But what about the inaudible spectrum? The Bose-X makes a lousy PNR headset so does it effectively filter out all the inaudible noises too? And is this filtering good enough to prevent hearing damage?
Hearing protection is complex. One can wear earplugs which give a high noise reduction rating, yet experience hearing damage. The plugs may allow the user to perceive less sound and feel less discomfort due to noise. Earplugs, however, don't prevent vibrations from passing through the bone around the ears, and this can cause significant damage, too.
Likewise, simply because we don't think we're hearing as much noise, or because we perceive less noise on an ANR installation, doesn't mean we aren't being exposed to high noise levels.
ANR generally works against high frequence levels, but only in a fairly narrow band. Noise occuring outside those ranges isn't affected much at all, and can still cause damage.
We experience hearing loss in differing ranges. One may experience loss in a high frequency range, but still be able to hear lower frequency noises. One may wear an ANR headset and experience some protection, but still receive hearing loss or damage from lower frequency noise, such as propeller vibration and engine sounds.
I had an option of adding ANR to my helmet, which I wear primarily in firefighting and ag flying. I elected not to do so, because I needed to hear the engine. Some have claimed that one can't be prevented from hearing the engine with ANR active, and that's sometimes true, but not always. I wanted to be able to hear changes in the airplane, the slipstream the engine, pumps, valves opening and closing, etc. I wanted to be able to hear gear noise such as wheels and brakes on landing.
ANR is great for improving communications, but it's not a panacea, and it's not for everyone, or every application.