30 Jan
2009
30 Jan
'09
5:08 p.m.
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 !