Diablo, I definitely agree with a lot of what you say, especially that it's the flight noise that offends neighbors. You're definitely right that prop bark is louder that any exhaust noise (and carries farther). My feeling is that the barking is something the PILOT does, not something the plane does. That same prop you picked for the DA will bark whenever you want it to in level flight, but it won't on an upline when loaded, right? It's the PILOT that chooses to bark the prop, right?
I can't say, though, that the ground test has zero relationship to flight noise, though. Your example about the DA meeting ground specs and loudly ripping a chosen prop being louder than the ZDZ with the *SAME* prop is valid, mainly because the ZDZ *CAN'T* rip that same prop that a DA barks easily. Choose a prop that the ZDZ CAN rip, though, and it's louder than the DA since the equal barks cancel each other, leaving the ZDZ's louder exhaust note to decide the difference. Take prop ripping out of the equation either by throttling back, or choosing props for both that can't be ripped, and the ZDZ at ALL throttle positions has a sharper and louder exhaust note than the DA does at similar throttle positions. I'm not saying that it's offensive to everybody, but it's a fact that it IS louder. One friend of mine uses a Supersonic (I think) Pitts style muffler on his ZDZ-80 and the twin exhaust stacks on that muffler are larger than the stacks on my BME 102 twin (!). Needless to say, it's also a LOT louder than my BME. Another flying buddy has a J&A Peacekeeper muffler on his ZDZ 80 with the same size can as the other one, but twin stacks the same as on my BME (smaller than the other) and his ZDZ is noticeably not as loud as the other one, but still too loud to pass IMAC standards. It is also several hundred rpm short in power to the other one.
The ZDZ is a great engine. If I had one, especially for IMAC, I'd go with a tuned pipe (and avoid using props that it can rip).
If props for each engine are chosen that neither can bark, then the ZXDZ is STILL louder in the air, just like the ground test showed it would be.
P.S. I sure hope that fact that you let Pugs fly your plane makes him get off his BUTT and get HIS biggun together!
