On Mon, Sep 24, 2012 at 07:49:42PM +0200, Jörn Nettingsmeier wrote: > on the other hand, i know that roads and highways are treated as > line sources as well for the purpose of emission control, i.e. with > 3dB attenuation per doubling of distance. > > maybe someone can explain why this should be so?
For a coherent line source this is simple: acoustic power is Watts per square meter, the surface of a cylinder is proportional to R while for a sphere this is R^2. So -3 dB per for double R instead of -6 dB. For a line of uncorrelated sources we have to add powers. Imagine the line source as the x-axis, with the origin being the point nearest to you. Let your distance be 'd'. Then the distance to a point 'x' on the line is sqrt(d^2 + x^d). The total power at distance 'd' is the integral from -inf to +inf of 1/(d^2 + x^2), which is 2 * pi / d, i.e. proportional to 1 / d, hence -3dB for each doubling of the distance. Ciao, -- FA A world of exhaustive, reliable metadata would be an utopia. It's also a pipe-dream, founded on self-delusion, nerd hubris and hysterically inflated market opportunities. (Cory Doctorow) _______________________________________________ Sursound mailing list [email protected] https://mail.music.vt.edu/mailman/listinfo/sursound
