I confess, I'm waiting for an Xjet/WASP III. Can't help it. I do agree that there is room for improvement, notably with efficiency. Do you have any estimate of the decibel level of the WASP?
Any estimate? Well... WASP was apparently a turbofan, and thus likely quieter than these small turbines - less high-frequency noise from shear. Quick googling turns up [1], which has a CJR900 small airliner as 78 SEL dBA @ 400 ft @ low 1k lb taxi thrust. So perhaps take that as a low bound. And [2] suggests an upper bound of 120 db at 9 ft for one of those small turbines. So...?
I was going to say "No idea, sorry", but when encouraging estimation and rough quantitative reasoning, I argue that one should never say "no idea", because its almost always untrue - one can almost always get some bounds. And surprisingly often, they are satisficingly narrow. Though perhaps not these.
One notable thought from [2] was the high-frequency noise attenuates rapidly with distance.
