Passive (PNR) vs. Active Noise Reduction (ANR)
Pilot headsets come in two basic flavors: active noise reduction (ANR) and passive noise reduction (PNR).
In an ANR headset, a tiny microphone inside the ear cup picks up the noise around it. The noise sample is passed to electronics that produce an exact opposite “mirror image” of the sound. Tiny speakers generate the new sound back out to the ear cups. Because the generated sound is an “anti-sound” to the original noise, they meet and cancel each other out. The result is silence.
ANR only affects certain low frequencies, so normal speech, changes in engine sound and airflow over the fuselage are all easily detected. Because ANR headsets rely on electronics to block damaging noise, they don’t need to clamp tightly to your head and can be lighter and smaller than other headsets.
PNR is more like soundproofing your garage when you’re in a band: it blocks damaging noise by stopping it with barriers. These headsets rely on clamping mechanisms to keep the ear cups sealed against the wearer’s head. The cups completely cover the ears, and dense foam inside the ear cups absorbs sound while gel ear seals conform around the ear to stop sound waves.
Above excerpt from Plane & Pilot Magazine: “Headset How-To” by Marc C. Lee. Read the entire article.