I was a truckdriver in the oilfield for 20 years, 16 gauge steel fo the firewall, no noise suppression AT ALL, 90% of the time you were trying to shove your foot through the floorboard, tacked out and screaming. ThE doc did a hearing check and knew exactly what I did for a living, but said evidently I hadn't been doing it for long,(that was after 20 years). I attribute my little loss of hearing to earwax. Everyone who has looked in my ears wants the wax out, I want it in, serves as a tympanic dampning system, prevents overexcursion. When that 55 gal bag blew up right beneath me that had the oxy/acetylene mix in it should have made me deaf, a little bleeding and noty being able to listen to music for 6 months and I was fine...
BTW---the 9's can get a little bright...