Well it includes those low frequencies. I'm sure if you've flown you've experienced the strange ear-plugging feeling of flight. The fuselage is highly sound dam

Well it includes those low frequencies. I'm sure if you've flown you've experienced the strange ear-plugging feeling of flight. The fuselage is highly sound damped from the engines but you still get the low frequencies. Also could be that pretty much everyone tried to not go outside during 9/11, probably a lot more than just planes stopped