I am trying to remember more of the details from when we did the testing. Essentially we found that exposed turbine engines, and those with biforcated exhaust ducts were equally loud and in some cases louder to a noise meter as a ducted fan. Those fully ducted bypassed with a straight pipe were quieter, but not that much. I agree that someone with some real knowledge about how sound works needs to be contacted because what the meter was telling us was a little different than what was percieved. in addition, once the aircraft was in the air with a little distance, the percieved noise is drastically differnt.