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

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