A couple things to keep in mind. First, the human ear is not a particularly good sensor when it comes to determining the relative loudness of noise. It takes roughly a 3db change in noise level before the human ear can even detect it (which, given the logarithmic nature of the decibel scale means a doubling (or halving) of the sound energy level - yet obtaining a 3db reduction is a huge engineering challenge. Further, the human ear doesn't detect all frequency levels the same - hence there is a db scale that is "weighted" for certain frequencies.
Second, the official jet aircraft Takeoff and Landing noise levels are determined at fairly specific points along the aircraft flight path - so getting a meaningful reduction in noise level at the official measurement sites doesn't necessarily mean the same thing at other locations along the flight path.