Well, funnily enough....
By profession I was an audio engineer. Most normally, when considering the risk and nuisance of sound, the "A" weighting curve is the one quoted because it most closely mirrors the response of the human ear.
Bored on my last long haul flight, I dragged my B&K meter out of my hand luggage and did a measurement in the cabin which worked out to be 79dB(SPL) A weighted. This was 5 seats from the rear of an Air New Zealand 744, with the measurement taken during a "sleep" phase of the flight so there was little or no passenger noise in that reading. If you want to get really precise, I was seated in an inboard aisle seat so away for the exterior "skin" of the aircraft.
Hope this helps. If it wasn't for the rules on flight deck visits, I'd offer to do the "pilots head" measurement for you in return for a spell in the jump seat! Ah well, thanks Osama for spoiling my aviation interest hobby.
Bob