Plane & Pilot
Wednesday, November 30, -0001

Headsets: Choosing The Right Tool


Technology and individuality drive this year’s headset selection



Lightspeed; Bose A20
Now, add vibration to the aural onslaught. Vibration noise creates a low-frequency bleat that's pure hell on your cilia—the tiny, hair-like cells inside your inner ear that vibrate in reaction to sound, and sway back and forth like a field of Kansas wheat in a breeze. Cilia are resilient; when they get hit by loud sounds, they bend and spring back, warning you with ringing that lasts hours or days. But you only have a fixed number of cilia. Abuse them enough and they won't spring back. That means permanent hearing loss. You can't regenerate cilia—ever.

Scientists tell us that hearing damage starts to happen at around 85 dB (a decibel is the unit to measure sound intensity). Our GA cockpits subject us to constant noise at and above 95 dB. As a comparison, an iPod at full volume plays at about 120 dB—the same sound pressure as sand blasting. And a human whisper measures about 30 dB. Exposure to 120 dB causes permanent hearing damage in just seven minutes. In our cockpits, ears begin to suffer serious damage in just two hours.

To prevent hearing damage, the aviation headset was introduced around 1975, and it's what we use today, essentially unchanged. There were some earlier variations of headsets, and in World War II, some pilots wore crude "radio sets" made by Western Electric, but the modern-type headset has only been around for about 40 years.

The ANR Versus Passive Myth
Today, we have two kinds of noise attenuation in headsets: passive and active. Active noise reduction is referred to as ANR. It's important to understand the differences between the two, and why the myth persists that ANR is better because it's more modern.

Hardly "new" technology, ANR was around in the 1950s in helicopters, originating from a patent by inventor, Paul Leug, in 1934. Bose introduced ANR headsets to general aviation in 1986. Since then, the technology has remained basically unchanged.

ANR headsets analyze the sounds hitting the ear using tiny microphones. When the ANR circuitry senses unwanted noise (fixed frequencies based on an algorithm), the headset's speaker emits a sound wave that matches the noise, but with an inverted phase to it, cancelling it out. The effect is known as "phase cancellation." ANR is mostly effective against low-frequency noise, and not so good at blocking high frequencies.

Passive noise reduction headsets (also called PNR) use only physical means to block unwanted noise, including barriers, absorption materials and sound damping. The ear cups act as both a sound enclosure and a barrier to noise by blocking its path and sound energy. Different kinds of foam and other absorbent materials also dissipate the energy of the offending noise. Gel seals, material coatings and headset hardware further act to dampen the travel of sound energy. The net effect is that all sound is attenuated (reduced) evenly by stopping it from reaching the ear.



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