Tuesday, August 11, 2009
Headset Guide: Technology Still Rules
New developments in sound technology
Clarity Aloft’s Pro headset uses in-ear foam tips to protect hearing.
Most pilots today are aware that headsets come in two basic types: passive noise reduction (PNR) and active noise reduction (ANR). These two terms refer to the methods used by a particular headset to attenuate the harmful noise in an airplane’s cockpit.
Sennheiser’s HMEC 250 ANR headset features ergonomic ear pads for a comfortable fit.
ANR headsets use a sound technology that electronically manipulates sound to reduce noise. Circuitry inside the headset samples the incoming sound (noise), and then generates a mirror image of that sound to cancel it out. The reason ANR headsets aren’t the universal best choice for sound attenuation has to do with the fact that ANR is most effective in very specific frequency ranges—usually in the lower spectrum. Some cockpits generate noise in higher frequencies, thus reducing ANR’s effectiveness. Open cockpits are one example.
Click on the image above to view in a larger scale.
Pilots must look at the entire performance of a headset, not only at its attenuation rating. Headset manufacturers give their headsets an attenuation rating in decibels, but pilots must also look into the frequency range of the attenuation. A headset rated at -24 db at 400 Hz means it attenuates noise only at that specific frequency, while attenuation in other frequencies could be less. Damaging frequencies in cockpits are typically around the lower frequency band of 40 to 250 Hz, though it varies with each particular airplane. Consulting a manufacturer’s published attenuation chart is a better way to evaluate any prospective headset.
Great strides are being made in headset technology, with many developments being driven by the music industry—a longtime pioneer of sound. From wireless technology to in-ear headsets, more options are constantly emerging for pilots.
In-ear headsets, for example, may look like they wouldn’t work. They’re tiny (they usually weigh less than three ounces!) and seem fragile, but they’re quite effective. They employ foam inserts that are pushed into the ear canal. The resulting seal is so good that it rivals the attenuation of both ANR and PNR headsets. Because they have no over-the-head clamping mechanism, in-ear headsets are almost imperceptible to the wearer. JH Audio offers custom-molded ear pieces that contain headset circuitry. Combined with three-way frequency crossovers (borrowed from the music world) and bone-conduction technology (using the wearer’s facial bones to amplify sound), the result is excellent sound and attenuation.
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