Those data are presented in Figure 1. The eardrum flexes in response to the frequency and intensity of the sound pressure. These vibrations are transmitted to the inner ear via three small bones collectively referred to as the ossicles. The fluid filled inner ear contains the organ of Corti. It is the cilia that translate the vibration sensed in the inner ear into electrical energy that makes its way to the brain via the auditory nerve.
Passive attenuation refers to providing a physical barrier to the sound waves.
Earplugs and full-cup headsets take advantage of this technique. The most important aspect of passive noise attenuation to note is that headsets alone provide little protection in the lower ranges of the frequency spectrum. To protect against those lower frequencies, the operator would have to use earplugs, but this would limit his ability to perceive most voice communications. Thanks to modern technology, ANR headsets are capable of protecting against unwanted lower frequency noise while allowing communications to continue. The typical Active Noise Reduction headset measures the noise near each ear via small microphones.