Those fully ducted bypassed with a straight pipe were quieter, but not that much.
Yep, agreed. The engine in my sport model is fully enclosed and is much quieter with the hatch on & secured, no whistle from the compressor at all. Not a lot you can do about the other end though.
in addition, once the aircraft was in the air with a little distance, the percieved noise is drastically differnt.
Right again. And the percceived noise is quieter & less annoying than glow powered models, particularly at 'cruise' power settings, lots of club members have commented how turbines make your ears ring on the ground but once flying are surprisingly quiet. - John.