Helmets and Hearing Loss
I use a custom Kevlar helmet from FlightSuits Ltd and wear foam earplugs underneath. I've been doing ag work in both phyxed wing and rotorcraft since about 1967.My high freq hearing shows a measurable loss in spite of my best efforts. While doing competitive pistol shooting I wear ear plugs under my shooting muffs.
If you don't think the plugs matter under the helmet, try a flight wearing just one ear plug under the helmet and prove it to yourself.
I'm just passed 22,000 hours, and my old shooting records indicate I shot more than a million rounds of just the .45acp in practice and competition. Now at 68 yrs old and ready to quit the cockpit.