[simonmeridew]

I asked my Ear, nose and Throat MD about the noise cancelling protective headphones. His comment was(for what it's worth) that the time delay where the loud sound is "heard" by the headphones and dangerous or harmful levels are "cancelled out"electronically, anyway the time delay allows some hearing damage to occur, while giving the perception of complete attenuation of dangerous levels of sound. Apparently there is an electronic delay, measured in milliseconds in the way they operate. Like I said, FWIW.

My second comment is that there is a school of thought that says that hearing isn't "lost" by loud noise, rather it is "used up" by fracturing off the little hairs in the cochlea of your inner ear by loud sounds, and that there are a finite number of the hairs and you don't regrow or grow more.

All the more reason to use the best protection you can.
simonmeridew