On Fri, Jan 30, 2009 at 09:15:10PM +0100, Jörn Nettingsmeier wrote: > 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.
Put the lines (the nunbers) above in a separate text file, and plot with gnuplot using a log x scale, e.g. to see the effect at 20 meters: plot 'thefile' u 1:($2)*20 w l 3 This will show you that a simple 2nd order lowpass will do the job - it's not a perfect match but good enough. It's not critical at all - for small distances you can even use a standard shelf or parametric. Ciao, -- FA Laboratorio di Acustica ed Elettroacustica Parma, Italia O tu, che porte, correndo si ? E guerra e morte ! _______________________________________________ Linux-audio-dev mailing list [email protected] http://lists.linuxaudio.org/mailman/listinfo/linux-audio-dev
