[LAD] sound dissipation in air - formulas and filters?

[Jörn Nettingsmeier]

hi everybody!


does anyone know a way to compute filters that simulate air dissipation
for a given temperature and humidity?

so far, all i've found is an online calculator at
http://www.sengpielaudio.com/calculator-air.htm, but the javascript in
there is not exactly fit for citation :)
plus i know there is a standard (ISO 9613-1:1993) that deals with sound
attenuation, but i don't have access to a standards library and don't
feel like buying it...

a rough calculation at 18°C and 85% relative humidity (using sengpiel's
tool) yields:

f[Hz]	dp[dBSPL/m]
----------------------
20	0
40	0
80	0
160	0
320	0.001
640	0.003
1280	0.006
2560	0.011
5120	0.032
10240	0.112
20480	0.404

which indicates that for my usecase (close-miked sounds that need to be
placed at distances between 10 and 45 m), the air-damping non-linearity
is really important.

question is: how do i design a filter to simulate this? would make a
cool ladspa tool eventually...

pointers to related papers or maybe even filters are most welcome.

best,


jörn