Does anyone know of any sites where I can find out about Noise Criteria (NC - ##).
I have a list of specific noise criteria for spaces, but I'm not sure how that equates to equipment & ductwork transmitting sound (if the equipment/ducting meet the criteria).
Silencer manufacturers are probably a good resource. Vibro-Acoustics has design software, as well as design assistance. VAW silencers might be another path to pursue.
Their software lets you start with noise levels of a fan and proceed to the NC of the space, incidentally selecting a silencer if required.
Fantech provide a fan & silencer selection CD catalog with an excellent downduct and room acoustics calculator. I use this all the time for simple systems. I'd still recommend an acoustics consultant for the big jobs though.
While the insertion losses and noise generation of the equipment is automatically placed from catalog selections, you can also enter your own non-fantech values. Lined and unlined ductwork configurations are entered to allow for losses through bends etc. Terminal and room acoustics allowed.