enforcing sound limits
FlyinBrian hit the nail on the head. The dB ground test has absolute zero relationship to the noise an airplane makes in the air. The noise in the air is what can offend the neighbors.
I can guarantee that if I pick the props I can make a DA-100 meet the ground dB maximum and rip the prop in the air. And conversely, a ZDZ-80 on the same prop will fail the ground test (because of muffler noise), yet be much quieter in the air because it won't rip the prop.