Headset Guide: Technology Still”€ˆRules

While it's no secret that doctors warn about cockpit noise seriously damaging your hearing, few pilots understand the mechanics of why it happens. Understanding how your hearing is affected by flying can help you choose the best headset for your particular environment. Also, it's not enough to focus only on the noise attenuation ratings given by headset manufacturers, because that's only one small factor in a headset's ability to protect your hearing. There's more to the headset than meets the ear.

Hearing Damage 101
The sound in a cockpit (or anywhere else) is a mechanical form of energy. Sound waves are variations in air pressure that can be measured by three distinct variables: frequency, intensity and duration. Frequency is measured in wave cycles per second, or hertz (Hz). Sound that's audible to the human ear falls in the frequency range of 20 to 20,000 Hz, with human speech in the range of 500 to 3,000 Hz.

Sound intensity is measured in decibels (dB), with the average human ear having greatest sensitivity between -10 dB and +25 dB. Duration is a measurement of how long a sound lasts. Coupled with intensity and frequency, the hearing damage caused by exposure to an intense short-duration sound can be as bad as exposure to a less intense sound for a long period. Finally, noise refers to any unpleasant or unwanted sound. In aviation, there are many sources of noise, with the two main culprits being engine noise and slipstream noise---the sound of air going over the airplane's fuselage.

Doctors warn that steady exposure to sounds around the 90 to 110 dB intensity range will cause permanent hearing loss. Unfortunately, the average small airplane cockpit noise level is right at that range. Sound duration is also a critical factor. While exposure to 90 dB for eight hours can cause permanent hearing damage, exposure to 110 dB for as little as 30 minutes can do the same harm. It's interesting to note that many busy city streets and public address systems fall right into the 100 dB range. Rock concerts are typically around 120 dB, and most airliner cabins are between 60 and 90 dB.

Passive & Active
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.

PNR headsets attenuate noise using mechanical means. These headsets block all noise across a frequency spectrum fairly evenly, and they do it by using barriers to stop the sound waves. Passive headsets close firmly against the wearer's ears and use optimally shaped ear cups packed with dense foam. Gel ear seals conform to the bones around the ear, serving to help block sound waves.

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.

Noise Attenuation Ratings
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.

What's New?
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.

A development from the ultralight and paraglider industry is the helmet headset. British company, Lynx Avionics offers a unique integrated helmet intercom system with individual components that fit together and are designed for high-noise environments, such as open cockpits. The headset component slides directly into either a hard "fighter pilot"--style helmet or a soft leather helmet and can be worn independently. Other companies in this arena include Sport-Link and Icaro.

Most manufacturers now offer cell phone and MP3 player connections. Wireless, Bluetooth and multichannel capability have emerged as well, allowing pilots to connect wireless smartphones, music players and just about any other device, all at once, to the headset. Smart or "adaptive" ANR has now been introduced that gives ANR headsets more intelligence in countering harmful noises, thus providing broader sound attenuation capability.

Choosing The Right Headset
Headset technology has developed to the point where there's no "one model is best" for all pilots, no matter the price. Close attention to manufacturers' noise attenuation charts is warranted, as is applying those figures to individual cockpit environments. Trying several headsets seems to be the best way to evaluate them, with aviation trade shows being prime ground for experiencing the nuances of different models.

Finally, comfort is a huge factor and is always a personal choice. Experts suggest buyers wear a headset for as long as possible, since pressure on the scalp and ears is only noticeable after several minutes. Just about anything feels okay for a 30- or 40-second trial. Always consider upgrading the ear cup seals to the gel variety and consider getting the best microphone you can---especially for noisier or open cockpits. And of course, with headsets, you get what you pay for. Always consider how long you'll be wearing a headset because nothing is worse than sitting in the pilot's seat with a bad headset distracting you from the task at hand: flying the airplane.