Call on the folks down in Austin, Texas for this information. I remember reading on this site a couple of years ago, that Patrick Fernandez (hope the spelling is correct)

Did some testing at a jet rally with Ducted Fan engines, and Turbine Engines. I believe the decibel level was on par with 110 or about that of a lawn mower from 10 feet away at idle.

I'm sorry I do not remember his user name here.