It probably lasts longer because it is a slower aircraft, therefore the time period you hear it lasts longer, a Ten though noisy tended to be a brief affair as it moved and climbed quicker. Also one would think the noise footprint on the Ten would be narrower and more direction orientated than the Herc.
Incidentally rumour has it at EGNX a few years back they used to have 727's regularly getting fined for failing the noise limits even though they were using noise abatement procedures ( reduced power ) take offs. They soon discovered as the sound monitoring equipment was off site that they could do full 100% power take offs to the detriment of the locality, climb like a dingbat, then throttle back as they whizzed over the sensors... Thus defeating the object of it all, but passing the checks.
Last edited by NutLoose; 30th Sep 2013 at 20:36.