Natural Science Forum / Physics / Acoustics / August 2007

Alain,

I don't know of anything in the literature that covers directivity for
this type of source.  Assuming it's a ducted outlet, applying the
sound power level of the fan over an area source equal in size to the
open area of the duct should suffice.  If your model allows it, place
a structure behind the area source to represent the duct - and hence
provide the appropriate shielding.  (Kind of a "poor man's"
directivity.)

If you just want to get an idea of worst-case noise, simply use a
point or area source.  Remermber that if your receptors are far enough
away, a dust collector fan outlet is going to act like a point source
in the general direction the outlet is facing.

Also, if it's possible to measure a similar fan outlet in accordance
with something like ASME PTC 36, it should give you enough information
to develop a specific fan directivity.