My 2 cents...
Having worked my whole life since college in steel plants, I am aware of some of the implications of loud sounds and hearing loss. And the implications of hearing, being based on a logarithmic scale, having an engineering degree.
Yep, you never get "used" or immune to loud noise. If it is loud enough to cause hearing damage, that damage happens every time exposed to it. (Kind of like friends come and go, but enemies accumulate?
, or something like that, but I digress).
The sound level, as well as the amount of time time exposed (Time Weighted Average), is what counts. IIRC, over 80dB constant for 8 hours, potential for hearing loss. And 80dB is about when you need to raise your voice above normal speech to be heard. (Is the sound in your helmet louder than your normal speech? Or would you have to raise your voice to be heard?) Again, IIRC, 90dB you are limited to 4 hours exposure (or maybe 2?), and I am guessing here. THe point is, the louder the sound, the shorter period of time before permanent loss occurs. I believe OSHA web site has more information, too, if you want to look.
Enough babbling for now...