation (primarily at HF) when you play around with humidity and temperature.

Let me know how much information you need and I can see what’s possible.

Best rgds,

Thomas

3

Hi Thomas,

Thank you for reply. One of Modeler users have to explain how Modeler calculate RT60 to his customer. Regarding the coefficient of the air absorption I thought I would offer the concrete value but it might be okay for him with having where that has come from. So can we tell him that Modeler uses ISO 9613-1 as the coefficient?

Best regards,
KI

4

Hi Kakudo,

we have received information from Engineering (Tom Birkle) regarding this matter.

The air absorption is not calculated according to ISO. The method used in Modeler has been described in a JAES article by Dennis Bohn. It can be downloaded here (it’s also a RANE application note).

Please let me know in case you have any additional questions.

best rgds,

Thomas

5

This is good info and discussion. Thanks Thomas for info.

6

Thank you, Thomas. I really appreciate your help.

KI